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binary evolution may lead to the production of more hot, luminous stars in a stellar population than expected for single star evolution. these hot luminous objects significantly contribute to the sed in b and uv bands, and then affect the determination of some basic parameters based on the sed. in a population synthesis code, the formation of such hot luminous objects mainly depends on the descriptions of two cruel unsolved processes in binary evolution: dynamically unstable mass transfer and common envelope evolution. in this contribution, i will present some new advances in binary evolution and discuss their impacts on the synthesis seds of populations. mass transfer from giant donors is generally dynamically unstable due to the giant’s structure. this is a major obstacle for forming some binary-related objects, e. g long-period blue stragglers, hot subdwarf stars (extreme horizontal branch/ehb stars) etc. from the adiabatic mass loss model we established in 2010, we studied the responses of giants in rapidly losing envelope, and by comparing with the responses of their roche lobes, we give a completely new theoretical view on this issue—many binaries which are thought to undergo unstable mass transfer previously are in fact to be stable for mass transfer. observations of some binary-related objects also imply that the critical mass ratio for which a binary would evolve stably should be much larger than previously believed. finally, we will discuss the impact of the advances on the formations of blue stragglers and ehb stars, then on the synthetic seds. the results show that it is necessary and important to improve the description of this criterion in population synthesis codes. | advances in binary evolution and their roles in the synthetic seds |
binaries are important in the galaxy studies. binaries, during their evolutions, can produce some kinds of hot and luminous objects (for example, helium star) and eject different amounts of energy and elements via stellar wind or sn ejections.%therefore, the inclusion of binaries would affect the determinations of galaxy parameters (such as the stellar mass m*, stellar metallicity z*, star formation rate [sfr], etc) and studies related to classic hii regions (for example, the selection criteria between star-forming galaxies and active galactic nuclei [agns], the type of central ionizing source, etc.).using the yunnan-ii evolutionary population synthesis models, which included various of binary systems, we found that the inclusion of binaries would raise the derived m* and z* and lower sfr of galaxies.%moreover, under the assumption that binaries are common in classic hii regions, we found that (i) the radiation fields emitted by intermediate-age (10^7-8yr) stellar populations (sps) comprising binaries are in theory possible candidates for significant central ionizing sources classic h ii regions, which breaks the previous conclusion that only young sps or ob-type stars can ionize the surrounding gas, and (ii) the selection criterion lines between star-forming galaxies and agns in the diagnostic diagrams would move into the region occupied originally by agns. | binaries on the galaxy parameters and studies related to hii regions |
detailed evolutionary models predict that massive stars (m > 20 m⊙) at low metallicity remain small throughout most of their lifetimes and do not expand significantly until just before core collapse. if this is true, interaction should occur late for a large fraction of binaries and may also proceed differently due to the evolved stage of the donor. envelope-stripping, which is thought to be an important step in the pathway to binary black hole mergers, could instead lead to nuclear timescale mass transfer or even a stellar merger. this should result in features in the mass distribution of envelope-stripped helium stars. to test the late expansion hypothesis, we use a stellar population synthesis code created specifically for mass-transferring binaries and based on detailed single and binary stellar evolution models. we create mass distributions of stripped stars for a range of metallicities. we find that for all the metallicities with z≤0.006, the mass distribution exhibits a sharp drop in the number of stripped stars above a certain mass. at z=0.006, the drop occurs at a stripped star mass of ~9-10 m⊙, while at z=0.002, the drop is sharper and occurs at 8 m⊙. by interpreting these results using the metallicity and star-formation history of the small magellanic cloud (smc), we find that only a handful of stripped stars more massive than 8 m⊙ should exist in the smc. as the population of stripped stars is revealed by an ongoing survey of the magellanic clouds, their mass distribution could provide a test of the hypothesis that massive stars expand late at low metallicity. | testing late stellar expansion with populations of stars stripped in binaries |
this talk will link the radio pulsars population of small magellanic cloud (smc) with the accreting x-ray pulsar population, using population synthesis models to predict what we might observe through future surveys of the smc. | the neutron star populations of the small magellanic cloud |
we performed population synthesis of cvs composed of highly magnetized wds (i.e. polars) and non-magnetic wds, and predicted period and mass transfer rate distributions, as well as space densities for both populations. the presented calculations are the first binary population models that properly include reduced magnetic braking in polars. in order to compare our predicted orbital period distributions with observations, we searched for all cvs with accurate orbital period determinations from the sloan digital sky survey (sdss). we found 199 systems, which are listed in table b1. sdss provides both photometric and spectroscopic data, and allows the unambiguous identification of cvs from hydrogen and helium emission lines. in addition, its deep magnitude limit allows the detection of intrinsically faint systems (gansicke et al. 2009mnras.397.2170g), characterized by low accretion rates, even at several scale heights above the galactic plane. this makes this sample one of the largest homogeneous cv samples available, as its broad colour selection range is superior to any previous surveys. (2 data files). | vizier online data catalog: evidenced reduced magnetic braking in polars (belloni+, 2020) |
bipos1 (binary population synthesizer) efficiently calculates binary distribution functions after the dynamical processing of a realistic population of binary stars during the first few myr in the hosting embedded star cluster. it is particularly useful for generating a realistic birth binary population as an input for n-body simulations of globular clusters. instead of time-consuming n-body simulations, bipos1 uses the stellar dynamical operator, which determines the fraction of surviving binaries depending on the binding energy of the binaries. the stellar dynamical operator depends on the initial star cluster density, as well as the time until the residual gas of the star cluster is expelled. at the time of gas expulsion, the dynamical processing of the binary population is assumed to effectively end due to the expansion of the star cluster related to that event. bipos1 has also a galactic-field mode, in order to synthesize the stellar population of a whole galaxy. | bipos1: dynamical processing of the initial binary star population |
recently, we have found, in the chandra deep field-south, that the emission from x-ray binary (xrb) populations in galaxies evolves significantly with cosmic time, most likely due to changes in the physical properties of galaxies like star-formation rate, stellar mass, stellar age, and metallicity. however, it has been challenging to directly show that these same physical properties are connected to xrb populations using data from nearby galaxies. we present a new technique for empirically calibrating how x-ray binary (xrb) populations evolve following their formation in a variety of environments. we first utilize detailed stellar population synthesis modeling of far-uv to far-ir broadband data of nearby (< 10 mpc) face-on spiral galaxies to construct maps of the star-formation histories on subgalactic scales. using chandra data, we then identify the locations of the xrbs within these galaxies and correlate their formation frequencies with local galaxy properties. in this talk, i will show promising first results for the whirlpool galaxy (m51), and will discuss how expanding our sample to an archival sample of 20 face-on spirals will lead to a detailed empirical timeline for how xrbs form and evolve in various environments. | tracing x-ray binary population evolution by galaxy dissection: first results from m51 |
we present the results recently published byhttps://doi.org/10.1051/0004-6361/202141980 {marfil et al. (2021, a&a, 656, a162)} regarding the determination of the stellar atmospheric parameters ($t_{\rm eff}$, $\log{g}$, and [fe/h]) of 343 m dwarfs observed with carmenes. we employed steparsyn, a bayesian spectral synthesis implementation particularly designed to infer the stellar atmospheric parameters of late-type stars following a markov chain monte carlo approach. we made use of the bt-settl model atmospheres and the radiative transfer code turbospectrum to compute a grid of synthetic spectra around 75 magnetically insensitive fe i and ti i lines plus the tio $\gamma$ and $\epsilon$ bands. to avoid any potential degeneracy in the parameter space, we imposed bayesian priors based on the photometric data available for the sample. we find that this methodology is suitable down to m7.0 v, where refractory metals such as ti are expected to condense in the stellar photospheres. although our $t_{\rm eff}$ scale is in good agreement with the literature, we report large discrepancies in the [fe/h] scales, which might arise from the different methodologies and sets of lines considered. however, our [fe/h] is in agreement with the metallicity distribution of fgk-type stars in the solar neighbourhood and correlates well with the kinematic membership of the targets in the galactic populations. lastly, excellent agreement in $t_{\rm eff}$ is found for m dwarfs with interferometric angular diameter measurements, as well as in the [fe/h] between the components in the wide physical fgk+m and m+m systems included in our sample. the steparsyn code https://doi.org/10.1051/0004-6361/202141763 {(tabernero et al. 2022, a&a, 657, a66)} is available at github: https://github.com/hmtabernero/steparsyn/. | written in the stars: spectral synthesis on carmenes gto m-dwarf spectra |
disk instability remains the leading formation pathway for some of observed giant planets. in particular, this model can more naturally explain giant planets at large separation, giant planets around m stars, and very young giant planets. however, there are still many open questions regarding this formation mechanism, and the expected population of planets.we are working on a new disc instability population synthesis (dipsy) that aims to address these questions and make predictions about the expected population of planets that can be tested observationally.we find that fragmentation (the formation of bound clumps in the disc, a necessary condition for planet formation in the disc instability model) depends sensitively on the precise physics during the disc formation (infall). we show that infall models that form discs compatible in size with observed young discs are likely to fragment, though this may happen only in a minority of systems. furthermore, we demonstrate how the intrinsics of orbital migration, mass accretion and clump interaction influence the fate of the formed clumps.the figure shows the fraction of systems that fragment as a function of the final stellar mass for different parameters studied [1].the results of the population synthesis, combined with current and future observations, will deepen our understanding of planet formation irrespective of the formation model.fig. 1: fraction of fragmenting discs as a function of the final stellar mass for different parameters. when an infall model motivated by non-ideal mhd simulations is applied, no fragmentation occurrs. in contrast, infall informed by radiation hydrodynamic simulations leads to a substantial fraction of discs fragmenting, especially at higher masses.references:[1] schib, o., mordasini, c., wenger, n., marleau, g. d., & helled, r. 2021, astronomy and astrophysics, 645, a43 | dipsy: a new disc instability population synthesis |
the merger of two neutron stars (a nsns merger) is suspected to be the most likely source of short-duration gamma-ray bursts (grbs) powerful explosions that can be seen from billions of light-years away. but whether a grb is launched is dependent on what remnant is created by the merging nss. do they form another ns? or a black hole (bh)?uncertain remnantif the nsns merger forms a bh remnant, a grb can be launched during the ensuing accretion. but if it instead forms a ns, a grb may only be launched if the remnant collapses to a bh within 100 milliseconds; any longer, and theory says that the grb jet will become loaded with baryons and choke.unfortunately, determining whether the merger will produce a ns or a bh is difficult. a major limitation is that we dont know what equation of state describes the interior of a ns which means we also dont know what maximum mass a ns can have before it collapses into a bh.led by chris fryer of the university of arizona and the los alamos national laboratory, a group of researchers undertook a highly collaborative study to better understand the fates of nsns mergers.maximum massthe fraction of mergers that produce bhs (and, consequently, grbs) and nss, as a function of the maximum ns mass allowed by the equation of state. lines labeled bhad are mergers that produce bhs (under two different initial conditions); lines labeled ns are those that produce nss. [fryer et al. 2015]the authors used a combination of merger calculations, neutron star equation of state studies, and population synthesis simulations to model the outcome of the merger of two nss. with this information, they determined the statistical likelihood that the remnant that forms in the merger collapses directly to a bh, collapses to a bh after a delay, or remains a ns.fryer and collaborators find that the outcome is highly dependent upon the maximum mass allowed by the uncertain ns equation of state. if this maximum ns mass is below 2.32.4 solar masses, most ns mergers will result in a bh within 100 milliseconds of the merger. in this case, most mergers would be capable of producing grbs. if, on the other hand, the maximum ns mass is above this cutoff, then the majority of ns mergers will form a ns remnant only rarely launching a grb.since, to match observed grb rates, the second scenario requires a rate of mergers significantly higher than what theory predicts, it seems more likely that ns masses are limited to 2.32.4 solar masses. upcoming observational projects like advanced ligo will help to test this theory and place further constraints on our models of nss.citationchris l. fryer et al 2015 apj 812 24. doi:10.1088/0004-637x/812/1/24 | what do you get when two neutron stars merge? |
