abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
a combination of nuv and optical imaging of m82, the nearest star-bursting galaxy, allows us to probe the properties of the dust, both in the interstellar medium of the galaxy, as well as the dust entrained in the extraplanar gas blown by the super wind. we compare the photometric observations with sets of population synthesis models to derive the characteristics of the illumination source, and compare the results with simple dust models, leading us to conclude that the dust entrained in the extraplanar region is made up of small grains. in the galaxy, the extinction law reveals a strong presence of an nuv bump at 2175a, at odds with the standard extinction law for star-forming systems. we compare our results with the recent analyses of the dust in the region around sn2014j (hosted by m82). | a panchromatic view of m82: dust properties |
we compute libraries of stellar + nebular spectra of populations of coeval stars with ages of <100 myr and metallicities of z=0.001 to 0.040, using different sets of massive-star evolution tracks, i.e., new padova tracks for single non-rotating stars, the geneva tracks for single non-rotating and rotating stars, and the auckland tracks for single non-rotating and binary stars. for the stellar component, we use population synthesis codes galaxev, starburst99, and bpass, depending on the set of tracks. for the nebular component we use photoionization code cloudy. from these spectra, we obtain magnitudes in filters f275w, f336w, f438w, f547m, f555w, f657n, and f814w of the hubble space telescope (hst) wide field camera three. we use i) our computed magnitudes, ii) new multi-band photometry of massive-star clusters in nearby (<11 mpc) galaxies spanning the metallicity range 12+log(o/h)=7.2-9.2, observed as part of hst programs 13364 (pi calzetti) and 13773 (pi chandar), and iii) bayesian inference to a) establish how well the different models are able to constrain the metallicities, extinctions, ages, and masses of the star clusters, b) quantify differences in the cluster properties obtained with the different models, and c) assess how properties of lower-mass clusters are affected by the stochastic sampling of the imf. in our models, the stellar evolution tracks, stellar atmospheres, and nebulae have similar chemical compositions. different metallicities are available with different sets of tracks and we compare results from models of similar metallicities. our results have implications for studies of the formation and evolution of star clusters, the cluster age and mass functions, and the star formation histories of galaxies. | photometrically-derived properties of massive-star clusters obtained with different massive-star evolution tracks and deterministic models |
massive luminous red galaxies (lrgs) are believed to be evolving passively and can be used as cosmic chronometers to estimate the hubble constant (the differential age method). however, different lrgs may locate in different environments and the environment effects may affect the accuracies of the measurements of both the mean ages of lrgs and the ages of the oldest lrgs at different redshift, and thus may limit the use of the lrgs as cosmic chronometers. in this paper, we investigate the environment and mass dependence of the formation of ``quiescent'' lrgs selected from the sloan digital sky survey date release 8. using the population synthesis software starlight, we derive the stellar populations in each lrg through the full spectrum fitting and obtain the mean age distribution and mean star formation history of those lrgs. we find that there is no apparent dependence of the mean age and star formation history (sfh) of quiescent lrgs on their environment, while the ages of those quiescent lrgs weakly depend on their mass. the mean star formation rate for those lrgs in the past 6 gyr is less than a few percent in stellar mass per gyr. we also compare the sfhs of the sdss lrgs with those given by a semi-analytical galaxy formation model, and find that they are consistent with each other if considering the systematic errors in the lrg age estimates obtained via the the full spectrum fitting by the starlight. we find that the later star formation of lrgs can lead to a systematical overestimation (~28%) of the hubble constant obtained from the differential age method, and the systematical errors in the age estimates can lead to a underestimation (~16%) of the hubble constant. however, these errors may be corrected by a detailed study of the mean star formation history of those lrgs and the systematic errors in the age estimates by calibration with other independently estimated ones. our results pave the way for using the lrgs as cosmic chronometers and suggest that an accurate estimation of the hubble constant on the percentage level can be obtained through the differential age method. | ``quiescent'' luminous red galaxies (lrgs) as cosmic chronometers: on the significance of the mass and environmental dependence of lrgs |
ultra-luminous x-ray sources are among the most extreme phases of binary evolution, characterized by x-ray luminosities exceeding 1e39 erg/s (approximately the eddington limit for a stellar mass black hole). the recent discovery of a neutron star accretor in the ultra-luminous x-ray source m82 x-2 challenges our understanding of high-mass x-ray binary formation and binary evolution in general. apart from the specific emission mechanism and the magnitude and influence of the neutron star's magnetic field, the measured orbital period and the lower limits on the donor mass and radius are both telling and puzzling at first glance: (1) the high inferred accretion rate onto the neutron star requires that the donor is in roche-lobe overflow, as wind-fed x-ray binaries with neutron star accretors are expected to have x-ray luminosities orders of magnitude below the ultr-luminous x-ray source range, (2) the donor star must be hydrogen rich, as a helium star with mass >5 msolar cannot fill its roche lobe in a 2.5 day period orbit, independent of its evolutionary stage, (3) the evolutionary mechanism must have either a long lifetime, or a high formation rate, in order for this one system to exist in the local universe.by combining binary population synthesis and detailed mass-transfer models, however, we show that the binary parameters of m82 x-2 are not surprising provided non-conservative mass transfer is allowed. specifically, the donor-mass lower limit and orbital period measured for m82 x-2 lie near the most probable values predicted by population synthesis models, and systems such as m82 x-2 should exist in approximately 13% of the galaxies with a star-formation history similar to m82. we conclude that the binary system that formed m82 x-2 is most likely less than 50 myr old and contains a donor star which had an initial mass of approximately 8-10 msolar, while the neutron star's progenitor star had an initial mass in the 8-25 msolar range. the donor star still currently resides on the main sequence, and is capable of continued mt on the thermal timescale, while in the ultra-luminous x-ray regime, for as long as 400,000 years. | on the formation of ultraluminous x-ray sources with neutron star accretors: the case of m82 x-2 |
as the former envelopes of evolved stars, planetary nebulae (pne) present an opportunity to study slow neutron-capture reactions (the “s-process”) during the agb. such studies differ from those of agb stars in two ways. first, pne represent the end point of self-enrichment and dredge-up in the star and most of its mass return to the ism, enabling us to infer the nucleosynthetic yield of a specific element. second, some s-process products are observable in pne but difficult or impossible to observe in cool stars. these include some species with nuclear charge z in the 30’s for which the major synthesis sites are uncertain. optical emission lines of trans-iron species have been observed in some pne, but are faint and can suffer from blending with lines of more abundant elements (péquignot & baluteau 1994, a&a, 283, 593; sharpee et al. 2007, apj, 659, 1265). observing infrared transitions from low energy states has proven to be a fruitful alternate approach. we used k-band lines of se (z=34) and kr (z=36) to study the demographics of their abundances in a large sample of milky way pne (dinerstein 2001, apj, 550, l223; sterling & dinerstein 2008, apj, 174, 158; sterling, porter, & dinerstein 2015, submitted). an l-band emission line of zn identified by dinerstein & geballe (2001, apj, 562, 515) and further observed by smith, zijlstra, & dinerstein 2014 (mnras, 441, 3161), can be used as a tracer of the fe-group, enabling determinations of the key stellar population diagnostic ratio [alpha/fe] in pne (see poster by dinerstein et al., focus meeting 4). using igrins, a high spectral resolution h and k band spectrometer (park & jaffe et al. 2014, proc spie, 9147), we have discovered several new lines not previously reported in any astronomical object. our detection of an h-band line of rb (z=37) confirms previous claims of optical rb detections and indicates enrichment by a factor of ~4 in the pn ngc 7027 (sterling, dinerstein, kaplan, & bautista, in preparation). we also detect lines that we tentatively identify as ge (z=32) and cd (z=48). this work was supported by nsf grants ast 0708429 and 1412928. | observing infrared emission lines of neutron-capture species in planetary nebulae: new detections with igrins |
detached white dwarf + main sequence (wd+ms) systems represent the simplest population of post-common envelope binaries (pcebs), and their ensemble properties carry important information about common-envelope phase. however, most population synthesis studies do not fully consider the effects of the observational selection biases of the samples used to compare with the theoretical simulations. we present a set of detailed monte carlo simulations of the population of wd+ms binaries in the sloan digital sky survey (sdss) data release 7, which allows us to make a sound comparison with the available observed data. we find that our simulations correctly reproduce the properties of the observed distribution of wd+ms pcebs. this includes the distribution of orbital periods and of masses of the white dwarf and main sequence stars. these distributions can be correctly reproduced for several choices of the free parameters, although models in which ≤ 10% of the internal energy is used to eject the common envelope, and in which a small common envelope efficiency ≤ 0.3 seem to fit the observational data better. we also find that systems with he-core white dwarfs are over-represented in the observed sample, because of selection effects. | a population synthesis study of the ms+wd population in the sdss |
we present a new medium resolution (full width at half-maximum fwhm ~ 2.4 å) spectral library containing 1903 stellar spectra with a wavelength coverage of 3800-9000 å based on miles spectral library which contains 985 blue arm spectra with wavelength coverage of 3500-7500 å at a spectral resolution of 2.5 å (fwhm). the spectra are observed with chinese xinglong 2.16 meter telescope of blue arm spectra (with wavelength coverage 3800-5180 å ) and gaomeigu 2.4 meter telescope of red arm spectra (with wavelength coverage 5150-9000 å ), respectively. this new library aims to improve the stellar atmospheric parameters determination accuracy of lamost stellar parameter pipeline at peking university (lsp3) and minimize the limitation of lsp3 . it also could be used in the spectral synthesis of stellar populations of galaxies and many other astronomical fields. now 560 blue arm and 496 red arm spectra have been observed and reduced. the accuracy of wavelength-calibration and flux-calibration are better than ~ 0.3 å and ~ 5 per cent, respectively. the mean signal to noise ratios of all spectra are almost larger than 100 per å. | expand miles spectral library for lamost stellar parameter determination using chinese 2.4 and 2.16 metereter telescopes |
many hot jupiter systems exhibit misalignment between the orbital axis of the planet and the spin axis of its host star. while this misalignment could be primordial in nature, a large fraction of hot jupiters are found in systems with distant stellar companions, and thus could have undergone lidov-kozai (lk) oscillations and acquired their misalignment dynamically. here we present a study of the effect of spin-orbit coupling during lk oscillations, and the resulting spin-orbit misalignment angle distributions. we show that spin-orbit coupling induces complex, often chaotic, behavior in the spin axis of the host star, and that this behavior depends significantly on the mass of the planet and the properties of the host star (mass and spin history). we develop a semi-analytical framework that successfully explains most of the possible stellar spin behaviors. we then present a comprehensive population synthesis of hot jupiters created via the lk mechanism, and discuss their possible observable signatures. | spin-orbit coupling and the production of misaligned hot jupiters via lidov-kozai oscillations |
we present a sample of synthetic images of simulated galaxies and their stellar haloes from the illustris volume, a cosmological gravity+hydrodynamics simulation which has been shown to reproduce many observational constraints on the galaxy population and gas content of the universe at z=0. based on the properties of the simulated stellar particles, mock data products are produced by using stellar population synthesis models to assign spectral energy distributions (sed) to each star particle in the galaxies. the result is a collection of thousands of images spanning a wide range of stellar/halo masses, morphologies and assembly histories. | the illustris simulation overview: mock observations of galaxies and their stellar haloes |
gj832 (hd 204961) is a nearby m1 v host star with two exoplanets: a jovian mass planet and a super-earth. we have obtained near-uv and far-uv spectra of gj832 with the stis and cos instruments on hst as part of the cycle 19 muscles pilot program (france et al. 2013). our objective is to obtain the first accurate physical model for a representative m-dwarf host star in order to understand the stellar radiative emission at all wavelengths and to infer the radiation environment of their exoplanets that drives their atmospheric photochemistry.we have calculated a full non-lte model for gj 832 including the photosphere, chromosphere, transition region, and corona to fit the observed emission lines formed over a wide range of temperatures and the x-ray flux. our one-dimensional semi-empirical model uses the solar-stellar physical modelling tools that are an offspring of the tools used by fontenla and collaborators for computing solar models. for this model of gj832, we calculate the populations of 52 atoms and ions and 20 molecules with 2 million spectral lines. we find excellent agreement with the observed h-alpha, caii, mgii, cii, siiv, civ, and nv lines. our model for gj832 has a temperature minimum in the lower chromosphere much cooler than the sun and then a steep temperature rise different from the sun. the different thermal structure of gj832 compared to the sun results in the formation regions of the emission lines being different for the two stars. we also compute theradiative cooling rates as a function of height and temperature in the atmosphere of gj832.this work is supported by grants from stsci to the university of colorado. | an empirically-derived non-lte xuv-visible spectral synthesis model of the m1 v exoplanet host star gj832 |
high-quality stellar spectra are in great demand now - they are the most important ingredient in the stellar population synthesis to study galaxies and star clusters. here we describe the procedures to increase the quality of flux calibration of stellar spectra. we use examples of nir intermediate-resolution echelle spectra collected with the folded infrared echellete (r~6500, magellan baade) and high-resolution uv-optical spectra observed with uves (r~80000, eso vlt). by using these procedures, we achieved the quality of the global spectrophotometric calibration as good as 1-2%, which fulfills the requirements for the quality of stellar spectra intended to be used in the stellar population synthesis | multi-segment and echelle stellar spectra processing issues and how to solve them |
as the lowest-mass products of star formation, brown dwarfs are essential to understanding the history of our galaxy. to this end, a complete volume-limited sample of brown dwarfs in the solar neighborhood is critical for testing formation theories. to create such a sample, our hawaii infrared parallax program has recently measured parallaxes for 350 l and t dwarfs, the largest single batch of parallaxes for brown dwarfs to date. using our work and literature measurements, we have constructed a volume-limited sample of brown dwarfs out to 25 pc. we augmented this with a large keck adaptive-optics imaging campaign to establish the binary properties of the sample. we use population synthesis analysis to establish the initial mass function and birth history of substellar objects in the solar neighborhood. we compare with imf measurements for the solar neighborhood. | the initial mass function and birth history of brown dwarfs in the solar neighborhood from a volume-limited sample |
