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herein, we present results from observations of the 12co (j = 1-0), 13co (j = 1-0), and 12co (j = 2-1) emission lines toward the carina nebula complex (cnc) obtained with the mopra and nanten2 telescopes. we focused on massive-star-forming regions associated with the cnc including the three star clusters tr 14, tr 15, and tr 16, and the isolated wr-star hd 92740. we found that the molecular clouds in the cnc are separated into mainly four clouds at velocities -27, -20, -14, and -8 km s-1. their masses are 0.7 × 104 m⊙, 5.0 × 104 m⊙, 1.6 × 104 m⊙, and 0.7 × 104 m⊙, respectively. most are likely associated with the star clusters, because of their high 12co (j = 2-1)/12co (j = 1-0) intensity ratios and their correspondence to the spitzer 8 μm distributions. in addition, these clouds show the observational signatures of cloud-cloud collisions. in particular, there is a v-shaped structure in the position-velocity diagram and a complementary spatial distribution between the -20 km s-1 cloud and the -14 km s-1 cloud. furthermore, we found that sio emission, which is a tracer of a shocked molecular gas, is enhanced between the colliding clouds by using alma archive data. based on these observational signatures, we propose a scenario wherein the formation of massive stars in the clusters was triggered by a collision between the two clouds. by using the path length of the collision and the assumed velocity separation, we estimate the timescale of the collision to be ∼1 myr. this is comparable to the ages of the clusters estimated in previous studies. | massive star formation in the carina nebula complex and gum 31. i. the carina nebula complex |
we present a broadband x-ray study of w50 (the "manatee" nebula), the complex region powered by the microquasar ss 433, that provides a test bed for several important astrophysical processes. the w50 nebula, a galactic pevatron candidate, is classified as a supernova remnant but has an unusual double-lobed morphology likely associated with the jets from ss 433. using nustar, xmm-newton, and chandra observations of the inner eastern lobe of w50, we have detected hard nonthermal x-ray emission up to ~30 kev, originating from a few-arcminute-sized knotty region ("head") located ≲18' (29 pc for a distance of 5.5 kpc) east of ss 433, and constrained its photon index to 1.58 ± 0.05 (0.5-30 kev band). the index gradually steepens eastward out to the radio "ear" where thermal soft x-ray emission with a temperature kt ~ 0.2 kev dominates. the hard x-ray knots mark the location of acceleration sites within the jet and require an equipartition magnetic field of the order of ≳12 μg. the unusually hard spectral index from the "head" region challenges classical particle acceleration processes and points to particle injection and reacceleration in the subrelativistic ss 433 jet, as seen in blazars and pulsar wind nebulae. | hard x-ray emission from the eastern jet of ss 433 powering the w50 "manatee" nebula: evidence for particle reacceleration |
after more than 26 years in quiescence, the black hole transient v404 cyg went into a luminous outburst in 2015 june, and additional activity was detected in late december of the same year. here, we present an optical spectroscopic follow-up of the december mini-outburst, together with x-ray, optical and radio monitoring that spanned more than a month. strong flares with gradually increasing intensity are detected in the three spectral ranges during the ∼10 d following the swift trigger. our optical spectra reveal the presence of a fast outflowing wind, as implied by the detection of a p-cyg profile (he i-5876 å) with a terminal velocity of ∼2500 km s-1 . nebular-like spectra - with an hα equivalent width of ∼500 å - are also observed. all these features are similar to those seen during the main 2015 june outburst. thus, the fast optical wind simultaneous with the radio jet is most likely present in every v404 cyg outburst. finally, we report on the detection of a strong radio flare in late 2016 january, when x-ray and optical monitoring had stopped due to sun constraints. | flares, wind and nebulae: the 2015 december mini-outburst of v404 cygni |
evidence for the capture of nebular gases by planetary interiors would place important constraints on models of planet formation. these constraints include accretion timescales, thermal evolution, volatile compositions and planetary redox states1-7. retention of nebular gases by planetary interiors also constrains the dynamics of outgassing and volatile loss associated with the assembly and ensuing evolution of terrestrial planets. but evidence for such gases in earth's interior remains controversial8-14. the ratio of the two primordial neon isotopes, 20ne/22ne, is significantly different for the three potential sources of earth's volatiles: nebular gas15, solar-wind-irradiated material16 and ci chondrites17. therefore, the 20ne/22ne ratio is a powerful tool for assessing the source of volatiles in earth's interior. here we present neon isotope measurements from deep mantle plumes that reveal 20ne/22ne ratios of up to 13.03 ± 0.04 (2 standard deviations). these ratios are demonstrably higher than those for solar-wind-irradiated material and ci chondrites, requiring the presence of nebular neon in the deep mantle. furthermore, we determine a 20ne/22ne ratio for the primordial plume mantle of 13.23 ± 0.22 (2 standard deviations), which is indistinguishable from the nebular ratio, providing robust evidence for a reservoir of nebular gas preserved in the deep mantle today. the acquisition of nebular gases requires planetary embryos to grow to sufficiently large mass before the dissipation of the protoplanetary disk. our observations also indicate distinct 20ne/22ne ratios between deep mantle plumes and mid-ocean-ridge basalts, which is best explained by addition of a chondritic component to the shallower mantle during the main phase of earth's accretion and by subsequent recycling of seawater-derived neon in plate tectonic processes. | capture of nebular gases during earth's accretion is preserved in deep-mantle neon |
the isotopic composition of oxygen as well as 26al-26mg and 36cl-36s systematics were studied in curious marie, an aqueously altered allende cai characterized by a group ii ree pattern and a large 235u excess produced by the decay of short-lived 247cm. oxygen isotopic compositions in the secondary minerals of curious marie follow a mass-dependent fractionation line with a relatively homogenous depletion in 16o (δ17o of -8‰) compared to unaltered minerals of cai components. both mg and s show large excesses of radiogenic isotopes (26mg∗ and 36s∗) that are uniformly distributed within the cai, independent of parent/daughter ratio. a model initial 26al/27al ratio [(6.2 ± 0.9) × 10-5], calculated using the bulk al/mg ratio and the uniform δ26mg∗ ∼ +43‰, is similar to the canonical initial solar system value within error. the exceptionally high bulk al/mg ratio of this cai (∼95) compared to other inclusions is presumably due to mg mobilization by fluids. therefore, the model initial 26al/27al ratio of this cai implies not only the early condensation of the cai precursor but also that aqueous alteration occurred early, when 26al was still at or near the canonical value. this alteration event is most likely responsible for the u depletion in curious marie and occurred at most 50 kyr after cai formation, leading to a revised estimate of the early solar system 247cm/235u ratio of (5.6 ± 0.3) × 10-5. the mg isotopic composition in curious marie was subsequently homogenized by closed-system thermal processing without contamination by chondritic mg. the large, homogeneous 36s excesses (δ36s∗ ∼ +97‰) detected in the secondary phases of curious marie are attributed to 36cl decay (t1/2 = 0.3 myr) that was introduced by cl-rich fluids during the aqueous alteration event that led to sodalite formation. a model 36cl/35cl ratio of (2.3 ± 0.6) × 10-5 is calculated at the time of aqueous alteration, translating into an initial 36cl/35cl ratio of ∼1.7-3 × 10-5 at solar system birth. the mg and s radiogenic excesses suggest that 26al and 36cl co-existed in the early solar nebula, raising the possibility that, in addition to an irradiation origin, 36cl could have also been derived from a stellar source. | in situ isotopic studies of the u-depleted allende cai curious marie: pre-accretionary alteration and the co-existence of 26al and 36cl in the early solar nebula |
synchrotron emission from astrophysical nonthermal sources usually assumes that the emitting particles are isotropic. by means of large-scale two- and three-dimensional particle-in-cell simulations, we demonstrate that the dissipation of magnetically dominated ( ${\sigma }_{0}\gg 1$ ) turbulence in pair plasmas leads to strongly anisotropic particle distributions. at lorentz factors $\sim {\sigma }_{0}{\gamma }_{\mathrm{th}0}$ (here, ${\gamma }_{\mathrm{th}0}$ is the initial lorentz factor), the particle velocity is preferentially aligned with the local magnetic field; instead, the highest energy particles are preferentially oriented in the plane perpendicular to the field. this energy-dependent anisotropy leads to a synchrotron spectral flux $\nu {f}_{\nu }\propto {\nu }^{s}$ that is much harder than for isotropic particles. remarkably, for ${\sigma }_{0}\gg 1$ we find that the angle-integrated spectral slope in the slow cooling regime is $s\sim 0.5-0.7$ for a wide range of turbulence fluctuations, $0.25\lesssim \delta {b}_{\mathrm{rms}0}^{2}/{b}_{0}^{2}\lesssim 4$ , despite significant variations in the power-law energy spectrum of nonthermal particles. this is because weaker turbulence levels imprint a stronger degree of anisotropy, thereby counteracting the effect of the steeper particle spectrum. the synchrotron spectral slope may be even harder, $s\gtrsim 0.7$ , if the observer is in the plane perpendicular to the mean magnetic field. our results are independent of domain size and dimensionality. our findings may help explain the origin of hard synchrotron spectra of astrophysical nonthermal sources, most notably the radio spectrum of pulsar wind nebulae. | hard synchrotron spectra from magnetically dominated plasma turbulence |
we have measured variations in scattering time-scales in the crab pulsar over a 30-yr period, using observations made at 610 mhz with the 42-ft telescope at jodrell bank observatory. over more recent years, where regular lovell telescope observations at frequencies around 1400 mhz were available, we have also determined the dispersion measure variations, after disentangling the scattering delay from the dispersive delay. we demonstrate a relationship between scattering and dispersion measure variations, with a correlation coefficient of 0.56 ± 0.01. the short time-scales over which these quantities vary, the size of the variations, and the close correlation between scattering and dispersion measure all suggest that the effects are due to discrete structures within the crab nebula, with size scales of ∼6 au (corresponding to an angular size of ∼2 mas at an assumed distance of 2200 pc). we mitigate the effects of scattering on the observed pulse shape by using the measured scattering information to modify the template used for generating the pulse arrival times, thus improving the precision to which the pulsar can be timed. we test this on timing data taken during periods of high scattering, and obtain a factor of two improvements in the root mean square of the timing residuals. | temporal variations in scattering and dispersion measure in the crab pulsar and their effect on timing precision |
red supergiants have been confirmed as the progenitor stars of the majority of hydrogen-rich type ii supernovae1. however, while such stars are observed with masses >25 m⊙ (ref. 2), detections of >18 m⊙ progenitors remain elusive1. red supergiants are also expected to form at all metallicities, but discoveries of explosions from low-metallicity progenitors are scarce. here, we report observations of the type ii supernova, sn 2015bs, for which we infer a progenitor metallicity of ≤0.1 z⊙ from comparison to photospheric-phase spectral models3, and a zero-age main-sequence mass of 17-25 m⊙ through comparison to nebular-phase spectral models4,5. sn 2015bs displays a normal `plateau' light-curve morphology, and typical spectral properties, implying a red supergiant progenitor. this is the first example of such a high-mass progenitor for a `normal' type ii supernova, suggesting a link between high-mass red supergiant explosions and low-metallicity progenitors. | the lowest-metallicity type ii supernova from the highest-mass red supergiant progenitor |
as the closest type ia supernova in decades, sn 2014j provides a unique opportunity for detailed investigation into observational signatures of the progenitor system, explosion mechanism, and burning product distribution. we present a late-time near-infrared spectral series from gemini-n at 307{--}466 {days} after the explosion. following the h-band evolution probes the distribution of radioactive iron group elements, the extent of mixing, and the presence of magnetic fields in the expanding ejecta. comparing the isolated 1.6440 μm [fe ii] emission line with synthetic models shows consistency with a chandrasekhar mass white dwarf of {ρ }c=0.7× {10}9 {{g}} {cm}}-3 undergoing a delayed detonation. the ratio of the flux in the neighboring 1.54 μ {{m}} emission feature to the flux in the 1.6440 μ {{m}} feature shows evidence of some limited mixing of stable and radioactive iron group elements in the central regions. additionally, the evolution of the 1.6440 μ {{m}} line shows an intriguing asymmetry. when measuring line width of this feature, the data show an increase in line width not seen in the evolution of the synthetic spectra, corresponding to ≈1000 km s-1, which could be caused by a localized transition to detonation producing asymmetric ionization in the ejecta. using the difference in width between the different epochs, an asymmetric component in the central regions, corresponding to approximately the inner 2 × 10-4 of white dwarf mass suggests an off-center ignition of the initial explosion and hence of the kinematic center from the chemical center. several additional models investigated, including a {he} detonation and a merger, have difficulty reproducing the features seen in these spectra. | near-infrared spectral evolution of the type ia supernova 2014j in the nebular phase: implications for the progenitor system |
we investigate the dynamics of dust grains of various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. small dust grains, which are well-coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk. intermediate-size grains float near the sonic point of the disk wind located at several scale heights from the midplane, where the grains are loosely coupled to the background gas. for the minimum mass solar nebula at 1 au, dust grains with size of 25-45 μm float around 4 scale heights from the midplane. considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. we also discuss the implications of our result for observations of dusty material around young stellar objects. | dust dynamics in protoplanetary disk winds driven by magnetorotational turbulence: a mechanism for floating dust grains with characteristic sizes |
the first bright objects to form in the universe at redshift $z \sim 10-20$ might have been dark stars, made primarily of hydrogen and helium but powered by dark matter. in this study, we investigate the detectability of supermassive dark stars (smds) by the roman space telescope. rst will be able to detect smdss at redshifts as high as $z\simeq 14$. in cases with gravitational lensing factors of $\mu\sim 100$, rst will be able to find smds as small as $\sim10^4 m_{\odot}$ at $z\sim 12$ with $\sim 10^6$ s of exposure. to differentiate smds from early galaxies containing zero metallicity stars at similar redshifts, we compare their spectra, photometry in rst bands, color indexes and image morphology. with rst alone, the differentiation is possible only for limited cases: smds formed via "adiabatic contraction" (dm pulled into the star via gravity alone) with $m\gtrsim 10^5m_{\odot}$ and lensed by $\mu\gtrsim 30$ have distinct photometric signatures from those of the first galaxies. for smdss formed via "dark matter capture," their spectra are degenerate to those of many galaxies with little to no nebular emission. thus with rst alone, the only way to tell them apart from first galaxies would be via image morphology: i.e. point object (smdss) vs. extended object (sufficiently magnified galaxies). however, if the same objects are further examined by jwst spectroscopy, a "smoking gun" for detection of smds is the heii $\lambda$1640 absorption line. while rst does not cover the wavelength band required to find this line (for $z_{\rm emi}\gtrsim 10$), jwst does. hence the two detectors can be used together in identifying smds. the confirmed detection of any smdss will provide evidence for a new type of star, powered by dark matter. moreover, such massive stars can also be natural progenitors of the supermassive black holes powering the extremely bright quasars observed at $z\gtrsim 6$. | detectability of supermassive dark stars with the roman space telescope |
we report on the source gaia 19ajj, identifying it as a young star associated with a little-studied star-forming region seen along a complex line of sight through the gum nebula. the optical lightcurve recently recorded by gaia exhibits a slow and unsteady 5.5 mag rise over about 3 yr, while the mid-infrared lightcurve from neowise over the same time period shows a 1.2 mag rise having similar structure. available color information is inconsistent with pure extinction reduction as the cause for the photometric brightening. optical spectroscopic characteristics in the current bright phase include: little in the way of absorption except for the hallmark li i 6707 å signature of youth plus weak, e.g., ca i and notably ba ii; strong wind/outflow in ca ii, mg i b, na i d, hα, k i, and o i; jet signatures in [o i], [s ii], [ca ii], [fe ii], and [ni ii]; and narrow rest-velocity emission in neutral species such as fe i, ni i, and mg i. the infrared spectrum is also characterized by outflow and emission, including: a hot he i wind, jet lines such as [fe ii] and h2; and weak narrow rest-velocity atomic line emission. the {}12{co} bandheads are weakly in emission, but there is also broad h2o absorption. gaia 19ajj exhibited a previous bright state in the 2010-2012 time frame. the body of photometric and spectroscopic evidence suggests that the source bears resemblance to v2492 cyg (ptf 10nvg) and pv cep, both of which similarly experience bright phases that recur on long timescales, with large-amplitude photometric variations and emission-dominated spectra. we interpret the behavior of gaia 19ajj as caused by cycles of enhanced disk accretion accompanied by reduced extinction. | gaia 19ajj: a young star brightening due to enhanced accretion and reduced extinction |
we explore the role that gravitational instability plays in ngc 1068, a nearby seyfert galaxy that exhibits unusually vigorous starburst activity. for this purpose, we use the romeo-falstad disc instability diagnostics and data from the bima survey of nearby galaxies, the sloan digital sky survey and the spectrographic areal unit for research on optical nebulae. our analysis illustrates that ngc 1068 is a gravitationally unstable `monster'. its starburst disc is subject to unusually powerful instabilities. several processes, including feedback from the active galactic nucleus and starburst activity, try to quench such instabilities from inside out by depressing the surface density of molecular gas across the central kpc, but they do not succeed. gravitational instability `wins' because it is driven by the stars via their much higher surface density. in this process, stars and molecular gas are strongly coupled, and it is such a coupling that ultimately triggers local gravitational collapse/fragmentation in the molecular gas. | what powers the starburst activity of ngc 1068? star-driven gravitational instabilities caught in the act |
