abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
m 31 has experienced a recent tumultuous merger history, as evidenced from the many substructures that are still present in its inner halo, particularly the g1-clump, ne-, and w-shelves and the giant stream (gs). we present planetary nebulae (pne) line-of-sight velocity (losv) measurements covering the entire spatial extent of these four substructures. we further use predictions for the satellite and host stellar particle phase space distributions for a major merger (mass ratio = 1:4) simulation to help interpret the data. the measured pn losvs for the two shelves and gs are consistent with those from red giant branch stars. their projected radius versus losv phase space, links the formation of these substructures in a single unique event, consistent with a major merger. we find the g1-clump to be dynamically cold compared to the m 31 disc ($\rm \sigma _{los, pn}=27$ km s-1), consistent with pre-merger disc material. such a structure can not form in a minor merger (mass ratio ~1:20) and is therefore a smoking gun for the recent major merger event in m 31. the simulation also predicts the formation of a predominantly in situ halo from splashed-out pre-merger disc material, in qualitative agreement with observations of a metal-rich inner halo in m 31. juxtaposed with previous results for its discs, we conclude that m 31 has had a recent (2.5-4 gyr ago) 'wet' major merger with the satellite falling along the gs, heating the pre-merger disc to form the m 31 thicker disc, rebuilding the m 31 thin disc, and creating the aforementioned inner-halo substructures. | the survey of planetary nebulae in andromeda (m 31) vi. kinematics of m 31 inner-halo substructures and comparison with major-merger simulation predictions |
to understand how massive galaxies at high z coevolve with enormous reservoirs of halo gas, it is essential to study the coldest phase of the circumgalactic medium (cgm), which directly relates to stellar growth. the supercold-cgm survey is the first statistical survey of cold molecular gas on cgm scales. we present atacama large millimeter array and atacama compact array observations of co(4-3) and continuum emission from 10 enormous lyα nebulae (elane) around ultraluminous type i quasi-stellar objects (qsos) at z ~ 2. we detect co(4-3) in 100% of our targets, with 60% showing extended co on scales of 15-100 kpc. q1228+3128 reveals the most extended co(4-3) reservoir of ~100 kpc and is the only radio-loud target in our sample. the co reservoir is located along the radio axis, which could indicate a link between the inner radio jet and cold halo gas. for the other five radio-quiet elane, four of them show extended co(4-3) predominantly in the direction of their companions. these extended co(4-3) reservoirs identify enrichment of the cgm and may potentially contribute to widespread star formation. however, there is no evidence from co(4-3) for diffuse molecular gas spread across the full extent of the lyα nebulae. one target in our sample (q0107) shows significant evidence for a massive co disk associated with the qso. moreover, 70% of our qso fields contain at least one co companion, two of which reveal extended co emission outside the elane. our results provide insight into roles of both the cold cgm and companions in driving the early evolution of massive galaxies. | the supercold-cgm survey. i. probing the extended co(4-3) emission of the circumgalactic medium in a sample of 10 enormous lyα nebulae at z 2 |
the remarkably tight relationship between galaxy optical color and stellar mass-to-light ratio (m */l) is widely used for efficient stellar mass estimates. however, it remains unclear whether this low scatter comes from a natural order in the galaxy population, or whether it is driven by simple relationships in the models used to describe them. in this work, we investigate the origins of the relationship by contrasting the derived relationship from a simple 4 parameter spectral energy distribution (sed) model with a more sophisticated 14d prospector-α model including nonparametric star formation histories (sfhs). we apply these models to 63,430 galaxies at 0.5 < z < 3 and fit a hierarchical bayesian model (hbm) to the population distribution in the (g - r)- $\mathrm{log}(m/{l}_{g})$ plane. we find that prospector-α infers systematically higher m */l by 0.12 dex, a result of nonparametric sfhs producing older ages, and also systematically redder rest frame (g - r) by 0.06 mag owing to the contribution from nebular emission. surprisingly, the combined effects of the m */l and (g - r) offsets produce a similar average relationship for the two models; though prospector-α produces a higher scatter of 0.28 dex compared to the simple model of 0.12 dex. also, unlike the simple model, the prospector-α relationship shows substantial redshift evolution due to stellar aging. these expected and testable effects produce overall older and redder galaxies; though the color-m */l relationship is measured only at 0.5 < z < 3. finally, we demonstrate that the hbm produces substantial shrinkage in the individual posteriors of faint galaxies, an important first step toward using the observed galaxy population directly to inform the sed-fitting priors. | flexible models for galaxy star formation histories both shift and scramble the optical color-mass-to-light ratio (m/l) relationship |
context. understanding the wavelength dependence of dust attenuation is vital for inferring the properties of galaxies from their spectral energy distribution (sed) fitting. the dust attenuation curves in star-forming galaxies depend on the complex interplay between the intrinsic physical dust properties and dust-to-star geometry. due to the lack of observational constraints at high redshift, dust attenuation and extinction laws measured in the local universe (e.g., the calzetti attenuation law and the small magellanic cloud and milky way extinction laws) have been employed to describe the dust attenuation at early epochs.aims: we exploit the high sensitivity and spectral resolution of the james webb space telescope (jwst) to constrain dust attenuation laws in z ∼ 7-8 galaxies. our goals are to: i) check whether dust attenuation curves at high-z differ from the ones measured in the local universe and ii) quantify the dependence of the inferred galaxy properties on the assumed dust attenuation law.methods: we developed a modified version of the sed fitting code bagpipes by including a detailed dust attenuation curve parameterization. we applied our method to the jwst near infrared spectrograph (nirspec) spectra in the ∼0.6-5.3 µm range to probe the nebular line (hα, hβ, hγ, [o ii] λ3727, [o iii] λλ4959, 5007, [ne iii] λ3869) and continuum emissions of three star-forming galaxies at z = 7-8. dust attenuation parameters and global galaxy properties are derived from the fit to the data.results: we find that the attenuation curves of the analyzed high-z galaxies differ from local templates. one out of the three galaxies shows a characteristic 2175å bump, typically associated with the presence of small carbonaceous dust grains such as polycyclic aromatic hydrocarbons (pahs). this is among the first pieces of evidence suggesting the presence of pahs in early galaxies. galaxy properties such as the stellar mass (m*) and star formation rate (sfr) inferred from the sed fitting are affected by the assumed attenuation curve (with deviations of up to ∼0.35 dex), however, the adopted star formation history plays the dominant role (up to ∼0.4 dex for the same galaxy properties).conclusions: our results highlight the importance of accounting for the potential diversity among dust attenuation laws when analyzing the spectra of high-z galaxies, whose dust properties and dust-to-star geometry are still poorly understood. the application of our method to a larger sample of galaxies observed with jwst can provide important insights into the properties of dust and galaxies in the early universe. | dust attenuation law in jwst galaxies at z ∼ 7-8 |
modern wide-field, optical time-domain surveys must solve a basic optimization problem: maximize the number of transient discoveries or minimize the follow-up needed for the new discoveries. here, we describe the color me intrigued experiment, the first from the intermediate palomar transient factory (iptf) to search for transients simultaneously in the g ptf and r ptf bands. during the course of this experiment, we discovered iptf 16fnm, a new member of the 02cx-like subclass of type ia supernovae (sne). iptf 16fnm peaked at {m}{g{ptf}}=-15.09+/- 0.17 {mag}, making it the second-least-luminous known sn ia. iptf 16fnm exhibits all the hallmarks of the 02cx-like class: (i) low luminosity at peak, (ii) low ejecta velocities, and (iii) a non-nebular spectrum several months after peak. spectroscopically, iptf 16fnm exhibits a striking resemblance to two other low-luminosity 02cx-like sne: sn 2007qd and sn 2010ae. iptf 16fnm and sn 2005hk decline at nearly the same rate, despite a 3 mag difference in brightness at peak. when considering the full subclass of 02cx-like sne, we do not find evidence for a tight correlation between peak luminosity and decline rate in either the g‧ or r‧ band. we measure the relative rate of 02cx-like sne to normal sne ia and find {r}{n02{cx}/{n}{ia}}={33}-25+158 % . we further examine the g‧ - r‧ evolution of 02cx-like sne and find that their unique color evolution can be used to separate them from 91bg-like and normal sne ia. this selection function will be especially important in the spectroscopically incomplete zwicky transient facility/large synoptic survey telescope (lsst) era. finally, we close by recommending that lsst periodically evaluate, and possibly update, its observing cadence to maximize transient science. | color me intrigued: the discovery of iptf 16fnm, an sn 2002cx-like object |
one of the major puzzles in the study of stellar evolution is the formation process of bipolar and multipolar planetary nebulae. there is growing consensus that collimated jets create cavities with dense walls in the slowly expanding (10-20 km s-1) envelope ejected in previous evolutionary phases, leading to the observed morphologies. however, the launching of the jet and the way it interacts with the circumstellar material to create such asymmetric morphologies have remained poorly known. here we present for the first time co emission from the asymptotic giant branch star w43a that traces the whole stream of a jet, from the vicinity of its driving stellar system out to the regions where it shapes the circumstellar envelope. we found that the jet has a launch velocity of 175 km s-1 and decelerates to a velocity of 130 km s-1 as it interacts with circumstellar material. the continuum emission reveals a bipolar shell with a compact bright dot in the center that pinpoints the location of the driving source of the jet. the kinematical ages of the jet and the bipolar shell are equal, τ ∼ 60 yr, indicating that they were created simultaneously, probably by a common underlying mechanism, and in an extremely short time. these results provide key initial conditions for the theoretical models that aim to explain the formation of bipolar morphologies in the circumstellar envelopes of low- and intermediate-mass stars. | shaping the envelope of the asymptotic giant branch star w43a with a collimated fast jet |
nova cen 2013 (v1369 cen) is the fourth bright nova observed panchromatically through high-resolution uv+optical multiepoch spectroscopy. it is also the nova with the richest set of spectra (in terms of both data quality and number of epochs) thanks to its exceptional brightness. here, we use the late nebular spectra taken between day ∼250 and day ∼837 after outburst to derive the physical, geometrical, and kinematical properties of the nova. we compare the results with those determined for the other panchromatic studies in this series: t pyx, v339 del (nova del 2013), and v959 mon (nova mon 2012). from this we conclude that in all these novae the ejecta geometry and phenomenology can be consistently explained by clumpy gas expelled during a single, brief ejection episode and in ballistic expansion, and not by a wind. for v1369 cen the ejecta mass (∼1 × 10-4 m⊙) and filling factor (0.1 ≤ f ≤ 0.2) are consistent with those of classical novae but larger (by at least an order of magnitude) than those of t pyx and the recurrent novae. v1369 cen has an anomalously high (relative to solar) n/c ratio that is beyond the range currently predicted for a co nova, and the ne emission line strengths are dissimilar to those of typical one or co white dwarfs. | v1369 cen high-resolution panchromatic late nebular spectra in the context of a unified picture for nova ejecta |
the nearby type ia supernovae (sne ia) 2011fe and 2011by had nearly identical photospheric phase optical spectra, light-curve widths, and photometric colours, but at peak brightness sn 2011by reached a fainter absolute magnitude in all optical bands and exhibited lower flux in the near-ultraviolet (nuv). based on those data, foley & kirshner argue that the progenitors of sne 2011by and 2011fe had supersolar and subsolar metallicity, respectively, and that sn 2011fe generated 1.7 times the amount of 56ni as sn 2011by. with this work, we extend the comparison of these sne ia to 10 d before and 300 d after maximum brightness with new spectra and photometry. we show that the nebular phase spectra of sne 2011fe and 2011by are almost identical, and do not support a factor of 1.7 difference in 56ni mass. instead, we find it plausible that the tully-fisher distance for sn 2011by is an underestimate, in which case these sne ia may have reached similar peak luminosity, formed similar amounts of 56ni, and had lower metallicity progenitors than previously estimated. regardless of the true distance to sn 2011by, we find that the relative progenitor metallicity difference remains well supported by their disparity in nuv flux, which we show to be even stronger at pre-maximum epochs - although contributions from differences in total ejecta mass, viewing angle, or progenitor density cannot be ruled out. we also demonstrate that, independent of distance modulus, sn 2011by exhibits a late-time luminosity excess that cannot be explained by a light echo, but is more likely to be the result of greater energy trapping by the nucleosynthetic products of sn 2011by. | twins for life? a comparative analysis of the type ia supernovae 2011fe and 2011by |
the compton spectrometer and imager (cosi), formerly known as the nuclear compton telescope (nct), is a balloon-borne soft gamma-ray telescope (0.2-5 mev) designed to study astrophysical sources of nuclear-line emission and gamma-ray polarization. the heart of cosi is a compact array of cross-strip germanium detectors (geds), providing excellent spectral resolution ( 0.2 - 1 %) and the capability to track individual photon interactions with full 3d position resolution to 1.6 mm3. cosi is built upon considerable heritage from the previous nct balloon instrument, which has flown successfully on two conventional balloon flights to date. the crab nebula was detected at a significance of 6σ in the second flight, which is the first reported detection of an astrophysical source by a compact compton telescope. cosi has been upgraded from the previous nct instrument to be an ultra long duration balloon (uldb) payload, utilizing a new detector configuration optimized for polarization sensitivity and employing a mechanical cryocooler to remove consumables (ln2) for uldb flights. the instrument is being integrated for a uldb flight in december 2014 from antarctica on a superpressure balloon. here we will present the redesign of the instrument and our current progress in preparing for the flight. | the upcoming balloon campaign of the compton spectrometer and imager (cosi) |
we examine the spectroscopic binary population for two massive nearby regions of clustered star formation, the orion nebula cluster (onc) and ngc 2264, supplementing the data presented by tobin et al. with more recent observations and more extensive analysis. the inferred multiplicity fraction up to 10 au based on these observations is 5.3 ± 1.2% for ngc 2264 and 5.8 ± 1.1% for the onc; these values are consistent with the distribution of binaries in the field in the relevant parameter range. eight of the multiple systems in the sample have enough epochs to perform an initial fit for the orbital parameters. two of these sources are double-lined spectroscopic binaries; for them, we determine the mass ratio. our reanalysis of the distribution of stellar radial velocities toward these clusters presents a significantly better agreement between stellar and gas kinematics than was previously thought. | spectroscopic binaries in the orion nebula cluster and ngc 2264 |
particle acceleration induced by magnetic reconnection is thought to be a promising candidate for producing the nonthermal emissions associated with explosive phenomena such as solar flares, pulsar wind nebulae, and jets from active galactic nuclei. laboratory experiments can play an important role in the study of the detailed microphysics of magnetic reconnection and the dominant particle acceleration mechanisms. we have used two- and three-dimensional particle-in-cell simulations to study particle acceleration in high lundquist number reconnection regimes associated with laser-driven plasma experiments. for current experimental conditions, we show that nonthermal electrons can be accelerated to energies more than an order of magnitude larger than the initial thermal energy. the nonthermal electrons gain their energy mainly from the reconnection electric field near the x points, and particle injection into the reconnection layer and escape from the finite system establish a distribution of energies that resembles a power-law spectrum. energetic electrons can also become trapped inside the plasmoids that form in the current layer and gain additional energy from the electric field arising from the motion of the plasmoid. we compare simulations for finite and infinite periodic systems to demonstrate the importance of particle escape on the shape of the spectrum. based on our findings, we provide an analytical estimate of the maximum electron energy and threshold condition for observing suprathermal electron acceleration in terms of experimentally tunable parameters. we also discuss experimental signatures, including the angular distribution of the accelerated particles, and construct synthetic detector spectra. these results open the way for novel experimental studies of particle acceleration induced by reconnection. | particle acceleration in laser-driven magnetic reconnection |
we present a new approach to study planetary nebulae using integral field spectroscopy. vlt@vimos datacube of the planetary nebula abell 14 is analysed in three different ways by extracting: (i) the integrated spectrum, (ii) one-dimensional simulated long-slit spectra for different position angles, and (iii) spaxel-by-spaxel spectra. these data are used to build emission-line diagnostic diagrams and explore the ionization structure and excitation mechanisms combining data from one- and three-dimensional photoionization models. the integrated and 1d simulated spectra are suitable for developing diagnostic diagrams, while the spaxel spectra can lead to misinterpretation of the observations. we find that the emission-line ratios of abell 14 are consistent with uv photoionised emission; however, there are some pieces of evidence of an additional thermal mechanism. the chemical abundances confirm its previous classification as a type i planetary nebula, without spatial variation. we find, though, variation in the ionization correction factors as a function of the slit's position angle. the star at the geometric centre of abell 14 has an a5 spectral type with an effective temperature of teff = 7909 ± 135 k and surface gravity log(g) = 1.4 ± 0.1 cm s-2. hence, this star cannot be responsible for the ionization state of the nebula. gaia parallaxes of this star yield distances between 3.6 and 4.5 kpc in good agreement with the distance derived from a three-dimensional photoionization modelling of abell 14, indicating the presence of a binary system at the centre of the planetary nebula. | exploring the differences of integrated and spatially resolved analysis using integral field unit data: the case of abell 14 |