the interstellar medium is the principal ingredient for star formation and hence, it is necessary to study the properties of the interstellar medium. radio sources in our galaxy and beyond can be used as a probe of the intervening medium. in this dissertation, i present an attempt to use radio transients like pulsars and fast radio bursts and their interactions with the environment around them to study interstellar medium. we show that radio emission from pulsars is absorbed by dense ionized gas in their surroundings, causing a turnover in their flux density spectrum that can be used to reveal information about the absorbing medium. we carried out a multi-wavelength observation campaign of psr b0611+22. the pulsar shows peculiar emission variability that is broadband in nature. moreover, we show that the flux density spectrum of b0611+22 is unusual which can be attributed to the environment it lies in. we also present predictions of fast radio burst detections from upcoming low frequency surveys. we show that future surveys with the canadian hydrogen intensity mapping experiment (chime) will be able to detect 1 radio burst per hour even if the radio burst undergoes significant absorption and scattering. finally, we present our results of pulsar population synthesis to understand the pulsar population in the galactic centre (gc) and place conservative upper limits on the gc pulsar population. we obtain an upper limit of 52 cps and 10,000 msps in the gc. the dense, ionized environment of the gc gives us the opportunity to predict the probability of detection by considering scattering and absorption as the principle sources of flux mitigation. our results suggest that the optimal frequency range for a pulsar survey in the gc is 9-14 ghz. a larger sample of absorbed spectrum pulsars and fast radio bursts will be beneficial not only for the study of emission processes but also for discerning the properties of the material permeating through space. | radio transients and their environments |
we compare the evolution of binary systems evolved in the mesa stellar evolution code to those in the cosmic population synthesis code. our aim is to: 1) convey the robustness of the equations that model binary evolution in the cosmic code, particularly for the cases of high mass stars with closely orbiting compact object companions, 2) present preliminary population synthesis results of these systems. our larger goal is to accurately model the rates of these systems, as they are promising candidates for the progenitor systems behind energetic, longer lasting, radio bright grb jets. these systems also play a key contribution to the rates of binary black hole mergers throughout our universe. | understanding binary systems - a comparison between cosmic and mesa |
since its discovery, the multiple population phenomenon is an enigma in the field of stellar populations. we propose combined spectroscopic and photometric jwst observations that will finally solve this long-standing issue. so far, two competing scenarios are available: 1) multiple bursts of star formation; 2) accretion of material onto existing stars. in the first scenario the population pattern is expected to be identical for stars with different masses, while the accretion scenario should result in substantially more pronounced chemical differences and fractions of second population stars at higher-masses. the exploration of the m dwarf realm and the comparison of the multiple population properties in this very-low mass regime with those of red giants will shed light on the origin of this enigmatic phenomenon. the nirspec+nircam facilities will provide the unique opportunity to gather spectra and precise photometric diagrams of faint m dwarfs in gcs, not easily accessible to other facilities. our spectral synthesis and simulated diagrams suggest that the requested data, combined with hst uv archival images, will allow us to infer the o abundance range in the m dwarfs, which will be compared to that observed among red giants, and precise mass functions of multiple populations from ~0.8 solar masses towards the h-burning limit. these first jwst observations will be a milestone in our understanding of such an eluding phenomenon, and a step forward for many closely related issues, e.g. star formation in dense early environments, stellar evolution and nucleosynthesis, the role of proto-clusters in the cosmic reionization and the contribution of gcs to the milky way halo. | solving the globular clusters multiple population enigma through jwst |
the ir emission from galaxies is a unique window into multiple aspects of galaxy evolution including star-formation rates, the age of galaxies, and galactic-scale dust processes. however, asymptotic giant branch (agb) stars continue to introduce uncertainty into stellar population synthesis (sps) models and limit our ability to interpret the ir light of galaxies. here we focus on incorporating circumstellar dust around agb stars in sps models and understanding the extent to which they influence the ir light of galaxies. we find that the significance of the agb dust contribution depends on the characteristics of the galaxy. for quiescent galaxies and metal-poor star forming galaxies, circumstellar dust emission can have a large effect, whereas for dusty star-forming galaxies the circumstellar emission is dwarfed by emission from dust in the ism. the models with circumstellar dust also suggest, in agreement with previous work, that ir colors can be a powerful age diagnostic for older stellar systems. models such as these will be essential for interpreting data that will be provided by jwst and other next generation ir facilities. | circumstellar dust around agb stars and implications for infrared emission from galaxies |
we present the full results of our decade-long astrometric monitoring programs targeting 31 ultracool binaries with component spectral types m7-t5. joint analysis of resolved imaging from keck and hst and unresolved astrometry from cfht/wircam yields parallactic distances for all systems, robust orbit determinations for 23 systems, and photocenter orbits for 19 systems. as a result, we measure 38 precise individual masses spanning 30-115 mjup. we determine a model-independent substellar boundary that is ≈70 mjup in mass (≈l4 in spectral type), and we validate bhac15 evolutionary model predictions for the lithium-depletion boundary (60 mjup at field ages). assuming each binary is coeval, we test models of the substellar mass-luminosity relation and find in the l/t transition only sm08 "hybrid" models accounting for cloud clearing match our data. our masses enable a novel direct determination of the age distribution of field brown dwarfs spanning l4-t5 and 30-70 mjup. we determine a median age of 1.3 gyr, and our population synthesis modeling indicates our sample is consistent with a constant star formation history modulated by dynamical heating in the galactic disk. overall, this work represents a major advance in the empirical view of very low-mass stars and brown dwarfs. | individual dynamical masses of ultracool dwarfs |
our knowledge of the formation and early evolution of globular clusters (gcs) has been totally shaken with the discovery of the peculiar chemical properties of their long-lived host stars. therefore, the interpretation of the observed colour magnitude diagrams (cmd) and of the properties of the gc stellar populations requires the use of new stellar models computed with relevant chemical compositions. in this paper we use the grid of evolution models for low-mass stars computed by chantereau et al. (2015) with the initial compositions of second-generation stars as predicted by the fast rotating massive stars scenario to build synthesis models of gcs. we discuss the implications of the assumed initial chemical distribution on 13 gyr isochrones. we build population synthesis models to predict the fraction of stars born with various helium abundances in present day globular clusters (assuming an age of 13 gyr). with the current assumptions, 61 % of stars on the main sequence are predicted to be born with a helium abundance in mass fraction, yini, smaller than 0.3 and only 11 % have a yini larger than 0.4. along the horizontal branch, the fraction of stars with yini inferior to 0.3 is similar to that obtained along the main sequence band (63 %), while the fraction of very he-enriched stars is significantly decreased (only 3 % with yini larger than 0.38). | globular clusters and the evolution of their multiple stellar populations |
some major uncertainties in the determination of the evolutionary status of unresolved old stellar populations, using stellar population synthesis models, are presented and discussed. it transpires that the unknown hb morphology of the target populations is a major potential source of error, together with the effect of interacting binaries, usually neglected in stellar population synthesis models. a few techniques aimed at revealing the presence in the target populations of a hb morphology different from the spsm assumptions are discussed. | uncertainties in determining the evolutionary status of unresolved old populations |
anisotropic nanomaterials, including zero-dimensional metallic nanoparticles (mnps), one-dimensional single-walled carbon nanotubes (swcnts), and two-dimensional few-layer black phosphorous (fl-p) exhibit interesting structure-dependent properties that could be exploited in biomedicine, plasmonics, and optoelectronics. in this thesis, centrifugation sorting of these nanomaterials is utilized for structure refinement, investigation of structure-dependent optical response, and applications in biomedical imaging and plasmonics. nobel nmps show unique shape- and size-dependent optical properties. controlled synthetic methods are developed to manipulate the structure of these nmps, but intrinsically produce dispersions of polydisperse nps with various shape and size, and synthetic byproducts. here, we describe a facile strategy for separating small (edge length <100 nm) faceted gold nps: rhombic dodecahedra (rd) and obtuse triangular bipyramids (bps), which form simultaneously during synthesis but are hard to separate via commercial filters. by utilizing centrifugation of the as-synthesized mixture in a shallow density gradient centrifugation (dgc), we are able to isolate a high purity of bps (>80%) and subsequently achieve a 2.5 fold enhancement in refractive index sensitivity, comparable to the unsorted mixture. this shallow dgc approach is robust and reliable, and therefore can be applied to other metal nanostructures for concomitant improvements in plasmonic properties and applications. using the identical separation strategy in the previous study, we are able to enrich gold nanostars as a function of branch number. in particular, we explore different variants of density gradient media to ensure compatibility with the star shape and colloid stability. we determine that sucrose is compatible with nanostars stability and surface functionalizaton. the refined population of gold stars are functionalized with gd(iii)-dna to act as mri contrast agents, and thus enables us to investigate how populations of nanostars with different branch numbers contribute to the relaxivity of surface bound gd(iii)-dna. it is shown that the increased relaxivity of dna-gd star is correlated with increased number of star branches, not with increased size of the stars. therefore, shape is a new parameter which can be tuned in the design of np-based mri contrast agent. these findings can also improve the performance of functionalized anisotropic nanoconjugates which have potential for applications such as lowering detection limits for sensors and diagnostics, or enabling new modes of self-assembly. finally, we have broadened the scope of dgc to other dimensional nanomaterials: 1d-swcnts and 2d-fl-p. despite their tunable and structure-dependent optical properties, intrinsic structural heterogeneity and poor quantum efficiency limit their potential applications. therefore, dgc is employed to separate the swcnts and fl-p by length and the number of layers, respectively, thereby incorporating them into optical cavity structures for enhancing their luminescence properties. these fundamental studies of low-dimensional nanomaterials assist in the design process for optoelectronic device fabrication. | monodisperse multidimensional nanostructures via centrifugal separation |
over much of the initial mass function, stars lose a significant fraction of their mass through a stellar wind during the late stages of their evolution when being a (super)giant star. as of today, we can not yet predict the mass-loss rate during the (super)giant phase for a given star with specific stellar parameters from first principles. this uncertainty directly impacts the accuracy of current stellar evolution and population synthesis models that predict the enrichment of the interstellar medium by these stellar winds. efforts to establish the link between the initial physical and chemical conditions at stellar birth and the mass-loss rate during the (super)giant phase have proceeded on two separate tracks: (1) more detailed studies of the chemical and morpho-kinematical structure of the stellar winds of (super)giant stars in our own milky way by virtue of the proximity, and (2) large scale and statistical studies of a (large) sample of stars in other galaxies (such as the lmc and smc) and globular clusters eliminating the uncertainty on the distance estimate and providing insight into the dependence of the mass-loss rate on the metallicity. in this review, i will present recent results of both tracks, will show how recent measurements confirm (some) theoretical predictions, but also how results from the first track admonish of common misconceptions inherent in the often more simplified analysis used to analyse the large samples from track 2. | mass-loss rates of cool stars |
stars, and collections of stars, encode rich signatures of stellar physics and galaxy evolution. with properties influenced by both their environment and intrinsic nature, stars retain information about astrophysical phenomena that are not otherwise directly observable. in the time-domain, the observed brightness variability of a star can be used to investigate physical processes occurring at the stellar surface and in the stellar interior. on a galactic scale, the properties of stars, including chemical abundances and stellar ages, serve as a multi-dimensional record of the origin of the galaxy. in the milky way, together with orbital properties, this informs the details of the evolution of our galaxy since its formation. extending beyond the local group, the attributes of unresolved stellar populations allow us to study the diversity of galaxies in the universe. by examining the properties of stars, and how they vary across a range of spatial and temporal scales, this dissertation connects the information residing within stars to global processes in galactic formation and evolution. we develop new approaches to determine stellar properties, including rotation and surface gravity, from the variability that we directly observe. we offer new insight into the chemical enrichment history of the milky way, tracing different stellar explosions that capture billions of years of evolution. we advance knowledge and understanding of how stars and galaxies are linked, by examining differences in the initial stellar mass distributions comprising galaxies, as they form. in building up this knowledge, we highlight current tensions between data and theory. by synthesizing numerical simulations, large observational data sets, and machine learning techniques, this work makes valuable methodological contributions to maximize insights from diverse ensembles of current and future stellar observations. | decoding starlight with big survey data, machine learning, and cosmological simulations |
studies of extagalactic x-ray binary populations have shown that the characteristics of these populations depend strongly on the characteristics of the host galaxy's parent stellar population (e.g. star-formation history and metallicity). these dependencies not only make x-ray binaries promising for aiding in the measurement of galaxy properties themselves, but they also have important astrophysical and cosmological implications. for example, due to the relatively young stellar ages and primordial metallicities in the early universe (z > 3), it is predicted that x-ray binaries were more luminous than today. the more energetic x-ray photons, because of their long mean-free paths, can escape the galaxies where they are produced, and interact at long distances with the intergalactic medium. this could result in a smoother spatial distribution of ionized regions, and more importantly in an overall warmer intergalactic medium. the energetic x-ray photons emitted from x-ray binaries dominate the x-ray radiation field over active galactic nuclei at z > 6 - 8, and hence χ-ray binary feedback can be a non-negligible contributor to the heating and reionization of the inter-galactic medium in the early universe. the spectral energy distribution shape of the xrb emission does not change significantly with redshift, suggesting that the same xrb subpopulation, namely black-hole xrbs in the high-soft state, dominates the cumulative emission at all times. on the contrary, the normalization of the spectral energy distribution does evolve with redshift. to zeroth order, this evolution is driven by the cosmic star-formation rate evolution. however, the metallicity evolution of the universe and the mean stellar population age are two important factors that affect the x-ray emission from high-mass and low-mass xrbs, respectively. in this talk, i will review recent studies on the potential feedback from accreting binary populations in galactic and cosmological scales. furthermore, i will discuss which are the next steps towards a more physically realisitc modelling of accreting compact object populations in the early universe. | accreting binary population synthesis and feedback prescriptions |
we have analyzed broadband hst photometry available to study the brightest cluster galaxies (bcgs) in x-ray luminous clusters of galaxies. these galaxies span a redshift interval of 0.152 < z < 0.55 and were identified by the canadian cluster comparison project. we used this sample to build a robust analysis pipeline to produce stellar mass estimates of the bcgs from hst images of galaxy clusters. we apply the observed colors to constrain the parameters in the simple stellar population synthesis models to produce the best light-to-mass ratios and stellar mass profiles of the bcgs. by applying variable fit-parameters, we can build metallicity profiles and trace the star-formation histories in the bcg. since bcgs sit at the potential wells of the host cluster and houses most of the cluster mass, the new stellar mass estimates will allow us to build improved mass profiles of the clusters to characterize the amount of dark matter present. | measuring stellar masses of the brightest cluster galaxies in x-ray luminous galaxy clusters using hubble space telescope archival data |
