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with a rising energy demand and anabatic environmental crisis arising from the fast growth in human population and society economics, numerous efforts have been devoted to explore and design plentiful multifunctional materials for meeting high‑efficiency energy transfer processes, which happen in various developed energy conversion and storage systems. as a special kind of multi‑metal oxides, perovskite with attractive physical and chemical properties, is becoming a rapidly rising star on the horizon of high‑performance catalytic materials with substantial research behaviors worldwide. the porous nanostructure in targeted catalysts is favorable to the catalytic activity and thus improves the overall efficiency of these energy‑related installations. in this review paper, recent advances made in the porous perovskite nanostructures for catalyzing several anodic or cathodic reactions in fuel cells and metal–air batteries are comprehensively summarized. plenty of general preparation methods employed to attain porous perovskite‑type oxides are provided, followed by a further discussion about the influence of various strategies on structures and catalytic properties of the porous perovskites. furthermore, deep insights gathered in the future development of porous perovskite‑based materials for energy conversion and storage technologies are also provided. | advances in porous perovskites: synthesis and electrocatalytic performance in fuel cells and metal–air batteries |
i investigate the roles of cluster dynamics and massive binary evolution in producing stellar-remnant binary black hole (bbh) mergers over the cosmic time. to that end, dynamical bbh mergers are obtained from long-term direct n-body evolutionary models of ∼104 m⊙ , pc-scale young massive clusters (ymc) evolving into moderate-mass open clusters. fast evolutionary models of massive isolated binaries yield bbhs from binary evolution. population synthesis in a model universe is then performed, taking into account observed cosmic star formation and enrichment histories, to obtain bbh-merger yields from these two channels observable at the present day and over cosmic time. the merging bbh populations from the two channels are combined by applying a proof-of-concept bayesian regression chain, taking into account observed differential intrinsic bbh merger rate densities from the second gravitational-wave transient catalog (gwtc-2). the analysis estimates an ob-star binary fraction of fobin≳90 % and a ymc formation efficiency of fymc∼10-2 , being consistent with recent optical observations and large scale structure formation simulations. the corresponding combined model universe present-day, differential intrinsic bbh merger rate density and the cosmic evolution of bbh merger rate density both agree well with those from gwtc-2. the analysis also suggests that despite significant "dynamical mixing" at low redshifts, bbh mergers at high redshifts (zevent≳1 ) could still be predominantly determined by binary-evolution physics. caveats in the present approach and future improvements are discussed. | merger rate density of stellar-mass binary black holes from young massive clusters, open clusters, and isolated binaries: comparisons with ligo-virgo-kagra results |
in this work we focus on a group of galactic double neutron star (dns) systems with long orbital periods of ≳1 day and low eccentricities of ≲0.4. the feature of these orbital parameters is used to constrain the evolutionary processes of progenitor binaries and the supernova (sn) kicks of the second born nss. adopting that the mass transfer during primordial binary evolution is highly nonconservative (rotation-dependent), the formation of dns systems involves a double helium star binary phase, the common envelope (ce) evolution initiates before the first ns formation. during the ce evolution the binary orbital energy is obviously larger when using a helium star rather than an ns to expel the donor envelope, this can help explain the formation of dns systems with long periods. sn kicks at ns birth can lead to eccentric orbits and even the disruption of binary systems, and the low eccentricities require that the dnss receive a small natal kick at the second collapse. compared with the overall distribution of orbital parameters for observed dns binaries, we propose that the second born nss in most dns systems are subject to small natal kicks with the maxwellian dispersion velocity of less than 80 km s-1, which can provide some constraints on the sn explosion processes. the mass distribution of dns binaries is also briefly discussed. we suggest that the rotation-dependent mass transfer mode and our results about sn kicks should be applied to massive binary evolution and population synthesis studies. | on the role of supernova kicks in the formation of galactic double neutron star systems |
we present a model of evolution of solitary neutron stars, including spin parameters, magnetic field decay, motion in the galactic potential, and birth inside spiral arms. we use two parametrizations of the radio-luminosity law and model the radio selection effects. dispersion measure is estimated from the recent model of free electron distribution in the galaxy (ymw16). model parameters are optimized using the markov chain monte carlo technique. the preferred model has a short decay scale of the magnetic field of 4.27^{+0.4}_{-0.38} myr. however, it has non-negligible correlation with parameters describing the pulsar radio luminosity. based on the best-fitting model, we predict that the square kilometre array surveys will increase the population of known single radio pulsars by between 23 and 137 per cent. the indri code used for simulations is publicly available to facilitate future population synthesis efforts. | markov chain monte carlo population synthesis of single radio pulsars in the galaxy |
both rotation and interactions with binary companions can significantly affect massive star evolution, altering interior and surface abundances, mass loss rates and mechanisms, observed temperatures and luminosities, and their ultimate core-collapse fates. the geneva and the binary population and spectral synthesis (bpass) stellar evolution codes include detailed treatments of the effects of rotation and binary evolution, respectively, and can illustrate the impact of these phenomena on massive stars and stellar populations. however, a direct comparison of these two widely used codes is vital if we hope to use their predictions for interpreting observations. in particular, rotating and binary models will predict different young stellar populations, impacting the outputs of stellar population synthesis (sps) and the resulting interpretation of large samples of massive stars based on commonly used tools such as star count ratios. here we compare the geneva and bpass evolutionary models, using an interpolated sps scheme introduced in our previous work and a novel bayesian framework to present the first in-depth direct comparison of massive stellar populations produced from single, rotating, and binary nonrotating evolution models. we calculate both models' predicted values of star count ratios and compare the results to observations of massive stars in westerlund 1, h + χ persei, and both magellanic clouds. we also consider the limitations of both the observations and the models, and how to quantitatively include observational completeness limits in sps models. we demonstrate that the methods presented here, when combined with robust stellar evolutionary models, offer a potential means of estimating the physical properties of massive stars in large stellar populations. | a comparison of rotating and binary stellar evolution models: effects on massive star populations |
we carry out a comparative analysis of the metallicities from the stellar, neutral-gas, and ionized-gas components in the metal-rich spiral galaxy m83. we analyze spectroscopic observations taken with the hubble space telescope, the large binocular telescope, and the very large telescope. we detect a clear depletion of the h i gas, as observed from the h i column densities in the nuclear region of this spiral galaxy. we find column densities of log[n(h i) cm-2] < 20.0 at galactocentric distances of <0.18 kpc, in contrast to column densities of log[n(h i) cm-2] ∼ 21.0 in the galactic disk, a trend observed in other nearby spiral galaxies. we measure a metallicity gradient of -0.03 ± 0.01 dex kpc-1 for the ionized gas, comparable to the metallicity gradient of a local benchmark of 49 nearby star-forming galaxies of -0.026 ± 0.002 dex kpc-1. our cospatial metallicity comparison of the multiphase gas and stellar populations shows excellent agreement outside of the nucleus of the galaxy, hinting at a scenario where the mixing of newly synthesized metals from the most massive stars in the star clusters takes longer than their lifetimes (∼10 myr). finally, our work shows that caution must be taken when studying the metallicity gradient of the neutral-gas component in star-forming galaxies, since this can be strongly biased, as these environments can be dominated by molecular gas. in these regions the typical metallicity tracers can provide inaccurate abundances, as they may trace both the neutral- and molecular-gas components. * based on observations made with the hubble space telescope under program id 14681. | first cospatial comparison of stellar, neutral-gas, and ionized-gas metallicities in a metal-rich galaxy: m83 |
we present a spectral analysis of four large magellanic cloud (lmc) wc-type wolf-rayet (wr) stars (bat99-8, bat99-9, bat99-11, and bat99-52) to shed light on two evolutionary questions surrounding massive stars. the first is: are wo-type wr stars more oxygen enriched than wc-type stars, indicating further chemical evolution, or are the strong high-excitation oxygen lines in wo-type stars an indication of higher temperatures. this study will act as a baseline for answering the question of where wo-type stars fall in wr evolution. each star's spectrum, extending from 1100 to 25000 å, was modeled using cmfgen to determine the star's physical properties such as luminosity, mass-loss rate, and chemical abundances. the oxygen abundance is a key evolutionary diagnostic, and with higher resolution data and an improved stellar atmosphere code, we found the oxygen abundance to be up to a factor of 5 lower than that of previous studies. the second evolutionary question revolves around the formation of wr stars: do they evolve by themselves or is a close companion star necessary for their formation? using our derived physical parameters, we compared our results to the geneva single-star evolutionary models and the binary population and spectral synthesis (bpass) binary evolutionary models. we found that both the geneva solar-metallicity models and bpass lmc-metallicity models are in agreement with the four wc-type stars, while the geneva lmc-metallicity models are not. therefore, these four wc4 stars could have been formed either via binary or single-star evolution. * this paper includes data gathered with the 6.5 meter magellan telescopes located at las campanas observatory, chile. | the physical parameters of four wc-type wolf-rayet stars in the large magellanic cloud: evidence of evolution |
we combine archival images for the nearby galaxy m33 (triangulum galaxy) from the ultraviolet (uv) to the infrared to derive ages, masses, and extinctions for the young star cluster population, and compare our physical parameters with published ones. our goal is to test the robustness of clusters ages and masses, and possibly improve on existing ones both by expanding the wavelength range of the spectral-energy distribution (sed) fits and by using more recent population synthesis models. the rationale for this experiment is to verify the sensitivity of the clusters physical parameters to observational setups and model choices that span those commonly found in the literature. we derive the physical parameters of 137 clusters, using seds measured in eight uv-to-i bands, including hα, from galex and ground-based images. we also add the 24 μm image from the spitzer space telescope to help break some age degeneracies. we find that our derived cluster ages show significant differences with earlier determinations, while the masses remain relatively insensitive to the fitting approach adopted. we also highlight an already known difficulty in recovering old, low-extinction clusters, as sed-fitting codes tend to prefer younger, higher extinction solutions when the extinction is a free parameter. we publish updated ages, masses, and extinctions, with uncertainties for all sample star clusters, together with their photometry. given the proximity of m33, this represents an important population to secure for the study of star formation and cluster evolution in spirals. | ages and masses of star clusters in m33: a multiwavelength study |
in this work, we used a grid of photoionization models combined with stellar population synthesis models to derive reliable ionization correction factors (icfs) for the sulphur in star-forming regions. these models cover a large range of nebular parameters and yielding ionic abundances in consonance with those derived through optical and infrared observational data of star-forming regions. from our theoretical icfs, we suggested an α value of 3.27 ± 0.01 in the classical stasińska formulae. we compared the total sulphur abundance in the gas phase of a large sample of objects by using our theoretical icf and other approaches. in average, the differences between the determinations via the use of the different icfs considered are similar to the uncertainties in the s/h estimations. nevertheless, we noted that for some objects it could reach up to about 0.3 dex for the low-metallicity regime. despite of the large scatter of the points, we found a trend of s/o ratio to decrease with the metallicity, independently of the icf used to compute the sulphur total abundance. | sulphur abundance determinations in star-forming regions - i. ionization correction factor |
recent work has suggested that mid-ir wavelengths are optimal for estimating the mass-to-light ratios of stellar populations and hence the stellar masses of galaxies. we compare stellar masses deduced from spectral energy distribution (sed) models, fitted to multiwavelength optical-nir photometry, to luminosities derived from wise photometry in the w1 and w2 bands at 3.6 and 4.5 μm for non-star forming galaxies. the sed-derived masses for a carefully selected sample of low-redshift (z ≤ 0.15) passive galaxies agree with the prediction from stellar population synthesis models such that m*/lw1 ≃ 0.6 for all such galaxies, independent of other stellar population parameters. the small scatter between masses predicted from the optical sed and from the wise measurements implies that random errors (as opposed to systematic ones such as the use of different initial mass functions) are smaller than previous, deliberately conservative, estimates for the sed fits. this test is subtly different from simultaneously fitting at a wide range of optical and mid-ir wavelengths, which may just generate a compromised fit: we are directly checking that the best-fitting model to the optical data generates an sed whose m*/lw1 is also consistent with separate mid-ir data. we confirm that for passive low-redshift galaxies a fixed m*/lw1 = 0.65 can generate masses at least as accurate as those obtained from more complex methods. going beyond the mean value, in agreement with expectations from the models, we see a modest change in m*/lw1 with sed fitted stellar population age but an insignificant one with metallicity. | galaxy and mass assembly (gama): the consistency of gama and wise derived mass-to-light ratios |
context. asymptotic giant branch (agb) stars are cool luminous evolved stars that are well observable across the galaxy and populating gaia data. they have complex stellar surface dynamics, which amplifies the uncertainties on stellar parameters and distances.aims: on the agb star cl lac, it has been shown that the convection-related variability accounts for a substantial part of the gaia dr2 parallax error. we observed this star with the mirc-x beam combiner installed at the chara interferometer to detect the presence of stellar surface inhomogeneities.methods: we performed the reconstruction of aperture synthesis images from the interferometric observations at different wavelengths. then, we used 3d radiative hydrodynamics (rhd) simulations of stellar convection with co5bold and the post-processing radiative transfer code optim3d to compute intensity maps in the spectral channels of mirc-x observations. then, we determined the stellar radius using the average 3d intensity profile and, finally, compared the 3d synthetic maps to the reconstructed ones focusing on matching the intensity contrast, the morphology of stellar surface structures, and the photocentre position at two different spectral channels, 1.52 and 1.70 μm, simultaneously.results: we measured the apparent diameter of cl lac at two wavelengths (3.299 ± 0.005 mas and 3.053 ± 0.006 mas at 1.52 and 1.70 μm, respectively) and recovered the radius (r = 307 ± 41 and r = 284 ± 38 r⊙) using a gaia parallax. in addition to this, the reconstructed images are characterised by the presence of a brighter area that largely affects the position of the photocentre. the comparison with 3d simulation shows good agreement with the observations both in terms of contrast and surface structure morphology, meaning that our model is adequate for explaining the observed inhomogenities.conclusions: this work confirms the presence of convection-related surface structures on an agb star of gaia dr2. our result will help us to take a step forward in exploiting gaia measurement uncertainties to extract the fundamental properties of agb stars using appropriate rhd simulations. | optical interferometry and gaia measurement uncertainties reveal the physics of asymptotic giant branch stars |
context. two distinct halo populations were found in the solar neighborhood by a series of works. they can be clearly separated by [α/fe] and several other elemental abundance ratios including [cu/fe]. very recently, a non-local thermodynamic equilibrium (non-lte) study revealed that relatively large departures exist between lte and non-lte results in copper abundance analysis. the study also showed that non-lte effects of neutral copper vary with stellar parameters and thus affect the [cu/fe] trend.aims: we aim to derive the copper abundances for the stars from the sample of nissen & schuster (2010) with both lte and non-lte calculations. based on our results, we study the non-lte effects of copper and investigate whether the high-α population can still be distinguished from the low-α population in the non-lte [cu/fe] results.methods: our differential abundance ratios are derived from the high-resolution spectra collected from vlt/uves and not/fies spectrographs. applying the mafags opacity sampling atmospheric models and spectrum synthesis method, we derive the non-lte copper abundances based on the new atomic model with current atomic data obtained from both laboratory and theoretical calculations.results: the copper abundances determined from non-lte calculations are increased by 0.01 to 0.2 dex depending on the stellar parameters compared with the lte results. the non-lte [cu/fe] trend is much flatter than the lte one in the metallicity range -1.6 < [ fe / h ] < -0.8. taking non-lte effects into consideration, the high- and low-α stars still show distinguishable copper abundances, which appear even more clear in a diagram of non-lte [cu/fe] versus [fe/h].conclusions: the non-lte effects are strong for copper, especially in metal-poor stars. our results confirmed that there are two distinct halo populations in the solar neighborhood. the dichotomy in copper abundance is a peculiar feature of each population, suggesting that they formed in different environments and evolved obeying diverse scenarios. based on observations made with the fibre fed echelle spectrograph (fies) at the nordic optical telescope (not) on la palma, and on data from the european southern observatory eso/st-ecf science archive facility (programs 65.l-0507, 67.d-0086, 67.d-0439, 68.d-0094, 68.b-0475, 69.d-0679, 70.d-0474, 71.b-0529, 72.b-0585, 76.b-0133 and 77.b-0507). | non-lte analysis of copper abundances for the two distinct halo populations in the solar neighborhood |