aims: we aim to determine individual distances to a small number of rather round, quite regularly shaped planetary nebulae by combining their angular expansion in the plane of the sky with a spectroscopically measured expansion along the line of sight.methods: we combined up to three epochs of hubble space telescope imaging data and determined the angular proper motions of rim and shell edges and of other features. these results are combined with measured expansion speeds to determine individual distances by assuming that line of sight and sky-plane expansions are equal. we employed 1d radiation-hydrodynamics simulations of nebular evolution to correct for the difference between the spectroscopically measured expansion velocities of rim and shell and of their respective shock fronts.results: rim and shell are two independently expanding entities, driven by different physical mechanisms, although their model-based expansion timescales are quite similar. we derive good individual distances for 15 objects, and the main results are as follows: (i) distances derived from rim and shell agree well; (ii) comparison with the statistical distances in the literature gives reasonable agreement; (iii) our distances disagree with those derived by spectroscopic methods; (iv) central-star "plateau" luminosities range from about 2000 l⊙ to well below 10 000 l⊙, with a mean value at about 5000 l⊙, in excellent agreement with other samples of known distance (galactic bulge, magellanic clouds, and k648 in the globular cluster m 15); (v) the central-star mass range is rather restricted: from about 0.53 to about 0.56 m⊙, with a mean value of 0.55 m⊙.conclusions: the expansion measurements of nebular rim and shell edges confirm the predictions of radiation-hydrodynamics simulations and offer a reliable method for the evaluation of distances to suited objects. results of this paper are based on observations made with the nasa/esa hubble space telescope in cycle 16 (go11122) and older data obtained from the data archive 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. | expansion patterns and parallaxes for planetary nebulae |
we interpret γ-ray flares from the crab nebula as the signature of turbulence in the pulsar’s electromagnetic outflow. turbulence is triggered upstream by dynamical instability of the wind’s oscillating magnetic field and accelerates non-thermal particles. on impacting the wind-termination shock, these particles emit a distinct synchrotron component {f}ν ,{flare}, which is constantly modulated by intermittency of the upstream plasma flow. flares are observed when the high-energy cutoff of {f}ν ,{flare} emerges above the fast-declining nebular emission around 0.1-1 gev. simulations carried out in the force-free electrodynamics approximation predict the striped wind to become fully turbulent well ahead of the wind-termination shock, provided its terminal lorentz factor is ≲ {10}4. | crab flares due to turbulent dissipation of the pulsar striped wind |
we study the nature of feedback mechanisms in the 11 clash brightest cluster galaxies (bcgs) that exhibit extended ultraviolet and nebular line emission features. we estimate star formation rates (sfrs), dust masses, and starburst durations using a bayesian photometry-fitting technique that accounts for both stellar and dust emission from the uv through far-ir. by comparing these quantities to intracluster medium (icm) cooling times and freefall times derived from x-ray observations and lensing estimates of the cluster mass distribution, we discover a tight relationship between the bcg sfr and the icm cooling time to freefall time ratio, {t}{cool}/{t}{ff}, with an upper limit on the intrinsic scatter of 0.15 dex. furthermore, starburst durations may correlate with icm cooling times at a radius of 0.025 {r}500, and the two quantities converge upon reaching the gigayear regime. our results provide a direct observational link between the thermodynamical state of the icm and the intensity and duration of bcg star formation activity, and appear consistent with a scenario where active galactic nuclei induce condensation of thermally unstable icm overdensities that fuel long-duration (>1 gyr) bcg starbursts. this scenario can explain (a) how gas with a low cooling time is depleted without causing a cooling flow and (b) the scaling relationship between sfr and {t}{cool}/{t}{ff}. we also find that the scaling relation between sfr and dust mass in bcgs with sfrs < 100 {m}⊙yr-1 is similar to that in star-forming field galaxies; bcgs with large (> 100 {m}⊙yr-1) sfrs have dust masses comparable to extreme starbursts. | the relationship between brightest cluster galaxy star formation and the intracluster medium in clash |
fast radio bursts (frbs) are mysterious transient sources. if extragalactic, as suggested by their relative large dispersion measures, their brightness temperatures must be extremely high. some frb models (e.g., young pulsar model, magnetar giant flare model, or supra-massive neutron star collapse model) suggest that they may be associated with a synchrotron nebula. here we study a synchrotron-heating process by an frb in a self-absorbed synchrotron nebula. if the frb frequency is below the synchrotron self-absorption frequency of the nebula, electrons in the nebula would absorb frb photons, leading to a harder electron spectrum and enhanced self-absorbed synchrotron emission. in the meantime, the frb flux is absorbed by the nebula electrons. we calculate the spectra of frb-heated synchrotron nebulae, and show that the nebula spectra would show a significant hump in several decades near the self-absorption frequency. identifying such a spectral feature would reveal an embedded frb in a synchrotron nebula. | synchrotron heating by a fast radio burst in a self-absorbed synchrotron nebula and its observational signature |
combined with measurements made by very-long-baseline interferometry, the observations of fast tev gamma-ray flares probe the structure and emission mechanism of blazar jets. however, only a handful of such flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked bl lac objects and flat-spectrum radio quasars. we report on a fast tev gamma-ray flare from the blazar bl lacertae observed by the very energetic radiation imaging telescope array system (veritas). with a rise time of ∼2.3 hr and a decay time of ∼36 min. the peak flux above 200 gev is (4.2 ± 0.6) × 10-6 photon m-2 s-1 measured with a 4-minute-binned light curve, corresponding to ∼180% of the flux that is observed from the crab nebula above the same energy threshold. variability contemporaneous with the tev gamma-ray flare was observed in gev gamma-ray, x-ray, and optical flux, as well as in optical and radio polarization. additionally, a possible moving emission feature with superluminal apparent velocity was identified in very long baseline array observations at 43 ghz, potentially passing the radio core of the jet around the time of the gamma-ray flare. we discuss the constraints on the size, lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models that invoke relativistic plasma passing stationary shocks. | multiwavelength observations of the blazar bl lacertae: a new fast tev gamma-ray flare |
r-matrix calculations combined with the adiabatic nuclei approximation are used to compute electron-impact rotational excitation rates for three closed-shell diatomic cations, heh+, ch+, arh+. comparisons with previous studies show that an improved treatment of threshold effects leads to significant changes in the low temperature rates; furthermore the new calculations suggest that excitation of ch+ is dominated by δj = 1 transitions as is expected for cations with a large dipole moment. a model for arh+ excitation in the crab nebula is presented which gives results consistent with the observations for electron densities in the range 2-3 × 103 cm-3. | electron-impact excitation of diatomic hydride cations - i. heh+, ch+, arh+ |
the radio source 3c 264, hosted by the giant elliptical galaxy ngc 3862, was observed with the very energetic radiation imaging telescope array system (veritas) between 2017 february and 2019 may. these deep observations resulted in the discovery of very high energy (vhe; e > 100 gev) γ-ray emission from this active galaxy. an analysis of ∼57 hr of quality-selected live time yields a detection at the position of the source, corresponding to a statistical significance of 7.8 standard deviations above background. the observed vhe flux is variable on monthly timescales, with an elevated flux seen in 2018 observations. the vhe emission during this elevated state is well characterized by a power-law spectrum with a photon index γ = 2.20 ± 0.27 and flux f(>315 gev) = ( $7.6\pm {1.2}_{\mathrm{stat}}\pm {2.3}_{\mathrm{syst}})\times {10}^{-13}$ cm-2 s-1, or approximately 0.7% of the crab nebula flux above the same threshold. 3c 264 (z = 0.0217) is the most distant radio galaxy detected at vhe, and the elevated state is thought to be similar to that of the famously outbursting jet in m87. consequently, extensive contemporaneous multiwavelength data were acquired in 2018 at the time of the vhe high state. an analysis of these data, including very long baseline array, very large array, hubble space telescope, chandra, and swift observations in addition to the veritas data, is presented, along with a discussion of the resulting spectral energy distribution. | veritas discovery of vhe emission from the radio galaxy 3c 264: a multiwavelength study |
in view of the many recent observations conducted by alma and sphere, it is becoming clear that protoplanetary disks form planets in narrow annular gaps at various distances from the central protostars before these protostars are actually fully formed and the gaseous disks have concluded their accretion/dispersal processes. this is in marked contrast to the many multi-planet exoplanetary systems that do not conform to this pristine picture. this major discrepancy calls for an explanation. we provide such an explanation in this work, based on analytical solutions of the cylindrical isothermal lane-emden equation with rotation which do not depend on boundary conditions. these ``intrinsic'' solutions of the differential equation attract the solutions of the cauchy problem and force them to oscillate permanently. the oscillations create density maxima in which dust and planetesimals are trapped and they can form protoplanetary cores during the very early isothermal evolution of such protoplanetary nebulae. we apply this model to our solar nebula that formed in-situ a minimum of eleven protoplanetary cores that have grown to planets which have survived undisturbed to the present day. we are also in the process of applying the same model to the alma/dsharp disks. | on the formation of our solar system and many other protoplanetary systems observed by alma and sphere |
we report comprehensive multi-wavelength observations of a peculiar type ia-like supernova (“sn ia-pec”) asassn-15pz. asassn-15pz is a spectroscopic “twin” of sn 2009dc, a so-called “super-chandrasekhar-mass” sn, throughout its evolution, but it has a peak luminosity {m}b,{peak}=-19.69+/- 0.12 {mag} that is ≈ 0.6 {mag} dimmer and comparable to the sn 1991t sub-class of sne ia at the luminous end of the normal width-luminosity relation. the synthesized 56ni mass of {m}{56{ni}}=1.13+/- 0.14 {m}⊙is also substantially less than that found for several 2009dc-like sne. previous well-studied 2009dc-like sne have generally suffered from large and uncertain amounts of host-galaxy extinction, which is negligible for asassn-15pz. based on the color of asassn-15pz, we estimate a host extinction for sn 2009dc of e{(b-v)}host}=0.12 {mag} and confirm its high luminosity ({m}b,{peak}[2009{dc}]≈ -20.3 {mag}). the 2009dc-like sn population, which represents ∼1% of sne ia, exhibits a range of peak luminosities, and do not fit onto the tight width-luminosity relation. their optical light curves also show significant diversity of late-time (≳50 days) decline rates. the nebular-phase spectra provide powerful diagnostics to identify the 2009dc-like events as a distinct class of sne ia. we suggest referring to these sources using the phenomenology-based “2009dc-like sn ia-pec” instead of “super-chandrasekhar sn ia,” which is based on an uncertain theoretical interpretation. this paper includes data gathered with the 6.5 m magellan telescopes located at las campanas observatory, chile. | asassn-15pz: revealing significant photometric diversity among 2009dc-like, peculiar sne ia |
observations by the fermi large area telescope of γ-ray millisecond pulsar (msp) light curves imply copious pair production in their magnetospheres, and not exclusively in those of younger pulsars. such pair cascades may be a primary source of galactic electrons and positrons, contributing to the observed enhancement in positron flux above ∼10 gev. fermi has also uncovered many new msps, impacting galactic stellar population models. we investigate the contribution of galactic msps to the flux of terrestrial cosmic-ray electrons and positrons. our population synthesis code predicts the source properties of present-day msps. we simulate their pair spectra invoking an offset-dipole magnetic field. we also consider positrons and electrons that have been further accelerated to energies of several tev by strong intrabinary shocks in black widow (bw) and redback (rb) systems. since msps are not surrounded by pulsar wind nebulae or supernova shells, we assume that the pairs freely escape and undergo losses only in the intergalactic medium. we compute the transported pair spectra at earth, following their diffusion and energy loss through the galaxy. the predicted particle flux increases for non-zero offsets of the magnetic polar caps. pair cascades from the magnetospheres of msps are only modest contributors around a few tens of gev to the lepton fluxes measured by the alpha magnetic spectrometer, pamela, and fermi, after which this component cuts off. the contribution by bws and rbs may, however, reach levels of a few tens of percent at tens of tev, depending on model parameters. | cosmic-ray positrons from millisecond pulsars |
the chemical content of the planetary nebula ngc 3918 is investigated through deep, high-resolution (r ∼ 40 000) uves (ultraviolet-visual echelle spectrograph) at vlt (very large telescope) spectrophotometric data. we identify and measure more than 750 emission lines, making ours one of the deepest spectra ever taken for a planetary nebula. among these lines we detect very faint lines of several neutron-capture elements (se, kr, rb, and xe), which enable us to compute their chemical abundances with unprecedented accuracy, thus constraining the efficiency of the s-process and convective dredge-up in ngc 3918 progenitor star. we find that kr is strongly enriched in ngc 3918 and that se is less enriched than kr, in agreement with the results of previous papers and with predicted s-process nucleosynthesis. we also find that xe is not as enriched by the s-process in ngc 3918 as is kr and, therefore, that neutron exposure is typical of modestly subsolar metallicity asymptotic giant branch (agb) stars. a clear correlation is found when representing [kr/o] versus log(c/o) for ngc 3918 and other objects with detection of multiple ions of kr in optical data, confirming that carbon is brought to the surface of agb stars along with s-processed material during third dredge-up episodes, as predicted by nucleosynthesis models. we also detect numerous refractory element lines (ca, k, cr, mn, fe, co, ni, and cu) and a large number of metal recombination lines of c, n, o, and ne. we compute physical conditions from a large number of diagnostics, which are highly consistent among themselves assuming a three-zone ionization scheme. thanks to the high ionization of ngc 3918 we detect a large number of recombination lines of multiple ionization stages of c, n, o and ne. the abundances obtained for these elements by using recently determined state-of-the-art ionization correction factor (icf) schemes or simply adding ionic abundances are in very good agreement, demonstrating the quality of the recent icf scheme for high-ionization planetary nebulae. | s-process enrichment in the planetary nebula ngc 3918. results from deep echelle spectrophotometry |
igr j11014-6103 (also known as the lighthouse nebula) is composed of a bow-shock pulsar wind nebula (pwn) and large-scale x-ray jet-like features, all powered by psr j1101-6101. previous observations suggest that the jet features stem from a ballistic jet of relativistic particles. in order to confirm the nature of the jet and the counter-jet, we obtained a new deep 250 ks chandra observation of the lighthouse nebula. we performed detailed spatial and spectral analysis of all x-ray components of the system. the x-ray pwn is now better resolved and shows a peculiar morphology resembling the shape of an arrow. the overall helical pattern of the main jet is confirmed. however, there are large deviations from a simple helical model at small and large scales. significant extended emission is now detected, encompassing the main jet all along its length. the presence of an apparent gap along the main jet at ~50″ distance from the pulsar is confirmed; however, the surrounding extended emission prevents conclusions on the coherence at this position of the jet. the counter-jet is now detected at high statistical significance. in addition, we found two small-scale arcs departing from the pulsar towards the jets. we also looked for possible bow-shock emission due to the pulsar motion, with a short vlt/fors2 h-α observation. no clear emission is found, most likely because of the contamination from a diffuse nebulosity. the results of our x-ray analysis show that both a ballistic jet scenario and an alternative scenario involving the diffusion of particles along pre-existing interstellar magnetic field lines are able to satisfactorily explain some of the observational evidence, but cannot fully reproduce the observations. | closer view of the igr j11014-6103 outflows |
i present the automated line fitting algorithm, alfa, a new code which can fit emission line spectra of arbitrary wavelength coverage and resolution, fully automatically. in contrast to traditional emission line fitting methods which require the identification of spectral features suspected to be emission lines, alfa instead uses a list of lines which are expected to be present to construct a synthetic spectrum. the parameters used to construct the synthetic spectrum are optimized by means of a genetic algorithm. uncertainties are estimated using the noise structure of the residuals. an emission line spectrum containing several hundred lines can be fitted in a few seconds using a single processor of a typical contemporary desktop or laptop pc. i show that the results are in excellent agreement with those measured manually for a number of spectra. where discrepancies exist, the manually measured fluxes are found to be less accurate than those returned by alfa. together with the code neat, alfa provides a powerful way to rapidly extract physical information from observations, an increasingly vital function in the era of highly multiplexed spectroscopy. the two codes can deliver a reliable and comprehensive analysis of very large data sets in a few hours with little or no user interaction. | alfa: an automated line fitting algorithm |
we study the optical evolution of the 2015 outburst in v404 cyg, with emphasis on the peculiar nebular phase and subsequent decay to quiescence. from the decay time-scale of the balmer emission associated with the nebula, we measure an outflow mass mwind ≃ 4 × 10-6 m⊙. remarkably, this is ∼100 times larger than the accreted mass and ∼10 per cent of the total mass stored in the disc. the wind efficiency must therefore be significantly larger than previous estimates for black hole transients, suggesting that radiation pressure (in addition to other mechanisms such as compton-heating) plays a key role in v404 cyg. in addition, we compare the evolution of the 2015 and 1989 outbursts and find not only clear similarities (namely a large luminosity drop ∼10 d after the x-ray trigger, followed by a brief nebular phase) but also remarkable differences in decay time-scales and long-term evolution of the h α profile. in particular, we see evidence for a rapid disc contraction in 2015, consistent with a burst of mass transfer. this could be driven by the response of the companion to hard x-ray illumination, most notably during the last gigantic (super-eddington) flare on 2015 june 25. we argue that irradiation and consequential disc wind are key factors to understand the different outburst histories in 1989 and 2015. in the latter case, radiation pressure may be responsible for the abrupt end of the outburst through depleting inner parts of the disc, thus quenching accretion and x-ray irradiation. we also present a refined orbital period and updated ephemeris. | accretion and outflow in v404 cyg |