we present a population synthesis study of the cooling sequence of the globular cluster 47 tucanae. we study the distribution of effective temperatures, the morphology of the color-magnitude diagram, and the magnitude and color distributions. we find that our simulations are in very good agreement with the observational data, once all the observational biases are taken into account. our study also rules out previous claims that there are still missing physics in the white dwarf cooling models at moderately high effective temperatures. we also fit the age of the cluster using the termination of the cooling sequence, finding an age consistent with that determined using the main-sequence turn-off. finally, we also investigate the star formation history of the cluster, finding that is compatible with that obtained using main sequence stars. | a population synthesis study of the white dwarf cooling sequence of 47 tucanae |
the vast majority of stars will end their lives as white dwarfs, earth-sized electron-degenerate stars. as part of close binaries, white dwarfs give rise to a wide range of spectacular phenomena, including accretion disc instabilities, explosive shell burning, and their total annihilation in type ia supernovae. due to their small radii, white dwarfs are intrinsically faint objects, and until recently, much of our knowledge regarding these stellar remnants has been based on serendipitous discoveries.i will review how large-area surveys providing colour information, time-domain photometry, and spectroscopy enable us to move from individual object studies to the analysis of large and homogeneous samples, and i will discuss the observational results in the context of population synthesis models. i will in particular focus on the impact that the sloan digital sky survey and the catalina real time transient survey had, and highlight the enormous potential of the gaia mission for the study of white dwarfs, both single and in binaries. finally, i will conclude with an outlook on a number of forthcoming spectroscopic and photometric surveys, including weave, desi, sdss-v, 4most, and lsst. | population studies of single and binary white dwarfs |
robustly measuring the specific star formation rate in galaxies -- the star formation rate per unit stellar mass -- is crucial to understanding galaxy evolution over cosmic time. future missions, such as the james webb space telescope (jwst) and the wide field infrared space telescope (wfirst) will observe the stellar component in galaxies out to the first galaxies, but the inferred stellar mass and star formation rates can be severely biased by the presence of dust. model galaxies of various types, luminosities, and redshifts with a range of star formation rates and stellar masses were generated with flexible stellar population synthesis for python (python-fsps). the spectral energy densities (seds) were fit with multiple combinations of photometric bands from current-generation instruments as well as next-generation instruments spanning wavelengths from optical to millimeter wavelengths. our goal is to study the optimal combination of photometric measurements in order to robustly recover a galaxy's specific star formation rate. our work will inform how well future missions will be able to measure the specific star formation rates in galaxies of different types and redshifts from sed fits, as well as inform which long wavelength bands will be best in breaking the degeneracies in the model fits caused by dust. | recovering specific star formation rate of simulated galaxies with spectral energy density fitting |
the recent ligo/virgo detections of gravitational waves (gws) from merging bhs and nss have prompted a resurgence in efforts to self-consistently model close binary populations and their evolution. x-ray binaries (xrbs) provide an important benchmark for such efforts, and scaling relations between high-mass xrb (hmxb) and low-mass xrb (lmxb) population demographics and physical properties, like stellar mass (m*), star-formation rate (sfr), metallicity, and stellar age are critical benchmarks for population synthesis models. thanks to data collected over the last 20 years by chandra and xmm-newton, substantial insight has been gained into how the xrb phase is manifested within a variety of galactic environments. we present here new results based on ~7 ms of archival chandra data for a sample of 38 nearby galaxies (d = 3.4-29 mpc), spanning all galactic morphologies, with excellent multiwavelength data (primarily from sings). we use new subgalactic analysis techniques to explore how the x-ray luminosity functions (xlfs) of xrbs vary with specific sfr (ssfr = sfr/m*) and self-consistently characterize the hmxb and lmxb contributions to the xlfs of all galaxies. we find that the hmxb and lmxb xlfs exhibit more complex shapes and variations with ssfr than previously reported, and we find evidence for metallicity and stellar age dependences in the xlf shapes and scalings. we put into context these findings with recent studies of xrb evolution reported from the chandra deep fields and cosmos surveys, and discuss ways forward for linking studies of xrbs to other astrophysical systems (e.g., gw sources). | x-ray binary population constraints in nearby galaxies from 20 years of chandra data |
nuclear starburst discs (nsds) are very compact star-forming regions in the centres of galaxies that have been studied as a possible origin for the absorbing gas around a central active galactic nucleus. nsds may be most relevant at z ∼ 1 when obscured accretion on to supermassive black holes (smbhs) is common. this paper describes the characteristics of the stellar remnants of nsds at z = 0.01, taking into account the evolution from z = 1. using a stellar synthesis model, the colours, masses, and luminosities of the stellar remnants are computed for a suite of 192 two-dimensional nsd models. these properties are compared to observations of local nuclear star clusters (nscs), and a good match is found between the predicted and observed properties. dynamical effects will likely cause the final remnant to be a rotating, nearly spherical distribution. in addition, ≈20 per cent of the nsd remnants have half-light radii ≲ 10 pc, consistent with nscs hosted in both late- and early-type galaxies, and all the remnants follow similar size-luminosity relationships as observed in nearby nscs. nsds require the presence of a central smbh and the most massive and compact stellar remnants are associated with the most massive smbhs, although stellar clusters with a variety of sizes can be produced by all considered smbh masses. overall, nsds at z ∼ 1 appear to be a promising origin for the ≫1 gyr nsc population in early- and late-type galaxies with large smbhs. | the stellar remnants of high-redshift nuclear starburst discs: a potential origin for nuclear star clusters? |
until the late sixties our knowledge about star evolution essentially rested on the hr diagram of open and globular clusters. already in the seventies, the early studies with the 40-cm objective prism astrograph at la silla revealed some striking population differences between the smc, lmc and milky way, as a result of differences in metallicity z and star formation history. a new window on stellar physics and stellar populations was further opened by the eso spectrographic observations of the elemental stellar abundances. these observations, particularly of cno and some isotopic ratios, brought a lot on the physics of notably the red giants, agb-stars, horizontal branch stars, red supergiants, massive and wr stars. the roles of mass loss, instabilities, tidal effects in binaries, rotation, internal mixing, often depending on z, were better understood, which had an impact on all model outputs: stellar parameters, ages, chemical yields, population synthesis, relation between supernovae, grbs and progenitors, sources of s-elements, of primary nitrogen, etc… several of these effects nowadays appear as essential for our understanding of the first stars (cf. case of cemp stars). asteroseismology studies with harps are providing a new insight on the stellar interiors, with a particular interest for planet hosting stars. | contributions of la silla instruments to our understanding of stars |
with the detection of compact-object mergers with ligo/virgo there is a resurgence in modeling efforts to understand the evolution of interacting close binaries, including x-ray binaries (xrbs). critical high-value empirical constraints on this effort can be gained by xrb x-ray luminosity functions (xlfs), which provide many degrees of freedom for testing models. using a sample of 38 nearby galaxies (d < 30 mpc) that have chandra observations (5.8 ms total), and a wealth of fuv-to-fir data, we characterized on subgalactic scales how the xrb xlf varies with specific-sfr (ssfr = sfr/m*). we find that the xlf clearly transitions from lmxb-dominant to hmxb-dominant going from low-to-high ssfr environments, and we characterize in detail the hmxb and lmxb xlf shapes and scaling relations with sfr and m*, respectively. with this rich data set, we show that the hmxb and lmxb xlfs exhibit more complex shapes and variations with ssfr than previously reported, and we find evidence for metallicity and stellar age dependences in the xlf shapes and scalings. we put discuss how these findings will have important implications for binary population synthesis modeling and interpretations of the heating of the intergalactic medium at high redshifts. | new x-ray binary scaling relations in the local universe based on subgalactic modeling |
in the stellar atmospheres, radiative energy transport is dominated by only the strongest spectral lines. for these lines, the approximation of local thermo-dynamic equilibrium (lte) is known to be very inaccurate, and a state of equilibrium cannot be assumed in general. therefore to understand the structure and dynamics of stellar atmospheres through evolving magneto-hydro-dynamic equations, one needs a non-equilibrium equation of state. to calculate the radiative energy transport under these conditions, the population evolution equation must be evaluated including all time dependent terms. to this end, we have developed a new numerical method to solve the non-lte non-equilibrium radiative transfer problem. we solve evolution equation for the atomic level populations in a time-implicit way, keeping all time dependent terms to first order. we have tested our method by reproducing earlier works, namely, a) determining chromosperic time-scales of ionization/recombination, b) showing that our non-equilibrium solver evolves to the statistical equilibrium solution obtained from an independent non-lte spectral synthesis code. in this presentation, i will describe the method, and discuss equilibrium solutions. | non-equilibrium equation-of-state in stellar atmospheres |
the initial mass function (imf) represents the distribution of stellar masses of stars formed in one star formation event and is one of the most crucial ingredients to understand the formation and evolution of stellar populations and galaxies. we use flexible stellar population synthesis (fsps) to study the impact of five different imfs (chabrier, kroupa, salpeter, bottom-light, and bottom-heavy) on the time evolution of the stellar mass-to-light ratio (m/l). we investigate a range of stellar metallicities from sub- to super-solar and star-formation histories in fsps to explore their impact on m/l evolution. we then use prospector, a package to conduct principled inference of stellar population properties, to model the 50-band galex ultraviolet to the mips 24 μm photometry from ultravista dr3 (marsan et al. 2022) of a sample of spectroscopically confirmed ultra-massive galaxies at 3 < z < 4 with estimated dynamical masses from measurements of stellar absorption velocity dispersions and size (forrest et al. 2022, submitted) to derive photometric stellar masses with different imf assumptions. we present the comparison of the dynamical masses and photometric stellar masses, and their implications on the imfs of distant massive galaxies and find that m/l differences over cosmic time from a bottom-heavy imf lead to significant variations in stellar mass measurements and derived stellar properties compared to those derived using a standard chabrier imf. | the impact of the initial mass function on the evolution of m/l |
using updated full-spectrum stellar population synthesis (sps) models, we present the first detailed stellar population analysis of m87 and its globular cluster (gc) system from spectroscopy. we applied the models to 322 gcs extending from the inner to outer halo. in villaume+ (2019apj...879...45v) we applied full-spectrum sps models to the keck/lris data set of m87 gcs (strader+ 2011, j/apjs/197/33) to obtain estimates of iron metallicity ([fe/h]) relative to solar. here, we do the same analysis for the mmt/hectospec sample. (1 data file). | vizier online data catalog: new m87 gcs metallicities from keck & mmt sp. (villaume+, 2020) |
the next-generation network of gravitational wave observatories are expected to detect many more compact object mergers inside their host galaxies. in light of this future circumstances, i developed a theoretical tool that investigates the properties of formation and host galaxies of compact objects. the starting point of my new methodology is a population of star-forming galaxies across cosmic time obtained from observed scale relations. i varied the metallicity of galaxies, considering the fundamental metallicity relation (fmr) and the mass-metallicity relation (mzr). with my fast methodology, we are also able to compare different populations of compact objects. in this talk, we will see the impact of different population-synthesis simulations, where i varied the value of the alpha common envelope (αce = 1 , 3 and 5). i evaluated the merger rate density of compact objects for this set of models and i compared it with the 90% credibile intervals inferred by the ligo-virgo-kagra collaboration. we will see how different metallicity distributions strongly affect the merger rate density evolution of binary black holes (bbhs) with redshift. by looking at the properties of host galaxies, i learnt that low mass galaxies with stellar mass <109 solar masses can host up to 50% of the total bbh mergers, with αce = 1 . for larger masses, the merger rate per galaxy correlates with stellar mass of galaxies for all compact objects types. moreover, the typical masses of the host galaxies increase significantly as we approach the local universe. an indicator of this trend is the rise in percentage of compact object mergers hosted in passive galaxies, which can be > 80% for αce = 5 . i acknowledge financial support from the european research council for the erc consolidator grant demoblack, under contract no. 770017. | the evolution of compact object mergers and their host galaxies across cosmic time |
the understanding of how, which, where and when stars form provides important information for the vast majority of astronomical fields. star-formation has a complex multi-scale physical nature. stars form in dense sub-parsec regions of molecular clouds, and since the very early stages of their life, their destiny is linked to the complex interplay between magneto-hydro-radiation-transfer-dynamics, stellar evolution and stellar dynamics. at the same time, star-forming regions are inevitably coupled to the galactic gravitational potential and as such are affected by tides and shears. this poses a computational challenge for theoretical investigations pushing technical feasibility to its limit in terms of computational time and the required spatial resolution. nowadays, front-end facilities allow us to obtain detailed observations of nearby (up to 500pc from the sun) star-forming regions. while such regions allow us to sample near-to-uniform environmental conditions in terms of cloud density, mass and metallicity, they do not allow us to investigate how star formation proceeds in the full range of diverse environmental conditions that can be found in local galaxies and at all redshifts where the stellar population cannot be resolved. thus, despite a large and fruitful community effort in this field, we are still lacking a complete and coherent picture of how stars and star-clusters form. this thesis investigates the physics of star-formation and stellar populations combining theoretical modeling with observations on multiple scales from resolved star-forming regions in the milky way through to stellar populations in galaxies reaching to cosmic star-formation. the discovery, my confirmation and theoretical explanation of the existence of three stellar populations in the orion nebula cluster is a clear example of the impact and crucial role played by the stellar dynamics on star and star-cluster formation. furthermore, the thesis presents the discovery, made possible with the advent of the gaia space mission, of large scale co-eval filaments of star formation, a new fact posing novel viable constraints for theories of star-formation. individual star-forming regions (in molecular cloud cores forming at least a few binary stellar systems) are used as building blocks of galaxy-wide stellar populations using the integrated galactic initial mass function (igimf) theory. the publicly available code, galimf, has been co-developed within this thesis to synthesise stellar populations of whole galaxies. this allowed me to compute, for the first time, a large grid of the empirically driven variable galaxy-wide stellar initial mass function for direct comparison with observations. this model and the associated code were used, for example, to construct the cosmic star-formation history with a variable stellar-initial mass function. the research presented in this thesis was published in four refereed publications led by its author and six refereed publications to which the author provided significantly. this thesis as a whole presents a multi-scale and multi-technique contribution to star-formation and stellar populations and opens novel and original routes for future research. | stellar populations in gravitationally bound systems |