we performed a uniform and detailed abundance analysis of 12 refractory elements (na, mg, al, si, ca, ti, cr, ni, co, sc, mn, and v) for a sample of 257 g- and k-type evolved stars from the coralie planet search programme. to date, only one of these stars is known to harbour a planetary companion. we aimed to characterize this large sample of evolved stars in terms of chemical abundances and kinematics, thus setting a solid base for further analysis of planetary properties around giant stars. this sample, being homogeneously analysed, can be used as a comparison sample for other planet-related studies, as well as for different type of studies related to stellar and galaxy astrophysics. the abundances of the chemical elements were determined using an local thermodynamic equilibrium (lte) abundance analysis relative to the sun, with the spectral synthesis code moog and a grid of kurucz atlas9 atmospheres. to separate the galactic stellar populations, both a purely kinematical approach and a chemical method were applied. we confirm the overabundance of na in giant stars compared to the field fgk dwarfs. this enhancement might have a stellar evolutionary character, but departures from lte may also produce a similar enhancement. our chemical separation of stellar populations also suggests a `gap' in metallicity between the thick-disc and high-α metal-rich stars, as previously observed in dwarfs sample from harps. the present sample, as most of the giant star samples, also suffers from the b - v colour cut-off, which excludes low-log g stars with high metallicities, and high-log g star with low [fe/h]. for future studies of planet occurrence dependence on stellar metallicity around these evolved stars, we suggest to use a subsample of stars in a `cut-rectangle' in the log g-[fe/h] diagram to overcome the aforementioned issue. | chemical abundances and kinematics of 257 g-, k-type field giants. setting a base for further analysis of giant-planet properties orbiting evolved stars |
wide black hole binaries (wide-bbhs; ≥103 au) in the field can be perturbed by random stellar flybys that excite their eccentricities. once a wide binary is driven to a sufficiently small pericentre approach, gravitational wave (gw) emission becomes significant, and the binary inspirals and merges. in our previous study, using simplified models for wide-bbhs, we found that successive flybys lead to significant merger fractions of wide-bbhs in less than hubble time, making the flyby perturbation mechanism a relevant contributor to the production rate of gw-sources. however, the exact rates and detailed properties of the resulting gw sources depend on the wide binary progenitors. in this paper, we use detailed population synthesis models for the initial wide-bbh population, considering several populations corresponding to different natal-kick models and metallicities, and then follow the wide-bbhs evolution due to flyby perturbations and gw-emission. we show that the cumulative effect of flybys is conducive for the production of gw sources in non-negligible rates of 1-20 gpc-3 yr-1, which are sensitive to the natal kicks model. such rates are relevant to the observationally inferred rate. our models, now derived from detailed population of binaries, provide detailed properties of the produced gw-sources, including mass-functions and delay times. the observational signatures from this channel include circular orbits in aligo band; preference for high-velocity dispersion host galaxies (in particular ellipticals); relatively uniform delay-time distribution; and, likely, mild - i.e. less than isolated evolution channels and more than dynamical channels - spin-spin and spin-orbit alignments. | detailed properties of gravitational-wave mergers from flyby perturbations of wide binary black holes in the field |
it was recently proposed that a significant fraction of ultraluminous x-ray sources (ulxs) actually host a neutron star (ns) accretor. we have performed a systematic study on the ns ulx population in milky way-like galaxies, by combining binary population synthesis and detailed stellar evolution calculations. besides a normal star, the ulx donor can be a helium star (the hydrogen envelope of its progenitor star was stripped during previous common envelope evolution) if the ns is accreting at a super-eddington rate via roche lobe overflow. we find that the ns-helium star binaries can significantly contribute to the ulx population, with the overall number of about several in a milky way-like galaxy. our calculations show that such ulxs are generally close systems with orbital period distribution peaked at ∼0.1 day (with a tail up to ∼100 days), and the helium stars have relatively low masses distributing with a maximum probability at ∼1m ⊙. | a population of neutron star ultraluminous x-ray sources with a helium star companion |
context. millimeter astronomy provides valuable information on the birthplaces of planetary systems. in order to compare theoretical models with observations, the dust component has to be carefully calculated.aims: here, we aim to study the effects of dust entrainment in photoevaporative winds, and the ejection and drag of dust due to the effects caused by radiation from the central star.methods: we improved and extended the existing implementation of a two-population dust and pebble description in the global bern/heidelberg planet formation and evolution model. modern prescriptions for photoevaporative winds were used and we accounted for settling and advection of dust when calculating entrainment rates. in order to prepare for future population studies with varying conditions, we explored a wide range of disk, photoevaporation, and dust parameters.results: if dust can grow to pebble sizes, that is, if they are resistant to fragmentation or turbulence is weak, drift dominates and the entrained mass is small but larger than under the assumption of no vertical advection of grains with the gas flow. for the case of fragile dust shattering at velocities of 1m s−1 - as indicated in laboratory experiments -, an order of magnitude more dust is entrained, which becomes the main dust removal process. radiation pressure effects disperse massive, dusty disks on timescales of a few hundred myr.conclusions: these results highlight the importance of dust entrainment in winds as a solid-mass removal process. furthermore, this model extension lays the foundations for future statistical studies of the formation of planets in their birth environment. | toward a population synthesis of disks and planets. i. evolution of dust with entrainment in winds and radiation pressure |
stellar rotation, age spread, and binary stars are thought to be the three most possible causes of the peculiar color-magnitude diagrams (cmds) of some star clusters, which exhibit extended main-sequence turnoffs (emstos). the answer is far from clear. this paper studies the effects of the three above causes on the cmds of star clusters systematically. a rapid stellar evolutionary code and a recently published database of rotational effects of single stars have been used, via an advanced stellar population synthesis technique. as a result, we find a similar result for rotation to recent works, which suggests that rotation is able to explain, at least partially, the emstos of clusters, if clusters are not too old (<2.0 gyr). in addition, an age spread of 200-500 myr reproduces extended turnoffs for all clusters younger than 2.5 gyr, in particular, for those younger than 2.2 gyr. age spread also results in extended red clumps (ercs) for clusters younger than 0.5 gyr. the younger the clusters, the clearer the erc structures. moreover, it is shown that binaries (including interactive binaries) affect the spread of mstos slightly for old clusters, but they can contribute to the emstos of clusters younger than 0.5 gyr. our result suggests a possible way to disentangle the roles of stellar rotation and age spread, i.e., checking the existence of cmds with both emstos and ercs in clusters younger than 0.5 gyr. | a systematic study of effects of stellar rotation, age spread, and binaries on color-magnitude diagrams with extended main-sequence turnoffs |
core-collapse supernovae (sne), which mark the deaths of massive stars, are among the most powerful explosions in the universe and are responsible, e.g., for a predominant synthesis of chemical elements in their host galaxies. the majority of massive stars are thought to be born in close binary systems. to date, putative binary companions to the progenitors of sne may have been detected in only two cases, sne 1993j and 2011dh. we report on the search for a companion of the progenitor of the type ic sn 1994i, long considered to have been the result of binary interaction. twenty years after explosion, we used the hubble space telescope to observe the sn site in the ultraviolet (f275w and f336w bands), resulting in deep upper limits on the expected companion: f275w > 26.1 mag and f336w > 24.7 mag. these allow us to exclude the presence of a main sequence companion with a mass ≳10 m⊙. through comparison with theoretical simulations of possible progenitor populations, we show that the upper limits to a companion detection exclude interacting binaries with semi-conservative (late case a or early case b) mass transfer. these limits tend to favor systems with non-conservative, late case b mass transfer with intermediate initial orbital periods and mass ratios. the most likely mass range for a putative main sequence companion would be ∼5-12 m⊙, the upper end of which corresponds to the inferred upper detection limit. | constraints on the binary companion to the sn ic 1994i progenitor |
with the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z > 5 that are hyper-luminous in the infrared (μ l ir > 1013 l⊙, where μ is a lensing magnification factor), the possibility has opened up for spica, the proposed esa m5 mid-/far-infrared mission, to extend its spectroscopic studies toward the epoch of reionisation and beyond. in this paper, we examine the feasibility and scientific potential of such observations with spica's far-infrared spectrometer safari, which will probe a spectral range (35-230 μm) that will be unexplored by alma and jwst. our simulations show that safari is capable of delivering good-quality spectra for hyper-luminous infrared galaxies at z = 5 - 10, allowing us to sample spectral features in the rest-frame mid-infrared and to investigate a host of key scientific issues, such as the relative importance of star formation versus agn, the hardness of the radiation field, the level of chemical enrichment, and the properties of the molecular gas. from a broader perspective, safari offers the potential to open up a new frontier in the study of the early universe, providing access to uniquely powerful spectral features for probing first-generation objects, such as the key cooling lines of low-metallicity or metal-free forming galaxies (fine-structure and h2 lines) and emission features of solid compounds freshly synthesised by population iii supernovae. ultimately, safari's ability to explore the high-redshift universe will be determined by the availability of sufficiently bright targets (whether intrinsically luminous or gravitationally lensed). with its launch expected around 2030, spica is ideally positioned to take full advantage of upcoming wide-field surveys such as lsst, ska, euclid, and wfirst, which are likely to provide extraordinary targets for safari. | probing the high-redshift universe with spica: toward the epoch of reionisation and beyond |
we present a new tool for color-magnitude diagram (cmd) studies, powerful cmd. this tool is built based on the advanced stellar population synthesis (asps) model, in which single stars, binary stars, rotating stars and star formation history have been taken into account. via powerful cmd, the distance modulus, color excess, metallicity, age, binary fraction, rotating star fraction and star formation history of star clusters can be determined simultaneously from observed cmds. the new tool is tested via both simulated and real star clusters. five parameters of clusters ngc 6362, ngc 6652, ngc 6838 and m67 are determined and compared to other works. it is shown that this tool is useful for cmd studies, in particular for those utilizing data from the hubble space telescope (hst). moreover, we find that inclusion of binaries in theoretical stellar population models may lead to smaller color excess compared to the case of single-star population models. | powerful cmd: a tool for color-magnitude diagram studies |
there is observational evidence of a dearth in core-collapse supernova (ccsn) explosions from stars with zero-age main-sequence (zams) mass m0 ≈ 17-30m⊙, referred to as the `red supergiant problem'. however, simulations now predict that above 20 m⊙ we should indeed only expect stars within certain pockets of m0 to produce a visible sn explosion. validating these predictions requires large numbers of ccsne of different types with measured m0, which is challenging. in this paper, we explore the reliability of using host galaxy emission lines and the h α equivalent width to constrain the age, and thus the m0 of ccsne progenitors. we use binary population and spectral synthesis models to infer a stellar population age from muse observations of the ionized gas properties and h α ew at the location of eleven ccsne with reliable m0 measurements. comparing our results to published m0 values, we find that models that do not consider binary systems yield stellar ages that are systematically too young (thus m0 too large), whereas accounting for binary system interactions typically overpredict the stellar age (thus underpredict m0). taking into account the effects of photon leakage bring our m0 estimates in much closer agreement with expectations. these results highlight the need for careful modelling of diffuse environments, such as are present in the vicinity of type ii sne, before ionized emission line spectra can be used as reliable tracers of progenitor stellar age. | the 50-100 pc scale parent stellar populations of type ii supernovae and limitations of single star evolution models |
we use the dr9 of the desi legacy imaging survey and sdss galaxy groups to measure the conditional luminosity function (clf) for groups with halo mass m h ≥ 1012 m ⊙ and redshift 0.01 ≤ z ≤ 0.08, down to a limiting r-band magnitude of m r = -10 to -12. for given halo masses we measure the clf for the total populations and for the red and blue populations classified using the (g - z) color. we find a clear faint-end upturn in the clf of red satellites, with a slope α ≈ -1.8, which is almost independent of halo mass. this faint-end upturn is not seen for the blue and total populations. our stellar population synthesis modeling shows that (g - z) provides a clean red/blue division and that red group galaxies defined by (g - z) are all dominated by old stellar populations. the fraction of old galaxies as a function of galaxy luminosity shows a minimum at m r ~ -18, corresponding to m * ~ 109.5 m ⊙. this scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin. the rising of the old fraction at the faint end for milky way (mw)-sized halos is in good agreement with the quenched fraction measured for the mw/m31 system and from the elves survey. we discuss the implications of our results for the formation and evolution of low-mass galaxies and for the stellar mass functions of low-mass galaxies to be observed at high redshift. | galaxy populations in groups and clusters: evidence for a characteristic stellar mass scale at m ∗ 109.5 m ⊙ |
hydrodynamic studies of stellar-mass compact objects (cos) in a common envelope (ce) have shown that the accretion rate onto the co is a few orders of magnitude below the bondi-hoyle-lyttleton (bhl) estimate. this is several orders of magnitude above the eddington limit and above the limit for neutrino-cooled accretion (i.e. hypercritical accretion or hca). considering that a binary system inside the ce of a third star accretes material at nearly the same rate as a single object of the same total mass, we propose stellar-evolution channels which form binary black hole (bbh) systems with its component masses within the pair-instability supernova (pisn) mass gap. our model is based on hca onto the bbh system engulfed into the ce of a massive tertiary star. furthermore, we propose a mass transfer mode which allows to store mass lost by the binary onto a third star. through the use of population synthesis simulations for the evolution of bbhs and standard binary-evolution principles for the interaction with a tertiary star, we are able to produce bbhs masses consistent with those estimated for gw190521. we also discuss the massive binary system mk34 as a possible progenitor of bbhs in the pisn gap. | hypercritical accretion during common envelopes in triples leading to binary black holes in the pair-instability-supernova mass gap |
massive binaries are vital sources of various transient processes, including gravitational-wave mergers. however, large uncertainties in the evolution of massive stars, both physical and numerical, present a major challenge to the understanding of their binary evolution. in this paper, we upgrade our interpolation-based stellar evolution code metisse to include the effects of mass changes, such as binary mass transfer or wind-driven mass loss, not already included within the input stellar tracks. metisse's implementation of mass loss (applied to tracks without mass loss) shows excellent agreement with the sse fitting formulae and with detailed mesa tracks, except in cases where the mass transfer is too rapid for the star to maintain equilibrium. we use this updated version of metisse within the binary population synthesis code bse to demonstrate the impact of varying stellar evolution parameters, particularly core overshooting, on the evolution of a massive (25 and 15 m⊙) binary system with an orbital period of 1800 d. depending on the input tracks, we find that the binary system can form a binary black hole or a black hole-neutron star system, with primary (secondary) remnant masses ranging between 4.47 (1.36) and 12.30 (10.89) m⊙, and orbital periods ranging from 6 d to the binary becoming unbound. extending this analysis to a population of isolated binaries uniformly distributed in mass and orbital period, we show that the input stellar models play an important role in determining which regions of the binary parameter space can produce compact binary mergers, paving the way for predictions for current and future gravitational-wave observatories. | modelling stellar evolution in mass-transferring binaries and gravitational-wave progenitors with metisse |
the metallicity of a star affects its evolution in a variety of ways, changing stellar radii, luminosities, lifetimes, and remnant properties. in this work, we use the population synthesis code binary_c to study how metallicity affects novae in the context of binary stellar evolution. we compute a 16-point grid of metallicities ranging from z = 10-4 to 0.03, presenting distributions of nova white dwarf masses, accretion rates, delay-times, and initial system properties at the two extremes of our 16-point metallicity grid. we find a clear anticorrelation between metallicity and the number of novae produced, with the number of novae at z = 0.03 roughly half that at z = 10-4. the white dwarf mass distribution has a strong systematic variation with metallicity, while the shape of the accretion rate distribution is relatively insensitive. we compute a current nova rate of approximately 33 novae per year for the milky way, a result consistent with observational estimates relying on extra-galactic novae but an under-prediction relative to observational estimates relying on galactic novae. however, the shape of our predicted galactic white dwarf mass distribution differs significantly to existing observationally derived distributions, likely due to our underlying physical assumptions. in m31, we compute a current nova rate of approximately 36 novae per year, under-predicting the most recent observational estimate of $65^{+15}_{-16}$. finally, we conclude that when making predictions about currently observable nova rates in spiral galaxies, or stellar environments where star formation has ceased in the distant past, metallicity can likely be considered of secondary importance compared to uncertainties in binary stellar evolution. | the impact of metallicity on nova populations |