the distribution of galaxies on a colour-magnitude diagram reveals a bimodality, featuring a passively evolving red sequence and a star-forming blue cloud. the region between these two, the green valley (gv), represents a fundamental transition where quenching processes operate. we exploit an alternative definition of the gv using the 4000 å break strength, an indicator that is more resilient than colour to dust attenuation. we compare and contrast our gv definition with the traditional one, based on dust-corrected colour, making use of data from the sloan digital sky survey. our gv selection - that does not need a dust correction and thus does not carry the inherent systematics - reveals very similar trends regarding nebular activity (star formation, agn, quiescence) to the standard dust-corrected 0.1(g - r). by use of high-snr stacked spectra of the quiescent gv subsample, we derive the simple stellar population (ssp) age difference across the gv, a rough proxy of the quenching time-scale (δt). we obtain an increasing trend with velocity dispersion (σ), from δt ∼ 1.5 gyr at σ = 100 km s-1, up to 3.5 gyr at σ = 200 km s-1, followed by a rapid decrease in the most massive gv galaxies (δt ∼ 1 gyr at σ = 250 km s-1), suggesting two different modes of quenching, or the presence of an additional channel (rejuvenation). | exploring a new definition of the green valley and its implications |
warm ionized and cold neutral outflows with velocities exceeding 100 km s-1 are commonly observed in galaxies and clusters. however, theoretical studies indicate that ram pressure from a hot wind, driven either by the central active galactic nucleus (agn) or a starburst, cannot accelerate existing cold gas to such high speeds without destroying it. in this work we explore a different scenario, where cold gas forms in a fast, radiatively cooling outflow with temperature t ≲ 107 k. using 3d hydrodynamic simulations, we demonstrate that cold gas continuously fragments out of the cooling outflow, forming elongated filamentary structures extending tens of kiloparsecs. for a range of physically relevant temperature and velocity configurations, a ring of cold gas perpendicular to the direction of motion forms in the outflow. this naturally explains the formation of transverse cold gas filaments such as the blue loop and the horseshoe filament in the perseus cluster. based on our results, we estimate that the agn outburst responsible for the formation of these two features drove bipolar outflows with velocity >2000 km s-1 and total kinetic energy >8 × 1057 erg about ~10 myr ago. we also examine the continuous cooling in the mixing layer between hot and cold gas, and find that radiative cooling only accounts for ~10% of the total mass cooling rate, indicating that observations of soft x-ray and far-ultraviolet emission may significantly underestimate the growth of cold gas in the cooling flow of galaxy clusters. | dynamics and morphology of cold gas in fast, radiatively cooling outflows: constraining agn energetics with horseshoes |
for mev gamma-ray astronomy, we have developed an electron-tracking compton camera (etcc) as a mev gamma-ray telescope capable of rejecting the radiation background and attaining the high sensitivity of near 1 mcrab in space. our etcc comprises a gaseous time-projection chamber (tpc) with a micro pattern gas detector for tracking recoil electrons and a position-sensitive scintillation camera for detecting scattered gamma rays. after the success of a first balloon experiment in 2006 with a small etcc (using a 10×10×15 cm3 tpc) for measuring diffuse cosmic and atmospheric sub-mev gamma rays (sub-mev gamma-ray imaging loaded-on-balloon experiment i; smile-i), a (30 cm)3 medium-sized etcc was developed to measure mev gamma-ray spectra from celestial sources, such as the crab nebula, with single-day balloon flights (smile-ii). to achieve this goal, a 100-times-larger detection area compared with that of smile-i is required without changing the weight or power consumption of the detector system. in addition, the event rate is also expected to dramatically increase during observation. here, we describe both the concept and the performance of the new data-acquisition system with this (30 cm)3 etcc to manage 100 times more data while satisfying the severe restrictions regarding the weight and power consumption imposed by a balloon-borne observation. in particular, to improve the detection efficiency of the fine tracks in the tpc from ~10% to ~100%, we introduce a new data-handling algorithm in the tpc. therefore, for efficient management of such large amounts of data, we developed a data-acquisition system with parallel data flow. | new readout and data-acquisition system in an electron-tracking compton camera for mev gamma-ray astronomy (smile-ii) |
in this chapter we review a new and rapidly growing area of research in high-energy plasma astrophysics—radiative magnetic reconnection, defined here as a regime of reconnection where radiation reaction has an important influence on the reconnection dynamics, energetics, and/or nonthermal particle acceleration. this influence be may be manifested via a variety of radiative effects that are critical in many high-energy astrophysical applications. the most notable radiative effects in astrophysical reconnection include radiation-reaction limits on particle acceleration, radiative cooling, radiative resistivity, braking of reconnection outflows by radiation drag, radiation pressure, viscosity, and even pair creation at highest energy densities. the self-consistent inclusion of these effects into magnetic reconnection theory and modeling sometimes calls for serious modifications to our overall theoretical approach to the problem. in addition, prompt reconnection-powered radiation often represents our only observational diagnostic tool available for studying remote astrophysical systems; this underscores the importance of developing predictive modeling capabilities to connect the underlying physical conditions in a reconnecting system to observable radiative signatures. this chapter presents an overview of our recent theoretical progress in developing basic physical understanding of radiative magnetic reconnection, with a special emphasis on astrophysically most important radiation mechanisms like synchrotron, curvature, and inverse-compton. the chapter also offers a broad review of key high-energy astrophysical applications of radiative reconnection, illustrated by multiple examples such as: pulsar wind nebulae, pulsar magnetospheres, black-hole accretion-disk coronae and hot accretion flows in x-ray binaries and active galactic nuclei and their relativistic jets, magnetospheres of magnetars, and gamma-ray bursts. finally, this chapter discusses the most critical open questions and outlines the directions for future research of this exciting new frontier of magnetic reconnection research. | radiative magnetic reconnection in astrophysics |
we present a study of the x-ray emission from numerical simulations of hot bubbles in planetary nebulae (pne). high-resolution, two-dimensional, radiation-hydrodynamical simulations of the formation and evolution of hot bubbles in pne, with and without thermal conduction, are used to calculate the x-ray emission and study its time-dependence and relationship to the changing stellar parameters. instabilities in the wind-wind interaction zone produce clumps and filaments in the swept-up shell of nebular material. turbulent mixing and thermal conduction at the corrugated interface can produce quantities of intermediate temperature and density gas between the hot, shocked wind bubble, and the swept-up photoionized nebular material, which can emit in soft, diffuse x-rays. we use the chianti software to compute synthetic spectra for the models and calculate their luminosities. we find that models both with conduction and those without can produce the x-ray temperatures and luminosities that are in the ranges reported in observations, although the models including thermal conduction are an order of magnitude more luminous than those without. our results show that at early times the diffuse x-ray emission should be dominated by the contribution from the hot, shocked stellar wind, whereas at later times the nebular gas will dominate the spectrum. we analyse the effect of sampling on the resultant spectra and conclude that a minimum of 200 counts is required to reliably reproduce the spectral shape. likewise, heavily smoothed surface-brightness profiles obtained from low-count detections of pne do not provide a reliable description of the spatial distribution of the x-ray-emitting gas. | formation and x-ray emission from hot bubbles in planetary nebulae - ii. hot bubble x-ray emission |
we perform a comprehensive analysis of the planetary nebula (pn) ngc 6781 to investigate the physical conditions of each of its ionized, atomic, and molecular gas and dust components and the object’s evolution, based on panchromatic observational data ranging from uv to radio. empirical nebular elemental abundances, compared with theoretical predictions via nucleosynthesis models of asymptotic giant branch (agb) stars, indicate that the progenitor is a solar-metallicity, 2.25{--}3.0 {m}⊙initial-mass star. we derive the best-fit distance of 0.46 kpc by fitting the stellar luminosity (as a function of the distance and effective temperature of the central star) with the adopted post-agb evolutionary tracks. our excitation energy diagram analysis indicates high-excitation temperatures in the photodissociation region (pdr) beyond the ionized part of the nebula, suggesting extra heating by shock interactions between the slow agb wind and the fast pn wind. through iterative fitting using the cloudy code with empirically derived constraints, we find the best-fit dusty photoionization model of the object that would inclusively reproduce all of the adopted panchromatic observational data. the estimated total gas mass (0.41 {m}⊙ ) corresponds to the mass ejected during the last agb thermal pulse event predicted for a 2.5 {m}⊙initial-mass star. a significant fraction of the total mass (about 70%) is found to exist in the pdr, demonstrating the critical importance of the pdr in pne that are generally recognized as the hallmark of ionized/h+ regions. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa. | the herschel planetary nebula survey (herplans): a comprehensive dusty photoionization model of ngc6781 |
e-astrogam is a gamma-ray space mission to be proposed as the m5 medium-size mission of the european space agency. it is dedicated to the observation of the universe with unprecedented sensitivity in the energy range 0.2 { 100 mev, extending up to gev energies, together with a groundbreaking polarization capability. it is designed to substantially improve the comptel and fermi sensitivities in the mev-gev energy range and to open new windows of opportunity for astrophysical and fundamental physics space research. e-astrogam will operate as an open astronomical observatory, with a core science focused on (1) the activity from extreme particle accelerators, including gamma-ray bursts and active galactic nuclei and the link of jet astrophysics to the new astronomy of gravitational waves, neutrinos, ultra-high energy cosmic rays, (2) the high-energy mysteries of the galactic center and inner galaxy, including the activity of the supermassive black hole, the fermi bubbles, the origin of the galactic positrons, and the search for dark matter signatures in a new energy window; (3) nucleosynthesis and chemical evolution, including the life cycle of elements produced by supernovae in the milky way and the local group of galaxies. e-astrogam will be ideal for the study of high-energy sources in general, including pulsars and pulsar wind nebulae, accreting neutron stars and black holes, novae, supernova remnants, and magnetars. and it will also provide important contributions to solar and terrestrial physics. the e-astrogam telescope is optimized for the simultaneous detection of compton and pair-producing gamma-ray events over a large spectral band. it is based on a very high technology readiness level for all subsystems and includes many innovative features for the detectors and associated electronics. | the e-astrogam gamma-ray space mission |
a newly recognized young galactic supernova (sn) remnant, pa 30 (g123.1+4.6), centered on a hot central star with a ~16,000 km s-1 wind velocity, has recently been proposed to be the result of a double-degenerate merger leading to an sn iax event associated with the guest star of 1181 ce. here we present deep optical [s ii] λλ6716,6731 images of pa 30 that reveal an extraordinary and highly structured nebula 170″ in diameter with dozens of long (5″-20″), radially aligned filaments with a convergence point near the hot central star. optical spectra of filaments indicate a peak expansion velocity ≃1100 km s-1 with electron densities of ≤100-700 cm-3 and a thick shell-like structure resembling its appearance in 22 μm wise images. no hα emission was seen ([s ii] λ6716/hα >5), with the only other line emission detected being faint [ar iii] λ7136, suggesting a s- and ar-rich but h-poor remnant. the nebula's angular size, estimated 2.3 kpc distance, and 1100 km s-1 expansion velocity are consistent with an explosion date around 1181 ce. the remnant's unusual appearance may be due to the photoionization of wind-driven ejecta due to clump-wind interactions caused by the central star's high-luminosity wind. | discovery of an exceptional optical nebulosity in the suspected galactic sn iax remnant pa 30 linked to the historical guest star of 1181 ce |
models of stellar population synthesis (sps) are the fundamental tool that relates the physical properties of a galaxy to its spectral energy distribution (sed). in this paper, we present dsps: a python package for sps. all of the functionality in dsps is implemented natively in the jax library for automatic differentiation, and so our predictions for galaxy photometry are fully differentiable, and directly inherit the performance benefits of jax, including portability onto gpus. dsps also implements several novel features, such as i) a flexible empirical model for stellar metallicity that incorporates correlations with stellar age, ii) support for the diffstar model that provides a physically-motivated connection between the star formation history of a galaxy (sfh) and the mass assembly of its underlying dark matter halo. we detail a set of theoretical techniques for using autodiff to calculate gradients of predictions for galaxy seds with respect to sps parameters that control a range of physical effects, including sfh, stellar metallicity, nebular emission, and dust attenuation. when forward modelling the colours of a synthetic galaxy population, we find that dsps can provide a factor of 5 speed-up over standard sps codes on a cpu, and a factor of 300-400 on a modern gpu. when coupled with gradient-based techniques for optimization and inference, dsps makes it practical to conduct expansive likelihood analyses of simulation-based models of the galaxy-halo connection that fully forward model galaxy spectra and photometry. | dsps: differentiable stellar population synthesis |
we present an igm h i tomographic map in a survey volume of $16\times 19\times 131\ {h}^{-3}\ \mathrm{comoving}\ {\mathrm{mpc}}^{3}$ (cmpc3) centered at mammoth-1 nebula and three neighboring quasars at z = 2.3. the mammoth-1 nebula is an enormous lyα nebula (elan), hosted by a type-ii quasar dubbed mammoth1-qso, that extends over $1\ {h}^{-1}$ cmpc with no clear physical origin. here we investigate the h i-gas distribution around mammoth1-qso with the elan and three neighboring type-i quasars, making the igm h i tomographic map with a spatial resolution of 2.6 h-1 cmpc. our h i tomographic map is reconstructed with h i lyα forest absorption of bright background objects at z = 2.4-2.9: one eboss quasar and 16 keck/lris galaxy spectra. we estimate the radial profile of h i overdensity for mammoth1-qso, and find that mammoth1-qso resides in a volume with fairly weak h i absorption. this suggests that mammoth1-qso may have a proximity zone where quasar illuminates and photoionizes the surrounding h i gas and suppresses h i absorption, and that the elan is probably a photoionized cloud embedded in the cosmic web. the h i radial profile of mammoth1-qso is very similar to those of three neighboring type-i quasars at z = 2.3, which is compatible with the agn unification model. we compare the distributions of the h i absorption and star-forming galaxies in our survey volume, and identify a spatial offset between density peaks of star-forming galaxies and h i gas. this segregation may suggest anisotropic uv background radiation created by star-forming galaxy density fluctuations. | three-dimensional distribution map of h i gas and galaxies around an enormous lyα nebula and three qsos at z = 2.3 revealed by the h i tomographic mapping technique |
there is a wide consensus that type ia supernovae (sne ia) originate from the thermonuclear explosion of co white dwarfs (wds), with the lack of hydrogen in the observed spectra as a distinctive feature. here, we present supernova (sn) 2016jae, which was classified as an sn ia from a spectrum obtained soon after its discovery. the sn reached a b-band peak of −17.93 ± 0.34 mag, followed by a fast luminosity decline with sbv0.56 ± 0.06 and inferred δm15(b) of 1.88 ± 0.10 mag. overall, the sn appears to be a `transitional' event between a `normal' sn ia and a very dim sn ia, such as 91bg-like sne. its peculiarity is that two late-time spectra, taken at +84 and +142 days after the peak, show a narrow line of hα (with full width at half maximum of ∼650 and 1000 km s−1, respectively). this is the third low-luminosity and fast-declining sn ia, after sn2018cqj/atlas18qtd and sn2018fhw/asassn-18tb, found in the 100ias survey to show a resolved narrow hα line in emission in its nebular-phase spectra. we argue that the nebular hα emission originates in an expanding hydrogen-rich shell (with velocity ≤1000 km s−1). the hydrogen shell velocity is too high to be produced during a common envelope phase, though it may be consistent with some material stripped from an h-rich companion star in a single-degenerate progenitor system. however, the derived mass of this stripped hydrogen is ∼0.002-0.003 m⊙, which is much less than that expected (> 0.1 m⊙) from standard models for these scenarios. another plausible sequence of events is a weak sn ejecta interaction with an h shell ejected by optically thick winds or a nova-like eruption on the co wd progenitor some years before the sn explosion. | nebular hα emission in type ia supernova 2016jae |
the mass-to-light ratio (m/l) is a key parameter in decomposing galactic rotation curves into contributions from the baryonic components and the dark halo of a galaxy. one direct observational method to determine the disc m/l is by calculating the surface mass density of the disc from the stellar vertical velocity dispersion and the scale height of the disc. usually, the scale height is obtained from near-ir studies of edge-on galaxies and pertains to the older, kinematically hotter stars in the disc, while the vertical velocity dispersion of stars is measured in the optical band and refers to stars of all ages (up to ∼10 gyr) and velocity dispersions. this mismatch between the scale height and the velocity dispersion can lead to underestimates of the disc surface density and a misleading conclusion of the submaximality of galaxy discs. in this paper, we present the study of the stellar velocity dispersion of the disc galaxy ngc 6946 using integrated star light and individual planetary nebulae as dynamical tracers. we demonstrate the presence of two kinematically distinct populations of tracers that contribute to the total stellar velocity dispersion. thus, we are able to use the dispersion and the scale height of the same dynamical population to derive the surface mass density of the disc over a radial extent. we find the disc of ngc 6946 to be closer to maximal with the baryonic component contributing most of the radial gravitational field in the inner parts of the galaxy (vmax(bar) = 0.76(±0.14)vmax). | resolving the disc-halo degeneracy - ii: ngc 6946 |
we discuss the detection of 14 rovibrational lines of ch+, obtained toward the planetary nebula ngc 7027 with the ishell spectrograph on nasa's infrared telescope facility (irtf) on maunakea. our observations in the 3.49-4.13 μm spectral region, obtained with a 0"375 slit width that provided a spectral resolving power λ/δλ ~ 80,000, have resulted in the unequivocal detection of the r(0)-r(3) and p(1)-p(10) transitions within the v = 1-0 band of ch+. the r-branch transitions are anomalously weak relative to the p-branch transitions, a behavior that is explained accurately by rovibronic calculations of the transition dipole moment reported in a companion paper. nine infrared transitions of h2 were also detected in these observations, comprising the s(8), s(9), s(13), and s(15) pure rotational lines; the v = 1-0 o(4)-o(7) lines; and the v = 2-1 o(5) line. we present a photodissociation model, constrained by the ch+ and h2 line fluxes that we measured, that includes a detailed treatment of the excitation of ch+ by inelastic collisions, optical pumping, and chemical ("formation") pumping. the latter process is found to dominate the excitation of the observed rovibrational lines of ch+, and the model is remarkably successful in explaining both the absolute and relative strengths of the ch+ and h2 lines. | observations and analysis of ch+ vibrational emissions from the young, carbon-rich planetary nebula ngc 7027: a textbook example of chemical pumping |
