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a scenario for the formation of multiple co-eval populations separated in age by about 1 myr in very young clusters (vycs, ages less than 10 myr) and with masses in the range 600-20 000 m⊙ is outlined. it rests upon a converging inflow of molecular gas building up a first population of pre-main sequence stars. the associated just-formed o stars ionise the inflow and suppress star formation in the embedded cluster. however, they typically eject each other out of the embedded cluster within 106 yr, that is before the molecular cloud filament can be ionised entirely. the inflow of molecular gas can then resume forming a second population. this sequence of events can be repeated maximally over the life-time of the molecular cloud (about 10 myr), but is not likely to be possible in vycs with mass <300 m⊙, because such populations are not likely to contain an o star. stellar populations heavier than about 2000 m⊙ are likely to have too many o stars for all of these to eject each other from the embedded cluster before they disperse their natal cloud. vycs with masses in the range 600-2000 m⊙ are likely to have such multi-age populations, while vycs with masses in the range 2000-20 000 m⊙ can also be composed solely of co-eval, mono-age populations. more massive vycs are not likely to host sub-populations with age differences of about 1 myr. this model is applied to the orion nebula cluster (onc), in which three well-separated pre-main sequences in the colour-magnitude diagram of the cluster have recently been discovered. the mass-inflow history is constrained using this model and the number of ob stars ejected from each population are estimated for verification using gaia data. as a further consequence of the proposed model, the three runaway o star systems, ae aur, μ col and ι ori, are considered as significant observational evidence for stellar-dynamical ejections of massive stars from the oldest population in the onc. evidence for stellar-dynamical ejections of massive stars in the currently forming population is also discussed. | evidence for feedback and stellar-dynamically regulated bursty star cluster formation: the case of the orion nebula cluster |
we develop a model of particle acceleration in explosive reconnection events in relativistic magnetically-dominated plasmas and apply it to explain gamma-ray flares from the crab nebula. the model relies on development of current-driven instabilities on macroscopic scales (not related to plasma skin depths). using analytical and numerical methods (fluid and particle-in-cell simulations), we study a number of model problems in relativistic magnetically-dominated plasma: (i) we extend syrovatsky's classical model of explosive x-point collapse to magnetically-dominated plasmas; (ii) we consider instability of two-dimensional force-free system of magnetic flux tubes; (iii) we consider merger of two zero total poloidal current magnetic flux tubes. in all cases regimes of spontaneous and driven evolution are investigated. we identify two stages of particle acceleration: (i) fast explosive prompt x-point collapse and (ii) ensuing island merger. the fastest acceleration occurs during the initial catastrophic x-point collapse, with the reconnection electric field of the order of the magnetic field. the explosive stage of reconnection produces non-thermal power-law tails with slopes that depend on the average magnetization. the x-point collapse stage is followed by magnetic island merger that dissipates a large fraction of the initial magnetic energy in a regime of forced reconnection, further accelerating the particles, but proceeds at a slower reconnection rate. crab flares result from the initial explosive stages of magnetic island mergers of magnetic flux tubes produced in the bulk of nebula at intermediate polar regions. the post-termination shock plasma flow in the wind sectors with mild magnetization naturally generates large-scale highly magnetized structures. internal kink-like instabilities lead to the formation of macroscopic current-carrying magnetic flux tubes that merge explosively. | particle acceleration in explosive relativistic reconnection events and crab nebula gamma-ray flares |
the emission of supernova remnants (snrs) reflects the properties of both the progenitor supernovae (sne) and the surrounding environment. the complex morphology of the remnants, however, hampers the disentanglement of the two contributions. here, we aim at identifying the imprint of sn 1987a on the x-ray emission of its remnant and at constraining the structure of the environment surrounding the sn. we performed high-resolution hydrodynamic simulations describing sn 1987a soon after the core-collapse and the following three-dimensional expansion of its remnant between days 1 and 15,000 after the sn. we demonstrated that the physical model reproducing the main observables of sn 1987a during the first 250 days of evolution also reproduces the x-ray emission of the subsequent expanding remnant, thus bridging the gap between sne and snrs. by comparing model results with observations, we constrained the explosion energy in the range 1.2-1.4 × 1051 erg and the envelope mass in the range 15-17 m ⊙. we found that the shape of x-ray lightcurves and spectra at early epochs (<15 years) reflects the structure of outer ejecta: our model reproduces the observations if the outermost ejecta have a post-explosion radial profile of density approximated by a power law with index α = -8. at later epochs, the shapes of x-ray lightcurves and spectra reflect the density structure of the nebula around sn 1987a. this enabled us to ascertain the origin of the multi-thermal x-ray emission, disentangle the imprint of the sn on the remnant emission from the effects of the remnant interaction with the environment, and constrain the pre-supernova structure of the nebula. | supernova 1987a: a template to link supernovae to their remnants |
context. markarian 501 (mrk 501) is a very high-energy (vhe) gamma-ray blazar located at z = 0.034, which is regularly monitored by a wide range of multi-wavelength instruments, from radio to vhe gamma rays. during a period of almost two weeks in july 2014, the highest x-ray activity of mrk 501 was observed in ∼14 years of operation of the neil gehrels swift gamma-ray burst observatory.aims: we characterize the broadband variability of mrk 501 from radio to vhe gamma rays during the most extreme x-ray activity measured in the last 14 years, and evaluate whether it can be interpreted within theoretical scenarios widely used to explain the broadband emission from blazars.methods: the emission of mrk 501 was measured at radio with metsähovi, at optical-uv with kva and swift/uvot, at x-ray with swift/xrt and swift/bat, at gamma ray with fermi-lat, and at vhe gamma rays with the fact and magic telescopes. the multi-band variability and correlations were quantified, and the broadband spectral energy distributions (seds) were compared with predictions from theoretical models.results: the vhe emission of mrk 501 was found to be elevated during the x-ray outburst, with a gamma-ray flux above 0.15 tev varying from ∼0.5 to ∼2 times the crab nebula flux. the x-ray and vhe emission both varied on timescales of 1 day and were found to be correlated. we measured a general increase in the fractional variability with energy, with the vhe variability being twice as large as the x-ray variability. the temporal evolution of the most prominent and variable segments of the sed, characterized on a day-by-day basis from 2014 july 16 to 2014 july 31, is described with a one-zone synchrotron self-compton model with variations in the break energy of the electron energy distribution (eed), and with some adjustments in the magnetic field strength and spectral shape of the eed. these results suggest that the main flux variations during this extreme x-ray outburst are produced by the acceleration and the cooling of the high-energy electrons. a narrow feature at ∼3 tev was observed in the vhe spectrum measured on 2014 july 19 (mjd 56857.98), which is the day with the highest x-ray flux (>0.3 kev) measured during the entire swift mission. this feature is inconsistent with the classical analytic functions to describe the measured vhe spectra (power law, log-parabola, and log-parabola with exponential cutoff) at more than 3σ. a fit with a log-parabola plus a narrow component is preferred over the fit with a single log-parabola at more than 4σ, and a dedicated monte carlo simulation estimated the significance of this extra component to be larger than 3σ. under the assumption that this vhe spectral feature is real, we show that it can be reproduced with three distinct theoretical scenarios: (a) a pileup in the eed due to stochastic acceleration; (b) a structured jet with two-ssc emitting regions, with one region dominated by an extremely narrow eed; and (c) an emission from an ic pair cascade induced by electrons accelerated in a magnetospheric vacuum gap, in addition to the ssc emission from a more conventional region along the jet of mrk 501. | study of the variable broadband emission of markarian 501 during the most extreme swift x-ray activity |
high-energy emission associated with star formation has been proposed as a significant source of interstellar medium (ism) ionization in low-metallicity starbursts and an important contributor to the heating of the intergalactic medium (igm) in the high-redshift (z ≳ 8) universe. using chandra observations of a sample of 30 galaxies at d ≈ 200-450 mpc that have high specific star formation rates of 3-9 gyr-1 and metallicities near z ≈ 0.3z ⊙, we provide new measurements of the average 0.5-8 kev spectral shape and normalization per unit star formation rate (sfr). we model the sample-combined x-ray spectrum as a combination of hot gas and high-mass x-ray binary (hmxb) populations and constrain their relative contributions. we derive scaling relations of $\mathrm{log}{l}_{0.5\mbox{--}8\ \mathrm{kev}}^{\mathrm{hmxb}}$ /sfr = 40.19 ± 0.06 and $\mathrm{log}{l}_{0.5\mbox{--}2\ \mathrm{kev}}^{\mathrm{gas}}$ /sfr $=\,{39.58}_{-0.28}^{+0.17};$ significantly elevated compared to local relations. the hmxb scaling is also somewhat higher than ${l}_{0.5\mbox{--}8\ \mathrm{kev}}^{\mathrm{hmxb}}$ -sfr-z relations presented in the literature, potentially due to our galaxies having relatively low hmxb obscuration and young and x-ray luminous stellar populations. the elevation of the hot gas scaling relation is at the level expected for diminished attenuation due to a reduction of metals; however, we cannot conclude that an ${l}_{0.5\mbox{--}2\ \mathrm{kev}}^{\mathrm{gas}}$ -sfr-z relation is driven solely by changes in ism metal content. finally, we present sfr-scaled spectral models (both emergent and intrinsic) that span the x-ray-to-ir band, providing new benchmarks for studies of the impact of ism ionization and igm heating in the early universe. | elevated hot gas and high-mass x-ray binary emission in low-metallicity galaxies: implications for nebular ionization and intergalactic medium heating in the early universe |
luminous blue variables are massive evolved stars, here we introduce this outstanding class of objects. described are the specific characteristics, the evolutionary state and what they are connected to other phases and types of massive stars. our current knowledge of lbvs is limited by the fact that in comparison to other stellar classes and phases only a few "true" lbvs are known. this results from the lack of a unique, fast and always reliable identification scheme for lbvs. it literally takes time to get a true classification of a lbv. in addition the short duration of the lbv phase makes it even harder to catch and identify a star as lbv. we summarize here what is known so far, give an overview of the lbv population and the list of lbv host galaxies. lbv are clearly an important and still not fully understood phase in the live of (very) massive stars, especially due to the large and time variable mass loss during the lbv phase. we like to emphasize again the problem how to clearly identify lbv and that there are more than just one type of lbvs: the giant eruption lbvs or η car analogs and the s dor cycle lbvs. | luminous blue variables |
we present optical and near-infrared photometric and spectroscopic observations of sn 2013ej, in galaxy m74, from 1 to 450 d after the explosion. sn 2013ej is a hydrogen-rich supernova, classified as a type iil due to its relatively fast decline following the initial peak. it has a relatively high peak luminosity (absolute magnitude mv = -17.6) but a small 56ni production of ∼0.023 m⊙. its photospheric evolution is similar to other type ii sne, with shallow absorption in the hα profile typical for a type iil. during transition to the radioactive decay tail at ∼100 d, we find the sn to grow bluer in b - v colour, in contrast to some other type ii supernovae. at late times, the bolometric light curve declined faster than expected from 56co decay and we observed unusually broad and asymmetric nebular emission lines. based on comparison of nebular emission lines most sensitive to the progenitor core mass, we find our observations are best matched to synthesized spectral models with a mzams = 12-15 m⊙ progenitor. the derived mass range is similar to but not higher than the mass estimated for type iip progenitors. this is against the idea that type iil are from more massive stars. observations are consistent with the sn having a progenitor with a relatively low-mass envelope. | 450 d of type ii sn 2013ej in optical and near-infrared |
the recent launch of jwst has enabled the exciting prospect of detecting the first generation of metal-free, population iii (pop. iii) stars. determining characteristics that robustly signify pop. iii stars against other possible contaminants represents a key challenge. to this end, we run high-resolution (sub-pc) cosmological radiation hydrodynamics simulations of the region around a dwarf galaxy at z ≥ 10 to predict the emission line signatures of the pop. iii/pop. ii transition. we show that the absence of metal emission lines is a poor diagnostic of pop. iii stars because metal-enriched galaxies can maintain low [o iii] 5007 å that may be undetectable due to sensitivity limits. combining spectral hardness probes (e.g. he ii 1640 å/h α) with metallicity diagnostics is more likely to probe metal-free stars, although contamination from wolf-rayet stars, x-ray binaries, or black holes may be important. the hard emission from pop. iii galaxies fades fast due to the short stellar lifetimes of massive stars, which could further inhibit detection. pop. iii stars may be identifiable after they evolve off the main sequence due to the cooling radiation from nebular gas or a supernova remnant; however, these signatures are also short-lived (i.e. few myr). contaminants including flickering black holes might confuse this diagnostic. while jwst will provide a unique opportunity to spectroscopically probe the nature of the earliest galaxies, both the short time-scales associated with pristine systems and ambiguities in interpreting emission lines may hinder progress. special care will be needed before claiming the discovery of systems with pure pop. iii stars. | the challenges of identifying population iii stars in the early universe |
when supernovae enter the nebular phase after a few months, they reveal spectral fingerprints of their deep interiors, glowing by radioactivity produced in the explosion. we are given a unique opportunity to see what an exploded star looks like inside. the line profiles and luminosities encode information about physical conditions, explosive and hydrostatic nucleosynthesis, and ejecta morphology, which link to the progenitor properties and the explosion mechanism. here, the fundamental properties of spectral formation of supernovae in the nebular phase are reviewed. the formalism between ejecta morphology and line profile shapes is derived, including effects of scattering and absorption. line luminosity expressions are derived in various physical limits, with examples of applications from the literature. the various physical processes at work in the supernova ejecta, including gamma deposition, non-thermal electron degradation, ionization and excitation, and radiative transfer, are described and linked to the computation and application of advanced spectral models. some of the results derived so far from nebular-phase supernova analysis are discussed. | spectra of supernovae in the nebular phase |
supernova (sn) 2021ocs was discovered in the galaxy ngc 7828 (z = 0.01911) within the interacting system arp 144 and subsequently classified as a normal type ic sn around peak brightness. very large telescope/fors2 observations in the nebular phase at 148 days reveal that the spectrum is dominated by oxygen and magnesium emission lines of different transitions and ionization states: o i, [o i], [o ii], [o iii], mg i, and mg ii. such a spectrum has no counterpart in the literature, though it bears a few features similar to those of some interacting type ibn and icn sne. additionally, sn 2021ocs showed a blue color, (g - r) ≲ -0.5 mag, after the peak and up to late phases, atypical for a type ic sn. together with the nebular spectrum, this suggests that sn 2021ocs underwent late-time interaction with an h/he-poor circumstellar medium (csm) resulting from the pre-sn progenitor mass loss during its final ~1000 days. the strong o and mg lines and the absence of strong c and he lines suggest that the progenitor star's o-mg layer is exposed, which places sn 2021ocs as the most extreme case of a massive progenitor star's envelope stripping in interacting sne, followed by type icn (stripped c-o layer) and ibn (stripped he-rich layer) sne. this is the first time such a case is reported in the literature. the sn 2021ocs emphasizes the importance of late-time spectroscopy of sne, even for those classified as normal events, to reveal the inner ejecta and progenitor star's csm and mass loss. *based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso program 108.2282.001. | late-time h/he-poor circumstellar interaction in the type ic supernova sn 2021ocs: an exposed oxygen-magnesium layer and extreme stripping of the progenitor |
i identify a point-symmetric structure in recently published vlt/muse velocity maps of different elements in a plane along the line of sight at the center of the supernova remnant snr 0540-69.3, and argue that jittering jets that exploded this core collapse supernova shaped this point-symmetric structure. the four pairs of two opposite clumps that compose this point symmetric structure suggest that two to four pairs of jittering jets shaped the inner ejecta in this plane. in addition, intensity images of several spectral lines reveal a faint strip (the main jet-axis) that is part of this plane of jittering jets and its similarity to morphological features in a few other snrs and in some planetary nebulae further suggests shaping by jets. my interpretation implies that in addition to instabilities, jets also mix elements in the ejecta of core collapse supernovae. based on the point-symmetric structure and under the assumption that jittering jets exploded this supernova, i estimate the component of the neutron star natal kick velocity on the plane of the sky to be ≃ 235 km s-1, and at an angle of ≃47° to the direction of the main jet-axis. i analyze this natal kick direction together with 12 other snrs in the frame of the jittering jets explosion mechanism. | imprints of the jittering jets explosion mechanism in the morphology of the supernova remnant snr 0540-69.3 |
we present a survey for the tightest visual binaries among 0.3-2 m⊙ members of the orion nebula cluster (onc). among 42 targets, we discovered 13 new 0.025-0.15 arcsec companions. accounting for the branch bias, we find a companion star fraction (csf) in the 10-60 au range of 21^{+8}_{-5} per cent, consistent with that observed in other star-forming regions (sfrs) and twice as high as among field stars; this excess is found with a high level of confidence. since our sample is dominated by disc-bearing targets, this indicates that disc disruption by close binaries is inefficient, or has not yet taken place, in the onc. the resulting separation distribution in the onc drops sharply outside 60 au. these findings are consistent with a scenario in which the initial multiplicity properties, set by the star formation process itself, are identical in the onc and in other sfrs and subsequently altered by the cluster's dynamical evolution. this implies that the fragmentation process does not depend on the global properties of a molecular cloud, but on the local properties of prestellar cores, and that the latter are self-regulated to be nearly identical in a wide range of environments. these results, however, raise anew the question of the origin of field stars as the tight binaries we have discovered will not be destroyed as the onc dissolves into the galactic field. it thus appears that most field stars formed in regions that differ from well-studied sfrs in the solar neighbourhood, possibly due to changes in core fragmentation on gyr time-scales. | is stellar multiplicity universal? tight stellar binaries in the orion nebula cluster |