context. the field of galaxy evolution will make a great leap forward in the next decade as a consequence of the huge effort by the scientific community in multi-object spectroscopic facilities. various future surveys will enormously increase the number of available galaxy spectra, providing new insights into unexplored areas of research. to maximise the impact of such incoming data, the analysis methods must also step up, extracting reliable information from the available spectra. it is therefore urgent to refine and test reliable analysis tools that are able to infer the properties of a galaxy from medium- or high-resolution spectra.aims: in this paper we aim to investigate the limits and the reliability of different spectral synthesis methods in the estimation of the mean stellar age and metallicity. these two quantities are fundamental to determine the assembly history of a galaxy by providing key insights into its star formation history. the main question this work aims to address is which signal-to-noise ratios (s/n) are needed to reliably determine the mean stellar age and metallicity from a galaxy spectrum and how this depends on the tool used to model the spectra.methods: to address this question we built a set of realistic simulated spectra containing stellar and nebular emission, reproducing the evolution of a galaxy in two limiting cases: a constant star formation rate and an exponentially declining star formation with a single initial burst. we degraded the synthetic spectra built from these two star formation histories (sfhs) to different s/n and analysed with three widely used spectral synthesis codes, namely fado, steckmap, and starlight, assuming similar fitting set-ups and the same base of spectral templates.results: for s/n ≤ 5 all the three tools show a large diversity in the results. the fado and starlight tools find median differences in the light-weighted mean stellar age of ∼0.1 dex, while steckmap shows a higher value of ∼0.2 dex. for s/n > 50 the median differences in fado are ∼0.03 dex (∼7%), a factor 3 and 4 lower than the 0.08 dex (∼20%) and 0.11 dex (∼30%) obtained from starlight and steckmap, respectively. detailed investigations of the best-fit spectrum for galaxies with overestimated mass-weighted quantities point towards the inability of purely stellar models to fit the observed spectral energy distribution around the balmer jump.conclusions: our results imply that when a galaxy enters a phase of high specific star formation rate (ssfr) the neglect of the nebular continuum emission in the fitting process has a strong impact on the estimation of its sfh when purely stellar fitting codes are used, even in presence of high s/n spectra. the median value of these differences are of the order of 7% (fado), 20% (starlight), and 30% (steckmap) for light-weighted quantities, and 20% (fado), 60% (starlight), and 20% (steckmap) for mass-weighted quantities. more specifically, for a continuous sfh both steckmap and starlight overestimate the stellar age by > 2 dex within the first ∼100 myr even for high s/n spectra. this bias, which stems from the neglect of nebular continuum emission, obviously implies a severe overestimation of the mass-to-light ratio and stellar mass. but even in the presence of a mild contribution from nebular continuum, there is still the possibility to misinterpret the data as a consequence of the poor quality of the observations. our work underlines once more the importance of a self-consistent treatment of nebular emission, as implemented in fado, which, according to our analysis, is the only viable route towards a reliable determination of the assembly of any high-ssfr galaxy at high and low redshift. | self-consistent population spectral synthesis with fado. ii. star formation history of galaxies in spectral synthesis methods |
mass-transfer interactions in binary stars can lead to accretion disc formation, mass-loss from the system, and spin-up of the accretor. to determine the trajectory of the mass-transfer stream, and whether it directly impacts the accretor, or forms an accretion disc, requires numerical simulations. the mass-transfer stream is approximately ballistic, and analytic approximations based on such trajectories are used in many binary population synthesis codes as well as in detailed stellar evolution codes. we use binary population synthesis to explore the conditions under which mass transfer takes place. we then solve the reduced three-body equations to compute the trajectory of a particle in the stream for systems with varying system mass ratio, donor synchronicity, and initial stream velocity. our results show that, on average, both more mass and more time are spent during mass transfer from a sub-synchronous donor than from a synchronous donor. moreover, we find that at low initial stream velocity, the asynchronous rotation of the donor leads to self-accretion over a large range of mass ratios, especially for supersynchronous donors. the stream (self-)intersects in a narrow region of parameter space where it transitions between accreting on to the donor or the accretor. increasing the initial stream velocity leads to larger areas of the parameter space where the stream accretes on to the accretor, but also more (self-)intersection. the radii of closest approach generally increase, but the range of specific angular momenta that these trajectories carry at the radius of closest approach gets broader. our results are made publicly available. | mass-stream trajectories with non-synchronously rotating donors |
modern large-scale surveys have allowed the identification of large numbers of white dwarfs. however, these surveys are subject to complicated target selection algorithms, which make it almost impossible to quantify to what extent the observational biases affect the observed populations. the lamost (large sky area multi-object fiber spectroscopic telescope) spectroscopic survey of the galactic anticentre (lss-gac) follows a well-defined set of criteria for selecting targets for observations. this advantage over previous surveys has been fully exploited here to identify a small yet well-characterized magnitude-limited sample of hydrogen-rich (da) white dwarfs. we derive preliminary lss-gac da white dwarf luminosity and mass functions. the space density and average formation rate of da white dwarfs we derive are 0.83 ± 0.16 × 10-3 pc-3 and 5.42 ± 0.08 × 10-13 pc-3 yr-1, respectively. additionally, using an existing monte carlo population synthesis code we simulate the population of single da white dwarfs in the galactic anticentre, under various assumptions. the synthetic populations are passed through the lss-gac selection criteria, taking into account all possible observational biases. this allows us to perform a meaningful comparison of the observed and simulated distributions. we find that the lss-gac set of criteria is highly efficient in selecting white dwarfs for spectroscopic observations (80-85 per cent) and that, overall, our simulations reproduce well the observed luminosity function. however, they fail at reproducing an excess of massive white dwarfs present in the observed mass function. a plausible explanation for this is that a sizable fraction of massive white dwarfs in the galaxy are the product of white dwarf-white dwarf mergers. | da white dwarfs from the lss-gac survey dr1: the preliminary luminosity and mass functions and formation rate |
we study the sources of biases and systematics in the derivation of galaxy properties from observational studies, focusing on stellar masses, star formation rates, gas and stellar metallicities, stellar ages, magnitudes and colours. we use hydrodynamical cosmological simulations of galaxy formation, for which the real quantities are known, and apply observational techniques to derive the observables. we also analyse biases that are relevant for a proper comparison between simulations and observations. for our study, we post-process the simulation outputs to calculate the galaxies' spectral energy distributions (seds) using stellar population synthesis models and also generate the fully consistent far-uv-submillimetre wavelength seds with the radiative transfer code sunrise. we compared the direct results of simulations with the observationally derived quantities obtained in various ways, and found that systematic differences in all studied galaxy properties appear, which are caused by: (1) purely observational biases, (2) the use of mass-weighted and luminosity-weighted quantities, with preferential sampling of more massive and luminous regions, (3) the different ways of constructing the template of models when a fit to the spectra is performed, and (4) variations due to different calibrations, most notably for gas metallicities and star formation rates. our results show that large differences can appear depending on the technique used to derive galaxy properties. understanding these differences is of primary importance both for simulators, to allow a better judgement of similarities and differences with observations, and for observers, to allow a proper interpretation of the data. | biases and systematics in the observational derivation of galaxy properties: comparing different techniques on synthetic observations of simulated galaxies |
context. smc ab 6 is the shortest-period (p = 6.5 d) wolf-rayet (wr) binary in the small magellanic cloud. this binary is therefore a key system in the study of binary interaction and formation of wr stars at low metallicity. the wr component in ab 6 was previously found to be very luminous (log l = 6.3 [l⊙]) compared to its reported orbital mass (≈8 m⊙), placing it significantly above the eddington limit.aims: through spectroscopy and orbital analysis of newly acquired optical data taken with the ultraviolet and visual echelle spectrograph (uves), we aim to understand the peculiar results reported for this system and explore its evolutionary history.methods: we measured radial velocities via cross-correlation and performed a spectral analysis using the potsdam wolf-rayet model atmosphere code. the evolution of the system was analyzed using the binary population and spectral synthesis evolution code.results: ab 6 contains at least four stars. the 6.5 d period wr binary comprises the wr primary (wn3:h, star a) and a rather rapidly rotating (veq = 265 km s-1) early o-type companion (o5.5 v, star b). static n iii and n iv emission lines and absorption signatures in he lines suggest the presence of an early-type emission line star (o5.5 i(f), star c). finally, narrow absorption lines portraying a long-term radial velocity variation show the existence of a fourth star (o7.5 v, star d). star d appears to form a second 140 d period binary together with a fifth stellar member, which is a b-type dwarf or a black hole. it is not clear that these additional components are bound to the wr binary. we derive a mass ratio of mo/mwr = 2.2 ± 0.1. the wr star is found to be less luminous than previously thought (log l = 5.9 [l⊙]) and, adopting mo = 41 m⊙ for star b, more massive (mwr = 18 m⊙). correspondingly, the wr star does not exceed the eddington limit. we derive the initial masses of mi,wr = 60 m⊙ and mi,o = 40 m⊙ and an age of 3.9 myr for the system. the wr binary likely experienced nonconservative mass transfer in the past supported by the relatively rapid rotation of star b.conclusions: our study shows that ab 6 is a multiple - probably quintuple - system. this finding resolves the previously reported puzzle of the wr primary exceeding the eddington limit and suggests that the wr star exchanged mass with its companion in the past. | the shortest-period wolf-rayet binary in the small magellanic cloud: part of a high-order multiple system. spectral and orbital analysis of smc ab 6 |
of the known microquasars, v4641 sgr boasts the most severe lower limit (>52°) on the misalignment angle between the relativistic jet axis and the binary orbital angular momentum. assuming the jet and black hole spin axes coincide, we attempt to explain the origin of this extreme spin-orbit misalignment with a natal kick model, whereby an aligned binary system becomes misaligned by a supernova kick imparted to the newborn black hole. the model inputs are the kick velocity distribution, which we measure customized to v4641 sgr, and the immediate pre/post-supernova binary system parameters. using a grid of binary stellar evolution models, we determine post-supernova configurations that evolve to become consistent with v4641 sgr today and obtain the corresponding pre-supernova configurations by using standard prescriptions for common envelope evolution. using each of these potential progenitor system parameter sets as inputs, we find that a natal kick struggles to explain the origin of the v4641 sgr spin-orbit misalignment. consequently, we conclude that evolutionary pathways involving a standard common envelope phase followed by a supernova kick are highly unlikely for v4641 sgr. an alternative interpretation is that the jet axis does not reliably trace the black hole spin axis. our results raise concerns about compact object merger statistics gleaned from binary population synthesis models, which rely on unverified prescriptions for common envelope evolution and natal kicks. we also challenge the spin-orbit alignment assumption routinely invoked to measure black hole spin magnitudes. | origin of spin-orbit misalignments: the microblazar v4641 sgr |
we performed a near-infrared (nir; ∼1.0 -2.4 μm) stellar population study in a sample of early-type galaxies. the synthesis was performed using five different evolutionary population synthesis libraries of models. our main results can be summarized as follows: low-spectral-resolution libraries are not able to produce reliable results when applied to the nir alone, with each library finding a different dominant population. the two newest higher resolution models, on the other hand, perform considerably better, finding consistent results to each other and to literature values. we also found that optical results are consistent with each other even for lower resolution models. we also compared optical and nir results and found out that lower resolution models tend to disagree in the optical and in the nir, with higher fraction of young populations in the nir and dust extinction ∼1 mag higher than optical values. for higher resolution models, optical and nir results tend to agree much better, suggesting that a higher spectral resolution is fundamental to improve the quality of the results. | probing evolutionary population synthesis models in the near infrared with early-type galaxies |
based on the observed high velocity of pulsars it is thought that neutron stars (nss) receive a significant velocity kick at birth. such natal kicks are considered to play an important role in the the evolution of binary-ns systems. the kick given to the ns (together with the effect of mass loss due to the supernova explosion of the ns progenitor) may result in the binary disruption or lead to a significant change of the binary orbital properties. here we explore in detail the dynamical aftermath of natal kicks in binary systems, determine their possible outcomes and characterize their relative frequency, making use of analytic arguments and detailed population synthesis models. in a fraction of the cases the kick may cast the ns in such a trajectory as to collide with the binary companion, or pass sufficiently close to it as to disrupt it (micro tidal disruption event; $\mu$tde), or alternatively it could be tidally-captured into a close orbit, eventually forming an x-ray binary. we calculate the rates of direct post-kick physical collisions and the possible potential production of thorne-zytkow objects or long-grbs through this process, estimate the rates x-ray binaries formation and determine the rates of $\mu$tdes and faint supernovae from white dwarf disruptions by nss. finally we suggest that natal kicks can produce bh-ns binaries with very short gravitational-wave merger time, possibly giving rise to a new type of promptly appearing elisa gravitational wave (gw) sources, as well as producing aligo binary-merger gw sources with a unique (likely type ib/c) supernova electromagnetic counterpart which precedes the gw merger. | neutron star natal kicks: collisions, $\\mu$tdes, faint sne, grbs and gw sources with preceding electromagnetic counterparts |
we used broad-band imaging data for 10 cool-core brightest cluster galaxies (bcgs) and conducted a bayesian analysis using stellar population synthesis to determine the likely properties of the constituent stellar populations. determination of ongoing star formation rates (sfrs), in particular, has a direct impact on our understanding of the cooling of the intracluster medium (icm), star formation and agn-regulated feedback. our model consists of an old stellar population and a series of young stellar components. we calculated marginalized posterior probability distributions for various model parameters and obtained 68 per cent plausible intervals from them. the 68 per cent plausible interval on the sfrs is broad, owing to a wide range of models that are capable of fitting the data, which also explains the wide dispersion in the sfrs available in the literature. the ranges of possible sfrs are robust and highlight the strength in such a bayesian analysis. the sfrs are correlated with the x-ray mass deposition rates (the former are factors of 4-50 lower than the latter), implying a picture where the cooling of the icm is a contributing factor to star formation in cool-core bcgs. we find that 9 out of 10 bcgs have been experiencing starbursts since 6 gyr ago. while four out of nine bcgs seem to require continuous sfrs, five out of nine seem to require periodic star formation on intervals ranging from 20 to 200 myr. this time-scale is similar to the cooling time of the icm in the central (<5 kpc) regions. | constraining star formation rates in cool-core brightest cluster galaxies |
currently, there are 24 black hole (bh) x-ray binary systems that have been dynamically confirmed in the galaxy. most of them are low-mass x-ray binaries (lmxbs) comprised of a stellar-mass bh and a low-mass donor star. although the formation of these systems has been extensively investigated, some crucial issues remain unresolved. the most noticeable one is that, the low-mass companion has difficulties in ejecting the tightly bound envelope of the massive primary during the spiral-in process. while initially intermediate-mass binaries are more likely to survive the common envelope (ce) evolution, the resultant bh lmxbs mismatch the observations. in this paper, we use both stellar evolution and binary population synthesis to study the evolutionary history of bh lmxbs. we test various assumptions and prescriptions for the supernova mechanisms that produce bhs, the binding energy parameter, the ce efficiency and the initial mass distributions of the companion stars. we obtain the birthrate and the distributions of the donor mass, effective temperature and orbital period for the bh lmxbs in each case. by comparing the calculated results with the observations, we put useful constraints on the aforementioned parameters. in particular, we show that it is possible to form bh lmxbs with the standard ce scenario if most bhs are born through failed supernovae. | on the formation of galactic black hole low-mass x-ray binaries |