star formation (sf) tracers in the optical spectral range are considerably well known nowadays and had been used to identify sf in galaxies over the years. the near-infrared (nir) regime, on the other hand, remains poorly explored, even though this is an important wavelength range which is less affected by dust obscuration than the optical and will be the regime probed by future observational facilities such as jwst, elt/mosaic and gmt/nirs. thus, one can use the well-studied visible regime to anchor the simple stellar population (sp) models, determine ages and compare the resulting predictions for the nir. in this work, the sp synthesis technique was applied from the uv to the nir using spectra from stis/hst and sinfoni/vlt of the low-luminosity active galactic nuclei ngc 4303. | a panchromatic study of the stellar populations in ngc 4303 |
the epoch of reionization (eor) was a period in the universe's history wherein the wholly neutral igm was ionized by the rapidly evolving ionizing background. due to the high opacity of the igm during this epoch, studying this period is difficult, yet it could reveal much about the traits of early galaxies. in this dissertation work, we demonstrate that reionization may also be studied through analysis of metal line absorption systems such as those seen in quasar spectra, arising from enriched gas in the cgm and igm, complementary to methods focused solely on neutral hydrogen. to accomplish this, we use cosmological simulations of the eor, including on-the-fly multi-frequency radiative transfer, using the technicolor dawn code. through generation of mock quasar sightlines and simulated spectra, we analyze metrics of metal absorption and other gas parameters to illuminate their connection to the process of reionization. additionally, by incorporating several stellar population synthesis models, including one with binary stars, we examine how differing stellar emissivities impact the timing of reionization and the preferred ionization states of metals in the enriched cgm and igm. we find that the ionization states of common absorbing transitions are sensitive to the amplitude and spectral shape of the ionizing background, suggesting that careful observations of these systems will place constraints on the nature of the primary contributors to reionization, particularly whether quasars could have played a major part. further, we determine the redshift evolution of metals is dependent on the ionizing background and, through abundance ratios of neutral oxygen and silicon, can be directly tied to the neutral fraction of hydrogen, assisting in studies of the timing of reionization. finally, we show that while the harder spectra of binary stars can affect elemental ionization states and lead to an accelerated reionization history, it can also lead to decreased star formation rate density through gas heating, and subsequently decreased levels of enrichment in the cgm and igm. this work reveals a complex interplay between several simulation parameters, and also highlights the usefulness of metal line studies at z>5. | investigating trends in the cgm and igm during reionization |
the human pathogenic bacteria bacillus cereus, bacillus anthracis and the entomopathogenic bacillus thuringiensis form spores encased in a protein coat surrounded by a balloon-like exosporium. these structures mediate spore interactions with its environment, including the host immune system, control the transit of molecules that trigger germination and thus are essential for the spore life cycle. formation of the coat and exosporium has been traditionally visualized by transmission electronic microscopy on fixed cells. recently, we showed that assembly of the exosporium can be directly observed in live b. cereus cells by super resolution-structured illumination microscopy (sr-sim) using the membrane mitotrackergreen (mtg) dye. here, we demonstrate that the different steps of coat formation can also be visualized by sr-sim using mtg and snap-cell tmr-star dyes during b. cereus sporulation. we used these markers to characterize a subpopulation of engulfment-defective b. cereus cells that develops at a suboptimal sporulation temperature. importantly, we predicted and confirmed that synthesis and accumulation of coat material, as well as synthesis of the σk-dependent protein bxpb, occur in cells arrested during engulfment. these results suggest that, unlike the well-studied model organism bacillus subtilis, the activity of σk is not strictly linked to the state of forespore development in b. cereus. | a new fluorescence-based approach for direct visualization of coat formation during sporulation in bacillus cereus |
in recent years, high resolution multi-object spectroscopy has enabled the measurement of detailed chemical compositions for tens to hundreds of thousands of stars in the milky way's oldest stellar populations. globular clusters and the galactic bulge have been a particular target of interest, and the accurate spectroscopic abundances can now be correlated with photometric indices that can expand the number of stars with abundance measurements by several orders of magnitude. underpinning much of this work is the moog line analysis code written by chris sneden, which has been used to calculate abundances from equivalent widths and spectrum synthesis. in this talk, i will highlight some recent developments in the field of globular cluster and galactic bulge research that have built off the legacy of moog. additionally, i will touch on some interesting but seldom discussed results from the past that shed light on the chemical evolution of our galaxy's oldest stars. | insights into globular clusters and bulge field stars with moog |
the favored core accretion model of planet formation predicts a deficit of planets between the masses of neptune and saturn. this planet desert is a consequence of the runaway gas accretion process, which is thought to cause protoplanetary cores of about 10 earth masses to rapidly grow to ~300 earth masses rapidly through rapid accretion of hydrogen and helium gas. this process is expected to result in jupiter-like planets and more numerous ~10 earth mass failed jupiter cores, in cases when the gas disk dissipated before runaway accretion could begin. this prediction can be tested with a comparison to results from ground-based microlensing surveys, which is sensitive to planets down to an earth mass orbiting beyond the snow line. in this talk, we compare the microlensing measurement of the planet mass-ratio distribution to population synthesis models based on the core accretion theory. we show that the models predict ~10 times fewer planets at mass-ratios of 10^{-4} < q < 4\times 10^{-4} than found by the microlensing observations. this implies that the formation of gas giants may involve more complicated processes than assumed by the standard core accretion theory. or, it implies that the planet formation process may vary significantly as a function of host star mass, because the population synthesis models have been calibrated for planets around solar-type stars while microlensing observations are biased toward lower-mass stars. finally, we briefly discuss the mass measurements of host stars (and planets) that the wfirst microlensing survey will make for most planetary microlensing events. | microlensing results challenge the core accretion run-away growth scenario for gas giants |
using stellar population synthesis, we construct a model for the distribution of high-redshift galaxies on the uvj diagram, i.e. the rest-frame u-v vs v-j plane. we find that stochastic star formation history models are able to reproduce the observed color distributions of star-forming galaxies, when combined with the assumption of a random distribution of dust attenuation values across the galaxy population. this may indicate that galaxy inclinations are a major contributor to the observed uvj distribution. we confirm this hypothesis using a simple geometric model, where the dust attenuation for each galaxy is uniquely determined by the viewing angle, total amount of dust, and disk thickness. we also find that the color distribution is substantially different for low- and high-mass galaxies. this can be explained by a systematic change in the disk thickness, where the most massive galaxies are almost spheroidal, and consequently have the smallest spread in dust attenuation. the sao reu program is funded in part by the national science foundation reu and department of defense assure programs under nsf grant no. ast-1852268, and by the smithsonian institution. | modeling galaxy colors with stochastic star formation histories |
there appears to be correlations between sn ia hubble diagram residuals and host galaxy mass, metallicity, and star formation history. an uncorrected bias may produce a systematic offset in cosmological measurements. rigault et al. (2013) found that the local environment can correlate with hubble residuals and possibly impact precision hubble constant measurements. global properties are the luminosity average of local environments, therefore the properties of local environments may hold stronger correlations than their global counterparts. we analyze host galaxies from the sdss-ii survey using both ground-based and hubble space telescope imaging. we generate local stellar environmental properties by selecting a best fit flexible stellar population synthesis model that matches the sdss scene modeling data. the derived properties, such as metallicity, stellar age, and star formation history, are then compared to the sn ia's hubble residual in the search for correlations. | correlations between hubble residuals and local stellar populations of type ia supernovae |
the ir emission from galaxies is a unique window into multiple aspects of galaxy evolution including star-formation rates, the age of galaxies, and galactic-scale dust processes. however, asymptotic giant branch (agb) stars continue to introduce uncertainty into stellar population synthesis (sps) models and limit our ability to interpret the ir light of galaxies. here we focus on incorporating circumstellar dust around agb stars in sps models and understanding the extent to which they influence the ir light of galaxies. we find that the significance of the agb dust contribution depends on the characteristics of the galaxy. for quiescent galaxies and metal-poor star forming galaxies, circumstellar dust emission can have a large effect, whereas for dusty star-forming galaxies the circumstellar emission is dwarfed by emission from dust in the ism. the models with circumstellar dust also suggest, in agreement with previous work, that ir colors can be a powerful age diagnostic for older stellar systems. models such as these will be essential for interpreting data that will be provided by jwst and other next generation ir facilities. | implications of including agb dust in sps models |
introduction:in recent years, we witnessed increasing numbers of migrants worldwide owing to famine, poverty, regional conflicts,etc.efforts by the united nations and various organizations to help these migrants are hampered by rising anti-migrant sentiments and xenophobic rhetoric in many parts of the world. to arrive at win-win solutions that benefit both natives and migrants, we must discuss the migration problem objectively and scientifically. to do this, we must first resolve the paradox in our understanding of human migration (widely touted as good) vis-a-vis biological invasion (generally regarded as bad).method:suspecting that the two similar phenomena are more complex than we think, we reviewed and synthesized the disjoint literatures on human migration and biological invasion in recent times, and that on the human diaspora and human-aided dispersal of plants and animals in our pre-historic past. we then developed models of niche-niche interactions to simulate isolated ecosystems and communities, as well as those experiencing invasions from non-native populations.results:in this paper, we simulated four invasion mechanisms on a star network: the direct introduction of a non-native population into existing periphery or core niches, or the non-native population first creating its own niche, which is thereafter attached to the periphery or core of the community. we found that periphery invasions can fail, i.e., the non-native population eventually disappears. when periphery invasion is successful, we found that there is little or no harm to the ecosystem or community. on the other hand, core invasion is always catastrophic, where the non-native population establishes itself at the expense of most or all of the native populations. for niche attachments, whether to the periphery or to the core, we found native and non-native populations coexisting in the end, sometimes with increased diversities.discussion:our results provide promising new insights and theoretical grounds for policymakers to discuss the ethics of immigration issues scientifically, and to ultimately discover win-win solutions for natives and migrants. the theoretical framework outlined in this paper can also be applied to the problem of introducing non-native biological species for economic gains, at acceptable ecological costs. | scientific debate on human migration: ethics, challenges, and solutions |
redback (rb) and black widow (bw) systems are compact binaries containing a millisecond pulsar (msp) and a low-mass stellar companion. for rbs, this companion is usually around 0.1-0.4 solar masses, while bw companions are <0.1 but tend to be a few percent of a solar mass. radio eclipses are a defining feature for many of these msps, and they also can show strong variability in the optical, x-rays, and γ-rays. the population of these rbs and bws — commonly referred to as "spiders" — is relatively small; however, sky surveys spanning the electromagnetic spectrum, combined with dedicated follow-up observation campaigns, have greatly increased the number of spiders discovered in recent years. our current knowledge of the properties and formation channels of spiders is still far from complete, though. here we outline some of our ongoing work with spiders, including results from radio searches of candidate systems as well as fermi unassociated sources, methods and preliminary results for timing a small sample of rbs in globular clusters, and an effort to synthesize known parameters of the current population. | cosmic arachnology: ongoing studies of redback and black widow pulsars |
researchers have reanalyzed nearly 10,000 light curves from the optical gravitational lensing experiment. the resulting catalog, which is publicly available, provides new opportunities to study black holes, exoplanets, and much more.making sense of microlensingan illustration of a gravitational microlensing event. in this case, the lensing object is a star with an exoplanet in orbit around it. click here to see an animation of this event. [nasa]when one astronomical object passes in front of another, the background objects light is lensed, or focused, by the foreground objects gravity, and we see a temporary jump in the background objects brightness. this process of gravitational microlensing can clue us in to the presence of objects that emit little or no light, like black holes, exoplanets, and dark matter candidate objects, as they pass in front of stars or other luminous sources. gravitational microlensing events are one of the most promising ways to find isolated stellar-mass black holes, which have long been difficult to track down.the optical gravitational lensing experiment (ogle) has observed more than 10,000 microlensing events since the survey began in 1992. but recording the event is just the first step to understanding what caused it. researchers model microlensing light curves to estimate the properties of the objects involved, but many factors can complicate these calculations; our vantage point earth is in constant motion, stars vary in brightness for a multitude of reasons, and instruments arent perfect. how can we account for all those factors and extract useful information from a microlensing light curve?an example of a gravitational microlensing event drawn from the sample analyzed in this work. in this event, ogle blg 156.7.141434, the brightness of the background source is variable. click to enlarge. [golovich et al. 2022]new and improvedthats where todays article comes in. in a new publication, a team led by nathan golovich (lawrence livermore national laboratory) reanalyzed nearly 10,000 microlensing events in the third and fourth ogle catalogs. the teams new model accounts for earths motion which affects our perception of how quickly the background and foreground objects move relative to one another as well as variability in the brightness of the background object and systematic instrumental effects.this type of model has been applied to a single microlensing event, but it has never been used on a full survey because of the immense computing power it requires golovich and coathors used about a million hours of computer processing time to analyze their sample! the team showed that their model was able to separate the desired signal from competing factors like earths motion and the variability of the object being lensed, greatly reducing sources of bias.a curated catalogan example light curve and model fit for ogle blg 156.7.141434, the same event shown in the previous figure. click to enlarge. [golovich et al. 2022]what does this updated catalog mean for the search for isolated black holes? golovich and collaborators used the open-source population synthesis for compact object lensing events tool (popsycle) to simulate microlensing events and identify locations in parameter space that isolated black holes are likely to inhabit. based on the results of these simulations, the authors estimate that 50% or more of the 390 ogle events in that region of parameter space are most likely due to foreground black holes.the catalog the largest of its kind, to date is free to anyone who wishes to use it; if youre interested in black holes, exoplanets, or any other kind of dark object, theres no better time to be on the hunt!citationa reanalysis of public galactic bulge gravitational microlensing events from ogle-iii and -iv, nathan golovich et al 2022 apjs 260 2. doi:10.3847/1538-4365/ac5969the post a massive reanalysis of microlensing events appeared first on aas nova. | a massive reanalysis of microlensing events |