we present the first detection of gas-phase s2h in the horsehead, a moderately uv-irradiated nebula. this confirms the presence of doubly sulfuretted species in the interstellar medium and opens a new challenge for sulfur chemistry. the observed s2h abundance is ∼5 × 10-11, only a factor of 4-6 lower than that of the widespread h2s molecule. h2s and s2h are efficiently formed on the uv-irradiated icy grain mantles. we performed ice irradiation experiments to determine the h2s and s2h photodesorption yields. the obtained values are ∼1.2 × 10-3 and <1 × 10-5 molecules per incident photon for h2s and s2h, respectively. our upper limit to the s2h photodesorption yield suggests that photodesorption is not a competitive mechanism to release the s2h molecules to the gas phase. other desorption mechanisms such as chemical desorption, cosmic-ray desorption, and grain shattering can increase the gaseous s2h abundance to some extent. alternatively, s2h can be formed via gas-phase reactions involving gaseous h2s and the abundant ions s+ and sh+. the detection of s2h in this nebula therefore could be the result of the coexistence of an active grain-surface chemistry and gaseous photochemistry. | first detection of interstellar s2h |
we measure the ionizing photon production efficiency (ξion) of low-mass galaxies (107.8-109.8 m⊙) at 1.4 < z < 2.7 to better understand the contribution of dwarf galaxies to the ionizing background and reionization. we target galaxies that are magnified by strong-lensing galaxy clusters and use keck/mosfire to measure nebular emission-line fluxes and hubble space telescope to measure the rest-uv and rest-optical photometry. we present two methods of stacking. first, we take the average of the log of hα-to-uv luminosity ratios (lhα/luv) of galaxies to determine the standard log(ξion). second, we take the logarithm of the total lhα over the total luv. we prefer the latter, as it provides the total ionizing uv luminosity density of galaxies when multiplied by the nonionizing uv luminosity density. log(ξion) calculated from the second method is ∼0.2 dex higher than the first method. we do not find any strong dependence between log(ξion) and stellar mass, far-uv magnitude (muv), or uv spectral slope (β). we report a value of log(ξion) ∼ 25.47 ± 0.09 for our uv-complete sample ( $-22\lt {m}_{\mathrm{uv}}\lt -17.3$ ) and ∼25.37 ± 0.11 for our mass-complete sample (7.8 < log(m*) < 9.8). these values are consistent with measurements of more massive, more luminous galaxies in other high-redshift studies that use the same stacking technique. our log(ξion) is 0.2-0.3 dex higher than low-redshift galaxies of similar mass, indicating an evolution in the stellar properties, possibly due to metallicity or age. we also find a correlation between log(ξion) and the equivalent widths of hα and [o iii] λ5007 fluxes, confirming that these equivalent widths can be used to estimate ξion. * some of the data presented herein were obtained at the w. m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and the national aeronautics and space administration. the observatory was made possible by the generous financial support of the w. m. keck foundation. this research is based on observations made with the nasa/esa hubble space telescope obtained from the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. these observations are associated with programs 12201, 12931, 13389, and 14209. | the ionizing photon production efficiency (ξion) of lensed dwarf galaxies at z ∼ 2 |
we present a detailed study of stellar rotation in the massive 1.5 gyr old cluster ngc 1846 in the large magellanic cloud. similar to other clusters at this age, ngc 1846 shows an extended main-sequence turn-off (emsto), and previous photometric studies have suggested it could be bimodal. in this study, we use muse integral-field spectroscopy to measure the projected rotational velocities (vsin i) of around 1400 stars across the emsto and along the upper main sequence of ngc 1846. we measure vsin i values up to ∼ 250 {km s^{-1}} and find a clear relation between the vsin i of a star and its location across the emsto. closer inspection of the distribution of rotation rates reveals evidence for a bimodal distribution, with the fast rotators centred around v sin i=140 {km s^{-1}} and the slow rotators centred around v sin i=60 {km s^{-1}}. we further observe a lack of fast rotating stars along the photometric binary sequence of ngc 1846, confirming results from the field that suggest that tidal interactions in binary systems can spin-down stars. however, we do not detect a significant difference in the binary fractions of the fast and slowly rotating sub-populations. finally, we report on the serendipitous discovery of a planetary nebula associated with ngc 1846. | how stellar rotation shapes the colour-magnitude diagram of the massive intermediate-age star cluster ngc 1846 |
context. the carina nebula complex (cnc) is one of the most massive and active star-forming regions in our galaxy and it contains several large young star clusters. the distances of the individual clusters and their physical connection were poorly known up to now, with strongly discrepant results reported in the literature.aims: we want to determine reliable distances of the young stellar clusters in the central carina nebula region (in particular, tr 14, 15, and 16) and the prominent clusters ngc 3324 and ngc 3293 in the northwestern periphery of the cnc.methods: we analyzed the parallaxes in gaia edr3 for a comprehensive sample of 237 spectroscopically identified ob stars, as well as for 9562 x-ray-selected young stars throughout the complex. we also performed an astrometric analysis to identify members of the young cluster vdbh 99, which is located in the foreground of the northwestern part of the carina nebula.results: we find that the distances of the investigated clusters in the cnc are equal within ≤2%, and yield very consistent most likely mean distance values of 2.36−0.05+0.05 kpc for the ob star sample and 2.34−0.06+0.05 kpc for the sample of x-ray-selected young stars.conclusions: our results show that the clusters in the cnc constitute a coherent star-forming region, in particular with regard to ngc 3324 and ngc 3293 at the northwestern periphery, which are (within ≤2%) at the same distance as the central carina nebula. for the foreground cluster vdbh 99, we find a mean distance of 441−2+2 pc and an age of ≃60 myr. we quantified the contamination of x-ray-selected samples of carina nebula stars based on members of this foreground cluster. table 1 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/660/a11 | gaia edr3 distances of the young stellar clusters in the extended carina nebula complex |
we present the results from deep suzaku observations of the central region of the perseus cluster. bulbul et al. (2014, apj, 789, 13) reported the detection by xmm-newton instruments of an unidentified x-ray emission line at an energy around 3.5 kev in spectra for the perseus and other clusters. they argued for a possibility of the decay of sterile neutrino, a dark matter candidate. we examine suzaku x-ray imaging spectrometer (xis) spectra of the perseus cluster for evidence in the 3.5 kev line and other possible dark matter features in the 2-6 kev energy band. in order to search for and constrain a weak line feature with the xis, observations of the crab nebula are used to evaluate the system's effective area. we found no line feature at the claimed position with a systematic line flux upper limit at a half (1.5 ev in line equivalent width) of the claimed best-fitting value by bulbul et al. (2014). we discuss this inconsistency in terms of instrumental calibration errors and modeling of continuum emission. future prospects for high-energy resolution spectroscopy with astro-h are presented. | an x-ray spectroscopic search for dark matter in the perseus cluster with suzaku |
we present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (grb) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. using spectroscopic and imaging observations of the afterglow and host of the long-duration swift grb 121024a at z = 2.30, we give one of the most complete views of a grb host/environment to date. we observe a strong damped lyα absorber (dla) with a hydrogen column density of log n({h i}) = 21.88± 0.10, h2 absorption in the lyman-werner bands (molecular fraction of log(f) ≈-1.4; fourth solid detection of molecular hydrogen in a grb-dla), the nebular emission lines hα, hβ, [o ii], [o iii] and [n ii], as well as metal absorption lines. we find a grb host galaxy that is highly star forming (sfr ∼ 40 m⊙ yr-1), with a dust-corrected metallicity along the line of sight of [zn/h]corr = -0.6 ± 0.2 ([o/h] ∼ -0.3 from emission lines), and a depletion factor [zn/fe] = 0.85 ± 0.04. the molecular gas is separated by 400 km s-1 (and 1-3 kpc) from the gas that is photoexcited by the grb. this implies a fairly massive host, in agreement with the derived stellar mass of log(m★/m⊙) = 9.9^{+0.2}_{-0.3}. we dissect the host galaxy by characterizing its molecular component, the excited gas, and the line-emitting star-forming regions. the extinction curve for the line of sight is found to be unusually flat (rv ∼ 15). we discuss the possibility of an anomalous grain size distributions. we furthermore discuss the different metallicity determinations from both absorption and emission lines, which gives consistent results for the line of sight to grb 121024a. | the warm, the excited, and the molecular gas: grb 121024a shining through its star-forming galaxy |
we present multiband ultraviolet, optical, and near-infrared photometry, along with visual-wavelength spectroscopy, of supernova (sn) 2014g in the nearby galaxy ngc 3448 (25 mpc). the early-phase spectra show strong emission lines of the high ionization species he ii/n iv/c iv during the first 2-3 d after explosion, traces of a metal-rich circumstellar material (csm) probably due to pre-explosion mass-loss events. these disappear by day 9 and the spectral evolution then continues matching that of normal type ii sne. the post-maximum light curve declines at a rate typical of type ii-l class. the extensive photometric coverage tracks the drop from the photospheric stage and constrains the radioactive tail, with a steeper decline rate than that expected from the 56co decay if γ-rays are fully trapped by the ejecta. we report the appearance of an unusual feature on the blue side of h α after 100 d, which evolves to appear as a flat spectral feature linking h α and the [o i] doublet. this may be due to interaction of the ejecta with a strongly asymmetric, and possibly bipolar csm. finally, we report two deep spectra at ∼190 and 340 d after explosion, the latter being arguably one of the latest spectra for a type ii-l sn. by modelling the spectral region around the [ca ii], we find a supersolar ni/fe production. the strength of the [o i] λλ6300,6363 doublet, compared with synthetic nebular spectra, suggests a progenitor with a zero-age main-sequence mass between 15 and 19 m⊙. | the multifaceted type ii-l supernova 2014g from pre-maximum to nebular phase |
the star formation histories (sfhs) of dwarf galaxies are thought to be bursty, with large - order of magnitude - changes in the star formation rate on time-scales similar to o-star lifetimes. as a result, the standard interpretations of many galaxy observables (which assume a slowly varying sfh) are often incorrect. here, we use the sfhs from hydrodynamical simulations to investigate the effects of bursty sfhs on sample selection and interpretation of observables and make predictions to confirm such sfhs in future surveys. first, because dwarf galaxies' star formation rates change rapidly, the mass-to-light ratio is also changing rapidly in both the ionizing continuum and, to a lesser extent, the non-ionizing ultraviolet continuum. therefore, flux limited surveys are highly biased towards selecting galaxies in the burst phase and very deep observations are required to detect all dwarf galaxies at a given stellar mass. second, we show that a log10[νlν(1500 å)/lhα] > 2.5 implies a very recent quenching of star formation and can be used as evidence of stellar feedback regulating star formation. third, we show that the ionizing continuum can be significantly higher than when assuming a constant sfh, which can affect the interpretation of nebular emission line equivalent widths and direct ionizing continuum detections. finally, we show that a star formation rate estimate based on continuum measurements only (and not on nebular tracers such as the hydrogen balmer lines) will not trace the rapid changes in star formation and will give the false impression of a star-forming main sequence with low dispersion. | consequences of bursty star formation on galaxy observables at high redshifts |
planets with sizes between those of earth and neptune divide into two populations: purely rocky bodies whose atmospheres contribute negligibly to their sizes, and larger gas-enveloped planets possessing voluminous and optically thick atmospheres. we show that whether a planet forms rocky or gas-enveloped depends on the solid surface density of its parent disc. assembly times for rocky cores are sensitive to disc solid surface density. lower surface densities spawn smaller planetary embryos; to assemble a core of given mass, smaller embryos require more mergers between bodies farther apart and therefore exponentially longer formation times. gas accretion simulations yield a rule of thumb that a rocky core must be at least 2m⊕ before it can acquire a volumetrically significant atmosphere from its parent nebula. in discs of low solid surface density, cores of such mass appear only after the gas disc has dissipated, and so remain purely rocky. higher surface density discs breed massive cores more quickly, within the gas disc lifetime, and so produce gas-enveloped planets. we test model predictions against observations, using planet radius as an observational proxy for gas-to-rock content and host star metallicity as a proxy for disc solid surface density. theory can explain the observation that metal-rich stars host predominantly gas-enveloped planets. | a metallicity recipe for rocky planets |
nature's most powerful high-energy sources are capable of accelerating particles to high energy and radiating it away on extremely short timescales, even shorter than the light crossing time of the system. it is yet unclear what physical processes can produce such an efficient acceleration, despite the copious radiative losses. by means of radiative particle-in-cell simulations, we show that magnetically dominated turbulence in pair plasmas subject to strong synchrotron cooling generates a nonthermal particle spectrum with a hard power-law range (slope p ∼1 ) within a few eddy turnover times. low pitch-angle particles can significantly exceed the nominal radiation-reaction limit, before abruptly cooling down. the particle spectrum becomes even harder (p <1 ) over time owing to particle cooling with an energy-dependent pitch-angle anisotropy. the resulting synchrotron spectrum is hard (ν fν∝νs with s ∼1 ). our findings have important implications for understanding the nonthermal emission from high-energy astrophysical sources, most notably the prompt phase of gamma-ray bursts and gamma-ray flares from the crab nebula. | pitch-angle anisotropy controls particle acceleration and cooling in radiative relativistic plasma turbulence |
we study the relation between the chemical composition and the type of dust present in a group of 20 galactic planetary nebulae (pne) that have high-quality optical and infrared spectra. the optical spectra are used, together with the best available ionization correction factors, to calculate the abundances of ar, c, cl, he, n, ne, and o relative to h. the infrared spectra are used to classify the pne in two groups depending on whether the observed dust features are representative of oxygen-rich or carbon-rich environments. the sample contains one object from the halo, eight from the bulge, and eleven from the local disc. we compare their chemical abundances with nucleosynthesis model predictions and with the ones obtained in seven galactic h ii regions of the solar neighbourhood. we find evidence of o enrichment (by ∼0.3 dex) in all but one of the pne with carbon-rich dust (crd). our analysis shows that ar, and especially cl, are the best metallicity indicators of the progenitors of pne. there is a tight correlation between the abundances of ar and cl in all the objects, in agreement with a lockstep evolution of both elements. the range of metallicities implied by the cl abundances covers one order of magnitude, and we find significant differences in the initial masses and metallicities of the pne with crd and oxygen-rich dust (ord). the pne with crd tend to have intermediate masses and low metallicities, whereas most of the pne with ord show higher enrichments in n and he, suggesting that they had high-mass progenitors. | oxygen enrichment in carbon-rich planetary nebulae |
context. our knowledge of the shape of radial metallicity gradients in disc galaxies has recently improved. conversely, the understanding of their time evolution is more complex, since it requires analysis of stellar populations with different ages or systematic studies of galaxies at different redshifts. in the local universe, h ii regions and planetary nebulae (pne) are important tools to investigate radial metallicity gradients in disc galaxies.aims: we present an in-depth study of all nearby spiral galaxies (m33, m31, ngc 300, and m81) with direct-method nebular abundances of both populations, aiming at studying the evolution of their radial metallicity gradients. for the first time, we also evaluate the radial migration of pn populations.methods: for the selected galaxies, we analysed h ii region and pn properties to: determine whether oxygen in pne is a reliable tracer for past interstellar medium (ism) composition; homogenise published datasets; estimate the migration of the oldest stellar populations; and determine the overall chemical enrichment and slope evolution.results: we confirm that oxygen in pne is a reliable tracer for past ism metallicity. we find that pn gradients are flatter than or equal to those of h ii regions. when radial motions are negligible, this result provides a direct measurement of the time evolution of the gradient. for galaxies with dominant radial motions, we provide upper limits on the gradient evolution. finally, the total metal content increases with time in all target galaxies, and early morphological types have a larger increment δ(o/h) than late-type galaxies.conclusions: our findings provide important constraints to discriminate among different galactic evolutionary scenarios, favouring cosmological models with enhanced feedback from supernovae. the advent of extremely large telescopes allows us to include galaxies in a wider range of morphologies and environments, thus putting firmer constraints on galaxy formation and evolution scenarios. | metallicity gradients in local universe galaxies: time evolution and effects of radial migration |
the guest star of ad 1181 is the only historical supernova of the past millennium that is without a definite counterpart. the previously proposed association with supernova remnant g130.7+3.1 (3c 58) is in strong doubt because of the inferred age of this remnant. here we report a new identification of sn 1181 with our codiscovery of the hottest known wolf-rayet star of the oxygen sequence (iras 00500+6713 or 2mass j00531123+6730023, here named by us as "parker's star") and its surrounding nebula pa 30. our spectroscopy of the nebula shows a fast shock with extreme velocities of ≈1100 km s-1. the derived expansion age of the nebula implies an explosive event ≈1000 yr ago that agrees with the 1181 event. the on-sky location also fits the historical chinese and japanese reports of sn 1181 to within 3°5. pa 30 and parker's star have previously been proposed to be the result of a double-degenerate merger, leading to a rare type iax supernova. the likely historical magnitude and the distance suggest the event was subluminous for normal supernova. this agrees with the proposed type iax association that would also be only the second of its kind in the galaxy. taken together, the age, location, event magnitude, and duration elevate pa 30 to prime position as the counterpart of sn 1181. this source is the only type iax supernova where detailed studies of the remnant star and nebula are possible. it provides strong observational support for the double-degenerate merger scenario for type iax supernovae. | the remnant and origin of the historical supernova 1181 ad |
we present optical photometry and spectroscopy of the type ia supernova sn2018cqj/atlas18qtd. the supernova exploded in an isolated region at ∼65 kpc from the s0 galaxy ic 550 at z = 0.0165 (d ≈ 74 mpc) and has a redshift consistent with a physical association to this galaxy. multicolor photometry show that sn2018cqj/atlas18qtd is a low-luminosity ( ${m}_{{b}_{\max }}\approx -17.9$ mag), fast-declining type ia, with color stretch sbv ≈ 0.6 and b-band decline rate δm15(b) ≈ 1.77 mag. two nebular-phase spectra obtained as part of the 100ias survey at +193 and +307 days after peak show the clear detection of a narrow hα line in emission that is resolved in the first spectrum with fwhm ≈ 1200 km s-1 and lhα ≈ 3.8 × 1037 erg s-1. the detection of a resolved hα line with a declining luminosity is broadly consistent with recent models where hydrogen is stripped from the nondegenerate companion in a single-degenerate progenitor system. however, the amount of hydrogen consistent with the luminosities of the hα line would be ∼10-3 m⊙, which is significantly less than theoretical model predictions in the classical single-degenerate progenitor systems. sn2018cqj/atlas18qtd is the second low-luminosity, fast-declining sn ia after sn2018fhw/asassn-18tb that shows narrow hα in emission in its nebular-phase spectra. | variable hα emission in the nebular spectra of the low-luminosity type ia sn2018cqj/atlas18qtd |