context. subdwarf b stars (sdbs) play a crucial role in stellar evolution, asteroseismology, and far-uv radiation of early-type galaxies, and have been intensively studied with observation and theory. it has theoretically been predicted that sdbs with neutron star (ns) companions exist in the galaxy, but none have been discovered yet. this remains a puzzle in this field. in a previous study (hereafter paper i), we have studied the formation channels of sdb+ns binaries from main-sequence (ms) stars plus ns binaries by establishing a model grid, but it is still unclear how these binaries consisting of ms stars and ns binaries came to be in the first place.aims: we systematically study the formation of sdb+ns binaries from their original zero-age main-sequence progenitors. we bridge the gap left by our previous study in this way. we obtain the statistical population properties of sdb+ns binaries and provide some guidance for observational efforts.methods: we first used hurley's rapid binary evolution code bse to evolve 107 primordial binaries to the point where the companions of ns+ms, ns+hertzsprung gap star, and ns+giant branch star binaries have just filled their roche lobes. next, we injected these binaries into the model grid we developed in paper i to obtain the properties of the sdb+ns populations. we adopted two prescriptions of ns natal kicks: the classical maxwellian distribution with a dispersion of σ = 265 km s-1, and a linear formula that assumes that the kick velocity is associated with the ratio of ejected to remnant mass. different values of αce, where αce is the common-envelope ejection efficiency, were chosen to examine the effect of common-envelope evolution on the results.results: in the galaxy, the birthrate of sdb+ns binaries is about 10-4 yr-1 and there are ∼7000 - 21 000 such binaries. this contributes 0.3-0.5% of all sdb binaries in the most favorable case. most galactic sdb+ns binaries (≳60%) arise from the channel of stable mass transfer. the value of αce has little effect on the results, but when we use the linear formula prescription of ns natal kick, the number and birthrate doubles in comparison to the results we obtained with the maxwellian distribution. the orbital periods of sdb+ns binaries from different formation channels differ significantly, as expected. this results in two peaks in the radial velocity (rv) semi-amplitude distribution: 100 - 150 km s-1 for stable mass transfer, and 400 - 600 km s-1 for common-envelope ejection. however, the two sdb+ns binary populations exhibit similar delay-time distributions, which both peak at about 0.2 gyr. this indicates that galactic sdb+ns binaries are born in very young populations, probably in the galactic disk. the sdb+ns binaries produced from the common-envelope ejection channel are potential sources of strong gravitational wave radiation (gwr), and about ∼100 - 300 could be detected by the laser interferometer space antenna (lisa) with a signal-to-noise ratio of 1.conclusions: most sdb+ns binaries are located in the galactic disk with small rv semi-amplitudes. sdb+ns binaries with large rv semi-amplitudes are expected to be strong gwr sources, some of which could be detected by lisa in the future. | hot subdwarf b stars with neutron star components. ii. binary population synthesis |
we employ population synthesis method to model the double neutron star (dns) population and test various possibilities on natal kick velocities gained by neutron stars after their formation. we first choose natal kicks after standard core collapse supernovae (ccsn) from a maxwellian distribution with velocity dispersion of σ = 265 km/s as proposed by hobbs and then modify this distribution by changing σ toward smaller and larger kick values. we also take into account the possibility of ns formation through electron capture supernova. in this case we test two scenarios: zero natal kick or small natal kick, drawn from maxwellian distribution with σ = 26.5 km/s. we calculate the present-day orbital parameters of binaries and compare the resulting eccentricities with those known for observed dnss. as an additional test we calculate galactic merger rates for our model populations and confront them with observational limits. we do not find any model unequivocally consistent with both observational constraints simultaneously. the models with low kicks after ccsn for binaries with the second ns forming through core collapse sn are marginally consistent with the observations. this means that either 14 observed dnss are not representative of the intrinsic galactic population, or that our modeling of dns formation needs revision. | constraints on the formation of double neutron stars from the observed eccentricities and current limits on merger rates |
we present artificial stellar populations (artpop), an open-source python package for synthesizing stellar populations and generating artificial images of stellar systems, populated star by star. the code is designed to be intuitive to use and as modular as possible, making it possible to use each of its functionalities independently or together. artpop has a wide range of scientific and pedagogical use cases, including the measurement of detection efficiencies in current and future imaging surveys, the calculation of integrated stellar population parameters, quantitative comparisons of isochrone models, and the development and validation of astronomical image-processing algorithms. in this paper, we give an overview of the artpop package, provide simple coding examples to demonstrate its implementation, and present results from some potential applications of the code. we provide links to the source code that created each example and figure throughout the paper. artpop is under active development, and we welcome bug reports, feature requests, and code contributions from the community. https://artpop.readthedocs.io/en/latest/ https://github.com/artificialstellarpopulations/artpop/ https://artpop.readthedocs.io/en/latest/tutorials/quickstart.html https://github.com/artificialstellarpopulations/artpop-paper-figures/blob/main/scripts/ | artpop: a stellar population and image simulation python package |
stellar population synthesis models can now reproduce the photometry of old stellar systems (age \gt 2 gyr) in the near-infrared (nir) bands at 3.4 and 4.6 μm (wise w1 and w2 or irac 1 and 2). in this paper, we derive stellar mass-to-light ratios for these and optical bands, and confirm that the nir m/l shows dramatically reduced sensitivity to both age and metallicity compared to optical bands, and further, that this behavior leads to significantly more robust stellar masses for quiescent galaxies with [fe/h] ≳ -0.5 regardless of star-formation history (sfh). we then use realistic early-type galaxy sfhs and metallicity distributions from the eagle simulations of galaxy formation to investigate two methods to determine the appropriate m/l for a galaxy. (1) we show that the uncertainties introduced by an unknown sfh can be largely removed using a spectroscopically inferred luminosity-weighted age and metallicity for the population to select the appropriate single stellar population (ssp) equivalent m/l. using this method, the maximum systematic error due to sfh on the m/l of an early-type galaxy is \lt 4 % at 3.4 μm and typical uncertainties due to errors in the age and metallicity create a scatter of ≲ 13 % . the equivalent values for optical bands are more than two to three times greater, even before considering uncertainties associated with internal dust extinction. (2) we demonstrate that if the eagle sfhs and metallicities accurately reproduce the true properties of early-type galaxies, the use of an iterative approach to select a mass dependent m/l can provide even more accurate stellar masses for early-type galaxies, with typical uncertainties of \lt 9 % . | being wise ii: reducing the influence of star formation history on the mass-to-light ratio of quiescent galaxies |
we use extensive gravity-sensitive ddo 51 photometry over 5100 square degrees, combined with sloan digital sky survey broadband photometry, to select a catalog of ∼4000 giant stars covering a large fraction of the high galactic latitude sky and reaching out to ∼80 kpc in the galactic halo. this sample of bright and unbiased tracers enables us to measure the radial profile and 3d structure of the stellar halo to large distances, which had previously only been measured with sparse tracers or small samples. using population synthesis models to reproduce the observed giant star luminosity function, we find that the halo maintains a {r}-3.5 profile from 30 to 80 kpc with no signs of a truncation or sharp break over this range. the radial profile measurement is largely insensitive to individual halo substructure components, but we find that attempting to measure the shape of the halo is overwhelmed by the sagittarius stream such that no elliposidal shape is a satisfactory description in this region. these measurements allow us to begin placing the milky way in context with the growing sample of external galaxies where similar halo profile measurements are available, with the goal of further linking the properties of stellar halos to the accretion histories that formed them. | the stellar density profile of the distant galactic halo |
centimetre-wavelength radio continuum emission in excess of free-free, synchrotron, and rayleigh-jeans dust emission (excess microwave emission, eme), and often called 'anomalous microwave emission', is bright in molecular cloud regions exposed to uv radiation, i.e. in photodissociation regions (pdrs). the eme correlates with infrared (ir) dust emission on degree angular scales. resolved observations of well-studied pdrs are needed to compare the spectral variations of the cm-continuum with tracers of physical conditions and of the dust grain population. the eme is particularly bright in the regions of the ρ ophiuchi molecular cloud (ρ oph) that surround the earliest type star in the complex, hd 147889, where the peak signal stems from the filament known as the ρ oph w pdr. here, we report on australia telescope compact array observations of ρ oph w that resolve the width of the filament. we recover extended emission using a variant of non-parametric image synthesis performed in the sky plane. the multifrequency 17-39 ghz mosaics reveal spectral variations in the centimetre-wavelength continuum. at ∼30 arcsec resolutions, the 17-20 ghz intensities tightly follow the mid-ir, $i_\mathrm{cm} \propto i(8\, \mu$ m), despite the breakdown of this correlation on larger scales. however, while the 33-39 ghz filament is parallel to infrared array camera 8 μm, it is offset by 15-20 arcsec towards the uv source. such morphological differences in frequency reflect spectral variations, which we quantify spectroscopically as a sharp and steepening high-frequency cutoff, interpreted in terms of the spinning dust emission mechanism as a minimum grain size $a_\mathrm{cutoff} \sim 6 \pm 1\,$ å that increases deeper into the pdr. | resolved spectral variations of the centimetre-wavelength continuum from the ρ oph w photodissociation region |
we explore the ability of four different inverse population synthesis codes to recover the physical properties of galaxies from their spectra by sed fitting. three codes, dynbas, tgaspex, and gaspex, have been implemented by the authors and are described in detail in the paper. starlight, the fourth code, is publicly available. dynbas selects dynamically a different spectral basis to expand the spectrum of each target galaxy; tgaspex uses an unconstrained age basis, whereas gaspex and starlight use for all fits a fixed spectral basis selected a priori by the code developers. variable and unconstrained basis reflect the peculiarities of the fitted spectrum and allow for simple and robust solutions to the problem of extracting galaxy parameters from spectral fits. we assemble a synthetic spectral atlas of galaxies (ssag), comprising 100,000 galaxy spectra corresponding to an equal number of star formation histories based on the recipe of chen et al. (2012). we select a subset of 120 galaxies from ssag with a colour distribution similar to that of local galaxies in the seventh data release (dr7) of the sloan digital sky survey (sdss) and produce 30 random noise realisations for each of these spectra. for each spectrum we recover the mass, mean age, metallicity, internal dust extinction, and velocity dispersion characterizing the dominant stellar population in the problem galaxy. all methods produce almost perfect fits to the target spectrum, but the recovered physical parameters can differ significantly. our tests provide a quantitative measure of the accuracy and precision with which these parameters are recovered by each method. from a statistical point of view all methods yield similar precisions, whereas dynbas produces solutions with minimal systematic biases in the distributions of residuals for all of these parameters. | on the recovery of galaxy properties from sed fitting solutions |
fast radio bursts (frbs) are highly dispersed, sporadic radio pulses which are likely extragalactic in nature. here, we investigate the constraints on the source population from surveys carried out at frequencies <1 ghz. all but one frb has so far been discovered in the 1-2 ghz band, but new and emerging instruments look set to become valuable probes of the frb population at sub-ghz frequencies in the near future. in this paper, we consider the impacts of free-free absorption and multipath scattering in our analysis via a number of different assumptions about the intervening medium. we consider previous low-frequency surveys along with an ongoing survey with university of technology digital backend for the molonglo observatory synthesis telescope (utmost) as well as future observations with the canadian hydrogen intensity mapping experiment (chime) and the hydrogen intensity and real-time analysis experiment (hirax). we predict that chime and hirax will be able to observe ∼30 or more frbs per day, even in the most extreme scenarios where free-free absorption and scattering can significantly impact the fluxes below 1 ghz. we also show that utmost will detect 1-2 frbs per month of observations. for chime and hirax, the detection rates also depend greatly on the assumed frb distance scale. some of the models we investigated predict an increase in the frb flux as a function of redshift at low frequencies. if frbs are truly cosmological sources, this effect may impact future surveys in this band, particularly if the frb population traces the cosmic star formation rate. | detecting fast radio bursts at decametric wavelengths |
the 11 mpc hα and ultraviolet galaxy survey (11hugs) traces the star formation activity of nearby galaxies. in addition, within this volume the detection completeness of core-collapse supernovae (ccsne) is high therefore by comparing these observed stellar births and deaths we can make a sensitive test of our understanding of how stars live and die. in this paper, we use the results of the binary population and spectral synthesis (bpass) code to simulate the 11hugs galaxies' hα and far-ultraviolet (fuv) star formation rate indicators (sfris) and simultaneously match the ccsn rate. we find that stellar population including interacting binary stars makes little difference to the total ccsn rate but increases the hα and fuv fluxes for a constant number of stars being formed. in addition, they significantly increase the predicted rate of type ibc sne relative to type ii sne to the level observed in the 11hugs galaxies. we also find that instead of assuming a constant star formation history for the galaxies our best-fitting models have an sfr that peaked more than 3 myr ago. | core-collapse supernova rate synthesis within 11 mpc |
we explore the connection between the gravitational wave (gw) merger rates of stellar-mass binary black holes (bbhs) and galaxy properties. we do this by generating populations of stars using the binary population synthesis code compas and evolving them in galaxies from the semi-analytic galaxy formation model shark, to determine the number of mergers occurring in each simulation time-step. we find that metal-rich and massive galaxies with star formation rate (sfr) greater than $1\, {\rm m}_{\odot }\, \rm yr^{-1}$ are 10 times more likely to have gw events compared to younger, less massive, and metal-poor galaxies. our simulation with the default input parameters predicts a higher local merger rate density compared to the third gw transient catalogue (gwtc-3) prediction from ligo, virgo, and kagra, due to short coalescence times, low metallicities, and a high sfr at low redshift in the simulation, which produces more bbhs that merge within the age of the universe compared to observations. we identify alternate remnant mass models that more accurately reproduce the volumetric rate and provide updated fits to the merger rate as a function of redshift. we then investigate the relative fraction of gw events in our simulation that are in observable host galaxies from upcoming galaxy surveys, determining which of those are ideal for tracing host galaxies with high merger rates. the implications of this work can be utilized for constraining stellar evolution models, better informing follow-up programs, and placing informative priors on host galaxies when measuring cosmological parameters such as the hubble constant. | exploring binary black hole mergers and host galaxies with shark and compas |
we present the implementation of a bayesian formalism within the stochastically lighting up galaxies (slug) stellar population synthesis code, which is designed to investigate variations in the initial mass function (imf) of star clusters. by comparing observed cluster photometry to large libraries of clusters simulated with a continuously varying imf, our formalism yields the posterior probability distribution function (pdf) of the cluster mass, age and extinction, jointly with the parameters describing the imf. we apply this formalism to a sample of star clusters from the nearby galaxy ngc 628, for which broad-band photometry in five filters is available as part of the legacy extragalactic uv survey (legus). after allowing the upper-end slope of the imf (α3) to vary, we recover pdfs for the mass, age and extinction that are broadly consistent with what is found when assuming an invariant kroupa imf. however, the posterior pdf for α3 is very broad due to a strong degeneracy with the cluster mass, and it is found to be sensitive to the choice of priors, particularly on the cluster mass. we find only a modest improvement in the constraining power of α3 when adding hα photometry from the companion hα-legus survey. conversely, hα photometry significantly improves the age determination, reducing the frequency of multi-modal pdfs. with the aid of mock clusters, we quantify the degeneracy between physical parameters, showing how constraints on the cluster mass that are independent of photometry can be used to pin down the imf properties of star clusters. | exploring the imf of star clusters: a joint slug and legus effort |
context. m-type subdwarfs are metal-poor low-mass stars and are probes for the old populations in our galaxy. accurate knowledge of their atmospheric parameters and especially their composition is essential for understanding the chemical history of our galaxy.aims: the purpose of this work is to perform a detailed study of m-subdwarf spectra covering the full wavelength range from the optical to the near-infrared. it allows us to perform a more detailed analysis of the atmospheric composition in order to determine the stellar parameters, and to constrain the atmospheric models. the study will allow us to further understand physical and chemical processes such as increasing condensation of gas into dust, to point out the missing continuum opacities, and to see how the main band features are reproduced by the models. the spectral resolution and the large wavelength coverage used is a unique combination that can constrain the processes that occur in a cool atmosphere.methods: we obtained medium-resolution spectra (r = 5000-7000) over the wavelength range 0.3-2.5 μm of ten m-type subdwarfs with x-shooter at vlt. these data constitute a unique atlas of m-subdwarfs from optical to near-infrared. we performed a spectral synthesis analysis using a full grid of synthetic spectra computed from bt-settl models and obtained consistent stellar parameters such as effective temperature, surface gravity, and metallicity.results: we show that state-of the-art atmospheric models correctly represent the overall shape of their spectral energy distribution, as well as atomic and molecular line profiles both in the optical and near-infrared. we find that the actual fitted gravities of almost all our sample are consistent with old objects, except for lhs 73 where it is found to be surprisingly low. based on observations made with the eso very large telescope at the paranal observatory under programme 092.d-0600(a). | spectral energy distribution of m-subdwarfs: a study of their atmospheric properties |
context. in the search of a sample of metal-poor bright giants using strömgren photometry, we serendipitously found a sample of 26 young (ages younger than 1 gyr) metal-rich giants, some of which have high rotational velocities.aims: we determined the chemical composition and rotational velocities of these stars in order to compare them with predictions from stellar evolution models. these stars where of spectral type a to b when on the main sequence, and we therefore wished to compare their abundance pattern to that of main-sequence a and b stars.methods: stellar masses were derived by comparison of the position of the stars in the colour-magnitude diagram with theoretical evolutionary tracks. these masses, together with gaia photometry and parallaxes, were used to derive the stellar parameters. we used spectrum synthesis and model atmospheres to determine chemical abundances for 16 elements (c, n, o, mg, al, ca, fe, sr, y, ba, la, ce, pr, nd, sm, and eu) and rotational velocities.results: the age-metallicity degeneracy can affect photometric metallicity calibrations. we identify 15 stars as likely binary stars. all stars are in prograde motion around the galactic centre and belong to the thin-disc population. all but one of the sample stars present low [c/fe] and high [n/fe] ratios together with constant [(c+n+o)/fe], suggesting that they have undergone cno processing and first dredge-up. the observed rotational velocities are in line with theoretical predictions of the evolution of rotating stars. based on observations obtained at observatoire de haute provence, canada-france-hawaii telescope and telescopio nazionale galileo. | young giants of intermediate mass. evidence of rotation and mixing |