context. the role of feedback in the self-regulation of star formation is a fundamental question in astrophysics. the orion nebula is the nearest site of ongoing and recent massive star formation. it is a unique laboratory for the study of stellar feedback. recent sofia [c ii] 158 μm observations have revealed an expanding bubble, the veil shell, that is powered by stellar winds and ionization feedback.aims: we have identified a protrusion-like substructure in the northwestern portion of the orion veil shell that may indicate additional, highly directional feedback mechanisms. our goal is to investigate the origin of the protrusion by quantifying its possible driving mechanisms.methods: we use the [c ii] 158 μm map of the orion nebula obtained with the upgreat instrument on board sofia. the spectral and spatial resolution of the observations are 0.3 km s−1 and 16", respectively. the velocity-resolved [c ii] observations allow us to construct position-velocity (pv) diagrams to measure the morphology and the expansion velocity of the protrusion. for the morphology, we also use new observations of 12co and 13co j = 2-1 (to trace molecular gas), spitzer 8 μm observations (to trace the far-ultraviolet-illuminated surfaces of photodissociation regions), and hα observations (to trace ionized gas). for the kinematics, we perform a line-profile analysis of [c ii], 13co, and 12co at 12 positions, covering the entire protrusion. to quantify the stellar feedback, we estimate the mass of the protrusion by fitting the dust thermal emission. we compare the kinetic energy with the stellar wind of θ1 ori c and the momentum of the outflows of massive protostars to investigate the driving mechanism of the protrusion.results: the pv diagrams reveal two half-shells expanding at velocities of +6 km s−1 and +12 km s−1. we find that the protrusion has a diameter of ~1.3 pc with a ~45 m⊙ shell expanding at +12 km s−1 at the northwestern rim of the veil. the thickness of the expanding shell is ~0.1 pc. using the mass in the limb-brightened shell and the maximum expansion velocity, we calculate the kinetic energy and the momentum of the protrusion to be ~7 × 1046 erg and 540 m⊙ km s−1, respectively. we consider three possible origins for this protrusion: fossil outflow cavities created by jets and outflows during the protostellar accretion phase, preexisting "clumpiness" in the omc-1 core, and the stellar wind during the main-sequence phase. based on the energetics and the morphology, we conclude that the northwestern part of the preexisting cloud was locally perturbed by outflows ejected from massive protostars in the trapezium cluster. this suggests that the protrusion of the veil is the result of mechanical rather than radiative feedback. furthermore, we argue that the location of the protrusion is a suitable place to break orion's veil owing to the photo-ablation from the walls of the protrusion.conclusions: we conclude that the outflows of massive protostars can influence the morphology of the future h ii region and even cause breakages in the ionization front. specifically, the interaction of stellar winds of main-sequence stars with the molecular core preprocessed by the protostellar jet is important. movie associated to figure 5 is available at https://www.aanda.org | breaking orion's veil with fossil outflows |
low-metallicity, compact starburst galaxies referred to as green peas (gps) provide a unique window to study galactic evolution across cosmic epochs. in this work, we present new deep optical spectra for three gps from osiris at the 10-m gran telescopio canarias, which are studied using a state-of-the-art methodology. a stellar population synthesis is conducted with 1098 spectral templates. the methodology succeeds at characterizing stellar populations from 0.5 myr to 10 gyr. the light distribution shows a large red excess from a single population with ${log}\left({age}\right) \gt 8.5\, \mathrm{yr}$ in the gp sample analysed. this points towards an incomplete characterization of the gas luminosity, whose continuum already accounts between 7.4 and $27.6{{\ \rm per\ cent}}$ in the galaxy sample. the emission spectra are fitted with the largest bayesian chemical model consisting of an electron temperature, an electron density, the logarithmic extinction coefficient and eleven ionic species under the direct method paradigm. additionally, building on previous work, we propose a neural networks sampler to constrain the effective temperature and ionization parameter of each source from photoionization model grids. finally, we combine both methodologies into a 16-dimensional model, which for the first time, simultaneously explores the direct method and photoionization parameter spaces. both techniques consistently indicate a low-metallicity gas, $7.76\lt 12+{\rm log}\left(o/h \right)\lt 8.04$, ionized by strong radiation fields, in agreement with previous works. | new insights on the nebular emission, ionizing radiation, and low metallicity of green peas from advanced modelling |
we present extensive optical/ultraviolet observations and modelling analysis for the nearby sn 1987a-like peculiar type ii supernova (sn) 2018hna. both photometry and spectroscopy covered phases extending to >500 d after the explosion, making it one of the best-observed sn ii of this subtype. sn 2018hna is obviously bluer than sn 1987a during the photospheric phase, suggesting higher photospheric temperature, which may account for weaker ba ii λ6142 lines in its spectra. analysis of early-time temperature evolution suggests a radius of ~45 r⊙ for the progenitor of sn 2018hna, consistent with a blue supergiant (bsg). by fitting the bolometric light curve with hydrodynamical models, we find that sn 2018hna has an ejecta mass of ~(13.7-17.7) m⊙, a kinetic energy of ~(1.0-1.2) × 1051 erg, and a 56ni mass of about 0.05 m⊙. moreover, based on standard stellar evolution and the oxygen mass (0.44-0.73 m⊙) deduced from nebular [o i] lines, the progenitor of sn 2018hna is expected to have an initial main-sequence mass <16 m⊙. in principle, such a relatively low-mass star cannot end as a bsg just before core-collapse, except some unique mechanisms are involved, such as rapid rotation, restricted semiconvection, etc. on the other hand, binary scenario may be more favourable, like in the case of sn 1987a. while the much lower oxygen mass inferred for sn 2018hna may imply that its progenitor system also had much lower initial masses than that of sn 1987a. | sn 2018hna: adding a piece to the puzzles of the explosion of blue supergiants |
context. the carina nebula is one of the major massive star-forming regions in the galaxy. its relatively nearby distance (2.35 kpc) makes it an ideal laboratory for the study of massive star formation, structure, and evolution, both for individual stars and stellar systems. thanks to the high-quality spectra provided by the gaia-eso survey and the lilimarlin library, as well as gaia edr3 astrometry, a detailed and homogeneous spectroscopic characterization of its massive stellar content can be carried out.aims: our main objective is to spectroscopically characterize all massive members of the carina nebula in the gaia-eso survey footprint to provide an updated census of massive stars in the region and an updated estimate of the binary fraction of o stars.methods: we performed accurate spectral classification using an interactive code that compares spectra with spectral libraries of ob standard stars, as well as line-based classic methods. we calculated membership using our own algorithm based on gaia edr3 astrometry. to check the correlation between the spectroscopic n-qualifier and the rotational velocity, we used a semi-automated tool for the line-broadening characterization of ob stars based on a combined fourier transform and goodness-of-fit methodology.results: the gaia-eso survey sample of massive ob stars in the carina nebula consists of 234 stars. the addition of brighter sources from the galactic o-star spectroscopic survey and additional sources from the literature allows us to create the most complete census of massive ob stars so far in the region. it contains a total of 316 stars, with 18 of them in the background and 4 in the foreground. of the 294 stellar systems in car ob1, 74 are of o type, 214 are of nonsupergiant b type, and 6 are of wr or nono supergiant (ii to ia) spectral class. we identify 20 spectroscopic binary systems with an o-star primary, of which 6 are reported for the first time, and another 18 with a b-star primary, of which 13 are new detections. the average observed double-lined binary fraction of o-type stars in the surveyed region is 0.35, which represents a lower limit. we find a good correlation between the spectroscopic n-qualifier and the projected rotational velocity of the stars. the fraction of candidate runaways among the stars with and without the n-qualifier is 4.4% and 2.4%, respectively, although nonresolved double-lined binaries could be contaminating the sample of fast rotators. tables a.1 and a.2 are only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/671/a20 | gaia-eso survey: massive stars in the carina nebula. i. a new census of ob stars |
the large-scale diffuse γ − ray flux observed by fermi large area telescope (fermi-lat) in the 1-100 gev energy range, parameterized as ∝ e−γ, has a spectral index γ that depends on the distance from the galactic center. this feature, if attributed to the diffuse emission produced by cosmic rays interactions with the interstellar gas, can be interpreted as the evidence of a progressive cosmic ray spectral hardening towards the galactic center. this interpretation challenges the paradigm of uniform cosmic rays diffusion throughout the galaxy. we report on the implications of tev pulsar wind nebulae observed by the high energy stereoscopic system (h.e.s.s.) galactic plane survey in the 1-100 tev energy range for the interpretation of fermi-lat data. we argue that a relevant fraction of this population cannot be resolved by fermi-lat in the gev domain providing a relevant contribution to the large-scale diffuse emission, ranging within ~4%-40% of the total diffuse γ-ray emission in the inner galaxy. this additional component may account for a large part of the spectral index variation observed by fermi-lat, weakening the evidence of cosmic ray spectral hardening in the inner galaxy. | the contribution of galactic tev pulsar wind nebulae to fermi large area telescope diffuse emission |
context. when stripped from their hydrogen-rich envelopes, stars with initial masses between ∼7 and 11 m⊙ may develop massive degenerate cores and collapse. depending on the final structure and composition, the outcome can range from a thermonuclear explosion, to the formation of a neutron star in an electron-capture supernova (ecsn). it has recently been demonstrated that stars in this mass range may be more prone to disruption than previously thought: they may initiate explosive oxygen burning when their central densities are still below ρc ≲ 109.6 g cm−3. at the same time, their envelopes expand significantly, leading to the complete depletion of helium. this combination makes them interesting candidates for type ia supernovae-which we call (c)one sne ia-and this might have broader implications for the formation of neutron stars via ecsne.aims: to constrain the observational counterparts of (c)one sne ia and the key properties that enable them, it is crucial to constrain the evolution, composition, and precollapse structure of their progenitors, as well as the evolution of these quantities with cosmic time. in turn, this requires a detailed investigation of the final evolutionary stages preceding the collapse, and their sensitivity to input physics.methods: here, we modeled the evolution of 252 single, nonrotating helium stars covering the initial mass range 0.8 − 3.5 m⊙, with metallicities between z = 10−4 and 0.02, and overshoot efficiency factors from fov = 0.0 to 0.016 across all convective boundaries. we used these models to constrain several properties of these stars, including their central densities, compositions, envelope masses, and radii at the onset explosive oxygen ignition, as well as the final outcome as a function of initial helium star mass. we further investigate the sensitivity of these properties to mass loss rate assumptions using an additional grid of 110 models with varying wind efficiencies.results: we find that helium star models with masses between ∼1.8 and 2.7 m⊙ are able to evolve onto 1.35−1.37 m⊙ (c)one cores that initiate explosive burning at central densities between log10(ρc/g cm−3) ∼ 9.3 and 9.6. we constrained the amount of residual carbon retained after core carbon burning as a function of initial conditions, and conclude that it plays a critical role in determining the final outcome: chandrasekhar-mass degenerate cores that retain more than approximately 0.005 m⊙ of carbon result in (c)one sne ia, while those with lower carbon mass become ecsne. we find that (c)one sne ia are more likely to occur at high metallicities, whereas at low metallicities ecsne dominate. however, both sn ia and ecsn progenitors expand significantly during the final evolutionary stages, so that for the most extended models, a further binary interaction may occur. we constrain the relative ratio between (c)one sne ia and sne ib/c to be 0.17−0.30 at z = 0.02, and 0.03−0.13 at z ≤ 10−3.conclusions: we conclude with a discussion on potential observational properties of (c)one sne ia and their progenitors. in the few thousand years leading to the explosion, at least some progenitors should be identifiable as luminous metal-rich super-giants, embedded in hydrogen-free circumstellar nebulae. | thermonuclear and electron-capture supernovae from stripped-envelope stars |
a nebular spectrum of the peculiar, low-luminosity type ia supernova 2010lp is modelled in order to estimate the composition of the inner ejecta and to illuminate the nature of this event. despite having a normally declining light curve, sn 2010lp was similar spectroscopically to sn 1991bg at early times. however, it showed a very unusual double-peaked [o i] $\lambda \lambda \, 6300,6363$ emission at late times (taubenberger et al.). modelling of the nebular spectrum suggests that a very small amount of oxygen (~0.05 m⊙), expanding at very low speed (≲ 2000 km s-1) is sufficient to reproduce the observed emission. the rest of the nebula is not too dissimilar from sn 1991bg, except that sn 2010lp is slightly more luminous. the double-peaked [o i] emission suggests that sn 2010lp may be consistent with the merger or collision of two low-mass white dwarfs. the low end of the sn ia luminosity sequence is clearly populated by diverse events, where different channels may contribute. | a very low central oxygen mass in the peculiar type ia sn 2010lp: further diversity at the low-luminosity end of sne ia |
we provide a new method for deriving heavy element abundances taking advantage of the unique suite of fine-structure lines in the mid- to far-infrared (ir) range. using grids of photo-ionisation models that cover a wide range in o/h and n/o abundances and ionisation parameter, our code hii-chi-mistry-ir (hcm-ir) provides model-based abundances based on extinction-free and temperature-insensitive tracers. these are two significant advantages over optical diagnostics when they are applied to dust-obscured regions or unresolved (stratified) nebulae, typical conditions found in high-z galaxies. the performance of the code is probed using three different samples of galaxies that extend over a wide range in metallicity, 7.2 ≲ 12 + log(o/h) ≲ 8.9, with available mid- to far-ir spectroscopic observations from spitzer and herschel, respectively. the samples correspond to 28 low-metallicity dwarf galaxies, 19 nearby starbursts, and 9 luminous ir galaxies. the ir model-based metallicities obtained are robust within a scatter of 0.03 dex when the hydrogen recombination lines, which are typically faint transitions in the ir range, are not available. when compared to the optical abundances obtained with the direct method, model-based methods, and strong-line calibrations, hcm-ir estimates show a typical dispersion of ∼ 0.2 dex. this is in line with previous studies comparing ir and optical abundances and does not introduce a noticeable systematic above 12 + log(o/h) ≳ 7.6. this accuracy can be achieved by measuring the sulphur ([s iv]10.5 μm and [s iii]18.7, 33.5 μm) and the neon lines ([ne iii]15.6 μm and [ne ii]12.8 μm). additionally, hcm-ir provides an independent n/o measurement when the oxygen ([o iii]52, 88 μm) and nitrogen ([n iii]57 μm) transitions are measured. the derived abundances in this case do not rely on particular assumptions on the n/o ratio. large uncertainties (∼ 0.4 dex) may affect the abundance determinations of galaxies at sub- or over-solar metallicities when a solar-like n/o ratio is adopted. finally, the code has been applied to 8 galaxies located at 1.8 < z < 7.5 with ground-based detections of far-ir lines redshifted in the submillimetre range, revealing solar-like n/o and o/h abundances in agreement with recent studies. a script to derive chemical abundances with hcm-ir has been made publicly available online. full tables 1 and 3 are 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/652/a23 | measuring chemical abundances with infrared nebular lines: hii-chi-mistry-ir |
in 1181 ad, chinese and japanese observers reported an unmoving bright 'guest star' in the constellation chuanshe, visible for 185 d. in 2013, d. patchick discovered what turned out to be a unique nebula surrounding a unique star, with the structure named 'pa 30', while subsequent workers made connections to mergers of white dwarfs, to the supernova subclass of low-luminosity type iax, and to the 1181 transient. here, i provide a wide range of new observational pieces of evidence: first, detailed analysis of the original chinese and japanese reports places the 'guest star' of 1181 into a small region with the only interesting source being pa 30. second, the ancient records confidently place the peak magnitude as 0.0 > vpeak > -1.4, and hence peak absolute magnitude -14.5 >mv, peak>-16.0 mag. third, the pa 30 central star is fading from b = 14.9 in 1889, to b = 16.20 in 1950, to b = 16.58 in 2022. fourth, recent light curves show typical variability with full amplitude of 0.24 mag on time-scales of 1 d and longer, critically with no coherent modulations for periods from 0.00046-10 d to strict limits. fifth, the spectral energy distribution from the far-infrared to the ultraviolet is a nearly perfect power law with fν ∝ ν0.99 ± 0.07, observed luminosity 128 ± 24 l⊙, and absolute magnitude mv = +1.07. i collect my new pieces of evidence with literature results to make a confident case to connect the east-asian observations to a supernova, then to pa 30, then to a low-luminosity type iax sn, then to the only possible explosion mechanism as a merger between co and one white dwarfs. | the path from the chinese and japanese observations of supernova 1181 ad, to a type iax supernova, to the merger of co and one white dwarfs |
this work presents theoretical calculations of infrared spectra of nitrogen (n)-containing polycyclic aromatic hydrocarbon (pah) molecules with the incorporation of n, nh, and nh2 using density functional theory (dft). the properties of their vibrational modes in 2-15 μm are investigated in relation to the unidentified infrared (uir) bands. it is found that neutral pahs, when incorporated with nh2 and n (at inner positions), produce intense infrared bands at 6.2, 7.7, and 8.6 μm that have been normally attributed to ionized pahs so far. the present results suggest that strong bands at 6.2 and 11.2 μm can arise from the same charge state of some n-containing pahs, arguing that there might be some n-abundant astronomical regions where the 6.2 to 11.2 μm band ratio is not a direct indicator of the pahs' ionization. pahs with nh2 and n inside the carbon structure show the uir band features characteristic to star-forming regions as well as reflection nebulae (class a), whereas pahs with n at the periphery have similar spectra to the uir bands seen in planetary nebulae and post-agb stars (class b). the presence of n atoms at the periphery of a pah may attract h or h+ to form n-h and n-h2 bonds, exhibiting features near 2.9-3.0 μm, which are not yet observationally detected. the absence of such features in the observations constrains the contribution of nh and nh2 substituted pahs that could be better tested with concentrated observations in this range. however, pahs with n without h either at the periphery or inside the carbon structure do not have the abundance constraint due to the absence of 2.9-3.0 μm features and are relevant in terms of positions of the uir bands. extensive theoretical and experimental studies are required to obtain deeper insight. | theoretical study of infrared spectra of interstellar pah molecules with n, nh, and nh2 incorporation |