the kinematics and dynamics of young stellar populations enable us to test theories of star formation. with this aim, we continue our analysis of the sdss-iii/apogee in-sync survey, a high-resolution near-infrared spectroscopic survey of young clusters. we focus on the orion a star-forming region, for which in-sync obtained spectra of ∼2700 stars. in paper iv we used these data to study the young stellar population. here we study the kinematic properties through radial velocities (vr ). the young stellar population remains kinematically associated with the molecular gas, following a ∼ 10 {km} {{{s}}}-1 gradient along the filament. however, near the center of the region, the vrdistribution is slightly blueshifted and asymmetric; we suggest that this population, which is older, is slightly in the foreground. we find evidence for kinematic subclustering, detecting statistically significant groupings of colocated stars with coherent motions. these are mostly in the lower-density regions of the cloud, while the onc radial velocities are smoothly distributed, consistent with it being an older, more dynamically evolved cluster. the velocity dispersion {σ }v varies along the filament. the onc appears virialized, or just slightly supervirial, consistent with an old dynamical age. here there is also some evidence for ongoing expansion, from a vr -extinction correlation. in the southern filament, {σ }v is ∼2-3 times larger than virial in the l1641n region, where we infer a superposition along the line of sight of stellar subpopulations, detached from the gas. in contrast, {σ }v decreases toward l1641s, where the population is again in agreement with a virial state. | in-sync. v. stellar kinematics and dynamics in the orion a molecular cloud |
a modified galaxy classification scheme for local galaxies is presented. it builds upon the aitken-jeans nebula sequence, by expanding the jeans-hubble tuning fork diagram, which itself contained key ingredients from curtis and reynolds. the two-dimensional grid of galaxy morphological types presented here, with elements from de vaucouleurs' three-dimensional classification volume, has an increased emphasis on the often overlooked bars and continua of disc sizes in early-type galaxies - features not fully captured by past tuning forks, tridents, or combs. the grid encompasses nuclear discs in elliptical (e) galaxies, intermediate-scale discs in ellicular (es) galaxies, and large-scale discs in lenticular (s0) galaxies, while the e4-e7 class is made redundant given that these galaxies are lenticular galaxies. today, these structures continue to be neglected, or surprise researchers, perhaps partly due to our indoctrination to galaxy morphology through the tuning fork diagram. to better understand the current and proposed classification schemes - whose origins reside in solar/planetary formation models - a holistic overview is given. this provides due credit to some of the lesser known pioneers, presents some rationale for the grid, and reveals the incremental nature of, and some of the lesser known connections in, the field of galaxy morphology. | a galaxy classification grid that better recognizes early-type galaxy morphology |
we present high-cadence, comprehensive data on the nearby (d ≃ 33 mpc) type ii supernova (sn ii) 2017ahn, discovered within about one day of the explosion, from the very early phases after explosion to the nebular phase. the observables of sn 2017ahn show a significant evolution over the ≃470 days of our follow-up campaign, first showing prominent, narrow balmer lines and other high-ionization features purely in emission (i.e., flash spectroscopy features), which progressively fade and lead to a spectroscopic evolution similar to that of more canonical sne ii. over the same period, the decline of the light curves in all bands is fast, resembling the photometric evolution of linearly declining h-rich core-collapse sne. the modeling of the light curves and early flash spectra suggests that a complex circumstellar medium surrounds the progenitor star at the time of explosion, with a first dense shell produced during the very late stages of its evolution that is swept up by the rapidly expanding ejecta within the first ∼6 days of the sn evolution, while signatures of interaction are observed also at later phases. hydrodynamical models support the scenario in which linearly declining sne ii are predicted to arise from massive yellow super- or hypergiants depleted of most of their hydrogen layers. | the early discovery of sn 2017ahn: signatures of persistent interaction in a fast-declining type ii supernova |
a characteristic feature that is frequently found in nearby supernova remnants (snrs) is the existence of two antisymmetric, local protrusions that are projected as two 'ears' in the morphology of the nebula. in this paper, we present a novel scenario for the 'ear' formation process, according to which the two lobes are formed through the interaction of the snr with a bipolar circumstellar medium (csm) that was surrounding the explosion's centre. we conduct two-dimensional hydrodynamic simulations and we show that the snr shock breakout from the bipolar csm triggers the inflation of two opposite protrusions at the equator of the remnant, which retain their size and shape from several hundreds up to a few thousand years of the snr evolution. we run a set of models by varying the supernova (sn) and csm properties and we demonstrate that the extracted results reveal good agreement with the observables, regarding the sizes, lifespan, morphology and kinematics of the 'ears'. we discuss the plausibility of our model in nature and we suggest that the most likely progenitors of the 'ear-carrying' snrs are the luminous blue variables or the red/yellow supergiants for the snrs resulting from core collapse sn events, and the symbiotic binaries or the planetary nebulae for the snrs formed by type ia sne. finally, we compare our model with other 'ear' formation models found in the literature and we show that there are distinctive differences among them, concerning the orientation of the 'ears' and the phase in which the 'ear' formation process occurs. | 'ears' formation in supernova remnants: overhearing an interaction history with bipolar circumstellar structures |
we report observations and modeling of the stellar remnant and presumed double-degenerate merger of type iax supernova pa 30, which is the probable remnant of sn 1181 ad. it is the only known bound stellar sn remnant and the only star with wolf-rayet features that is neither a planetary nebula central star nor a massive population i progenitor. we model the unique emission-line spectrum with broad, strong o vi and o viii lines as a fast stellar wind and shocked, hot gas. non-lte wind modeling indicates a mass-loss rate of ~10-6 m ⊙ yr-1 and a terminal velocity of ~15,000 km s-1, consistent with earlier results. o viii lines indicate shocked gas temperatures of t ≃ 4 mk. we derive a magnetic field upper limit of b < 2.5 mg, below earlier suggestions. the luminosity indicates a remnant mass of 1.0-1.65 m ⊙ with ejecta mass 0.15 ± 0.05 m ⊙. archival photometry suggests the stellar remnant has dimmed by ~0.5 mag over 100 yr. a low ne/o < 0.15 argues against an o-ne white dwarf in the merger. a cold dust shell is only the second detection of dust in an sn iax and the first of cold dust. our ejecta mass and kinetic energy estimates of the remnant are consistent with type iax extragalactic sources. | a new study on a type iax stellar remnant and its probable association with sn 1181 |
superluminous supernovae are among the most energetic stellar explosions in the universe, but their energy sources remain an open question. here we present long-term observations of one of the closest examples of the hydrogen-poor superluminous supernovae subclass slsne-i, supernova sn 2017egm, revealing the most complicated known luminosity evolution of slsne-i. three distinct post-peak bumps were recorded in its light curve collected at about 100-350 days after maximum brightness, challenging current popular power models such as magnetar, fallback accretion, and interaction between ejecta and a circumstellar shell. however, the complex light curve can be well modelled by successive interactions with multiple circumstellar shells with a total mass of about 6.8-7.7 m⊙. in this scenario, large energy deposition from interaction-induced reverse shocks results in ionization of neutral oxygen in the supernova ejecta and hence a much lower nebular-phase line ratio of [o i] λ6,300/([ca ii] + [o ii]) λ7,300 (~0.2) compared with that derived for other superluminous and normal stripped-envelope supernovae. the pre-existing multiple shells indicate that the progenitor of sn 2017egm experienced pulsational mass ejections triggered by pair instability within 2 years before explosion, in robust agreement with theoretical predictions for a pre-pulsation helium-core mass of 48-51 m⊙. | a superluminous supernova lightened by collisions with pulsational pair-instability shells |
gas-giant planets, like jupiter and saturn, acquire massive gaseous envelopes during the approximately 3 myr-long lifetimes of protoplanetary discs. in the core accretion scenario, the formation of a solid core of around ten earth masses triggers a phase of rapid gas accretion. previous 3d grid-based hydrodynamical simulations found that runaway gas accretion rates correspond to approximately 10 to 100 jupiter masses per myr. such high accretion rates would result in all planets with larger than ten earth-mass cores to form jupiter-like planets, which is in clear contrast to the ice giants in the solar system and the observed exoplanet population. in this work, we used 3d hydrodynamical simulations, that include radiative transfer, to model the growth of the envelope on planets with different masses. we find that gas flows rapidly through the outer part of the envelope, but this flow does not drive accretion. instead, gas accretion is the result of quasi-static contraction of the inner envelope, which can be orders of magnitude smaller than the mass flow through the outer atmosphere. for planets smaller than saturn, we measured moderate gas accretion rates that are below one jupiter mass per myr. higher mass planets, however, accrete up to ten times faster and do not reveal a self-driven mechanism that can halt gas accretion. therefore, the reason for the final masses of saturn and jupiter remains difficult to understand, unless their completion coincided with the dissipation of the solar nebula. | quasi-static contraction during runaway gas accretion onto giant planets |
we have produced for the first time a detailed velocity map of the giant filamentary nebula surrounding ngc 1275, the perseus cluster's brightest galaxy, and revealed a previously unknown rich velocity structure across the entire nebula. these new observations were obtained with the optical imaging fourier transform spectrometer sitelle at cfht. with its wide field of view ( ∼11 arcmin × 11 arcmin), sitelle is the only integral field unit spectroscopy instrument able to cover the 80 kpc × 55 kpc ( 3.8 arcmin × 2.6 arcmin) large nebula in ngc 1275. our analysis of these observations shows a smooth radial gradient of the [n ii]λ6583/h α line ratio, suggesting a change in the ionization mechanism and source across the nebula. the velocity map shows no visible general trend or rotation, indicating that filaments are not falling uniformly onto the galaxy, nor being uniformly pulled out from it. comparison between the physical properties of the filaments and hitomi measurements of the x-ray gas dynamics in perseus is also explored. | revealing the velocity structure of the filamentary nebula in ngc 1275 in its entirety |
chondritic meteorites, the building blocks of terrestrial planets, are made of an out-of-equilibrium assemblage of solids formed at high and low temperatures, either in our solar system or previous generations of stars. for decades this was considered to result from large-scale transport processes in the sun’s isolated accretion disk. however, mounting evidence suggests that refractory inclusions in chondrites formed contemporaneously with the disk building. here we numerically investigate, using a 1d model and several physical and chemical processes, the formation and transport of rocky materials during the collapse of the sun’s parent cloud and the consequent assembling of the solar nebula. the interplay between the cloud collapse, the dynamics of gas and dust, vaporization, recondensation, and thermal processing of different species in the disk results in a local mixing of solids with different thermal histories. moreover, our results also explain the overabundance of refractory materials far from the sun and their short-formation timescales, during the first tens of kyr of the sun, corresponding to class 0-i, opening new windows into the origin of the compositional diversity of chondrites. | making the planetary material diversity during the early assembling of the solar system |
context.aims: in order to study the effects of rotating disks in the post-asymptotic giant branch (post-agb) evolution, we observe a class of binary post-agb stars that seem to be systematically surrounded by equatorial disks and slow outflows. although the rotating dynamics had only been well identified in three cases, the study of such structures is thought to be fundamental to the understanding of the formation of disks in various phases of the late evolution of binary stars and the ejection of planetary nebulae from evolved stars.methods: we present alma maps of 12co and 13co j = 3-2 lines in the source iras 08544-4431, which belongs to the above mentioned class of objects. we analyzed the data by means of nebula models, which account for the expectedly composite source and can reproduce the data. from our modeling, we estimated the main nebula parameters, including the structure and dynamics and the density and temperature distributions. we discuss the uncertainties of the derived values and, in particular, their dependence on the distance.results: our observations reveal the presence of an equatorial disk in rotation; a low-velocity outflow is also found, probably formed of gas expelled from the disk. the main characteristics of our observations and modeling of iras 08544-4431 are similar to those of better studied objects, confirming our interpretation. the disk rotation indicates a total central mass of about 1.8 m⊙, for a distance of 1100 pc. the disk is found to be relatively extended and has a typical diameter of 4 × 1016 cm. the total nebular mass is 2 × 10-2 m⊙, of which 90% corresponds to the disk. assuming that the outflow is due to mass loss from the disk, we derive a disk lifetime of 10 000 yr. the disk angular momentum is found to be comparable to that of the binary system at present. assuming that the disk angular momentum was transferred from the binary system, as expected, the high values of the disk angular momentum in this and other similar disks suggest that the size of the stellar orbits has significantly decreased as a consequence of disk formation. | high-resolution observations of iras 08544-4431. detection of a disk orbiting a post-agb star and of a slow disk wind |
the search for extraterrestrial intelligence (seti) attempts to address the possibility of the presence of technological civilizations beyond the earth. benefiting from high sensitivity, large sky coverage, and an innovative feed cabin for china's five-hundred-meter aperture spherical radio telescope (fast), we performed seti's first observations with fast's newly commissioned 19 beam receiver; we report preliminary results in this paper. using the data stream produced by the serendip vi real-time multibeam seti spectrometer installed at fast, as well as its off-line data processing pipelines, we identify and remove four kinds of radio frequency interference (rfi): zone, broadband, multibeam, and drifting, utilizing the nebula seti software pipeline combined with machine-learning algorithms. after rfi mitigation, the nebula pipeline identifies and ranks interesting narrowband candidate et signals, scoring candidates by the number of times candidate signals have been seen at roughly the same sky position and same frequency, signal strength, proximity to a nearby star or object of interest, along with several other scoring criteria. we show four example candidate groups that demonstrate this rfi mitigation and candidate selection. this preliminary testing on fast data helps to validate our seti instrumentation techniques as well as our data processing pipeline. | first seti observations with china's five-hundred-meter aperture spherical radio telescope (fast) |
we present optical, ultraviolet, and infrared data of the type ii supernova (sn ii) 2020jfo at 14.5 mpc. this wealth of multiwavelength data allows us to compare different metrics commonly used to estimate progenitor masses of sn ii for the same object. using its early light curve, we infer sn 2020jfo had a progenitor radius of ≈700 r⊙, consistent with red supergiants of initial mass mzams =11-13 m⊙. the decline in its late-time light curve is best fit by a 56ni mass of 0.018 ± 0.007 m⊙ consistent with that ejected from sn ii-p with ≈13 m⊙ initial mass stars. early spectra and photometry do not exhibit signs of interaction with circumstellar matter, implying that sn 2020jfo experienced weak mass-loss within the final years prior to explosion. our spectra at >250 d are best fit by models from 12 m⊙ initial mass stars. we analysed integral field unit spectroscopy of the stellar population near sn 2020jfo, finding its massive star population had a zero age main sequence mass of 9.7$\substack{+2.5\\ -1.3}~{\rm m}_{\odot }$. we identify a single counterpart in pre-explosion imaging and find it has an initial mass of at most $7.2\substack{+1.2\\ -0.6}~{\rm m}_{\odot }$. we conclude that the inconsistency between this mass and indirect mass indicators from sn 2020jfo itself is most likely caused by extinction with av = 2-3 mag due to matter around the progenitor star, which lowered its observed optical luminosity. as sn 2020jfo did not exhibit extinction at this level or evidence for interaction with circumstellar matter between 1.6 and 450 d from explosion, we conclude that this material was likely confined within ≈3000 r⊙ from the progenitor star. | type ii-p supernova progenitor star initial masses and sn 2020jfo: direct detection, light-curve properties, nebular spectroscopy, and local environment |
context. the spectral classifications of the galactic o-star spectroscopic survey (gosss) and the astrometric and photometric data from gaia have significantly improved our ability to measure distances and determine memberships of stellar groups (clusters, associations, or parts thereof) with ob stars. in the near future, the situation will be further improved thanks to subsequent gaia data releases and new photometric and spectroscopic surveys.aims: we initiated a program to identify and determine the membership of galactic stellar groups with ob stars and measure distances to them. given the data currently available, we started with the identification and distance determinations of groups with o stars. in this paper, we concentrate on groups that contain stars with the earliest spectral subtypes.methods: we used gosss to select galactic stellar groups with o2-o3.5 stars and the method described in paper 0 of this series, which combines gaia dr2 g + gbp + grp photometry, positions, proper motions, and parallaxes to assign robust memberships and measure distances. we also included collinder 419 and ngc 2264, the clusters cited in that paper, to generate our first list of 16 o-type galactic stellar groups.results: we derived distances, determined the membership, and analyzed the structure of sixteen galactic stellar groups with o stars, villafranca o-001 to villafranca o-016, including the fourteen groups with the earliest-o-type optically accessible stars known in the milky way. we compared our distance with previous results from the literature and establish that the best consistency is with (the small number of) vlbi parallaxes and the worst is with kinematic distances. our results indicate that very massive stars can form in relatively low-mass clusters or even in near-isolation, as is the case for the bajamar star in the north america nebula. this lends support to the hierarchical scenario of star formation, where some stars are born in well-defined bound clusters but others are born in associations that are unbound from the beginning: groups of newborn stars come in many shapes and sizes. we propose that hd 64 568 and hd 64 315 ab could have been ejected simultaneously from haffner 18 (villafranca o-012 s). our results are consistent with a difference of ≈20 μas in the gaia dr2 parallax zero point between bright and faint stars. | the villafranca catalog of galactic ob groups. i. systems with o2-o3.5 stars |
lyα emission is widely used to detect and confirm high-redshift galaxies and characterize the evolution of the intergalactic medium (igm). however, many galaxies do not display lyα emission in typical spectroscopic observations, and intrinsic lyα emitters represent a potentially biased set of high-redshift galaxies. in this work, we analyze a set of 703 galaxies at 2 ≲ z ≲ 3 with both lyα spectroscopy and measurements of other rest-frame ultraviolet and optical properties in order to develop an empirical model for lyα emission from galaxies and understand how the probability of lyα emission depends on other observables. we consider several empirical proxies for the efficiency of lyα photon production, as well as the subsequent escape of these photons through their local interstellar medium. we find that the equivalent width of metal-line absorption and the o3 ratio of rest-frame optical nebular lines are advantageous empirical proxies for lyα escape and production, respectively. we develop a new quantity, {x}lis}{{o}3}, that combines these two properties into a single predictor of net lyα emission, which we find describes ∼90% of the observed variance in lyα equivalent width when accounting for our observational uncertainties. we also construct conditional probability distributions demonstrating that galaxy selection based on measurements of galaxy properties yield samples of galaxies with widely varying probabilities of net lyα emission. the application of the empirical models and probability distributions described here may be used to infer the selection biases of current galaxy surveys and evaluate the significance of high-redshift lyα (non)detections in studies of reionization and the igm. based on data obtained at the w. m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa, and was made possible by the generous financial support of the w. m. keck foundation. | predicting lyα emission from galaxies via empirical markers of production and escape in the kbss |
carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur (chnops) play key roles in the origin and proliferation of life on earth. given the universality of physics and chemistry, not least the ubiquity of water as a solvent and carbon as a backbone of complex molecules, chnops are likely crucial to most habitable worlds. to help guide and inform the search for potentially habitable and ultimately inhabited environments, we begin by summarizing the chnops budget of various reservoirs on earth, their role in shaping our biosphere, and their origins in the solar nebula. we then synthesize our current understanding of how these elements behave and are distributed in diverse astrophysical settings, tracing their journeys from synthesis in dying stars to molecular clouds, protoplanetary settings, and ultimately temperate rocky planets around main sequence stars. we end by identifying key branching points during this journey, highlighting instances where a forming planet's distribution of chnops can be altered dramatically, and speculating about the consequences for the chemical habitability of these worlds. | chemical habitability: supply and retention of life's essential elements during planet formation |
the contemporaneous detection of gravitational waves and gamma rays from gw170817/grb 170817a, followed by kilonova emission a day after, confirmed compact binary neutron star mergers as progenitors of short-duration gamma-ray bursts (grbs) and cosmic sources of heavy r-process nuclei. however, the nature (and life span) of the merger remnant and the energy reservoir powering these bright gamma-ray flashes remains debated, while the first minutes after the merger are unexplored at optical wavelengths. here, we report the earliest discovery of bright thermal optical emission associated with short grb 180618a with extended gamma-ray emission-with ultraviolet and optical multicolor observations starting as soon as 1.4 minutes post-burst. the spectrum is consistent with a fast-fading afterglow and emerging thermal optical emission 15 minutes post-burst, which fades abruptly and chromatically (flux density fν∝ t -α , α = 4.6 ± 0.3) just 35 minutes after the grb. our observations from gamma rays to optical wavelengths are consistent with a hot nebula expanding at relativistic speeds, powered by the plasma winds from a newborn, rapidly spinning and highly magnetized neutron star (i.e., a millisecond magnetar), whose rotational energy is released at a rate l th ∝ t -(2.22±0.14) to reheat the unbound merger-remnant material. these results suggest that such neutron stars can survive the collapse to a black hole on timescales much larger than a few hundred milliseconds after the merger and power the grb itself through accretion. bright thermal optical counterparts to binary merger gravitational wave sources may be common in future wide-field fast-cadence sky surveys. | a short gamma-ray burst from a protomagnetar remnant |
in galaxy clusters, the hot intracluster medium (icm) can develop a striking multiphase structure around the brightest cluster galaxy. much work has been done on understanding the origin of this central nebula, but less work has studied its eventual fate after the originally filamentary structure is broken into individual cold clumps. in this paper, we perform a suite of 30 (magneto)hydrodynamical simulations of kpc-scale cold clouds with typical parameters as found by galaxy cluster simulations, to understand whether clouds are mixed back into the hot icm or can persist. we investigate the effects of radiative cooling, small-scale heating, magnetic fields, and (anisotropic) thermal conduction on the long-term evolution of clouds. we find that filament fragments cool on time-scales shorter than the crushing time-scale, fall out of pressure equilibrium with the hot medium, and shatter, forming smaller clumplets. these act as nucleation sites for further condensation, and mixing via kelvin-helmholtz instability, causing cold gas mass to double within 75 myr. cloud growth depends on density, as well as on local heating processes, which determine whether clouds undergo ablation- or shattering-driven evolution. magnetic fields slow down but do not prevent cloud growth, with the evolution of both cold and warm phase sensitive to the field topology. counterintuitively, anisotropic thermal conduction increases the cold gas growth rate compared to non-conductive clouds, leading to larger amounts of warm phase as well. we conclude that dense clumps on scales of 500 pc or more cannot be ignored when studying the long-term cooling flow evolution of galaxy clusters. | shattering and growth of cold clouds in galaxy clusters: the role of radiative cooling, magnetic fields, and thermal conduction |
we have investigated the fine-grained matrix of the least-altered unequilibrated ordinary chondrite (uoc) semarkona (ll3.00) using different electron microscope techniques. unlike previous studies, which found that the matrix of semarkona was extensively altered to phyllosilicates, we have discovered the widespread occurrence of much more pristine amorphous silicates in the sample that we have studied. detailed tem study shows that these materials occur pervasively in the matrix as (1) continuous groundmass; (2) distinct, circular to subrounded features, which contain nanometric-size sulfides and carbides; or (3) distinct objects containing parallel, linear features composed of sulfides and voids. these amorphous silicates have many textural and compositional similarities to the occurrences of amorphous silicates found in pristine carbonaceous chondrites (ccs); however, minor differences were also identified. most of the textural and chemical differences suggest that these materials formed at different times and locations in the solar nebula, compared to matrix materials in ccs. nevertheless, their occurrence suggests that the amorphous silicates in semarkona formed by similar processes to those proposed for amorphous silicates in ccs, that is, rapid cooling that favored disequilibrium condensation of material evaporated during chondrule-forming events. in addition, the occurrence of minimally altered amorphous silicates in semarkona demonstrates that the effects of aqueous alteration, which have been widely described in this meteorite, are not pervasive. instead, our new observations demonstrate that aqueous alteration has affected semarkona heterogeneously and that locally, regions of much more pristine matrix that have escaped extensive alteration are still preserved within this meteorite. such materials provide significant new insights into the pristine characteristics of ordinary chondrite matrix material that has not been previously available. | amorphous silicates in the matrix of semarkona: the first evidence for the localized preservation of pristine matrix materials in the most unequilibrated ordinary chondrites |
when corrected for the effects of cosmic ray exposure, mo and ru nucleosynthetic isotope anomalies in iron meteorites from at least nine different parent bodies are strongly correlated in a manner consistent with variable depletion in s-process nucleosynthetic components. in contrast to prior studies, the new results show no significant deviations from a single correlation trend. in the refined mo-ru cosmic correlation, a distinction between the non-carbonaceous (nc) group and carbonaceous chondrite (cc) group is evident. members of the nc group are characterized by isotope compositions reflective of variable s-process depletion. members of the cc group analyzed here plot in a tight cluster and have the most s-process depleted mo and ru isotopic compositions, with mo isotopes also slightly enriched in r- and possibly p-process contributions. this indicates that the nebular feeding zone of the nc group parent bodies was characterized by mo and ru with variable s-process contributions, but with the two elements always mixed in the same proportions. the cc parent bodies sampled here, by contrast, were derived from a nebular feeding zone that had been mixed to a uniform s-process depleted mo-ru isotopic composition. six molybdenite samples, four glacial diamictites, and two ocean island basalts were analyzed to provide a preliminary constraint on the average mo isotope composition of the bulk silicate earth (bse). combined results yield an average μ97mo value of +3 ± 6. this value, coupled with a previously reported μ100ru value of +1 ± 7 for the bse, indicates that the isotopic composition of the bse falls precisely on the refined mo-ru cosmic correlation. the overlap of the bse with the correlation implies that there was homogeneous accretion of siderophile elements for the final accretion of 10 to 20 wt% of earth's mass. the only known cosmochemical materials with an isotopic match to the bse, with regard to mo and ru, are some members of the iab iron meteorite complex and enstatite chondrites. | new insights into mo and ru isotope variation in the nebula and terrestrial planet accretionary genetics |
the c iii] and c iv rest-frame uv emission lines are powerful probes of the ionization states of galaxies. they have furthermore been suggested as alternatives for spectroscopic redshift confirmation of objects at the epoch of reionization (z> 6), where the most frequently used redshift indicator, lyα, is attenuated by the high fraction of neutral hydrogen in the intergalactic medium. however, currently only very few confirmations of carbon uv lines at these high redshifts exist, making it challenging to quantify these claims. here, we present the detection of c iv λλ1548, 1551 å in hubble space telescope slitless grism spectroscopy obtained by glass of a lyα emitter at z = 6.11 multiply imaged by the massive foreground galaxy cluster rxc j2248.7-4431. the c iv emission is detected at the 3σ-5σ level in two images of the source, with marginal detection in two other images. we do not detect significant c iii]λλ1907, 1909 å emission implying an equivalent width {{ew}}{{c}{{iii}}]}< 20 å (1σ) and {{c}} {{iv}}/{{c}} {{iii}}> 0.7 (2σ). combined with limits on the rest-frame uv flux from the he ii λ1640 å emission line and the o iii]λλ1661, 1666 å doublet, we put constraints on the metallicity and the ionization state of the galaxy. the estimated line ratios and equivalent widths do not support a scenario where an agn is responsible for ionizing the carbon atoms. sed fits, including nebular emission lines, imply a source with a mass of log(m/m ⊙) ∼ 9, sfr of around 10 m ⊙ yr-1, and a young stellar population < 50 {myr} old. the source shows a stronger ionizing radiation field than objects with detected c iv emission at z< 2 and adds to the growing sample of low-mass (log(m/m ⊙) ≲ 9) galaxies at the epoch of reionization with strong radiation fields from star formation. | the grism lens-amplified survey from space (glass). xi. detection of c iv in multiple images of the z = 6.11 lyα emitter behind rxc j2248.7-4431 |
context. the class 0 protostellar binary iras 16293-2422 is an interesting target for (sub)millimeter observations due to, both, the rich chemistry toward the two main components of the binary and its complex morphology. its proximity to earth allows the study of its physical and chemical structure on solar system scales using high angular resolution observations. such data reveal a complex morphology that cannot be accounted for in traditional, spherical 1d models of the envelope.aims: the purpose of this paper is to study the environment of the two components of the binary through 3d radiative transfer modeling and to compare with data from the atacama large millimeter/submillimeter array. such comparisons can be used to constrain the protoplanetary disk structures, the luminosities of the two components of the binary and the chemistry of simple species.methods: we present 13co, c17o and c18o j = 3-2 observations from the alma protostellar interferometric line survey (pils), together with a qualitative study of the dust and gas density distribution of iras 16293-2422. a 3d dust and gas model including disks and a dust filament between the two protostars is constructed which qualitatively reproduces the dust continuum and gas line emission.results: radiative transfer modeling in our sampled parameter space suggests that, while the disk around source a could not be constrained, the disk around source b has to be vertically extended. this puffed-up structure can be obtained with both a protoplanetary disk model with an unexpectedly high scale-height and with the density solution from an infalling, rotating collapse. combined constraints on our 3d model, from observed dust continuum and co isotopologue emission between the sources, corroborate that source a should be at least six times more luminous than source b. we also demonstrate that the volume of high-temperature regions where complex organic molecules arise is sensitive to whether or not the total luminosity is in a single radiation source or distributed into two sources, affecting the interpretation of earlier chemical modeling efforts of the iras 16293-2422 hot corino which used a single-source approximation.conclusions: radiative transfer modeling of source a and b, with the density solution of an infalling, rotating collapse or a protoplanetary disk model, can match the constraints for the disk-like emission around source a and b from the observed dust continuum and co isotopologue gas emission. if a protoplanetary disk model is used around source b, it has to have an unusually high scale-height in order to reach the dust continuum peak emission value, while fulfilling the other observational constraints. our 3d model requires source a to be much more luminous than source b; la 18 l⊙ and lb 3 l⊙. | the alma-pils survey: 3d modeling of the envelope, disks and dust filament of iras 16293-2422 |
we use planetary nebulae (pne) as probes to determine the galactic radial oxygen gradients and other abundance patterns. we select data homogeneously from recent data sets, including pne at large galactocentric distances. the radial oxygen gradient calculated for the general pn population, which probes the region from the galactic center out to ∼28 kpc, is shallow, with slope ∼-0.02 dex kpc-1, in agreement with previous findings. we looked for time evolution of the metallicity gradient using pne with different age progenitors as metallicity probes. we identify pne whose progenitor stars are younger than 1 gyr (yppne) and those whose progenitor stars are older than 7.5 gyr (oppne) based on the comparison between evolutionary yields and elemental abundances of the pne. by studying oppne and yppne separately, we found that (i) the oppne oxygen gradient is shallower (∼-0.015 dex kpc-1) than that derived from yppne (∼-0.027 dex kpc-1) (ii) the oppne inner radial distribution of oxygen is compatible with no gradient to the radial extent of the thick disk population (∼10 kpc), similarly to what has been observed in thick disk stars; and (iii) pne (especially oppne) indicate that significant gradient slope is limited to galactocentric distances between ∼10 and ∼13.5 kpc, as observed for open clusters and field stars. outside this range, the distribution is almost flat. we found that the radial oxygen gradient is steeper for a pn population closer to the galactic disk, similar to what is observed in the general stellar population by the segue survey. we use our novel population dating to compare our results with current chemical evolutionary models and gradients from other galactic populations for insight on galaxy chemical evolution. | galactic planetary nebulae as probes of radial metallicity gradients and other abundance patterns |
studies of internal structure of gas giant planets suggest that their envelopes are enriched with heavier elements than hydrogen and helium relative to their central stars. such enrichment likely occurred by solid accretion during late formation stages of gas giant planets in which gas accretion dominates protoplanetary growth. some previous studies performed orbital integration of planetesimals around a growing protoplanet with the assumption of an uniform circumstellar disc to investigate how efficiently the protoplanet captures planetesimals. however, not only planetesimals but also disc gas are gravitationally perturbed by the protoplanet in its late formation stages, resulting in gap opening in the circumstellar disc. in this study, we investigate the effects of such gap formation on the capture of planetesimals by performing dynamical simulations of planetesimals around a growing proto-gas giant planet. gap formation reduces the surface density of disc gas, makes a steep pressure gradient and limits the growth rate of the protoplanet. we find that the first effect enhances the capture of planetesimals, while the others reduce it. consequently the amount of planetesimals captured during the gas accretion is estimated to be at most ∼3 m⊕. we conclude that the in situ capture of planetesimals needs the initial solid surface density more than five times higher than that of the minimum mass solar nebula for explaining the inferred large amount of heavy element in jupiter. for highly dense warm jupiters, we would need additional processes enhancing the capture and/or supply of planetesimals. | capture of solids by growing proto-gas giants: effects of gap formation and supply limited growth |
if very massive stars (m ≳ 100 m⊙) can form and avoid too strong mass-loss during their evolution, they are predicted to explode as pair-instability supernovae (pisne). one critical test for candidate events is whether their nucleosynthesis yields and internal ejecta structure, being revealed through nebular-phase spectra at t ≳ 1 yr, match those of model predictions. here, we compute theoretical spectra based on model pisn ejecta at 1-3 yr post-explosion to allow quantitative comparison with observations. the high column densities of pisne lead to complete gamma-ray trapping for t ≳ 2 yr which, combined with fulfilled conditions of steady state, leads to bolometric supernova luminosities matching the 56co decay. most of the gamma-rays are absorbed by the deep-lying iron and silicon/sulphur layers. the ionization balance shows a predominantly neutral gas state, which leads to emission lines of fe i, si i, and s i. for low-mass pisne, the metal core expands slowly enough to produce a forest of distinct lines, whereas high-mass pisne expand faster and produce more featureless spectra. line blocking is complete below ∼5000 å for several years, and the model spectra are red. the strongest line is typically [ca ii] λλ7291, 7323, one of few lines from ionized species. we compare our models with proposed pisn candidates sn 2007bi and ptf12dam, finding discrepancies for several key observables and thus no support for a pisn interpretation. we discuss distinct spectral features predicted by the models, and the possibility of detecting pair-instability explosions among non-superluminous supernovae. | nebular spectra of pair-instability supernovae |
the planetary nebula stage is the ultimate fate of stars with masses one to eight times that of the sun (). the origin of their complex morphologies is poorly understood, although several mechanisms involving binary interaction have been proposed. in close binary systems, the orbital separation is short enough for the primary star to overfill its roche lobe as the star expands during the asymptotic giant branch phase. the excess gas eventually forms a common envelope surrounding both stars. drag forces then result in the envelope being ejected into a bipolar planetary nebula whose equator is coincident with the orbital plane of the system. systems in which both stars have ejected their envelopes and are evolving towards the white dwarf stage are said to be double degenerate. here we report that henize 2-428 has a double-degenerate core with a combined mass of ~1.76, which is above the chandrasekhar limit (the maximum mass of a stable white dwarf) of 1.4. this, together with its short orbital period (4.2 hours), suggests that the system should merge in 700 million years, triggering a type ia supernova event. this supports the hypothesis of the double-degenerate, super-chandrasekhar evolutionary pathway for the formation of type ia supernovae. | the double-degenerate, super-chandrasekhar nucleus of the planetary nebula henize 2-428 |
we present measurements of the electron-temperature-based oxygen abundance for a highly star-forming galaxy at z = 3.08, cosmos-1908. this is the highest redshift at which [o iii]λ4363 has been detected and the first time that this line has been measured at z\gt 2. we estimate an oxygen abundance of 12+{log}({{o}}/{{h}})={8.00}-0.14+0.13. this galaxy is a low-mass ({10}9.3 {m}⊙ ), highly star-forming (∼50 {m}⊙yr-1) system that hosts a young stellar population (∼160 myr). we investigate the physical conditions of the ionized gas in cosmos-1908 and find that this galaxy has a high ionization parameter, little nebular reddening (e{(b-v)}{{gas}}\lt 0.14), and a high electron density ({n}e∼ 500 cm-3). we compare the ratios of strong oxygen, neon, and hydrogen lines to the direct-method oxygen abundance for cosmos-1908 and additional star-forming galaxies at z=0-1.8 with [o iii]λ4363 measurements and show that galaxies at z∼ 1{--}3 follow the same strong-line correlations as galaxies in the local universe. this agreement suggests that the relationship between ionization parameter and o/h is similar for z∼ 0 and high-redshift galaxies. these results imply that metallicity calibrations based on lines of oxygen, neon, and hydrogen do not strongly evolve with redshift and can reliably estimate abundances out to z∼ 3, paving the way for robust measurements of the evolution of the mass-metallicity relation to high redshift. based on data obtained at the w.m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa, and was made possible by the generous financial support of the w.m. keck foundation. | the mosdef survey: detection of [o iii]λ4363 and the direct-method oxygen abundance of a star-forming galaxy at z = 3.08 |