we study the properties of the foreground galaxy of the ruby, the brightest gravitationally lensed high-redshift galaxy on the sub-millimeter sky as probed by the planck satellite, and part of our sample of planck's dusty gems. the ruby consists of an einstein ring of 1.4'' diameter at z = 3.005 observed with alma at 0.1'' resolution, centered on a faint, red, massive lensing galaxy seen with hst/wfc3, which itself has an exceptionally high redshift, z = 1.525 ± 0.001, as confirmed with vlt/x-shooter spectroscopy. here we focus on the properties of the lens and the lensing model obtained with lenstool. the rest-frame optical morphology of this system is strongly dominated by the lens, while the ruby itself is highly obscured, and contributes less than 10% to the photometry out to the k band. the foreground galaxy has a lensing mass of (3.70 ± 0.35) × 1011m⊙. magnification factors are between 7 and 38 for individual clumps forming two image families along the einstein ring. we present a decomposition of the foreground and background sources in the wfc3 images, and stellar population synthesis modeling with a range of star-formation histories for chabrier and salpeter initial mass functions (imfs). only the stellar mass range obtained with the latter agrees well with the lensing mass. this is consistent with the bottom-heavy imfs of massive high-redshift galaxies expected from detailed studies of the stellar masses and mass profiles of their low-redshift descendants, and from models of turbulent gas fragmentation. this may be the first direct constraint on the imf in a lens at z = 1.5, which is not a cluster central galaxy. based on alma data obtained with program 2015.1.01518s and vlt data obtained with programs 291.a-5014 and 295.a-5017. | planck's dusty gems. iii. a massive lensing galaxy with a bottom-heavy stellar initial mass function at z = 1.5 |
observational evidence exists for the formation of gas giant planets on wide orbits around young stars by disk gravitational instability, but the roles of disk instability and core accretion for forming gas giants on shorter period orbits are less clear. the controversy extends to population synthesis models of exoplanet demographics and to hydrodynamical models of the fragmentation process. the latter refers largely to the handling of radiative transfer in three-dimensional (3d) hydrodynamical models, which controls heating and cooling processes in gravitationally unstable disks, and hence dense clump formation. a suite of models using the β cooling approximation is presented here. the initial disks have masses of 0.091 m ⊙ and extend from 4 to 20 au around a 1 m ⊙ protostar. the initial minimum toomre qivalues range from 1.3 to 2.7, while β ranges from 1 to 100. we show that the choice of qiis equal in importance to the β value assumed: high qidisks can be stable for small β, when the initial disk temperature is taken as a lower bound, while low qidisks can fragment for high β. these results imply that the evolution of disks toward low qimust be taken into account in assessing disk fragmentation possibilities, at least in the inner disk, i.e., inside about 20 au. the models suggest that if low qidisks can form, there should be an as yet largely undetected population of gas giants orbiting g dwarfs between about 6 au and 16 au. | the effect of protoplanetary disk cooling times on the formation of gas giant planets by gravitational instability |
context. the white dwarf luminosity function is an important tool to understand the properties of the solar neighborhood, like its star formation history, and its age.aims: here we present a population synthesis study of the white dwarf population within 40 pc from the sun, and compare the results of this study with the properties of the observed sample.methods: we use a state-of-the-art population synthesis code based on monte carlo techniques, which incorporates the most recent and reliable white dwarf cooling sequences, an accurate description of the galactic neighborhood, and a realistic treatment of all the known observational biases and selection procedures.results: we find a good agreement between our theoretical models and the observed data. in particular, our simulations reproduce a previously unexplained feature of the bright branch of the white dwarf luminosity function, which we argue is due to a recent episode of star formation. we also derive the age of the solar neighborhood employing the position of the observed cut-off of the white dwarf luminosity function, to obtain ~8.9 ± 0.2 gyr.conclusions: we conclude that a detailed description of the ensemble properties of the population of white dwarfs within 40 pc of the sun allows us to obtain interesting constraints on the history of the solar neighborhood. | the white dwarf population within 40 pc of the sun |
aims: we extend the results of planetary formation synthesis by computing the long-term evolution of synthetic systems from the clearing of the gas disk into the dynamical evolution phase.methods: we use the symplectic integrator symba to numerically integrate the orbits of planets for 100 myr, using populations from previous studies as initial conditions.results: we show that within the populations studied, mass and semimajor axis distributions experience only minor changes from post-formation evolution. we also show that, depending upon their initial distribution, planetary eccentricities can statistically increase or decrease as a result of gravitational interactions. we find that planetary masses and orbital spacings provided by planet formation models do not result in eccentricity distributions comparable to observed exoplanet eccentricities, requiring other phenomena, such as stellar fly-bys, to account for observed eccentricities. | theoretical models of planetary system formation. ii. post-formation evolution |
galaxy mergers are central to our understanding of galaxy formation, especially within the context of hierarchical models. besides having a large impact on the star formation history, mergers are also able to influence gas motions at the centre of galaxies and trigger an active galactic nucleus (agn). in this paper, we present a case study of the seyfert galaxy ngc 2992, which together with ngc 2993 forms the early-stage merger system arp 245. using gemini multi-object spectrograph integral field unit data from the inner 1.1 kpc of the galaxy, we were able to spatially resolve the stellar populations, the ionization mechanism, and kinematics of ionized gas. from full spectral synthesis, we found that the stellar population is primarily composed by old metal-rich stars (t ≥ 1.4 gyr, z ≥ 2.0 z⊙), with a contribution of at most 30 per cent of the light from a young and metal-poor population (t ≤ 100 myr, z ≤ 1.0 z⊙). we detect h α and h β emission from the broad-line region with a full width at half-maximum of ∼2000 $\rm km\, s^{-1}$ . the narrow-line region kinematics presents two main components: one from gas orbiting the galaxy disc and a blueshifted (velocity ≈ -200 $\rm km\, s^{-1}$ ) outflow, possibly correlated with the radio emission, with mass outflow rate of ∼2 m⊙ yr-1 and a kinematic power of ∼2 × 1040 erg s-1 ( $\dot{e}_{\mathrm{ out}}$ /lbol ≈ 0.2 per cent). we also show even though the main ionization mechanism is the agn radiation, ionization by young stars and shocks may also contribute to the emission line ratios presented in the innermost region of the galaxy. | exploring the agn-merger connection in arp 245 i: nuclear star formation and gas outflow in ngc 2992 |
we present the first asymmetric drift (ad) measurements for unresolved stellar populations of different characteristic ages above and below 1.5 gyr. these measurements sample the age-velocity relation in galaxy disks. in this first paper, we develop two efficient algorithms to extract ad on a spaxel-by-spaxel basis from optical integral-field spectroscopic data cubes. the algorithms apply different spectral templates, one using simple stellar populations and the other a stellar library; their comparison allows us to assess systematic errors in derived multicomponent velocities, such as template mismatch. we test algorithm reliability using mock spectra and monte carlo markov chains on real data from the manga survey in sloan digital sky survey iv. we quantify random and systematic errors in ad as a function of signal-to-noise and stellar population properties with the aim of applying this technique to large subsets of the manga galaxy sample. as a demonstration of our methods, we apply them to an initial sample of seven galaxies with comparable stellar mass and color to the milky way. we find a wide range of distinct ad radial profiles for young and old stellar populations. | stellar population synthesis with distinct kinematics: multiage asymmetric drift in sdss-iv manga galaxies |
in the era of vast spectroscopic surveys focusing on galactic stellar populations, astronomers want to exploit the large quantity and good quality of data to derive their atmospheric parameters without losing precision from automatic procedures. in this work, we developed a new spectral package, fasma, to estimate the stellar atmospheric parameters (namely effective temperature, surface gravity and metallicity) in a fast and robust way. this method is suitable for spectra of fgk-type stars in medium and high resolution. the spectroscopic analysis is based on the spectral synthesis technique using the radiative transfer code, moog. the line list is comprised of mainly iron lines in the optical spectrum. the atomic data are calibrated after the sun and arcturus. we use two comparison samples to test our method, (i) a sample of 451 fgk-type dwarfs from the high-resolution harps spectrograph; and (ii) the gaia-eso benchmark stars using both high and medium resolution spectra. we explore biases in our method from the analysis of synthetic spectra covering the parameter space of our interest. we show that our spectral package is able to provide reliable results for a wide range of stellar parameters, different rotational velocities, different instrumental resolutions and for different spectral regions of the vlt-giraffe spectrographs, used amongst others for the gaia-eso survey. fasma estimates stellar parameters in less than 15 m for high-resolution and 3 m for medium-resolution spectra. the complete package is publicly available to the community. | atmospheric stellar parameters for large surveys using fasma, a new spectral synthesis package |
we evaluate the thermal torques exerted on low-mass planets embedded in gaseous protoplanetary discs with thermal diffusion, by means of high-resolution three-dimensional hydrodynamics simulations. we confirm that thermal torques essentially depend on the offset between the planet and its corotation, and find a good agreement with analytic estimates when this offset is small compared to the size of the thermal disturbance. for larger offsets that may be attained in discs with a large pressure gradient or a small thermal diffusivity, thermal torques tend towards an asymptotic value broadly compatible with results from a dynamical friction calculation in an unsheared medium. we perform a convergence study and find that the thermal disturbance must be resolved over typically 10 zones for a decent agreement with analytic predictions. we find that the luminosity at which the net thermal torque changes sign matches that predicted by linear theory within a few percents. our study confirms that thermal torques usually supersede lindblad and corotation torques by almost an order of magnitude for low-mass planets. as we increase the planetary mass, we find that the ratio of thermal torques to lindblad and corotation torques is progressively reduced, and that the thermal disturbance is increasingly distorted by the horseshoe flow. overall, we find that thermal torques are dominant for masses up to an order of magnitude larger than implemented in recent models of planetary population synthesis. we finally briefly discuss the case of stellar or intermediate-mass objects embedded in discs around active galactic nuclei. | numerical study of coorbital thermal torques on cold or hot satellites |
context. the flux-weighted gravity-luminosity relationship (fglr) of blue supergiant stars (bsg) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g/t_text{eff ^4}. bsg are the brightest stars in the universe at visual light and the application of the fglr has become a powerful tool for determining extragalactic distances.aims: observationally, the fglr is a tight relationship with only small scatter. it is, therefore, ideal for using as a constraint for stellar evolution models. the goal of this work is to investigate whether stellar evolution can reproduce the observed fglr and to develop an improved foundation for the fglr as an extragalactic distance indicator.methods: we used different grids of stellar models for initial masses between 9 and 40 m⊙ and for metallicities between z = 0.002 and 0.014, with and without rotation, which were computed with various mass loss rates during the red supergiant phase. for each of these models, we discuss the details of post-main sequence evolution and construct theoretical fglrs by means of population synthesis models that we then compare with the observed fglr.results: in general, the stellar evolution model fglrs agree reasonably well with the observed one. there are, however, differences between the models, in particular with regard to the shape and width (scatter) in the flux-weighted gravity-luminosity plane. the best agreement is obtained with models that include the effects of rotation and assume that the large majority, if not all, of the observed bsg evolve toward the red supergiant phase and that only a few are evolving back from this stage. the effects of metallicity on the shape and scatter of the fglr are small.conclusions: the shape, scatter, and metallicity dependence of the observed fglr are explained well by stellar evolution models. this provides a solid theoretical foundation for using this relationship as a robust extragalactic distance indicator. | the flux-weighted gravity-luminosity relationship of blue supergiant stars as a constraint for stellar evolution |
we examine the relation between surface brightness, velocity dispersion, and size—the fundamental plane (fp)—for quiescent galaxies at intermediate redshifts in the cosmos field. the cosmos sample consists of ∼150 massive quiescent galaxies with an average velocity dispersion of σ ∼ 250 km s-1 and redshifts between 0.2 < z < 0.8. more than half of the galaxies in the sample are compact. the cosmos galaxies exhibit a tight relation (∼0.1 dex scatter) between surface brightness, velocity dispersion, and size. at a fixed combination of velocity dispersion and size, the cosmos galaxies are brighter than galaxies in the local universe. these surface brightness offsets are correlated with the rest-frame g - z color and dn4000 index; bluer galaxies and those with smaller dn4000 indices have larger offsets. stellar population synthesis models indicate that the massive cosmos galaxies are younger and therefore brighter than similarly massive quiescent galaxies in the local universe. passive evolution alone brings the massive compact quiescent (mcq) cosmos galaxies onto the local fp at z = 0. therefore, evolution in size or velocity dispersion for mcq galaxies since z ∼ 1 is constrained by the small scatter observed in the fp. we conclude that mcq galaxies at z ≲ 1 are not a special class of objects but rather the tail of the mass and size distribution of the normal quiescent galaxy population. | quiescent compact galaxies at intermediate redshift in the cosmos field. ii. the fundamental plane of massive galaxies |
the binary fraction of a stellar population can have pronounced effects on its properties, and, in particular, the number counts of different massive star types, and the relative subtype rates of the supernovae (sne) that end their lives. here we use binary population synthesis models with a binary fraction that varies with initial mass to test the effects on resolved stellar pops and sne, and ask whether these can constrain the poorly-known binary fraction in different mass and metallicity regimes. we show that wolf-rayet (wr) star subtype ratios are valuable binary diagnostics, but require large samples to distinguish by models. uncertainties in which stellar models would be spectroscopically classified as wr stars are explored. the ratio of thermonuclear, stripped-envelope, and other core-collapse sne may prove a more accessible test and upcoming surveys will be sufficient to constrain both the high- and low-mass binary fraction in the z < 1 galaxy population. | binary fraction indicators in resolved stellar populations and supernova-type ratios |
since the gaia data release 2, several works have been published describing a bifurcation in the observed white dwarf colour-magnitude diagram for ${g_{\mathrm{bp}}}{}-{g_{\mathrm{rp}}}{} \gt 0$ . some possible explanations in the literature include the existence of a double population with different initial mass functions or two distinct populations, one formed by hydrogen-envelope and one formed by helium-envelope white dwarfs. we propose instead spectral evolution to explain the bifurcation. from a population synthesis approach, we find that spectral evolution occurs for effective temperatures below ${\simeq }11\, 000\, \mathrm{k}$ and masses mainly between $0.64\, \mathrm{m}_\odot$ and $0.74\, \mathrm{m}_\odot$ , which correspond to around 16 per cent of all da white dwarfs. we also find that the gaia white dwarf colour-magnitude diagram indicates a star formation history that decreases abruptly for objects younger than $1.4\, \mathrm{gyr}$ and a top-heavy initial mass function for the white dwarf progenitors. | evidence of spectral evolution on the white dwarf sample from the gaia mission |
many aspects of the evolution of stars, and in particular the evolution of binary stars, remain beyond our ability to model them in detail. instead, we rely on observations to guide our often phenomenological models and pin down uncertain model parameters. to do this statistically requires population synthesis. populations of stars modelled on computers are compared to populations of stars observed with our best telescopes. the closest match between observations and models provides insight into unknown model parameters and hence the underlying astrophysics. in this brief review, we describe the impact that modern big-data surveys will have on population synthesis, the large parameter space problem that is rife for the application of modern data science algorithms, and some examples of how population synthesis is relevant to modern astrophysics. | population synthesis of binary stars |
photoevaporation and planet formation have both been proposed as mechanisms responsible for the creation of a transition disc. we have studied their combined effect through a suite of 2d simulations of protoplanetary discs undergoing x-ray photoevaporation with an embedded giant planet. in a previous work, we explored how the formation of a giant planet triggers the dispersal of the inner disc by photoevaporation at earlier times than what would have happened otherwise. this is particularly relevant for the observed transition discs with large holes and high mass accretion rates that cannot be explained by photoevaporation alone. in this work, we significantly expand the parameter space investigated by previous simulations. in addition, the updated model includes thermal sweeping, needed for studying the complete dispersal of the disc. after the removal of the inner disc, the disc is a non-accreting transition disc, an object that is rarely seen in observations. we assess the relative length of this phase, to understand if it is long lived enough to be found observationally. depending on the parameters, especially on the x-ray luminosity of the star, we find that the fraction of time spent as a non-accretor greatly varies. we build a population synthesis model to compare with observations and find that in general thermal sweeping is not effective enough to destroy the outer disc, leaving many transition discs in a relatively long lived phase with a gas-free hole, at odds with observations. we discuss the implications for transition disc evolution. in particular, we highlight the current lack of explanation for the missing non-accreting transition discs with large holes, which is a serious issue in the planet hypothesis. | the long-term evolution of photoevaporating transition discs with giant planets |