the large high altitude air shower observatory (lhaaso) observed a dozen gamma-ray sources with significant emission above 100 tev that may be strong candidates for pevatrons. neutrino observations are crucial for diagnosing whether the gamma-ray radiative process is hadronic or leptonic. we use the bayesian method to analyse the 10-yr (2008-2018) icecube data, and hence constrain the hadronic gamma-ray emission in the lhaaso sources. the present neutrino data show that the hadronic gamma-ray flux from the crab nebula is lower than the observed gamma-ray flux at the 90 per cent confidence level and contributes less than 86 per cent, which disfavours the hadronic origin of gamma-rays below tens of tev. for the other lhaaso sources, the present neutrino observations cannot put useful constraints on the gamma-ray radiative process. we consider the uncertainty of the source extension: the upper limits on the hadronic gamma-ray flux tend to increase with the extension; and some sources, namely lhaaso j2032+4102, lhaaso j1929+1745, and lhaaso j1908+0621, show a relatively high statistical significance of neutrino signals if the extension is ≲ 0.°6. finally, we estimate the future observational results of lhaaso sources by proposed neutrino telescopes. if the lhaaso-observed pev gamma-rays are of hadronic origin, the crab nebula may be detected at >100 tev at the 3σ confidence level within 20 years by a neutrino detector with an effective area 30 times that of icecube. | neutrino observations of lhaaso sources: present constraints and future prospects |
as a science verification study of the newly released akari/fis faint source catalog ver. 1, this paper discusses the different levels of dust attenuation toward stellar light and nebular emission lines within local star-forming galaxies at 0.02 < z < 0.10. by constructing an updated version of the akari-sdss-galex matched galaxy catalog (with >2000 sources), we compare the dust attenuation levels toward stellar light (from the lir/luv ratio) and nebular emission lines (from the hα/hβ ratio). we find that there is a clear trend that more massive galaxies tend to have higher "extra" attenuation toward nebular regions, while galaxies with higher specific star formation rates tend to have lower extra attenuation. we also confirm these trends by using the wise mid-infrared photometry with a significantly large sample size of the wise-sdss-galex galaxies (>50000 sources). finally, we study how the levels of extra attenuation toward nebular regions change across the sfr-m⋆ plane. we find that, even at a fixed stellar mass, galaxies located below the main sequence tend to have higher levels of extra attenuation toward nebular regions, suggesting a change in dust geometry within the galaxies across the star-forming main sequence during the course of the star formation quenching process. | on the different levels of dust attenuation to nebular and stellar light in star-forming galaxies |
we report on the properties of the low-mass stars that recently formed in the central ∼ 2\buildrel{ \prime}\over{.} 7× 2\buildrel{ \prime}\over{.} 7 of 30 dor, including the r136 cluster. using the photometric catalog of de marchi et al., based on observations with the hubble space telescope, and the most recent extinction law for this field, we identify 1035 bona fide pre-main-sequence (pms) stars showing {{h}}α excess emission at the 4σ level with an {{h}}α equivalent width of 20 å or more. we find a wide spread in age spanning the range ∼ 0.1{--}50 {myr}. we also find that the older pms objects are placed in front of the r136 cluster and are separated from it by a conspicuous amount of absorbing material, indicating that star formation has proceeded from the periphery into the interior of the region. we derive physical parameters for all pms stars, including masses m, ages t, and mass accretion rates {\dot{m}}{acc}. to identify reliable correlations between these parameters, which are intertwined, we use a multivariate linear regression fit of the type {log}{\dot{m}}{acc}=a× {log}t+b× {log}m+c. the values of a and b for 30 dor are compatible with those found in ngc 346 and ngc 602. we extend the fit to a uniform sample of 1307 pms stars with 0.5< m/{m}⊙< 1.5 and t< 16 {myr} in six star-forming regions in the large and small magellanic clouds and milky way with metallicities in the range of 0.1-1.0 {{z}}⊙ . we find a=-0.59+/- 0.02 and b=0.78+/- 0.08. the residuals are systematically different between the six regions and reveal a strong correlation with metallicity z, of the type c=(-3.69+/- 0.02)-(0.30+/- 0.04)× {log}z/{z}⊙ . a possible interpretation of this trend is that when the metallicity is higher so is the radiation pressure, and this limits the accretion process, in both its rate and duration. based on observations with the nasa/esa hubble space telescope, obtained at the space telescope science institute, which is operated by aura, inc., under nasa contract nas5-26555. | photometric determination of the mass accretion rates of pre-main-sequence stars. v. recent star formation in the 30 dor nebula |
if confirmed, the neptune-size exomoon candidate in the kepler 1625 system will be the first natural satellite outside our solar system. its characteristics are nothing alike we know for a satellite. kepler 1625b i is expected to be as massive as neptune and to orbit at 40 planetary radii around a ten jupiter mass planet. because of its mass and wide orbit, this satellite was first thought to be captured instead of formed in situ. in this work, we investigated the possibility of an in situ formation of this exomoon candidate. to do so, we performed n-body simulations to reproduce the late phases of satellite formation and use a massive circumplanetary disc to explain the mass of this satellite. our setups started soon after the gaseous nebula dissipation, when the satellite embryos are already formed. also for selected exomoon systems, we take into account a post-formation tidal evolution. we found that in situ formation is viable to explain the origin of kepler 1625b i, even when different values for the star-planet separation are considered. we show that for different star-planet separations the minimum amount of solids needed in the circumplanetary disc to form such a satellite varies, the wider is this separation more material is needed. in our simulations of satellite formation, many satellites were formed close to the planet, this scenario changed after the tidal evolution of the systems. we concluded that if the kepler1625 b satellite system was formed in situ, tidal evolution was an important mechanism to sculpt its final architecture. | exploring formation scenarios for the exomoon candidate kepler 1625b i |
we have observed the symbiotic stellar system r aqr, aiming to describe the gravitational interaction between the white dwarf (wd) and the wind from the mira star, the key phenomenon driving the symbiotic activity and the formation of nebulae in such systems. we present high-resolution alma maps of the 12co and 13co j = 3-2 lines, the 0.9 mm continuum distribution, and some high-excitation molecular lines in r aqr. the maps, which have resolutions ranging between 40 mas and less than 20 mas probe the circumstellar regions at suborbital scales as the distance between the stars is 40 mas. our observations show the gravitational effects of the secondary on the stellar wind. the agb star was identified in our maps from the continuum and molecular line data, and we estimated the probable position of the secondary from a new estimation of the orbital parameters. the (preliminary) comparison of our maps with theoretical predictions is surprisingly satisfactory and the main expected gravitational effects are directly mapped for the first time. we find a strong focusing in the equatorial plane of the resulting wind, which shows two plumes in opposite directions that have different velocities and very probably correspond to the expected double spiral due to the interaction. our continuum maps show the very inner regions of the nascent bipolar jets, at scales of some au. continuum maps obtained with the highest resolution show the presence of a clump that very probably corresponds to the emission of the ionized surroundings of the wd and of a bridge of material joining both stars, which is likely material flowing from the agb primary to the accretion disk around the wd secondary. | high-resolution observations of the symbiotic system r aqr. direct imaging of the gravitational effects of the secondary on the stellar wind |
we present the first high spatial resolution radio continuum survey of the southern galactic plane. the cornish project has mapped the region defined by 295° < l < 350°; |b| < 1° at 5.5 ghz, with a resolution of 2.5 arcsec (fwhm). as with the cornish-north survey, this is designed to primarily provide matching radio data to the spitzer glimpse survey region. the cornish-south survey achieved a root mean square noise level of ~0.11 mjy beam-1, using the 6a configuration of the australia telescope compact array (atca). in this paper, we discuss the observations, data processing and measurements of the source properties. above a 7σ detection limit, 4701 sources were detected, and their ensemble properties show similar distributions with their northern counterparts. the catalogue is highly reliable and is complete to 90 per cent at a flux density level of 1.1 mjy. we developed a new way of measuring the integrated flux densities and angular sizes of non-gaussian sources. the catalogue primarily provides positions, flux density measurements, and angular sizes. all sources with ir counterparts at 8 μm have been visually classified, utilizing additional imaging data from optical, near-ir, mid-ir, far-ir, and sub-millimetre galactic plane surveys. this has resulted in the detection of 524 h ii regions of which 255 are ultra-compact h ii regions, 287 planetary nebulae, 79 radio stars, and 6 massive young stellar objects. the rest of the sources are likely to be extragalactic. these data are particularly important in the characterization and population studies of compact ionized sources such as uchii regions and pne towards the galactic mid-plane. | the coordinated radio and infrared survey for high-mass star formation - v. the cornish-south survey and catalogue |
we study six luminous lyα emitters (laes) with very blue rest-frame uv continua at 5.7 ≤ z ≤ 6.6. these laes have previous hubble space telescope (hst) and spitzer irac observations. combining our newly acquired hst images, we find that their uv-continuum slopes β are in a range of -3.4 ≤ β ≤ -2.6. unlike previous, tentative detections of β ≃ -3 in photometrically selected, low-luminosity galaxies, our laes are spectroscopically confirmed and luminous (muv < -20 mag). we model their broadband spectral energy distributions (seds), and find that two β ≃ -2.6 ± 0.2 galaxies can be well fitted with young and dust-free stellar populations. however, it becomes increasingly difficult to fit bluer galaxies. we explore further interpretations by including the non-zero lyc escape fraction fesc, very low metallicities, and/or active galactic nucleus contributions. assuming fesc ≃ 0.2, we achieve the bluest slopes β ≃ -2.7 when nebular emission is considered. this can nearly explain the seds of two galaxies with β ≃ -2.8 and -2.9 (σβ = 0.15). larger fesc values and very low metallicities are not favored by the strong nebular line emission (evidenced by the irac flux) or the observed (irac 1 - irac 2) color. finally, we find that the β ≃ -2.9 galaxy can potentially be well explained by the combination of a very young population with a high fesc (≥0.5) and an old, dusty population. we are not able to produce two β ≃ -3.4 ± 0.4 galaxies. future deep spectroscopic observations are needed to fully understand these galaxies. | luminous lyα emitters with very blue uv-continuum slopes at redshift 5.7 ≤ z ≤ 6.6 |
we have used the 150 mhz radio continuum survey (tgss adr) from the giant metrewave radio telescope (gmrt) to search for phase-averaged emission toward all well-localized radio pulsars north of -53° decl. we detect emission toward 200 pulsars with high confidence (≥slant 5σ ) and another 88 pulsars at fainter levels. we show that most of our identifications are likely from pulsars, except for a small number where the measured flux density is confused by an associated supernova or pulsar-wind nebula, or a globular cluster. we investigate the radio properties of the 150 mhz sample and find an unusually high number of gamma-ray binary millisecond pulsars with very steep spectral indices. we also note a discrepancy in the measured flux densities between gmrt and lofar pulsar samples, suggesting that the flux density scale for the lofar pulsar sample may be in error by approximately a factor of two. we carry out a separate search of 30 well-localized gamma-ray, radio-quiet pulsars in an effort to detect a widening of the radio beam into the line of sight at lower frequencies. no steep-spectrum emission was detected either toward individual pulsars or in a weighted stack of all 30 images. | known pulsars identified in the gmrt 150 mhz all-sky survey |
at the age of about 1 yr, the spectra of most type ia supernovae (sne ia) are dominated by strong forbidden nebular emission lines of fe ii and fe iii. later observations (at about 2 yr) of the nearby sn 2011fe showed an unexpected shift of ionization to fe i and fe ii. spectra of the very nearby sn ia 2014j at an intermediate phase (1-1.5 yr) that are presented here show a progressive decline of fe iii emission, while fe i is not yet strong. the decrease in ionization can be explained if the degree of clumping in the ejecta increases significantly at ∼1.5 yr, at least in the fe-dominated zone. models suggest that clumps remain coherent after about one year, behaving like shrapnel. the high density in the clumps, combined with the decreasing heating rate, would then cause recombination. these data may witness the phase of transition from relatively smooth ejecta to the very clumpy morphology that is typical of sn remnants. the origin of the increased clumping may be the development of local magnetic fields. | the intermediate nebular phase of sn 2014j: onset of clumping as the source of recombination |
ultraluminous x-ray sources (ulxs) are extragalactic x-ray emitters located off-centre of their host galaxy and with a luminosity in excess of a few 1039 erg s-1, if emitted isotropically1,2. the discovery of periodic modulation revealed that in some ulxs the accreting compact object is a neutron star3-7, indicating luminosities substantially above their eddington limit. the most extreme object in this respect is ngc 5907 ulx-1 (ulx1), with a peak luminosity that is 500 times its eddington limit. during a chandra observation to probe a low state of ulx1, we detected diffuse x-ray emission at the position of ulx1. its diameter is 2.7 ± 1.0 arcsec and contains 25 photons, none below 0.8 kev. we interpret this extended structure as an expanding nebula powered by the wind of ulx1. its diameter of about 200 pc, characteristic energy of ~1.9 kev and luminosity of ~2 × 1038 erg s-1 imply a mechanical power of 1.3 × 1041 erg s-1 and an age of ~7 × 104 yr. this interpretation suggests that a genuinely super-eddington regime can be sustained for timescales much longer than the spin-up time of the neutron star powering the system. as the mechanical power from a single ulx nebula can rival the injection rate of cosmic rays of an entire galaxy8, ulx nebulae could be important cosmic ray accelerators9. | diffuse x-ray emission around an ultraluminous x-ray pulsar |
volatile elements are thought to have been delivered to solar system terrestrial planets late in their formation through accretion of chondritic meteorites. mars can provide information on inner solar system volatile delivery during the earliest planet formation stages. we measured krypton isotopes in the martian meteorite chassigny, representative of the planet’s interior. we found chondritic krypton isotope ratios, which imply early incorporation of chondritic volatiles. the atmosphere of mars has different (solar-type) krypton isotope ratios, indicating that it is not a product of magma ocean outgassing or fractionation of interior volatiles. atmospheric krypton instead originates from accretion of solar nebula gas after formation of the mantle but before nebular dissipation. our observations contradict the common hypothesis that during planet formation, chondritic volatile delivery occurred after solar gas acquisition. | krypton in the chassigny meteorite shows mars accreted chondritic volatiles before nebular gases |
we measured the nickel isotope composition of troilites from chondritic meteorites using the nanosims to put constraints on the abundance of iron-60 in the early solar system. the troilites were selected from petrologic type 3 ordinary and carbonaceous chondrites. based on petrographic observations and mineral chemistry, the troilites targeted for isotope analysis crystallized from melts, most likely in a nebular setting. our isotope analyses did not reveal any significant correlation between nickel-60 enrichments and fe/ni ratios, either in the entire set of troilite grains or in individual troilites. the average inferred initial 60fe/56fe ratio of the studied troilites (i.e., the 60fe/56fe ratio calculated for the entire troilite population) is 1.05 (±1.48) ×10-8. this value is very similar to those estimated in the past for semarkona chondrules, angrites, as well as diogenites and eucrites, based on the isotope analyses of bulk samples (10-9-10-8), but about two orders of magnitude smaller than the average initial 60fe/56fe ratios inferred previously for semarkona troilites and many chondrules from ordinary and carbonaceous chondrites (10-7-10-6) using in situ analysis techniques. based on petrographic evidence, and the generally unequilibrated nature of our samples, as well as on the timing of chondrule formation and planetary evolution, the lack of discernible signs of in situ iron-60 decay in the studied troilites is probably unrelated to metamorphic re-equilibration, and it is also not the result of a late formation of the troilites. we suggest that the highest inferred initial 60fe/56fe ratios reported in the literature are probably inaccurate. | iron-60 in the early solar system revisited: insights from in situ isotope analysis of chondritic troilite |
we present new chandra and xmm-newton observations of a sample of eight radio-quiet (rq) γ-ray pulsars detected by the fermi large area telescope. for all eight pulsars we identify the x-ray counterpart, based on the x-ray source localization and the best position obtained from γ-ray pulsar timing. for psr j2030+4415 we found evidence for a ∼10″-long pulsar wind nebula. our new results consolidate the work from marelli et al. and confirm that, on average, the γ-ray-to-x-ray flux ratios (fγ/fx) of rq pulsars are higher than for the radio-loud (rl) ones. furthermore, while the fγ/fx distribution features a single peak for the rq pulsars, the distribution is more dispersed for the rl ones, possibly showing two peaks. we discuss possible implications of these different distributions based on current models for pulsar x-ray emission. | radio-quiet and radio-loud pulsars: similar in gamma-rays but different in x-rays |
we present a detailed study of the stellar and orbital parameters of the post-common envelope binary central star of the planetary nebula ou 5. low-resolution spectra obtained during the primary eclipse - to our knowledge the first isolated spectra of the companion to a post-common-envelope planetary nebula central star - were compared to catalogue spectra, indicating that the companion star is a late k- or early m-type dwarf. simultaneous modelling of multiband photometry and time-resolved radial velocity measurements was then used to independently determine the parameters of both stars as well as the orbital period and inclination. the modelling indicates that the companion star is low mass (~0.25 m⊙) and has a radius significantly larger than would be expected for its mass. furthermore, the effective temperature and surface gravity of nebular progenitor, as derived by the modelling, do not lie on single-star post-agb evolutionary tracks, instead being more consistent with a post-rgb evolution. however, an accurate determination of the component masses is challenging. this is principally due to the uncertainty on the locus of the spectral lines generated by the irradiation of the companion's atmosphere by the hot primary (used to derive companion star's radial velocities), as well as the lack of radial velocities of the primary. | the post-common-envelope binary central star of the planetary nebula ou 5: a doubly eclipsing post-red-giant-branch system |