we will survey with chandra and hst 11 nearby elliptical galaxies to make first-ever robust empirical measurements of how field lmxbs evolve as their parent stellar populations age. our observations will robustly test (to the 96.5-99.4% confidence level) theoretical population synthesis models, which predict a decline in field lmxbs with increasing age. our survey will also contain detections for ~800 globular cluster (gc) lmxbs, dramatically improving constraints on whether gc lmxbs seed field lmxbs by being kicked out of their host gcs. to perform this experiment, we will leverage >4 ms of chandra exposures and >35 hst orbits for 9 galaxies that exist in the archive, and will add 255 ks of new chandra time and two new hst orbits for two young early-type galaxies. | a statistically robust constraint on the evolution of field lmxbs |
the origin of the metal enrichment of the intracluster medium (icm) represents a fundamental problem in extragalactic astrophysics, with implications for our understanding of how stars and galaxies form, the nature of type ia supernova (snia) progenitors, and the thermal history of the icm. these heavy elements are ultimately synthesized by supernova (sn) explosions; however, the details of the sites of metal production and mechanisms that transport metals to the icm remain unclear. to make progress, accurate abundance profiles for multiple elements extending from the cluster core out to the virial radius (r180) are required for a significant cluster sample. we propose an x-ray spectroscopic study of a carefully-chosen sample of archival suzaku and xmm-newton observations of 23 clusters: xmm-newton data probe the cluster temperature and abundances out to (0.5-1)r500, while suzaku data probe the cluster outskirts. a method devised by our team to utilize all elements with emission lines in the x-ray bandpass to measure the relative contributions of supernova explosions by direct modeling of their x-ray spectra will be applied in order to constrain the demographics of the enriching supernova population. in addition we will conduct a stacking analysis of our already existing suzaku and xmm-newton cluster spectra to search for weak emssion lines that are important sn diagnostics, and to look for trends with cluster mass and redshift. the funding we propose here will also support the data analysis of our recent suzaku observations of the archetypal cluster a3112 (200 ks each on the core and outskirts). our data analysis, intepreted using theoretical models we have developed, will enable us to constrain the star formation history, sn demographics, and nature of snia progenitors associated with galaxy cluster stellar populations - and, hence, directly addresess nasa s strategic objective 2.4.2 in astrophysics that aims to improve the understanding of how the universe works, and explore how it began and evolved. | a detailed study of chemical enrichment history of galaxy clusters out to virial radius |
in astrophysics, population synthesis models are tools used to determine what mix of stars could be consistent with the observations, e.g. how the intrinsic mass-to-light ratio changes by the measurement process. a similar technique could be used to understand the production of tgfs. the models used for this type of population study probe the conditions of electron acceleration inside the high electric field regions of thunderstorms, i.e. acceleration length, electric field strength, and beaming angles. in this work, we use a monte carlo code to generate bremsstrahlung photons from relativistic electrons that are accelerated by a large-scale rrea thunderstorm electric field. the code simulates the propagation of photons through the atmosphere at various source altitudes, where they interact with air via compton scattering, pair production, and photoelectric absorption. we then show the differences in the hardness ratio at spacecraft altitude between these different simulations and compare them with tgf data from fermi-gbm. such comparisons can lead to constraints that can be applied to popular tgf beaming models, and help determine whether the population presented in this study is consistent or not with reality. | a population synthesis study of terrestrial gamma-ray flashes |
metal-poor stars allow us to establish the early history of the milky way, furthermore the stars on advanced evolution stage (e.g. giants, agb stars etc.) give the opportunity to research the peculiarities of stellar evolution at low metallicity. on the base of the 11m southern african large telescope (salt) spectra obtained using hrs fibre-fed echelle-spectrograph during 2018 -2020, the atmospheric parameters and elemental abundances of four metal-poor stars he 1523-0901, hd 6268, hd 121135, and hd 195636 ([fe/h] ∼ -1.5 - -3.0) have been obtained. the iron abundance was determined based on the equivalent widths of absorption lines. the carbon abundance was obtained using the molecular synthesis fitting for the ch (4300-4330 åå) region, nitrogen from cn at 3883 å, oxygen from [o] line at 6300 å and ir triplet at 7770 å the relationship between the chemical enrichment of stars and their stellar evolution is considered. it may be associated with the processes of mixing inside the stars, and the mechanisms of matter transfer during stellar evolution. | manifestation of stellar evolution in metal-deficient stars |
stellar evolution can nowadays be modelled with a high degree of accuracy and completeness up to the most advanced stages. however in spite of the progresses, complex physical processes exist that still suffer of large uncertainties even in the most placid evolutionary phases. the straightforward drawback is that models lose their predictive power and this is particularly critical for stellar population synthesis. here i will focus on one of such processes, convective mixing, and briefly review potentially helpful observational tests to decipher its efficiency during the main nuclear burning phases of intermediate mass stars. | convective mixing in intermediate mass stars |
stellar rotation period (prot) studies have produced numerous insights into the angular momentum evolution of low-mass stars, but previous investigations have focused on single stars even though roughly half of sun-like stars are in stellar binaries. we examine the impact of unresolved stellar binaries on the stellar prot distribution of the kepler field by performing monte carlo simulations of a population composed of single and double stars by modeling stellar evolution, magnetic braking, and tidal forces. we find that tides modify stellar rotations in all binaries with orbital periods less than 50 days, and up to 70 days in some cases. at short orbital periods, most stellar binaries tidally-lock into synchronous rotation, naturally explaining the observed population of fast rotators in the kepler field that cannot be reproduced by single-star-only models. many binaries with longer orbital periods, some up to orbital periods of 70 days, tidally-lock, synchronizing the stellar prot with the binary orbital period, causing prot to not be a valid proxy for age in all cases, i.e. gyrochronology methods must be applied carefully. we find the best match to the observations occurs when using an equilibrium tidal model with stellar tidal quality factor ranging from 105 - 108, coupled to the magnetic braking law of matt et al. (2015). however, our assumed flat stellar age distribution over 1-4 gyr underpredicts the number of fast rotators in the kepler field. if instead we assume a bimodal stellar age distribution in the kepler field, hypothesized by davenport (2017), composed of a young (100 myr - 1 gyr) and an old (1 - 4 gyr) population, we successfully reproduce the kepler prot distribution. we show that tidal forces are important for binary stars at orbital periods longer than previously considered, the kepler prot distribution is significantly impacted by unresolved binaries, and that population synthesis models that couple stellar and tidal evolution can constrain the ages and physical properties of field stars. | reproducing stellar rotation periods in the kepler field via magnetic braking and tidal torques |
with analysis of gw190521 potentially indicating the existence of a high eccentricity stellar black hole binary, the idea that active galactic nuclei (agn) are the birthplaces for binary black holes (bbhs) has picked up a lot of steam in recent months. an accretion disk of gas circling around the super massive black hole (smbh), agn disks are potential hosts to many black holes. sbhs in the agn are either pulled in, through gas torques, from the surrounding nuclear stellar cluster, or are simply born in the disk through in-situ star formation and evolution. playing host to these bhs, the environment of the agn disk can form bbhs through both dynamical and gaseous processes. our study sheds new light on how gaseous dynamical friction, the slowing of bodies in a medium by the gravitational pull of their wakes, can form bound sbh binaries from two single, close approach, sbhs. performing 2d 3-body integrations with rebound we find that gaseous dynamical friction not only can form bbhs but it does so quite effectively, being able to capture close approaches of different impact parameters, and in different astrophysical systems. we discover that, unlike previous prescriptions, high levels of dynamical friction (equivalently over-dense gas) can actually hinder binary formation. we determine characteristics of the captured binaries, reporting general trends in eccentricity, semi major axis, direction of rotation, precession, and more across astrophysical parameters. we provide an analytic formula that determines the strength of dynamical friction in any astrophysical system and subsequently provide numerical limits to such formula, dictating when and where binaries form. our work not only provides a strong case for the importance of gaseous capture as a method for bbh formation in agn, but it also yields a detailed analytic formula that will provide much aid to population synthesis projects in their study of intermediate mass black hole growth, updating older, and not entirely accurate, semi-analytic models. in future work we hope to further study the implications our newly powerful dynamical friction has on the picture of agn as source for gw events and bbh mergers. | gas dynamical friction as a binary formation mechanism in agn disks |
because of their dense stellar environments, globular clusters are an important place for investigating stellar evolution and stellar dynamics, but there is much yet to learn about their formation. in this project, we considered the globular cluster ngc 6681 (m70) with the goal of characterizing its stellar population. we used archival data from the hubble space telescope’s advanced camera for surveys. the data was drawn from thirteen different filters ranging from the far-uv to the near infrared. using this range of filters, we constructed spectral energy distributions (seds) for each of the sources in our field of view. we then generated color-magnitude diagrams (cmds) in a variety of wavelengths which we used to identify a number of sources that fell outside the regions occupied by normal stars. we determined the likely stellar type of several of these unusual sources using the cmds and by comparing their seds to a number of synthesized seds. | from the ultraviolet to the infrared: the stellar population of the globular cluster m70 |
we review the properties of observed populations of radio pulsars in the milky way field and globular clusters, contrasting in particular binary properties and taking into account selection effects. using a combination of monte carlo dynamical modeling for dense star clusters and population synthesis for the field, we discuss how the observations compare to theoretical expectations from binary evolution and stellar dynamics. | comparing binary pulsar properties in the field and in globular clusters |
according to stellar evolution models, massive ob stars form neutron stars after the end of their life. but does the initial magnetic field of a neutron star depend on the magnetic field of a predecessor star? some pulsar population synthesis (e.g. gullón et al. 2015) which included thermally emitting neutron stars showed that magnetars (and for example the group of young cooling neutron stars called "the magnificent seven") could originate from a peculiar subpopulation of massive stars. moreover, we can see that massive stars also can be divided into two groups: magnetic stars with average magnetic fields from several hundreds of gauss to tens of kilogauss (only 5-7% of all) and nonmagnetic or weakly magnetic stars whose magnetic fields can not yet be measured accurately. therefore, we want to check the hypothesis if magnetic ob stars in the milky way could be progenitors of magnetars. we also aim to explain how the magnetic fields depend on the stellar radii, binarity, and other parameters using modern observational data for various values (narval measurements, magnetar outburst online catalog, gaia dr2, etc). to do so, we study the distribution of magnetic fields of massive stars using the maximum likelihood technique and run a new pulsar population synthesis code. as a result of our analysis, we can claim that normal pulsars seem to be plausible descendants of the weakly magnetic ob stars and the precursors of magnetars are magnetic ob stars. | is a number of strongly magnetised ob stars enough to produce all known magnetars? |