we test the predictions of spectral synthesis models based on seven different massive-star prescriptions against legacy extragalactic uv survey (legus) observations of eight young massive clusters in two local galaxies, ngc 1566 and ngc 5253, chosen because predictions of all seven models are available at the published galactic metallicities. the high angular resolution, extensive cluster inventory, and full near-ultraviolet to near-infrared photometric coverage make the legus data set excellent for this study. we account for both stellar and nebular emission in the models and try two different prescriptions for attenuation by dust. from bayesian fits of model libraries to the observations, we find remarkably low dispersion in the median e(b - v) (∼0.03 mag), stellar masses (∼104 m⊙), and ages (∼1 myr) derived for individual clusters using different models, although maximum discrepancies in these quantities can reach 0.09 mag and factors of 2.8 and 2.5, respectively. this is for ranges in median properties of 0.05-0.54 mag, 1.8-10 × 104 m⊙, and 1.6-40 myr spanned by the clusters in our sample. in terms of best fit, the observations are slightly better reproduced by models with interacting binaries and least well reproduced by models with single rotating stars. our study provides a first quantitative estimate of the accuracies and uncertainties of the most recent spectral synthesis models of young stellar populations, demonstrates the good progress of models in fitting high-quality observations, and highlights the needs for a larger cluster sample and more extensive tests of the model parameter space. | a comprehensive comparative test of seven widely used spectral synthesis models against multi-band photometry of young massive-star clusters |
context. surveys of protoplanetary disks in star-forming regions of similar age revealed significant variations in average disk mass in some regions. for instance, disks in the orion nebular cluster (onc) and corona australis (cra) are on average smaller than disks observed in lupus, taurus, chamaeleon i, or ophiuchus.aims: in contrast to previous models that studied the truncation of disks at a late stage of their evolution, we investigate whether disks may already be born with systematically smaller disk sizes in more massive star-forming regions as a consequence of higher ionization rates.methods: assuming various cosmic-ray ionization rates, we computed the resistivities for ambipolar diffusion and ohmic dissipation with a chemical network, and performed 2d nonideal magnetohydrodynamical protostellar collapse simulations.results: a higher ionization rate leads to stronger magnetic braking, and hence to the formation of smaller disks. accounting for recent findings that protostars act as forges of cosmic rays and considering only mild attenuation during the collapse phase, we show that a high average cosmic-ray ionization rate in star-forming regions such as the onc or cra can explain the detection of smaller disks in these regions.conclusions: our results show that on average, a higher ionization rate leads to the formation of smaller disks. smaller disks in regions of similar age can therefore be the consequence of different levels of ionization, and may not exclusively be caused by disk truncation through external photoevaporation. we strongly encourage observations that allow measuring the cosmic-ray ionization degrees in different star-forming regions to test our hypothesis. | ionization: a possible explanation for the difference of mean disk sizes in star-forming regions |
we present the largest and deepest late-time radio and millimeter survey to date of superluminous supernovae (slsne) and long-duration gamma-ray bursts (lgrbs) to search for associated nonthermal synchrotron emission. using the karl g. jansky very large array (vla) and the atacama large millimeter/submillimeter array (alma), we observed 43 sources at 6 and 100 ghz on a timescale of ∼ 1-19 yr post-explosion. we do not detect radio/millimeter emission from any of the sources, with the exception of a 6 ghz detection of ptf10hgi, as well as the detection of 6 ghz emission near the location of the slsn ptf12dam, which we associate with its host galaxy. we use our data to place constraints on central engine emission due to magnetar wind nebulae and off-axis relativistic jets. we also explore nonrelativistic emission from the sn ejecta, and place constraints on obscured star formation in the host galaxies. in addition, we conduct a search for fast radio bursts (frbs) from some of the sources using vla phased-array observations; no frbs are detected to a limit of 16 mjy (7σ; 10 ms duration) in about 40 minutes on source per event. a comparison to theoretical models suggests that continued radio monitoring may lead to detections of persistent radio emission on timescales of ≳ a decade. | late-time radio and millimeter observations of superluminous supernovae and long gamma-ray bursts: implications for central engines, fast radio bursts, and obscured star formation |
optical, near-infrared (nir) photometric and spectroscopic studies, along with the optical imaging polarimetric results for sn 2012au, are presented in this article to constrain the nature of the progenitor and other properties. well-calibrated multiband optical photometric data (from -0.2 to +413 d since b-band maximum) were used to compute the bolometric light curve and to perform semi-analytical light-curve modelling using the minim code. a spin-down millisecond magnetar-powered model explains the observed photometric evolution of sn 2012au reasonably. early-time imaging polarimetric follow-up observations (-2 to +31 d) and comparison with other similar cases indicate signatures of asphericity in the ejecta. good spectral coverage of sn 2012au (from -5 to +391 d) allows us to trace the evolution of layers of sn ejecta in detail. sn 2012au exhibits higher line velocities in comparison with other sne ib. late nebular phase spectra of sn 2012au indicate a wolf-rayet star as the possible progenitor for sn 2012au, with oxygen, he-core, and main-sequence masses of ~1.62 ± 0.15 m⊙, ~4-8 m⊙, and ~17-25 m⊙, respectively. there is a clear absence of a first overtone of carbon monoxide (co) features up to +319 d in the k-band region of the nir spectra. overall analysis suggests that sn 2012au is one of the most luminous slow-decaying type ib sne, having comparatively higher ejecta mass (~ 4.7-8.3 m⊙) and kinetic energy (~ [4.8-5.4] × 1051 erg). detailed modelling using mesa and the results obtained through stella and snec explosions also strongly support spin-down of a magnetar with mass of around 20 m⊙ and metallicity z = 0.04 as a possible powering source of sn 2012au. | photometric, polarimetric, and spectroscopic studies of the luminous, slow-decaying type ib sn 2012au |
cr isotopic compositions have been measured on carbonaceous chondrites (cc): tafassasset, paris, niger i, nwa 5958, nwa 8157 and jbilet winselwan. in bulk samples, the 54cr/52cr ratios (expressed as ɛ54cr) range from 0.93 to 1.58 ɛ units. these values are in agreement with values characteristic for distinct petrologic types. despite this 54cr heterogeneity, the variability in the 53cr/52cr ratios (expressed as ɛ53cr) of 0.2 ɛ units and the mn/cr ratios is consistent with the previous finding of an isochron in the mn-cr evolution diagram. the mn/cr ratio in cc corresponds to variable abundances of high-t condensate formed and separated at the beginning of the solar system, thus the canonical 53mn/55mn ratio can be defined. based on a consistent chronology for u-pb and mn-cr between the earliest objects formed in the solar nebula and the d'orbigny angrite we define a canonical 53mn/55mn ratio and ɛ53cri of 6.8 × 10-6 and -0.177, respectively. the internal mn/cr systematics in tafassasset and paris were studied by two approaches: leaching technique and mineral separation. despite variable ɛ54cr values (up to >30 ɛ) linear co-variations were found between ɛ53cr and mn/cr ratio. the mineral separates as well as the leachates of tafassasset fall on a common isochron indicating that (1) cooling of the tafassasset's parent body occurred at 4563.5 ± 0.25 ma, and that (2) 54cr is decoupled from the other isotopes even though temperatures >900 °c have been reached during metamorphism. in the case of paris, the leachates form an alignment with a 53mn/55mn ratio higher than the canonical value. this alignment is not an isochron but rather a mixing line. based on leachates from various cm and ci, we propose the occurrence of three distinct cr reservoirs in meteoritic material: pure54, high53 and low53 characterized by a ɛ53cr and ɛ54cr of 0 and 25,000, -2.17 and 8, and 0.5 and -151, respectively. pure54 has already been described and is carried by highly refractory nano-spinel; high53 is mn-rich and most probably carried by sulfides in the matrix, whereas low53 is characterized by low mn/cr ratios and it is sensitive to metamorphism. this component could correspond to mineral phases such as refractory oxides and carbide. variable mixing proportions of high53 and low53 would explain the larger-than-expected uncertainty (mswd of 5.5) on the cc bulk regression line. a monte carlo simulation allows us to evaluate the impact of the dispersion of the initial cr isotopic ratios (as a function of variable high53). the co-variation of the mn/cr ratio and the ɛ53cr defined by the mineral separates from paris corresponds to an age of 4566.44 +0.66/-0.75 ma, while their ɛ54cr still differ by at least 0.42 ɛ. this age is likely to date the segregation of forsteritic olivines (most probably from type i chondrules) from fayalitic olivines (from type ii chondrules) and, given the sampling procedure by handpicking of hundreds of grains, corresponds to the average age of chondrule formation. | mn-cr systematics in primitive meteorites: insights from mineral separation and partial dissolution |
we have used hydrodynamical simulations to model the formation of the closest giant elliptical galaxy centaurus a. we find that a single major merger event with a mass ratio of up to 1.5, and which has happened ~2 gyr ago, is able to reproduce many of its properties, including galaxy kinematics, the inner gas disc, stellar halo ages and metallicities, and numerous faint features observed in the halo. the elongated halo shape is mostly made of progenitor residuals deposited by the merger, which also contribute to stellar shells observed in the centaurus a halo. the current model also reproduces the measured planetary nebula line-of-sight velocity and their velocity dispersion. models with a small mass ratio and relatively low gas fraction result in a de vaucouleurs profile distribution, which is consistent with observations and model expectations. a recent merger left imprints in the age distribution that are consistent with the young stellar and globular cluster populations (2-4 gyr) found within the halo. we conclude that even if not all properties of centaurus a have been accurately reproduced, a recent major merger has likely occurred to form the centaurus a galaxy as we observe it at present day. | a recent major merger tale for the closest giant elliptical galaxy centaurus a |
the rotten egg nebula has at its core a binary composed of a mira star and an a-type companion at a separation >10 au. it has been hypothesized to have formed by strong binary interactions between the mira and a companion in an eccentric orbit during periastron passage ∼800 yr ago. we have performed hydrodynamic simulations of an asymptotic giant branch (agb) star interacting with companions with a range of masses in orbits with a range of initial eccentricities and periastron separations. for reasonable values of the eccentricity, we find that roche lobe overflow can take place only if the periods are ≪100 yr. moreover, mass transfer causes the system to enter a common envelope phase within several orbits. since the central star of the rotten egg nebula is an agb star, we conclude that such a common envelope phase must have lead to a merger, so the observed companion must have been a tertiary companion of a binary that merged at the time of nebula ejection. based on the mass and time-scale of the simulated disc formed around the companion before the common envelope phase, we analytically estimate the properties of jets that could be launched. allowing for super-eddington accretion rates, we find that jets similar to those observed are plausible, provided that the putative lost companion was relatively massive. | hydrodynamic simulations of the interaction between an agb star and a main-sequence companion in eccentric orbits |
photoionization models of h ii regions require as input a description of the ionizing spectral energy distribution (sed) and of the gas distribution, in terms of ionization parameter u and chemical abundances (e.g., o/h and n/o).a strong degeneracy exists between the hardness of the sed and u, which in turn leads to high uncertainties in the determination of the other parameters, including abundances. one way to resolve the degeneracy is to fix one of the parameters using additional information. for each of the ~20 000 sources of the califa h ii regions catalog, a grid of photoionization models is computed assuming the ionizing sed to be described by the underlying stellar population obtained from spectral synthesis modeling. the ionizing sed is then defined as the sum of various stellar bursts of different ages and metallicities. this solves the degeneracy between the shape of the ionizing sed and u. the nebular metallicity (associated with o/h) is defined using the classical strong line method o3n2 (which gives our models the status of "hybrids"). the remaining free parameters are the abundance ratio n/o and the ionization parameter u, which are determined by looking for the model fitting [n ii]/hα and [o iii]/hβ. the models are also selected to fit [o ii]/hβ. this process leads to a set of ~3200 models that reproduce the three observations simultaneously. we find that the regions associated with young stellar bursts (i.e., ionized by ob stars) are affected by leaking of ionizing photons,the proportion of escaping photons having a median of 80%. the set of photoionization models satisfactorily reproduces the electron temperature derived from the [o iii]λ4363/5007 line ratio. we determine new relations between the nebular parameters, like the ionization parameter u and the [o ii]/[o iii] or [s ii]/[s iii] line ratios. a new relation between n/o and o/h is obtained, mostly compatible with previous empirical determinations (and not with previous results obtained using photoionization models). a new relation between u and o/h is also determined. all the models are publicly available on the mexican million models database 3mdb. | photoionization models of the califa h ii regions. i. hybrid models |
we investigate the environmental effect on the metal enrichment of star-forming galaxies (sfgs) in the farthest spectroscopically confirmed and x-ray-detected cluster, cl j1449+0856 at z = 1.99. we combined hubble space telescope/wfc3 g141 slitless spectroscopic data, our thirteen-band photometry, and a recent subaru/multi-object infrared camera and spectrograph (moircs) near-infrared spectroscopic follow-up to constrain the physical properties of sfgs in cl j1449+0856 and in a mass-matched field sample. after a conservative removal of active galactic nuclei, stacking individual moircs spectra of 6 (31) sources in the cluster (field) in the mass range 10 ≤ log(m/m⊙) ≤ 11, we find a ∼4σ lower [n ii]/hα ratio in the cluster than in the field. stacking a subsample of 16 field galaxies with hβ and [o iii] in the observed range, we measure an [o iii]/hβ ratio fully compatible with the cluster value. converting these ratios into metallicities, we find that the cluster sfgs are up to 0.25 dex poorer in metals than their field counterparts, depending on the adopted calibration. the low metallicity in cluster sources is confirmed using alternative indicators. furthermore, we observe a significantly higher hα luminosity and equivalent width in the average cluster spectrum than in the field. this is likely due to the enhanced specific star formation rate; even if lower dust reddening and/or an uncertain environmental dependence on the continuum-to-nebular emission differential reddening may play a role. our findings might be explained by the accretion of pristine gas around galaxies at z = 2 and from cluster-scale reservoirs, possibly connected with a phase of rapid halo mass assembly at z > 2 and of a high galaxy merging rate. | metal deficiency in cluster star-forming galaxies at z = 2 |
context. studies of nearby galaxies reveal that around 50% of the total hα luminosity in late-type spirals originates from diffuse ionised gas (dig), which is a warm, diffuse component of the interstellar medium that can be associated with various mechanisms, the most important ones being "leaking" hii regions, evolved field stars, and shocks.aims: using muse wide field mode adaptive optics-assisted data, we study the condition of the ionised medium in the nearby (d = 3.4 mpc) flocculent spiral galaxy ngc 7793 at a spatial resolution of ∼10 pc. we construct a sample of hii regions and investigate the properties and origin of the dig component.methods: we obtained stellar and gas kinematics by modelling the stellar continuum and fitting the hα emission line. we identified the boundaries of resolved hii regions based on their hα surface brightness. as a way of comparison, we also selected regions according to the hα/[sii] line ratio; this results in more conservative boundaries. using characteristic line ratios and the gas velocity dispersion, we excluded potential contaminants, such as supernova remnants (snrs) and planetary nebulae (pne). the continuum subtracted heii map was used to spectroscopically identify wolf rayet stars (wr) in our field of view. finally, we computed electron densities and temperatures using the line ratio [sii]6716/6731 and [siii]6312/9069, respectively. we studied the properties of the ionised gas through "bpt" emission line diagrams combined with velocity dispersion of the gas.results: we spectroscopically confirm two previously detected wr and snr candidates and report the discovery of the other seven wr candidates, one snr, and two pne within our field of view. the resulting dig fraction is between ∼27 and 42% depending on the method used to define the boundaries of the hii regions (flux brightness cut in hα = 6.7 × 10-18 erg s-1 cm-2 or hα/[sii] = 2.1, respectively). in agreement with previous studies, we find that the dig exhibits enhanced [sii]/hα and [nii]/hα ratios and a median temperature that is ∼3000 k higher than in hii regions. we also observe an apparent inverse correlation between temperature and hα surface brightness. in the majority of our field of view, the observed [sii]6716/6731 ratio is consistent within 1σ with ne < 30 cm-3, with an almost identical distribution for the dig and hii regions. the velocity dispersion of the ionised gas indicates that the dig has a higher degree of turbulence than the hii regions. comparison with photoionisation and shock models reveals that, overall, the diffuse component can only partially be explained via shocks and that it is most likely consistent with photons leaking from density bounded hii regions or with radiation from evolved field stars. further investigation will be conducted in a follow-up paper. | studying the ism at ∼10 pc scale in ngc 7793 with muse. i. data description and properties of the ionised gas |
context. recently published high-quality omegacam photometry of the 3 × 3 deg around the orion nebula cluster (onc) in r, and i filters revealed three well-separated pre-main sequences in the color-magnitude diagram (cmd). the objects belonging to the individual sequences are concentrated toward the center of the onc. the authors concluded that there are two competitive scenarios: a population of unresolved binaries and triples with an exotic mass ratio distribution, or three stellar populations with different ages (≈1 myr age differences).aims: we use gaia dr2 in combination with the photometric omegacam catalog to test and confirm the presence of the putative three stellar populations. we also study multiple stellar systems in the onc for the first time using gaia dr2.methods: we selected onc members based on parallaxes and proper motions and take advantage from omegacam photometry that performs better than gaia dr2 photometry in crowded regions. we identify two clearly separated sequences with a third suggested by the data. we used pisa stellar isochrones to estimate ages of the stellar populations with absolute magnitudes computed using gaia parallaxes on a star by star basis.results: (1) we confirm that the second and third sequence members are more centrally concentrated toward the center of the onc. in addition we find an indication that the parallax and proper motion distributions are different among the members of the stellar sequences. the age difference among stellar populations is estimated to be 1-2 myr. (2) we use gaia proper motions and other measures to identify and remove as many unresolved multiple system candidates as possible. nevertheless we are still able to recover two well-separated sequences with evidence for the third one, supporting the existence of the three stellar populations. (3) due to having onc members with negligible fore- or background contamination we were able to identify a substantial number of wide binary objects (separation between 1000 and 3000 au) and with relative proper motions of the binary components consistent with zero. this challenges previously inferred values that suggested no wide binary stars exist in the onc. our inferred wide-binary fraction is ≈5%.conclusions: we confirm the three populations correspond to three separated episodes of star formation. based on this result, we conclude that star formation is not happening in a single burst in this region. in addition we identify 5% of wide-binary stars in the onc that were thought not to be present. | when the tale comes true: multiple populations and wide binaries in the orion nebula cluster |