we present the analysis of physical conditions, chemical composition, and kinematic properties of two bow shocks - hh 529 ii and hh 529 iii - of the fully photoionized herbig-haro object hh 529 in the orion nebula. the data were obtained with the ultraviolet and visual echelle spectrograph at the 8.2m very large telescope and 20 yr of hubble space telescope imaging. we separate the emission of the high-velocity components of hh 529 ii and iii from the nebular one, determining ne and te in all components through multiple diagnostics, including some based on recombination lines (rls). we derive ionic abundances of several ions, based on collisionally excited lines and rls. we find a good agreement between the predictions of the temperature fluctuation paradigm (t2) and the abundance discrepancy factor (adf) in the main emission of the orion nebula. however, t2 cannot account for the higher adf found in hh 529 ii and iii. we estimate 6 per cent of fe in the gas phase of the orion nebula, while this value increases to 14 per cent in hh 529 ii and between 10 and 25 per cent in hh 529 iii. we find that such increase is probably due to the destruction of dust grains in the bow shocks. we find an overabundance of c, o, ne, s, cl, and ar of about 0.1 dex in hh 529 ii and iii that might be related to the inclusion of h-deficient material from the source of the hh 529 flow. we determine the proper motions of hh 529 finding multiple discrete features. we estimate a flow angle with respect to the sky plane of 58° ± 4° for hh 529. | photoionized herbig-haro objects in the orion nebula through deep high-spectral resolution spectroscopy - i. hh 529 ii and iii |
insights into the earliest stages of our solar system can be derived from its oldest dated solids, calcium-aluminum-rich inclusions (cais). in particular, investigating isotopic anomalies of nucleosynthetic origin in cais offers potential clues to the genetic heritage of refractory inclusions and the reservoir(s) involved in their formation. to this point, however, nucleosynthetic anomalies in refractory inclusions have almost exclusively been recognized in (1) relatively large cais from cv3 chondrites, employing chemical purification and high-precision mass spectrometry, or (2) from sub-mm-sized hibonite-rich objects (e.g., placs, shibs) from the murchison cm2 chondrite using much less precise in-situ techniques. whereas the latter have been shown to be highly anomalous in their isotopic compositions, their genetic connection to 'regular' cais from carbonaceous chondrites remains poorly understood. here, we aim to address this issue by taking advantage of a new technique that allows for high-precision analysis of sub-mm-sized inclusions. using this method, we report ti isotope anomalies in a suite of twelve cais from five different co carbonaceous chondrites, as well as ten refractory inclusions from the cm2 chondrite jbilet winselwan using mc-icpms. we find that these co and cm cais exhibit ti isotopic compositions very similar to those of previously investigated cv3 (and of two ck3) cais, suggesting a fundamental genetic relationship of cais found within these chondrite groups. as such, our data indicates that cais from various groups of carbonaceous chondrites formed from similar matter and in a single region of the solar nebula (i.e., derived from a single common cai-formation region). collectively, these data show evidence of large-scale transport of cais over a significant range of heliocentric distances, covering at least the accretion areas of the cv, ck, co, and cm chondrites. in addition, we report two inclusions consisting of hibonite-rich crystal aggregates from jbilet winselwan that exhibit highly irregular nucleosynthetic ti signatures, implying a distinct origin from the aforementioned cais. these inclusions may represent an earlier generation of refractory material, perhaps more akin to the previously mentioned placs and/or shibs. | titanium isotopic evidence for a shared genetic heritage of refractory inclusions from different carbonaceous chondrites |
context. there are known differences between the physical properties of h ii and diffuse ionized gas (dig). however, most of the studied regions in the literature are relatively bright, with log10 l(hα)[erg s−1] ≳ 37.aims: we compiled an extremely faint sample of 390 h ii regions with a median hα luminosity of 34.7 in the flocculent spiral galaxy ngc 300, derived their physical properties in terms of metallicity, density, extinction, and kinematics, and performed a comparative analysis of the properties of the dig.methods: we used muse data of nine fields in ngc 300, covering a galactocentric distance of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm regions. we binned the data in dendrogram leaves and extracted all strong nebular emission lines. we identified h ii and dig regions and compared their electron densities, metallicity, extinction, and kinematic properties. we also tested the effectiveness of unsupervised machine-learning algorithms in distinguishing between the h ii and dig regions.results: the gas density in the h ii and dig regions is close to the low-density limit in all fields. the average velocity dispersion in the dig is higher than in the h ii regions, which can be explained by the dig being 1.8 kk hotter than h ii gas. the dig manifests a lower ionization parameter than h ii gas, and the dig fractions vary between 15-77%, with strong evidence of a contribution by hot low-mass evolved stars and shocks to the dig ionization. most of the dig is consistent with no extinction and an oxygen metallicity that is indistinguishable from that of the h ii gas. we observe a flat metallicity profile in the central region of ngc 300, without a sign of a gradient.conclusions: the differences between extremely faint h ii and dig regions follow the same trends and correlations as their much brighter cousins. both types of objects are so heterogeneous, however, that the differences within each class are larger than the differences between the two classes. the catalog is only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/668/a74 | muse crowded field 3d spectroscopy in ngc 300. iii. characterizing extremely faint hii regions and diffuse ionized gas |
n103b is a type ia supernova remnant (snr) in the large magellanic cloud (lmc). we carried out new 12co(j = 3-2) and 12co(j = 1-0) observations using aste and alma. we have confirmed the existence of a giant molecular cloud at v lsr ∼ 245 km s-1 toward the southeast of the snr using aste 12co(j = 3-2) data at an angular resolution of ∼25″ (∼6 pc in the lmc). using the alma 12co(j = 1-0) data, we have spatially resolved co clouds along the southeastern edge of the snr with an angular resolution of ∼1.″8 (∼0.4 pc in the lmc). the molecular clouds show an expanding gas motion in the position-velocity diagram with an expansion velocity of ∼5 km s-1. the spatial extent of the expanding shell is roughly similar to that of the snr. we also find tiny molecular clumps in the directions of optical nebula knots. we present a possible scenario that n103b exploded in the wind-bubble formed by the accretion winds from the progenitor system, and is now interacting with the dense gas wall. this is consistent with a single-degenerate scenario. | molecular clouds associated with the type ia snr n103b in the large magellanic cloud |
x-ray-emitting diffuse nebulae around hot stars are observed to have soft-band temperatures in the narrow range [1-3] × 106k, independent of the stellar wind parameters and the evolutionary stage of the central star. we discuss the origin of this x-ray temperature for planetary nebulae, wolf-rayet (wr) nebulae, and interstellar wind bubbles around hot young stars in our galaxy and the magellanic clouds. we calculate the differential emission measure (dem) distributions as a function of temperature from previously published simulations and combine these with the x-ray emission coefficient for the 0.3-2.0 kev band to estimate the x-ray temperatures. we find that all simulated nebulae have dem distributions with steep negative slopes, which is due to turbulent mixing at the interface between the hot shocked stellar wind and the warm photoionized gas. sharply peaked emission coefficients act as temperature filters and emphasize the contribution of gas with temperatures close to the peak position, which coincides with the observed x-ray temperatures for the chemical abundance sets we consider. higher metallicity nebulae have lower temperature and higher luminosity x-ray emission. we show that the second temperature component found from spectral fitting to x-ray observations of wr nebulae is due to a significant contribution from the hot shocked stellar wind, while the lower temperature principal component is dominated by nebular gas. we suggest that turbulent mixing layers are the origin of the soft x-ray emission in the majority of diffuse nebulae. | on the x-ray temperature of hot gas in diffuse nebulae |
we present 1 yr of optical and near-infrared photometry and spectroscopy of the type iip sne 2013k and 2013am. both objects are affected by significant extinction, due to their location in dusty regions of their respective host galaxies, eso 009-10 and ngc 3623 (m65). from the photospheric to nebular phases, these objects display spectra congruent with those of underluminous type iip sne (i.e. the archetypal sne 1997d or 2005cs), showing low photospheric velocities (∼2 × 103 km s-1 at 50 d) together with features arising from ba ii that are particularly prominent in faint sne iip. the peak v-band magnitudes of sn 2013k (-15.6 mag) and sn 2013am (-16.2 mag) are fainter than standard-luminosity type iip sne. the ejected nickel masses are 0.012 ± 0.010 and 0.015 ± 0.006 m⊙ for sn 2013k and sn 2013am, respectively. the physical properties of the progenitors at the time of explosion are derived through hydrodynamical modelling. fitting the bolometric curves, the expansion velocity and the temperature evolution, we infer total ejected masses of 12 and 11.5 m⊙, pre-sn radii of ∼460 and ∼360 r⊙, and explosion energies of 0.34 foe and 0.40 foe for sn 2013k and sn 2013am. late time spectra are used to estimate the progenitor masses from the strength of nebular emission lines, which turn out to be consistent with red supergiant progenitors of ∼15 m⊙. for both sne, a low-energy explosion of a moderate-mass red supergiant star is therefore the favoured scenario. | sne 2013k and 2013am: observed and physical properties of two slow, normal type iip events |
theoretical investigations suggest that magnetic fields may have played an important role in driving rapid stellar accretion rates and efficient planet formation in protoplanetary disks. experimental constraints on magnetic field strengths throughout the solar nebula can test the occurrence of magnetically driven disk accretion and the effect of magnetic fields on planetary accretion. here we conduct paleomagnetic experiments on chondrule samples from primitive cr (renazzo type) chondrites gra 95229 and lap 02342, which likely originated in the outer solar system between 3 and 7 au approximately 3.7 million years after calcium aluminum-rich inclusion formation. by extracting and analyzing 18 chondrule subsamples that contain primary, igneous ferromagnetic minerals, we show that cr chondrules carry internally non-unidirectional magnetization that requires formation in a nebular magnetic field of ≤8.0 ± 4.3 μt (2σ). these weak magnetic fields may be due to the secular decay of nebular magnetic fields by 3.7 million years after calcium aluminum-rich inclusions, spatial heterogeneities in the nebular magnetic field, or a combination of both effects. the possible inferred existence of spatial variations in the nebular magnetic field would be consistent with a prominent role for disk magnetism in the formation of density structures leading to gaps and planet formation. | weak magnetic fields in the outer solar nebula recorded in cr chondrites |
in order to establish the role and expression of silicate-metal fractionation in early planetesimal bodies, we have conducted a highly siderophile element (hse: os, ir, ru, pt, pd, re) abundance and 187re-187os study of acapulcoite-lodranite meteorites. these data are reported with new petrography, mineral chemistry, bulk-rock major and trace element geochemistry, and oxygen isotopes for acapulco, allan hills (alha) 81187, meteorite hills (met) 01195, northwest africa (nwa) 2871, nwa 4833, nwa 4875, nwa 7474 and two examples of transitional acapulcoite-lodranites, elephant moraine (eet) 84302 and graves nunataks (gra) 95209. these data support previous studies that indicate that these meteorites are linked to the same parent body and exhibit limited degrees (<2-7%) of silicate melt removal. new hse and osmium isotope data demonstrate broadly chondritic relative and absolute abundances of these elements in acapulcoites, lower absolute abundances in lodranites and elevated (>2 × ci chondrite) hse abundances in transitional acapulcoite-lodranite meteorites (eet 84302, gra 95209). all of the meteorites have chondritic re/os with measured 187os/188os ratios of 0.1271 ± 0.0040 (2 st. dev.). these geochemical characteristics imply that the precursor material of the acapulcoites and lodranites was broadly chondritic in composition, and were then heated and subject to melting of metal and sulfide in the fe-ni-s system. this resulted in metallic melt removal and accumulation to form lodranites and transitional acapulcoite-lodranites. there is considerable variation in the absolute abundances of the hse, both among samples and between aliquots of the same sample, consistent with both inhomogeneous distribution of hse-rich metal, and of heterogeneous melting and incomplete mixing of silicate material within the acapulcoite-lodranite parent body. oxygen isotope data for acapulcoite-lodranites are also consistent with inhomogeneous melting and mixing of accreted components from different nebular sources, and do not form a well-defined mass-dependent fractionation line. modeling of hse inter-element fractionation suggests a continuum of melting in the fe-ni-s system and partitioning between solid metal and sulfur-bearing mineral melt, where lower s contents in the melt resulted in lower pt/os and pd/os ratios, as observed in lodranites. the transitional meteorites, eet 84302 and gra 95209, exhibit the most elevated hse abundances and do not follow modelled pt/os and pd/os solid metal-liquid metal partitioning trends. we interpret this to reflect metal melt pooling into domains that were sampled by these meteorites, suggesting that they may originate from deeper within the acapulcoite-lodranite parent body, perhaps close to a pooled metallic 'core' region. petrographic examination of transitional samples reveals the most extensive melting, pooling and networking of metal among the acapulcoite-lodranite meteorites. overall, our results show that solid metal-liquid metal partitioning in the fe-ni-s system in primitive achondrites follows a predictable sequence of limited partial melting and metal melt pooling that can lead to significant hse inter-element fractionation effects in proto-planetary materials. | early metal-silicate differentiation during planetesimal formation revealed by acapulcoite and lodranite meteorites |
confronting theoretical models with observations of thermal radiation emitted by neutron stars is one of the most important ways to understand the properties of both, superdense matter in the interiors of the neutron stars and dense magnetized plasmas in their outer layers. here we review the theory of thermal emission from the surface layers of strongly magnetized neutron stars, and the main properties of the observational data. in particular, we focus on the nearby sources for which a clear thermal component has been detected, without being contaminated by other emission processes (magnetosphere, accretion, nebulae). we also discuss the applications of the modern theoretical models of the formation of spectra of strongly magnetized neutron stars to the observed thermally emitting objects. | neutron stars—thermal emitters |
millisecond magnetars can be formed via several channels: core collapse of massive stars, accretion-induced collapse of white dwarfs (wds), double wd mergers, double neutron star (ns) mergers, and wd-ns mergers. because the mass of ejecta from these channels could be quite different, their light curves are also expected to be diverse. we evaluate the dynamic evolution of optical transients powered by millisecond magnetars. we find that the magnetar with a short spin-down timescale converts its rotational energy mostly into the kinetic energy of the transient, while the energy of a magnetar with a long spin-down timescale goes into radiation of the transient. this leads us to speculate that hypernovae could be powered by magnetars with short spin-down timescales. at late times the optical transients will gradually evolve into a nebular phase because of the photospheric recession. we treat the photosphere and nebula separately because their radiation mechanisms are different. in some cases the ejecta could be light enough that the magnetar can accelerate it to a relativistic speed. it is well known that the peak luminosity of a supernova (sn) occurs when the luminosity is equal to the instantaneous energy input rate, as shown by arnett. we show that photospheric recession and relativistic motion can modify this law. the photospheric recession always leads to a delay of the peak time {t}{pk} relative to the time {t}×at which the sn luminosity equals the instantaneous energy input rate. relativistic motion, however, may change this result significantly. | optical transients powered by magnetars: dynamics, light curves, and transition to the nebular phase |
using ukirt on mauna kea, we have carried out a new near-infrared j, h, k monitoring survey of almost a square degree of the star-forming orion nebula cluster with observations on 120 nights over three observing seasons, spanning a total of 894 days. we monitored ∼15,000 stars down to j≈ 20 using the wfcam instrument, and have extracted 1203 significantly variable stars from our data. by studying variability in young stellar objects (ysos) in the h - k, k color-magnitude diagram, we are able to distinguish between physical mechanisms of variability. many variables show color behavior indicating either dust-extinction or disk/accretion activity, but we find that when monitored for longer periods of time, a number of stars shift between these two variability mechanisms. further, we show that the intrinsic timescale of disk/accretion variability in young stars is longer than that of dust-extinction variability. we confirm that variability amplitude is statistically correlated with evolutionary class in all bands and colors. our investigations of these 1203 variables have revealed 73 periodic aa tau type variables, many large-amplitude and long-period (p\gt 15 days) ysos, including three stars showing widely spaced periodic brightening events consistent with circumbinary disk activity, and four new eclipsing binaries. these phenomena and others indicate the activity of long-term disk/accretion variability processes taking place in young stars. we have made the light curves and associated data for these 1203 variables available online. | near-infrared variability in the orion nebula cluster |
in this paper, we describe integral field spectroscopic observations of four southern galactic planetary nebulae (pne), m3-4, m3-6, hen2-29 and hen2-37 covering the spectral range 3400-7000 å. we derive the ionization structure, the physical conditions, the chemical compositions and the kinematical characteristics of these pne and find good agreement with previous studies that relied upon the long-slit technique in their co-spatial area. from their chemical compositions as well as their spatial and kinematic characteristics, we determined that hen2-29 is of the peimbert type i (he- and n-rich), while the other three are of type ii. the strength of the nebular he ii line reveals that m3-3, hen2-29 and hen2-37 are of mid to high excitation classes while m3-6 is a low-excitation pn. a series of emission-line maps extracted from the data cubes were constructed for each pn to describe its overall structure. these show remarkable morphological diversity. spatially resolved spectroscopy of m3-6 shows that the recombination lines of c ii, c iii, c iv and n iii are of nebular origin, rather than arising from the central star as had been previously proposed. this result increases doubts regarding the weak emission-line star (wels) classification raised by basurah et al. in addition, they reinforce the probability that most genuine cases of wels arise from irradiation effects in close binary central stars. | ifu spectroscopy of southern planetary nebulae - iii |