neutron stars are known to host extremely powerful magnetic fields. among other effects, one of the consequences of harboring such fields is the deformation of the neutron star structure, leading, together with rotation, to the emission of continuous gravitational waves (cgws). we present an extensive numerical study of magnetized neutron stars in gr with a large variety of different equations of state (eoss) and show that it is possible to find simple relations between the magnetic deformation of a neutron star, its mass and radius, that are mostly independent on the eos or magnetic configuration. we discuss how these relations can be used in conjunction with possible future cgws detection to set constrains on the eos and magnetic configurations of nss (e.g. the presence of a superconducting phase). by carrying out a population synthesis, we estimate the possible cgws detectability of galactic millisecond pulsars, with third generation gw detectors. | modelling the deformability of magnetized neutron stars in the light of future continuous gravitational waves detection |
many hot jupiters (hjs) have been observed to have large obliquities or misalignments between the stellar spin axis and the orbital angular momentum of the planet. this observation hints that at least a portion of hjs formed through high-eccentricity migration, in which a cold jupiter is excited onto a highly eccentric orbit that circularizes over time due to tidal dissipation in the planet. one variety of high-e migration occurs when eccentricity oscillations are excited by an inclined stellar companion (von zeipel-kozai-lidov, or zkl oscillations). previous population studies of this mechanism assumed initial spin-orbit alignment. however, a star's obliquity may be significantly excited during the dissipation of its protoplanetary disk. by using a disk-excited obliquity for the initial condition of a new population synthesis, we demonstrate that the expected obliquity distribution from zkl-driven high-e migration has a peak near 90 degrees, similar to the recently-observed preponderance of perpendicular planets close to their host stars. | forming hot jupiters via high-eccentricity migration: a preference for perpendicular planets |
the study of orbital resonances allows for the constraint of planetary properties of compact systems. mean motion resonance occurs when two or more planets repeatedly exchange angular momentum and energy as they orbit their host star, since the planets will always conjunct at the same point in their orbits. we can predict a system's resonances by observing the orbital periods of the planets, as planets in or near mean motion resonance have period ratios that reduce to a ratio of small numbers. however, a period ratio near commensurability does not guarantee a resonance; we must study the system's dynamics and resonant angles to confirm resonance. because resonances require in-depth study to confirm, and because two-body resonances require a measurement of the eccentricity vector which is quite challenging, very few resonant pairs or chains have been confirmed. we thus remain in the era of small number statistics, not yet able to perform large population synthesis or informatics studies. to address this problem, we build a python package to find, confirm, and analyze mean motion resonances, primarily through n-body simulations. we verify our package by recovering the known resonances of kepler-80 and kepler-223. we then analyze all near-resonant planets in the kepler/k2 and tess catalogues, confirming over 40 new resonant pairs and various new resonant chains. we additionally demonstrate the package's functionality and potential by characterizing the mass-eccentricity degeneracy of kepler-80g, exploring the likelihood of an exterior giant planet in kepler-80 and kepler-223, and studying the formation history of k2-138. | confirming and characterizing new mean motion resonances in the kepler and tess catalogues |
fado comes from the latin word "fatum" that means fate or destiny. it is also a well known genre of portuguese music, and by choosing this acronym for this spectral synthesis tool we would like to pay tribute to portugal. the main goal of fado is to explore the star-formation and chemical enrichment history (the "fado") of galaxies based on two hitherto unique elements in spectral fitting models: a) self-consistency between the best-fitting star formation history (sfh) and the nebular characteristics of a galaxy (e.g., hydrogen balmer-line luminosities and equivalent widths; shape of the nebular continuum, including the balmer and paschen discontinuity) and b) genetic optimization and artificial intelligence algorithms. this document is part of the fado v.1 distribution package, which contains two different ascii files, readme and read_f, and one tarball archive fadov1.tar.gz. fadov1.tar.gz contains the binary (executable) compiled in both opensuse 13.2 64bit linux (fado) and mac os x (fado_macosx). the former is compatible with most linux distributions, while the latter was only tested for yosemite 10.10.3. it contains the configuration files for running fado: fado.config and plot.config, as well as the "simple stellar population" (ssp) base library with the base file list base.bc03.l, the fado v.1 short manual read_f and this file (in the readme directory) and, for testing purposes, three characteristic de-redshifted spectra from sdss-dr7 in ascii format, corresponding to a star-forming (spec1.txt), composite (spec2.txt) and liner (spec3.txt) galaxy. auxiliary files needed for execution of fado (.hifboundem.ascii, .heiifbound.ascii, .heifboundem.ascii, grfont.dat and grfont.txt) are also included in the tarball. by decompressing the tarball the following six directories are created: input, output, plots, readme, ssps and tables (see below for a brief explanation). (2 data files). | vizier online data catalog: fado code (gomes+, 2017) |
stellar population synthesis (sps) models are routinely used to interpret extragalactic observations at all redshifts. currently, the dominant source of uncertainty in sps modeling lies in the degeneracies associated with synthesizing and fitting complex stellar populations to observed galaxy spectra. to remedy this, we propose an empirical calibration of sps models using resolved stellar population observations from hubble space telescope (hst) to constrain the stellar masses, ages, and star formation histories (sfhs) in regions matched to 2d spectroscopic observations from manga. we will take advantage of the state of the art observations from the panchromatic hubble andromeda treasury (phat), which maps the dust content, history of chemical enrichment, and history of star formation across the disk of m31 in exquisite detail. recently, we have coupled these observations with an unprecedented, spatially-resolved suite of ifu observations from manga. with these two comprehensive data sets we can use the true underlying stellar properties from phat to properly interpret the aperture-matched integrated spectra from manga. our manga observations target 20 regions within the phat footprint that fully sample the available range in metallicity, sfr, dust content, and stellar density. this transformative dataset will establish a comprehensive link between resolved stellar populations and the inferred properties of unresolved stellar populations across astrophysically important environments. the net data product will be a library of galaxy spectra matched to the true underlying stellar properties, a comparison set that has lasting legacy value for the extragalactic community. | phat+manga: using resolved stellar populations to improve the recovery of star formation histories from galaxy spectra |
the tess mission has the potential to probe stellar rotation in millions of stars across the entire sky, but mission systematics—instrumental noise, observing gaps, and changes in detector sensitivity—have prevented recovery of rotation periods longer than 13.7 days. i used deep learning to see through tess systematics and recover periods from year-long light curves. my approach uses a training set of synthesized light curves from realistic star spot evolution simulations, with real light curve systematics from quiet tess stars. evaluating the network on real tess data, i recovered periods for 20,000 cool dwarfs. the period distribution resembles the kepler and k2 distributions, including periods up to 90 days. using gyrochronology, i estimated masses, ages, and other fundamental stellar parameters for 1,000 tess stars with apogee spectroscopy. we combine this with a similar sample from kepler and show that we can use rotation-based ages to recover galactic chemical evolution trends previously seen only in stars more massive or more evolved than the sun. with rotation periods across the entire sky, we can characterize stars along many more lines of sight than before, enabling detailed study of the galaxy's stellar populations. | rotational characterization of tess stars with deep learning |
currently, we know of nearly one hundred compact binary mergers from the first three observation runs of ligo and virgo, and expect a "deluge" of new detections in the next few years. this wealth of new data provides us with crucial insights on the populations of binary compact objects, helping us to tackle some of the main open questions: what is the mass function of compact objects? what is the distribution of black hole spins? what are the formation channels of binary compact objects? in this talk, i will present the latest results of our population-synthesis simulations, which allow us to probe a large portion of the parameter space, inferring the impact of stable/unstable mass transfer and different core-collapse supernova models on binary compact object mergers. also, i will present a new study of the merger rate evolution and the properties of the host galaxies of binary compact objects, based on observational scaling relations of metallicity and star formation rate. the astrophysical models indicate a possible tension between the predicted merger rate of binary compact objects and the latest results from the ligo-virgo collaboration. | populations of binary compact-object mergers |
a robust numerical method for discrete two-sample ks-test calculation for is presented. the method is binning-independent and computationally efficient at large ratios of sample sizes. the method is used for binary stars population synthesis problem to test distributions of synthesized binary parameters against distributions of observed parameters. | numerical method for discrete two-sample ks-test in binary stars population synthesis problem |
binary_c-python provides a manager for and interface to the binary_c framework (ascl:2307.035), and rapidly evolves individual systems and populations of stars. it provides functions such as data processing tools and initial distribution functions for stellar properties. binary_c-python also includes tools to run large grids of (binary) stellar systems on servers or distributed systems. | binary_c-python: stellar population synthesis tool and interface to binary_c |
we present our analysis of metal contributions from galaxies as observed in quasar absorption line spectra from 10 ≥ z ≥ 5.5 during the end of the epoch of reionization (eor). this was done with particle tracking done in-parallel in the latest technicolor dawn run and then linking absorbers to potential host galaxies in post-processing. when we look at all the species in our test (cii, civ, siii, siiv, mgii, and oi) we see that all galaxies contribute roughly equally to each absorber. we then did the analysis while splitting the absorbers into stronger (≥ 0.01 å) and weaker absorbers and we see that galaxies still equally contribute to both the population of stronger and weaker absorbers. we also do not see any relation between the absorber strength and the stellar mass of the contributing galaxy. from these results, we conclude that we cannot reject most metals being synthesized and ejected from less luminous, less massive galaxies if one assumes current uvlf and stellar mass function assuming flat λcdm with implications that most metal absorbers may be associated with galaxies currently below the observational limits of even jwst. | galaxy-absorber association in the epoch of reionization: galactic population luminosity distribution for different absorbers at 10 ≤ z ≤ 5.5 |
wind roche-lobe overflow (wrlof) is a mechanism of mass transfer in a binary system where the wind acceleration zone radius of the donor exceeds the roche-lobe radius and the stellar wind transfers mass to the accretor. the disagreement between the observed and modeled population of carbon-enhanced metal-poor (cemp) stars has been reduced when including the effect of wrlof. however, apart from fast population synthesis codes, wrlof has not yet been applied to detailed binary evolution with a large parameter range. we implement wrlof in mesa and posydon for low mass stars with metallicity z = 0.01 solar metallicity. we find that when using wrlof, the accretor gains ~0.05 solar masses from wind accretion and evolves off the main sequence earlier. after gaining mass from the donor through wind accretion, the wind of the accretor is enhanced because the accretor begins to leave the main sequence, and therefore the mass loss rate of the accretor increases. modeling wrlof in binaries will therefore be integral to understanding these systems. | applying wind roche-lobe overflow in binary evolution using mesa and posydon |
after 50 years, the moog spectrum synthesis code remains an essential and popular tool for the analysis of stellar spectra. this meeting-in-meeting will highlight some of the diverse applications and new directions of research enabled by moog, as well as impact this code has had on our understanding of stars and stellar populations over the decades. | synthesizing the music of the stars |
we can learn a lot about the formation of compact objects, such as neutron stars and black holes, by studying the x-ray emission from accreting systems in nearby star-forming galaxies. the harder (e>10 kev) x-ray emission in particular allows strong discrimination among the accretion states and compact object types.a nustar survey of m33 was conducted to study the distribution of x-ray binary (xrb) accretion states in an actively star-forming environment. the 6 nustar observations of m33 allow us to construct diagnostic diagrams, which is used to infer xrb accretion states.we have characterized xrb accretion states for ≈32 sources. the xrbs are classified by their compact object types using nustar color-intensity and color-color diagrams. we further characterize the black holes by their accretion states (soft, intermediate, and hard) and the neutron stars by their weak or strong (accreting pulsar) magnetic field. in contrast to a similar nustar survey of m31 (with a low-mass xrb-dominant population), the source population is dominated by high-mass xrbs, allowing the study of a very different population with similar sensitivity. these results provide a significant improvement in our knowledge of high-mass xrb accretion states that proves valuable for theoretical xrb population synthesis studies. | young black hole and neutron star systems in the nearby star-forming galaxy m33: the nustar view |
modeling low mass stellar populations, like clusters and dwarf galaxies, with population synthesis models requires that we evaluate the role played by stochastic fluctuations in the sampling of the imf on the spectro-photometric properties of these sparse populations. interacting binaries may also modify the integrated spectra of these systems depending on the final product of the binary interaction and on the frequency of binary stars. in this work we compare the relative importance of stochastic fluctuations and binary evolution on low mass galaxy properties as a function of the population age and total mass. in most cases the effects of stochastic fluctuations dominate those produced by binary interactions. we explore and quantify the relative importance of these effects through cosmic times. | modeling low mass stellar populations |
using an evolutionary population synthesis code, we modeled the universal, featureless x-ray luminosity function of high-mass x-ray binaries (hmxbs) in star-forming galaxies. we put constraints on the natal kicks, super-eddington accretion factor, as well as common envelope prescriptions usually adopted (i.e., the αce formalism and the γ algorithm), and presented the detailed properties of hmxbs under different models, which may be investigated further by future high-resolution x-ray and optical observations. | high-mass x-ray binaries: evolutionary population synthesis modeling |
the synthesis of dust grains mostly takes place in the circumstellar envelopes (cses) of asymptotic giant branch (agb) stars. what are the precursor seeds of condensation nuclei and how do these particles evolve toward the micrometer sized grains that populate the interstellar medium? these are key questions of the nanocosmos project. in this study, we carried out an observational study to constrain what the main gas-phase precursors of dust in c-rich agb stars are. | abundance estimates in carbon star envelopes |
connecting star and planet properties in a single model is not straightforward. stellar population synthesis models are key to explore combined statistical constraints from stars and planets observations. the besançon stellar population synthesis model (robin et al. 2003, lagarde et al. 2017) includes now the stellar evolutionary tracks computed with the stellar evolution code starevol (lagarde et al. 2012, amard et al. 2016). it provides the global (m, r, teff, etc) and chemical properties of stars for 54 chemical species. it enables to study the different galactic populations of the milky way (the halo, the bulge, the thin and thick disc) and a specific observational survey. here, we couple the besançon model with a simple stoichiometric model (santos et al. 2017) in order to determine the expected composition of the planet building blocks (pbb). we investigate the trends and correlations of the expected chemical abundances of pbb in the different stellar populations of the milky way (cabral et al. 2018). | chemical connections between low-mass stars and planets building blocks investigated by stellar population synthesis |