using recently acquired hubble space telescope nir observations (j, paβ, and h bands) of the nearby galaxy ngc 1313, we investigate the timescales required by a young star cluster to emerge from its natal cloud. we search for extincted star clusters, potentially embedded in their natal cloud as either (1) compact sources in regions with high hα/paβ extinctions or (2) compact h ii regions that appear as point-like sources in the paβ emission map. the nuv-optical-nir photometry of the candidate clusters is used to derive their ages, masses, and extinctions via a least-χ2 spectral energy distribution broad- and narrowband fitting process. the 100 clusters in the final samples have masses in the range ${\mathrm{log}}_{10}(m/{m}_{\odot })=2.5\mbox{--}3.5$ and moderate extinctions, e(b - v) ≲ 1.0 mag. focusing on the young clusters (0-6 myr), we derive a weak correlation between extinction and age of the clusters. almost half of the clusters have low extinctions, e(b - v) < 0.25 mag, already at very young ages (≤3 myr), suggesting that dust is quickly removed from clusters. a stronger correlation is found between the morphology of the nebular emission (compact, partial or absent, both in hα and paβ) and cluster age. relative fractions of clusters associated with a specific nebular morphology are used to estimate the typical timescales for clearing the natal gas cloud, resulting in between 3 and 5 myr, ∼1 myr older than what was estimated from nuv-optical-based cluster studies. this difference hints at a bias for optical-only-based studies, which james webb space telescope will address in the coming years. | looking for obscured young star clusters in ngc 1313 |
context. we present our observations and analysis of sn 2020cxd, a low-luminosity (ll), long-lived type iip supernova (sn). this object is a clear outlier in the magnitude-limited sn sample recently presented by the zwicky transient facility's (ztf) bright transient survey.aims: we demonstrate that sn 2020cxd is an additional member of the group of ll sne and we discuss the rarity of ll sne in the context of the ztf survey. we consider how further studies of these faintest members of the core-collapse (cc) sn family might help improve the general understanding of the underlying initial mass function for stars that explode.methods: we used optical light curves (lcs) from the ztf in the gri bands and several epochs of ultraviolet data from the neil gehrels swift observatory as well as a sequence of optical spectra. we constructed the colour curves and a bolometric lc. then we compared the evolution of the ejecta velocity and black-body temperature for ll sne as well as for typical type ii sne. furthermore, we adopted a monte carlo code that fits semi-analytic models to the lc of sn 2020cxd, which allows for the estimation of the physical parameters. using our late-time nebular spectra, we also make a comparison against sn ii spectral synthesis models from the literature to constrain the progenitor properties of sn 2020cxd.results: the lcs of sn 2020cxd show a great similarity with those of ll sne iip in terms of luminosity, timescale, and colours. also, the spectral evolution of sn 2020cxd is that of a type iip sn. the spectra show prominent and narrow p-cygni lines, indicating low expansion velocities. this is one of the faintest ll sne observed, with an absolute plateau magnitude of mr = −14.5 mag and also one with the longest plateau lengths, with a duration of 118 days. finally, the velocities measured from the nebular emission lines are among the lowest ever seen in a sn, with an intrinsic full width at half maximum value of 478 km s−1. the underluminous late-time exponential lc tail indicates that the mass of 56ni ejected during the explosion is much smaller than the average of normal sne iip, we estimate m56ni = 0.003 m⊙. the monte carlo fitting of the bolometric lc suggests that the progenitor of sn 2020cxd had a radius of r0 = 1.3 × 1013 cm, kinetic energy of ekin = 4.3 × 1050 erg, and ejecta mass of mej = 9.5 m⊙. from the bolometric lc, we estimated the total radiated energy erad = 1.52 × 1048 erg. using our late-time nebular spectra, we compared these results against sn ii spectral synthesis models to constrain the progenitor zero-age main sequence mass and found that it is likely to be ≲15 m⊙.conclusions: sn 2020cxd is a ll type iip sn. the inferred progenitor parameters and the features observed in the nebular spectrum favour a low-energy, ni-poor, iron cc sn from a low-mass (∼12 m⊙) red supergiant. photometry is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/655/a90 | a low-energy explosion yields the underluminous type iip sn 2020cxd |
the nature of the peculiar "ca-rich" sn 2019ehk in the nearby galaxy m100 remains unclear. its origin has been debated as either a stripped core-collapse supernova or a thermonuclear helium detonation event. here, we present very late-time photometry of the transient obtained with the keck i telescope at ≈280 days from peak light. using the photometry to perform accurate flux calibration of a contemporaneous nebular phase spectrum, we measure an [o i] luminosity of (0.19-1.08) × 1038 erg s-1 and [ca ii] luminosity of (2.7-15.6) × 1038 erg s-1 over the range of the uncertain extinction along the line of sight and distance to the host galaxy. we use these measurements to derive lower limits on the synthesized oxygen mass of ≈0.004-0.069 m⊙. the oxygen mass is a sensitive tracer of the progenitor mass for core-collapse supernovae, and our estimate is consistent with explosions of very low-mass co cores of 1.45-1.5 m⊙, corresponding to he core masses of ≈1.8-2.0 m⊙. we present high-quality peak light optical spectra of the transient and highlight features of hydrogen in both the early ("flash") and photospheric phase spectra that suggest the presence of ≳0.02 m⊙ of hydrogen in the progenitor at the time of explosion. the presence of h, together with the large [ca ii]/[o i] ratio (≈10-15) in the nebular phase, is consistent with sn 2019ehk being a type iib core-collapse supernova from a stripped low-mass (≈9-9.5 m⊙) progenitor, similar to the ca-rich sn iib iptf 15eqv. these results provide evidence for a likely class of "ca-rich" core-collapse supernovae from stripped low-mass progenitors in star-forming environments, distinct from the thermonuclear ca-rich gap transients in old environments. | the peculiar ca-rich sn2019ehk: evidence for a type iib core-collapse supernova from a low-mass stripped progenitor |
we present the first quantitative spectral analysis of blue supergiant stars in the nearby galaxy ngc 2403. out of a sample of 47 targets observed with the lris spectrograph at the keck i telescope we have extracted 16 b- and a-type supergiants for which we have data of sufficient quality to carry out a comparison with model spectra of evolved massive stars and infer the stellar parameters. the radial metallicity gradient of ngc 2403 that we derive has a slope of -0.14(±0.05) dex ${r}_{e}^{-1}$ , and is in accordance with the analysis of h ii region oxygen abundances. we present evidence that the stellar metallicities that we obtain in extragalactic systems in general agree with the nebular abundances based on the analysis of the auroral lines, over more than 1 order of magnitude in metallicity. adopting the known relation between stellar parameters and intrinsic luminosity we find a distance modulus μ = 27.38 ± 0.08 mag. while this can be brought into agreement with cepheid-based determinations, it is 0.14 mag short of the value measured from the tip of the red giant branch. we update the mass-metallicity relation secured from chemical abundance studies of stars in resolved star-forming galaxies. | the metallicity and distance of ngc 2403 from blue supergiants |
infrared emission lines arising from transitions between fine structure levels of heavy elements are expected to produce kilonova nebular emission. for the kilonova in gw170817, strong emission at $4.5\, {\rm \mu m}$ at late times was detected by the spitzer space telescope but no source was detected at $3.6\, {\rm \mu m}$. this peculiar spectrum indicates that strong line emitters exist around $4.5\, {\rm \mu m}$ and the absence of strong lines around $3.6\, {\rm \mu m}$. to model the spectrum we prepare a line list based on the selection rules in ls coupling from the experimentally calibrated energy levels in the nist database. this method enables to generate the synthetic spectra with accurate line wavelengths. we find that the spectrum is sensitive to the abundance pattern whether or not the first r-process peak elements are included. in both cases, the synthetic spectra can match the observed data, leading to two possible interpretations. if the first peak elements are abundant, a se iii line dominates the flux. if otherwise, w iii with os iii, rh iii, and ce iv can be the main sources. observing nebular spectra for the future kilonova in a wider wavelength range can provide more conclusive elemental identification. | tungsten versus selenium as a potential source of kilonova nebular emission observed by spitzer |
oxygen isotope ratios and corresponding 26al-26mg isotope systematics of refractory inclusions from the least metamorphosed carbonaceous chondrites, acfer 094 (c-ungrouped 3.00) and yamato 81020 (co3.05), were measured with an ion microprobe. most of the samples are fine-grained refractory inclusions which are considered as condensates from high temperature solar nebular gas. the refractory inclusions consistently exhibit 16o-enriched signatures among their interior phases (spinel, melilite, and high-ca pyroxene), as well as phases within their rim structures (spinel, high-ca pyroxene, and adjacent anorthite). this observation indicates that aggregated refractory condensates and the formation of rim structures occurred in the same 16o-rich environment. evidence for mass-dependent isotopic fractionation in oxygen and magnesium, which would indicate a later flash heating process, was not observed in rims. all oxygen isotope data from fine-grained cais are distributed between the carbonaceous chondrite anhydrous mineral (ccam) line and the primitive chondrule mineral (pcm) regression line based on oxygen isotope data from the acfer 094 chondrules. the inferred initial 26al/27al ratios, (26al/27al)0, of spinel-melilite-rich cais are (4.08 ± 0.75) × 10-5 to (5.05 ± 0.18) × 10-5 (errors are 2σ), which are slightly lower than the canonical value of 5.25 × 10-5. as there is no petrologic evidence for re-melting after condensation, the lower (26al/27al)0 values of these cais indicate either they formed up to ∼0.3 ma after canonical cais or they formed before 26al was homogeneously distributed in the solar nebula. a pyroxene-anorthite-rich cai, g92, has an 16o-rich signature like other cais but also has an order-of-magnitude less 26mg-excess in anorthite, corresponding to a (26al/27al)0 of (5.21 ± 0.54) × 10-6. as there is no evidence for a later mg isotopic disturbance, g92 anorthite is interpreted to have formed by interaction with 16o-rich nebular gas at 2-3 ma after cai formation. with the observation that 16o-rich refractory inclusions, relatively 16o-poor chondrules, and extremely 16o-poor cosmic symplectites within acfer 094 all plot on the pcm line, it suggests that 16o-rich nebular gas and extremely 16o-poor primordial volatiles represent mass-independent fractionated endmembers in the early solar system and that the pcm line represents a mixing line of these two endmembers. | a long duration of the 16o-rich reservoir in the solar nebula, as recorded in fine-grained refractory inclusions from the least metamorphosed carbonaceous chondrites |
short-lived radionuclides (slrs) once present in the solar nebula can be used as probes of the formation environment of our solar system within the milky way galaxy. the first-formed solids in the solar system, calcium-, aluminum-rich inclusions (cais) in meteorites, record the one-time existence of slrs such as 10be and 26al in the solar nebula. we measured the 10be-10b isotope systematics in 29 cais from several cv3, co3, cr2, and ch/cb chondrites and show that all except for a fun cai record a homogeneous initial 10be/9be with a single probability density peak at 10be/9be = 7.4 × 10-4. integrating these data with those of previous studies, we find that most cais (81%) for which 10be-10b isotope systematics have been determined, record a homogeneous initial 10be/9be ratio in the early solar system with a weighted mean 10be/9be = (7.1 ± 0.2) × 10-4. this uniform distribution provides evidence that 10be was predominantly formed in the parent molecular cloud and inherited by the solar nebula. possible explanations for why unusual cais (funs, placs, those from ch/cbs, and those irradiated on the parent body) recorded a 10be/9be ratio outside of 7.1 × 10-4 include the following: 1) they incorporated a component of 10be that was produced in the nebula by irradiation; 2) they formed after normal cais; and 3) they were processed (post-formation) in a way that affected their original 10be signatures. given the rarity of these examples, the overall uniformity of initial 10be/9be suggests that solar system 10be was predominantly inherited from the molecular cloud. | uniform initial 10be/9be inferred from refractory inclusions in cv3, co3, cr2, and ch/cb chondrites |
a growing number of elements show well-resolved nucleosynthetic isotope anomalies in bulk-rock samples of solar system materials. in order to establish the occurrence and extent of such isotopic heterogeneities in zr, and to investigate the origin of the widespread heterogeneities in our solar system, new high-precision zr isotope data are reported for a range of primitive and differentiated meteorites. the majority of the carbonaceous chondrites (cv, cm, co, ck) display variable ɛ96zr values (⩽1.4) relative to the earth. the data indicate the heterogeneous distribution of 96zr-rich cais in these meteorites, which sampled supernova (sn) material that was likely synthesized by charged-particle reactions or neutron-captures. other carbonaceous chondrites (ci, cb, cr), ordinary chondrites and eucrites display variable, well-resolved 96zr excesses correlated with potential, not clearly resolved variations in 91zr relative to the bulk-earth and enstatite chondrites. this tentative correlation is supported by nucleosynthetic models and provides evidence for variable contributions of average solar system s-process material to different regions of the solar system, with the earth representing the most s-process enriched material. new s-process model calculations indicate that this s-process component was produced in both low and intermediate mass asymptotic giant branch (agb) stars. the isotopic heterogeneity pattern is different to the s-process signature resolved in a previous zr leaching experiment, which was attributed to low mass agb stars. the bulk-rock heterogeneity requires several nucleosynthetic sources, and therefore opposes the theory of the injection of material from a single source (e.g., supernova, agb star) and argues for a selective dust-sorting mechanism within the solar nebula. thermal processing of labile carrier phases is considered and, if correct, necessitates the destruction and removal of non-s-process material from the innermost solar system. new zr isotope data on mineral separates and a fusion crust sample from chondrites indicate that this non-s-process material could be silicates. | zirconium isotope evidence for the heterogeneous distribution of s-process materials in the solar system |
this work extends previous kinematic studies of young stars in the head of the orion a cloud (omc-1/2/3/4/5). it is based on large samples of infrared, optical, and x-ray selected pre-main-sequence stars with reliable radial velocities and gaia-derived parallaxes and proper motions. stellar kinematic groups are identified assuming they mimic the motion of their parental gas. several groups are found to have peculiar kinematics: the ngc 1977 cluster and two stellar groups in the extended orion nebula (eon) cavity are caught in the act of departing their birthplaces. the abnormal motion of ngc 1977 may have been caused by a global hierarchical cloud collapse, feedback by massive ori ob1ab stars, supersonic turbulence, cloud-cloud collision, and/or slingshot effect; the former two models are favoured by us. eon groups might have inherited anomalous motions of their parental cloudlets due to small-scale `rocket effects' from nearby ob stars. we also identify sparse stellar groups to the east and west of orion a that are drifting from the central region, possibly a slowly expanding halo of the orion nebula cluster. we confirm previously reported findings of varying line-of-sight distances to different parts of the cloud's head with associated differences in gas velocity. 3d movies of star kinematics show contraction of the groups of stars in omc-1 and global contraction of omc-123 stars. overall, the head of orion a region exhibits complex motions consistent with theoretical models involving hierarchical gravitational collapse in (possibly turbulent) clouds with ob stellar feedback. | gaia stellar kinematics in the head of the orion a cloud: runaway stellar groups and gravitational infall |
this paper is the second in a series presenting the results of our deep h α-line survey towards protoclusters at z > 2, based on narrow-band imaging with the subaru telescope. this work investigates massive galaxies in a protocluster region associated with a radio galaxy (pks 1138 - 262), the spiderweb galaxy, at z = 2.2. our 0.5 mag deeper narrow-band imaging than previous surveys collects a total of 68 h α emitters (hae). here, 17 out of the 68 are newly discovered protocluster members. first, a very high characteristic stellar mass of m_\star ^\ast = 10^{11.73} m⊙ is measured from a schechter function fit to the mass distribution of haes. together with the chandra x-ray data, we find that four out of six massive haes (m⋆ > 1011 m⊙) show bright x-ray emission, suggesting that they host active galactic nuclei (agns). their mass estimates, therefore, would be affected by the nuclear emission from agns. notably, the x-ray-detected haes are likely positioned near the boundary between star-forming and quiescent populations in the rest-frame uvj plane. moreover, our deep narrow-band data succeed in probing the bright h α (+ [n ii]) line nebula of the spiderweb galaxy extending over ∼100 physical kpc. these results suggest that the massive galaxies in the spiderweb protocluster are on the way to becoming the bright red sequence objects seen in local galaxy clusters, where agns might play an essential role in their quenching processes, though a more statistical database is needed to build a general picture. | mahalo deep cluster survey ii. characterizing massive forming galaxies in the spiderweb protocluster at z = 2.2 |
the single-degenerate scenario for type ia supernovae should yield metal-rich ejecta that enclose some stripped material from the non-degenerate h-rich companion star. we present a large grid of non-local thermodynamic equilibrium steady-state radiative transfer calculations for such hybrid ejecta and provide analytical fits for the hα luminosity and equivalent width. our set of models covers a range of masses for 56ni and the ejecta, for the stripped material (mst), and post-explosion epochs from 100 to 300 d. the brightness contrast between stripped material and metal-rich ejecta challenges the detection of h i and he i lines prior to ~100 d. intrinsic and extrinsic optical depth effects also influence the radiation emanating from the stripped material. this inner denser region is marginally thick in the continuum and optically thick in all balmer lines. the overlying metal-rich ejecta blanket the inner regions, completely below about 5000 å, and more sparsely at longer wavelengths. as a consequence, hβ should not be observed for all values of mst up to at least 300 days, while hα should be observed after ~100 d for all mst ≥ 0.01 m⊙. observational non-detections capable of limiting the hα equivalent width to <1 å set a formal upper limit of mst < 0.001m⊙. this contrasts with the case of circumstellar-material (csm) interaction, not subject to external blanketing, which should produce hα and hβ lines with a strength dependent primarily on csm density. we confirm previous analyses that suggest low values of order 0.001 m⊙ for mst to explain the observations of the two type ia supernovae with nebular-phase hα detection, in conflict with the much greater stripped mass predicted by hydrodynamical simulations for the single-degenerate scenario. a more likely solution is the double-degenerate scenario, together with csm interaction, or enclosed material from a tertiary star in a triple system or from a giant planet. | spectral signatures of h-rich material stripped from a non-degenerate companion by a type ia supernova |