atomic data are an important source of systematic uncertainty in our determinations of nebular chemical abundances. however, we do not have good estimates of these uncertainties since it is very difficult to assess the accuracy of the atomic data involved in the calculations. we explore here the size of these uncertainties by using 52 different sets of transition probabilities and collision strengths, and all their possible combinations, to calculate the physical conditions and the total abundances of o, n, s, ne, cl and ar for a sample of planetary nebulae and h ii regions. we find that atomic data variations introduce differences in the derived abundance ratios as low as 0.1-0.2 dex at low density, but that reach or surpass 0.6-0.8 dex at densities above 104 cm-3 in several abundance ratios, like o/h and n/o. removing from the 52 data sets the four data sets that introduce the largest differences, the total uncertainties are reduced, but high-density objects still reach uncertainty factors of four for their values of o/h and n/o. we identify the atomic data that introduce most of the uncertainty, which involves the ions used to determine density, namely, the transition probabilities of the s+, o+, cl++ and ar+3 density diagnostic lines, and the collision strengths of ar+3. improved calculations of these data will be needed in order to derive more reliable values of chemical abundances in high-density nebulae. in the meantime, our results can be used to estimate the uncertainties introduced by atomic data in nebular abundance determinations. | the impact of atomic data selection on nebular abundance determinations |
context. the nearby orion kleinmann-low nebula is one of the most prolific sources of molecular line emission. it has served as a benchmark for spectral line searches throughout the (sub)millimeter regime.aims: the main goal is to systematically study the spectral characteristics of orion kl in the λ ~ 1.3 cm band.methods: we carried out a spectral line survey with the effelsberg-100 m telescope toward orion kl. it covers the frequency range between 17.9 ghz and 26.2 ghz, i.e., the radio "k band". we also examined alma maps to address the spatial origin of molecules detected by our 1.3 cm line survey.results: in orion kl, we find 261 spectral lines, yielding an average line density of about 32 spectral features per ghz above 3σ (a typical value of 3σ is 15 mjy). the identified lines include 164 radio recombination lines (rrls) and 97 molecular lines. the rrls, from hydrogen, helium, and carbon, stem from the ionized material of the orion nebula, part of which is covered by our beam. the molecular lines are assigned to 13 different molecular species including rare isotopologues. a total of 23 molecular transitions from species known to exist in orion kl are detected for the first time in the interstellar medium. non-metastable (j>k) 15nh3 transitions are detected in orion kl for the first time. based on the velocity information of detected lines and the alma images, the spatial origins of molecular emission are constrained and discussed. a narrow feature is found in so2 (81,7 - 72,6), but not in other so2 transitions, possibly suggesting the presence of a maser line. column densities and fractional abundances relative to h2 are estimated for 12 molecules with local thermodynamic equilibrium (lte) methods. rotational diagrams of non-metastable 14nh3 transitions with j = k + 1 to j = k + 4 yield different results; metastable (j = k) 15nh3 is found to have a higher excitation temperature than non-metastable 15nh3, also indicating that they may trace different regions. elemental and isotopic abundance ratios are also estimated: he/h = (8.7 ± 0.7)% derived from the ratios between helium rrls and hydrogen rrls; 12c/13c = 63 ± 17 from 12ch3oh/13ch3oh; 14n/15n =100 ± 51 from 14nh3/15nh3; and d/h = (8.3 ± 4.5) × 10-3 from nh2d/nh3. the dispersion of the he/h ratios derived from hα/heα pairs to hδ/heδ pairs is very small, which is consistent with theoretical predictions that the departure coefficients bn factors for hydrogen and helium are nearly identical. based on a non-lte code that neglects excitation by the infrared radiation field and a likelihood analysis, we find that the denser regions have lower kinetic temperature, which favors an external heating of the hot core. tables 2 and 4 and appendices are available in electronic form at http://www.aanda.orgthe reduced spectra as fits files are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/581/a48 | a 1.3 cm line survey toward orion kl |
the first direct detections of gravitational waves (gws) from black hole (bh) mergers, gw 150914, gw 151226 and lvt 151012, give a robust lower limit {∼ } 70 000^{+170 000}_{-61 000} on the number of merged, highly spinning bhs in our galaxy. the total spin energy is comparable to all the kinetic energy of supernovae that ever happened in our galaxy. the bhs release the spin energy to relativistic jets by accreting matter and magnetic fields from the interstellar medium (ism). by considering the distributions of the ism density, bh mass and velocity, we calculate the luminosity function of the bh jets, and find that they can potentially accelerate tev-pev cosmic ray particles in our galaxy with total power ∼1037 ± 3 erg s-1 as pevatrons, positron factories and/or unidentified tev gamma-ray sources. additional ∼300 bh jet nebulae could be detectable by cherenkov telescope array. we also argue that the accretion from the ism can evaporate and blow away cold material around the bh, which has profound implications for some scenarios to predict electromagnetic counterparts to bh mergers. | gw 150914-like black holes as galactic high-energy sources |
we characterize the accuracy of linear-polarization mosaics made using the atacama large millimeter/submillimeter array (alma). first, we observed the bright, highly linearly polarized blazar 3c 279 at bands 3, 5, 6, and 7 (3 mm, 1.6 mm, 1.3 mm, and 0.87 mm, respectively). at each band, we measured the blazar's polarization on an 11 × 11 grid of evenly spaced offset pointings covering the full-width at half-maximum (fwhm) area of the primary beam. after applying calibration solutions derived from the on-axis pointing of 3c 279 to all of the on- and off-axis data, we find that the residual polarization errors across the primary beam are similar at all frequencies: the residual errors in linear polarization fraction pfrac and polarization position angle χ are ≲0.001 (≲0.1% of stokes i) and ≲ 1° near the center of the primary beam; the errors increase to ∼0.003-0.005 (∼0.3%-0.5% of stokes i) and ∼1°-5° near the fwhm as a result of the asymmetric beam patterns in the (linearly polarized) q and u maps. we see the expected double-lobed "beam squint" pattern in the circular polarization (stokes v) maps. second, to test the polarization accuracy in a typical alma project, we performed observations of continuum linear polarization toward the kleinmann-low nebula in orion (orion-kl) using several mosaic patterns at bands 3 and 6. we show that after mosaicking, the residual off-axis errors decrease as a result of overlapping multiple pointings. finally, we compare the alma mosaics with an archival 1.3 mm combined array for research in millimeter-wave astronomy polarization mosaic of orion-kl and find good consistency in the polarization patterns. | characterizing the accuracy of alma linear-polarization mosaics |
we present the first linear-polarization mosaicked observations performed by the atacama large millimeter/submillimeter array (alma). we mapped the orion-kleinmann-low (orion-kl) nebula using super-sampled mosaics at 3.1 and 1.3 mm as part of the alma extension and optimization of capabilities program. we derive the magnetic field morphology in the plane of the sky by assuming that dust grains are aligned with respect to the ambient magnetic field. at the center of the nebula, we find a quasi-radial magnetic field pattern that is aligned with the explosive co outflow up to a radius of approximately 12″ (∼5000 au), beyond which the pattern smoothly transitions into a quasi-hourglass shape resembling the morphology seen in larger-scale observations by the james-clerk-maxwell telescope (jcmt). we estimate an average magnetic field strength $\left\langle b\right\rangle =9.4$ mg and a total magnetic energy of 2 × 1045 erg, which is three orders of magnitude less than the energy in the explosive co outflow. we conclude that the field has been overwhelmed by the outflow and that a shock is propagating from the center of the nebula, where the shock front is seen in the magnetic field lines at a distance of ∼5000 au from the explosion center. | the explosion in orion-kl as seen by mosaicking the magnetic field with alma |
we use a sample of 706 galaxies, selected as [o ii]λ3727 ([o ii]) emitters in the survey for high-z absorption red and dead sources (shards) on the candels/goods-n field, to study the differential attenuation of the nebular emission with respect to the stellar continuum. the sample includes only galaxies with a counterpart in the infrared and log10(m*/m⊙) > 9, over the redshift interval 0.3 ≲ z ≲ 1.5. our methodology consists in the comparison of the star formation rates inferred from [o ii] and hα emission lines with a robust quantification of the total star-forming activity (sfr tot) that is independently estimated based on both infrared and ultraviolet (uv) luminosities. we obtain $f\, =\, e(b-v)_{\mathrm{stellar}}$/e(b - v)nebular = 0.69$^{0.71}_{0.69}$ and 0.55$^{0.56}_{0.53}$ for [o ii] and hα, respectively. our resulting f-factors display a significant positive correlation with the uv attenuation and shallower or not-significant trends with the stellar mass, the sfrtot, the distance to the main sequence, and the redshift. finally, our results favour an average nebular attenuation curve similar in shape to the typical dust curve of local starbursts. | differential attenuation in star-forming galaxies at 0.3 ≲ z ≲ 1.5 in the shards/candels field |
blue large-amplitude pulsators (blaps) are a relatively new class of blue variable stars showing periodic variations in their light curves with periods shorter than a few tens of minutes and amplitudes of more than 10 per cent. we report nine blue variable stars identified in the omegawhite survey conducted using eso's vst, which shows a periodic modulation in the range 7-37 min and an amplitude in the range 0.11-0.28 mag. we have obtained a series of followup photometric and spectroscopic observations made primarily using salt and telescopes at saao. we find four stars which we identify as blaps, one of which was previously known. one star, ow j0820-3301, appears to be a member of the v361 hya class of pulsating stars and is spatially close to an extended nebula. one further star, ow j1819-2729, has characteristics similar to the sdav pulsators. in contrast, ow j0815-3421 is a binary star containing an sdb and a white dwarf with an orbital period of 73.7 min, making it only one of six white dwarf-sdb binaries with an orbital period shorter than 80 min. finally, high cadence photometry of four of the candidate blaps show features that we compare with notch-like features seen in the much longer period cepheid pulsators. | the omegawhite survey for short-period variable stars - vii. high amplitude short-period blue variables |
aims: temperature uncertainties plague our understanding of abundance variations within the interstellar medium. using the phangs-muse large program, we develop and apply a new technique to model the strong emission lines arising from h ii regions in 19 nearby spiral galaxies at ~50 pc resolution and infer electron temperatures for the nebulae.methods: due to the charge-exchange coupling of the ionization fraction of the atomic oxygen to that of hydrogen, the emissivity of the observed [o i]λ6300/hα line ratio can be modeled as a function of the gas phase oxygen abundance (o/h), ionization fraction (fion), and electron temperature (te). we measure o/h using a strong-line metallicity calibration and identify a correlation between fion and [s iii]λ9069/[s ii]λ6716,6730, tracing ionization parameter variations.results: we solve for te and test the method by reproducing direct measurements of te([n ii]λ5755) based on auroral line detections to within ~600 k. we apply this"charge-exchange method" of calculating te to 4129 h ii regions across 19 phangs-muse galaxies. we uncover radial temperature gradients, increased homogeneity on small scales, and azimuthal temperature variations in the disks that correspond to established abundance patterns. this new technique for measuring electron temperatures leverages the growing availability of optical integral field unit spectroscopic maps across galaxy samples, increasing the statistics available compared to direct auroral line detections. | a physically motivated "charge-exchange method" for measuring electron temperatures within h ii regions |
incremental particle growth in turbulent protoplanetary nebulae is limited by a combination of barriers that can slow or stall growth. moreover, particles that grow massive enough to decouple from the gas are subject to inward radial drift, which could lead to the depletion of most disk solids before planetesimals can form. compact particle growth is probably not realistic. rather, it is more likely that grains grow as fractal aggregates, which may overcome this so-called radial drift barrier because they remain more coupled to the gas than compact particles of equal mass. we model fractal aggregate growth and compaction in a viscously evolving solar-like nebula for a range of turbulent intensities α t = 10-5-10-2. we do find that radial drift is less influential for porous aggregates over much of their growth phase; however, outside the water snowline fractal aggregates can grow to much larger masses with larger stokes numbers more quickly than compact particles, leading to rapid inward radial drift. as a result, disk solids outside the snowline out to ~10-20 au are depleted earlier than in compact growth models, but outside ~20 au material is retained much longer because aggregate stokes numbers there remain lower initially. nevertheless, we conclude even fractal models will lose most disk solids without the intervention of some leapfrog planetesimal forming mechanism such as the streaming instability (si), though conditions for the si are generally never satisfied, except for a brief period at the snowline for α t = 10-5. | global modeling of nebulae with particle growth, drift, and evaporation fronts. ii. the influence of porosity on solids evolution |
we present the results of an extensive observational campaign on the nearby type ibn sn 2015g, including data from radio through ultraviolet wavelengths. sn 2015g was asymmetric, showing late-time nebular lines redshifted by ∼1000 km s-1. it shared many features with the prototypical sn ibn 2006jc, including extremely strong he i emission lines and a late-time blue pseudo-continuum. the young sn 2015g showed narrow p-cygni profiles of he i, but never in its evolution did it show any signature of hydrogen - arguing for a dense, ionized and hydrogen-free circumstellar medium moving outward with a velocity of ∼1000 km s-1 and created by relatively recent mass-loss from the progenitor star. ultraviolet through infrared observations show that the fading sn 2015g (which was probably discovered some 20 d post-peak) had a spectral energy distribution that was well described by a simple, single-component blackbody. archival hst images provide upper limits on the luminosity of sn 2015g's progenitor, while non-detections of any luminous radio afterglow and optical non-detections of outbursts over the past two decades provide constraints upon its mass-loss history. | the nearby type ibn supernova 2015g: signatures of asymmetry and progenitor constraints |
we present an astrometric and photometric wide-field study of the galactic open star cluster m37 (ngc 2099). the studied field was observed with ground-based images covering a region of about four square degrees in the sloan-like filters ugi. we exploited the gaia catalogue to calibrate the geometric distortion of the large field mosaics, developing software routines that can be also applied to other wide-field instruments. the data are used to identify the hottest white dwarf (wd) member candidates of m37. thanks to the gaia edr3 exquisite astrometry we identified seven such wd candidates, one of which, besides being a high-probability astrometric member, is the putative central star of a planetary nebula. to our knowledge, this is a unique object in an open cluster, and we have obtained follow-up low-resolution spectra that are used for a qualitative characterization of this young wd. finally, we publicly release a three-colour atlas and a catalogue of the sources in the field of view, which represents a complement of existing material. | astro-photometric study of m37 with gaia and wide-field ugi-imaging |
paris is the least aqueously altered cm chondrite identified to date, classified as subtype 2.7; however, literature data indicate that some regions of this apparently brecciated meteorite may be subtype 2.9. the suite of cais in paris includes 19% spinel-pyroxene inclusions, 19% spinel inclusions, 8% spinel-pyroxene-olivine inclusions, 43% pyroxene inclusions, 8% pyroxene-olivine inclusions, and 3% hibonite-bearing inclusions. both simple and complex inclusions are present; some have nodular, banded, or distended structures. no melilite was identified in any of the inclusions in the present suite, but other recent studies have found a few rare occurrences of melilite in paris cais. because melilite is highly susceptible to aqueous alteration, it is likely that it was mostly destroyed during early-stage parent-body alteration. two of the cais in this study are part of compound cai-chondrule objects. their presence suggests that there were transient heating events (probably associated with chondrule formation) in the nebula after chondrules and cais were admixed. also present in paris are a few amoeboid olivine inclusions (aoi) consisting of relatively coarse forsterite rims surrounding fine-grained, porous zones containing diopside and anorthite. the interior regions of the aois may represent fine-grained rimless cais that were incorporated into highly porous forsterite-rich dustballs. these assemblages were heated by an energy pulse that collapsed and coarsened their rims, but failed to melt their interiors. | an american on paris: extent of aqueous alteration of a cm chondrite and the petrography of its refractory and amoeboid olivine inclusions |
a prediction of the classic active galactic nucleus (agn) unification model is the presence of ionization cones with different orientations depending on the agn type. confirmations of this model exist for present times, but it is less clear in the early universe. here, we use the morphology of giant ly α nebulae around agns at redshift z ∼ 3 to probe agn emission and therefore the validity of the agn unification model at this redshift. we compare the spatial morphology of 19 nebulae previously found around type i agns with a new sample of four ly α nebulae detected around type ii agns. using two independent techniques, we find that nebulae around type ii agns are more asymmetric than around type i, at least at radial distances r > 30 physical kpc (pkpc) from the ionizing source. we conclude that the type i and type ii agns in our sample show evidence of different surrounding ionizing geometries. this suggests that the classical agn unification model is also valid for high-redshift sources. finally, we discuss how the lack of asymmetry in the inner parts (r ≲ 30 pkpc) and the associated high values of the he ii to ly α ratios in these regions could indicate additional sources of (hard) ionizing radiation originating within or in proximity of the agn host galaxies. this work demonstrates that the morphologies of giant ly α nebulae can be used to understand and study the geometry of high-redshift agns on circumnuclear scales and it lays the foundation for future studies using much larger statistical samples. | probing the agn unification model at redshift z ∼ 3 with muse observations of giant ly α nebulae |
we present the results of a calculation of recombination coefficients for o2++ e- using an intermediate coupling treatment that fully accounts for the dependence of the distribution of population among the ground levels of o2+ on electron density and temperature. the calculation is extended down to low electron temperatures, where dielectronic recombination arising from rydberg states converging on the o2+ ground levels is an important process. the data that consist of emission coefficients for 8889 recombination lines and recombination coefficients for the ground and metastable states of o+ are in cases a, b and c, and are organized as a function of the electron temperature and number density, as well as wavelength. an interactive fortran 77 data server is also provided as an accessory for mining the line emission coefficients and obtaining lagrange interpolated values for any choice of the two variables between the explicitly provided values for any set of wavelengths. some illustrations of the application of the new data to nebular observations are also provided. | recombination coefficients for o ii lines in nebular conditions |