for decades, a subset of carbon-rich wr (wc) stars have been known to actively form dust despite their extreme environments. although these systems can produce copious amounts of dust, they have been commonly overlooked as significant sources of dust in the ism of galaxies in the local and early universe due to the persisting mysteries on their dust formation and the influence of binary companions. in this talk, i will discuss the results and plans from our research program that combines archival data thermal ir observations, new imaging and spectroscopic data from subaru/comics, and approved early release science observations with jwst in cycle 1. i will highlight our major results that uniquely combine a comprehensive dust sed analysis of galactic dust-forming wc stars with binary population and spectral synthesis (bpass) models and show that wc binaries are early sources and significant sources of dust at lmc-like and solar metallicities in constant star-forming environments. | revisiting and resolving carbon-rich wolf-rayet dust factories |
binary systems are prevalent in both stellar clusters with high central densities and in the galactic field. i aim to understand the effects of dynamics by presenting a systematic comparison between the evolution and properties of identical initial binary populations placed in different environments. i explore a full range of environments, from the densest stellar clusters where binaries are strongly affected by dynamical interactions, to less dense stellar clusters affected somewhat by dynamics, to the galactic field, where binaries evolve in isolation. i present our results based on a combination of monte carlo dynamical modeling for dense star clusters and population synthesis for the field, and i compare them to theoretical expectations. | dynamics vs. isolated evolution: how do different environments affect binary populations? |
searching for distinctive signatures, which characterize different formation channels and environments of binary black holes (bbhs), is a crucial step towards the interpretation of current and future gravitational wave detections. in this talk, i will discuss the formation of merging bbhs in young star clusters (scs), which are the nursery of massive stars. in particular, i will show the results of a large set of n-body simulations of scs with a large primordial binary fraction and novel population-synthesis prescriptions. the simulated scs have fractal initial conditions, to mimic the clumpiness of star forming regions. i will discuss the impact of star cluster dynamics on the properties (total masses, mass ratios and delay times) of merging bbhs. more than 50% of merging bbhs formed by dynamical exchange in our simulations. bbhs formed via exchanges are significantly more massive than bbhs formed from primordial binaries, reaching chirp masses larger than 30 m⊙. in our simulations, dynamical exchanges are the only channel able to form merging bbhs similar to gw170729, the most massive gravitational wave event observed by ligo-virgo. stellar collisions lead to the formation of intermediate mass black holes (imbhs) with mass up to 440 m⊙. imbhs represent <~ 0.1 % of all black holes in our simulations. finally ∼2 % of merging bbhs in young scs have mass in the pair-instability mass gap (∼60-120 m⊙). this represents a unique fingerprint of merging bbhs in scs. | young star clusters: a nursery of merging binary black holes |
our understanding of galactic structure and evolution is far from complete. within the past twelve months we have learnt that the milky way is about 50% wider than was previously thought. as a consequence, new models are being developed that force us to reassess the kinematic structure of our galaxy. similarly, we need to take a fresh look at the halo structure of external galaxies in our local group. studies of stellar populations, star-forming regions, clusters, the interstellar medium, elemental abundances and late stellar evolution are all required in order to understand how galactic assembly has occurred as we see it. pne play an important role in this investigation by providing a measure of stellar age, mass, abundances, morphology, kinematics and synthesized matter that is returned to the interstellar medium (ism). through a method of chemical tagging, halo pne can reveal evidence of stellar migration and galactic mergers. this is an outline of the advances that have been made towards uncovering the full number of pne in our local group galaxies and beyond. current numbers are presented and compared to total population estimates based on galactic mass and luminosity. a near complete census of pne is crucial to understanding the initial-to-final mass relation for stars with mass >1 to <8 times the mass of the sun. it also allows us to extract more evolutionary information from luminosity functions and compare dust-to-gas ratios from pne in different galactic locations. with new data provided by the gaia satellite, space-based telescopes and the rise of giant and extra-large telescopes, we are on the verge of observing and understanding objects such as pne in distant galaxies with the same detail we expected from galactic observations only a decade ago. | pn populations in the local group and distant stellar populations |
this negative image of ngc 5907 (originally published inmartinez-delgadoet al. 2008; click for the full view!) reveals the faint stellar stream that encircles the galaxy, forming loops around it a fossil of a recent merger. mergers between galaxies come in several different flavors: major mergers, in which the merging galaxies are within a 1:5 ratio in stellar mass; satellite cannibalism, in which a large galaxy destroys a small satellite less than a 50th of its size; and the in-between case of minor mergers, in which the merging galaxieshave stellar mass ratios between 1:5 and 1:50. these minor mergers are thought to be relatively common, and they can have a significant effect on the dynamics and structure of the primary galaxy. a team of scientists led by seppo laine (spitzer science center caltech) has recently analyzed the metallicity and age of the stellar population in the stream around ngc 5907. by fitting these observations with a stellar population synthesis model, they conclude that this stream is an example of a massive minor merger, with a stellar mass ratio of at least 1:8. for more information, check out the paper below!citationseppo laine et al 2016 aj 152 72. doi:10.3847/0004-6256/152/3/72 | featured image: a looping stellar stream |
stellar formation and evolution, as they apply to binary stars, reveal their underlying physical mechanisms through the properties of the observed binary star samples. by analyzing populations of binaries, we can study these processes in detail. in the era of large-scale time domain surveys, the acquisition of large samples of eclipsing binaries is all but guaranteed. the kepler eclipsing binary catalog (kebc; kirk et al 2016) provides a glimpse of what these large scale surveys will produce and offers an opportunity to develop extensible methodologies as we prepare for the massive influx of data from the large synoptic survey telescope (lsst). in this contribution we forward-model the underlying kepler binary population using the state-of-the-art in synthetic survey generation code and constraints provided by binary population studies (raghavan et al. 2010, duchene & kraus 2013, moe & di stefano 2017). we simulate kepler observations of the underlying synthetic binary population to obtain a synthetic eclipsing binary survey. these synthetic eclipsing binaries are compared to the ~90% complete kebc. using the catalog as a baseline, we iteratively modify the input distributions from which we generate binary orbital parameters and re-synthesize the binary population until the discrepancy between the synthetic and observed reference population is minimized. comparing the adjusted population with the initial input model, we are able to provide a quantitative assessment of how well our input assumptions are able to account for the observed population. in this pilot study we focus only on the observed period distribution of detached eclipsing binaries; other observables, most notably mass-ratio or eccentricity, will also be used to tune the synthetic binary population in future work. | synthesizing a sample of detached binary stars in the kepler field to probe the underlying stellar population |
we analyze the optical continuum of star-forming galaxies in the sloan digital sky survey by fitting stacked spectra with stellar population synthesis models to investigate the relation between stellar mass, stellar metallicity, dust attenuation, and star formation rate. we fit models calculated with star formation and chemical evolution histories that are derived empirically from multi-epoch observations of the stellar mass-star formation rate and the stellar mass-gas-phase metallicity relations, respectively. we also fit linear combinations of single-burst models with a range of metallicities and ages. star formation and chemical evolution histories are unconstrained for these models. the stellar mass-stellar metallicity relations obtained from the two methods agree with the relation measured from individual supergiant stars in nearby galaxies. these relations are also consistent with the relation obtained from emission-line analysis of gas-phase metallicity after accounting for systematic offsets in the gas-phase metallicity. we measure dust attenuation of the stellar continuum and show that its dependence on stellar mass and star formation rate is consistent with previously reported results derived from nebular emission lines. however, stellar continuum attenuation is smaller than nebular emission line attenuation. the continuum-to-nebular attenuation ratio depends on stellar mass and is smaller in more massive galaxies. our consistent analysis of stellar continuum and nebular emission lines paves the way for a comprehensive investigation of stellar metallicities of star-forming and quiescent galaxies. (2 data files). | vizier online data catalog: mass, z, dust attenuation, and sfr relations (zahid+, 2017) |
in the last decade great strides have been made in understanding the role of binary stars in the evolution and shaping of planetary nebulæ (pne). observational efforts have mainly focused on finding close binaries with orbital periods of 1 day or less. those close binary systems make up around 1 in 5 pne, and constitute the youngest accessible window into the aftermath of the critical and unobserved common-envelope (ce) phase of binary-star evolution. the poster focused on our recent work with the high resolution spectrograph (hrs) on the southern african large telescope (salt) to search for long-period binaries in pne. considerably less is known about such long-period binaries with orbital periods of weeks to years, but they may be fundamental to improving ce population synthesis models and for determining the total binary fraction of pne. the queue-mode operation of salt and the excellent sensitivity and stability of hrs (which is enclosed in a vacuum tank) are ideally suited to detecting binaries with low radial-velocity amplitudes over the expected timescales of weeks to years. many exciting new discoveries about binaries have already been made in this newly-accessible southern horizon in time-domain astronomy thanks to the many unique advantages of salt. | searching for long-period binary central stars of planetary nebulae with salt hrs |
the first glimpse of the spectral properties of z 7-10 galaxies has recently emerged. deep uv spectra have revealed intense emission from nebular ciii] and civ, implying a hard radiation field that is rarely seen at lower redshifts. unfortunately, we are currently unprepared to interpret these features, owing to shortcomings in our understanding of the radiation field powered by low metallicity stellar populations. recent work with hst/cos in the local universe has provided a way forward, unveiling four nearby metal poor galaxies with uv nebular line spectra approaching those seen at z>7. the discovery of these galaxies opens the door for the first comprehensive investigation of the low metallicity stellar populations that likely dominate at z>7. here we propose to obtain ultra-deep (10 orbit) cos/g160m spectra capable of measuring stellar photospheric and wind absorption features in these four galaxies. the data will provide the first quantitative constraints on the metallicity of massive stars required to power the hard radiation fields implied by the nebular lines and will allow us to investigate whether the stellar metallicity (sensitive to iron) departs from the metallicity of the nebular gas (sensitive to oxygen) in the extreme uv line emitters. using new spectral tools, we will simultaneously fit the stellar absorption features and nebular lines, providing a powerful stress test of population synthesis models at low metallicity. if this uv spectral database is not obtained while cos is still functioning, the interpretation of reionization era galaxy spectra will be severely jeopardized throughout the jwst era. | massive stellar populations at reionization-era metallicities with ultra-deep hst/cos spectroscopy |
we propose an ambitious adap to provide a statistically rigorous characterization of how the x-ray binary luminosity function (xlf) depends on host stellar population age and metallicity. we will make unique use of archival chandra, galex, swift, sdss, hubble, 2mass, spitzer, herschel, and a variety of other ancillary data sets (including spectroscopy-based metallicity measurements) to measure x-ray and environmental properties on subgalactic and galaxy-wide scales. to this end, our galaxy samples include ~100 nearby galaxies where x-ray point sources are detected individually and ~2000 additional distant galaxies where the global galaxy-wide emission is unresolved. we will further identify, and study in detail, interesting outlier galaxies that strain our understanding of x-ray binary population formation and evolution. our projects will introduce robust empirical measurements that are vastly expanded beyond what is currently available (e.g., in terms of degrees of freedom) and will be used to constrain directly close binary population synthesis models. in the next decade, these constraints will be used in tandem with available and forthcoming measurements of ligo/virgo gravitational-wave merger-rate measurements to provide powerful insight into how close binaries form and evolve along with their host populations. | a framework characterizing the metallicity and age dependent formation of x-ray binaries in galaxies near and far |
a neutron star emerging from the common-envelope phase may be paired with a helium-star companion. the helium star may eventually undergo a supernova explosion and form a double neutron-star system. compact-binary population-synthesis codes often treat the transition from the pre-supernova to the post-supernova state as an instantaneous process. we investigate this phase transition with a more sophisticated model that accounts for the finite timescales of the supernova mass loss and natal kick. we compare how treating the finite timescales affects the final orbital characteristics of double neutron star populations with those predicted from the prescriptions often used in binary population-synthesis codes. a. miguel holgado is supported by the doe nnsa stewardship science fellowship. | double neutron-star formation from supernova natal kicks |
connecting star and planet properties in a single model is not straightforward. stellar population synthesis models are key to explore combined statistical constraints from stars and planets observations. the besançon stellar population synthesis model includes now the stellar evolutionary tracks computed with the stellar evolution code starevol. it provides the global (m, r, teff, etc) and chemical properties of stars for 54 chemical species. it enables to study the different galactic populations of the milky way (the halo, the bulge, the thin and thick disc) and a specific observational survey. here, we couple the besançon model with a simple stoichiometric model in order to determine the expected composition of the planet building blocks (pbb). we investigate the trends and correlations of the expected chemical abundances of pbb in the different stellar populations of the milky way (cabral et al. 2018). | chemical connections between low-mass stars and planets building blocks investigated by stellar population synthesis |
x-ray and extreme ultraviolet (xuv) radiation is likely shaping the observed population of short period exoplanets by powering blow-off of their atmospheres. the amount of atmosphere an individual planet might lose to xuv erosion depends on the history of its xuv irradiation, which could be 10-1000× higher when it formed than at present day. this can explain two classes of "missing" planets: sub-jovians with short orbital periods (<5 d) and planets with radii between super-earths and sub-neptunes out to longer periods (< 25 d), colloquially known as the "sub-jovian desert" and the "radius gap," respectively. however, a star's present xuv flux is likely not a good tracer of its xuv past. in consequence, we found correlating the properties of planets with their present-day xuv irradiation yielded no clear dependence in the location of the desert or the gap. we will present this test, along with simulations determining whether such correlations could be detected in yet-to-be-discovered tess planets in this talk. accurate knowledge of a individual stars' xuv histories could permit a robust test of the photoevaporation hypothesis for the missing planets and constrain the timespan over which photoevaporation is most effective. we will synthesize the current state of knowledge regarding the evolution of stellar xuv emission from the time of planet formation onwards for f-m stars, outlining the obstacles and opportunities for revealing the past lives of highly irradiated planets. | planets are shaped by their past: reconstructing the early xuv emission of exoplanet host stars |