a significant obstacle to improving the quality of education is the lack of easy-to-use assessments of higher-order thinking. most existing assessments focus on recall and understanding questions, which demonstrate lower-order thinking. traditionally, higher-order thinking is assessed with practical tests and written responses, which are time-consuming to analyze and are not easily scalable. computer-based learning environments offer the possibility of assessing such learning outcomes based on analysis of students' actions within an adaptive learning environment. our fully online introductory science course, habitable worlds, uses an intelligent tutoring system that collects and responds to a range of behavioral data, including actions within the keystone project. this central project is a summative, game-like experience in which students synthesize and apply what they have learned throughout the course to identify and characterize a habitable planet from among hundreds of stars. student performance is graded based on completion and accuracy, but two additional properties can be utilized to gauge higher-order thinking: (1) how efficient a student is with the virtual currency within the project and (2) how many of the optional milestones a student reached. in the project, students can use the currency to check their work and "unlock" convenience features. high-achieving students spend close to the minimum amount required to reach these goals, indicating a high-level of concept mastery and efficient methodology. average students spend more, indicating effort, but lower mastery. low-achieving students were more likely to spend very little, which indicates low effort. differences on these metrics were statistically significant between all three of these populations. we interpret this as evidence that high-achieving students develop and apply efficient problem-solving skills as compared to lower-achieving student who use more brute-force approaches. | assessing complex learning objectives through analytics |
the origin and evolution of magnetic fields (mfs) of young neutron stars (nss) is an open question. mfs could be generated through a dynamo during the formation of nss, or they could be a relic of a pre-supernova magnetic field. we want to test whether mfs of young nss are the relics of their progenitors, massive ob stars. this could happen through magnetic flux conservation; the mf of massive stars is core confined, so the collapsed core might keep exactly the same magnetic flux as the whole star. only 5-7% of massive ob stars have well-measured magnetic fields (reaching tens of kg). they can be divided into two groups: highly magnetic stars (b > ∼$20$ g) and weakly magnetic stars (b < ∼$20$ g). nss are also divided into normal pulsars (b $\sim10^{12}$ g) and magnetars (b > ∼$4 \cdot 10^{13}$ g). we therefore assume that normal pulsars are descendants of weakly magnetic stars, while magnetars originate from highly-magnetic ob stars. to test this hypothesis, our population synthesis code takes into account some severe selection effects in the ns sample, and enables us to compare observed fractions of pulsars and magnetars with the observed fractions of weakly magnetic and highly magnetic ob stars. we also investigated independently the distribution of mfs of massive stars using the maximum likelihood technique. | from ancestors to offspring: tracing the connection between magnetic fluxes of ob and neutron stars |
in the galaxy studies, binaries are often neglected. however, binaries are common in the universe.%stellar populations (sps) and galaxies, comprising binaries, would produce some kinds of hot and luminous objects (such as, helium star) and eject different amounts of energy and elements via stellar wind or sn ejections when comparing with those without binaries.%therefore, the inclusion of binary systems would alter the integrated properties of sps and affect the star formation history (sfh) of galaxies.using the yunnan-ii evolutionary population synthesis models, which included various of binary systems, we found that the inclusion of binaries would raise the derived stellar mass (m*) and metallicity (z*) and lower the star formation rate (sfr) of galaxies.%because m* and z* embody the long-term accumulation processes of gas and star formation (sf) and sfr denotes the current one (longer than 107-8yr), the combination of sfr with m* and z* can reflect the sfh of galaxies.%the above result means that the process, galaxy accumulates gas to form stars in the early times, is rapider and that at late states is slower for galaxies (with lifetime greater than 10^8yr) when considering binaries. | binaries on the galaxy sfh |
star formation rate (sfr) inferences are based in the so-called constant sfr approximation, where synthesis models are require to provide a calibration; we aims to study the key points of such approximation to produce accurate sfr inferences. we use the intrinsic algebra used in synthesis models, and we explore how sfr can be inferred from the integrated light without any assumption about the underling star formation history (sfh). we show that the constant sfr approximation is actually a simplified expression of more deeper characteristics of synthesis models: it is a characterization of the evolution of single stellar populations (ssps), acting the ssps as sensitivity curve over different measures of the sfh can be obtained. as results, we find that (1) the best age to calibrate sfr indices is the age of the observed system (i.e. about 13 gyr for z = 0 systems); (2) constant sfr and steady-state luminosities are not requirements to calibrate the sfr ; (3) it is not possible to define a sfr single time scale over which the recent sfh is averaged, and we suggest to use typical sfr indices (ionizing flux, uv fluxes) together with no typical ones (optical/ir fluxes) to correct the sfr from the contribution of the old component of the sfh, we show how to use galaxy colors to quote age ranges where the recent component of the sfh is stronger/softer than the older component. particular values of sfr calibrations are (almost) not affect by this work, but the meaning of what is obtained by sfr inferences does. in our framework, results as the correlation of sfr time scales with galaxy colors, or the sensitivity of different sfr indices to sort and long scale variations in the sfh, fit naturally. in addition, the present framework provides a theoretical guideline to optimize the available information from data/numerical experiments to improve the accuracy of sfr inferences. more info en cerviño, bongiovanni & hidalgo a&a 588, 108c (2016) | about recent star formation rates inferences |
the halogas (hydrogen accretion in local galaxies) survey with the westerbork synthesis radio telescope is the most sensitive systematic survey of the diffuse neutral hydrogen component in nearby spiral galaxies so far. the 5-sigma column density sensitivity reached for the sample of 22 galaxies is 10^19 atoms cm^-2 over the typical line width of the neutral gas in our target galaxies. the 3d observations are sensitive enough to perform detailed kinematical and dynamical analyses of the extended (vertical) disk structure of our targets. additionally, we are able to provide a census of the complete cold neutral cloud population above the mass detection limit for individual objects of 10^5 solar masses on average. our results are relevant in the context of theories describing star formation feedback on the gaseous interface of the galaxy disks with their surroundings, as well as gas accretion from the intergalactic medium. most notably, we find that the presence of anomalous, slowly rotating extraplanar gas is related to the star formation surface density. i will present the consequences of our observations for the current accretion in local galaxies, and discuss the implied constraints on the accretion process more generally. | hi disks in nearby galaxies from the halogas survey |
x-ray observations of nearby galaxies provide one of the best laboratories in the universe for studying the populations of two exotic classes of object: black holes and neutron stars. because they are directly connected to past and current stellar populations through binary synthesis modeling, studies of accreting black hole and neutron star populations can provide insights into the history of star formation and evolution in a galaxy. using hard x-ray observations attainable with nustar, we are able to differentiate between the accretion states, and thus compact object types, of x-ray binaries (xrbs) in the andromeda galaxy, our nearest spiral neighbor. this tells us not only about its own xrb population, but also provides hints about the population and distribution of xrbs in the milky way, where this type of population characterization is more difficult due to the ambiguity of the spatial distribution of sources. using ten ~50ks observations of the disc of andromeda, we detect 21 sources at 3 σ above the background in the 4-25kev bandpass, and make 1 σ classifications of 12 of those sources with the use of diagnostic color-rate and color-color diagrams, which separate sources into various neutron star and black hole regimes. in addition, we create x-ray luminosity functions for both the full (4-25kev) and hard (12-25kev) band luminosities. we combine this with additional ~500ks coverage to create a luminosity function for the disc, and fit and compare to functions from past softer energy coverage. these classifications will be added to those already included in a deeper m31 survey of the bulge and a more limited coverage of the disc, expanding the knowledge of both the types of sources present in the population as well as their distribution throughout the galaxy. | identifying compact objects in the x-ray binary population of andromeda's disc |
using hard x-ray observations attainable with nustar, we are able to differentiate between the accretion states, and thus compact object types, of x-ray binaries (xrbs) in the andromeda galaxy, our nearest spiral neighbor. because they are directly connected to past and current stellar populations through binary synthesis modeling, studies of accreting black hole and neutron star populations can provide insights into the history of star formation and evolution in a galaxy, as well as the population of potentially detectable gravitational wave sources. this tells us not only about the xrb population of the m31 disk, but also provides hints about the population and distribution of xrbs in the milky way, where this type of population characterization is more difficult due to the ambiguity of the spatial distribution of sources. using ten ~50ks observations of the disk of m31, we detect 19 xrb sources in the 4-25kev bandpass, and make classifications of 10 of those sources with the use of diagnostic color-rate and color-color diagrams, which separate sources into various neutron star and black hole regimes. we combine this with 3 additional ~400ks fields with disk coverage to create x-ray luminosity functions (xlfs) for both the full (4-25kev) and hard (12-25kev) band luminosities, and fit and compare to functions from past softer energy coverage of the milky way. we include preliminary fits of the xlfs of sub-populations of the characterized xrbs, making distinctions based on whether sources are in or outside of globular clusters and by compact object type. these classifications are added to those already included in a deeper m31 survey of the bulge and a more limited coverage of the disk, expanding the knowledge of both the types of sources present in the population as well as their distribution throughout the galaxy. | characterizing the x-ray binary population of the m31 disk |
the origin of half of the elements heavier than iron -- the so-called r-process elements -- is a central unsolved mystery in astrophysics. these atoms include both precious metals (e.g. gold) as well as radioactive elements required for geophysical processes on the earth (e.g. thorium) and even some which are necessary on earth for advanced life (e.g. iodine). recent observations with both light and gravitational waves have demonstrated that at least some of these elements are formed through the merger of two neutron stars, but such a population struggles to reproduce the enrichment patterns seen in stars within the milky way as well apparent early enrichment in some dwarf galaxies. instead, recent work implies that the accretion disks formed in the stellar collapse that powers a long duration gamma-ray burst could in-fact be a dominant site. if this is true we should be able to observe r-process synthesis in the associated supernovae. the presence of lanthanides in r-process material creates strong opacity, such that the signature of their synthesis should be a late time infrared component visible in the supernova light. here we propose sensitive hst observations that will search for both spectroscopic and photometric evidence of the r-process, providing the opportunity to test, for the first time, if collapsars are responsible for heavy element production. | do collapsars make the heavy elements: a sensitive search in a nearby gamma-ray burst? |
we investigate the internal structure of elliptical galaxies at z~0.2 from a joint lensing-dynamics analysis. we model hubble space telescope images of a sample of 23 galaxy-galaxy lenses selected from the sloan lens acs (slacs) survey. whereas the original slacs analysis estimated the logarithmic slopes by combining the kinematics with the imaging data, we estimate the logarithmic slopes only from the imaging data. we find that the distribution of the lensing-only logarithmic slopes has a median 2.08 ± 0.03 and intrinsic scatter 0.13 ± 0.02, consistent with the original slacs analysis. we combine the lensing constraints with the stellar kinematics and constrain the amount of adiabatic contraction in the dark matter (dm) halos. we find that the dm halos are well described by a standard navarro-frenk-white halo with no contraction on average for both of a constant stellar mass-to-light ratio (m/l) model and a stellar m/l gradient model. for the m/l gradient model, we find that most galaxies are consistent with no m/l gradient. comparison of our inferred stellar masses with those obtained from the stellar population synthesis method supports a heavy initial mass function (imf) such as the salpeter imf. we discuss our results in the context of previous observations and simulations, and argue that our result is consistent with a scenario in which active galactic nuclei feedback counteracts the baryonic-cooling-driven contraction in the dm halos. | massive elliptical galaxies at z 0.2 live inside uncontracted nfw halos and follow the salpeter stellar imf |