in the years to come, the javalambre-physics of the accelerated universe astrophysical survey (j-pas) will observe 8000 deg2 of the northern sky with 56 photometric bands. j-pas is ideal for the detection of nebular emission objects. this paper presents a new method based on artificial neural networks (anns) that is aimed at measuring and detecting emission lines in galaxies up to z = 0.35. these lines are essential diagnostics for understanding the evolution of galaxies through cosmic time. we trained and tested anns with synthetic j-pas photometry from califa, manga, and sdss spectra. to this aim, we carried out two tasks. first, we clustered galaxies in two groups according to the values of the equivalent width (ew) of hα, hβ, [n ii], and [o iii] lines measured in the spectra. then we trained an ann to assign a group to each galaxy. we were able to classify them with the uncertainties typical of the photometric redshift measurable in j-pas. second, we utilized another ann to determine the values of those ews. subsequently, we obtained the [n ii]/hα, [o iii]/hβ, and o 3n 2 ratios, recovering the bpt diagram ([o iii]/hβ versus [n ii]/hα). we studied the performance of the ann in two training samples: one is only composed of synthetic j-pas photo-spectra (j-spectra) from manga and califa (calma set) and the other one is composed of sdss galaxies. we were able to fully reproduce the main sequence of star-forming galaxies from the determination of the ews. with the calma training set, we reached a precision of 0.092 and 0.078 dex for the [n ii]/hα and [o iii]/hβ ratios in the sdss testing sample. nevertheless, we find an underestimation of those ratios at high values in galaxies hosting an active galactic nuclei. we also show the importance of the dataset used for both training and testing the model. such anns are extremely useful for overcoming the limitations previously expected concerning the detection and measurements of the emission lines in such surveys as j-pas. furthermore, we show the capability of the method to measure a ew of 10 å in hα, hβ, [n ii] and [o iii] lines with a signal-to-noise ratio (s/n) of 5, 1.5, 3.5, and 10, respectively, in the photometry. finally, we compare the properties of emission lines in galaxies observed with minijpas and sdss. despite the limitation of such a comparison, we find a remarkable correlation in their ews. | j-pas: measuring emission lines with artificial neural networks |
the rate at which interstellar gas is converted into stars, and its dependence on environment, is one of the pillars on which our understanding of the visible universe is build. we present a comparison of the surface density of young stars (σ⋆) and dust surface density (σdust) across ngc 346 (n66) in 115 independent pixels of 6 × 6 pc2. we find a correlation between σ⋆ and σdust with a considerable scatter. a power-law fit to the data yields a steep relation with an exponent of 2.6 ± 0.2. we convert σdust to gas surface density (σgas) and σ⋆ to star formation rate (sfr) surface densities (σsfr), using simple assumptions for the gas-to-dust mass ratio and the duration of star formation. the derived total sfr (4 ± 1×10-3 m⊙ yr-1) is consistent with sfr estimated from the hα emission integrated over the hα nebula. on small scales the σsfr derived using hα systematically underestimates the count-based σsfr, by up to a factor of 10. this is due to ionizing photons escaping the area, where the stars are counted. we find that individual 36 pc2 pixels fall systematically above integrated disc galaxies in the schmidt-kennicutt diagram by on average a factor of ∼7. the ngc 346 average sfr over a larger area (90 pc radius) lies closer to the relation but remains high by a factor of ∼3. the fraction of the total mass (gas plus young stars) locked in young stars is systematically high (∼10 per cent) within the central 15 pc and systematically lower outside (2 per cent), which we interpret as variations in star formation efficiency. the inner 15 pc is dominated by young stars belonging to a centrally condensed cluster, while the outer parts are dominated by a dispersed population. therefore, the observed trend could reflect a change of star formation efficiency between clustered and non-clustered star formation. | star formation rates from young-star counts and the structure of the ism across the ngc 346/n66 complex in the smc |
context. in a recent study, star-forming galaxies with he ii λ1640 emission at moderate redshifts between 2 and 4.6 have been found to occur in two modes that are distinguished by the width of their he ii emission lines. broad he ii emission has been attributed to stellar emission from a population of evolved wolf-rayet (wr) stars. the origin of narrow he ii emission is less clear but has been attributed to nebular emission excited by a population of very hot pop iii stars formed in pockets of pristine gas at moderate redshifts.aims: we propose an alternative scenario for the origin of the narrow he ii emission, namely very massive stars (vms) at low metallicity (z), which form strong but slow wr-type stellar winds due to their proximity to the eddington limit.methods: we estimated the expected he ii line fluxes and equivalent widths based on wind models for vms and starburst99 population synthesis models and compared the results with recent observations of star-forming galaxies at moderate redshifts.results: the observed he ii line strengths and equivalent widths are in line with what is expected for a population of vms in one or more young super-clusters located within these galaxies.conclusions: in our scenario the two observed modes of he ii emission originate from massive stellar populations in distinct evolutionary stages at low z (~0.01 z⊙). if this interpretation is correct, there is no need to postulate the existence of pop iii stars at moderate redshifts to explain the observed narrow he ii emission. an interesting possibility is the existence of self-enriched vms with similar wr-type spectra at extremely low z. stellar he ii emission from such very early generations of vms may be detectable in future studies of star-forming galaxies at high redshifts with the james webb space telescope (jwst). the fact that the he ii emission of vms is largely neglected in current population synthesis models will generally affect the interpretation of the integrated spectra of young stellar populations. | narrow he ii emission in star-forming galaxies at low metallicity. stellar wind emission from a population of very massive stars |
we investigate the intrinsic stellar populations (estimated total numbers of ob and pre-main-sequence stars down to 0.1 {{m}⊙ }) that are present in 17 massive star-forming regions (msfrs) surveyed by the mystix project. the study is based on the catalog of >31,000 mystix probable complex members with both disk-bearing and disk-free populations, compensating for extinction, nebulosity, and crowding effects. correction for observational sensitivities is made using the x-ray luminosity function and the near-infrared initial mass function—a correction that is often not made by infrared surveys of young stars. the resulting maps of the projected structure of the young stellar populations, in units of intrinsic stellar surface density, allow direct comparison between different regions. several regions have multiple dense clumps, similar in size and density to the orion nebula cluster. the highest projected density of ∼34,000 stars pc-2 is found in the core of the rcw 38 cluster. histograms of surface density show different ranges of values in different regions, supporting the conclusion of bressert et al. that no universal surface-density threshold can distinguish between clustered and distributed star formation. however, a large component of the young stellar population of msfrs resides in dense environments of 200-10,000 stars pc-2 (including within the nearby orion molecular clouds), and we find that there is no evidence for the b10 conclusion that such dense regions form an extreme “tail” of the distribution. tables of intrinsic populations for these regions are used in our companion study of young cluster properties and evolution. | the spatial structure of young stellar clusters. ii. total young stellar populations |
we use spatially extended measurements of lyα as well as less optically thick emission lines from an ≈80 kpc lyα nebula at z ≈ 1.67 to assess the role of resonant scattering and to disentangle kinematic signatures from lyα radiative transfer effects. we find that the lyα, c iv, he ii, and c iii] emission lines all tell a similar story in this system, and that the kinematics are broadly consistent with large-scale rotation. first, the observed surface brightness profiles are similar in extent in all four lines, strongly favoring a picture in which the lyα photons are produced in situ instead of being resonantly scattered from a central source. second, we see low kinematic offsets between lyα and the less optically thick he ii line (~100-200 km s-1), providing further support for the argument that the lyα and other emission lines are all being produced within the spatially extended gas. finally, the full velocity field of the system shows coherent velocity shear in all emission lines: ≈500 km s-1 over the central ≈50 kpc of the nebula. the kinematic profiles are broadly consistent with large-scale rotation in a gas disk that is at least partially stable against collapse. these observations suggest that the lyα nebula represents accreting material that is illuminated by an offset, hidden active galactic nucleus or distributed star formation, and that is undergoing rotation in a clumpy and turbulent gas disk. with an implied mass of m(<r = 20 kpc) ~3 × 1011 m ⊙, this system may represent the early formation of a large milky way mass galaxy or galaxy group. | spatially resolved gas kinematics within a lyα nebula: evidence for large-scale rotation |
aims: we measure the crab nebula γ-ray spectral energy distribution in the ~100 tev energy domain and test the validity of existing leptonic emission models at these high energies.methods: we used the novel very large zenith angle observations with the magic telescope system to increase the collection area above 10 tev. we also developed an auxiliary procedure of monitoring atmospheric transmission in order to assure proper calibration of the accumulated data. this employs recording optical images of the stellar field next to the source position, which provides a better than 10% accuracy for the transmission measurements.results: we demonstrate that magic very large zenith angle observations yield a collection area larger than a square kilometer. in only ~ 56 h of observations, we detect the γ-ray emission from the crab nebula up to 100 tev, thus providing the highest energy measurement of this source to date with imaging atmospheric cherenkov telescopes. comparing accumulated and archival magic and fermi/lat data with some of the existing emission models, we find that none of them provides an accurate description of the 1 gev to 100 tev γ-ray signal. | magic very large zenith angle observations of the crab nebula up to 100 tev |
in this paper we examine the direct method for measuring electron temperatures in h ii regions, and the extent to which such measurements can provide meaningful information on the physical conditions in these regions. we discuss the limits to what can be inferred about electron temperatures from nebular emission line fluxes. we provide a new simplified method for estimating electron temperatures, including parameters that can be used to determine this from uv [o iii] and [o ii] oxygen lines observable in high-redshift objects using ground-based telescopes. we test this method on published uv high redshift observations and compare the results with reported electron temperatures. | estimating electron temperatures in ionized nebulae: the direct method and its limitations |
we present the results of a wide spectroscopic survey aimed at detecting extragalactic globular clusters (gcs) in the core of the fornax cluster. about 4500 low-resolution spectra (from 4800 to 10000 å) were observed in 25 vlt/vimos masks covering the central 1 deg2 around the dominant galaxy ngc 1399 corresponding to ∼175 kpc galactocentric radius. we describe the methodology used for data reduction and data analysis. we found a total of 387 unique physical objects (372 gcs and 15 ultracompact dwarfs) in the field covered by our observations. most of these objects lie in the region of ngc 1399 halo, with only 10 per cent likely belonging to other giant galaxies 48 of these objects have a literature counterpart. the new vimos data set is complementary to the many gc catalogues already present in the literature and it brings the total number of tracer particles around ngc 1399 to more than 1130 objects. with this comprehensive radial velocity sample, we have found that the velocity dispersion of the gc population (equally for red and blue gc populations) shows a relatively sharp increase from low velocity dispersion ({∼ } 250{-}350 {km s^{-1}}) to high velocity dispersion ({∼ } 300 {-}400 {km s^{-1}}) at projected radius of ≈10 arcmin (∼60 kpc) from the galaxy centre. this suggests that at a projected radius of ≈60 kpc both blue and red gc populations begin to be governed by the dominating fornax cluster potential, rather than by the central ngc 1399 galaxy potential. this kinematic evidence corroborates similar results found using surface brightness analysis and planetary nebulae kinematics. | the fornax cluster vlt spectroscopic survey - i. vimos spectroscopy of compact stellar systems in the fornax core region |
infrared observations of the dusty, massive homunculus nebula around the luminous blue variable η carinae are crucial to characterize the mass-loss history and help constrain the mechanisms leading to the great eruption. we present the 2.4-670 μm spectral energy distribution, constructed from legacy infrared space observatory observations and new spectroscopy obtained with the herschel space observatory. using radiative transfer modeling, we find that the two best-fit dust models yield compositions that are consistent with cno-processed material, with iron, pyroxene and other metal-rich silicates, corundum, and magnesium-iron sulfide in common. spherical corundum grains are supported by the good match to a narrow 20.2 μm feature. our preferred model contains nitrides aln and si3n4 in low abundances. dust masses range from 0.25 to 0.44 {m}⊙ , but {m}{tot}≥slant 45 {m}⊙in both cases, due to an expected high fe gas-to-dust ratio. the bulk of dust is within a 5\prime\prime × 7\prime\prime central region. an additional compact feature is detected at 390 μm. we obtain {l}{ir} = 2.96 × 106 {l}⊙ , a 25% decline from an average of mid-ir photometric levels observed in 1971-1977. this indicates a reduction in circumstellar extinction in conjunction with an increase in visual brightness, allowing 25%-40% of optical and uv radiation to escape from the central source. we also present an analysis of 12co and 13co j = 5-4 through 9-8 lines, showing that the abundances are consistent with expectations for cno-processed material. the [12c ii] line is detected in absorption, which we suspect originates in foreground material at very low excitation temperatures. | η carinae's dusty homunculus nebula from near-infrared to submillimeter wavelengths: mass, composition, and evidence for fading opacity |
we studied the pevatron nature of the pulsar wind nebula (pwn) g75.2+0.1 ("dragonfly") as part of our nustar observational campaign of energetic pwne. the dragonfly is spatially coincident with lhaaso j2018+3651, whose maximum photon energy is 0.27 pev. we detected a compact (radius $1^{\prime} $ ) inner nebula of the dragonfly without a spectral break in 3-20 kev using nustar. a joint analysis of the inner nebula with archival chandra and xmm-newton (xmm) observations yields a power-law spectrum with γ = 1.49 ± 0.03. synchrotron burnoff is observed from the shrinkage of the nustar nebula at higher energies, from which we infer the magnetic field in the inner nebula of 24 μg at 3.5 kpc. our analysis of archival xmm data and 13 yr of fermi-lat data confirms the detection of an extended ( $\sim 10^{\prime} $ ) outer nebula in 2-6 kev (γ = 1.82 ± 0.03) and the nondetection of a gev nebula, respectively. using the vla, xmm, and hawc data, we modeled a multiwavelength spectral energy distribution of the dragonfly as a leptonic pevatron. the maximum injected particle energy of 1.4 pev from our model suggests that the dragonfly is likely a pevatron. our model prediction of the low magnetic field (2.7 μg) in the outer nebula and recent interaction with the host supernova remnant's reverse shock (4 kyr ago) align with common features of pevatron pwne. the origin of its highly asymmetric morphology, pulsar proper motion, pwn-supernova remnant (snr) interaction, and source distance will require further investigations in the future, including a multiwavelength study using radio, x-ray, and gamma-ray observations. | hard x-ray observation and multiwavelength study of the pevatron candidate pulsar wind nebula "dragonfly" |
compound chondrules, i.e. chondrules fused together, make a powerful probe of the density and compositional diversity in chondrule-forming environments, but their abundance among the dominating porphyritic textures may have been drastically underestimated. i report herein microscopic observations and la-icp-ms analyses of lobate chondrules in the co3 chondrites miller range 07193 and 07342. lobes in a given chondrule show correlated volatile and moderately volatile element abundances but refractory element concentrations are essentially independent. this indicates that they formed by the collision of preexisting droplets whose refractory elements behaved in closed system, while their more volatile elements were buffered by the same gaseous medium. the presence of lobes would otherwise be difficult to explain, as surface tension should have rapidly imposed a spherical shape at the temperature peak. in fact, since most chondrules across chondrite groups are nonspherical, a majority are probably compounds variously relaxed toward sphericity. the lack of correlation of refractory elements between conjoined compound chondrule components is inconsistent with derivation of chondrules from the disruption of homogenized melt bodies as in impact scenarios and evokes rather the melting of independent mm-size nebular aggregates. yet a "nebular" setting for chondrule formation would need to involve not only increased solid concentration, e.g. by settling to the midplane, but also a boost in relative velocities between droplets during chondrule-forming events to account for observed compound chondrule frequencies. | collisions and compositional variability in chondrule-forming events |
we have been undertaking a systematic survey at 850 μm based on a sample of four prototypical z ∼ 2 − 3 enormous lyα nebulae (elane) as well as their megaparsec-scale (mpc-scale) environments to study the physical connections between elane and their coeval dusty submillimeter galaxies (smgs). by analysing the scuba-2 data with self-consistent monte carlo simulations to construct the number counts, here, we report on the overabundance of 850 μm-selected submillimeter sources around all the four elane, by a factor of 3.6 ± 0.6 (weighted average) compared to the blank fields. this suggests that the excessive number of submillimeter sources are likely to be part of the mpc-scale environment around the elane, corroborating the co-evolution scenario for smgs and quasars; this is a process which may be more commonly observed in the elan fields. if the current form of the underlying count models continues toward the fainter end, our results would suggest an excess of the 850 μm extragalactic background light by a factor of between 2-10, an indication of significant background light fluctuations on the survey scales. finally, by assuming that all the excessive submillimeter sources are associated with their corresponding elan environments, we estimate the sfr densities of each elan field, as well as a weighted average of σsfr = 1200 ± 300 m⊙ yr−1 mpc−3, consistent with that found in the vicinity of other quasar systems or proto-clusters at similar redshifts; in addition, it is a factor of about 300 greater than the cosmic mean. | a multiwavelength study of elan environments (amuse2). ubiquitous dusty star-forming galaxies associated with enormous lyα nebulae on megaparsec scales |