the nearby dwarf starburst galaxy ngc 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the “radio nebula”). to investigate the role of these clusters in the starburst energetics, we combine new and archival hubble space telescope images of ngc 5253 with wavelength coverage from 1500 å to 1.9 μm in 13 filters. these include hα, pβ, and pα, and the imaging from the hubble treasury program legus (legacy extragalactic uv survey). the extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (mv < -8.8) and the two young radio nebula clusters. the clusters have ages ∼1-15 myr and masses ∼1 × 104-2.5 × 105 m⊙. the clusters’ spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last ∼15 myr. the most massive cluster is in the radio nebula; with a mass ∼2.5 × 105 m⊙ and an age ∼1 myr, it is 2-4 times less massive and younger than previously estimated. it is within a dust cloud with av ∼ 50 mag, and shows a clear near-ir excess, likely from hot dust. the second radio nebula cluster is also ∼1 myr old, confirming the extreme youth of the starburst region. these two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. additional sources are required to supply the remaining ionizing radiation, and may include very massive stars. based on observations obtained with the nasa/esa hubble space telescope, at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. | the brightest young star clusters in ngc 5253. |
in this paper we present the results of our search for and study of z≳ 6 galaxy candidates behind the third frontier fields (ffs) cluster, macs j0717.5+3745, and its parallel field, combining data from hubble and spitzer. we select 39 candidates using the lyman break technique, for which the clear non-detection in optical make the extreme mid-z interlopers hypothesis unlikely. we also take benefit from z≳ 6 samples selected using the previous ff data sets of abell 2744 and macs 0416 to improve the constraints on the properties of very high redshift objects. we compute the redshift and the physical properties such emission lines properties, star formation rate, reddening, and stellar mass for all ff objects from their spectral energy distribution using templates including nebular emission lines. we study the relationship between several physical properties and confirm the trend already observed in previous surveys for evolution of star formation rate with galaxy mass and between the size and the uv luminosity of our candidates. the analysis of the evolution of the uv luminosity function with redshift seems more compatible with an evolution of density. moreover, no robust z≥slant 8.5 object is selected behind the cluster field and few z∼ 9 candidates have been selected in the two previous data sets from this legacy survey, suggesting a strong evolution in the number density of galaxies between z∼ 8 and 9. thanks to the use of the lensing cluster, we study the evolution of the star formation rate density produced by galaxies with l > 0.03 {l}\star , and confirm the strong decrease observed between z∼ 8 and 9. | young galaxy candidates in the hubble frontier fields. iii. macs j0717.5+3745 |
galaxy proto-clusters at z≳ 2 provide a direct probe of the rapid mass assembly and galaxy growth of present-day massive clusters. because of the need for precise galaxy redshifts for density mapping and the prevalence of star formation before quenching, nearly all the proto-clusters known to date were confirmed by spectroscopy of galaxies with strong emission lines. therefore, large emission-line galaxy surveys provide an efficient way to identify proto-clusters directly. here we report the discovery of a large-scale structure at z = 2.44 in the hobby eberly telescope dark energy experiment (hetdex) pilot survey. on a scale of a few tens of mpc comoving, this structure shows a complex overdensity of lyα emitters (lae), which coincides with broadband selected galaxies in the cosmos/ultravista photometric and zcosmos spectroscopic catalogs, as well as overdensities of intergalactic gas revealed in the lyα absorption maps of lee et al. we construct mock lae catalogs to predict the cosmic evolution of this structure. we find that such an overdensity should have already broken away from the hubble flow, and part of the structure will collapse to form a galaxy cluster with {10}14.5+/- 0.4 {m}⊙by z = 0. the structure contains a higher median stellar mass of broadband selected galaxies, a boost of extended lyα nebulae, and a marginal excess of active galactic nuclei relative to the field, supporting a scenario of accelerated galaxy evolution in cluster progenitors. based on the correlation between galaxy overdensity and the z = 0 descendant halo mass calibrated in the simulation, we predict that several hundred 1.9\lt z\lt 3.5 proto-clusters with z = 0 mass of \gt {10}14.5 {m}⊙will be discovered in the 8.5 gpc3 of space surveyed by the hetdex. | surveying galaxy proto-clusters in emission: a large-scale structure at z = 2.44 and the outlook for hetdex |
context. atomic gas in the diffuse interstellar medium (ism) is organized in filamentary structures. these structures usually host cold and dense molecular clumps. the galactic magnetic field is considered to play an important role in the formation of these clumps.aims: our goal is to explore the role of the magnetic field in the hi-h2 transition process.methods: we targeted a diffuse ism filamentary cloud toward the ursa major cirrus where gas transitions from atomic to molecular. we probed the magnetic field properties of the cloud with optical polarization observations. we performed multiwavelength spectroscopic observations of different species in order to probe the gas phase properties of the cloud. we observed the co (j = 1−0) and (j = 2−1) lines in order to probe the molecular content of the cloud. we also obtained observations of the [c ii] 157.6µm emission line in order to trace the co-dark h2 gas and estimate the mean volume density of the cloud.results: we identified two distinct subregions within the cloud. one of the regions is mostly atomic, while the other is dominated by molecular gas, although most of it is co-dark. the estimated plane-of-the-sky magnetic field strength between the two regions remains constant within uncertainties and lies in the range 13-30 µg. the total magnetic field strength does not scale with density. this implies that gas is compressed along the field lines. we also found that turbulence is trans-alfvénic, with ma ≈ 1. in the molecular region, we detected an asymmetric co clump whose minor axis is closer, with a 24° deviation, to the mean magnetic field orientation than the angle of its major axis. the h i velocity gradients are in general perpendicular to the mean magnetic field orientation except for the region close to the co clump, where they tend to become parallel. this phenomenon is likely related to gas undergoing gravitational infall. the magnetic field morphology of the target cloud is parallel to the h i column density structure of the cloud in the atomic region, while it tends to become perpendicular to the h i structure in the molecular region. on the other hand, the magnetic field morphology seems to form a smaller offset angle with the total column density shape (including both atomic and molecular gas) of this transition cloud.conclusions: in the target cloud where the h i-h2 transition takes place, turbulence is trans-alfvénic, and hence the magnetic field plays an important role in the cloud dynamics. atomic gas probably accumulates preferentially along the magnetic field lines and creates overdensities where molecular gas can form. the magnetic field morphology is probed better by the total column density shape of the cloud, and not its h i column density shape. polarization and co data are only available in electronic form at the cds via anonymous ftp to ftp://cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/665/a77 | hi-h2 transition: exploring the role of the magnetic field. a case study toward the ursa major cirrus |
we present three new spectra of the nearby type ia supernova (sn ia) 2011fe covering ≈480-850 days after maximum light and show that the ejecta undergoes a rapid ionization shift at ~500 days after explosion. the prominent fe iii emission lines at ≈4600 å are replaced with fe i+fe ii blends at ~4400 å and ~5400 å. the ≈7300 å feature, which is produced by [fe ii]+[ni ii] at ≲400 days after explosion, is replaced by broad (≈±15,000 km s-1) symmetric [ca ii] emission. models predict this ionization transition occurring ~100 days later than what is observed, which we attribute to clumping in the ejecta. finally, we use the nebular-phase spectra to test several proposed progenitor scenarios for sn 2011fe. nondetections of h and he exclude nearby nondegenerate companions, [o i] nondetections disfavor the violent merger of two white dwarfs, and the symmetric emission-line profiles favor a symmetric explosion. | a rapid ionization change in the nebular-phase spectra of the type ia sn 2011fe |
the kinematics and dynamics of stellar and substellar populations within young, still-forming clusters provide valuable information for constraining theories of formation mechanisms. using keck ii nirspec+ao data, we have measured radial velocities for 56 low-mass sources within 4' of the core of the orion nebula cluster (onc). we also remeasure radial velocities for 172 sources observed with sdss/apogee. these data are combined with proper motions measured using hst acs/wfpc2/wfc3ir and keck ii nirc2, creating a sample of 135 sources with all three velocity components. the velocities measured are consistent with a normal distribution in all three components. we measure intrinsic velocity dispersions of ( ${\sigma }_{{v}_{\alpha }}$ , ${\sigma }_{{v}_{\delta }}$ , ${\sigma }_{{v}_{r}}$ ) = (1.64 ± 0.12, 2.03 ± 0.13, ${2.56}_{-0.17}^{+0.16}$ ) km s-1. our computed intrinsic velocity dispersion profiles are consistent with the dynamical equilibrium models from da rio et al. (2014) in the tangential direction but not in the line-of-sight direction, possibly indicating that the core of the onc is not yet virialized, and may require a nonspherical potential to explain the observed velocity dispersion profiles. we also observe a slight elongation along the north-south direction following the filament, which has been well studied in previous literature, and an elongation in the line-of-sight to tangential velocity direction. these 3d kinematics will help in the development of realistic models of the formation and early evolution of massive clusters. | the 3d kinematics of the orion nebula cluster: nirspec-ao radial velocities of the core population |
jupiter's deep abundances help to constrain the formation history of the planet and the environment of the protoplanetary nebula. juno recently measured jupiter's deep oxygen abundance near the equator to be 2 .2−2.1+3.9 times the protosolar value (2σ uncertainties). even if the nominal value is supersolar, subsolar abundances cannot be ruled out. here we use a state-of-the-art one-dimensional thermochemical and diffusion model with updated chemistry to constrain the deep oxygen abundance with upper tropospheric co observations. we find a value of 0 .3−0.2+0.5 times the protosolar value. this result suggests that jupiter could have a carbon-rich envelope that accreted in a region where the protosolar nebula was depleted in water. however, our model can also reproduce a solar/supersolar water abundance if vertical mixing is reduced in a radiative layer where the deep oxygen abundance is obtained. more precise measurements of the deep water abundance are needed to discriminate between these two scenarios and understand jupiter's internal structure and evolution. | a subsolar oxygen abundance or a radiative region deep in jupiter revealed by thermochemical modelling |
interstellar carbonaceous dust is mainly formed in the innermost regions of circumstellar envelopes around carbon-rich asymptotic giant branch stars (agbs). in these highly chemically stratified regions, atomic and diatomic carbon, along with acetylene, are the most abundant species after h2 and co. in a previous study, we addressed the chemistry of carbon (c and c2) with h2 showing that acetylene and aliphatic species form efficiently in the dust formation region of carbon-rich agbs whereas aromatics do not. still, acetylene is known to be a key ingredient in the formation of linear polyacetylenic chains, benzene, and polycyclic aromatic hydrocarbons (pahs), as shown by previous experiments. however, these experiments have not considered the chemistry of carbon (c and c2) with c2h2. in this work, by employing a sufficient amount of acetylene, we investigate its gas-phase interaction with atomic and diatomic carbon. we show that the chemistry involved produces linear polyacetylenic chains, benzene, and other pahs, which are observed with high abundances in the early evolutionary phase of planetary nebulae. more importantly, we have found a nonnegligible amount of pure and hydrogenated carbon clusters as well as aromatics with aliphatic substitutions, both being a direct consequence of the addition of atomic carbon. the incorporation of alkyl substituents into aromatics can be rationalized by a mechanism involving hydrogen abstraction followed by methyl addition. all the species detected in the gas phase are incorporated into nanometric-sized dust analogs, which consist of a complex mixture of sp, sp2, and sp3 hydrocarbons with amorphous morphology. | the chemistry of cosmic dust analogs from c, c2, and c2h2 in c-rich circumstellar envelopes |
during the common envelope (ce) phase, a giant star in a binary system overflows its roche lobe and unstable mass transfer leads to a spiral-in of the companion, resulting in a close binary system or in a merger of the stellar cores. dynamo processes during the ce phase have been proposed as a mechanism to generate magnetic fields that are important for forming magnetic white dwarfs (mwds) and for shaping planetary nebulae. here, we present the first magnetohydrodynamics simulations of the dynamical spiral-in during a ce phase. we find that magnetic fields are strongly amplified in the accretion stream around the 1 m⊙ companion as it spirals into the envelope of a 2 m⊙ rg. this leads to field strengths of 10-100 kg throughout the envelope after 120 d. the magnetic field amplification is consistent with being driven by the magnetorotational instability. the field strengths reached in our simulation make the magnetic field interesting for diagnostic purposes, but they are dynamically irrelevant. they are also too small to explain the formation of the highest fields found in mwds, but may be relevant for luminous red novae, and detecting magnetic fields in these events would support the scenario as proposed here. | magnetic field amplification during the common envelope phase |
we study the morphologies of core collapse supernova remnants (ccsnrs) and find that about third of ccsnrs in our sample have two opposite 'ears' protruding from their main shell. we assume that the ears are formed by jets, and argue that these properties are compatible with the expectation from the explosion jet feedback mechanism. based on previous studies of ears in ccsnrs and the similarity of some ears to those found in planetary nebulae, we assume that the ears are inflated by jets that are launched during the explosion, or a short time after it. under simple geometrical assumptions, we find that the extra kinetic energy of the ears is in the range of 1-10 per cent of the explosion energy. as not all of the kinetic energy of the jets ends in the ears, we estimate that the typical kinetic energy in the jets that inflated the ears, under our assumptions, is about 5-15 per cent of the explosion energy. this study supports a serious consideration of jet-driven core-collapse supernova mechanisms. | core collapse supernova remnants with ears |
we present near-ir imaging polarimetry of five classical fu ori-type objects (fu ori, v1057 cyg, v1515 cyg, v1735 cyg, z cma) with an ∼0.″1 resolution observed using hiciao+ao188 at the subaru telescope. we observed scattered light associated with circumstellar dust around four of them (i.e., all but v1515 cyg). their polarized intensity distribution shows a variety of morphologies with arms, tails or streams, spikes, and fragmented distributions, many of which were reported in our previous paper. the morphologies of these reflection nebulae significantly differ from many other normal young stellar objects (class i-ii objects). these structures are attributed to gravitationally unstable disks, trails of clump ejections, dust blown by a wind or a jet, and a stellar companion. we can consistently explain our results with the scenario that their accretion outbursts (fuor outbursts) are triggered by gravitationally fragmenting disks, and with the hypothesis that many low-mass young stellar objects experience such outbursts. based on data collected at the subaru telescope, which is operated by the national astronomical observatory of japan. | near-infrared high-resolution imaging polarimetry of fu ori-type objects: toward a unified scheme for low-mass protostellar evolution |
ultrafast proton migration and isomerization are key processes for acetylene and its ions. however, the mechanism for ultrafast isomerization of acetylene [hcch]2+ to vinylidene [h2cc]2+ dication remains nebulous. theoretical studies show a large potential barrier ( > 2 ev) for isomerization on low-lying dicationic states, implying picosecond or longer isomerization timescales. however, a recent experiment at a femtosecond x-ray free-electron laser suggests sub-100 fs isomerization. here we address this contradiction with a complete theoretical study of the dynamics of acetylene dication produced by auger decay after x-ray photoionization of the carbon atom k shell. we find no sub-100 fs isomerization, while reproducing the salient features of the time-resolved coulomb imaging experiment. this work resolves the seeming contradiction between experiment and theory and also calls for careful interpretation of structural information from the widely applied coulomb momentum imaging method. | ultrafast isomerization in acetylene dication after carbon k-shell ionization |
we combined the spectroscopic information from the 3d-hst survey with herschel data to characterize the hα dust attenuation properties of a sample of 79 main sequence star-forming galaxies at z ~ 1 in the goods-s field. the sample was selected in the far-ir at λ = 100 and/or 160 μm and only includes galaxies with a secure hα detection (s/n > 3). from the low resolution 3d-hst spectra we measured the redshifts and the hα fluxes for the whole sample. (a factor of 1/1.2 was applied to the observed fluxes to remove the [nii] contamination.) the stellar masses (m⋆), infrared (lir), and uv luminosities (luv) were derived from the spectral energy distributions by fitting multiband data from galex near-uv to spire 500 μm. we estimated the continuum extinction estar(b-v) from both the irx = lir/luv ratio and the uv-slope, β, and found excellent agreement between the two. the nebular extinction was estimated from comparison of the observed sfrhα and sfruv. we obtained f = estar(b-v) /eneb(b-v) = 0.93 ± 0.06, which is higher than the canonical value of f = 0.44 measured in the local universe. our derived dust correction produces good agreement between the hα and ir+uv sfrs for galaxies with sfr ≳ 20m⊙/yr and m⋆ ≳ 5 × 1010m⊙, while objects with lower sfr and m⋆ seem to require a smaller f-factor (i.e. higher hα extinction correction). our results then imply that the nebular extinction for our sample is comparable to extinction in the optical-uv continuum and suggest that the f-factor is a function of both m⋆ and sfr, in agreement with previous studies. | dust attenuation in z ~ 1 galaxies from herschel and 3d-hst hα measurements |
the observation of cosmic sub-pev gamma rays from the crab nebula opens up the possibility of testing cosmic ray photon transparency at the multi-hundred-tev scale. assuming no deviation from a source gamma-ray emission due to accelerated electron inverse-compton scattering, higher event energies can extend constraints on the effects of new physics; we consider oscillation between gamma rays and axions, plus attenuation effects from gamma-ray absorption in the case of dark photon dark matter. combining the recent as γ and hawc sub-pev data with earlier magic and hegra data, axionlike particles are most constrained in the 2 ×10-7- 6 ×10-7 ev mass range, where the coupling ga γ γ is constrained to be below 1.8 ×10-10 gev-1 . direct scattering from dark photon dark matter limits kinetic mixing ε ≲10-3 for masses between 0.01 and 1 ev. | axion and dark photon limits from crab nebula high-energy gamma rays |
stellar kinematics is a powerful tool for understanding the formation process of stellar associations. here, we present a kinematic study of the young stellar population in the rosette nebula using recent gaia data and high-resolution spectra. we first isolate member candidates using the published mid-infrared photometric data and the list of x-ray sources. a total of 403 stars with similar parallaxes and proper motions are finally selected as members. the spatial distribution of the members shows that this star-forming region is highly substructured. the young open cluster ngc 2244 in the center of the nebula has a pattern of radial expansion and rotation. we discuss its implication on the cluster formation, e.g., monolithic cold collapse or hierarchical assembly. on the other hand, we also investigate three groups located around the border of the h ii bubble. the western group seems to be spatially correlated with the adjacent gas structure, but their kinematics is not associated with that of the gas. the southern group does not show any systematic motion relative to ngc 2244. these two groups might be spontaneously formed in filaments of a turbulent cloud. the eastern group is spatially and kinematically associated with the gas pillar receding away from ngc 2244. this group might be formed by feedback from massive stars in ngc 2244. our results suggest that the stellar population in the rosette nebula may form through three different processes: the expansion of stellar clusters, hierarchical star formation in turbulent clouds, and feedback-driven star formation. | a kinematic perspective on the formation process of the stellar groups in the rosette nebula |