the study of the rest-frame ultraviolet (uv) is fundamental to our understanding of star-forming galaxies, as it provides a unique window on massive stellar populations, chemical evolution, and reionization. the success of james webb space telescope (jwst) programs, with star-forming galaxies at high redshifts, hinges on the comprehensive understanding of these uv spectral properties. i present an archival study of 21 local star-forming galaxies with both low-resolution spectra from the international ultraviolet explorer (iue), to mimic the anticipated observations from jwst, and high-resolution spectra from the cosmic origins spectrograph (cos) hubble space telescope (hst). the comparisons of cluster-scale hst and galaxy-scale iue observations, in the 1200 - 3000 å wavelength range, permit establishing trends with galaxy properties. this includes uv beta slopes, stellar continuum fits compared to synthesis models, and ism absorption-line equivalent width (ew) comparisons in low and high ionization zones. we use ancillary optical data to update oxygen abundances and find relationships between these and the measured ews. we also find that there is an offset between low and high ionization zone ews when comparing between the two aperture sizes. | cluster-scale versus galaxy-scale ultraviolet spectral properties of star forming galaxies |
using hst/wfc3 grism spectroscopy from the candels lyman-alpha emission at reionization (clear) survey, we constrain the metallicities and ages of massive quiescent galaxies, at z ~ 1.5. clear provides deep spectroscopy (12 hst orbits per pointing) with the wfc3/g102 grism over the wavelength range ~ 7,500 < λ < 12,000 å, at a spectral resolution of r ~ 200, within the goods-n and goods-s deep regions of candels. these data cover important age and metallicity sensitive spectral features for galaxies at 1 < z < 2, including the redshifted ca hk lines, 4000 å break, balmer-series lines, and hg+g features. we stack the g102 spectra of a stellar-mass limited sample of 34 quiescent galaxies, with log(m*/m⊙) > 10 and 1 < z < 2, and fit the spectra using two sets of stellar population synthesis models, bc03 (bruzual & charlot 2003) and fsps (flexible stellar population synthesis, conroy & gunn 2010). from these fits, we construct probability distribution functions of age and metallicity for these galaxies, separated into two mass bins, 10 < log(m*/m⊙) < 10.9 and log(m*/m⊙) > 10.9. the model fits favor higher metallicity for the more massive quiescent galaxies, with z/z⊙ ~ 1, with some systematics possibly leading from differences in the stellar population models. therefore, there is no evidence for significant evolution in metallicity for the most massive quiescent galaxies since z ~ 1.5. the model fits to the lower mass quiescent galaxies favor lower metallicites, z/z⊙ ~ 0.4, with an offset of ~ 0.3 dex from the present-day relation (e.g., galazzi et al. 2005). for quiescent galaxies in this mass range, 10.0 < log(m*/m⊙) < 10.9, this requires evolution in metallicity, either as a result of continued chemical enrichment of current galaxies, or the formation of additional quiescent galaxies (presumably quenching of star-forming galaxies at z > 1), or a combination of the two. | constraining metallicity and age for massive quiescent galaxies in a redshift range of 1 |
the metal content of high redshift galaxies is typically measured in the gas phase using strong optical emission line diagnostics that are calibrated locally, suffering significant uncertainties. for direct estimates of gas-phase metallicities, faint auroral lines need to be detected to determine the electron temperature of the ionized gas, which is challenging. alternatively, the stellar continuum emission can be used to measure the metallicity (known as stellar metallicity). the far-ultraviolet (fuv) part of the spectrum contains important information about the underlying stellar population of galaxies with absorption features that can be used to estimate the metallicity of galaxies. the photospheres of hot o and b stars, metal-dependent stellar winds, and interstellar lines all contribute to these absorption features. these features usually have complex dependencies on age, metallicity, and initial mass function. in this work, we present the stellar mass-stellar metallicity relation for 3775 star-forming galaxies at 2 ≲ z ≲ 3 using rest-frame fuv spectra from the lyα tomography imacs survey (latis; newman et al. 2020). we fit high-resolution stellar population synthesis models to high signal-to-noise (>40 per å over a wavelength range of 1270-1800 å) composite spectra of galaxies in bins of stellar mass to determine their stellar metallicity (primarily tracing fe/h), age, and α-elements-to-iron ratio. we use the latest release of synthesis models from the binary population and spectral synthesis code (bpass v2.3) which, for the first time, incorporates stellar spectra with α-enhanced compositions. although the fuv stellar absorption lines are relatively insensitive to [α/fe], with high signal-to-noise composite spectrum we constrain the average [α/fe] to be ~0.4 across the stellar mass range of our sample, log(m∗/m⊙)=9-11, at z~2.5. we find strong correlation between stellar mass and stellar metallicity, with stellar metallicity monotonically increasing with stellar mass and flattening at high stellar mass end (m∗≳1010 m⊙). analytic chemical evolution models suggest that the flattening of the stellar mass-metallicity relation can be explained if the mass-loading parameter decreases as stellar mass increases with both parameters flattening at m∗≳1010 m⊙. | the stellar mass-metallicity relation of star-forming galaxies at z 2.5 |
we present a new set of synthesis models for stellar populations obtained with starburst99, which are based on new stellar evolutionary tracks with rotation. we discuss models with zero rotation velocity and with velocities of 40% of the break-up velocity on the zero-age main-sequence. these values are expected to bracket realistic rotation velocity distributions in stellar populations. the new rotating models for massive stars are more luminous and hotter due to a larger convective core and enhanced surface abundances. this results in pronounced changes in the integrated spectral energy distribution of a population containing massive stars. | the effects of stellar rotation in starburst99 models |
detections of gravitational waves have revolutionized the understanding of black-hole binaries and double neutron stars, as well as their coalescence. these detections have provided a new way to test our best predictions for the evolution of binary stars which ultimately merge as black-hole or neutron-star binaries. however, the evolution of compact-object binaries is still riddled with enigmas such as the effect of different supernova-explosion prescriptions. specifically, modern supernova models predict that the outcome of the explosion is set by the compactness (not just the mass!) of the stellar core. we present the first implementation of such advances in the state-of-the-art population-synthesis code mobse. we test how different possible physics of the supernova mechanisms impact the key gravitational-wave observables. how does the core-collapse explosion mechanism affect the resulting remnant? how does the pre-supernova compactness affect the mass spectrum of gravitational-wave sources? | impact of the pre-supernova stellar compactness in gravitational-wave populations |
the properties of gas and dust in galaxies' interstellar media are a valuable tool for understanding their cosmic evolution. unfortunately, for many ism tracers the signal that is detected from any individual galaxy tends to be very faint (i.e., the ratio of signal to noise [s/n] is low). by using stacking, a technique in which one averages the flux densities at the positions (and in some cases redshifts) of sources in a large sample, we can boost s/n and achieve an overall statistical detection. in support of the forthcoming laduma (looking at the distant universe with the meerkat array) survey of neutral atomic hydrogen (hi) in galaxies out to z = 1.4, we have characterized a stacking sample of 2248 galaxies with spectroscopic redshifts z < 1.4 in the musyc (multi-wavelength survey by yale-chile) survey of the well-studied ecdfs (extended chandra deep field south). we have used the "prospector" markov chain monte carlo (mcmc) implementation of the flexible stellar population synthesis code to find the maximum posterior probabilities for stellar mass, metallicity, dust attenuation, stellar age, and exponential star formation timescale. as a first test, we have stacked stellar mass-selected samples in maps made by blast (the balloon-borne large-area sub-millimeter telescope) at 250, 350, and 500 microns. looking ahead to the start of laduma observations, we will use stacking samples that are defined by their stellar mass, redshift, and possibly dust attenuation and stellar age to probe the evolution of galaxies' hi content across cosmic time. this project has been supported by funding from national science foundation grant phy-1560077. | probing the evolution of galaxies by stacking stellar mass selected samples |
classical, hydrogen-depleted wolf-rayet (wr) stars mark an evolved stage of massive stars with major impacts to their environment. the high temperatures of wr stars, the progenitors of massive black holes, turn them into major sources of ionizing flux. in the last two decades, the discovery of strong high-ionization emission lines in both high-redshift galaxies and extremely low-metal local galaxies has raised more questions than answers about the origin of the he ii ionizing radiation and its implications for the cosmic reionization and galaxy evolution. the current generation of stellar population synthesis models fails to reproduce the necessary hard ionizing fluxes. yet, their treatment of hydrogen-depleted stars is still insufficient with regards to both theoretical insights as well as observational template material. here, we propose a crucial observational solution by studying whether certain types of wr stars may be the missing ingredient required for stellar population synthesis models to reproduce the nebular emission line characteristics of high-redshift galaxies, enabling the inference of the properties of the first galaxies in the universe. most wr stars are consuming the necessary high-energy photons to drive their strong winds, but model calculations show that a subset of early-type wr stars with weaker winds can produce large amounts of he ii ionizing photons. the proposed cos observations will allow us to probe the stellar and wind properties of this subset of the wr population, distinguish sources of strong he ii ionizing flux, constrain pre-supernova feedback, and provide the necessary templates for a new generation of population synthesis models. | benchmarking early-type wolf-rayet stars as sources of he ii ionizing flux in stellar populations |
the companion mass ratio distribution (cmrd) of main sequence binaries is a crucial physical quantity for understanding the evolution of stars in binary systems and for constraining models of binary star formation. however, although much work has been done during the last years, the shape of the cmrd remains rather uncertain. we present a population synthesis study of white dwarf-main sequence (wdms) binaries in the galactic disk aimed at constraining the properties of the cmrd. to this end, we computed a set of monte carlo simulations aimed at reproducing the wdms binary population observed by the sdss. we used different prescriptions for the cmrd and we took into account all the known observational biases. we show that our simulations reproduce reasonably well the observed distributions of masses and luminosities of the white dwarf star and of spectral type of the main sequence star. moreover, our simulations place constraints, albeit weak, on the shape of the cmrd. | a population synthesis study of white dwarf-main sequence binaries in the galactic disk |
we analyze the intrinsic flux ratios of simple and composite stellar populations for various visible--near-infrared filters with respect to ∼3.5μm (l-band), and their dependence on metallicity, star-formation history, and effective mean age. this study is motivated by the fact that light from galaxies is reddened and attenuated by dust via scattering and absorption, where different sightlines across the face of a galaxy suffer various amounts of extinction. ignoring the effects of this extinction could lead one to infer lower stellar mass, and sfr, or higher metallicity. tamura et al. (2009) developed an approximate method, dubbed the "βv" method, which corrects for dust-extinction on a pixel-by-pixel basis, by comparing the observed flux ratio and empirical estimate of the intrinsic flux ratio of optical and ∼3.5μm broadband data. here, we aim to validate and test the limits of the βv method for various filters spanning the visible through near-infrared wavelength range. through extensive modeling, we test their assumptions for the intrinsic flux ratios for a wide variety of simple and composite stellar populations. we build spectral energy distributions (seds) of simple stellar populations (ssps), by adopting starburst99 and bc03 models for young (<9myr) and old (>100myr) stellar populations, respectively, and linear combinations of these for intermediate ages. we then construct composite stellar population (csp) seds by combining ssp seds for various realistic star-formation histories (sfhs). we convolve filter response curves of visible--near-infrared filters for hst imaging surveys and mid-infrared filters in current (wise, spitzer/irac) and near-future use (jwst/nircam) with each model sed, to obtain intrinsic flux ratios (βλ,0). we find that βnir,0 is only varying slightly as a function of metallicity but is insensitive to sfh or redshift (z≤2). we also find a narrow range of βv,0 (0.7+0.05-0.08) for early hubble type galaxies (e and s0) using seds of randomly generated multi-burst sfhs together with age and metallicity profiles of nearby galaxies from the literature. | predicting intrinsic mid-ir to optical flux ratios for galaxies of different types using spectral synthesis models of composite stellar populations |