direct observations of low-mass, low-metallicity galaxies at z ≳ 4 provide an indispensable opportunity for detailed inspection of the ionization radiation, gas flow, and metal enrichment in sources similar to those that reionized the universe. combining the james webb space telescope (jwst), very large telescope/muse, and atacama large millimeter/submillimeter array, we present detailed observations of a strongly lensed, low-mass (≈107.6 m ⊙) galaxy at z = 3.98 (also see vanzella et al.). we identify strong narrow nebular emission, including c iv λ λ1548, 1550, he ii λ1640, o iii] λ λ1661, 1666, [ne iii] λ3868, [o ii] λ3727, and the balmer series of hydrogen from this galaxy, indicating a metal-poor h ii region (≲0.12 z ⊙) powered by massive stars. further, we detect a metal-enriched damped lyα system (dla) associated with the galaxy with the h i column density of n h i ≈ 1021.8 cm-2. the metallicity of the associated dla may reach the supersolar metallicity (≳z ⊙). moreover, thanks to jwst and gravitational lensing, we present the resolved uv slope (β) map at the spatial resolution of ≈100 pc at z = 4, with steep uv slopes reaching β ≈ -2.5 around three star-forming clumps. combining with low-redshift analogs, our observations suggest that low-mass, low-metallicity galaxies, which dominate reionization, could be surrounded by a high covering fraction of the metal-enriched, neutral-gaseous clouds. this implies that the metal enrichment of low-mass galaxies is highly efficient, and further supports that in low-mass galaxies, only a small fraction of ionizing radiation can escape through the interstellar or circumgalactic channels with low-column-density neutral gas. | metal-enriched neutral gas reservoir around a strongly lensed low-mass galaxy at z = 4 identified by jwst/niriss and vlt/muse |
pulsar wind nebula (pwn) boomerang and the associated supernova remnant (snr) g106.3+2.7 are among candidates for the ultra-high-energy (uhe) gamma-ray counterparts published by lhaaso. although the centroid of the extended source, lhaaso j2226+6057, deviates from the pulsar's position by about 0.3∘, the source partially covers the pwn. therefore, we cannot totally exclude the possibility that part of the uhe emission comes from the pwn. previous studies mainly focus on whether the snr is a pevatron, while neglecting the energetic pwn. here, we explore the possibility of the boomerang nebula being a pevatron candidate by studying its x-ray radiation. by modeling the diffusion of relativistic electrons injected in the pwn, we fit the radial profiles of x-ray surface brightness and photon index. the solution with a magnetic field b=140μg can well reproduce the observed profiles and implies a severe suppression of ic scattering of electrons. hence, if future observations reveal part of the uhe emission originating from the pwn, we propose to introduce a proton component to account for the uhe emission in light of the recent lhaaso measurement on crab nebula. in this sense, boomerang nebula would be a hadronic pevatron. | a pevatron candidate: modeling the boomerang nebula in x-ray band |
we present accretion-disk structure measurements from uv-optical reverberation mapping (rm) observations of a sample of eight quasars at 0.24 < z < 0.85. ultraviolet photometry comes from two cycles of hubble space telescope monitoring, accompanied by multiband optical monitoring by the las cumbres observatory network and liverpool telescopes. the targets were selected from the sloan digital sky survey reverberation mapping project sample with reliable black hole mass measurements from hβ rm results. we measure significant lags between the uv and various optical griz bands using javelin and cream methods. we use the significant lag results from both methods to fit the accretion-disk structure using a markov chain monte carlo approach. we study the accretion disk as a function of disk normalization, temperature scaling, and efficiency. we find direct evidence for diffuse nebular emission from balmer and fe ii lines over discrete wavelength ranges. we also find that our best-fit disk color profile is broadly consistent with the shakura & sunyaev disk model. we compare our uv-optical lags to the disk sizes inferred from optical-optical lags of the same quasars and find that our results are consistent with these quasars being drawn from a limited high-lag subset of the broader population. our results are therefore broadly consistent with models that suggest longer disk lags in a subset of quasars, for example, due to a nonzero size of the ionizing corona and/or magnetic heating contributing to the disk response. | the sloan digital sky survey reverberation mapping project: uv-optical accretion disk measurements with the hubble space telescope |
we present an extensive, panchromatic photometric (uv, optical, and near-ir) and low-resolution optical spectroscopic coverage of a type iip supernova sn 2018gj that occurred on the outskirts of the host galaxy ngc 6217. from the v-band light curve, we estimate the plateau length to be ~ 70 ± 2 days, placing it among the very few well-sampled short plateau supernovae (sne). with v-band peak absolute magnitude mv≤ -17.0 ± 0.1 mag, it falls in the middle of the luminosity distribution of the type ii sne. the color evolution is typical to other type ii sne except for an early elbow-like feature in the evolution of v - r color owing to its early transition from the plateau to the nebular phase. using the expanding photospheric method, we present an independent estimate of the distance to sn 2018gj. we report the spectral evolution to be typical of a type ii sne. however, we see a persistent blueshift in emission lines until the late nebular phase, not ordinarily observed in type ii sne. the amount of radioactive nickel (56ni) yield in the explosion was estimated to be 0.026 ± 0.007 m ⊙. we infer from semianalytical modeling, nebular spectrum, and 1d hydrodynamical modeling that the probable progenitor was a red supergiant with a zero-age-main-sequence mass ≤13 m ⊙. in the simulated hydrodynamical model light curves, reproducing the early optical bolometric light curve required an additional radiation source, which could be the interaction with the proximal circumstellar matter. | sn 2018gj: a short plateau type ii supernova with persistent blueshifted ha emission |
we present high-cadence photometric and spectroscopic observations of sn 2020jfo in ultraviolet and optical/near-infrared bands starting from ~3 to ~434 d after the explosion, including the earliest data with the 10.4-m gtc. sn 2020jfo is a hydrogen-rich type ii sn with a relatively short plateau duration (67.0 ± 0.6 d). when compared to other type ii supernovae (sne) of similar or shorter plateau lengths, sn 2020jfo exhibits a fainter peak absolute v-band magnitude (mv = -16.90 ± 0.34 mag). sn 2020jfo shows significant hα absorption in the plateau phase similar to that of typical sne ii. the emission line of stable [ni ii] λ7378, mostly seen in low-luminosity sne ii, is very prominent in the nebular-phase spectra of sn 2020jfo. using the relative strengths of [ni ii] λ7378 and [fe ii] λ7155, we derive the ni/fe production (abundance) ratio of 0.08-0.10, which is ~1.5 times the solar value. the progenitor mass of sn 2020jfo from nebular-phase spectral modelling and semi-analytical modelling falls in the range of 12-15 m⊙. furthermore, semi-analytical modelling suggests a massive h envelope in the progenitor of sn 2020jfo, which is unlikely for sne ii having short plateaus. | photometric and spectroscopic analysis of the type ii sn 2020jfo with a short plateau |
if the envelope of a massive star is not entirely removed during common envelope (ce) interaction with an orbiting compact (e.g., black hole (bh) or neutron star (ns)) companion, the residual bound material eventually cools, forming a centrifugally supported disk around the binary containing the stripped he core. we present a time-dependent height-integrated model for the long-term evolution of post-ce circumbinary disks (cbds), accounting for mass and angular momentum exchange with the binary, irradiation heating by the he core, and photoevaporation wind mass loss. a large fraction of the cbd's mass is accreted prior to its outwards viscous spreading and wind dispersal on a timescale of ~104-105 yr, driving significant orbital migration, even for disks containing ~10% of the original envelope mass. insofar that the cbd lifetime is comparable to the thermal (and, potentially, nuclear) timescale of the he core, over which a second mass-transfer episode onto the companion can occur, the presence of the cbd could impact the stability of this key phase. disruption of the core by the bh/ns would result in a jetted energetic explosion into the dense gaseous cbd (≲1015 cm) and its wind (≳1016 cm), consistent with the environments of luminous fast blue optical transients like at2018cow. evolved he cores that undergo core collapse still embedded in their cbd could generate type ibn/icn supernovae. thousands of dusty wind-shrouded massive-star cbds may be detectable as extragalactic luminous infrared sources with the roman space telescope; synchrotron radio nebulae powered by the cbd-fed bh/ns may accompany these systems. | long-term evolution of massive-star post-common-envelope circumbinary disks and the environments of fast luminous transients |
the observed diversity in type ia supernovae (sne ia) - the thermonuclear explosions of carbon-oxygen white dwarf stars used as cosmological standard candles - is currently met with a variety of explosion models and progenitor scenarios. to help improve our understanding of whether and how often different models contribute to the occurrence of sne ia and their assorted properties, we present a comprehensive analysis of seven nearby sne ia. we obtained one to two epochs of optical spectra with gemini observatory during the nebular phase (>200 d past peak) for each of these events, all of which had time series of photometry and spectroscopy at early times (the first ~8 weeks after explosion). we use the combination of early- and late-time observations to assess the predictions of various models for the explosion (e.g. double-detonation, off-centre detonation, stellar collisions), progenitor star (e.g. ejecta mass, metallicity), and binary companion (e.g. another white dwarf or a non-degenerate star). overall, we find general consistency in our observations with spherically symmetric models for sn ia explosions, and with scenarios in which the binary companion is another degenerate star. we also present an in-depth analysis of sn 2017fzw, a member of the subgroup of sne ia which appear to be transitional between the subluminous '91bg-like' events and normal sne ia, and for which nebular-phase spectra are rare. | nebular-phase spectra of type ia supernovae from the las cumbres observatory global supernova project |
the systematic targeting of extended lyα emission around high-redshift quasars resulted in the discovery of rare and bright enormous lyα nebulae (elane) associated with multiple active galactic nuclei (agns). we initiate here "a multiwavelength study of elan environments" (amuse2) focusing on the elan around the z ~ 3 quasar sdss j1040+1020, aka the fabulous elan. we report on vlt/hawk-i, apex/laboca, jcmt/scuba-2, sma/850μm, and alma co(5-4), and 2 mm observations and compare them to previously published vlt/muse data. the continuum and line detections enable a first estimate of the star formation rates, dust, stellar, and molecular gas masses in four objects associated with the elan (three agns and one lyα emitter), confirming that the quasar host is the most star-forming (star formation rate of ~500 m ⊙ yr-1) and massive galaxy (m star ~ 1011 m ⊙) in the system, and thus can be assumed as central. all four embedded objects have similar molecular gas reservoirs ( ${m}_{{{\rm{h}}}_{2}}\sim {10}^{10}$ m ⊙), resulting in short depletion timescales. this fact together with the estimated total dark matter halo mass, m dm = (0.8-2) × 1013 m ⊙, imply that this elan will evolve into a giant elliptical galaxy. consistently, the constraint on the baryonic mass budget for the whole system indicates that the majority of baryons should reside in a massive warm/hot reservoir (up to 1012 m ⊙), needed to complete the baryons count. additionally, we discuss signatures of gas infall on the compact objects as traced by lyα radiative transfer effects and the evidence for the alignment between the satellites' spins and their directions to the central. | a multiwavelength study of elan environments (amuse2). mass budget, satellites spin alignment, and gas infall in a massive z 3 quasar host halo |
we derive a catalog of early-type emission-line stars including 30,023 spectra of 25,867 stars from lamost data release 7, in which 4189 have simbad records. the spectra are classified into three morphological types (10 subtypes) based on hα emission-line profiles. some spectra contaminated by nebula emission lines such as from h ii regions are flagged in the catalog. we also provide a specific catalog of 20 stars with stellar winds or accretion flows by calculating the terminal and peak velocities based on p-cygni or inverse p-cygni profiles. more important, with two color-color diagrams, (h-ks, j-h) and (ks-w1, h-ks), of a collection of known herbig ae/be stars (haebes) and classical ae/be stars (caebes), we propose an updated criterion to separate haebes from caebes. by the criterion, we select 118 haebe candidates and 2636 caebe candidates from the sample. we confirm 71 of the 118 haebes based on the data from lamost (optical spectra) and wise (photometry and images), 62 of which are newly identified. the 71 identified haebes are compiled into a specific catalog, and their seds and mir images are also presented. the distances of 76% confirmed haebes are further than 1 kpc, which enlarges the number of known haebes in further distance. most of the 71 haebes are located in the galactic disk while 6 of them have ∣z gal∣ > 400 pc. four haebes show the forbidden emission lines of [fe ii] and [o i], in which j051425.20+411310.7 is a newly discovered b[e]. in addition, four haebes having spitzer irs spectra all show pah features. | a catalog of early-type hα emission-line stars and 62 newly confirmed herbig ae/be stars from lamost data release 7 |
we present alma observations of the orion nebula that cover the omc1 outflow region. our focus in this paper is on compact emission from protoplanetary disks. we mosaicked a field containing ∼600 near-ir-identified young stars, around which we can search for sub-millimeter emission tracing dusty disks. approximately 100 sources are known proplyds identified with the hubble space telescope. we detect continuum emission at 1 mm wavelengths toward ∼20% of the proplyd sample, and ∼8% of the larger sample of near-ir objects. the noise in our maps allows 4σ detection of objects brighter than ∼1.5 mjy, corresponding to protoplanetary disk masses larger than 1.5 m j (using standard assumptions about dust opacities and gas-to-dust ratios). none of these disks are detected in contemporaneous co(2-1) or c18o(2-1) observations, suggesting that the gas-to-dust ratios may be substantially smaller than the canonical value of 100. furthermore, since dust grains may already be sequestered in large bodies in orion nebula cluster (onc) disks, the inferred masses of disk solids may be underestimated. our results suggest that the distribution of disk masses in this region is compatible with the detection rate of massive planets around m dwarfs, which are the dominant stellar constituent in the onc. | protoplanetary disks in the orion omc1 region imaged with alma |
al-mg mineral isochrons of three ca-al-rich inclusions (cais) that formed primarily by condensation, one fine-grained, spinel-rich inclusion and two fluffy type a cais, from the reduced cv chondrites efremovka and vigarano were obtained by in situ al-mg isotope measurements using secondary ion mass spectrometry. the slope of the isochron obtained for the fine-grained, spinel-rich inclusion gives an initial 26al/27al value, (26al/27al)0, of (5.19 ± 0.17) × 10-5. this is essentially identical to the solar system initial 26al/27al determined by whole-rock al-mg isochron studies for cais in cv chondrites. in contrast, the isochron slopes for the two fluffy type a cais from their al-mg mineral isochrons, (4.703 ± 0.082) × 10-5 and (4.393 ± 0.084) × 10-5, are significantly lower than the solar system initial value. the range of (26al/27al)0 values of the three cais, from (5.19 ± 0.17) to (4.393 ± 0.084) × 10-5, corresponds to a formation age spread of 0.17 ± 0.04 myr. this formation age spread is similar to that of igneous cais from cv chondrites. the data suggest that condensation and melting of minerals occurred in the hot nebular gas contemporaneously for ∼0.2 myr at the very beginning of our solar system, if 26al was distributed homogeneously in the cai forming region. alternatively, the observed variations in (26al/27al)0 among fluffy type a cais would also raise a possibility of heterogeneous distributions of 26al in the forming region. | variations in initial 26al/27al ratios among fluffy type a ca-al-rich inclusions from reduced cv chondrites |
cool (t ~ 104 k) gas is commonly observed around z > 2 quasars as traced by extended lyα emission. these large-scale nebulae are usually studied using circularly averaged surface-brightness profiles, which suppress information on morphological differences. here, we revisit the lyα nebulae around 78 z ~ 2-3 quasars to obtain a novel estimate of their area and asymmetry using a common redshift-corrected surface-brightness threshold. we find a luminosity-area relation of the form $\mathrm{log}({l}_{\mathrm{ly}\alpha }^{\mathrm{neb}})={a}_{1}\mathrm{log}({\mathrm{area}}^{\mathrm{neb}})+{a}_{0}$ . most nebulae are symmetric and bright, the most lopsided ones being the faintest and less extended. the enormous lyα nebulae, asymmetric due to the presence of active companions, are the exceptions to this trend. by using simulations able to reproduce z ~ 6 quasars' nebulae, we show that the observed relation should not vary with redshift. finally, we discuss possible mechanisms that drive the relation and future work needed to constrain them. | the luminosity-area relation of z > 2 quasars' lyα nebulae |
the nucleosynthetic mo, ru, and w isotopic compositions of the south byron trio iron meteorite grouplet (sbt) are consistent with all three meteorites originating on a single parent body that formed in the carbonaceous chondrite (cc) isotopic domain within the solar nebula. consistent with a common origin, the highly siderophile element (hse) concentrations of the sbt can be related to one another by moderate degrees of fractional crystallization of a parental melt with initially chondritic relative abundances of hse, and with initial s and p contents of ∼7 and ∼1 wt.%, respectively. tungsten-182 isotopic data for the sbt indicate the parent body underwent metal-silicate differentiation 2.1 ± 0.8 myr after calcium aluminum rich inclusion formation, and thermal modeling suggests the parent body formed 1.1 ± 0.5 myr after cai formation. this accretion age is not resolved from the accretion ages of other cc and most noncarbonaceous (nc) type iron meteorite parent bodies. comparison of the projected parental melt composition of the sbt to those projected for the iva and ivb iron meteorite groups suggests that at least some portions of the cc nebular domain were more oxidized compared to the nc domain. in addition, comparison of the sbt parental melt s content to estimates for parent bodies of the iiab, iiiab, iva, iid, and ivb "magmatic" iron meteorite groups suggests that cc type iron meteorite parental melts were characterized by a general depletion in s, in addition to depletions in some other moderately volatile elements. based on chemical and o isotope similarities, prior studies have suggested the possibility of a common parent body for the sbt and the milton pallasite. molybdenum and ru isotopic compositions of milton also provide permissive evidence for this. the hse concentrations in the milton metal, however, cannot be related to the sbt by any known crystal-liquid fractionation or mixing path. thus, milton more likely formed on a different, chemically distinct, but genetically identical parent body present in the cc nebular domain. | genetics, crystallization sequence, and age of the south byron trio iron meteorites: new insights to carbonaceous chondrite (cc) type parent bodies |