the hubble deep and ultra deep fields are iconic, and almost certainly the most studied hst observations. wfirst will also have the opportunity to reach galaxies at the same extremely faint magnitudes, but with a fov 140 times that of hst wf3. this will open up the study of the highest redshift galaxies to the type of statistical studies that have made modern cosmology a precision science. jwst will also dramatically increase our ability to probe faint galaxies and higher redshifts. in our proposal we aim to make theoretical predictions for what will be seen in the wfirst and jwst deep fields, propose and test analysis methods and investigate sources of systematic error. our main tool will be state of the art cosmological hydrodynamic simulations that are well matched to the large volumes involved. these simulations include our flagship run, bluetides, a 0.5 gpc on a side, 0.7 trillion particle run that is by far the largest hydro simulation yet. we have published many early results from phase i of bluetides, which evolved to redshift z=8 and are currently using a large allocation on the ncsa bluewaters supercomputer to carry out phase ii of bluetides, which is evolving to lower redshifts (z 5), enabling us to make contact with much larger datasets and simulate the population of galaxies, bright and faint that will be seen by wfirst, jwst and euclid. bluetides represents a significant advance on our massiveblack simulation which previously reached these z 5 redshifts. improvements include a model for inhomogeneous reionization, a pressure-entropy formulation of sph and a model for star formation from molecular hydrogen. many significant code optimizations now allow it to run at the trillion plus particle level, so that mass resolution is 20 times better than massiveblack. the volumes are well matched: the wfirst fov is 0.75 degrees wide and bluetides spans 3.89 degrees at redshift z=6. in our proposed work, full population synthesis modelling applied to tens of billions of star particles means that fully spatially resolved spectra will be available for every galaxy. we will make simulated wfirst and jwst deep fields and cross-reference sources detected in them with galaxy properties in the fully 3 dimensional simulation outputs. this should be an invaluable resource to test the reliability of galaxy properties at redshifts z>5 inferred from observations. unlike bluetides phase i, phase ii is allowing the simulation to enter into the lower redshift regime which hosts the currently farthest known quasars. we will be able to validate the simulation modeling of black hole accretion and growth and make predictions for a whole new population of faint agn to be observed by wfirst. our inclusion of reionization physics will mean that we will be able to search for the signatures in wfirst observations of the effects of patchy reionization on galaxy formation. for example it has been predicted that uv radiation will suppress cooling and cause large scale fluctuations in galaxy properties (colors, star formation rates). perhaps most excitingly for cosmology, our initial studies have show that baryon acoustic oscillations in clustering may be detectable by wfirst at redshifts z 6-8. this is dependent on the wfirst high latitude survey observing strategy and also the final design and spectral coverage of the wfirst grism, both of which our proposed modeling could conceivably influence. our proposed theoretical study of the widest planned deep fields links directly to the nasa objective of understanding of the structure and evolution of the universe. the predictions for what wfirst and jwst will see in these integrations, from large scale clustering down to individual galaxy properties will be both state of the art and start from first principles. this will lead to the opportunity for surprising new theoretical results and for reliable tests of observational analysis techniques. | simulating the first galaxies and quasars |
wickramasinghe et al. (2014) and briggs et al. (2015) have proposed that the strong magnetic fields observed in some single white dwarfs (mwds) are formed by an α—ω dynamo driven by differential rotation when two stars, the more massive one with a degenerate core, merge during common envelope (ce) evolution (ferrario et al., 2015b). we synthesise a population of binaries to investigate if fields in the magnetic cataclysmic variables (mcvs) may also originate during stellar interaction in the ce phase. | magnetic fields in interacting binaries |
the ligo/virgo detections of gravitational waves from merging black holes of ~= 30 solar mass suggest progenitor stars of low metallicity (z/z⊙ <~ 0.3). in this talk i will provide constrains on where the progenitors of gw150914 and gw170104 may have formed, based on advanced models of galaxy formation and evolution combined with binary population synthesis models. first i will combine estimates of galaxy properties (star-forming gas metallicity, star formation rate and merger rate) across cosmic time to predict the low redshift bbh merger rate as a function of present day host galaxy mass, formation redshift of the progenitor system and different progenitor metallicities. i will show that the signal is dominated by binaries formed at the peak of star formation in massive galaxies with and binaries formed recently in dwarf galaxies. then, i will present what very high resolution hydrodynamic simulations of different galaxy types can learn us about their black hole populations. | merging massive black holes the right place and the right time |
we present lte analysis of high resolution optical spectra for b-type hot pagb stars ls iv-04 1 and lb3116 (lse 237). the spectra of these high galactic latitude stars were obtained with the 3.9-m anglo-australian telescope (aat) and the ucles spectrograph. the standard 1d lte analysis with line-blanketed lte model atmospheres and spectral synthesis provided fundamental atmospheric parameters of t eff= 15 000±1000 k, log g= 2.5±0.2, ξ = 5.0±1.0 km s-1, [m/h] = -1.81 dex, and v sin i= 5 km s-1 for lsiv-04 1 and t eff= 16 000±1000 k, log g= 2.5±0.1, v sin i= 25 km s-1, and [fe/h] = -0.93 dex for lb 3116. chemical abundances of ten different elements were obtained. for ls iv-04 1, its derived model temperature contradicts with previous analysis results. the upper limits for its nitrogen and oxygen abundances were reported for the first time. the magnesium, silicon and calcium were overabundant (i.e. [mg/fe] = 0.8 dex, [si/fe] = 0.5 dex, [ca/fe] = 0.9 dex). with its metal-poor photosphere and vlsr ≈ 96 km s-1, lsiv-04 1 is likely a population ii star and most probably a pagb star. lte abundances of lb 3116 were reported for the first time. the spectrum of this helium rich star shows 0.9 dex enhancement in the nitrogen. the photosphere of the star is slightly deficient in mg, si, and s. (i.e. [mg/fe] = -0.2 dex, [si/fe] = -0.4 dex, [s/fe] = -0.2 dex). the al is slightly enhanced. the phosphorus is overabundant, i.e. [p/fe] ≈ 1.7 ± 0.47 dex, hence lb3116 may be the first example of a pagb star which is rich in phosphorus. with its high radial velocity (i.e. v lsr = 73 km s-1), and the deficiencies observed in c, mg, si, and s indicate that lb 3116 is likely a hot pagb star at high galactic latitude. | high resolution optical spectroscopy of hot post-agb star candidates ls iv-04 1 and lb3116 |
this initial release provides a tool for a stellar population synthesis in our galaxy using the galactic model optimized for the bulge direction developed by koshimoto, baba, and bennett (2021), apj, 917, 78, and a forthcoming paper. the copyright of an included supplementary code, "option.c", belongs to ian a. bond and takahiro sumi. data values of files in input_files/ mostly come from other people's studies. see the header of each file for references. | nkoshimoto/genstars: a tool for stellar population synthesis toward the galactic bulge |
rapster (rapid cluster evolution) models binary black hole population synthesis and the evolution of star clusters based on simple, yet realistic prescriptions. the code can generate large populations of dynamically formed binary black holes. rapster uses sevn (ascl:2206.019) to model the initial black hole mass spectrum and precession (ascl:1611.004) to model the mass, spin, and gravitational recoil of merger remnants. | rapster: rapid population synthesis for binary black hole mergers in dynamical environments |
around 300,000 years after the big bang, the universe had cooled enough to combine and form neutral atoms. this signified the beginning of a time known as the dark ages. neutral matter began to fall into the dark matter gravitational wells that were seeded after the initial moments of the big bang. as the first stars and galaxies formed within these gravitational wells, the surrounding baryonic matter was heated and started to ionize. the source of energetic photons that heated and reionized the early universe remains uncertain. early galaxies had low metallicity and recent population synthesis calculations suggest that the number and luminosity of high-mass x-ray binaries are enhanced in star-forming galaxies with low metallicity, offering a potentially important and previously overlooked source of heating and reionization. here we examine two types of local galaxies that have been shown to be good analogs to the early galaxies in the universe: blue compact dwarf galaxies (bcds) and lyman break analogs (lbas).a bcd is defined by its blue optical colors, low metallicities, and physically small size. this makes bcds the best available local analogs for early star formation. we analyzed data from a sample of 25 metal-poor bcds and compared our results with those of near-solar metallicity galaxies. using a bayesian approach, we showed that the x-ray luminosity function for the low-metallicity bcds is significantly elevated relative to the xlf for near-solar metallicity galaxies.larger, gas-rich galaxies may have formed shortly after these first galaxies. these larger galaxies would be similar in their properties to the high-redshift lyman break galaxies (lbgs). lbas provide the best local comparison to the lbgs. we studied a sample of 10 lbas in order to measure the relation between star formation rate and x-ray luminosity for these galaxies. we found that for lbas with intermediate sub-solar metallicities, there is enhanced x-ray emission relative to the expected value from near-solar metallicity galaxies.by incorporating our results into simulations used to predict the redshifted 21cm signal from the early universe, unique and observable predictions could be made for future 21cm observations. | x-ray emission from early universe analog galaxies |
agn feedback is a critical regulator of galaxy growth. as well as curtailing star formation in diffuse, hot gas, it is increasingly understood to sometimes enhance star formation in the clumpy ism through shock-induced collapse of clouds. simulations have shown that such positive feedback may play a significant role in determining the stellar populations of galaxies. minkowsi's object (mo) provides an excellent local laboratory to probe this poorly-studied process in detail. the detection of a type ii supernova in mo (unexpected given the low mass of mo) suggests that jet-induced star formation may overproduce massive stars, and that models of the initial mass function in such systems may need to be revised. recent results also suggest that star formation efficiency is enhanced in mo. using wfc3, we will obtain morphologies, seds, h-a luminosities, equivalent widths, sizes, and population synthesis models of star forming regions across mo in order to address these questions, critical for understanding not just this single object, but the general process: 1. does jet induced star formation change the luminosities and initial mass functions of star clusters? 2. what do the age gradients of the star clusters tell us about the process of conversion of gas (hi, co) into stars as the radio jet progressed through the parent cloud? does this match numerical simulations? 3. by using observations to refine simulations, what can we learn about intrinsic properties of these kinds of radio jets, such as propagation speed, age, pressure and jet energy flux? | a local laboratory for studying positive feedback from supermassive black holes |
spectral synthesis enables the reconstruction of the star formation and chemical evolution histories (sfh & ceh) of a galaxy that are encoded in its spectral energy distribution (sed). most state-of-the-art population synthesis codes however consider only purely stellar emission and are hence inadequate for modelling studies of galaxies where non-stellar emission components contribute significantly to the sed. this work combines evolutionary and population synthesis techniques to quantify the impact of active galactic nucleus (agn) and nebular emission on the determination of the stellar population properties in galaxies. we have developed an evolutionary synthesis code called rebetiko - reckoning galaxy emission by means of evolutionary tasks with input key observables - to compute and study the time evolution of the sed of agn-hosts and starburst galaxies. our code takes into account the main ingredients of a galaxy's sed (e.g. non-thermal emission and/or nebular continuum and lines) for various commonly used parameterizations of the sfh, such as instantaneous burst, constant, exponentially decreasing, and gradually increasing peaking at a redshift between 1-10. synthetic seds computed with rebetiko have been subsequently fitted with the starlight population synthesis code (psc) which can be regarded as representative for currently available state-of-the-art (i.e. purely stellar) pscs. the objective is to study the impact of non-stellar sed components on the recovery of the true total stellar mass m_{star} and sfh of a galaxy, as well as other evolutionary properties, such as ceh and light- and mass-weighted mean stellar age and metallicity. we find that purely stellar fits in galaxies with a strong non-stellar continuum (e.g. seyfert and/or starburst galaxies) can for instance overestimate m_{star} by up to 3 orders of magnitude, while the mean stellar age and metallicity can deviate from their true values up to 2 and 4 dex, respectively. these results imply that determinations of the galaxy mass assembly history through standard pscs can be severely biased in galaxies exhibiting strong agn and/or starburst activity. | quantifying the impact of agn and nebular emission on stellar population properties with rebetiko |
the formation efficiency of x-ray binaries (xrbs) is a key parameter for constraining their formation and evolution channels and for modeling the x-ray emission of galaxies at cosmological distances. we present results from our direct measurement of the formation efficiency of xrbs associated with young stellar populations in the magellanic clouds. more specifically, we find that the formation efficiency of xrbs in the smc peaks at ages between 20-50myr. on the other hand, the formation efficiency of xrbs associated with stellar populations in the 6-25myr age range in the higher metallicity lmc is ~17 times lower than that in the smc in the same age range. we compare these results with measurements of the formation efficiency of young xrbs in other nearby galaxies (e.g m81) and we discuss them in the context of xrb population synthesis models. | the formation efficiency of x-ray binaries: insights from nearby galaxies |
we present an lte analysis of high resolution echelle optical spectra obtained with the 3.9-m anglo-australian telescope (aat) and the ucles spectrograph for a b1ib high galactic latitude supergiant hd119608. a fresh determination of the atmospheric parameters using line-blanketed lte model atmospheres and spectral synthesis provided t eff = 23 300 ± 1000 k, log g = 3.0 ± 0.3, and the microturbulent velocity ξ = 6.0 ± 1.0 kms-1 and [fe/h] = 0.16. the rotational velocity of the star was derived fromc, o, n, al, and fe lines as v sin i = 55.8 ± 1.3 kms-1. elemental abundances were obtained for 10 different species. he, al, and p abundances of the star were determined for the first time. in the spectra, hot post-agb status as well as the pop i characteristics of the star were examined. the approximately solar carbon and oxygen abundances, along with mild excess in helium and nitrogen abundances do not stipulate a cno processed surface composition, hence a hot post-agb status. the lte abundances analysis also indicates solar sulphur and moderately enriched magnesium abundances. the average abundances of b dwarfs of well studied ob associations and population i stars show a striking resemblance to abundances obtained for hd119608 in this study. this may imply a runaway status for the star. | high resolution optical spectroscopy of an intriguing high-latitude b-type star hd119608 |