we will survey with chandra and hst 11 nearby elliptical galaxies to make first-ever robust empirical measurements of how field lmxbs evolve as their parent stellar populations age. our observations will robustly test (to the 96.5-99.4% confidence level) theoretical population synthesis models, which predict a decline in field lmxbs with increasing age. our survey will also contain detections for 800 globular cluster (gc) lmxbs, dramatically improving constraints on whether gc lmxbs seed field lmxbs by being kicked out of their host gcs. to perform this experiment, we will leverage >4 ms of chandra exposures and >35 hst orbits for 9 galaxies that exist in the archive, and will add 255 ks of new chandra time and two new hst orbits for two young early-type galaxies. | a statistically robust constraint on the evolution of field lmxbs |
we present the new approach to the ionisation structure modelling for the high-metallicity hii regions. the method is based on the multicomponent photoionisation modelling (mphm) of these objects that takes into account their complicate structure due to superwind from the central star-forming region. the complex structure of hii region has been divided into internal and external components. internal components correspond to the region of free expanding superwind and the cavity of superwind, respectively, while the external ones - to a thick layer of gas compressed by a superwind shock, and hydrodynamically undisturbed outer part of hii region, where the most of observed strong emission lines are formed. the components of the model were calculated within the assumption of spherical symmetry. the gas photoinisation was caused by the ionising quanta of both direct and diffuse ionising radiation. the fluxes of this radiation were calculated during the simulation using the radiative transfer equations which account for all important processes in the hii region causing this transfer. the diffuse ionising radiation was calculated in the outward only approach. in the region of free expansion of the superwind the chemical abundances were determined using the evolutionary population synthesis models of a star-forming region. the distributions of the electron temperature and density in the external components were obtained in such modelling as the solutions of the photoionisation energy balance equation. the stop criterion for evolutionary modelling corresponding to the condition of equilibrium of pressure on the boundary between the third and fourth components was adopted. the evolutionary grid of multicomponent high-metallicity models of the hii regions was calculated. it was shown that the internal structure of a hii region under certain conditions can cause the lack of quanta in the spectrum of ionising radiation. | photoionisation modelling of the hii regions surrounding star-forming regions within the metallicity range z=0.003-0.012 |
spops is a database of populations synthesis simulations of spinning black-hole binary systems, together with a python module to query it. data are obtained with the startrack and precession [ascl:1611.004] numerical codes to consistently evolve binary stars from formation to gravitational-wave detection. spops allows quick exploration of the interplay between stellar physics and black-hole spin dynamics. | spops: spinning black-hole binary population synthesis |
using the yunnan-ii evolutionary population synthesis models comprising binary stars, we find that the inclusion of binary stars can raise the derived stellar metallicity z* and/or age t (degeneracy problem), raise the stellar mass m*, lower the gaseous metallicity z gas and star formation rate (sfr) of galaxies. this means that a few stars form recently in galaxies, while more stars form during the entire evolution process when considering binary stars. if the degeneracy between t and z* can be broken, its effect on the feedback process and star formation history can be determined. | binary stars on the galaxy sfh |
we present a new set of planetary population syntheses with an updated model compared to alibert, 2013. in particular, changes to the collisonal treatment, stellar evolution and disk photoevaporation can shape the resulting population. the influence of the stellar mass is studied and the distribution of resulting planets presented. a comparison with key systems - such as the solar system or the trappist-1 system - is possible thanks to the multiple stellar masses. | the next generation planetary population synthesis - stellar mass influence |
population synthesis models can be used to create artificial star clusters through monte carlo modeling of input functions that include the star-formation history, initial mass function, and reddening from circumstellar disk excess. observed quantities such as k-band luminosity functions and stellar colors can be compared with that of real clusters to help constrain cluster properties. we present a new model that uses the mass-luminosity relationships from the latest theoretical evolutionary models for both low- and high-mass stars. we use analytic functions to model parameters for binary star systems, including companion frequencies, excess twin fractions, companion mass ratios, and period distributions. early results from simulation runs show how the choice of binary distributions and evolutionary history affect the cluster observables. we also present preliminary work on comparing these model results with real clusters. | a new synthetic model for studying young star clusters |
table 3 provides the cluster name (column 1), object identification (column 2), position (column 3), stellar mass (column 4, assuming a bruzual & charlot (2003mnras.344.1000b) stellar population synthesis model with solar metallicity and salpeter initial mass function), log10 of half-light radius (column 5), and the adopted psf correction (column 6) of 158 galaxies in 13 galaxy clusters. stellar mass and radii assume ωm=0.3, ωλ=0.7, h0=70km/s/mpc. the 14th cluster is published in andreon et al., cats. j/a+as/116/429 and j/a+as/126/67. (2 data files). | vizier online data catalog: red-sequence early-type galaxies in clusters (andreon+, 2016) |
over the last several years, surprising detections of strong high-ionization nebular emission lines in star-forming galaxies ranging in distance from a few megaparsecs to deep into the reionization era have challenged the accuracy of modern stellar population synthesis models. meanwhile, deep spectroscopy of massive ob stars in the magellanic clouds has uncovered increasingly strong evidence that canonical models of stellar evolution may already break down at the moderately-low metallicity of the smc (20% solar). both lines of evidence suggest that yet more metal-poor massive stars may be far more abundant producers of hard ionizing radiation than predicted by the latest generation of stellar models; but no direct test of stellar physics in this regime has yet been possible. fortunately, over the next few hst cycles, the ullyses ddt program will help amass the ultraviolet spectra of a statistical sample of massive ob stars at sub-smc metallicities necessary to conduct such an experiment for the first time. we propose to complete the ullyses spectral atlas below 20% solar metallicity with additional uv and optical spectra, and build the accompanying theoretical stellar atmosphere library necessary to constrain fundamental stellar parameters with these data. leveraging the wealth of uv data ullyses will provide in the magellanic clouds, we will derive the first robust measurement of the gradient in stellar wind strengths and cno surface abundances at fixed stellar class down to 10% solar metallicity. this work will provide the crucial framework for calibrating stellar models into the metallicity regime relevant to the interpretation of reionization-era galaxies with jwst. | painting the first empirical picture of massive stars below the metallicity of the smc with ullyses |
young star clusters are a promising environment for forming binary black holes. such binaries may form dynamically or via binary star evolution or through the interplay of these two channels. to study these formation pathways, we have performed high precision direct n-body simulations of low-mass (m < 1000 m⊙) young star clusters. the simulations were carried out with the code nbody6++gpu coupled with the population synthesis code mobse. our results highlight the importance of dynamics to form massive black hole binaries even in low-mass young star clusters. | black hole dynamics in young star clusters |
interpreting the photometry and spectroscopy of galaxies often requires consideration of their integrated light. for this, models which accurately represent the emission from a stellar population as a function of its age, metallicity and other properties are essential. such stellar population modelling is a mature field where old, metal-rich stellar populations are concerned. however galaxies exist at all redshifts which are much younger and lower in metal enrichment than a typical local galaxy. amongst distant galaxies, or the hosts of stripped-envelope transients, such systems become the norm. modelling these population requires a detailed understanding of massive star evolution and its effects on the integrated light. in particular, it has become clear that interactions between stellar binaries and other multiples may have significant effects on the observed population. here i will discuss the current status of stellar population synthesis modelling and the remaining uncertainties, particularly with respect to multiple star evolution and factors affecting emission line galaxies in the distant universe. | key uncertainties in modelling emission line galaxies |
a galaxy can be broadly decomposed into a few baryonic components: gas disc, stellar disc, and bulge (if present). the conversion from 21cm flux to atomic gas mass is specified by the physics of the spin-flip transition, fixing the gas contribution. the conversion from stellar light to stellar mass is less well determined. for bulge and stellar disc, we need to introduce mass-to-light ratios, denoted as ybul and ydisc, respectively. the values of ybul and ydisc can be fixed using stellar population synthesis models (bell & de jong 2001apj...550..212b; mcgaugh & schombert 2014aj....148...77m; schombert & mcgaugh 2014pasa...31...36s; lelli et al. 2016aj....152..157l, 2016apj...827l..19l), but in this work we will use them as free parameters to determine their maximum allowed values from a dynamical perspective. we develop a fitting scheme that matches the baryonic rotation curve to the observed one at small radii, specifically near the 'turning radius' where the rotation curves start to approach a flat part. the algorithm produces good results in disc-dominated cases. however, for galaxies with bulges, the mass-to-light ratios of bulge and disc can be degenerated. in these cases, we break the degeneracy by imposing ybul>ydisc. this choice is motivated by stellar population synthesis models. to confirm the algorithm's efficacy and estimate the uncertainties, a markov chain monte carlo (mcmc) routine was also run on all galaxies, giving consistent results. (2 data files). | vizier online data catalog: quantifying maximum discs in galaxies (starkman+, 2018) |
as population iii (pop. iii) stars die in supernovae, they pollute the interstellar clouds of dust and gas from which next generation, pop. ii stars, form. during their deaths, elements heavier than li are ejected, increasing the metallicity of subsequent stellar generations. which elements are synthesized both in the ejecta and from the evolutionary stages of the progenitor star depends on the initial mass of the exploding star. the elemental abundances of the enriched pop. ii stars speak to the approximate mass of the pop. iii stars which polluted the material from which the pop. ii stars formed. we study the abundances of a chemo-dynamically tagged group (cdtg) which shares, amongst other features, significantly similar dynamical properties and metallicities ([fe/h]). the mutually held characteristics of the stars within our cdtg are a result of their common ancestry, as they were likely stars of an extinct minor galaxy. using light-element (c, n, o, to zn) abundances in the pop. ii stars of a particular cdtg, this work derives the approximate mass distribution of pop. iii stars in the low-galaxy-mass environment in which the pop. ii stars formed. we find that most of the stars in the cdtg were enriched by the death of a progenitor star of approximately 26m⊙, which either implies enrichment by a single event, or that the distribution of the progenitor pop. iii stars was strongly peaked at 26m⊙. | deriving the first stellar mass function from the light-element abundances of metal-poor stars |
with the aid of a detailed monte carlo simulator we built a thorough population synthesis model of the thin disc, thick disc, and halo white dwarf population of our galaxy. our synthetic models incorporate updated evolutionary sequences for both co-core and one-core white dwarfs, as well as hydrogen-rich and hydrogen-deficient atmospheres. additionally, we included in our models a complete treatment of the different selection criteria and photometric and astrometric errors predicted by gaia performances. this permitted us to define the regions within the gaia hr diagram where we expected to identify white dwarfs, as well as to predict its completeness and to estimate its possible contamination. we followed the recommendations given by evans et al. (2018a&a...616a...4e) and lindegren et al. (2018a&a...616a...2l), to search for white dwarf candidates in the gaia-dr2 catalogue with accurate gaia parallax and photometry. after adopting the photometric criteria and colour limit, our query returned 73221 gaia-dr2 counterparts, 72178 co-core, and 1043 one-core white dwarf candidates. they all form our catalogue of gaia white dwarfs. (1 data file). | vizier online data catalog: a white dwarf catalogue from gaia-dr2 (jimenez-esteban+, 2018) |