we present a spectroscopic survey of over 3400 potential members in the north america and pelican nebulae (nap) using several low-resolution (r ≈ 1300-2000) spectrographs: palomar/norris, wiyn/hydra, keck/deep imaging multi-object spectrograph (deimos), and the multiple mirror telescope (mmt)/hectospec. we identify 580 young stars as likely members of the nap region based on criteria involving infrared excess, li i 6708 å absorption, x-ray emission, parallax, and proper motions. the spectral types of individual spectra are derived by fitting them with templates that are either empirical spectra of pre-main-sequence stars or model atmospheres. the templates are artificially veiled, and a best-fit combination of spectral type and veiling parameter is derived for each star. we use the spectral types with archival photometry to derive v-band extinction and stellar luminosity. from the hertzsprung-russell diagram, the median age of the young stars is about 1 myr, with a luminosity dispersion of ∼0.3-0.4 dex. we investigate the photometric variability of the spectroscopic member sample using zwicky transient facility data and conclude that photometric variability, while present, does not significantly contribute to the luminosity dispersion. while larger than the formal errors, the luminosity dispersion is smaller than if veiling were not taken into account in our spectral typing process. the measured ages of the stellar kinematic groups, combined with the inferred ages for embedded stellar populations revealed by spitzer, suggest a sequential history of star formation in the nap region. | the first extensive spectroscopic study of young stars in the north america and pelican nebulae |
fine-grained rims (fgrs) are ubiquitous in chondrites. they consist of unequilibrated mineral assemblages that surround chondrules and refractory inclusions. as such, they carry information about the material that was accreted onto chondrules. to decipher the nature and the formation mechanism of fgrs and compare them to adjacent matrix material, we investigated their composition, mineralogy, density and texture in the pristine paris cm chondrite. we coupled a new method at the sem scale (academy) that allows high-resolution quantitative petrology and an analytical tem study. significant differences in modal abundance, grain size and porosity are observed between the fgrs and their adjacent matrix. amorphous silicates domains embedding nanosulfides are indicative of a high preservation degree. they are less abundant in the matrix than in the rims. in contrast, secondary alteration phases (phyllosilicates, carbonates and tochilinites) are more abundant in the matrix and associated with larger and fewer sulfides grains. the similar composition of the amorphous silicate in the rims and the matrix attests for a close relationship between the two reservoirs. however, matrix underwent more aqueous alteration. we interpret it as the result of the accretion of material with a higher water/rock ratio in the matrix, leading to a more aqueously altered microenvironment. we also find that coarse-grained anhydrous silicates (olivine and pyroxene) are present in the matrix but not in the fgrs, likely as a result of a chondrule fragmentation episode that occurred after fgr but before matrix accretion. most of the time, fgrs display distinct inner and outer layers. the inner part is compact and displays larger sulfide grains than the outer part, which is more porous (porosity ∼ 45%) and altogether more pristine. these mineral and textural differences are not easily explained by differential aqueous alteration. instead, a pre-accretion thermal process that preferentially affected the inner rim could have induced loss of porosity, compaction of the amorphous silicate domains as well as sulfides growth. we therefore suggest that fgrs acquired their characteristics in the nebula before matrix accretion and discuss possible mechanisms such as dust heating in the chondrule formation environment or secondary heating episode of the previously rimmed chondrule. | nebular thermal processing of accretionary fine-grained rims in the paris cm chondrite |
it has recently been established that unsaturated water-soluble organic compounds (uwsocs) might efficiently form oligomers in polluted fogs and wet aerosol particles, even for weakly soluble ones like methyl vinyl ketone (mvk). the atmospheric relevance of these processes is explored by means of multiphase process model studies in a companion paper. in the present study, we investigate the aging of these aqueous-phase mvk oligomers formed via •oh oxidation, as well as their ability to form secondary organic aerosol (soa) upon water evaporation. the comparison between aqueous-phase composition and aerosol composition after nebulization of the corresponding solutions shows similar trends for oligomer formation and aging. the measurements reveal that oligomer aging leads to the formation of organic diacids. quantification of the soa mass formed after nebulization is performed, and the obtained soa mass yields seem to depend on the spectral irradiance of the light used to initiate the photochemistry. investigating a large range of initial mvk concentrations (0.2-20 mm), the results show that their •oh oxidation undergoes competition between functionalization and oligomerization that is dependent on the precursor concentration. at high initial mvk concentrations (≥ 2 mm), oligomerization prevails over functionalization, while at lower initial concentrations, oligomerization is not the major process, and functionalization dominates, resulting in small carbonyls, dicarbonyls and monoacids. the atmospheric implications of these processes are discussed. | aqueous-phase oligomerization of methyl vinyl ketone through photooxidation - part 1: aging processes of oligomers |
the spectral energy distribution of a galaxy emerges from the complex interplay of many physical ingredients, including its star formation history (sfh), metallicity evolution, and dust properties. using galaxpy, a new galaxy spectral prediction tool, and sfhs predicted by the empirical model universemachine and the cosmological hydrodynamical simulation illustristng, we isolate the influence of sfh on optical and near-infrared colours from 320 to 1080 å at z = 0. by carrying out a principal component analysis, we show that physically motivated sfh variations modify galaxy colours along a single direction in colour space: the sfh-direction. we find that the projection of a galaxy's present-day colours on to the sfh-direction is almost completely regulated by the fraction of stellar mass that the galaxy formed over the last billion years. together with cosmic downsizing, this results in galaxies becoming redder as their host halo mass increases. we additionally study the change in galaxy colours due to variations in metallicity, dust attenuation, and nebular emission lines, finding that these properties vary broad-band colours along distinct directions in colour space relative to the sfh-direction. finally, we show that the colours of low-redshift sloan digital sky survey galaxies span an ellipsoid with significant extent along two independent dimensions, and that the sfh-direction is well-aligned with the major axis of this ellipsoid. our analysis supports the conclusion that variations in sfh are the dominant influence on present-day galaxy colours, and that the nature of this influence is strikingly simple. | surrogate modelling the baryonic universe - i. the colour of star formation |
x-ray earth occultation sounding (xeos) is an emerging method for measuring the neutral density in the lower thermosphere. in this paper, the x-ray earth occultation (xeo) of the crab nebula is investigated using the hard x-ray modulation telescope (insight-hxmt). the pointing observation data on the 30 september 2018 recorded by the low-energy x-ray telescope (le) of insight-hxmt are selected and analysed. the extinction light curves and spectra during the x-ray earth occultation process are extracted. a forward model for the xeo light curve is established, and the theoretical observational signal for light curve is predicted. the atmospheric density model is built with a scale factor to the commonly used mass spectrometer incoherent scatter radar extended model (msis) density profile within a certain altitude range. a bayesian data analysis method is developed for the xeo light curve modelling and the atmospheric density retrieval. the posterior probability distribution of the model parameters is derived through the markov chain-monte carlo (mcmc) algorithm with the nrlmsise-00 model and the nrlmsis 2.0 model as basis functions, and the respective best-fit density profiles are retrieved. it is found that in the altitude range of 105-200 km, the retrieved density profile is 88.8 % of the density of nrlmsise-00 and 109.7 % of the density of nrlmsis 2.0 by fitting the light curve in the energy range of 1.0-2.5 kev based on the xeos method. in the altitude range of 95-125 km, the retrieved density profile is 81.0 % of the density of nrlmsise-00 and 92.3 % of the density of nrlmsis 2.0 by fitting the light curve in the energy range of 2.5-6.0 kev based on the xeos method. in the altitude range of 85-110 km, the retrieved density profile is 87.7 % of the density of nrlmsise-00 and 101.4 % of the density of nrlmsis 2.0 by fitting the light curve in the energy range of 6.0-10.0 kev based on the xeos method. goodness-of-fit testing is carried out for the validation of the results. the measurements of density profiles are compared to the nrlmsise-00 and nrlmsis 2.0 model simulations and the previous retrieval results with nasa's rossi x-ray timing explorer (rxte) satellite. for further confirmation, we also compare the measured density profile to the ones by a standard spectrum retrieval method with an iterative inversion technique. finally, we find that the retrieved density profile from insight-hxmt based on the nrlmsise-00 and nrlmsis 2.0 models is qualitatively consistent with the previous retrieved results from rxte. the results of light curve fitting and standard energy spectrum fitting are in good agreement. this research provides a method for the evaluation of the density profiles from msis model predictions. this study demonstrates that the xeos from the x-ray astronomical satellite insight-hxmt can provide an approach for the study of the upper atmosphere. the insight-hxmt satellite can join the family of the xeos. the insight-hxmt satellite with other x-ray astronomical satellites in orbit can form a space observation network for xeos in the future. | measurement of the vertical atmospheric density profile from the x-ray earth occultation of the crab nebula with insight-hxmt |
the origin and abundance of mantle volatiles present major questions for earth's evolution. here we quantify volatile capture from an atmosphere derived from the solar nebula during accretion, using a boundary layer model of magma ocean dynamics coupled to a nebular atmosphere model adapted to earth formation. key elements include (i) nebular atmosphere winds based on scaling laws for deep rotating fluids; (ii) water production at the magma surface; and (iii) gas transfer between magma and atmosphere based on the systematics of air-sea gas exchange by wind and diffusion. provided the earth accreted to 30% or more of its final mass in the presence of the solar nebula, the mantle is expected to have ingassed several ocean mass equivalents of water plus hydrogen, along with hundreds of petagrams of helium-3 and other light noble gases. in contrast to light gases, nebular ingassing does not provide the mantle with enough heavy noble gases to account for their present-day atmosphere abundances. our model also predicts that thermal insulation by the nebular atmosphere led to very hot conditions in earth's interior during accretion, with peak temperatures above 6000 k at the core-mantle boundary and possible dynamo conditions in the early hadean. | nebular atmosphere to magma ocean: a model for volatile capture during earth accretion |
magnetic reconnection is a key process that explosively accelerates charged particles, generating phenomena such as nebular flares1, solar flares2 and stunning aurorae3. in planetary magnetospheres, magnetic reconnection has often been identified on the dayside magnetopause and in the nightside magnetodisc, where thin-current-sheet conditions are conducive to reconnection4. the dayside magnetodisc is usually considered thicker than the nightside due to the compression of solar wind, and is therefore not an ideal environment for reconnection. in contrast, a recent statistical study of magnetic flux circulation strongly suggests that magnetic reconnection must occur throughout saturn's dayside magnetosphere5. additionally, the source of energetic plasma can be present in the noon sector of giant planetary magnetospheres6. however, so far, dayside magnetic reconnection has only been identified at the magnetopause. here, we report direct evidence of near-noon reconnection within saturn's magnetodisc using measurements from the cassini spacecraft. the measured energetic electrons and ions (ranging from tens to hundreds of kev) and the estimated energy flux of 2.6 mw m-2 within the reconnection region are sufficient to power aurorae. we suggest that dayside magnetodisc reconnection can explain bursty phenomena in the dayside magnetospheres of giant planets, which can potentially advance our understanding of quasi-periodic injections of relativistic electrons6 and auroral pulsations7. | rotationally driven magnetic reconnection in saturn's dayside |
we present a new method to derive oxygen and carbon abundances using the ultraviolet (uv) lines emitted by the gas phase ionized by massive stars. the method is based on the comparison of the nebular emission-line ratios with those predicted by a large grid of photoionization models. given the large dispersion in the o/h-c/o plane, our method first fixes c/o using ratios of appropriate emission lines and, in a second step, calculates o/h and the ionization parameter from carbon lines in the uv. we find abundances totally consistent with those provided by the direct method when we apply this method to a sample of objects with an empirical determination of the electron temperature using optical emission lines. the proposed methodology appears as a powerful tool for systematic studies of nebular abundances in star-forming galaxies at high redshift. | using photo-ionisation models to derive carbon and oxygen gas-phase abundances in the rest uv |
context. m49 (ngc 4472) is the dominant galaxy in subcluster b of the virgo cluster, and a benchmark for studying the build-up of the extended halos of brightest group galaxies in the outskirts of galaxy clusters.aims: we investigate the kinematics in the outer halo of m49, look for substructures, and describe the transition to the surrounding intra-group light.methods: as kinematic tracers, we use planetary nebulae (pne), combining kinematics from the extended planetary nebula spectrograph (pn.s) early-type galaxy survey with our recent deep photometric sample. we study the position-velocity-plane for bright and faint pn populations out to 95 kpc radius, and employ a multi-gaussian model for the velocity distribution to identify stellar populations with distinct kinematics and histories.results: we report the detection of stellar-kinematic substructure associated with the interaction of m49 with the dwarf irregular galaxy vcc 1249. we find two kinematically distinct pn populations associated with the main m49 halo and the extended intra-group light (igl). these have velocity dispersions σhalo ≃ 170 km s-1 and σigl ≃ 400 km s-1 at 10-80 kpc radii. the overall luminosity profile and velocity dispersion at 80 kpc are consistent with a flat circular velocity curve extrapolated from x-ray observations. the dispersion of the pne associated with the igl joins onto that of the satellite galaxies in subcluster b at 100 kpc radius. this is the first time that the transition from halo to igl is observed based on the velocities of individual stars.conclusions: therefore the halo of m49, consisting of at least three distinct components, has undergone an extended accretion history within its parent group potential. the blue colours of the igl component are consistent with a population of stars formed in low-mass galaxies at redshift 0.5 that has since evolved passively, as suggested by other data. based on data collected at subaru telescope, which is operated by the national astronomical observatory of japan under programme s14a-006 and with the william herschel telescope operated on the island of la palma by the isaac newton group of telescopes in the spanish observatorio del roque de los muchachos of the instituto de astrofísica de canarias. | three dynamically distinct stellar populations in the halo of m49 |
how very young massive star clusters (vymcs; also known as "starburst" clusters), which typically are of ≳ 104 m ⊙ and are a few myr old, form out of giant molecular clouds is still largely an open question. increasingly detailed observations of young star clusters and star-forming molecular clouds and computational studies provide clues about their formation scenarios and the underlying physical processes involved. this chapter is focused on reviewing the decade-long studies that attempt to computationally reproduce the well-observed nearby vymcs, such as the orion nebula cluster, r136 and ngc 3603 young cluster, thereby shedding light on birth conditions of massive star clusters, in general. on this regard, focus is given on direct n-body modelling of real-sized massive star clusters, with a monolithic structure and undergoing residual gas expulsion, which have consistently reproduced the observed characteristics of several vymcs and also of young star clusters, in general. the connection of these relatively simplified model calculations with the structural richness of dense molecular clouds and the complexity of hydrodynamic calculations of star cluster formation is presented in detail. furthermore, the connections of such vymcs with globular clusters, which are nearly as old as our universe, is discussed. the chapter is concluded by addressing long-term deeply gas-embedded (at least apparently) and substructured systems like w3 main. while most of the results are quoted from existing and up-to-date literature, in an integrated fashion, several new insights and discussions are provided. | formation of very young massive clusters and implications for globular clusters |
we present the discovery of a 3h5m orbital-period binary star at the heart of the planetary nebula m 3-1 - the shortest period photometrically variable central star known and second only to v458 vul, in general. combined modelling of light and radial velocity curves reveals both components to be close to roche lobe filling, strongly indicating that the central star will rapidly evolve to become a cataclysmic variable, perhaps experiencing a similar evolution to v458 vul resulting in a nova eruption before the planetary nebula has fully dissipated. while the short orbital period and near roche lobe filling natures of both components make the central binary of m 3-1 an important test case with which to constrain the formation processes of cataclysmic variables, novae, and perhaps even supernovae type ia. | the short orbital period binary star at the heart of the planetary nebula m 3-1 |
as part of the ongoing effort to characterize the low-mass (sub)stellar population in a sample of massive young clusters, we have targeted the ∼2 myr old cluster ngc 2244. the distance to ngc 2244 from gaia dr2 parallaxes is 1.59 kpc, with errors of 1% (statistical) and 11% (systematic). we used the flamingos-2 near-infrared camera at the gemini-south telescope for deep multi-band imaging of the central portion of the cluster (∼2.4 pc2). we determined membership in a statistical manner, through a comparison of the cluster’s color-magnitude diagram to that of a control field. masses and extinctions of the candidate members are then calculated with the help of evolutionary models, leading to the first initial mass function (imf) of the cluster extending into the substellar regime, with the 90% completeness limit around 0.02 m ⊙. the imf is well represented by a broken power law (dn/dm ∝ m -α ) with a break at ∼0.4 m ⊙. the slope on the high-mass side (0.4-7 m ⊙) is α = 2.12 ± 0.08, close to the standard salpeter slope. in the low-mass range (0.02-0.4 m ⊙), we find a slope α = 1.03 ± 0.02, which is at the high end of the typical values obtained in nearby star-forming regions (α = 0.5-1.0), but still in agreement within the uncertainties. our results reveal no clear evidence for variations in the formation efficiency of brown dwarfs (bds) and very low-mass stars due to the presence of ob stars, or for a change in stellar densities. our finding rules out photoevaporation and fragmentation of infalling filaments as substantial pathways for bd formation. | looking deep into the rosette nebula’s heart: the (sub)stellar content of the massive young cluster ngc 2244 |