the death of massive stars due to supernova explosions is a key ingredient in stellar evolution and stellar population synthesis. electron capture (ec) plays a vital role in supernova explosions. using the shell-model monte carlo method, based on the nuclear random phase approximation and linear response theory model for electrons, we study the strong screening ec rates of 52, 53, 59, 60fe in pre-supernovae. the results show that the screening rates can decrease by about 18.66%. our results may become a good foundation for future investigation of the evolution of late-type stars, supernova explosion mechanisms and numerical simulations. supported by national natural science foundation of china (11565020), counterpart foundation of sanya (2016pt43), special foundation of science and technology cooperation for advanced academy and regional of sanya (2016yd28), scientific research staring foundation for 515 talented project of hainan tropical ocean university (rhdrc201701) and natural science foundation of hainan province (114012) | strongly screening electron capture for nuclides 52, 53, 59, 60fe by the shell-model monte carlo method in pre-supernovae |
the evolution of an accreting white dwarf (wd) with a strong magnetic field toward a type ia supernova (sn ia) may differ from the classical single-degenerate (sd) channel. in this paper, we perform binary population synthesis simulations for the sd channel with a main-sequence (ms) companion, including the strongly magnetized wd accretion. under a reasonable assumption that the fraction of such systems is ∼15%, the resulting delay-time distribution roughly follows the t -1 power-law distribution. within the (wd/ms) sd channel, the contribution from the highly magnetized wd is estimated to be comparable to that from the classical, non-magnetized wd channel. the contribution of the sd channel toward sne ia can be at least ∼30% among the whole sn ia population. we suggest that the sne ia resulting from the highly magnetized wd systems would not share the observational properties expected for the classical sd channel; for every (potentially peculiar) sn observationally associated with the sd channel, we expect a comparable number of the “hidden” sd population to be in the normal class. | possible contribution of magnetized white dwarf binaries to type ia supernova populations |
context. spectral synthesis is a powerful tool for interpreting the physical properties of galaxies by decomposing their spectral energy distributions (seds) into the main luminosity contributors (e.g. stellar populations of distinct age and metallicity or ionised gas). however, the impact nebular emission has on the inferred properties of star-forming (sf) galaxies has been largely overlooked over the years, with unknown ramifications to the current understanding of galaxy evolution.aims: the objective of this work is to estimate the relations between stellar properties (e.g. total mass, mean age, and mean metallicity) of sf galaxies by simultaneously fitting the stellar and nebular continua and comparing them to the results derived through the more common purely stellar spectral synthesis approach.methods: the main galaxy sample from sdss dr7 was analysed with two distinct population synthesis codes: fado, which estimates self-consistently both the stellar and nebular contributions to the sed, and the original version of starlight, as representative of purely stellar population synthesis codes.results: differences between codes regarding average mass, mean age and mean metallicity values can go as high as ∼0.06 dex for the overall population of galaxies and ∼0.12 dex for sf galaxies (galaxies with ew(hα) > 3 å), with the most prominent difference between both codes in the two populations being in the light-weighted mean stellar age. fado presents a broader range of mean stellar ages and metallicities for sf galaxies than starlight, with the latter code preferring metallicity solutions around the solar value (z⊙ = 0.02). a closer look into the average light- and mass-weighted star formation histories of intensively sf galaxies (ew(hα) > 75 å) reveals that the light contributions of simple stellar populations (ssps) younger than ≤107 (109) years in starlight are higher by ∼5.41% (9.11%) compared to fado. moreover, fado presents higher light contributions from ssps with metallicity ≤z⊙/200 (z⊙/50) of around 8.05% (13.51%) when compared with starlight. this suggests that starlight is underestimating the average light-weighted age of intensively sf galaxies by up to ∼0.17 dex and overestimating the light-weighted metallicity by up to ∼0.13 dex compared to fado (or vice versa). the comparison between the average stellar properties of passive, sf and intensively sf galaxy samples also reveals that differences between codes increase with increasing ew(hα) and decreasing total stellar mass. moreover, comparing sf results from fado in a purely stellar mode with the previous results qualitatively suggests that differences between codes are primarily due to mathematical and statistical differences and secondarily due to the impact of the nebular continuum modelling approach (or lack thereof). however, it is challenging to adequately quantify the relative role of each factor since they are likely interconnected.conclusions: this work finds indirect evidence that a purely stellar population synthesis approach negatively impacts the inferred stellar properties (e.g. mean age and mean metallicity) of galaxies with relatively high star formation rates (e.g. dwarf spirals, `green peas', and starburst galaxies). in turn, this can bias interpretations of fundamental relations such as the mass-age or mass-metallicity, which are factors worth bearing in mind in light of future high-resolution spectroscopic surveys at higher redshifts (e.g. moons and 4most-4hs). | revisiting stellar properties of star-forming galaxies with stellar and nebular spectral modelling |
context. given that mergers are often invoked to explain many exotic phenomena in massive star evolution, understanding the evolutionary phase directly preceding a merger, the overcontact phase, is of crucial importance. despite this, large uncertainties exist in our understanding of the evolution of massive overcontact binaries.aims: we aim to provide robust observational constraints on the future dynamical evolution of massive overcontact systems by measuring the rate at which the periods change for a sample of six such objects. furthermore, we aim to investigate whether the periods of unequal-mass systems show higher rates of change than their equal mass counterparts, as theoretical models predict.methods: using archival photometric data from various ground- and space-based missions covering up to ∼40 years, we measure the periods of each system over several smaller time spans. we then fit a linear regression through the measured periods to determine the rate at which the period is changing over the entire data set.results: we find that all of the stars in our sample have very small period changes and that there does not seem to be a correlation with the mass ratio. this implies that the orbital periods for these systems are stable on the nuclear timescale, and that the unequal-mass systems may not equalize as expected.conclusions: when comparing our results with population synthesis distributions, we find large discrepancies between the expected mass ratios and period stabilities. we find that these discrepancies can be mitigated to a degree by removing systems with shorter initial periods, suggesting that the observed sample of overcontact systems may originate from binary systems with longer initial orbital periods. | constraining the overcontact phase in massive binary evolution. ii. period stability of known o+o overcontact systems |
the condensation of baryons within a dark matter (dm) halo during galaxy formation should result in some contraction of the halo as the combined system settles into equilibrium. we quantify this effect on the cuspy primordial halos predicted by dm-only simulations for the baryon distributions observed in the galaxies of the sparc database. we find that the dm halos of high surface brightness galaxies (with σeff ≳ 100 l⊙ pc−2 at 3.6 μm) experience strong contraction. halos become more cuspy as a result of compression: the inner dm density slope increases with the baryonic surface mass density. we iteratively fit rotation curves to find the balance between initial halo parameters (constrained by abundance matching), compression, and stellar mass-to-light ratio. the resulting fits often require lower stellar masses than expected for stellar populations, particularly in galaxies with bulges: stellar mass must be reduced to make room for the dm it compresses. this trade off between dark and luminous mass is reminiscent of the cusp-core problem in dwarf galaxies, but occurs in more massive systems: the present-epoch dm halos cannot follow from cuspy primordial halos unless (1) the stellar mass-to-light ratios are systematically smaller than expected from standard stellar population synthesis models, and/or (2) there is a net outward mass redistribution from the initial cusp, even in massive galaxies widely considered to be immune from such effects. | incorporating baryon-driven contraction of dark matter halos in rotation curve fits |
we use the modules for experiments in stellar astrophysics (mesa) code to calculate the yields of {}7{li} in the ejecta of classical novae, occurring on the surface of carbon-oxygen (co) and oxygen-neon-magnesium (onemg) white dwarfs (wds). taking the masses and the mass accretion rates of wds as input parameters, this article presents a grid showing the yield of {}7{li} from classical novae, including a total of 79 models. under similar input parameters, the {}7{li} yields in our models are consistent with previous ones in the literature. {}7{li} yields recently inferred spectroscopically from classical nova v1369 cen are then compared with the theoretical values obtained in this work. using the grid as its basis and population synthesis as its method, this paper estimates the amount of {}7{li} produced by classical novae compared to the total {}7{li} in the galaxy. our simulations suggest that novae can eject about {10}-9{{m}}⊙of {}7{li} every year. hence, one may estimate that approximately 10% of {}7{li} in the galaxy originates from classical novae, which is significantly higher than the {}7{li} produced by asymptotic giant branch stars. | novae contribution to the galactic lithium enhancement |
we investigate the resolved kiloparsec-scale stellar and nebular dust distribution in eight star-forming galaxies at z ∼ 0.4 in the great observatories origins deep survey fields. this is to get a better understanding of the effect of dust attenuation on measurements of physical properties and its variation with redshift. constructing the observed spectral energy distributions (seds) per pixel, based on seven bands of photometric data from hubble space telescope/advanced camera for surveys and wfc3, we performed pixel-by-pixel sed fits to population synthesis models and estimated the small-scale distribution of stellar dust extinction. we use hα/hβ nebular emission line ratios from keck/deimos high-resolution spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the centers of galaxies. we find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. the ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate (sfr). we find that inclination plays an important role in the variation of the nebular to stellar excess ratio. the stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. however, for lower mass galaxies, a similar trend is not found for the nebular color excess. we find that the nebular color excess increases with stellar mass surface density. this explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. using standard conversions of sfr surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust-to-gas ratio in regions with high gas mass surface densities over the scales probed in this study. | nebular and stellar dust extinction across the disk of emission-line galaxies on kiloparsec scales |
modified gravity (mog) and non-local gravity (nlg) are two alternative theories to general relativity. they are able to explain the rotation curves of spiral galaxies and clusters of galaxies without including dark matter. in the weak-field approximation, these two theories have similar forms, with an effective gravitational potential that has two components: (i) newtonian gravity with the gravitational constant enhanced by a factor (1 + α) and (ii) a yukawa-type potential that produces a repulsive force with length-scale 1/μ. in this work, we compare the rotation curves of dwarf galaxies in the little things catalogue with predictions of mog, nlg and modified newtonian dynamics (mond). we find that the universal parameters of the mog and nlg theories can fit the rotation curves of dwarf galaxies only at the expense of systematically high stellar mass-to-light ratios at 3.6 μm. for instance, in mog, half of the galaxies have best-fitting stellar m/l ratios larger than 10. it seems that such a big stellar mass-to-light ratio is in contradiction with observations of nearby stars in the milky way and with stellar population synthesis models; however, the stellar mass-to-light ratio of dwarf galaxies is not observed directly by the astrophysical methods. future observations of binary stars in the dwarf galaxies will identify m/l and consequently examine different modified gravity models. | testing mog, non-local gravity and mond with rotation curves of dwarf galaxies |
in a series of recent papers, it has been proposed that high-field magnetic white dwarfs are the result of close binary interaction and merging. population synthesis calculations have shown that the origin of isolated highly magnetic white dwarfs is consistent with the stellar merging hypothesis. in this picture, the observed fields are caused by an α-ω dynamo driven by differential rotation. the strongest fields arise when the differential rotation equals the critical break up velocity and result from the merging of two stars (one of which has a degenerate core) during common envelope evolution or from the merging of two white dwarfs. we now synthesize a population of binary systems to investigate the hypothesis that the magnetic fields in the magnetic cataclysmic variables also originate during stellar interaction in the common envelope phase. those systems that emerge from common envelope more tightly bound form the cataclysmic variables with the strongest magnetic fields. we vary the common envelope efficiency parameter and compare the results of our population syntheses with observations of magnetic cataclysmic variables. we find that common envelope interaction can explain the observed characteristics of these magnetic systems if the envelope ejection efficiency is low. | origin of magnetic fields in cataclysmic variables |
the effect of the featureless power-law (pl) continuum of an active galactic nucleus (agn) on the estimation of physical properties of galaxies with optical population spectral synthesis (pss) remains largely unknown. with the goal of a quantitative examination of this issue, we fit synthetic galaxy spectra representing a wide range of galaxy star formation histories (sfhs) and including distinct pl contributions of the form fν ∝ ν- α with the pss code starlight to study to which extent various inferred quantities (e.g. stellar mass, mean age, and mean metallicity) match the input. the synthetic spectral energy distributions (seds) computed with our evolutionary spectral synthesis code include an agn pl component with 0.5 ≤ α ≤ 2 and a fractional contribution 0.2 ≤ xagn ≤ 0.8 to the monochromatic flux at 4020 å. at the empirical agn detection threshold xagn ≃ 0.26 that we previously inferred in a pilot study on this subject, our results show that the neglect of a pl component in spectral fitting can lead to an overestimation by 2 dex in stellar mass and by up to 1 and 4 dex in the light- and mass-weighted mean stellar age, respectively, whereas the light- and mass-weighted mean stellar metallicity are underestimated by up to 0.3 and 0.6 dex, respectively. these biases, which become more severe with increasing xagn, are essentially independent of the adopted sfh and show a complex behaviour with evolutionary time and α. other fitting set-ups including either a single pl or multiple pls in the base reveal, on average, much lower unsystematic uncertainties of the order of those typically found when fitting purely stellar seds with stellar templates, however, reaching locally up to 1, 3 and 0.4 dex in mass, age and metallicity, respectively. our results underscore the importance of an accurate modelling of the agn spectral contribution in pss fits as a minimum requirement for the recovery of the physical and evolutionary properties of stellar populations in active galaxies. in particular, this study draws attention to the fact that the neglect of a pl in spectral modelling of these systems may lead to substantial overestimates in stellar mass and age, thereby leading to potentially significant biases in our understanding of the co-evolution of agn with their galaxy hosts. | impact of an agn featureless continuum on estimation of stellar population properties |
we investigated the properties of the stellar populations in the discs of a sample of 10 spiral galaxies. our analysis focused on the galaxy region where the disc contributes more than 95 per cent of total surface brightness in order to minimize the contamination of the bulge and bar. the luminosity-weighted age and metallicity were obtained by fitting the galaxy spectra with a linear combination of stellar population synthesis models, while the total overabundance of α-elements over iron was derived by measuring the line-strength indices. most of the sample discs display a bimodal age distribution and they are characterized by a total [α/fe] enhancement ranging from solar and supersolar. we interpreted the age bimodality as due to the simultaneous presence of both a young (age ≤ 4 gyr) and an old (age > 4 gyr) stellar population. the old stellar component usually dominates the disc surface brightness and its light contribution is almost constant within the observed radial range. for this reason, no age gradient is observed in half of the sample galaxies. the old component is slightly more metal poor than the young one. the metallicity gradient is negative and slightly positive in the old and young components, respectively. these results are in agreement with an inside-out scenario of disc formation and suggest a reduced impact of the radial migration on the stellar populations of the disc. the young component could be the result of a second burst of star formation in gas captured from the environment. | study of the stellar population properties in the discs of ten spiral galaxies |