we trained a neural network that can obtain selected starlight parameters directly from s-plus photometry. the training set consisted of over 55 thousand galaxies with their stellar population parameters obtained from a starlight application by cid fernandes et al. (2005). these galaxies were crossmatched with the s-plus idr 3 database, thus, recovering the photometry for the 12 band filters for 55803 objects. we also considered the spectroscopic redshift for each object which was obtained from the sdss. finally, we trained a fully connected neural network with the 12-band photometry + redshift as features, and targeted some of the starlight parameters, such as stellar mass and mean stellar age. the model performed very well for some parameters, for example, the stellar mass, with an error of 0.23 dex. in the future, we aim to apply the model to all s-plus galaxies, obtaining never-before-seen photometric synthesis for most objects in the catalogue. | stellar population photometric synthesis with ai of s-plus galaxies |
thermally-pulsing (tp-)agb stars and red helium-burning (rheb) stars dominate the near-infrared (nir) flux in star-forming galaxies (up to 70%) and thus have a strong impact on the appearance of galaxies. these stars are notoriously difficult to model, and the only empirical constraints on their evolution come from the magellanic clouds, at just 20% and 50% solar metallicity. lower metallicity models are entirely uncalibrated and these uncertainties propagate to stellar population synthesis, leading to (sometimes wildly) inaccurate derived galaxy properties such as the star-formation rate and stellar mass. the hst is capable of rectifying this. by adding nir and some additional optical imaging to existing optical and uv imaging of an optimally selected sample of nearby (< 3.1 mpc) metal-poor dwarf galaxies, we can produce observables (luminosity functions, stellar counts, cmd morphology, stellar seds) that stringently constrain the metallicity dependencies on the processes that drive model uncertainties, including mass loss, dredge up, convective overshoot, and rotation. understanding the metallicity dependence of these parameters is invaluable to interpreting observations of metal-poor galaxies, which dominate the number density of galaxies in the universe. given the prior hst investment of observations in these galaxies, this relatively modest amount of observing time promises to revolutionize the field and leave a lasting hst legacy in the local volume. | solving the metallicity dependence of evolved star evolution and completing hst's near-ir legacy in the local volume |
the hydrogen ionizing photon production rate $q_h$ of massive stars ($ m > 8 \: m_{\odot}$) must be known to interpret important observable quantities including galaxy star formation rates, the energy budget for nebular emission and the re-ionization epoch of the universe. recently it has been shown that stellar population synthesis (sps) predictions for $q_h$ diverge by a factor of $\gtrsim 2$ in low-metallicity environments. to test these predictions we use sps to model the spectra of galaxies with different stellar evolution models. we analyze three different input physics models that account for single-star evolution (parsec), stellar rotation (mist) and binary evolution (bpass). these parameters and models affect $q_h$. we create grids of metallicity, star formation history and dust then plot data onto them to compare our models. we find that stellar rotation and binary interactions both produce significantly more ionizing photons than single-star models. the results suggest that single, non-rotating stars are unable to reproduce the ionizing flux needed to model the bluest and highly star forming galaxies in our dataset. the primary challenge present in this analysis is accounting for the many parameters that can affect $q_h$ so moving forward we must verify galaxy properties on a case by case basis. | using distant galaxies to constrain the ionizing photon budget of massive stars |
in the past few years, several clusters of red supergiants have been discovered in a small region of the milky way, close to the base of the scutum-crux arm and the tip of the long bar, between l=24º and l=29º. according to the number of observed red supergiants and using population synthesis models, they must contain very large stellar populations to harbour so many rsgs, some of them being candidates to the most massive young clusters in the galaxy. these massive open clusters are part of a huge structure most likely containing hundreds of red supergiants. these results suggest that the scutum complex represents a giant star formation region triggered by dynamical excitation by the galactic bar, whose tip is believed to intersect the scutum-crux arm close to this region. if this scenario is correct, a similar structure would be expected close to the opposite end of the galactic long bar. we must find in an area between l=347º-350º (these sight lines include the expected location of the far tip of the galactic bar in the model of gonzález-fernández et al. (2012)) likely candidates to very massive open clusters.we are carrying out a comprehensive optical and infrared photometric and spectroscopic study of this region containing the open clusters vdbh 222, teutsch 85 and their surroundings. we have analyzed the population of vdbh 222 and we have found a large population of luminous supergiants and ob stars. the cluster lies behind ~7.5 mag of extinction and has a probable distance of ~ 10 kpc and an age of ~12 ma. vdbh 222 is a young massive cluster with a likely mass > 20000 msolar. now, we are analyzing the population of the open cluster teutsch 85 and surroundings, finding a numerous population of supergiants.in this work, we will discuss the possible role of the galactic bar in triggering the formation of starburst clusters. | a starburst region at the tip of the galactic bar around l=347-350 |
neutron stars present a wide variety from the observational point of view. the advent of new and powerful detectors and instruments has opened a new era where the classical picture of neutrons stars seen as radio-pulsars has been modified with new classes such as magnetars, x-ray isolated neutron stars (xinss) or central compact objects (ccos) in supernova remnants . in addition to the more than 2500 sources detected in the radio band, more than two hundred have also been detected as x-ray and gamma-ray sources. this number is expected to increase in the near future. despite this apparent diversity, some studies demand a theory able to explain the different classes in terms of the same physical scenario (kaspi, 2010), in which the evolution of the magnetic field appears to play an important role (viganò et al., 2013). the population synthesis of neutron stars, which is the central subject of this thesis, is an interesting approach to understand the problem, as both intrinsic properties and observational biases are taken into account. these technique is based on monte carlo methods, applied to simulate the whole population of neutron stars. the main objective of the thesis has been to perform a multi-wavelength study of the different populations of neutron stars focusing in the effects of magneto-thermal evolution. this report consists of a global summary of the objectives, methods and main results of the thesis. it is structured as follows. the first chapter gives an introduction to neutron stars. chapter two is a description of the method of population synthesis of neutron stars. in chapter three a global discussion of the main results is presented. chapter four closes the report with the conclusions. an appendix is also included which constitutes a description of a method based on the pulsar current analysis. | population synthesis of isolated neutron stars |
accreting neutron star binary (ansb) systems can provide some important information about neutron stars (nss), especially on the structure and the equation of state of nss. however, only a few ansbs are known so far. the upcoming chinese space station telescope (csst) provides an opportunity to search for a large number of ansb candidates. we aim to investigate whether or not a machine learning method may efficiently search for ansbs based on csst photometric system. in this paper, we generate some ansbs and normal binaries under csst photometric system by binary evolution and binary population synthesis method and use a machine learning method to train a classification model. we consider the classical multi-color disk and the irradiated accretion disk, then compare their effects on the classification results. we find that no matter whether the x-ray reprocessing effect is included or not, the machine learning classification accuracy is always very high, i.e., higher than 96%. if a significant magnitude difference exists between the accretion disk and the companion of an ansb, machine learning may not distinguish it from some normal stars such as massive main sequence stars, white dwarf binaries, etc. false classifications of the ansbs and the normal stars highly overlap in a color-color diagram. our results indicate that machine learning would be a powerful way to search for potential ansb candidates from the csst survey. | machine learning to search for accreting neutron star binary candidates using chinese space station telescope photometric system |
the lyman continuum (lyc = hydrogen-ionizing radiation at wavelengths < 912 ang) of galaxies plays a fundamental role in determining the physical and observational properties of the ism and igm, including cosmic reionization. yet it is basically inaccessible to direct observations, and one therefore heavily relies on theoretical, yet untested predictions from synthesis models. furthermore the ionizing spectra differ significantly between different models, with important implications on widely used emission line diagnostics and other observables. we here propose to observe for the first time the shape of the ionizing continuum of several star-forming galaxies shortward of (from ~600 to 912 angstroem) and across the lyman break. this can be achieved with cos by targeting lyc emitters at z~0.6-0.8. the observations will measure for the first time stellar and nebular emission features in the lyc, and thus provide the first direct constraints for stellar population models in this spectral range. the proposed observations will provide unique insight on the hardness of the ionizing spectra of star-forming galaxies, with numerous possible implications on our understanding of the emission line properties of distant galaxies, sources of cosmic reionization, emission line diagnostics, and related topics. | a new window on the uv sed of star-forming galaxies: direct measurements of ionizing spectra in the lyman continuum |
rotation is a fundamental property of stars. the kepler mission revolutionized the field of stellar rotation, delivering periods of over 50,000 stars near the plane of the milky way. the distribution of periods revealed unexpected gaps, dips, and edges that cannot be described by current rotational evolution models, demanding new physical explanations. to sharpen the features in the distribution and to disentangle the effects of star formation history, more measurements of rotation are needed across the entire sky. 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. we used deep learning to see through tess systematics and recover periods from year-long light curves. our 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, we estimated reliable periods for 9,837 cool dwarfs. we recovered key features of the kepler and k2 distributions, including periods up to 60 days. we reproduced the intermediate rotation period gap for the first time using tess, as well as a dip in photometric activity surrounding it. combining our tess rotation periods with spectroscopic temperatures and abundances from apogee, we examined the detectability of rotation across fundamental stellar parameters, finding a strong dependence on temperature and age. using gyrochronology, we inferred masses, ages, and other fundamental properties for the 6,632 tess stars with apogee spectroscopy and corroborated evolution trends of galactic chemistry and magnetic activity seen with kepler. now with the ability to estimate rotation periods, including long 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 |
gravitational lensing studies have radically improved our understanding of the internal structure of galaxies and cluster-scale systems. in particular, the combination of strong lensing and stellar dynamics or stellar population synthesis models have made it possible to characterize numerous fundamental properties of the galaxies as well as dark matter halos and subhalos with unprecedented robustness and accuracy. here we demonstrate the usefulness and accuracy of strong lensing as a probe for characterising the properties of cluster members as well as dark matter halos, to show that such characterisation carried out via lensing analyses alone is as viable as those carried out through a combination of spectroscopy and lensing analyses.our study uses focuses on the early-type galaxy cluster macs j1149.5+2223 at redshift 0.54 in the hubble frontier fields (hff) program, where the first magnified and spatially resolved multiple images of supernova (sn) “refsdal” and its late-type host galaxy at redshift 1.489 were detected. the refsdal system is unique in being the first ever multiply-imaged supernova, with it’s first four images appearing in an einstein cross configuration around one of the cluster members in 2015. in our lensing analyses we use hst data of the multiply-imaged sn refsdal to constrain the dynamical masses, velocity dispersions, and virial radii of individual galaxies and dark matter halos in the macs j1149.5+2223 cluster. for our lensing models we select a sample of 300 cluster members within approximately 500 kpc from the bcg, and a set of reliable multiple images associated with 18 distinct knots in the sn host spiral galaxy, as well as multiple images of the supernova itself. our results provide accurate measurements of the masses, velocity dispersions, and radii of the cluster’s dark matter halo as well as three chosen members galaxies, in strong agreement with those obtained by grillo et al 2015, demonstrating the usefulness of strong lensing in characterising the properties of cluster-scale systems. | investigating the internal structure of galaxies and clusters through strong gravitational lensing |