saturn formed beyond the snow line in the primordial solar nebula, and that made it possible for it to accrete a large mass. disk instability and core accretion models have been proposed for saturn's formation, but core accretion is favored on the basis of its volatile abundances, internal structure, hydrodynamic models, chemical characteristics of protoplanetary disk, etc. the observed frequency, properties, and models of exoplanets provide additional supporting evidence for core accretion. the heavy elements with mass greater than 4he make up the core of saturn, but are presently poorly constrained, except for carbon. the c/h ratio is super-solar, and twice that in jupiter. the enrichment of carbon and other heavy elements in saturn and jupiter requires special delivery mechanisms for volatiles to these planets. in this chapter we will review our current understanding of the origin and evolution of saturn and its atmosphere, using a multi-faceted approach that combines diverse sets of observations on volatile composition and abundances, relevant properties of the moons and rings, comparison with the other gas giant planet, jupiter, and analogies to the extrasolar giant planets, as well as pertinent theoretical models. | the origin and evolution of saturn, with exoplanet perspective |
context. in very young clusters, stellar age distribution is empirical proof of the duration of star cluster formation and thus it gives indications of the physical mechanisms involved in the star formation process. determining the amount of interstellar extinction and the correct reddening law are crucial steps to derive fundamental stellar parameters and in particular accurate ages from the hertzsprung-russell diagram.aims: in this context, we seek to derive accurate stellar ages for ngc 6530, the young cluster associated with the lagoon nebula to infer the star formation history of this region.methods: we used the gaia-eso survey observations of the lagoon nebula, together with photometric literature data and gaia dr2 kinematics, to derive cluster membership and fundamental stellar parameters. using spectroscopic effective temperatures, we analysed the reddening properties of all objects and derived accurate stellar ages for cluster members.results: we identified 652 confirmed and 9 probable members. the reddening inferred for members and non-members allows us to distinguish foreground objects, mainly main-sequence stars, and background objects, mainly giants, and to trace the three-dimensional structure of the nebula. this classification is in agreement with the distances inferred from gaia dr2 parallaxes for these objects. finally, we derive stellar ages for 382 confirmed cluster members for which we obtained the individual reddening values. in addition, we find that the gravity-sensitive γ index distribution for the m-type stars is correlated with stellar age.conclusions: for all members with teff < 5500 k, the mean logarithmic age is 5.84 (units of years) with a dispersion of 0.36 dex. the age distribution of stars with accretion or discs, i.e. classical t tauri stars with excess (cttse), is similar to that of stars without accretion and without discs, i.e. weak t tauri stars with photospheric emission (wttsp). we interpret this dispersion as evidence of a real age spread since the total uncertainties on age determinations, derived from monte carlo simulations, are significantly smaller than the observed spread. this conclusion is supported by evidence of the decrease of the gravity-sensitive γ index as a function of stellar ages. the presence of a small age spread is also supported by the spatial distribution and kinematics of old and young members. in particular, members with accretion or discs, formed in the last 1 myr, show evidence of subclustering around the cluster centre, in the hourglass nebula and in the m8-e region, suggesting a possible triggering of star formation events by the o-type star ionization fronts. full tables a.1 and a.2 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/623/a159based on observations made with the eso/vlt, at paranal observatory, under programme 188.b-3002 (the gaia-eso public spectroscopic survey). | the gaia-eso survey: age spread in the star forming region ngc 6530 from the hr diagram and gravity indicators |
we present extensive optical photometric and spectroscopic observations of the high-velocity (hv) type ia supernova (sn ia) 2017fgc, covering the phase from ~12 days before to ~389 days after maximum brightness. sn 2017fgc is similar to normal sne ia, with an absolute peak magnitude of ${m}_{\max }^{b}\approx $ -19.32 ± 0.13 mag and a post-peak decline of δm15(b) = 1.05 ± 0.07 mag. its peak bolometric luminosity is derived as (1.32 ± 0.13) × 1043 erg s-1, corresponding to a 56ni mass of 0.51 ± 0.03 m⊙. the light curves of sn 2017fgc are found to exhibit excess emission in the ubv bands in the early nebular phase and pronounced secondary shoulder/maximum features in the rrii bands. its spectral evolution is similar to that of hv sne ia, with a maximum-light si ii velocity of 15,000 ± 150 km s-1 and a post-peak velocity gradient of ~120 ± 10 km s-1 day-1. the fe ii and mg ii lines blended near 4300 å and the fe ii, si ii, and fe iii lines blended near 4800 å are obviously stronger than those of normal sne ia. inspecting a large sample reveals that the strength of the two blends in the spectra, and the secondary peak in the i/r-band light curves, are found to be positively correlated with the maximum-light si ii velocity. such correlations indicate that hv sne ia may experience more complete burning in the ejecta and/or that their progenitors have higher metallicity. examining the birthplace environment of sn 2017fgc suggests that it likely arose from a stellar environment with young and high-metallicity populations. | sn 2017fgc: a fast-expanding type ia supernova exploded in massive shell galaxy ngc 474 |
in this work, we propose a proper plasma analysis practice (ppap), an updated procedure of plasma diagnostics in the era of spatially resolved spectroscopy. in particular, we emphasize the importance of performing both of the extinction correction and the direct method of plasma diagnostics simultaneously as an integrated process. this approach is motivated by the reciprocal dependence between critical parameters in these analyses, which can be resolved by iteratively seeking a converged solution. the use of ppap allows us to eliminate unnecessary assumptions that prevent us from obtaining an exact solution at each element of the spectral imaging data. using a suite of hubble space telescope/wfc3 narrowband images of the planetary nebula, ngc 6720, we validate ppap by (1) simultaneously and self-consistently deriving the extinction, c(hβ), and electron density/temperature distribution, (ne([s ii]), te([n ii])), maps that are consistent with each other, and (2) obtaining identical metal abundance distribution maps, (n(n+)/n(h+), n(s+)/n(h+)), from multiple emission line maps at different wavelengths/transition energies. we also determine that the derived c(hβ) consists both of the interstellar medium and circumsource components and that the ionized gas-to-dust mass ratio in the main ring is at least 437 and as high as about 1600. we find that, unless we deliberately seek self-consistency, uncertainties at tens of % can easily arise in outcomes, making it impossible to discern actual spatial variations that occurs at the same level, defeating the purpose of conducting spatially resolved spectroscopic observations. | proper plasma analysis practice (ppap), an integrated procedure of extinction correction and plasma diagnostics: a demo with an hst/wfc3 image set of ngc 6720 |
context. planet traps and snow lines are structures that may promote planetary formation in protoplanetary disks. they are very sensitive to the disk density and temperature structure. it is therefore necessary to follow the time evolution of the disk thermal structure throughout its viscous spreading. since the snowlines are thought to generate density and temperature bumps, it is important to take into account the disk opacity variations when the various dust elements are sublimated.aims: we track the time evolution of planet traps and snowlines in a viscously evolving protoplanetary disk using an opacity table that accounts for the composition of the dust material.methods: we coupled a dynamical and thermodynamical disk model with a temperature-dependent opacity table (that accounts for the sublimation of the main dust components) to investigate the formation and evolution of snowlines and planet traps during the first million years of disk evolution.results: starting from a minimum mass solar nebula, we find that the disk mid-plane temperature profile shows several plateaux (0.1-1 au wide) at the different sublimation temperatures of the species that make up the dust. for water ice, the corresponding plateau can be larger than 1 au, which means that this is a snow "region" rather than a snow "line". as a consequence, the surface density of solids in the snow region may increase gradually, not abruptly. several planet traps and desert regions appear naturally as a result of abrupt local changes in the temperature and density profiles over the disk lifetime. these structures are mostly located at the edges of the temperature plateaux (surrounding the dust sublimation lines) and at the heat-transition barrier where the disk stellar heating and viscous heating are of the same magnitude (around 10 au after 1 myr).conclusions: several traps are identified: although a few appear to be transient, most of them slowly migrate along with the heat-transition barrier or the dust sublimation lines. these planet traps may temporarily favor the growth of planetary cores. | time evolution of snow regions and planet traps in an evolving protoplanetary disk |
circumplanetary disks (cpds) control the growth of planets, supply material for satellites to form, and provide observational signatures of young forming planets. we have carried out two-dimensional hydrodynamical simulations with radiative cooling to study cpds and suggested a new mechanism to drive the disk accretion. two spiral shocks are present in cpds, excited by the central star. we find that spiral shocks can at least contribute to, if not dominate, the angular momentum transport and energy dissipation in cpds. meanwhile, dissipation and heating by spiral shocks have a positive feedback on shock-driven accretion itself. as the disk is heated up by spiral shocks, the shocks become more open, leading to more efficient angular momentum transport. this shock-driven accretion is, on the other hand, unsteady due to production and destruction of vortices in disks. after being averaged over time, a quasi-steady accretion is reached from the planet’s hill radius all the way to the planet surface, and the disk α coefficient characterizing angular momentum transport is ∼0.001-0.02. the disk surface density ranges from 10 to 1000 g cm-2 in our simulations, which is at least three orders of magnitude smaller than the “minimum-mass subnebula” model used to study satellite formation; instead it is more consistent with the “gas-starved” satellite formation model. finally, we calculate the millimeter flux emitted by cpds at alma and evla wavelength bands and predict the flux for several recently discovered cpd candidates, which suggests that alma is capable of discovering these accreting cpds. | shock-driven accretion in circumplanetary disks: observables and satellite formation |
we present the largest and most spatially extended planetary nebulae (pne) catalogue ever obtained for the fornax cluster. we measured velocities of 1452 pne out to 200 kpc in the cluster core using a counter-dispersed slitless spectroscopic technique with data from fors2 on the very large telescope (vlt). with such an extended spatial coverage, we can study separately the stellar haloes of some of the cluster main galaxies and the intracluster light. in this second paper of the fornax cluster vlt spectroscopic survey, we identify and classify the emission-line sources, describe the method to select pne, and calculate their coordinates and velocities from the dispersed slitless images. from the pn 2d velocity map, we identify stellar streams that are possibly tracing the gravitational interaction of ngc 1399 with ngc 1404 and ngc 1387. we also present the velocity dispersion profile out to ∼200 kpc radii, which shows signatures of a superposition of the bright central galaxy and the cluster potential, with the latter clearly dominating the regions outside r ∼ 1000 arcsec (∼100 kpc). | the fornax cluster vlt spectroscopic survey ii - planetary nebulae kinematics within 200 kpc of the cluster core |
supernova (sn) 2008bk is a well-observed low-luminosity type ii event visually associated with a low-mass red-supergiant progenitor. to model sn 2008bk, we evolve a 12 m⊙ star from the main sequence until core collapse, when it has a total mass of 9.88 m⊙, a he-core mass of 3.22 m⊙ and a radius of 502 r⊙. we then artificially trigger an explosion that produces 8.29 m⊙ of ejecta with a total energy of 2.5 × 1050 erg and ∼0.009 m⊙ of 56ni. we model the subsequent evolution of the ejecta with non-local thermodynamic equilibrium time-dependent radiative transfer. although somewhat too luminous and energetic, this model reproduces satisfactorily the multiband light curves and multi-epoch spectra of sn 2008bk, confirming the suitability of a low-mass massive star progenitor. as in other low-luminosity sne ii, the structured hα profile at the end of the plateau phase is probably caused by ba ii 6496.9 å rather than asphericity. we discuss the sensitivity of our results to changes in progenitor radius and mass, as well as chemical mixing. a 15 per cent increase in progenitor radius causes a 15 per cent increase in luminosity and a 0.2 mag v-band brightening of the plateau but leaves its length unaffected. an increase in ejecta mass by 10 per cent lengthens the plateau by ∼10 d. chemical mixing introduces slight changes to the bolometric light curve, limited to the end of the plateau, but has a large impact on colours and spectra at nebular times. | a study of the low-luminosity type ii-plateau supernova 2008bk |
we present late-time (∼240-260 days after peak brightness) optical photometry and nebular (+236 and +264 days) spectroscopy of sn 2018oh, the brightest supernova (sn) ia observed by the kepler telescope. the kepler/k2 30 minute cadence observations started days before explosion and continued past peak brightness. for several days after explosion, sn 2018oh had blue “excess” flux in addition to a normal sn rise. the flux excess can be explained by the interaction between the sn and a roche-lobe filling non-degenerate companion star. such a scenario should also strip material from the companion star that would emit once the sn ejecta become optically thin, imprinting relatively narrow emission features in its nebular spectrum. we search our nebular spectra for signs of this interaction, including close examination of wavelengths of hydrogen and helium transitions, finding no significant narrow emission. we place upper limits on the luminosity of these features of 2.6, 2.9 and 2.1 × 1037 erg s-1 for hα, he i λ5875, and he i λ6678, respectively. assuming a simple model for the amount of swept-up material, we estimate upper mass limits for hydrogen of 5.4 × 10-4 m ⊙ and helium of 4.7 × 10-4 m ⊙. such stringent limits are unexpected for the companion-interaction scenario consistent with the early data. no known model can explain the excess flux, its blue color, and the lack of late-time narrow emission features. | nebular spectroscopy of kepler’s brightest supernova |
calcium-aluminum-rich inclusions (cais) are the first solids to form in the early solar system, and they exhibit nucleosynthetic anomalies in many isotope systems. the overwhelming majority of isotopic data for cais is limited to inclusions from the cv chondrite allende and a few other cv, co, cm, and ordinary chondrites. it is therefore important to ascertain whether previously reported values for cais are representative of the broader cai-forming region and to make a more rigorous assessment of the extent and implications of isotopic heterogeneity in the early solar system. here, we report the mass-independent ti isotopic compositions of a suite of 23 cais of diverse petrologic and geochemical types, including 11 from allende and 12 from 7 other cv3 and ck3 chondrites; the data for cais from ck chondrites are the first reported measurements of ti isotopic compositions of cais from this meteorite class. the resolved variation in the mass-independent ti isotopic compositions of these cais indicates that the cai-forming region of the early solar system preserved isotopic variability. nevertheless, the range of ti isotopic compositions reported here for cais from cv and ck chondrites falls within the range observed in previously analyzed cais from cv, co, cm, and ordinary chondrites. this implies that cais from cv, ck, co, cm, and ordinary chondrites originated from a common nebular source reservoir characterized by mass-independent isotopic variability in ti (and certain other elements). we further interpret these data to indicate that the ti isotopic anomalies in cais represent the isotopic signatures of supernova components in presolar grains that were incorporated into the solar system in an initially poorly mixed reservoir that was progressively homogenized over time. we conclude that the differing degrees of isotopic variability observed for different elements in normal cais are the result of distinct carrier phases and that these cais were likely formed towards the final stages of homogenization of the large-scale isotopic heterogeneity that initially existed in the solar nebula. | titanium isotope signatures of calcium-aluminum-rich inclusions from cv and ck chondrites: implications for early solar system reservoirs and mixing |
we present keck/mosfire (multi-object spectrometer for infrared exploration) and keck/lris (low resolution imaging spectrometer) spectroscopy of a1689-217, a lensed (magnification ∼7.9), star-forming (sfr ∼ 16 m ⊙ yr-1), dwarf (log(m */m ⊙) = 8.07-8.59) lyα emitter (ew0 ∼ 138 å) at z = 2.5918. dwarf galaxies similar to a1689-217 are common at high redshift and likely responsible for reionization, yet few have been studied with detailed spectroscopy. we report a 4.2σ detection of the electron-temperature-sensitive [o iii] λ4363 emission line and use this line to directly measure an oxygen abundance of 12 + log(o/h) = 8.06 ± 0.12 (∼1/4 z ⊙). a1689-217 is the lowest-mass galaxy at z > 2 with an [o iii] λ4363 detection. using the rest-optical emission lines, we measure a1689-217’s other nebular conditions, including electron temperature (te ([o iii]) ∼ 14,000 k), electron density (ne∼ 220 cm-3), and reddening (e(b-v) ∼ 0.39). we study relations between strong-line ratios and direct metallicities with a1689-217 and other galaxies with [o iii] λ4363 detections at z ∼ 0-3.1, showing that the locally calibrated, oxygen-based, strong-line relations are consistent from z ∼ 0 to 3.1. we also show additional evidence that the o32 versus r23 excitation diagram can be utilized as a redshift-invariant, direct-metallicity-based, oxygen abundance diagnostic out to z ∼ 3.1. from this excitation diagram and the strong-line ratio-metallicity plots, we observe that the ionization parameter at fixed o/h is consistent with no redshift evolution. although a1689-217 is metal-rich for its m * and star formation rate, we find it to be consistent within the large scatter of the low-mass end of the fundamental metallicity relation. the data presented herein were obtained at the w. m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and the national aeronautics and space administration. the observatory was made possible by the generous financial support of the w. m. keck foundation. based on observations made with the nasa/esa hubble space telescope, 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 nas5-26555. these observations are associated with programs #9289, #11710, #11802, #12201, #12931. | the detection of [o iii] λ4363 in a lensed, dwarf galaxy at z = 2.59: testing metallicity indicators and scaling relations at high redshift and low mass |