far from the galactic suburbs where the sun resides, a cluster of stars in the nucleus of the milky way orbits a supermassive black hole. can chemical abundance measurements help us understand the formation history of the galactic center nuclear star cluster?studying stellar populationsmetallicity distributions for stars in the inner two degrees of the milky way (blue) and the central parsec (orange). [do et al. 2018]while many galaxies host nuclear star clusters, most are too distant for us to study in detail; only in the milky way can we resolve individual stars within one parsec of a supermassive black hole. the nucleus of our galaxy is an exotic and dangerous place, and its not yet clear how these stars came to be where they are were they siphoned off from other parts of the galaxy, or did they form in place, in an environment rocked by tidal forces?studying the chemical abundances of stars provides a way to separate distinct stellar populations and discern when and where these stars formed. previous studies using medium-resolution spectroscopy have revealed that many stars within the central parsec of our galaxy have very high metallicities possibly higher than any other region of the milky way. can high-resolution spectroscopy tell us more about this unusual population of stars?spectral lines on displaytuan do (university of california, los angeles, galactic center group) and collaborators performed high-resolution spectroscopic observations of two late-type giant starslocated half a parsec from the milky ways supermassive black hole.comparison of the observed spectra of the two galactic center stars (black) with synthetic spectra with low (blue) and high (orange) [sc/fe] values. click to enlarge. [do et al. 2018]in order to constrain the metallicities of these stars, do and collaborators compared the observed spectra to a grid of synthetic spectra and used a spectral synthesis technique to determine the abundances of individual elements. they found that while one star is only slightly above solar metallicity, the other is likely more than four times as metal-rich as the sun.the features in the observed and synthetic spectra generally matched well, but the absorption lines of scandium, vanadium, and yttrium were consistently stronger in the observed spectra than in the synthetic spectra. this led the authors to conclude that these galactic center stars are unusually rich in these metals trace elements that could reveal the formation history of the galactic nucleus.old stars, new trends?scandium to iron ratio versusiron abundance for stars in the disk of the milky way (blue) and the stars in this sample (orange). the value reported for this sample is a 95% lower limit. [do et al. 2018]for stars in the disk of the milky way, the abundance of scandium relative to iron tends to decrease as the overall metallicity increases, but the stars investigated in this study are both iron-rich and anomalously high in scandium. this hints that the nuclear star cluster might represent a distinct stellar population with different metallicity trends.however, its not yet clear what could cause the elevated abundances of scandium, vanadium, and yttrium relative to other metals. each of these elements is linked to a different source; scandium and vanadium are mainly produced in type ii and type ia supernovae, respectively, while yttrium is likely synthesized in asymptotic giant branch stars. future observations of stars near the center of the milky way may help answer this question and further constrain the origin of our galaxys nuclear star cluster.citationtuan do et al 2018 apjl 855 l5. doi:10.3847/2041-8213/aaaec3 | unusual metals in galactic center stars |
the kilo degree survey (kids) is one of the eso public surveys carried out with the vlt survey telescope (vst), equipped with the one square degree field of view and high angular resolution (0.2''/pixel) omegacam camera. kids is mainly designed for weak lensing studies, providing deep imaging in four optical bands (ugri), over a 1500 square degree of the sky with excellent seeing (e.g. 0.65'' median fwhm in r-band). the high image quality and deep photometry are ideal for galaxy evolution studies and for hunting peculiar and rare objects, as massive compact galaxies and gravitational lenses. for the latest data release 3 we have determined structural parameters (effective radii, re, and sérsic indices, n), planning to collect at the end of the survey the largest sample of galaxies with measured structural parameters in u, g, r and i bands, up to redshift z=0.5. high-quality photometric redshifts are derived using a machine learning method, which has demonstrated to reach accuracies down to sigma_z 0.03 with optical band only. stellar masses are derived from stellar population synthesis (sps) and standard sed fitting. with our unprecedented homogeneous dataset, among the most massive galaxies (with m > 8*10^10) we search for the most compact objects (with sizes re < 1.5 kpc), which do not follow the size-mass relation. these systems are thought to be relic of superdense and massive galaxies living during earlier stages of the universe (z > 2), which have survived intact having stellar populations with old ages. they represent a crucial test bench for galaxy formation processes. but, these galaxies do not have a spectral confirmation, thus we have started a multi-site/multi-facility program to determine their redshifts, velocity dispersions and the properties of the environment. finally, the deep, subarcsecond seeing kids images are also suitable for a census of gravitational lensing systems, based on the (visual and automated) identification of arc-like structures around galaxies. i will discuss our first results using data from the second and third kids data releases. | rare treasures in the kids survey |
globular clusters has been proposed as testbeds for type ia supernovae (sne ia), which have high values in astrophysics, especially in cosmology and galactic chemical evolution. here, by using a detailed binary population synthesis (bps) approach, we studied the birthrates of sne ia from various of progenitor models in globular clusters, including the single degenerate model and the double-degenerate model. in the single degenerate model, a carbon-oxygen white dwarfs (co wd) accretes material from a non-degenerate star to increase its mass to the chandrasekhar mass limit, which then leads to an sn ia explosion. in the double-degenerate model, two co wds in a close binary are brought together by gravitational wave radiation and merge, which results in an sn ia explosion. we also discussed the properties of these progenitor models in globular clusters. | the birthrates of type ia supernovae in globular clusters |
we calculate the spectral energy distribution of the first galaxies which contain pre-main-sequence stars by using the stellar evolution code modules for experiments in stellar astrophysics, the spectra model bt-settl, and the stellar population synthesis code pegase. we calculate the galaxy spectral energy distribution for salpeter initial mass function. we find that very young first galaxies are bright also in mid-infrared, and the contribution of pre-main-sequence stars can be significant over 0.1 myr after a star-formation episode. | first galaxy sed: contribution from pre-main-sequence stars |
each file contains the output of our population synthesis simulations (see table 1). the data files include both systems remaining bound and those that are disrupted. each system is logged at the time of the first sn and we store initial values of masses and period, the pre-cor-collapse and post-core collapse masses, period, eccentricity, separation, and information on the explosion (kick amplitude and direction, fallback fraction) and the pre-cc and post-cc orbital and kinematic properties. we also provide the time each system spends in phases with at least one of the two stars on the main sequence. (2 data files). | vizier online data catalog: massive runaway and walkaway stars models (renzo+, 2019) |
the chemical and kinematical properties of stars in the galactic halo provide a means to study the formation history of the milky way. stars formed within a satellite galaxy will bear the imprint of their host dark matter subhalo: star formation is less efficient in less massive protogalactic clumps, so we should observe a specific pattern in [fe/h] as a function of α-elements and slow/rapid neutron capture elements that reflects this efficiency. due to their formation in type ii supernovae, α-elements probe the relative timescale of formation for populations of stars. the addition of s- and r-process elements gives a more complete evolutionary picture of the galaxy. the yields of s- and r-process elements, which are synthesized in type ii supernovae and thermally pulsating agb stars, respectively, are coupled to the fe seed nuclei present in the formation site; thus, neutron capture element yields vary with metallicity and provide further constraints on the subhalo’s star formation history.we will report chemical abundances for a sample of 109 m giants in the nearby halo of the milky way. the stars were selected for high-resolution spectroscopy based upon their radial velocities: the radial velocities vary significantly from those expected for stars moving on uniform circular orbits in the galactic disk. thus, we expect a sample dominated by halo stars. abundances are derived for α-elements and neutron capture elements. by analyzing the multi-dimensional abundance space, the formation site of the halo giants can be assessed. of particular interest are a class of stars that form in situ, deep in the milky way’s gravitational potential well, but are “kicked out” of the disk into the halo due to a perturbation event. a kicked-out population has recently been identified in andromeda. n-body simulations predict a range in the percentage of stars belonging to the kicked-out disk population in galaxies. we will present our results within the context of andromeda’s kicked-out population and discuss the implications for theoretical models. | contributions to the galactic halo from in-situ, kicked-out, and accreted stars |
we applied hydrodynamic modelling to the close-in sub-neptune corot-24b (m<5.7 mearth; r~3.7 rearth; 5-days orbit). because of its high temperature and low surface gravity, we obtained an unphysical mass-loss rate, three orders of magnitude higher than the maximum possible value given by the energy limited escape formula. the observed transit radius must therefore be caused by mie scattering and we conclude that the transit radius overestimates the "true" planet radius by about 50%. similar differences between planet and transit radii will be present for most of the sub-neptune planets already discovered by kepler and foreseen to be found by future missions. these findings have dramatic implications, e.g. in the determination of the mass-radius relation for low-mass planets and for planet population synthesis studies. this kind of analysis allows one to constrain the minimum mass of hot sub-neptunes. the kepler satellite revealed that low-mass planets are ubiquitous in the galaxy, but the majority of the kepler host stars is too faint to be followed-up with radial velocity measurements. our findings will be able to partly overcome this problem. | the "true" radius of hot sub-neptune planets and a theoretical way to estimate their minimum mass |
the majority of young massive stars are found in close binary systems. recently, dedicated observing campaigns have provided strong constraints on the binary fraction as well as the distribution of the parameters that characterize the binary systems: the masses of both components, the orbital period and eccentricities. most strikingly these findings imply that the majority of massive stars experience strong interaction (roche lobe overflow, a common envelope phase and or a merger) with a binary companion before their final explosion. i will discuss recent results from detailed binary star models and population synthesis models. | massive binaries as progenitors for stellar explosions |
in most population synthesis calculations of close binary stars, the common envelope (ce) phase is modeled using a standard prescription based upon conservation of energy. in this prescription, the orbital separation of the secondary and giant core at the end of the ce phase is taken to be the orbital separation when the envelope becomes unbound. in this poster, we explore a modified treatment of the ce phase, in which the final orbital separation is dictated additionally by the dynamical constraint that the spiral-in of the secondary will be halted when the frictional torque on the secondary is reduced to approximately zero. we crudely estimate this separation as a function of core mass based upon existing stellar interior models of agb stars. | on the final orbital separation in common envelope evolution |
white dwarf-neutron star binaries are among the main progenitors for ultra-compact x-ray binaries. they spiral in to contact by emitting gravitational waves and depending on the mass of the white dwarf turn into stably transferring ultra-compact x-ray binaries or produce supernova-like events following a tidal disruption of the white dwarf. nearly all the stably transferring systems evolve through a phase during which mass transfer rates exceed the eddington rate by orders of magnitude. standard population synthesis codes assume that during this phase all the excess material is lost from the system through a tightly collimated jet originating at the accretor. this is in contrast to observations of systems accreting at highly super-eddington rates, such as ss 433, which are characterised by significant outflows from the accretion disc. to assess the role of such disc outflows, we perform hydrodynamic simulations of super-eddington accretion in white dwarf-neutron star binaries. we measure the specific angular momentum lost through disc winds in our simulations and find that it is significantly larger than the angular momentum carried away through a jet. we use the measured angular momentum to construct a model of the long-term evolution of white dwarf-neutron star binaries and predict the outcomes of mass transfer. we find that more binaries result in unstable mass transfer than previously thought. in particular, all the binaries with co white dwarfs and he white dwarfs more massive than about 0.2 solar masses, which were assumed to be stable, were found to be unstable. this result leads to a better agreement between the empirical inspiral rates of binary pulsars containing white dwarfs and empirical formation rates and compositions of ultra-compact x-ray binaries in the galaxy. | white dwarf-neutron star binary progenitors for ultra-compact x-ray binaries |
we propose to find the optical counterparts for at least 40 high-mass x-ray binaries (hmxbs) in m33 using archival hst imaging data. we will align the data to the deep chandra x-ray catalog to search for optical counterpart candidates to the x-ray sources. the optical morphology and photometry of these counterparts will identify which x-ray sources are most likely to be hmxbs. the colors of the counterpart stars will allow each hmxb to be typed. because hmxbs are young systems, we will measure the recent star formation histories (sfhs) of their surrounding populations to determine their ages. we will then compare the distribution of ages to those we've measured for other nearby galaxies to look for patterns with metallicity and star formation rate, and we will compare the distribution to those predicted by binary formation and evolution models. this project will yield state-of-the-art observational constraints on population synthesis models for interacting binary stars. | finding and aging the population of high-mass x-ray binaries in m33 |
the ways in which galaxies acquire, process, enrich, and expel their gas---known as the "baryon cycle"---are among the most complex and important processes in astrophysics. hubble and its contemporaries have revealed much about the gas-galaxy connection at z<1. we anticipate rapid progress in observational studies of the gas-galaxy connection at the z>2 epoch thanks to jwst, which will reach much deeper into the galaxy population, and to much higher redshifts, than has been possible to date, drawing a richer picture of this connection when added to the already large body of ground-based spectroscopy of the gas. to address the baryon cycle at z<1, our group has developed novel approaches to simulating the gas-galaxy connection and synthesizing mock data. we have achieved 10^4-5 times finer mass resolution in galactic gas flows than conventional cosmological simulations, and we are developing new tools for making synthetic data. we propose to apply these new techniques at z>2, when star formation and black hole accretion rates were rising, when the potential impacts for feedback on the baryon cycle are strongest. new data expected from jwst will revolutionize the galaxy side of the gas/galaxy equation at these redshifts, offering a new window into the important physics and drawing solid links to hubble's work at z<1. fully interpreting these new data, however, will require new theoretical models, synthetic observations, and analysis methods: foggie will explore both the physical and observable effects of feedback on z>2 galaxies. our main scientific goal for this work is to understand the cgm and ism gas processes that govern star formation and morphology in observable ways. we will focus on four inter-related science questions: (1) stars: how do feedback, accretion, and gas recycling affect resolved star formation histories? (2) ism: how do star formation and agn feedback affect the physical properties of the ism at z>2, and what diagnostics accurately trace these properties? (3) cgm: how does feedback affect the physical and observable properties of the cgm? (4) metals: how does feedback affect galactic metal budgets and metallicity scaling relations? we will address these important questions with a novel combination of extreme resolution in the gas flows around galaxies, a suite of synthetic data, and new treatments of stellar and agn feedback. we plan to address these unanswered questions with a major step forward in our ability to analyze the connection between galaxies and their circumgalactic gas. our program consists of (1) a new suite of cosmological hydrodynamic simulations of unprecedented resolution in the gas flows around and within galaxies, (2) a novel refinement scheme for achieving this resolution, (3) synthetic observations of simulation data and an opensource pipeline for producing mock data from other simulations, and (4) a novel approach to varying feedback recipes and assessing their effects on observable data of both stars and gas. our goals are consistent with nasa's strategic objective 1.6 to "discover how the universe works. . . ". we will provide physical models and synthetic data for comparisons to observations from current and future nasa facilities such as hubble and jwst. with jwst set to be commissioned for science by spring 2019 (before the next atp deadline), it is important that we begin this work now. | figuring out gas & galaxies in enzo (foggie): the gas-galaxy connection at z>2 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.