using a novel, mcmc-driven inference framework, we have modeled the stellar and dust emission of 32 composite spectral energy distributions (seds), which span from the near-ultraviolet (nuv) to far infrared (fir). the composite seds were originally constructed in a previous work from the photometric catalogs of the newfirm medium-band survey, in which seds of individual galaxies at 0.5 < z < 2.0 were iteratively matched and sorted into types based on their rest-frame uv-to-nir photometry. in a subsequent work, mips 24 μm was added for each sed type, and in this work, pacs 100 μm, pacs160 μm, spire 25 μm, and spire 350 μm photometry have been added to extend the range of the composite seds into the fir. we fit the composite seds with the prospector code, which utilizes an mcmc sampling to explore the parameter space for models created by the flexible stellar population synthesis (fsps) code, in order to investigate how specific star formation rate (ssfr), dust temperature, and other galaxy properties vary with sed type.this work is also being used to better constrain the sps models within fsps. | modeling well sampled composite spectral energy distributions of distant galaxies via an mcmc-driven inference framework |
in recent years, observations have shown that multiple-star systems such as hierarchical triple and quadruple-star systems are common, especially among massive stars. they are potential sources of interesting astrophysical phenomena such as compact object mergers, leading to supernovae, and gravitational wave events. however, many uncertainties remain in their often complex evolution. here, we present the population synthesis code {\it multiple stellar evolution} (mse), designed to rapidly model the stellar, binary, and dynamical evolution of multiple-star systems. mse includes a number of new features not present in previous population synthesis codes: (1) an arbitrary number of stars, as long as the initial system is hierarchical, (2) dynamic switching between secular and direct $n$-body integration for efficient computation of the gravitational dynamics, (3) treatment of mass transfer in eccentric orbits, which occurs commonly in multiple-star systems, (4) a simple treatment of tidal, common-envelope, and mass transfer evolution in which the accretor is a binary instead of a single star, (5) taking into account planets within the stellar system, and (6) including gravitational perturbations from passing field stars. mse, written primarily in the c++} anguage, will be made publicly available and has few prerequisites; a convenient python interface is provided. we give a short description of mse and illustrate how to use the code in practice. we demonstrate its operation in a number of examples. | multiple stellar evolution: a population synthesis algorithm to model the stellar, binary, and dynamical evolution of multiple-star systems |
the recent discovery of a neutron star accretor in the ultra-luminous x-ray (ulx) source m82 x-2 challenges our understanding of high-mass x-ray binary formation and evolution. 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 exist in approximately 13% of the galaxies with star formation history similar to m82. this work is presented in detail in fragos et al. | the formation of ultraluminous x-ray sources with neutron star accretors |
the globular clusters that orbit the milky way are a treasure trove, providing evidence on a wide range of topics of astrophysical interest, from the scale of individual stars to the entire galaxy itself. the relative ease with which they can be observed, the massive volume of published data on them, and their very nature have also garnered the population of galactic globular clusters (ggcs) an exalted status in the field of stellar population synthesis (sps). this field seeks to interpret the integrated light from extragalactic stellar systems in terms of their underlying physical characteristics and relies on ggcs to enable baseline calibrations of the models that connect data to inference. over the past decade, sps analyses have begun to target galaxies at red/optical wavelengths and found tantalizing evidence that the stellar imf varies systematically with galactic properties, like mass and metallicity. these results motivate the study of ggcs over an as-yet little explored wavelength regime and in this talk i will describe our survey with the gemini observatory to obtain integrated red/optical spectroscopy of these objects. by combining our data with published blue/optical spectroscopy for the same targets, we are able to address pressing issues surrounding sps, such as (i) the limiting accuracy of model-inferred ages, chemical abundances, and mass functions for old stellar populations; and (ii) systematic biases between the analysis of blue versus red spectroscopy. this talk will focus on the urgent need for these data, highlight interesting empirical trends, and present detailed examinations of our modelling for a few clusters. | seeing red: spectroscopy of galactic globular clusters from 6500 å to 1 µm |
the structure of our galaxy has been studied from ultraviolet (uv) star counts obtained with the ultra-violet imaging telescope (uvit) on board the astrosat satellite, in far-uv (fuv) and near-uv (nuv) bands. the f154w (baf2) and n263m (nuvb4) filters were used in the fuv and nuv bands, respectively. the point sources are separated from the extra-galactic sources of uvit observations using infrared (ir) color cut method. the observed uvit star counts match well with the simulations obtained from the besançon model of stellar population synthesis towards several galactic directions. we also estimated the scale length and scale height of the thick disc and the scale height of the thin disc using the space density function and the exponential density law for the stars of intermediate galactic latitudes. the scale length of the thick disc ranges from 3.11 to 5.40 kpc whereas the scale height ranges from 530 ±32 pc to 630 ±29 pc. the scale height of the thin disc comes out to be in the range of 230 ±20 pc to 330 ±11 pc. | study of galactic structure using uvit/astrosat star counts |
the advancement of infrared (ir) detectors opened a range of observational probes of galaxy physics. one of the most important advancements in recent years is the measurement of a variable imf in certain high-mass, high-metallicity systems. however, the models used to make imf measurements lagged in their ability to probe low-mass, low-metallicity systems which has hindered our ability to discern the cause of these variations. in this work we use a new suite of stellar population synthesis (sps) models to probe the imf in low-mass systems over a much wider range of metallicity than in previous studies. we compare our results to massive early-type galaxies (etgs) and available dynamical measurements. variation among the sample in this paper is only ∼50% in normalized m/l compared to the ∼4× among the etg sample. this suggests that metallicity is not the sole driver of imf variability and additional parameters need to be considered. | testing the extremes of imf variability with new stellar population models |
in this work, we investigate the reliability of spectral synthesis methods in the estimation of the mean stellar age and metallicity, addressing the question of which signal-to-noise ratios (s/n) are needed to determine these quantities. to address this problem we used simulated spectra containing stellar and nebular emission, reproducing the evolution of a galaxy for a constant and exponentially declining star formation law. the spectra have been degraded to different s/n and analysed with three different spectral synthesis codes: fado, starlight, and steckmap assuming similar fitting set-ups and the same spectral bases. for s/n > 5 all tools considered show a large diversity in the results. fado and starlight find median differences in light-weighted mean stellar ages of ~0.1 dex, while steckmap shows a higher value of ~0.2 dex. for s/n > 50 the median differences in fado are ~0.03 dex (~7%), a factor 3 and 4 lower than the 0.08 dex (~20%) and 0.11 dex (~30%) obtained from starlight and steckmap, respectively. our results indicate that phases of high specific star formation rate (ssfr) in galaxies require analysis tools that do not neglect the nebular continuum emission in the fitting process, since purely stellar models would have strong problems in the estimation of star formation history, even in presence of high s/n spectra. the median values of these differences are of the order of 7% (fado), 20% (starlight), and 30% (steckmap) for light-weighted quantities, and 20% (fado), 60% (starlight), and 20% (steckmap) for mass-weighted quantities. that implies a severe overestimation of the mass-to-light ratio and stellar mass, even in the presence of a mild contribution from the nebular continuum. our work underlines the importance of a self-consistent treatment of nebular emission, which is the only route towards a reliable determination of the assembly of any high-ssfr galaxy. | self-consistent population spectral synthesis with fado: mean stellar metallicity of galaxies in spectral synthesis methods |
planet population synthesis is a statistical approach that serves as a bridge between theoretical planet formation and the observed population of exoplanets. it has led to testable predictions, such as the now-confirmed minimum in the planetary mass distribution between a few earth masses and 40 earth masses. in order to apply this technique to low-mass host stars, we have extended the bern model of planet formation (mordasini et al. 2009) to the different conditions in their protoplanetary disks. changes to the original setup include a smaller inner disk radius and a down-scaled disk mass distribution. we present a population of systems with a host star mass of 0.1 solar masses which we compare to observables of the trappist-1 multi-planet system (gillon et al. 2017). we find that most of its features can be robustly reproduced. using the mean planetary mass as a metric, we find a domain in initial disk solid mass and disk extent favorable for the formation of similar systems. the fact that a well-established formation model can produce similar systems with little additional assumptions suggests that trappist-1 is not an exotic outlier but a rather typical outcome for very-low-mass systems. this raises important implications for exoplanet demographics at the limit of detectability. " | planet population synthesis: the cradle of the trappist-1 multiplanet system |
we present here a short summary of a forthcoming paper on photoionization models based on califa observations of hii regions. for each of the ∼ 20,000 sources of the califa h ii regions catalog, a grid of photoionization models is computed assuming the ionizing sed being described by the underlying stellar population obtained from spectral synthesis modeling. the nebular metallicity (associated to o/h) is defined using the classical strong line method o3n2. the remaining free parameters are the abundance ratio n/o and the ionization parameter u, which are determined by looking for the model fitting [n ii]/hα and [o iii]/hβ. the models are also selected to fit [o ii]/hβ. this process leads to a set of ∼ 3,200 models that reproduce simultaneously the three observations. we determine new relations between the nebular parameters, like the ionization parameter u and the [o ii]/[o iii] or [s ii]/[s iii] line ratios. a new relation between n/o and o/h is obtained, mostly compatible with previous empirical determinations (and not with previous results obtained using photoionization models). a new relation between u and o/h is also determined. all the models are publicly available on the mexican millions models database 3mdb. | photoionization models of the califa hii regions |
classical novae are optical transients powered by thermonuclear processes in the surface layers of accreting white dwarfs (wds) in binary stellar systems termed cataclysmic variables (cvs). with dozens of outbursts per year in the milky way, classical novae have been observed by humans for millenia. however, despite their rich observational history, researchers still do not have a fundamental understanding of their most basic properties. what powers their luminosity? how are the recently discovered gamma-rays that accompany most classical novae produced? how is mass ejected, why is it enriched in core material, and does the underlying wd increase or decrease in mass during a nova cycle? here, we propose a theoretical investigation of classical novae using modern computational tools. we will begin by using the state-of-the-art open-source stellar evolution code, mesa, to simulate the hydrodynamic launching of classical nova winds for a wide range of cv parameters. these results will be used as input for a population synthesis study of cvs that may provide the answer to a long-standing discrepancy between the mass distribution of wds in cvs and in the field. the mesa results will also guide an exploration of the effects that convective excitation of gravity waves has on mixing of the underlying wd material into the nova ejecta. recent observations have shown that the wd's companion may play a dominant role in the ejection of the nova envelope. thus, we propose to use the one-dimensional mesa calculations as input for three-dimensional smooth particle hydrodynamics simulations that account for the companion's influence on the ejected material for the first time in the literature. the results from these multi-dimensional simulations will then be analyzed with a radiation transport code to produce synthetic light curves and spectra to compare directly to observations. the gamma-ray emission from these ejecta simulations will also be calculated and compared to the recent fermi discoveries of ubiquitous gamma-rays in classical novae. our goal of answering fundamental questions regarding the physics of classical novae will also have direct bearing on a variety of other astrophysical subfields. the mutual interaction of the white dwarf accretor and companion within the expanding nova envelope has applications to stellar mergers and common envelopes, which in turn impact all close binary stellar systems. the possibility that internal gravity waves excited by convection may dredge up underlying core material into the nova envelope is relevant to mixing inside any stars with convective layers on top of stably stratified material with a compositional gradient. this enrichment also leads to interesting nucleosynthesis in the convective burning envelope and subsequent ejecta, with applications to studies of galactic chemical evolution. pi shen and a graduate student will undertake the bulk of this work, and collaborators kasen, metzger, pejcha, and schreiber will contribute code and experience. with their combined arenas of expertise, the pi and team have the potential to enact a true paradigm shift in our understanding of classical novae. | classical novae in the modern era |