ck vul erupted in 1670 and is considered a galactic stellar-merger candidate. its remnant, observed 350 yr after the eruption, contains a molecular component of surprisingly rich composition, including polyatomic molecules as complex as methylamine (ch3nh2). we present interferometric line surveys with subarcsec resolution with alma and sma. the observations provide interferometric maps of molecular line emission at frequencies between 88 and 243 ghz that allow imaging spectroscopy of more than 180 transitions of 26 species. we present, classify, and analyze the different morphologies of the emission regions displayed by the molecules. we also perform a non-lte radiative-transfer analysis of emission of most of the observed species, deriving the kinetic temperatures and column densities in five parts of the molecular nebula. non-lte effects are clearly seen in complex species including methanol absorption against the cosmic microwave background. the temperatures are about 17 k in the inner remnant and 14 k in the extended lobes, both higher than excitation temperatures estimated earlier in an lte approach and based on single-dish spectra. we find total (hydrogen plus helium) densities in the range of 104 - 106 cm-3. the column densities provide rough relative abundance patterns in the remnant which currently are not understood. attempts to derive elemental abundances within the assumption of a chemical equilibrium give only loose constraints on the cno elements. that the formation of many of the observed molecules requires a major involvement of circumstellar shocks remains the preferred possibility. the molecular gas could have formed 350 yr ago or more recently. the molecules are well shielded from the interstellar radiation field by the circumstellar dust. their presence alone indicates that the unobservable central star cannot be a hot object such as a white dwarf. this excludes some of the proposed scenarios on the nature of ck vul. the general characteristics of the molecular environment of ck vul derived in this study resemble quite well those of some pre-planetary nebulae and asymptotic giant branch stars, most notably that of oh231.8+4.2. | molecular remnant of nova 1670 (ck vulpeculae). i. properties and enigmatic origin of the gas |
low-resolution lamost and keck spectra of blue supergiant stars distributed over the disks of the local group spiral galaxies m31 and m33 are analyzed to determine stellar effective temperatures, gravities, metallicities, and reddening. logarithmic metallicities at the center of the galaxies (in solar units) of 0.30 ± 0.09 and 0.11 ± 0.04 and metallicity gradients of -0.37 ± 0.13 dex/r 25 and -0.36 ± 0.16 dex/r 25 are measured for m31 and m33, respectively. for m33 the 2d distribution of metallicity indicates a deviation from azimuthal symmetry with an off-center peak. the flux-weighted gravity-luminosity relationship (fglr) of blue supergiant stars is used to determine a distance modulus of 24.51 ± 0.13 mag for m31 and 24.93 ± 0.07 mag for m33. for m31 the fglr distance agrees well with other methods. for m33 the fglr-based distance is larger than the distances from cepheids studies, but it is in good agreement with work on eclipsing binaries, planetary nebulae, long-period variables, and the tip of the red giant branch. | a spectroscopic study of blue supergiant stars in local group spiral galaxies: andromeda and triangulum |
low-resolution spitzer-irs spectral map data of a reflection nebula (ngc 7023), h ii region (m17), and planetary nebula (ngc 40), totaling 1417 spectra, are analyzed using the data and tools available through the nasa ames pah ir spectroscopic database. the polycyclic aromatic hydrocarbon (pah) emission is broken down into pah charge and size subclass contributions using a database-fitting approach. the resulting charge breakdown results are combined with those derived using the traditional pah band strength ratio approach, which interprets particular pah band strength ratios as proxies for pah charge. here the 6.2/11.2 μm pah band strength ratio is successfully calibrated against its database equivalent: the {n}pah}+}/{n}pah}0} ratio. in turn, this ratio is converted into the pah ionization parameter, which relates it to the strength of the radiation field, gas temperature, and electron density. population diagrams are used to derive the {{{h}}}2 density and temperature. the bifurcated plot of the 8.6 versus 11.2 μm pah band strength for the northwest photo dissociation region in ngc 7023 is shown to be a robust diagnostic template for the {n}pah}+}/{n}pah}0} ratio in all three objects. template spectra for the pah charge and size subclasses are determined for each object and shown to favorably compare. using the determined template spectra from ngc 7023 to fit the emission in all three objects yields, upon inspection of the structure similarity maps, satisfactory results. the choice of extinction curve proves to be critical. concluding, the distinctly different astronomical environments of a reflection nebula, h ii region, and planetary nebula are reflected in their pah emission spectra. | the charge state of polycyclic aromatic hydrocarbons across a reflection nebula, an h ii region, and a planetary nebula |
earth's origins are challenging to elucidate, given the lack of surviving terrestrial geology from the first 500 myr of the solar system. in this review, we discuss breakthroughs in geochemistry and theoretical modelling that have advanced understanding of earth accretion. theory holds that solar nebula dust particles stuck together to form pebbles, concentrations of which gravitationally collapsed into ∼100-km-sized planetesimals, which in turn accreted to yield planets. isotopic variations in meteorites indicate that pebbles formed within the first 100 kyr of the solar system, planetesimals melted and differentiated within a few 100 kyr, and mars accreted quickly within 5 myr. earth's growth was more protracted, with >98% of its mass being accreted by the time of the moon-forming giant impact at ∼70-120 myr. earth is more enriched in s-process nuclides than chondritic meteorites, with a chemical composition affected by condensation, melting and loss. early volatiles acquired from the nebula largely escaped, with the remnant volatiles being diluted by main-stage earth accretion, accompanied by loss of nitrogen to the core and/or space. areas for further research should include assessing mixing during large collisions and investigating the origin of very early mantle isotopic heterogeneities, which might indicate mass transfer from core to mantle over time. | the accretion of planet earth |
emission-line stars are typically surrounded by dense circumstellar material, often in form of rings or disc-like structures. line emission from forbidden transitions trace a diversity of density and temperature regimes. of particular interest are the forbidden lines of [o i] λλ6300, 6364 and [ca ii] λλ7291, 7324. they arise in complementary, high-density environments, such as the inner-disc regions around b[e] supergiants. to study physical conditions traced by these lines and to investigate how common they are, we initiated a survey of emission-line stars. here, we focus on a sample of nine b[e] stars in different evolutionary phases. emission of the [o i] lines is one of the characteristics of b[e] stars. we find that four of the objects display [ca ii] line emission: for the b[e] supergiants v1478 cyg and 3 pup, the kinematics obtained from the [o i] and [ca ii] line profiles agrees with a keplerian rotating disc scenario; the forbidden lines of the compact planetary nebula oy gem display no kinematical broadening beyond spectral resolution; the luminous blue variable candidate v1429 aql shows no [o i] lines, but the profile of its [ca ii] lines suggests that the emission originates in its hot, ionized circumbinary disc. as none of the b[e] stars of lower mass displays [ca ii] line emission, we conclude that these lines are more likely observable in massive stars with dense discs, supporting and strengthening the suggestion that their appearance requires high-density environments. | spectroscopic survey of emission-line stars - i. b[e] stars |
magnetic reconnection and non-thermal particle distributions associated with current-driven instabilities are investigated by means of resistive magnetohydrodynamics (mhd) simulations combined with relativistic test particle methods. we propose a system with two parallel, repelling current channels in an initially force-free equilibrium, as a simplified representation of flux ropes in a stellar magnetosphere. the current channels undergo a rotation and separation on alfvénic time-scales, forming secondary islands and (up to tearing unstable) current sheets in which non-thermal energy distributions are expected to develop. using the recently developed particle module of our open-source grid-adaptive mpi-amrvac software, we simulate mhd evolution combined with test particle treatments in mhd snapshots. we explore under which plasma-β conditions the fastest reconnection occurs in 2.5d scenarios, and in these settings, test particles are evolved. we quantify energy distributions, acceleration mechanisms, relativistic corrections to the particle equations of motion and effects of resistivity in magnetically dominated proton-electron plasmas. due to large resistive electric fields and indefinite acceleration of particles in the infinitely long current channels, hard energy spectra are found in 2.5d configurations. solutions to these numerical artefacts are proposed for both 2.5d setups and future 3d work. we discuss the mhd of an additional kink instability in 3d setups and the expected effects on energy distributions. the obtained results hold as a proof-of-principle for test particle approaches in mhd simulations, relevant to explore less idealized scenarios like solar flares and more exotic astrophysical phenomena, like black hole flares, magnetar magnetospheres and pulsar wind nebulae. | reconnection and particle acceleration in interacting flux ropes - i. magnetohydrodynamics and test particles in 2.5d |
we report confirmation of a large, evolved, bipolar planetary nebula and its blue, white dwarf central star as a member of the ~500 myr old galactic open star cluster m37 (ngc 2099). this is only the third known example of a planetary nebula in a galactic open cluster and was found via our ongoing program of identifying and studying planetary nebulae-open cluster associations. high confidence in the association comes from the consistent radial velocities and proper motions for the confirmed central star and cluster stars from gaia, reddening agreement, and location of the planetary nebula well within the tidal cluster boundary. interestingly, all three galactic examples have bipolar morphology and likely type-i chemistry, both characteristics of higher mass progenitors. in this case the progenitor star mass is in the midrange of ~2.8 m ☉. it provides a valuable, additional point on the key stellar initial-to-final mass relation independent of cluster white dwarf estimates and also falls in a gap in the poorly sampled mass region. this planetary nebula also appears to have the largest kinematical age ever determined and implies increased visibility lifetimes when they are located in clusters. | the planetary nebula in the 500 myr old open cluster m37 |
we conjecture that observed protoplanetary disc accretion rates may be explained with low viscosities, which could be the result of hydrodynamic turbulence. we show that viscosities parametrized in the usual way with α ≳ 10-4, comparable to values suggested for hydrodynamic turbulence, can explain the observed accretion rates and lifetimes with plausible inner disc surface densities. our models are also in better agreement with surface density estimates of the minimum mass solar nebula than models with rapid transport for a given mass accretion rate, such as recent models of accretion driven by magnetic winds. the required surface densities are a natural result of the protostellar infall phase, as long as non-gravitational transport is limited. we argue that, in addition to possible non-ideal magnetic transport due to disc winds possibly modified by the hall effect, the effects of low-viscosity hydrodynamic accretion deserve more consideration. | how do t tauri stars accrete? |
we described the design and operation principles of a new tunable-filter photometer developed for the 1-m telescope of the special astrophysical observatory of the russian academy of sciences and the 2.5-m telescope of the sternberg astronomical institute of the moscow state university. the instrument is mounted on the scanning fabry-perot interferometer operating in the tunable-filter mode in the spectral range of 460-800 nm with a typical spectral resolution of about 1.3 nm. it allows one to create images of galactic and extragalactic nebulae in the emission lines having different excitation conditions and to carry out diagnostics of the gas ionization state. the main steps of observations, data calibration, and reduction are illustrated by examples of different emission-line objects: galactic h ii regions, planetary nebulae, active galaxies with extended filaments, starburst galaxies, and perseus galaxy cluster. | mapper of narrow galaxy lines (mangal): new tunable filter imager for caucasian telescopes |
we discuss the observational properties of pulsar wind nebulae (pwne) linking them to the injected (at the termination shock) electron spectral energy distribution and parameters of pulsar magnetospheres. in particular, we (1) present spatially-resolved chandra acis spectral maps of twelve pwne and measure the slopes of the uncooled pwn spectra just downstream of the termination shock obtained from these maps, (2) consider the connections between pwn morphologies and predictions of the magnetospheric emission models and (3) discuss the limits on the maximum energies of particles in pwne from x-ray and γ-ray observations. | toward understanding the physical underpinnings of spatial and spectral morphologies of pulsar wind nebulae |
the projection factor (p-factor) is an essential component of the classical baade-wesselink (bw) technique, which is commonly used to determine the distances to pulsating stars. it is a multiplicative parameter used to convert radial velocities into pulsational velocities. as the bw distances are linearly proportional to the p-factor, its accurate calibration for cepheids is of critical importance for the reliability of their distance scale. we focus on the observational determination of the p-factor of the long-period cepheid rs pup (p = 41.5 days). this star is particularly important as this is one of the brightest cepheids in the galaxy and an analog of the cepheids used to determine extragalactic distances. an accurate distance of 1910 ± 80 pc (± 4.2%) has recently been determined for rs pup using the light echoes propagating in its circumstellar nebula. we combine this distance with new vlti/pionier interferometric angular diameters, photometry, and radial velocities to derive the p-factor of rs pup using the code spectro-photo-interferometry of pulsating stars (spips). we obtain p = 1.250 ± 0.064 ( ± 5.1%), defined for cross-correlation radial velocities. together with measurements from the literature, the p-factor of rs pup confirms the good agreement of a constant \overline{p=\meanp ± \meanperr (± \meanprelerr%)} model with the observations. we conclude that the p-factor of cepheids is constant or mildly variable over a broad range of periods (3.7 to 41.5 days). based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programs 093.d-0316(a), 094.d-0773(b), 096.d-0341(a) and 098.d-0067(a). based in part on observations with the 1.3 m telescope operated by the smarts consortium at cerro tololo interamerican observatory. | observational calibration of the projection factor of cepheids. iii. the long-period galactic cepheid rs puppis |
we present a catalogue of 618 high-amplitude infrared variable stars (1 < δk < 5 mag) detected by the two widely separated epochs of 2.2 μm data in the ukidss galactic plane survey, from searches covering ∼1470 deg2. most were discovered by a search of all fields at 30 < l < 230°. sources include new dusty mira variables, three new cataclysmic variable candidates, a blazar and a peculiar source that may be an interacting binary system. however, ∼60 per cent are young stellar obbjects (ysos), based on spatial association with star-forming regions at distances ranging from 300 pc to over 10 kpc. this confirms our initial result in contreras peña et al. (paper i) that ysos dominate the high-amplitude infrared variable sky in the galactic disc. it is also supported by recently published vista variables in the via lactea (vvv) results at 295 < l < 350°. the spectral energy distributions of the ysos indicate class i or flat-spectrum systems in most cases, as in the vvv sample. a large number of variable ysos are associated with the cygnus x complex and other groups are associated with the north america/pelican nebula, the gemini ob1 molecular cloud, the rosette complex, the cone nebula, the w51 star-forming region and the s86 and s236 h ii regions. most of the yso variability is likely due to variable/episodic accretion on time-scales of years, albeit usually less extreme than classical fuors and exors. luminosities at the 2010 wide-field infrared survey explorer epoch range from ∼0.1 to 103 l⊙ but only rarely exceed 102.5 l⊙. | extreme infrared variables from ukidss - ii. an end-of-survey catalogue of eruptive ysos and unusual stars |
we report on the results of deep and wide-field (1.1 deg2) narrow-band observations with subaru/hyper suprime-cam (hsc) of a field around a hyperluminous qso (hlqso), hs 1549+1919, residing in a protocluster at z = 2.84, to map the large-scale structure of lyα emitters (laes). one hsc pointing enables us to detect 3490 laes and 76 extended lyα blobs (labs), probing diverse environments from voids to protoclusters. the hlqso is found to be near the center of the protocluster, which corresponds to the intersection of ∼ 100 comoving mpc-scale structures of laes. labs are basically distributed along the large-scale structure, with larger ones particularly clustering around the hlqso, confirming a previously noted tendency of labs to prefer denser environments. moreover, the shapes of labs near the hlqso appear to be aligned with the large-scale structure. finally, a deep lyα image reveals a diffuse lyα nebula along a filamentary structure with no luminous uv/sub-mm counterpart. we suggest that the diffuse nebula is due to a cold filament with high clumping factor illuminated by the qso, with the required high clumpiness provided by unresolved residing halos of mass ≤ 10^{9-10} m_⊙. | lyα view around a z = 2.84 hyperluminous qso at a node of the cosmic web† |
we present analysis of the gas kinematics of the integral-shaped filament (isf) in orion a using four different molecular lines, 12co (1-0), 13co (1-0), nh3 (1,1), and n2h+ (1-0). we describe our method to visualize the position-velocity (pv) structure using the intensity-weighted line velocity centroid, which enables us to identify structures that were previously muddled or invisible. we observe a north-to-south velocity gradient in all tracers that terminates in a velocity peak near the centre of the orion nebula cluster (onc), consistent with the previously reported `wave-like' properties of the isf. we extract the velocity dispersion profiles and compare the non-thermal line widths to the gas gravitational potential. we find supersonic mach number profiles, yet the line widths are consistent with the gas being deeply gravitationally bound. we report the presence of two 12co velocity components along the northern half of the isf; if interpreted as circular rotation, the angular velocity is ω =1.4 myr^{-1}. on small scales we report the detection of n2h+ and nh3 `twisting and turning' structures, with short associated time-scales that give the impression of a torsional wave. neither the nature of these structures nor their relation to the larger scale wave is presently understood. | gas velocity structure of the orion a integral-shaped filament |