current models predict that binary interactions are a major ingredient in the formation of bipolar planetary nebulae (pne) and pre-planetary nebulae (ppne). despite years of radial velocity (rv) monitoring, the paucity of known binaries amongst the latter systems means data are insufficient to examine this relationship in detail. in this work, we report on the discovery of a long-period (p = 2654 ± 124 d) binary at the centre of the galactic bipolar ppn iras 08005-2356 (v510 pup), determined from long-term spectroscopic and near-infrared time-series data. the spectroscopic orbit is fitted with an eccentricity of 0.36 ± 0.05, which is similar to that of other long-period post-agb binaries. time-resolved hα profiles reveal high-velocity outflows (jets) with deprojected velocities up to 231$_{-27}^{+31}$ km s-1 seen at phases when the luminous primary is behind the jet. the outflow traced by hα is likely produced via accretion on to a main-sequence companion, for which we calculate a mass of 0.63 ± 0.13 m⊙. this discovery is one of the first cases of a confirmed binary ppn and demonstrates the importance of high-resolution spectroscopic monitoring surveys using large telescopes in revealing binarity among these systems. | the binary central star of the bipolar pre-planetary nebula iras 08005-2356 (v510 pup) |
van der waals (vdw) heterostructures have recently been introduced as versatile building blocks for a variety of novel nanoscale and quantum technologies. harnessing the unique properties of these heterostructures requires a deep understanding of the involved interfacial interactions and a meticulous control of the growth of 2d materials on weakly interacting surfaces. although several epitaxial vdw heterostructures have been achieved experimentally, the mechanisms governing their synthesis are still nebulous. with this perspective, herein, the growth dynamics of antimonene on graphene are investigated in real time. in situ low‑energy electron microscopy reveals that nucleation predominantly occurs on 3d nuclei followed by a self‑limiting lateral growth with morphology sensitive to the deposition rate. large 2d layers are observed at high deposition rates, whereas lower growth rates trigger an increased multilayer nucleation at the edges as they become aligned with the z2 orientation leading to atoll‑like islands with thicker, well‑defined bands. this complexity of the vdw growth is elucidated based on the interplay between the growth rate, surface diffusion, and edges orientation. this understanding lays the groundwork for a better control of the growth of vdw heterostructures, which is critical to their large‑scale integration. | dynamics of antimonene–graphene van der waals growth |
we have found two refractory inclusions in the co3.00 carbonaceous chondrite dominion range (dom) 08006 that appear to be primary condensates from the early solar nebula. one, inclusion 56-1, contains the first four phases predicted to form by equilibrium gas-solid condensation: corundum; hibonite; grossite; and perovskite. the other, 31-2, contains nine predicted condensate phases: hibonite; grossite; perovskite; melilite; spinel; feni metal; diopside; forsterite; and enstatite. except for melilite/spinel, the phases occur in the predicted sequence from core to rim of the inclusion, which has an irregular shape inconsistent with a molten stage. this inclusion preserves the most complete record of condensation in the early solar nebula that has yet been found. the physical evidence reported here supports equilibrium condensation calculations that predict the observed sequence as well as the assumptions upon which they are based, such as total pressure (∼10-3 atm), bulk system composition (solar), and csbnd osbnd h proportions. all phases in both inclusions and the associated ferromagnesian silicates are 16o-rich, with δ17o between -25 and -20‰, implying that this is the original composition of the vast majority of primary condensates and that 16o-poor compositions observed in many isotopically heterogeneous inclusions are largely due to subsequent isotopic exchange. while the nebula was well-mixed with respect to oxygen isotopic composition, clearly resolved anomalies in ca and ti isotopic compositions indicate that some isotopic heterogeneity existed early and was preserved during condensation. inclusion 31-2 did not incorporate live 26al and has nucleosynthetic anomalies in the heavy ca and ti isotopes (i.e., δ48ca = 4.3 ± 1.9‰; δ50ti = 8.8 ± 2.0‰). in contrast, inclusion 56-1 has radiogenic 26mg excesses yielding a (26al/27al)0 ratio of (1.0 ± 0.1) × 10-5 and negative nucleosynthetic isotopic anomalies in ca (δ48ca = -10.3 ± 4.2‰) and ti (δ50ti = -4.3 ± 2.9‰). thus, it represents a deviation from the mutual exclusivity relationship between 26al incorporation and large nucleosynthetic anomalies. the reservoirs in which these inclusions formed had similar o-isotopic and different al-, ca- and ti-isotopic compositions, suggesting that while the cai-forming region was well-mixed with respect to oxygen isotopic composition, clearly resolved anomalies in ca and ti isotopic compositions indicate that some isotopic heterogeneity existed and was preserved during condensation. | condensate refractory inclusions from the co3.00 chondrite dominion range 08006: petrography, mineral chemistry, and isotopic compositions |
the relatively nearby spiral galaxy ngc 6946 is one of the most actively star-forming galaxies in the local universe. ten supernovae (sne) have been observed since 1917, and hence ngc 6946 surely contains a large number of supernova remnants (snrs). here we report a new optical search for these snrs using narrowband images obtained with the wiyn telescope. we identify 147 emission nebulae as likely snrs, based on elevated [s ii]:hα ratios compared to h ii regions. we have obtained spectra of 102 of these nebulae with gemini north-gmos of these, 89 have [s ii]:hα ratios greater than 0.4, the canonical optical criterion for identifying snrs. there is very little overlap between our sample and the snr candidates identified by lacey et al. from radio data. also, very few of our snr candidates are known x-ray sources, unlike the situation in some other galaxies such as m33 and m83. the emission-line ratios, e.g., [n ii]:hα, of the candidates in ngc 6946 are typical of those observed in snr samples from other galaxies with comparable metallicity. none of the candidates observed in our low-resolution spectra show evidence of anomalous abundances or significant velocity broadening. a search for emission at the sites of all the historical sne in ngc 6946 resulted in detections for only two: sn 1980k and sn 2004et. spectra of both show very broad, asymmetric line profiles, consistent with the interaction between sn ejecta and the progenitor star’s circumstellar material, as seen in late spectra from other core-collapse sne of similar age. | a new, larger sample of supernova remnants in ngc 6946 |
ofek identified first j141918.9+394036 (hereafter first j1419+3940) as a radio source sharing similar properties and host galaxy type to the compact, persistent radio source associated with the first known repeating fast radio burst, frb 121102. law et al. showed that first j1419+3940 is a transient source decaying in brightness over the last few decades. one possible interpretation is that first j1419+3940 is a nearby analog to frb 121102 and that the radio emission represents a young magnetar nebula (as several scenarios assume for frb 121102). another interpretation is that first j1419+3940 is the afterglow of an “orphan” long gamma-ray burst (grb). the environment is similar to where most such events are produced. to distinguish between these hypotheses, we conducted very long baseline interferometric (vlbi) radio observations using the european vlbi network (evn) at 1.6 ghz to spatially resolve the emission and to search for millisecond-duration radio bursts. we detect first j1419+3940 as a compact radio source with a flux density of 620 ± 20 μjy (on 2018 september 18) and a source size of 3.9 ± 0.7 mas (i.e., 1.6 ± 0.3 pc given the angular diameter distance of 83 mpc). these results confirm that the radio emission is nonthermal and imply an average expansion velocity of (0.10 ± 0.02)c. contemporaneous high-time-resolution observations using the 100 m effelsberg telescope detected no millisecond-duration bursts of astrophysical origin. the source properties and lack of short-duration bursts are consistent with a grb jet expansion, whereas they disfavor a magnetar birth nebula. | resolving the decades-long transient first j141918.9+394036: an orphan long gamma-ray burst or a young magnetar nebula? |
the primary goal of this paper is to make a direct comparison between the measured and model-predicted abundances of he, c, and n in a sample of 35 well-observed galactic planetary nebulae (pne). all observations, data reductions, and abundance determinations were performed in house to ensure maximum homogeneity. progenitor star masses (m ≤ 4 m⊙) were inferred using two published sets of post-asymptotic giant branch model tracks and l and teff values. we conclude the following: (1) the mean values of n/o across the progenitor mass range exceeds the solar value, indicating significant n enrichment in the majority of our objects; (2) the onset of hot bottom burning appears to begin around 2 m⊙, i.e. lower than ∼5 m⊙ implied by theory; (3) most of our objects show a clear he enrichment, as expected from dredge-up episodes; (4) the average sample c/o value is 1.23, consistent with the effects of third dredge up; and (5) model grids used to compare to observations successfully span the distribution over metallicity space of all c/o and many he/h data points but mostly fail to do so in the case of n/o. the evident enrichment of n in pn and the general discrepancy between the observed and model-predicted n/o abundance ratios signal the need for extra mixing as an effect of rotation and/or thermohaline mixing in the models. the unexpectedly high n enrichment that is implied here for low-mass stars, if confirmed, will likely impact our conclusions about the source of n in the universe. | on the production of he, c, and n by low- and intermediate-mass stars: a comparison of observed and model-predicted planetary nebula abundances |
a prediction of the current paradigm of the hierarchical assembly of galaxies is the presence of supermassive dual black holes at separations of a few kpc or less. in this context, we report the detection of a narrow-line emitter within the extended lyα nebula ( 120 kpc diameter) of the luminous radio-quiet quasi-stellar object (qso) lbqs 0302-0019 at z = 3.286. we identify several high-ionization narrow emission lines (he ii, c iv, c iii) associated with this point-like source, which we have named “jil”, which is only 20 kpc (2.̋9) away from the qso in projection. emission-line diagnostics confirm that the source is likely powered by photoionization of an obscured active galactic nucleus (agn) three orders of magnitude fainter than the qso. the system represents the tightest unobscured/obscured dual agn currently known at z > 3, highlighting the power of muse to detect these elusive systems. | discovery of a dual agn at z ≃ 3.3 with 20 kpc separation |
current planet formation theories provide successful frameworks with which to interpret the array of new observational data in this field. however, each of the two main theories (core accretion, gravitational instability) is unable to explain some key aspects. in many planet formation calculations, it is usual to treat the initial properties of the planet-forming disc (mass, radius, etc.) as free parameters. in this paper, we stress the importance of setting the formation of planet-forming discs within the context of the formation of the central stars. by exploring the early stages of disc formation, we introduce the concept of the maximum mass solar nebula, as opposed to the oft-used minimum mass solar nebula. it is evident that almost all protoplanetary discs start their evolution in a strongly self-gravitating state. in agreement with almost all previous work in this area, we conclude that on the scales relevant to planet formation these discs are not gravitationally unstable to gas fragmentation, but instead form strong, transient spiral arms. these spiral arms can act as efficient dust traps allowing the accumulation and subsequent fragmentation of the dust (but not the gas). this phase is likely to populate the disc with relatively large planetesimals on short time-scales while the disc is still veiled by a dusty-gas envelope. crucially, the early formation of large planetesimals overcomes the main barriers remaining within the core accretion model. a prediction of this picture is that essentially all observable protoplanetary discs are already planet hosting. | the maximum mass solar nebula and the early formation of planets |
massive stars play an important role in both cluster and galactic evolution and the rate at which they lose mass is a key driver of both their own evolution and their interaction with the environment up to and including their terminal sne explosions. young massive clusters provide an ideal opportunity to study a co-eval population of massive stars, where both their individual properties and the interaction with their environment can be studied in detail. we aim to study the constituent stars of the galactic cluster westerlund 1 in order to determine mass-loss rates for the diverse post-main sequence population of massive stars. to accomplish this we made 3mm continuum observations with the atacama large millimetre/submillimetre array. we detected emission from 50 stars in westerlund 1, comprising all 21 wolf-rayets within the field of view, plus eight cool and 21 ob super-hypergiants. emission nebulae were associated with a number of the cool hypergiants while, unexpectedly, a number of hot stars also appear spatially resolved. we were able to measure the mass-loss rates for a unique population of massive post-main sequence stars at every stage of evolution, confirming a significant increase as stars transitioned from ob supergiant to wr states via lbv and/or cool hypergiant phases. fortuitously, the range of spectral types exhibited by the ob supergiants provides a critical test of radiatively-driven wind theory and in particular the reality of the bi-stability jump. the extreme mass-loss rate inferred for the interacting binary wd1-9 in comparison to other cluster members confirmed the key role binarity plays in massive stellar evolution. the presence of compact nebulae around a number of ob and wr stars is unexpected; by analogy to the cool super-hypergiants we attribute this to confinement and sculpting of the stellar wind via interaction with the intra-cluster medium/wind. given the morphologies of core collapse sne depend on the nature of the pre-explosion circumstellar environment, if this hypothesis is correct then the properties of the explosion depend not just on the progenitor, but also the environment in which it is located. | an alma 3 mm continuum census of westerlund 1 |
previous analyses of the spectra of ob-type stars in the magellanic clouds have identified targets with low projected rotational velocities and relatively high nitrogen abundances; the evolutionary status of these objects remains unclear. the vlt-flames tarantula survey obtained spectroscopy for over 800 early-type stars in 30 doradus of which 434 stars were classified as b-type. we have estimated atmospheric parameters and nitrogen abundances using tlusty model atmospheres for 54 b-type targets that appear to be single, have projected rotational velocities, ve sin i ≤ 80 km s-1 and were not classified as supergiants. in addition, nitrogen abundances for 34 similar stars observed in a previous flames survey of the large magellanic cloud have been re-evaluated. for both samples, approximately 75-80% of the targets have nitrogen enhancements of less than 0.3 dex, consistent with them having experienced only small amounts of mixing. however, stars with low projected rotational velocities, ve sini ≤ 40 km s-1 and significant nitrogen enrichments are found in both our samples and simulations imply that these cannot all be rapidly rotating objects observed near pole-on. for example, adopting an enhancement threshold of 0.6 dex, we observed five and four stars in our vfts and previous flames survey samples, yet stellar evolution models with rotation predict only 1.25 ± 1.11 and 0.26 ± 0.51 based on our sample sizes and random stellar viewing inclinations. the excess of such objects is estimated to be 20-30% of all stars with current rotational velocities of less than 40 km s-1. this would correspond to 2-4% of the total non-supergiant single b-type sample. given the relatively large nitrogen enhancement adopted, these estimates constitute lower limits for stars that appear inconsistent with current grids of stellar evolutionary models. including targets with smaller nitrogen enhancements of greater than 0.2 dex implies larger percentages of targets that are inconsistent with current evolutionary models, viz. 70% of the stars with rotational velocities less than 40 km s-1 and 6-8% of the total single stellar population. we consider possible explanations of which the most promising would appear to be breaking due to magnetic fields or stellar mergers with subsequent magnetic braking. based on observations at the european southern observatory in programmes 171.d0237, 073.d0234 and 182.d-0222. | the vlt-flames tarantula survey. xxviii. nitrogen abundances for apparently single dwarf and giant b-type stars with small projected rotational velocities |
we present continuum and molecular line emission alma observations of oh 231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (agb) star. the high-angular resolution ( 0.''2-0.''3) and sensitivity of our alma maps provide the most detailed and accurate description of the overall nebular structure and kinematics of this object to date. we have identified a number of outflow components previously unknown. species studied in this work include 12co, 13co, cs, so, so2, ocs, sio, sis, h3o+, na37cl, and ch3oh. the molecules na37cl and ch3oh are first detections in oh 231.8+4.2, with ch3oh being also a first detection in an agb star. our alma maps bring to light the totally unexpected position of the mass-losing agb star (qx pup) relative to the large-scale outflow. qx pup is enshrouded within a compact (≲60 au) parcel of dust and gas (clump s) in expansion (vexp 5-7 km s-1) that is displaced by 0.''6 to the south of the dense equatorial region (or waist) where the bipolar lobes join. our sio maps disclose a compact bipolar outflow that emerges from qx pup's vicinity. this outflow is oriented similarly to the large-scale nebula but the expansion velocities are about ten times lower (vexp ≲ 35 km s-1). we deduce short kinematical ages for the sio outflow, ranging from 50-80 yr, in regions within 150 au, to 400-500 yr at the lobe tips ( 3500 au). adjacent to the sio outflow, we identify a small-scale hourglass-shaped structure (mini-hourglass) that is probably made of compressed ambient material formed as the sio outflow penetrates the dense, central regions of the nebula. the lobes and the equatorial waist of the mini-hourglass are both radially expanding with a constant velocity gradient (vexp ∝ r). the mini-waist is characterized by extremely low velocities, down to 1 km s-1 at 150 au, which tentatively suggest the presence of a stable structure. the spatio-kinematics of the large-scale, high-velocity lobes (hv lobes), and the dense equatorial waist (large waist) known from previous works are now precisely determined, indicating that both were shaped nearly simultaneously about 800-900 yr ago. we report the discovery of two large ( 8'' × 6''), faint bubble-like structures (fish bowls) surrounding the central parts of the nebula. these are relatively old structures, although probably slightly ( 100-200 yr) younger than the large waist and the hv lobes. we discuss the series of events that may have resulted in the complex array of nebular components found in oh 231.8+4.2 as well as the properties and locus of the central binary system. the presence of ≲80 yr bipolar ejections indicate that the collimated fast wind engine is still active at the core of this outstanding object. the reduced datacubes are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/618/a164 | through the magnifying glass: alma acute viewing of the intricate nebular architecture of oh 231.8+4.2 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.