context. black hole neutron star (bhns) mergers have recently been detected through their gravitational-wave (gw) emission. while no electromagnetic emission has yet been confidently associated with these systems, observing any such emission could provide information on, for example, the neutron star equation of state. black hole neutron star mergers could produce electromagnetic emission as a short gamma-ray burst (sgrb) and/or an sgrb afterglow upon interaction with the circum-merger medium.aims: we make predictions for the expected detection rates with the square kilometre array phase 1 (ska1) of sgrb radio afterglows associated with bhns mergers. we also investigate the benefits of a multi-messenger analysis in inferring the properties of the merging binary.methods: we simulated a population of bhns mergers, making use of recent stellar population synthesis results, and estimated their sgrb afterglow flux to obtain the detection rates with ska1. we investigate how this rate depends on the gw detector sensitivity, the primary black hole spin, and the neutron star equation of state. we then performed a multi-messenger bayesian inference study on a fiducial bhns merger. we simulated its sgrb afterglow and gw emission as input to this study, using recent models for both, and take systematic errors into account.results: the expected rates of a combined gw and radio detection with the current-generation gw detectors are likely low. due to the much increased sensitivity of future gw detectors such as the einstein telescope, the chances of an sgrb localisation and radio detection increase substantially. the unknown distribution of the black hole spin has a big influence on the detection rates, however, and it is a large source of uncertainty. furthermore, when placing our fiducial bhns merger at 50 and 100 mpc, we are able to infer both the binary source parameters and the parameters of the sgrb afterglow simultaneously if we combine the gw and radio data. the radio data provide useful extra information on the binary parameters, such as the mass ratio, but this is limited by the systematic errors involved. for our fiducial binary at 200 mpc, it is considerably more difficult to adequately infer the parameters of the system.conclusions: the probability of finding an sgrb afterglow of a bhns merger is low in the near future but will rise significantly when the next-generation gw detectors come online. combining information from gw data with radio data is crucial for characterising the jet properties. a better understanding of the systematics will further increase the amount of information on the binary parameters that can be extracted from this radio data. data used to plot the images have been uploaded at: http://doi.org/10.5281/zenodo.6573093 | investigating the detection rates and inference of gravitational-wave and radio emission from black hole neutron star mergers |
the metallicity enrichment history (meh) of a galaxy is determined by its star formation history (sfh) and the gas cycling process. in this paper, we construct a chemical evolution model that is regulated by the sfh of the system. in this sfh-regulated model, the evolution of all other variables, including the meh, can be determined by the sfh. we test this model on six locally isolated dwarf galaxies covering three dwarf types that were observed by the local cosmology from isolated dwarfs (lcid) project. the sfhs and mehs of these lcid galaxies are relatively reliable because they have been measured from deep color-magnitude diagrams that reach the main-sequence turnoff stars with good photometric accuracy. with simple assumptions of the star formation law and the mass-dependent outflows, our sfh-regulated model successfully reproduces the mehs of all six lcid galaxies from their sfhs, with only one free parameter, the wind efficiency η ~ 1.0, for all six galaxies. this model provides a physically motivated link that directly connects the sfh and meh of a galaxy, which will be useful to accommodate into the state-of-the-art stellar population synthesis models to help relieve the nuisance of the heavy degeneracy between the ages and metallicities of the stellar populations. | linking the metallicity enrichment history to the star formation history: an sfh-regulated chemical evolution model and its implications for the gas cycling process |
binary neutron star mergers (nsms) have been confirmed as one source of the heaviest observable elements made by the rapid neutron-capture (r-) process. however, modeling nsm outflows-from the total ejecta masses to their elemental yields-depends on the unknown nuclear equation of state (eos) that governs neutron star structure. in this work, we derive a phenomenological eos by assuming that nsms are the dominant sources of the heavy element material in metal-poor stars with r-process abundance patterns. we start with a population synthesis model to obtain a population of merging neutron star binaries and calculate their eos-dependent elemental yields. under the assumption that these mergers were responsible for the majority of r-process elements in the metal-poor stars, we find parameters representing the eos for which the theoretical nsm yields reproduce the derived abundances from observations of metal-poor stars. for our proof-of-concept assumptions, we find an eos that is slightly softer than, but still in agreement with, current constraints, e.g., by the neutron star interior composition explorer, with r 1.4 = 12.25 ± 0.03 km and m tov = 2.17 ± 0.03 m ⊙ (statistical uncertainties, neglecting modeling systematics). | a nuclear equation of state inferred from stellar r-process abundances |
superthin galaxies (sts) are edge-on disc galaxies with strikingly high planar-to-vertical axes ratios of ~10-20 with no bulge component, and central surface brightness in the b band > 23 mag arcsec-2 comparable to low-surface-brightness galaxies (lsbs). although sts and lsbs have similar dynamical, stellar, and atomic hydrogen (h i) masses on an average, it is tricky to conclude if they constitute the same galaxy population, given the edge-on and face-on orientations of the sts and the lsbs, respectively. we systematically study star formation rate (sfr) in a sample of sts and lsbs using sed fitting of photometric data in 10 bands including galex: fuv, nuv, sdss: u,g,r,i,z and 2mass: j, h, ks using stellar population synthesis models employing the publicly available software magphys (multi-wavelength analysis of galaxy physical properties). the estimated median sfrs for lsbs and sts are $0.4^{+2.2}_{-0.3}$$ and $0.2^{+0.9}_{-0.2}\, {\rm m}_{\odot }{\rm yr}^{-1}$, respectively. our calculations indicate that this deficit in the sfr of an st can be attributed to inclination and opacity effects. therefore, we conclude that sts and lsbs have equal intrinsic sfr over and above other physical properties, which possibly implies that sts are just lsbs seen in edge-on. | are superthin galaxies low-surface-brightness galaxies seen edge-on? the star formation probe |
massive early-type galaxies (etgs) in the local universe are believed to be the most mature stage of galaxy evolution. their stellar population content reveals the evolutionary history of these galaxies. however, while state-of-the-art stellar population synthesis (sps) models provide an accurate description of observed galaxy spectra in the optical range, the modelling in the near-infrared (nir) is still in its infancy. here, we focus on nir co absorption features to show, in a systematic and comprehensive manner, that for massive etgs, all co indices, from h through to k band, are significantly stronger than currently predicted by sps models. we explore and discuss several possible explanations of this 'co mismatch', including the effect of intermediate-age, asymptotic-giant-branch-dominated, stellar populations, high-metallicity populations, non-solar abundance ratios, and the initial mass function. while none of these effects is able to reconcile models and observations, we show that ad hoc 'empirical' corrections, taking into account the effect of co-strong giant stars in the low-temperature regime, provide model predictions that are closer to the observations. our analysis points to the effect of carbon abundance as the most likely explanation of nir co line-strengths, indicating possible routes for improving the sps models in the nir. | strong co absorption features in massive etgs |
context. wolf-rayet (wr) stars of the wnh category contain a significant fraction of hydrogen at their surface. they can be hydrogen-burning, very massive stars or stars in a post-main sequence phase of evolution. also, wnh stars are sometimes not included in population synthesis models.aims: we aim to better characterise the properties of single wnh stars in the galaxy and the magellanic clouds. in particular, we want to constrain their surface chemistry beyond the hydrogen content by determining the helium, carbon, and nitrogen surface abundances.methods: we perform a spectroscopic analysis of 22 single wnh stars. we fit their ultraviolet and/or optical spectra using synthetic spectra computed with the code cmfgen. we determine the main stellar parameters (temperature, luminosity, mass-loss rates) and the surface h, he, c, and n mass fractions. we investigate the ability of current evolutionary models to reproduce all parameters at the same time.results: we find that all wnh stars show the signatures of cno-cycle material at their surface: they are carbon-depleted and nitrogen-rich. a clear trend of higher nitrogen content at higher metallicity is observed, as expected. the amount of hydrogen (x) varies significantly from one star to another, independently of luminosity. values of x larger than 0.4 are not exceptional. the majority of galactic wnh stars can be explained by evolutionary models, provided sufficient fine-tuning of the input parameters of evolutionary calculations. at lower metallicity, most stars escape predictions from evolutionary models. this has been noted in the literature but constraints on the surface nitrogen content exacerbate this severe issue.conclusions: our study highlights the need to refine the treatment of wr stars in both stellar evolution and population synthesis models. | surface chemical composition of single wnh stars |
context. although type ia supernovae (sne ia) play a key role in astrophysics, the companions of the exploding carbon-oxygen white dwarfs (co wds) are still not completely identified. it has been suggested recently that a he-rich wd (a he wd or a hybrid heco wd) that merges with a co wd may produce an sn ia. this theory was based on the double-detonation model, in which the shock compression in the co core caused by the surface explosion of the he-rich shell might lead to the explosion of the whole co wd. however, so far, very few binary population synthesis (bps) studies have been made on the merger scenario of a co wd and a he-rich wd in the context of sne ia.aims: we aim to systematically study the galactic birthrates and delay-time distributions of sne ia based on the merger scenario of a co wd and a he-rich wd.methods: we performed a series of monte carlo bps simulations to investigate the properties of sne ia from the merging of a co wd and a he-rich wd based on the hurley rapid binary evolution code. we also considered the influence of different metallicities on the final results.results: from our simulations, we found that no more than 15% of all sne ia stem from the merger scenario of a co wd and a he-rich wd, and their delay times range from 110 myr to the hubble time. this scenario mainly contributes to sn ia explosions with intermediate and long delay times. the present work indicates that the merger scenario of a co wd and a he-rich wd can roughly reproduce the birthrates of sn 1991bg-like events, and cover the range of their delay times. we also found that sn ia birthrates from this scenario would be higher for the cases with low metallicities. | merging of a co wd and a he-rich wd to produce a type ia supernovae |
the lack of a strong correlation between agn x-ray luminosity (lx; a proxy for agn power) and the star formation rate (sfr) of their host galaxies has recently been attributed to stochastic agn variability. studies using population synthesis models have incorporated this by assuming a broad, universal (i.e. does not depend on the host galaxy properties) probability distribution for agn specific x-ray luminosities (i.e. the ratio of lx to host stellar mass; a common proxy for eddington ratio). however, recent studies have demonstrated that this universal eddington ratio distribution fails to reproduce the observed x-ray luminosity functions beyond z ∼ 1.2. furthermore, empirical studies have recently shown that the eddington ratio distribution may instead depend upon host galaxy properties, such as sfr and/or stellar mass. to investigate this further, we develop a population synthesis model in which the eddington ratio distribution is different for star-forming and quiescent host galaxies. we show that, although this model is able to reproduce the observed x-ray luminosity functions out to z ∼ 2, it fails to simultaneously reproduce the observed flat relationship between sfr and x-ray luminosity. we can solve this, however, by incorporating a mass dependency in the agn eddington ratio distribution for star-forming host galaxies. overall, our models indicate that a relative suppression of low eddington ratios (λedd ≲ 0.1) in lower mass galaxies (m* ≲ 1010 - 11 m⊙) is required to reproduce both the observed x-ray luminosity functions and the observed flat sfr/x-ray relationship. | evidence for a mass-dependent agn eddington ratio distribution via the flat relationship between sfr and agn luminosity |
fast (fitting and assessment of synthetic templates) fits stellar population synthesis templates to broadband photometry and/or spectra. fast is compatible with the photometric redshift code eazy (ascl:1010.052) when fitting broadband photometry; it uses the photometric redshifts derived by eazy, and the input files (for examply, photometric catalog and master filter file) are the same. fast fits spectra in combination with broadband photometric data points or simultaneously fits two components, allowing for an agn contribution in addition to the host galaxy light. depending on the input parameters, fast outputs the best-fit redshift, age, dust content, star formation timescale, metallicity, stellar mass, star formation rate (sfr), and their confidence intervals. though some of fast's functions overlap with those of hyperz (ascl:1108.010), it differs by fitting fluxes instead of magnitudes, allows the user to completely define the grid of input stellar population parameters and easily input photometric redshifts and their confidence intervals, and calculates calibrated confidence intervals for all parameters. note that fast is not a photometric redshift code, though it can be used as one. | fast: fitting and assessment of synthetic templates |
we perform binary evolution calculations on helium star—carbon-oxygen white dwarf (co wd) binaries, using the stellar evolution code mesa. this single degenerate channel may contribute significantly to thermonuclear supernovae at short delay times. we examine the thermal-timescale mass transfer from a 1.1 to 2.0 {m}⊙helium star to a 0.90-1.05 {m}⊙co wd for initial orbital periods in the range 0.05-1 day. systems in this range may produce a thermonuclear supernova, helium novae, a helium star—oxygen-neon wd binary, or a detached double co wd binary. our time-dependent calculations that resolve the stellar structures of both binary components allow accurate distinction between the eventual formation of a thermonuclear supernova (via central ignition of carbon burning) and that of an one wd (in the case of off-center ignition). furthermore, we investigate the effect of a slow wd wind, which implies a specific angular momentum loss from the binary that is larger than typically assumed. we find that this does not significantly alter the region of parameter space over which systems evolve toward thermonuclear supernovae. our determination of the correspondence between initial binary parameters and the final outcome informs population synthesis studies of the contribution of the helium donor channel to thermonuclear supernovae. in addition, we constrain the orbital properties and observable stellar properties of the progenitor binaries of thermonuclear supernovae and helium novae. | evolution of helium star-white dwarf binaries leading up to thermonuclear supernovae |
subdwarf a-type stars (sdas) are objects that have hydrogen-rich spectra with surface gravity similar to that of hot subdwarf stars but effective temperature below the zero-age horizontal branch. they are considered to be metal-poor main-sequence (ms) stars or extremely low-mass white dwarfs (elm wds). in this work, using the stellar evolution code modules for experiments in stellar astrophysics, we investigate the sdas formed both by the evolution of (pre-)elm wds in double-degenerate systems and metal-poor ms stars with single evolution models. we find that both of the evolutionary tracks of elm wds and metal-poor ms stars can explain the observation properties of sdas. however, the proportions between these two populations are uncertain. in this work, we adopt the method of binary population synthesis of both elm wds in the disk and metal-poor ms stars in the halo to obtain their populations at different stellar population ages and calculate their proportions. we find that the proportion of metal-poor ms stars to sdas for a stellar population of 10 gyr is ∼98.5%, which is consistent with the conclusion that most sdas (>95%) are metal-poor ms stars. and the proportion of elm wds (metal-poor ms stars) to sdas increases (decreases) from 0.1% (99.9%) to 20% (80%) with stellar population ages from 5 to 13.7 gyr. | the formation of subdwarf a-type stars |
novae are some of the most commonly detected optical transients and have the potential to provide valuable information about binary evolution. binary population synthesis codes have emerged as the most effective tool for modelling populations of binary systems, but such codes have traditionally employed greatly simplified nova physics, precluding detailed study. in this work, we implement a model treating h and he novae as individual events into the binary population synthesis code binary_c. this treatment of novae represents a significant improvement on the 'averaging' treatment currently employed in modern population synthesis codes. we discuss the evolutionary pathways leading to these phenomena and present nova event rates and distributions of several important physical parameters. most novae are produced on massive white dwarfs, with approximately 70 and 55 per cent of nova events occurring on o/ne white dwarfs for h and he novae, respectively. only 15 per cent of h-nova systems undergo a common-envelope phase, but these systems are responsible for the majority of h nova events. all he-accreting he-nova systems are considered post-common-envelope systems, and almost all will merge with their donor star in a gravitational-wave-driven inspiral. we estimate the current annual rate of novae in m31 (andromeda) to be approximately 41 ± 4 for h novae, underpredicting the current observational estimate of $65^{+15}_{-16}$, and 0.14 ± 0.015 for he novae. when varying common-envelope parameters, the h nova rate varies between 20 and 80 events per year. | population synthesis of accreting white dwarfs: rates and evolutionary pathways of h and he novae |
accurately determining the age of h ii regions and the stars they host is as important as it is challenging. historically, the most popular method has been isochrone fitting to hertzsprung-russell diagrams or colour-magnitude diagrams. here, we introduce a different method for age determination using bpass (binary population and spectral synthesis) and hoki . we infer the most likely ages of the regions d118 and d119 ngc 300 to be log(age/yr) = $6.86^{+0.05}_{-0.06}$ and we also deduce stellar mass and number counts by comparison with the bpass models. we compare how our binary and single-star models perform and find that the latter are unable to predict 20 per cent (±10 per cent) of our sample. we also discuss how results obtained from isochrone fitting would differ. we conclude that ages could be underestimated by ∼0.2 dex and that the limitations of the isochrone method is not solely due to the lack of binary stars. we propose that the method presented here is more reliable and more widely applicable since it can be used on smaller samples. alongside this study, we release new hoki features to allow easy implementation of this method. | a systematic ageing method i: h ii regions d118 and d119 in ngc 300 |
the equator of star k2-290a was recently found to be inclined by 124° ± 6° relative to the orbits of both its known transiting planets. the presence of a companion star b at ~100 au suggested that the birth protoplanetary disk could have tilted, thus providing an explanation for the peculiar retrograde state of this multi-planet system. in this work, we show that a primordial misalignment is not required and that the observed retrograde state is a natural consequence of the chaotic stellar obliquity evolution driven by a wider-orbit companion c at ≳2000 au long after the disk disperses. the star c drives eccentricity and/or inclination oscillations on the inner binary orbit, leading to widespread chaos from the periodic resonance passages between the stellar spin and planetary secular modes. based on a population synthesis study, we find that the observed stellar obliquity is reached in ~40%-70% of the systems, making this mechanism a robust outcome of the secular dynamics, regardless of the spin-down history of the central star. this work highlights the unusual role that very distant companions can have on the orbits of close-in planets and the host star's spin evolution, connecting four orders of magnitude in distance scale over billions of orbits. we finally comment on the application to other exoplanet systems, including multi-planet systems in wide binaries. | the chaotic history of the retrograde multi-planet system in k2-290a driven by distant stars |