context. many if not most planetary nebulae (pne) are now thought to be the outcome of binary evolutionary scenarios. however, only a few percent of the pne in the milky way are known to host binary systems. the high-precision repeated observing and long time baseline of gaia make it well suited for detecting new close binaries through photometric variability.aims: we aim to find new close binary central stars of pne (cspne) using data from the gaia mission, building towards a statistically significant sample of post-common envelope, close binary cspne.methods: as the vast majority of gaia sources do not have published epoch photometry, we used the uncertainty in the mean photometry as a proxy for determining the variability of our cspn sample in the second gaia data release. we derived a quantity that expresses the significance of the variability, and considered what is necessary to build a clean sample of genuine variable sources.results: our selection recovers a large fraction of the known close binary cspn population, while other cspne lying in the same region of the parameter space represent a promising set of targets for ground-based confirmatory follow-up observations. gaia epoch photometry for four of the newly identified variable sources confirms that the variability is genuine and consistent with binarity. | towards a more complete sample of binary central stars of planetary nebulae with gaia |
we report results from a new hubble space telescope campaign that targets the o vi λ λ 1032,1038 å doublet in emission around intensely star-forming galaxies. the program aims to characterize the energy balance in starburst galaxies and gas cooling in the difficult-to-map coronal temperature regime of 2{--}5× {10}5 k. we present the first resolved image of gas emission in the o vi line. our target, sdss j115630.63+500822.1, is very compact in the continuum but displays o vi emission to radii of 23 kpc. the surface brightness profile is well fit by an exponential with a scale length of 7.5 kpc. this is 10 times the size of the photoionized gas, and we estimate that about 1/6 the total o vi luminosity comes from resonantly scattered continuum radiation. spectroscopy—which closely resembles a stacked sample of archival spectra—confirms the o vi emission, and determines the column density and outflow velocity from blueshifted absorption. the combination of measurements enables a large number of calculations with few assumptions. the o vi regions fill only ∼ {10}-3 of the volume. by comparing the cooling time with the cloud sound-crossing time, the cooling distance with the size, and the pressure in the o vi and nebular gas, we conclude that the o vi-bearing gas cannot have been lifted to the scale height at this temperature, and must be cooling in situ through this coronal temperature regime. the coronal phase contains ∼1% of the ionized mass, and its kinetic energy at a given instant is ∼1% of the budget set by supernova feedback. however, a much larger amount of the gas must have cooled through this phase during the star formation episode. the outflow exceeds the escape velocity and the gas may become unbound, but it will recombine before it escapes and become visible to lyman (and o i) spectroscopy. the mapping of this gas represents a crucial step in further constraining galaxy formation scenarios and guiding the development of future astronomical satellites. based on observations made with the nasa/esa hubble space telescope, obtained 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. these observations are associated with program #13656. | o vi emission imaging of a galaxy with the hubble space telescope: a warm gas halo surrounding the intense starburst sdss j115630.63+500822.1 |
we present a deep centimeter-wavelength catalog of the orion nebula cluster (onc), based on a 30 hr single-pointing observation with the karl g. jansky very large array in its high-resolution a-configuration using two 1 ghz bands centered at 4.7 and 7.3 ghz. a total of 556 compact sources were detected in a map with a nominal rms noise of 3 μjy bm-1, limited by complex source structure and the primary beam response. compared to previous catalogs, our detections increase the sample of known compact radio sources in the onc by more than a factor of seven. the new data show complex emission on a wide range of spatial scales. following a preliminary correction for the wideband primary-beam response, we determine radio spectral indices for 170 sources whose index uncertainties are less than ±0.5. we compare the radio to the x-ray and near-infrared point-source populations, noting similarities and differences. | the population of compact radio sources in the orion nebula cluster |
we report on simultaneous x-ray and radio observations of the radio-mode-switching pulsar psr b1822-09 with esa's xmm-newton and the westerbork synthesis radio telescope, giant metrewave radio telescope and lovell radio telescopes. psr b1822-09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. we discovered x-ray (energies 0.2-1.4 kev) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ∼0.15 at 0.3 kev to ∼0.6 at 1 kev. no evidence is found for simultaneous x-ray and radio mode switching. the total x-ray spectrum consists of a cool component (t ∼0.96 × 106 k, hotspot radius r ∼2.0 km) and a hot component (t ∼2.2 × 106 k, r ∼100 m). the hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. the high-energy characteristics of psr b1822-09 resemble those of middle-aged pulsars such as psr b0656+14, psr b1055-52 and geminga, including an indication for pulsed high-energy gamma-ray emission in fermi large area telescope data. explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. in our x-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from psr b1822-09, which might be a pulsar wind nebula. | simultaneous x-ray and radio observations of the radio-mode-switching pulsar psr b1822-09 |
during its early evolution, a pulsar wind nebula (pwn) sweeps the inner part of the supernova ejecta and forms a thin massive shell. later on, when the shell has been reached by the reverse shock of the supernova remnant, the evolution becomes more complex, in most cases reverting the expansion into a compression: this later phase is called 'reverberation'. computations done so far to understand this phase have been mostly performed in the thin-shell approximation, where the evolution of the pwn radius is assimilated to that of the swept-up shell under the effect of both the inner pressure from the pwn, and the outer pressure from the supernova remnant. despite the thin-shell approach seems rather justifiable, its implementations have so far been inaccurate, and its correctness, never tested. the outer pressure was naively assumed to be scaled according to the sedov solution (or a constant fraction of it) along the entire evolution. the thin-shell assumption itself fails along the process, being the shell no longer thin in comparison with the size of the pwn. here, through a combination of numerical models, dimensional arguments, and analytical approximations, we present a detailed analysis of the interaction of the pwn with the supernova remnant. we provide a new analytical approximation of the outer pressure, beyond the sedov solution, and a revised 'thin-shell' able to reproduce results from numerical simulations. finally, we compute the efficiency by which the pwn is compressed during reverberation over a wide population of sources. | reverberation of pulsar wind nebulae - ii. anatomy of the 'thin-shell' evolution |
we present the data and analysis of sn 2018gjx, an unusual low-luminosity transient with three distinct spectroscopic phases. phase i shows a hot blue spectrum with signatures of ionized circumstellar material (csm), phase ii has the appearance of broad sn features, consistent with those seen in a type iib supernova at maximum light, and phase iii is that of a supernova interacting with helium-rich csm, similar to a type ibn supernova. this event provides an apparently rare opportunity to view the inner workings of an interacting supernova. the observed properties can be explained by the explosion of a star in an aspherical csm. the initial light is emitted from an extended csm (~4000 r⊙), which ionizes the exterior unshocked material. some days after, the sn photosphere envelops this region, leading to the appearance of a sn iib. over time, the photosphere recedes in velocity space, revealing interaction between the supernova ejecta and the csm that partially obscures the supernova nebular phase. modelling of the initial spectrum reveals a surface composition consistent with compact h-deficient wolf-rayet and luminous blue variable (lbv) stars. such configurations may not be unusual, with sne iib being known to have signs of interaction so at least some sne iib and sne ibn may be the same phenomena viewed from different angles, or possibly with differing csm configurations. | sn 2018gjx reveals that some sne ibn are sne iib exploding in dense circumstellar material |
context. accurate distance measurements are fundamental to the study of planetary nebulae (pne) but they have long been elusive. the most accurate and model-independent distance measurements for galactic pne come from the trigonometric parallaxes of their central stars, which were only available for a few tens of objects prior to the gaia mission.aims: the accurate identification of pn central stars in the gaia source catalogues is a critical prerequisite for leveraging the unprecedented scope and precision of the trigonometric parallaxes measured by gaia. our aim is to build a complete sample of pn central star detections with minimal contamination.methods: we developed and applied an automated technique based on the likelihood ratio method to match candidate central stars in gaia data release 2 (dr2) to known pne in the hong kong/aao/strasbourg hα pn catalogue, taking into account the bp - rp colours of the gaia sources as well as their positional offsets from the nebula centres. these parameter distributions for both true central stars and background sources were inferred directly from the data.results: we present a catalogue of over 1000 gaia sources that our method has automatically identified as likely pn central stars. we demonstrate how the best matches enable us to trace nebula and central star evolution and to validate existing statistical distance scales, and we discuss the prospects for further refinement of the matching based on additional data. we also compare the accuracy of our catalogue to that of previous works. table b.1 is 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/cat/j/a+a/638/a103 | searching for central stars of planetary nebulae in gaia dr2 |
young massive stars regulate the physical conditions, ionization, and fate of their natal molecular cloud and surroundings. it is important to find tracers that quantify the stellar feedback processes that take place on different spatial scales. we present 85 arcmin2 velocity-resolved maps of several submillimeter molecular lines, taken with herschel/hifi, toward the closest high-mass star-forming region, the orion molecular cloud 1 core (omc-1). the observed rotational lines include probes of warm and dense molecular gas that are difficult, if not impossible, to detect from ground-based telescopes: ch+ (j = 1-0), co (j = 10-9), hco+ (j = 6-5), hcn (j = 6-5), and ch (n, j = 1, 3/2-1, 1/2). these lines trace an extended but thin layer (av ≃ 3-6 mag or 1016 cm) of molecular gas at high thermal pressure, pth = nh ṡ tk ≈ 107-109 cm-3 k, associated with the far-ultraviolet (fuv) irradiated surface of omc-1. the intense fuv radiation field - emerging from massive stars in the trapezium cluster - heats, compresses, and photoevaporates the cloud edge. it also triggers the formation of specific reactive molecules such as ch+. we find that the ch+ (j = 1-0) emission spatially correlates with the flux of fuv photons impinging the cloud: g0 from 103 to 105. this relationship is supported by constant-pressure photodissociation region (pdr) models in the parameter space pth/g0 ≈ [5 × 103 - 8 × 104] cm-3 k where many observed pdrs seem to lie. the ch+ (j = 1-0) emission also correlates with the extended infrared emission from vibrationally excited h2 (v ≥ 1), and with that of [c ii] 158 μm and co j = 10-9, all emerging from fuv-irradiated gas. these spatial correlations link the presence of ch+ to the availability of c+ ions and of fuv-pumped h2 (v ≥ 1) molecules. we conclude that the parsec-scale ch+ emission and narrow-line (δv ≃ 3 km s-1) mid-j co emission arises from extended pdr gas and not from fast shocks. pdr line tracers are the smoking gun of the stellar feedback from young massive stars. the pdr cloud surface component in omc-1, with a mass density of 120-240 m⊙ pc-2, represents 5-10% of the total gas mass; however, it dominates the emitted line luminosity, the average co j = 10-9 surface luminosity in the mapped region being 35 times brighter than that of co j = 2-1. these results provide insights into the source of submillimeter ch+ and mid-j co emission from distant star-forming galaxies. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa.includes iram 30m observations. iram is supported by insu/cnrs (france), mpg (germany), and ign (spain).all maps (fits) 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/622/a91. | molecular tracers of radiative feedback in orion (omc-1). widespread ch+ (j = 1-0), co (10-9), hcn (6-5), and hco+ (6-5) emission |
context. energy and momentum injected by young, massive stars into the surrounding gas play an important role in regulating further star formation and in determining the galaxy's global properties. before supernovae begin to explode, stellar feedback consists of two main processes: radiation pressure and photoionisation.aims: we study pre-supernova feedback and constrain the leakage of lyman continuum (lyc) radiation in a sample of ∼4700 h ii regions in the nearby spiral galaxy m 83. we explore the impact that the galactic environment and intrinsic physical properties (metallicity, extinction, and stellar content) have on the early phases of h ii region evolution.methods: we combined vlt/muse observations of the ionised gas with young star cluster physical properties derived from hst multiwavelength data. we identified h ii regions based on their hα emission, and cross-matched the sample with planetary nebulae and supernova remnants to assess contaminant sources and identify evolved h ii regions. we also spectroscopically identified wolf-rayet (wr) stars populating the star-forming regions. we estimated the physical properties of the h ii regions (luminosity, size, oxygen abundance, and electron density). for each h ii region, we computed the pressure of ionised gas (pion) and the direct radiation pressure (pdir) acting in the region, and investigated how they vary with galactocentric distance, with the physical properties of the region, and with the pressure of the galactic environment (pde). for a subset of ∼500 regions, we also investigated the link between the pressure terms and the properties of the cluster population (age, mass, and lyc flux). by comparing the lyc flux derived from hα emission with the one modelled from their clusters and wrs, we furthermore constrained any escape of lyc radiation (fesc).results: we find that pion dominates over pdir by at least a factor of 10 on average over the disk. both pressure terms are strongly enhanced and become almost comparable in the central starburst region. in the disk (r ≥ 0.15 re), we observe that pdir stays approximately constant with galactocentric distance. we note that pdir is positively correlated with an increase in radiation field strength (linked to the negative metallicity gradient in the galaxy), while it decreases in low extinction regions, as is expected if the amount of dust to which the momentum can be imparted decreases. in addition, pion decreases constantly for increasing galactocentric distances; this trend correlates with the decrease in extinction - indicative of more evolved and thus less compact regions - and with changes in the galactic environment (traced by a decrease in pde). in general, we observe that h ii regions near the centre are underpressured with respect to their surroundings, whereas regions in the rest of the disk are overpressured and hence expanding. we find that regions hosting younger clusters or those that have more mass in young star clusters have a higher internal pressure, indicating that clustered star formation likely plays a dominant role in setting the pressure. finally, we estimate that only 13% of h ii regions hosting young clusters and wr stars have fesc ≥ 0, which suggests that star formation taking place outside young clusters makes a non-negligible contribution to ionising h ii regions. | stellar feedback in m 83 as observed with muse. ii. analysis of the h ii region population: ionisation budget and pre-sn feedback |
english and spanish translations are provided for fritz zwicky's seminal article on "the redshift of extragalactic nebulae", published in german in helvetica physica acta in 1933 <https://www.e-periodica.ch/digbib/view?pid=hpa-001:1933:6#112>. this paper is usually cited as the first evidence for dark matter ("dunkle materie", not "missing matter"). zwicky's conclusion is based on the velocity dispersion of only seven galaxies in the coma cluster of galaxies. now, 84 years later, with 1000+ radial velocities measured for coma cluster members, coma's velocity dispersion is very close to that found by zwicky. the translation is as literal as possible, and annotations on the translation of certain terms are given. doubts on the meaning of the original phrasing are given in square brackets at a few places where they occur. the pdf version of my english translation was kindly prepared by cren frayer at the nasa/ipac extragalactic database (ned), also available at ned's level5 repository since june 2017 (<http://ned.ipac.caltech.edu/level5/march17/zwicky/frames.html>). a spanish translation, without figures, prepared by myself with the help of martha margarita lópez gutiérrrez is appended within the same pdf file. as translator i take responsibilty for the quality of the translation. | english and spanish translation of zwicky's (1933) the redshift of extragalactic nebulae |
we present the first far-uv (fuv) imaging results of the intermediate-age galactic open cluster ngc 2818 that has a planetary nebula (pn) within the field using images taken from the ultra violet imaging telescope (uvit) aboard astrosat. we identify cluster members by combining uvit-detected sources with gaia edr3 data. we detect four bright and hot blue straggler stars (bsss) and two yellow straggler stars (ysss) based on their location in optical and fuv-optical color-magnitude diagrams. based on the parameters estimated using spectral energy distributions, we infer that bsss are either collisional products or might have undetectable white dwarf (wd) companions. our photometric analysis of ysss confirms their binarity, consistent with the spectroscopic results. we find ysss to be formed through a mass-transfer scenario and the hot components are likely to be a-type subdwarfs. a comparison of the radial velocity, gaia edr3 proper motion of the pn with the cluster, and reddening toward the pn and the cluster does not rule out the membership of the pn. comparing the central star's position with theoretical post‑agb (pagb) models suggest that it has already entered the wd cooling phase, and its mass is deduced to be ~0.66 m ⊙. the corresponding progenitor mass turns out to be ~2.1 m ⊙, comparable to the turn-off mass of the cluster, implying that the progenitor could have formed in the cluster. we suggest that the ngc 2818 might be one of the few known clusters to host a pn, providing a unique opportunity to test stellar evolution models. | uocs-ix. astrosat/uvit study of the open cluster ngc 2818: blue stragglers, yellow stragglers, planetary nebula, and their membership |
we present a detailed analysis of broadband x-ray observations of the pulsar psr j1420-6048 and its wind nebula (pwn) in the kookaburra region with chandra, xmm-newton, and nustar. using the archival xmm-newton and new nustar data, we detected 68 ms pulsations of the pulsar and characterized its x-ray pulse profile, which exhibits a sharp spike and a broad bump separated by ~0.5 in phase. a high-resolution chandra image revealed a complex morphology of the pwn: a torus-jet structure, a few knots around the torus, one long (~7') and two short tails extending in the northwest direction, and a bright diffuse emission region to the south. spatially integrated chandra and nustar spectra of the pwn out to 2.'5 are well-described by a power-law model with a photon index γ ≈ 2. a spatially resolved spectroscopic study, as well as nustar radial profiles of the 3-7 kev and 7-20 kev brightness, showed a hint of spectral softening with increasing distance from the pulsar. a multiwavelength spectral energy distribution (sed) of the source was then obtained by supplementing our x-ray measurements with published radio, fermi-lat, and h.e.s.s. data. the sed and radial variations of the x-ray spectrum were fit with a leptonic multizone emission model. our detailed study of the pwn may be suggestive of (1) particle transport dominated by advection, (2) a low magnetic-field strength (b ~ 5 μg), and (3) electron acceleration to ~pev energies. | x-ray studies of the pulsar psr j1420-6048 and its tev pulsar wind nebula in the kookaburra region |