we present photometric and spectroscopic observations of the interacting transient sn 2009ip taken during the 2013 and 2014 observing seasons. we characterize the photometric evolution as a steady and smooth decline in all bands, with a decline rate that is slower than expected for a solely 56co-powered supernova at late phases. no further outbursts or eruptions were seen over a two year period from 2012 december until 2014 december. sn 2009ip remains brighter than its historic minimum from pre-discovery images. spectroscopically, sn 2009ip continues to be dominated by strong, narrow (≲2000 km s- 1) emission lines of h, he, ca, and fe. while we make tenuous detections of [fe ii] λ7155 and [o i] λλ6300, 6364 lines at the end of 2013 june and the start of 2013 october, respectively, we see no strong broad nebular emission lines that could point to a core-collapse origin. in general, the lines appear relatively symmetric, with the exception of our final spectrum in 2014 may, when we observe the appearance of a redshifted shoulder of emission at +550 km s- 1. the lines are not blueshifted, and we see no significant near- or mid-infrared excess. from the spectroscopic and photometric evolution of sn 2009ip until 820 d after the start of the 2012a event, we still see no conclusive evidence for core-collapse, although whether any such signs could be masked by ongoing interaction is unclear. | sn 2009ip at late times - an interacting transient at +2 years |
this study reports the bulk rare earth element (rees, la-lu) compositions of 41 chondrites, including 32 falls and 9 finds from carbonaceous (ci, cm, co and cv), enstatite (eh and el) and ordinary (h, l and ll) groups, as well as 2 enstatite achondrites (aubrite). the measurements were done in dynamic mode using multi-collector inductively coupled plasma mass spectrometers (mc-icpms), allowing precise quantification of mono-isotopic rees (pr, tb, ho and tm). the ci-chondrite-normalized ree patterns (lan/lun; a proxy for fractionation of light vs. heavy rees) and eu anomalies in ordinary and enstatite chondrites show more scatter in more metamorphosed (petrologic types 4-6) than in unequilibrated (types 1-3) chondrites. this is due to parent-body redistribution of the rees in various carrier phases during metamorphism. a model is presented that predicts the dispersion of elemental and isotopic ratios due to the nugget effect when the analyzed sample mass is limited and elements are concentrated in minor grains. the dispersion in ree patterns of equilibrated ordinary chondrites is reproduced well by this model, considering that rees are concentrated in 200 μm-size phosphates, which have high lan/lun ratios and negative eu anomalies. terrestrial rocks and samples from ordinary and enstatite chondrites display negative tm anomalies of ∼-4.5% relative to ci chondrites. in contrast, cm, co and cv (except allende) show no significant tm anomalies. allende cv chondrite shows large excess tm (∼+10%). these anomalies are similar to those found in group ii refractory inclusions in meteorites but of much smaller magnitude. the presence of tm anomalies in meteorites and terrestrial rocks suggests that either (i) the material in the inner part of the solar system was formed from a gas reservoir that had been depleted in refractory dust and carried positive tm anomalies or (ii) ci chondrites are enriched in refractory dust and are not representative of solar composition for refractory elements. a new reference composition relevant to inner solar system bodies (ci∗) is calculated by subtracting 0.15% of group ii refractory inclusions to ci. the observed tm anomalies in ordinary and enstatite chondrites and terrestrial rocks, relative to carbonaceous chondrites, indicate that material akin to carbonaceous chondrites must have represented a small fraction of the constituents of the earth. tm anomalies may be correlated with ca isotopic fractionation in bulk planetary materials as they are both controlled by addition or removal of refractory material akin to fine-grained group ii refractory inclusions. | thulium anomalies and rare earth element patterns in meteorites and earth: nebular fractionation and the nugget effect |
nearby type iii (galaxy-spanning) kardashev supercivilizations would have high mid-infrared (mir) luminosities. we have used the wide-field infrared survey explorer (wise) to survey ∼ 1× {{10}5} galaxies for extreme mir emission, 1 × 103 times more galaxies than the only previous such search. we have calibrated the wise all-sky catalog pipeline products to improve their photometry for extended sources. we present 563 extended sources with |b|≥slant 10 and red mir colors, having visually vetted them to remove artifacts. no galaxies in our sample host an alien civilization reprocessing more than 85% of its starlight into the mir, and only 50 galaxies, including arp 220, have mir luminosities consistent with \gt 50% reprocessing. ninety of these (likely) extragalactic sources have little literature presence; in most cases, they are likely barely resolved galaxies or pairs of galaxies undergoing large amounts of star formation. five are new to science and deserve further study. the be star 48 librae sits within a mir nebula, and we suggest that it may be creating dust. wise, 2mass, and spitzer imagery shows that iras 04287+6444 is consistent with a previously unnoticed, heavily extinguished cluster of young stellar objects. we identify five “passive” (i.e., red) spiral galaxies with unusually high mir and low nuv luminosity. we search a set of h i dark galaxies for mir emission and find none. these 90 poorly understood sources and 5 anomalous passive spirals deserve follow-up via both seti and conventional astrophysics. | the ĝ infrared search for extraterrestrial civilizations with large energy supplies. iii. the reddest extended sources in wise |
binary evolution is indispensable in stellar evolution to understand the formation and evolution of most peculiar and energetic objects, such as binary compact objects, type ia supernovae, x-ray binaries, cataclysmic variables, blue stragglers, hot subdwarfs, and central binaries in planetary nebulae. mass transfer in binary stars can change the evolutionary path and fate of the components compared to what is expected from single stellar evolution. the critical mass ratio at which unstable mass transfer occurs is an unsolved fundamental problem in binary evolution. to resolve this issue, we construct the thermal equilibrium mass-loss model and derive critical mass ratios for both thermal-timescale mass transfer and unstable mass transfer, the latter of which occurs when the outer lagrangian point, l2, is overfilled. using several 3.2 m⊙ stellar models as examples, we study the stellar response to thermal equilibrium mass loss and present the thresholds for thermal-timescale mass transfer. we study the possible mass-transfer channels of binary systems containing a 3.2 m⊙ donor star, taking into account thermal-timescale mass transfer, unstable mass transfer through l2, and dynamical-timescale mass transfer. we repeat this simulation for a grid of donor stars with different masses (from 0.1 to 100 m⊙ with z = 0.02) and at different evolutionary stages, and present our results. the results show that unstable mass transfer due to the overfilling of the outer lagrangian point may also play an essential role in the formation of common envelopes for late red giant branch and asymptotic giant branch donors. | the thermal equilibrium mass-loss model and its applications in binary evolution |
we present the alma band 3 and band 6 results of 12co(2-1), 13co(2-1), h30α recombination line, free-free emission around 98 ghz, and the dust thermal emission around 230 ghz toward the n159 east giant molecular cloud (n159e) in the large magellanic cloud (lmc). lmc is the nearest active high-mass star-forming face-on galaxy at a distance of 50 kpc and is the best target for studing high-mass star formation. alma observations show that n159e is the complex of filamentary clouds with the width and length of ∼1 pc and several parsecs. the total molecular mass is 0.92 × 105 m⊙ from the 13co(2-1) intensity. n159e harbors the well-known papillon nebula, a compact high-excitation h ii region. we found that a yso associated with the papillon nebula has the mass of 35 m⊙ and is located at the intersection of three filamentary clouds. it indicates that the formation of the high-mass yso was induced by the collision of filamentary clouds. fukui et al. reported a similar kinematic structure toward two ysos in the n159 west region, which are the other ysos that have the mass of ≳35 m⊙. this suggests that the collision of filamentary clouds is a primary mechanism of high-mass star formation. we found a small molecular hole around the yso in papillon nebula with a sub-parsec scale. it is filled by free-free and h30α emission. the temperature of the molecular gas around the hole reaches ∼80 k. it indicates that this yso has just started the distruction of parental molecular cloud. | kinematic structure of molecular gas around high-mass yso, papillon nebula, in n159 east in the large magellanic cloud: a new perspective with alma |
we investigate the kinematic properties of nine nearby early-type galaxies with evidence of a disc-like component. three of these galaxies are located in the field, five in the group, and only one in the cluster environment. by combining the kinematics of the stars with those of the globular clusters (gcs) and planetary nebulae (pne), we probe the outer regions of our galaxies out to $\sim 4\!-\!6\, r_{\mathrm{e}}$. six galaxies have pne and red gcs that show good kinematic alignment with the stars, whose rotation occurs along the photometric major-axis of the galaxies, suggesting that both the pne and red gcs are good tracers of the underlying stellar population beyond that traced by the stars. additionally, the blue gcs also show rotation that is overall consistent with that of the red gcs in these six galaxies. the remaining three galaxies show kinematic twists and misalignment of the pne and gcs with respect to the underlying stars, suggesting recent galaxy interactions. from the comparison with simulations, we propose that all six aligned galaxies that show similar dispersion-dominated kinematics at large radii ($\gt 2\!-\!3\, r_{\mathrm{e}}$) had similar late (z ≲ 1) assembly histories characterized by mini mergers (mass-ratio < 1:10). the different vrot/σ profiles are then the result of an early (z > 1) minor merger (1:10 < mass-ratio < 1:4) for the four galaxies with peaked and decreasing vrot/σ profiles and of a late minor merger for the two galaxies with flat vrot/σ profiles. the three misaligned galaxies likely formed through multiple late minor mergers that enhanced their velocity dispersion at all radii, or a late major merger that spun-up both the gc subpopulations at large radii. therefore, lenticular galaxies can have complex merger histories that shape their characteristic kinematic profile shapes. | the sluggs survey: combining stars, globular clusters, and planetary nebulae to understand the assembly history of early-type galaxies from their large radii kinematics |
the [o iii] λ5007 planetary nebula luminosity function (pnlf) is an established distance indicator that has been used for more than 30 yr to measure the distances of galaxies out to ~15 mpc. with the advent of the multi-unit spectroscopic explorer on the very large telescope (muse) as an efficient wide-field integral-field spectrograph, the pnlf method is due for a renaissance, as the spatial and spectral information contained in the instrument's data cubes provides many advantages over classical narrowband imaging. here we use archival muse data to explore the potential of a novel differential emission-line filter (delf) technique to produce spectrophotometry that is more accurate and more sensitive than other methods. we show that delf analyses are superior to classical techniques in high surface brightness regions of galaxies, and we validate the method both through simulations and via the analysis of data from two early-type galaxies (ngc 1380 and ngc 474) and one late-type spiral (ngc 628). we demonstrate that with adaptive optics support or under excellent seeing conditions, the technique is capable of producing precision (≲0.05 mag) [o iii] photometry out to distances of 40 mpc while providing discrimination between planetary nebulae and other emission-line objects such as h ii regions, supernova remnants, and background galaxies. these capabilities enable us to use muse to measure precise pnlf distances beyond the reach of cepheids and the tip of the red giant branch method and become an additional tool for constraining the local value of the hubble constant. | toward precision cosmology with improved pnlf distances using vlt-musei. methodology and tests |
nebular emission lines associated with galactic h ii regions carry information about both physical properties of the ionized gas and the source of ionizing photons as well as providing the opportunity of measuring accurate redshifts and thus distances once a cosmological model is assumed. while nebular-line emission has been extensively studied at lower redshift there are currently only few constraints within the epoch of reionization (eor; z > 6), chiefly due to the lack of sensitive near-ir spectrographs. however, this will soon change with the arrival of the webb telescope providing sensitive near-ir spectroscopy covering the rest-frame uv and optical emission of galaxies in the eor. in anticipation of webb, we combine the large cosmological hydrodynamical simulation bluetides with photoionization modelling to predict the nebular emission-line properties of galaxies at z = 8 → 13. we find good agreement with the, albeit limited, existing direct and indirect observational constraints on equivalent widths though poorer agreement with luminosity function constraints. | nebular-line emission during the epoch of reionization |
the merger of two white dwarfs (wds) is a natural outcome of the evolution of many binary stars. recently, a wd merger product, iras 00500+6713, was identified. iras 00500+6713 consists of a central star embedded in a circular nebula. the analysis of the optical spectrum of the central star revealed that it is hot, hydrogen, and helium free, and it drives an extremely fast wind with a record breaking speed. the nebula is visible in infrared and in the [o iii] λ5007 å line images. no nebula spectroscopy was obtained prior to our observations. here we report the first deep x-ray imaging spectroscopic observations of iras 00500+6713. both the central star and the nebula are detected in x-rays, heralding the wd merger products as a new distinct type of strong x-ray sources. low-resolution x-ray spectra reveal large neon, magnesium, silicon, and sulfur enrichment of the central star and the nebula. we conclude that iras 00500+6713 resulted from a merger of an one and a co wd, which supports earlier suggestion for a super-chandrasekhar mass of this object. x-ray analysis indicates that the merger was associated with an episode of carbon burning and possibly accompanied by an sn iax. in x-rays, we observe the point source associated with the merger product while the surrounding diffuse nebula is a supernova remnant. iras 00500+6713 will likely terminate its evolution with another peculiar type i supernova, where the final core collapse to a neutron star might be induced by electron captures. based on the observations with the id numbers 0841640101, 0841640201 obtained with the esa science mission xmm-newton. | x-rays observations of a super-chandrasekhar object reveal an one and a co white dwarf merger product embedded in a putative sn iax remnant |
the goal of population spectral synthesis (pss; also referred to as inverse, semi-empirical evolutionary- or fossil record approach) is to decipher from the spectrum of a galaxy the mass, age and metallicity of its constituent stellar populations. this technique, which is the reverse of but complementary to evolutionary synthesis, has been established as fundamental tool in extragalactic research. it has been extensively applied to large spectroscopic data sets, notably the sdss, leading to important insights into the galaxy assembly history. however, despite significant improvements over the past decade, all current pss codes suffer from two major deficiencies that inhibit us from gaining sharp insights into the star-formation history (sfh) of galaxies and potentially introduce substantial biases in studies of their physical properties (e.g., stellar mass, mass-weighted stellar age and specific star formation rate). these are i) the neglect of nebular emission in spectral fits, consequently; ii) the lack of a mechanism that ensures consistency between the best-fitting sfh and the observed nebular emission characteristics of a star-forming (sf) galaxy (e.g., hydrogen balmer-line luminosities and equivalent widths-ews, shape of the continuum in the region around the balmer and paschen jump). in this article, we present fado (fitting analysis using differential evolution optimization) - a conceptually novel, publicly available pss tool with the distinctive capability of permitting identification of the sfh that reproduces the observed nebular characteristics of a sf galaxy. this so-far unique self-consistency concept allows us to significantly alleviate degeneracies in current spectral synthesis, thereby opening a new avenue to the exploration of the assembly history of galaxies. the innovative character of fado is further augmented by its mathematical foundation: fado is the first pss code employing genetic differential evolution optimization. this, in conjunction with various other currently unique elements in its mathematical concept and numerical realization (e.g., mid-analysis optimization of the spectral library using artificial intelligence, test for convergence through a procedure inspired by markov chain monte carlo techniques, quasi-parallelization embedded within a modular architecture) results in key improvements with respect to computational efficiency and uniqueness of the best-fitting sfhs. furthermore, fado incorporates within a single code the entire chain of pre-processing, modeling, post-processing, storage and graphical representation of the relevant output from pss, including emission-line measurements and estimates of uncertainties for all primary and secondary products from spectral synthesis (e.g., mass contributions of individual stellar populations, mass- and luminosity-weighted stellar ages and metallicities). this integrated concept greatly simplifies and accelerates a lengthy sequence of individual time-consuming steps that are generally involved in pss modeling, further enhancing the overall efficiency of the code and inviting to its automated application to large spectroscopic data sets. the distribution package of the fado v.1 tool contains the binary and its auxiliary files. fado v.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/603/a63 | fitting analysis using differential evolution optimization (fado):. spectral population synthesis through genetic optimization under self-consistency boundary conditions |
we report oxygen, calcium, titanium and 26al-26mg isotope systematics for spinel-hibonite inclusions (shibs), a class of calcium-aluminum-rich inclusions (cai) common in cm chondrites. in contrast to previous studies, our analyses of 33 shibs and four shib-related objects obtained with high spatial resolution demonstrate that these cais have a uniform δ17o value of approximately -23‰, similar to many other mineralogically pristine cais from unmetamorphosed chondrites (e.g., cr, cv, and acfer 094). five shibs studied for calcium and titanium isotopes have no resolvable anomalies beyond 3σ uncertainties. this suggests that nucleosynthetic anomalies in the refractory elements had been significantly diluted in the environment where shibs with uniform δ17o formed. we established internal 26al-26mg isochrons for eight shibs and found that seven of these formed with uniformly high levels of 26al (a multi-cai mineral isochron yields an initial 26al/27al ratio of ∼4.8 × 10-5), but one shib has a smaller initial 26al/27al of ∼ 2.5 × 10-5, indicating variation in 26al/27al ratios when shibs formed. the uniform calcium, titanium and oxygen isotopic characteristics found in shibs with both high and low initial 26al/27al ratios allow for two interpretations. (1) if subcanonical initial 26al/27al ratios in shibs are due to early formation, as suggested by liu et al. (2012), our data would indicate that the cai formation region had achieved a high degree of isotopic homogeneity in oxygen and refractory elements before a homogeneous distribution of 26al was achieved. (2) alternatively, if subcanonical ratios were the result of 26al-26mg system resetting, the clustering of shibs at a δ17o value of ∼-23‰ would imply that a 16o-rich gaseous reservoir existed in the nebula until at least ∼0.7 ma after the formation of the majority of cais. | new constraints on the relationship between 26al and oxygen, calcium, and titanium isotopic variation in the early solar system from a multielement isotopic study of spinel-hibonite inclusions |
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