two blue-straggler sequences discovered in globular cluster m30 provide a strong constraint on the formation mechanisms of blue stragglers. we study the formation of blue-straggler binaries through binary evolution, and find that binary evolution can contribute to the blue stragglers in both of the sequences. whether a blue-straggler is located in the blue sequence or red sequence depends on the contribution of the mass donor to the total luminosity of the binary, which is generally observed as a single star in globular clusters. the blue stragglers in the blue sequence have a cool white dwarf companion, while the majority (∼60%) of the objects in the red sequence are binaries that are still experiencing mass transfer. however, there are also some objects for which the donors have just finished the mass transfer (the stripped-core stars, ∼10%) or the blue stragglers (the accretors) have evolved away from the blue sequence (∼30%). meanwhile, w uma contact binaries found in both sequences may be explained by various mass ratios, that is, w uma contact binaries in the red sequence have two components with comparable masses (e.g., mass ratio q ∼ 0.3-1.0), while those in the blue sequence have low mass ratios (e.g., q< 0.3). however, the fraction of the blue sequence in m30 cannot be reproduced by binary population synthesis if we assumed the initial parameters of a binary sample to be the same as those of the field. this possibly indicates that dynamical effects on binary systems are very important in globular clusters. | contribution of primordial binary evolution to the two blue-straggler sequences in globular cluster m30 |
core accretion (ca), the de-facto accepted theory of planet formation, requires formation of massive solid cores as a prerequisite for assembly of gas giant planets. the observed metallicity correlations of exoplanets are puzzling in the context of ca. while gas giant planets are found preferentially around metal-rich host stars, planets smaller than neptune orbit hosts with a wide range of metallicities. we propose an alternative interpretation of these observations in the framework of a recently developed planet formation hypothesis called tidal downsizing (td). we perform population synthesis calculations based on td, and find that the connection between the populations of the gas giant and the smaller solid-core dominated planets is non linear and not even monotonic. while gas giant planets formed in the simulations in the inner few au region follow a strong positive correlation with the host star metallicity, the smaller planets do not. the simulated population of these smaller planets shows a shallow peak in their formation efficiency at around the solar metallicity. this result is driven by the fact that at low metallicities the solid core's growth is damped by the scarcity of metals, whereas at high metallicities the fragments within which the cores grow contract too quickly, cutting the core's growth time window short. finally, simulated giant gas planets do not show a strong host star metallicity preference at large separations, which may explain why one of the best known directly imaged gas giant planet systems, hr 8799, is metal poor. | tidal downsizing model. ii. planet-metallicity correlations |
the first version of the binary population synthesizer (bipos1) is made publicly available. it allows to efficiently calculate binary distribution functions after the dynamical processing of a realistic population of binary stars during the first few myr in the hosting embedded star cluster. instead of time-consuming n-body simulations, bipos1 uses the stellar dynamical operator $\omega _{\rm dyn}^{\rho _{\rm ecl}}(\log _{10}(e_{\rm b}),t)$, which determines the fraction of surviving binaries depending on the binding energy of the binaries, eb. the ω-operator depends on the initial star cluster density, ρecl, as well as the time, t, until the residual gas of the star cluster is expelled. bipos1 has also a galactic-field mode, in order to synthesize the stellar population of a whole galaxy. at the time of gas expulsion, the dynamical processing of the binary population is assumed to efficiently end due to the subsequent expansion of the star cluster. while bipos1 has been used previously unpublished, here we demonstrate its use in the modelling of the binary populations in the orion nebula cluster, in ob associations and as an input for simulations of globular clusters. | bipos1 - a computer programme for the dynamical processing of the initial binary star population |
accurate detection of the cosmological 21 cm global signal requires galactic foreground models that can remove power over 106. although foreground and global signal models unavoidably exhibit overlap in their vector spaces inducing bias error in the extracted signal, a second source of bias and error arises from inadequate foreground models, i.e., models that cannot fit spectra down to the noise level of the signal. we therefore test the level to which seven commonly employed foreground models-including nonlinear and linear forward models, polynomials, and maximally smooth polynomials-fit realistic simulated mock foreground spectra, as well as their dependence upon model inputs. the mock spectra are synthesized for an edges-like experiment and we compare all models' goodness of fit and preference using a kolmogorov-smirnov (k-s) test of the noise-normalized residuals in order to compare models with differing, and sometimes indeterminable, degrees of freedom. for a single local sidereal time (lst) bin spectrum and p-value threshold of p = 0.05, the nonlinear forward model with four parameters is preferred (p = 0.99), while the linear forward model fits well with six to seven parameters (p = 0.94, 0.97, respectively). the polynomials and maximally smooth polynomials, like those employed by the edges and saras3 experiments, cannot produce good fits with five parameters for the experimental simulations in this work (p < 10-6). however, we find that polynomials with six parameters pass the k-s test (p = 0.4), although a nine-parameter fit produces the highest p-value (p ~ 0.67). when fitting multiple lst bins simultaneously, we find that the linear forward model outperforms (a higher p-value) the nonlinear model for 2, 5, and 10 lst bins. importantly, the k-s test consistently identifies best-fit and preferred models. | fitting and comparing galactic foreground models for unbiased 21 cm cosmology |
by a method of population synthesis we construct a model of dark matter (dm) accretion onto binary black holes (bhs) and investigate the merger rate of the binary bhs. we find that the merger rate can weakly increase (less than 10%). however, the dm accretion can efficiently enhance the masses of binary bhs. in our model, the result for z = 0.01 without the dm accretion cannot explain gw170104, gw170814, and gw150914, while with the dm accretion it can cover all observations well. for the higher metallicity (z = 0.02), our model cannot explain the mergers of high-mass binary bhs like gw170104, gw170814, and gw150914. we estimate that the merger rate of binary bhs lies between 55 and 197 gpc-3 yr-1. | an alternative channel for high-mass binary black holes—dark matter accretion onto black holes |
we develop a theoretical framework that extracts a deeper understanding of galaxy formation from empirically derived relations among galaxy properties by extending the main-sequence integration method for computing galaxy star formation histories. we properly account for scatter in the stellar mass-star formation rate relation and the evolving fraction of passive systems and find that the latter effect is almost solely responsible for the age distributions among z ∼ 0 galaxies with stellar masses above ∼1010 m⊙. however, while we qualitatively agree with the observed median stellar metallicity as a function of stellar mass, we attribute our inability to reproduce the distribution in detail largely to a combination of imperfect gas-phase metallicity and α/fe ratio calibrations. our formalism will benefit from new observational constraints and, in turn, improve interpretations of future data by providing self-consistent star formation histories for population synthesis modelling. | a framework for empirical galaxy phenomenology: the scatter in galaxy ages and stellar metallicities |
we seek to improve the accuracy of joint galaxy photometric redshift estimation and spectral energy distribution (sed) fitting. by simulating different sources of uncorrected systematic errors, we demonstrate that if the uncertainties in the photometric redshifts are estimated correctly, so are those on the other sed fitting parameters, such as stellar mass, stellar age, and dust reddening. furthermore, we find that if the redshift uncertainties are over(under)-estimated, the uncertainties in sed parameters tend to be over(under)-estimated by similar amounts. these results hold even in the presence of severe systematics and provide, for the first time, a mechanism to validate the uncertainties on these parameters via comparison with spectroscopic redshifts. we propose a new technique (annealing) to re-calibrate the joint uncertainties in the photo-z and sed fitting parameters without compromising the performance of the sed fitting + photo-z estimation. this procedure provides a consistent estimation of the multi-dimensional probability distribution function in sed fitting + z parameter space, including all correlations. while the performance of joint sed fitting and photo-z estimation might be hindered by template incompleteness, we demonstrate that the latter is “flagged” by a large fraction of outliers in redshift, and that significant improvements can be achieved by using flexible stellar populations synthesis models and more realistic star formation histories. in all cases, we find that the median stellar age is better recovered than the time elapsed from the onset of star formation. finally, we show that using a photometric redshift code such as eazy to obtain redshift probability distributions that are then used as priors for sed fitting codes leads to only a modest bias in the sed fitting parameters and is thus a viable alternative to the simultaneous estimation of sed parameters and photometric redshifts. | simultaneous estimation of photometric redshifts and sed parameters: improved techniques and a realistic error budget |
a grid of 20 millions 3-1100 μm spectral energy distribution (sed) models is presented for synthetic young clusters embedded in dense clumps. the models depend on four primary parameters: the clump mass mclump and dust temperature tdust, the fraction of mass fcore locked in dense cores, and the age of the clump tsf. we populate the young stellar object (yso) clusters using the kroupa initial mass function and the ysos sed models grid of robitaille et al. we conduct extensive testing of sed fitting using a simulated data set and we find that mclump essentially depends on the submillimetre portion of the sed, while tdust is mostly determined from the shape of the sed in the 70-350 μm range. thanks to the large number of models computed, we verify that the combined analysis of l/m, [8-24] and [24-70] colours removes much of the seds fcore-tsf degeneracy. the l/m values are particularly useful to diagnose fcore. l/m ≤ 1 identifies protoclusters with fcore ≤ 0.1 and tsf \lower.6ex{∼ }\raise.65ex< 10^5 yr, while l/m \lower.6ex{∼ }\raise.65ex> 10 excludes fcore ≤ 0.1. we characterize lower limits of l/m where zero-age main sequence (zams) stars are not found in models, and we also find models with l/m ≥10 and no zams stars, in which [8-24] \lower.6ex{∼ }\raise.65ex> 0.8± 0.1 independently from mclump, temperature, and luminosity. this is the first set of synthesis sed models suited to model for embedded and unresolved clusters of ysos. a set of new evolutionary tracks in the l/m diagram is also presented. | evolution of young protoclusters embedded in dense massive clumps. a new grid of population synthesis sed models and a new set of l/m evolutionary tracks |
we map optical and near-infrared (nir) stellar population properties of the inner 320 × 535 pc2 of the elliptical galaxy ngc 1052. the optical and nir spectra were obtained using the gemini integral field units of the gmos instrument and nifs, respectively. by performing stellar population synthesis in the optical alone, we find that this region of the galaxy is dominated by old (t > 10 gyr) stellar populations. using the nir, we find the nucleus to be dominated by old stellar populations, and a circumnuclear ring with younger (∼2.5 gyr) stars. we also combined the optical and nir datacubes and performed a panchromatic spatially resolved stellar population synthesis, which resulted in a dominance of older stellar populations, in agreement with optical results. we argue that the technique of combining optical and nir data might be useful to isolate the contribution of stellar population ages with strong nir absorption bands. we also derive the stellar kinematics and find that the stellar motions are dominated by a high (∼240 km s-1) velocity dispersion in the nucleus, with stars also rotating around the centre. lastly, we measure the absorption bands, both in the optical and in the nir, and find a nuclear drop in their equivalent widths. the favoured explanation for this drop is a featureless continuum emission from the low luminosity active galactic nucleus. | a panchromatic spatially resolved study of the inner 500 pc of ngc 1052 - i. stellar population |
a large fraction of massive stars evolve in interacting binary systems, which dramatically modifies the outcome of stellar evolution. we investigated the properties of blue supergiants in binary systems and whether they are suitable for extragalactic distance determinations using the flux-weighted gravity luminosity relationship (fglr). this is a relationship between the absolute bolometric magnitude mbol and the spectroscopically determined flux-weighted gravity gf = g/t4eff, where g is the surface gravity and teff is the effective temperature. we computed a grid of binary stellar evolution models with mesa and use the v2.1 bpass models to examine whether they are compatible with the relatively small scatter shown by the observed relationship. our models have initial primary masses of 9-30 m⊙, initial orbital periods of 10-2511 days, mass ratio q = 0.9, and metallicity z = 0.02. we find that the majority of primary stars that produce blue supergiant stages are consistent with the observed fglr, with a small offset towards brighter bolometric magnitudes. in between 1%-24% of cases, binary evolution may produce blue supergiants after a mass transfer episode, that lie below the observed fglr. a very small number of such stars have been found in extragalactic fglr studies, suggesting that they may have evolved through binary interaction. some models with shorter periods could resemble blue hypergiants and luminous blue variables. we used cmfgen radiative transfer models to investigate the effects of unresolved secondaries on diagnostics for teff and g, and the biases on the determination of interstellar reddening and mbol. we find that the effects are small and within the observed scatter, but could lead to a small overestimate of the luminosity, of teff and of g for extreme cases. we conclude that the observed fglr can, in principle, be well reproduced by close binary evolution models. we outline directions for future work, including rotation and binary population synthesis techniques. | impact of binary interaction on the evolution of blue supergiants. the flux-weighted gravity luminosity relationship and extragalactic distance determinations |
we construct a new catalog of extragalactic x-ray binaries (xrbs) by matching the latest chandra source catalog with local galaxy catalogs. our xrb catalog contains 4430 xrbs hosted by 237 galaxies within ~130 mpc. as xrbs dominate the x-ray activity in galaxies, the catalog enables us to study the correlations between the total x-ray luminosity of a galaxy lx,tot, star formation rate $\dot{\rho }_\star$, and stellar mass m⋆. as previously reported, lx,tot is correlated with $\dot{\rho }_\star$ and m⋆. in particular, we find that there is a fundamental plane in those three parameters; $\log l_{\rm x,tot}={38.80^{+0.09}_{-0.12}}+\log (\dot{\rho }_\star + \alpha m_\star )$, where α = (3.36 ± 1.40) × 10-11 yr-1. in order to investigate this relation, we construct a phenomenological binary population synthesis model. we find that the high-mass xrb and low-mass xrb fraction in formed compact object binary systems is $\sim\! 9\%$ and ${0.04}\%$, respectively. utilizing the latest xmm-newton and swift x-ray source catalog data sets, additional xrb candidates are also found, resulting in a total of 5757 xrbs hosted by 311 galaxies. | a fundamental plane in x-ray binary activity of external galaxies |
we explore the relation between the dynamical mass-to-light ratio (m/l) and rest-frame color of massive quiescent galaxies out to z ~ 2. we use a galaxy sample with measured stellar velocity dispersions in combination with hubble space telescope and ground-based multi-band photometry. our sample spans a large range in log m dyn/l g (of 1.6 dex) and log m dyn/l k (of 1.3 dex). there is a strong, approximately linear correlation between the m/l for different wavebands and rest-frame color. the root-mean-square scatter in log m dyn/l residuals implies that it is possible to estimate the m/l with an accuracy of ~0.25 dex from a single rest-frame optical color. stellar population synthesis (sps) models with a salpeter stellar initial mass function (imf) cannot simultaneously match m dyn/l g versus (g - z)rest-frame and m dyn/l k versus (g - k)rest-frame. by changing the slope of the imf we are still unable to explain the m/l of the bluest and reddest galaxies. we find that an imf with a slope between α = 2.35 and α = 1.35 provides the best match. we also explore a broken imf with a salpeter slope at m < 1 m ⊙ and m > 4 m ⊙ and a slope α in the intermediate region. the data favor a slope of α = 1.35 over α = 2.35. nonetheless, our results show that variations between different sps models are comparable to the imf variations. in our analysis we assume that the variation in m/l and color is driven by differences in age, and that other contributions (e.g., metallicity evolution, dark matter) are small. these assumptions may be an important source of uncertainty as galaxies evolve in more complex ways. | the relation between dynamical mass-to-light ratio and color for massive quiescent galaxies out to z ~ 2 and comparison with stellar population synthesis models |
we present a pilot study on the nearby massive barred galaxy ngc 1291, in which we use dynamical modelling to constrain the disc mass-to-light ratio (m/l), thus breaking the degeneracy between the baryonic and dark matter in its central regions. we use the gas, specifically the morphology of the dust lanes on the leading side of the bar, as a tracer of the underlying gravitational potential. we run a large number of hydrodynamic gas response simulations, in potentials obtained directly from near-infrared images of the galaxy, which have three free parameters: the m/l, the bar pattern speed and the height function. we explore the three-dimensional parameter space, by comparing the morphology of the shocks created in the gas response simulations with those of the observed dust lanes, and find the best-fitting models; these suggest that the m/l of ngc 1291 agrees with that predicted by stellar population synthesis models in the near-infrared (≈0.6 m⊙/l⊙), which leads to a borderline maximum disc for this galaxy. furthermore, we find that the bar rotates fast, with a corotation radius that is ≤1.4 times the bar length. | constraining the dark matter content of ngc 1291 using hydrodynamic gas response simulations |
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