magnetars have been considered as progenitors of magnetar giant flares (mgfs) and fast radio bursts (frbs). we present detailed studies on afterglow emissions caused by bursts that occur in their wind nebulae and surrounding baryonic ejecta. in particular, following the bursts-in-bubble model, we analytically and numerically calculate spectra and light curves of such afterglow emission. we scan parameter space for the detectability of radio signals, and find that a burst with ~1045 erg is detectable with the very large array or other next-generation radio facilities. the detection of multiwavelength afterglow emission from mgfs and/or frbs is of great significance for their localization and revealing their progenitors, and we estimate the number of detectable afterglow events. | multiwavelength afterglow emission from bursts associated with magnetar flares and fast radio bursts |
fast, ejected stars have been found around several young star-forming regions, such as the orion nebula cluster. these ejected stars can be used to constrain the initial density, spatial and kinematic substructure when compared to predictions from n-body simulations. we search for runaway and slower walkaway stars using gaia data release 2 (dr2) within 100 pc of ngc 2264, which contains subclustered regions around higher mass ob stars (s mon, irs 1, and irs 2). we find five runaways and nine walkaways that trace back to s monocerotis (s mon) and six runaways and five walkaways that trace back to irs 1/2 based on their 3d kinematics. we compare these numbers to a range of n-body simulations with different initial conditions. the number of runaways/walkaways is consistent with initial conditions with a high initial stellar density (~10 000 m⊙ pc-3), a high initial amount of spatial substructure, and either a subvirial or virialized ratio for all subclusters. we also confirm the trajectories of our ejected stars using the data from gaia early data release 3 (edr3), which reduces the number of runaways from irs 1/2 from six to four but leaves the number of runaways from s mon unchanged. the reduction in runaways is due to smaller uncertainties in the proper motion and changes in the parallax/distance estimate for these stars in gaia edr3. we find further runaway/walkaway candidates based on proper motion alone in gaia dr2, which could increase these numbers once radial velocities are available. we also expect further changes in the candidate list with upcoming gaia data releases. | constraining the initial conditions of ngc 2264 using ejected stars found in gaia dr2 |
we investigated the inventory of presolar silicate, oxide, and silicon carbide (sic) grains of fine-grained chondrule rims in six mighei-type (cm) carbonaceous chondrites (banten, jbilet winselwan, maribo, murchison, murray and yamato 791198), and the cm-related carbonaceous chondrite sutter's mill. sixteen o-anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix-normalized abundance of ~18 ppm, together with 21 presolar sic grains (~42 ppm). twelve of the o-rich grains are enriched in 17o, and could originate from low-mass asymptotic giant branch stars. one grain is enriched in 17o and significantly depleted in 18o, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core-collapse supernova origin showing enhanced 18o/16o ratios relative to the solar system ratio. we find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. this may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. nevertheless, the low o-anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. six o-rich presolar grains were studied by auger electron spectroscopy, revealing two fe-rich silicates, one forsterite-like mg-rich silicate, two al-oxides with spinel-like compositions, and one fe-(mg-)oxide. scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm × 735 nm) revealed that it was crystalline åkermanite (ca2mg[si2o7]) or a an åkermanite-diopside (mgcasi2o6) intergrowth. | the presolar grain inventory of fine-grained chondrule rims in the mighei-type (cm) chondrites |
the southern h ii region discovery survey (shrds) is a 900 hr australia telescope compact array 4-10 ghz radio continuum and radio recombination line (rrl) survey of galactic h ii regions and infrared-identified h ii region candidates in the southern sky. for this data release, we reprocess all previously published shrds data and include an additional ∼450 hr of observations. the search for new h ii regions is now complete over the range 259° < ℓ < 346°, ∣b∣ < 4° for h ii region candidates with predicted 6 ghz continuum peak brightnesses ≳30 mjy beam-1. we detect radio continuum emission toward 730 targets altogether including previously known nebulae and h ii region candidates. by averaging ∼18 rrl transitions, we detect rrl emission toward 206 previously known h ii regions and 436 h ii region candidates. including the northern sky surveys, over the last decade the h ii region discovery surveys have more than doubled the number of known galactic h ii regions. the census of h ii regions in the wide-field infrared survey explorer (wise) catalog of galactic h ii regions is now complete for nebulae with 9 ghz continuum flux densities ≳250 mjy. we compare the rrl properties of the newly discovered shrds nebulae with those of all previously known h ii regions. the median rrl fwhm line width of the entire wise catalog h ii region population is 23.9 km s-1 and is consistent between galactic quadrants. the observed galactic longitude-velocity asymmetry in the population of h ii regions probably reflects underlying spiral structure in the milky way. | the southern h ii region discovery survey. ii. the full catalog |
meteorites are fascinating cosmic visitors. using accessible language, this book documents the history of mineralogy and meteorite research, summarizes the mineralogical characteristics of the myriad varieties of meteorites, and explains the mineralogical characteristics of solar system bodies visited by spacecraft. some of these bodies contain minerals that do not occur naturally on earth or in meteorites. the book explains how to recognize different phases under the microscope and in back-scattered electron images. it summarizes the major ways in which meteoritic minerals form - from condensation in the expanding atmospheres of dying stars to crystallization in deep-seated magmas, from flash-melting in the solar nebula to weathering in the terrestrial environment. containing spectacular back-scattered electron images, colour photographs of meteorite minerals, and with an accompanying online list of meteorite minerals, this book provides a useful resource for meteorite researchers, terrestrial mineralogists, cosmochemists and planetary scientists, as well as graduate students in these fields | meteorite mineraology |
the majority of gas giants (planets of masses ≳102 m ⊕) are found to reside at distances beyond ∼1 au from their host stars. within 1 au, the planetary population is dominated by super-earths of 2-20 m ⊕. we show that this dichotomy between inner super-earths and outer gas giants can be naturally explained should they form in nearly inviscid disks. in laminar disks, a planet can more easily repel disk gas away from its orbit. the feedback torque from the pile-up of gas inside the planet’s orbit slows down and eventually halts migration. a pressure bump outside the planet’s orbit traps pebbles and solids, starving the core. gas giants are born cold and stay cold: more massive cores are preferentially formed at larger distances, and they barely migrate under disk feedback. we demonstrate this using two-dimensional hydrodynamical simulations of disk-planet interaction lasting up to 105 years: we track planet migration and pebble accretion until both come to an end by disk feedback. whether cores undergo runaway gas accretion to become gas giants or not is determined by computing one-dimensional gas accretion models. our simulations show that in an inviscid minimum mass solar nebula, gas giants do not form inside ∼0.5 au, nor can they migrate there while the disk is present. we also explore the dependence on disk mass and find that gas giants form further out in less massive disks. | inner super-earths, outer gas giants: how pebble isolation and migration feedback keep jupiters cold |
context. most of the optically classified low-ionisation, narrow emission-line regions (liners) nuclei host an active galactic nucleus (agn). however, how they fit into the unified model (um) of agn is still an open question.aims: the aims of this work are to study at mid-infrared (mid-ir) (1) the compton-thick nature of liners (i.e. hydrogen column densities of nh> 1.5 × 1024 cm-2) and (2) the disappearance of the dusty torus in liners predicted from theoretical arguments.methods: we have compiled all the available low spectral-resolution, mid-ir spectra of liners from the infrared spectrograph (irs) onboard spitzer. the sample contains 40 liners. we have complemented the liner sample with spitzer/irs spectra of pg qsos, type-1 seyferts (s1s), type-2 seyferts (s2s), and starburst (sb) nuclei. we studied the agn compared to the starburst content in our sample using different indicators: the equivalent width of the polycyclic aromatic hydrocarbon at 6.2 μm, the strength of the silicate feature at 9.7 μm, and the steepness of the mid-ir spectra. we classified the spectra as sb-dominated and agn-dominated, according to these diagnostics and compared the average mid-ir spectra of the various classes. moreover, we studied the correlation between the 12 μm luminosity, νlν(12 μm), and the 2-10 kev energy band x-ray luminosity, lx(2-10 kev).results: in 25 out of the 40 liners (i.e. 62.5%), the mid-ir spectra are not sb-dominated, similar to the comparison s2 sample (67.7%). the average spectra of both sb-dominated liners and s2s are very similar to the average spectrum of the sb class. the average spectrum of agn-dominated liners is different from the average spectra of the other optical classes, showing a rather flat spectrum at 6-28 μm. we find that the average spectrum of agn-dominated liners with x-ray luminosities lx(2-10 kev) > 1041 erg/s is similar to the average mid-ir spectrum of agn-dominated s2s. however, faint liners (i.e. lx(2-10 kev) < 1041 erg/s) show flat spectra different from any of the other optical classes. the correlation between νlν(12 μm) and lx(2-10 kev) for agn nicely extends towards low luminosities only if sb-dominated liners are excluded and if the 2-10 kev band x-ray luminosity is corrected in compton-thick liner candidates.conclusions: we find that liners proposed as compton-thick candidates at x-ray wavelengths may be confirmed according to the x-ray to mid-ir luminosity relation. we show evidence that the dusty-torus disappear when their bolometric luminosity is below lbol ≃ 1042 erg/s. we suggest that the dominant emission at mid-ir of faint liners might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or adaf emission. alternatively, the mid-ir emission of some of these faint liners could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. to reconcile the compton-thick nature of a large number of liners without dusty-torus signatures, we suggest that the material producing the compton-thick x-ray obscuration is free of dust. table 1 is available in electronic form at http://www.aanda.org | nuclear obscuration in liners. clues from spitzer/irs spectra on the compton thickness and the existence of the dusty torus |
certain planetary nebulae (pne) contain shells, filaments, or globules of cold gas and dust whose heating and chemistry are likely driven by uv and x-ray emission from their central stars and from wind-collision-generated shocks. we present the results of a survey of molecular line emission in the 88-236 ghz range from nine nearby (<1.5 kpc) planetary nebulae spanning a range of uv and x-ray luminosities, using the 30 m telescope of the institut de radioastronomie millimétrique. rotational transitions of thirteen molecules, including co isotopologues and chemically important trace species, were observed and the results compared with and augmented by previous studies of molecular gas in pne. lines of the molecules hco+, hnc, hcn, and cn, which were detected in most objects, represent new detections for four planetary nebulae in our study. specifically, we present the first detections of 13co (1-0, 2-1), hco+, cn, hcn, and hnc in ngc 6445; hco+ in bd+30°3639; 13co (2-1), cn, hcn, and hnc in ngc 6853; and 13co (2-1) and cn in ngc 6772. flux ratios were analyzed to identify correlations between the central star and/or nebular uv and x-ray luminosities and the molecular chemistries of the nebulae. this analysis reveals a surprisingly robust dependence of the hnc/hcn line ratio on pn central star uv luminosity. there exists no such clear correlation between pn x-rays and various diagnostics of pn molecular chemistry. the correlation between hnc/hcn ratio and central star uv luminosity demonstrates the potential of molecular emission line studies of pne for improving our understanding of the role that high-energy radiation plays in the heating and chemistry of photodissociation regions. | a new radio molecular line survey of planetary nebulae. hnc/hcn as a diagnostic of ultraviolet irradiation |
this paper explores the influences and consequences of toroidal magnetic fields in shaping the visible lobes of pre-planetary nebulae (prepne). to probe these influences we start with the steady, diverging, and field-free wind model of our previous papers and add weak to moderate toroidal fields to the winds in order to generate arrays of outcomes after 500 yr, after which the structures grow almost homologously. as expected, toroidal fields in the stellar winds invariably form very thin and dense axial features whose structure is best described as a thin cold jet with an ultra-dense and neutral leading knot, or bullet, at its tip. the speed of the leading knot depends only on the density contrast (the ratio of injected to ambient gas densities at the nozzle) and wind injection speed, but not on the field strength or opening angle. the lobes formed by the ram pressure of the winds take a variety of forms and sizes that depend primarily on the geometric structure of the injected gas and the density contrast. about 20% of the hubble space telescope images of prepne show unique signatures of shaping by toroidal fields. pairs of low-ionization knots seen along the major axis of fully ionized pne, often called fliers, are easily explained as the very dense, cold, and neutral remnants of magnetically formed knots. | models of the mass-ejection histories of pre-planetary nebulae. iv. magnetized winds and the origins of jets, bullets, and fliers |
the standard approach to the long-term evolution of pulsar wind nebulae (pwne) is based on one-zone models treating the nebula as a uniform system. in particular for the late phase of evolved systems, many of the generally used prescriptions are based on educated guesses for which a proper assessment lacks. using an advanced radiative code, we evaluate the systematic impact of various parameters, like the properties of the supernova ejecta, of the inner pulsar, as well of the ambient medium, upon the extent of the reverberation phase of pwne. we investigate how different prescriptions shift the starting time of the reverberation phase, how this affects the amount of the compression, and how much of this can be ascribable to the radiation processes. some critical aspects are the description of the reverse shock evolution, the efficiency by which at later times material from the ejecta accretes on to the swept-up shell around the pwn, and finally the density, velocity, and pressure profiles in the surrounding supernova remnant. we have explicitly treated the cases of the crab nebula, and of j1834.9-0846, taken to be representatives of the more and the less energetic pulsars, respectively. especially for the latter object, the prediction of large compression factors is confirmed, even larger in the presence of radiative losses, also confirming our former prediction of periods of superefficiency during the reverberation phase of some pwne. | reverberation of pulsar wind nebulae (i): impact of the medium properties and other parameters upon the extent of the compression |
we examine the images of hundreds of planetary nebulae (pne) and find that for about one in six pne the morphology is too “messy” to be accounted for by models of stellar binary interaction. we speculate that interacting triple stellar systems shaped these pne. in this preliminary study, we qualitatively classify pne by one of four categories. (1) pne that show no need for a tertiary star to account for their morphology. (2) pne whose structure possesses a pronounced departure from axial-symmetry and/or mirror-symmetry. we classify these, according to our speculation, as “having a triple stellar progenitor.” (3) pne whose morphology possesses departure from axial-symmetry and/or mirror-symmetry, but not as pronounced as in the previous class, and are classified as “likely shaped by triple stellar system.” (4) pne with minor departure from axial-symmetry and/or mirror-symmetry that could have been also caused by an eccentric binary system or the interstellar medium. these are classified as “maybe shaped by a triple stellar system.” given a weight ηt= 1, ηl= 0.67, and ηm= 0.33 to classes 2, 3, and 4, respectively, we find that according to our assumption about 13%-21% of pne have been shaped by triple stellar systems. although in some evolutionary scenarios not all three stars survive the evolution, we encourage the search for a triple stellar systems at the center of some pne. | planetary nebulae that cannot be explained by binary systems |
the common assumption that {θ }1 {ori} {{c}} is the dominant ionizing source for the orion nebula is critically examined. this assumption underlies much of the existing analysis of the nebula. in this paper we establish through comparison of the relative strengths of emission lines with expectations from cloudy models and through the direction of the bright edges of proplyds that {θ }2 {ori} {{a}}, which lies beyond the bright bar, also plays an important role. {θ }1 {ori} {{c}} does dominate ionization in the inner part of the orion nebula, but outside of the bright bar as far as the southeast boundary of the extended orion nebula, {θ }2 {ori} {{a}} is the dominant source. in addition to identifying the ionizing star in sample regions, we were able to locate those portions of the nebula in 3d. this analysis illustrates the power of muse spectral imaging observations to identify sources of ionization in extended regions. | which stars are ionizing the orion nebula? |
we present two new radio continuum images from the australian square kilometre array pathfinder (askap) survey in the direction of the small magellanic cloud (smc). these images are part of the evolutionary map of the universe (emu) early science project (esp) survey of the small and large magellanic clouds. the two new source lists produced from these images contain radio continuum sources observed at 960 mhz (4489 sources) and 1320 mhz (5954 sources) with a bandwidth of 192 mhz and beam sizes of 30.0 × 30.0 arcsec2 and 16.3 × 15.1 arcsec2, respectively. the median root mean square (rms) noise values are 186 μjy beam-1 (960 mhz) and 165 μjy beam-1 (1320 mhz). to create point source catalogues, we use these two source lists, together with the previously published molonglo observatory synthesis telescope (most) and the australia telescope compact array (atca) point source catalogues to estimate spectral indices for the whole population of radio point sources found in the survey region. combining our askap catalogues with these radio continuum surveys, we found 7736 point-like sources in common over an area of 30 deg2. in addition, we report the detection of two new, low surface brightness supernova remnant candidates in the smc. the high sensitivity of the new askap esp survey also enabled us to detect the bright end of the smc planetary nebula sample, with 22 out of 102 optically known planetary nebulae showing point-like radio continuum emission. lastly, we present several morphologically interesting background radio galaxies. | the askap emu early science project: radio continuum survey of the small magellanic cloud |
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