the catalog of gravitational-wave events is growing, and so are our hopes of constraining the underlying astrophysics of stellar-mass black-hole mergers by inferring the distributions of, e.g., masses and spins. while conventional analyses parametrize this population with simple phenomenological models, we propose an innovative physics-first approach that compares gravitational-wave data against astrophysical simulations. we combine state-of-the-art deep-learning techniques with hierarchical bayesian inference and exploit our approach to constrain the properties of repeated black-hole mergers from the gravitational-wave events in the most recent ligo/virgo catalog. deep neural networks allow us to (i) construct a flexible population model that accurately emulates simulations of hierarchical mergers, (ii) estimate selection effects, and (iii) recover the branching ratios of repeated-merger generations. among our results, we find that binaries with a higher-generation component make up at least 15% of the underlying population. the deep-learning pipeline we present is ready to be used in conjunction with realistic astrophysical population-synthesis predictions. | machine learning and the origin of ligo's black holes |
ligo/virgo/kagra's gravitational wave revolution ushered in a novel and independent way to constrain large-scale structure and cosmology. notably, compact object binaries have already been used to measure the hubble constant; with only a few dozen detections and poor sky localization, however, the hubble constant uncertainty is currently too large to provide meaningful constraints. the wealth of data from next-generation gravitational wave observatories promises better constraints and more sophisticated measurements. for example, prior work has investigated the proof-of-concept ability to probe the baryonic acoustic oscillation peak using clustering statistics with idealized models. to analyze the performance, biases, and robustness of future gravitational wave probes of large-scale structure and cosmology, we require realistic models of large scale structure, galaxy growth and enrichment, binary stellar populations, and instrument models to create mock gravitational wave catalogs. as a first step, we calculate the spatial autocorrelation function of mock catalogs of the binary black hole mergers in 3g. we use a post-processed version of the illustris cosmological hydrodynamic simulation, one which seeds star particles with binary black holes based on population synthesis models (mapelli et al. 2017) and which incorporates empirical knowledge of the mass and redshift distribution of the binary black hole population. future work includes additional refinements to predict the spatial distributions of measurable stellar mass compact object mergers in hydrodynamic simulations. | spatial distribution of binary black hole mergers in illustris |
the galaxy ugc10205 is analyzed using integral field spectroscopy (ifs) data from the calar alto legacy integral field area survey (califa). the understanding of the current state of this object represents a challenge because it is an extremely isolated galaxy, located in a void, which shows evidence of a possible recent merger. our aim is to confirm whether there was such a merger and try to infer their precursors by means of a complete analysis of the properties of stellar populations, corresponding to metallicity, age, extinction and mass in stars. we first applied an uncertainty study taking on account two error sources, one directly from the data and the second from the fitting codes (fit3d and starlight), and models derived from population synthesis used for determining the physical properties of the galaxy. we found from our study of uncertainties that the optimal value of s/n to determine the properties of the stellar populations is 30, then we proceeded to apply a voronoi binning on the datacube with this s/n value as lower limit. we then obtain star formation histories in different regions of this galaxy and also the radial variations of the physical properties, which suggest this galaxy was formed inside-out. we also looked for local outliers from the mean values of the physical properties as tracers of a possible merger. we contrast the star formation histories with the hypothesis from the n-body simulation of an encounter between ugc10205 and a small elliptical galaxy, performed by reshetnikov and evstigneeva (1999, astron. rep., 43, 367), where they determined by the dispersion of the particles and the current distribution of the tidal structure that the interaction took place ∼ 200 myrs ago. we also present a preliminary study on the state of ionization of the gas that agrees this is a star-forming galaxy. | testing the merging hypothesis for the isolated galaxy ugc10205 using califa data |
m dwarfs are the most common type of stars in the galaxy, and seem to host a higher number of planets on average, compared to fgk stars. yet, due to their lower stellar (and disk) masses — and associated slower formation time scales — gas giants are expected to be infrequent around m dwarfs. in this presentation, we discuss the trends seen in a transiting sample of gas giants (rp > 4 re), with respect to the dependence on host stellar metallicity and mass. we then compare this dependence with a similar sample of non-transiting gas giants discovered by rv surveys. while more detailed high resolution spectral synthesis routines are required to robustly determine abundances; using both empirical and photometric metallicities we note an emerging trend which suggests that the transiting planets (closer-in; warmer) typically orbit more metal-rich and massive m dwarfs compared to the rv sample (further-out; colder). we also compare the m dwarf giant planet sample (transiting + rv) with planets around fgk stars, and find statistically significant evidence that the metallicity distributions for the two differ. we contextualize these trends with planetary formation theories, and discuss future prospects for improving the robustness of studies such as this, with upcoming samples from tess, and gaia. we also note the potential of this sample for population level comparative studies using transmission spectroscopy due to the narrow range of stellar and planetary parameters it spans. finally, we present a new planet discovered using a combination of tess photometry and radial velocities (rv) from the precision rv spectrographs — hpf and neid. this low-density (rho ~ 0.3 g/cm3) jovian sized planet around an early m dwarf presents a corner-case thereby testing the hypotheses of planet formation presented earlier. furthermore, its large scale height (~ 400 km) makes it an excellent target for studies of atmospheric escape as well as transmission spectroscopy to determine atmospheric composition. along these lines, we also present preliminary results from hpf observations which use helium atomic transitions as a tracer to place upper limits on atmospheric escape. | do short-period gas giants predominantly form around metal-rich early m dwarfs? |
we model x-ray luminosity functions (xlf) of accreting neutron stars and black holes in 1035 ≤ lx ≤ 1041 erg s−1 range in star-forming galaxies and galaxies with the initial star formation burst. xlfs are obtained by combining a fast generation of compact object+normal star population using the binary population synthesis code bse and calculation of the subsequent detailed binary evolution by the mesa code. | x-ray luminosity function of accreting neutron stars and black holes |
unique clues about the formation processes of giant planets can be found in their bulk compositions. transiting planets provide us with bulk density determinations that can then be compared to models of planetary structure and evolution, to deduce planet bulk metallicities. at a given mass, denser planets have a higher mass fraction of metals. however, the unknown hot jupiter "radius inflation" mechanism leads to under-dense planets that severely biases this work. here we look at cooler transiting gas giants (teff < 1000 k), which do not exhibit the radius inflation effect seen in their warmer cousins. we identified 40 such planets between 20 m_earth and 20 m_jup from the literature and used evolution models to determine their bulk heavy-element ("metal") mass. several important trends are apparent. we see that all planets have at least ~10 m_earth of metals, and that the mass of metal correlates strongly with the total mass of the planet. the heavy-element mass goes as the square root of the total mass. both findings are consistent with the core accretion model. we also examined the effect of the parent star metallicity [fe/h], finding that planets around high-metallicity stars are more likely to have large amounts of metal, but the relation appears weaker than previous studies with smaller sample sizes had suggested. we also looked for connections between bulk composition and planetary orbital parameters and stellar parameters, but saw no pattern, which is also an important result. this work can be directly compared to current and future outputs from planet formation models, including population synthesis. | the metallicity of giant planets |
we have modeled the universal x-ray luminosity function (xlf) of high mass x-ray binaries (hmxbs) in star-forming galaxies with an evolutionary population synthesis code. we compare the simulated hmxb population under both common envelope mechanisms usually adopted, i.e., the αce formalism and the γ algorithm, and suggest that the distinct observational properties may serve as potential evidence to discriminate between these two types of models. | use hmxb luminosity function to constrain the common envelope mechanisms |
asymptotic giant branch (agb) stars represent one of the main stellar sources for dust production in the universe. we provide a description of the formation and growth of dust particles in the circumstellar envelope of agbs, based on detailed calculations of the agb evolutionary phase. we use stellar population synthesis to interpret the spitzer observations of dusty agbs in the large magellanic cloud (lmc). our results show that carbon-rich and oxygen-rich stars evolve into different and separated regions of the observational diagrams obtained with the spitzer bands. this allows a straight comparison with the spectroscopically confirmed samples of agbs in the lmc present in the literature. the overall impact of agbs on the dust production rate in the lmc is also discussed.the interpretation of the agb population of the lmc is used to describe the observed chemical abundances of the planetary nebulae in the same galaxy. this analysis outlines a clear distinction between stars which experience hot bottom burning and those the third dredge up. | from agbs to pne: understanding the observations of evolved stars in the large magellanic cloud |
we model the mass distribution of newborn black holes (bhs) using a new population synthesis code for massive stars in the milky way. the calculated distributions agree well with those obtained for the galactic bhs in binary systems. the explosions of wolf-rayet (wr) precursors may be responsible for the origin of bhs. | massive stars and black holes |
we present the host galaxy properties of a large sample of ~ 4000 x-ray selected active galactic nuclei (agn) in the chandra cosmos legacy survey to investigate the connection between bh accretion and host galaxy. the cosmos legacy survey reaching x-ray fluxes of 2x10-16 (cgs) in the 0.5-2 kev band, bridges the gap between large area shallow surveys and pencil beamed one. making use of the existing multi-wavelength photometric data available for 96.6% of the sources, cosmos legacy survey provides a uniquely large sample to derive host galaxy properties for both obscured and unobscured sources. we perform a multi-component modeling from far-infrared (500 μm) when available to uv (1500 å) using a 3-component fitting (nuclear hot dust, galaxy and starburst components) for obscured agn and a 4-component fitting (nuclear hot dust, agn big blue bump, galaxy, and starburst components) for unobscured agn. galaxy templates are from the stellar population synthesis models of bruzual & charlot (2003), nuclear hot dust templates are taken from silva et al. (2004), and agn big blue bump templates are from richards et al. (2006). we use the column density information measured in the x-ray to constrain the agn in the infrared band when available. through detailed analysis of the broad-band spectral energy distribution, we derive the stellar masses and the star formation rates of the host galaxy as well as the nuclear and galaxy contribution at each frequency. we study the dependence of host galaxy properties on redshifts, luminosities, and black hole masses to infer the growth history of galaxies and black holes and we compare with a sample of inactive galaxies. | a spectral energy distribution analysis of agn host galaxies in the chandra-cosmos legacy survey |
it is widely anticipated that the first direct detections of gravitational waves will be made by advanced gravitational-wave detectors, such as the two laser interferometer gravitational-wave observatories (ligo) and the virgo interferometer. in preparation for the advanced detector era, i have worked on both detection and post-detection efforts involving two gravitational wave sources: isolated rotating neutron stars (nss) and compact binary coalescences (cbcs). my dissertation includes three main research projects: 1) a population synthesis study assessing the detectability of isolated nss, 2) a cbc search for intermediate-mass black-hole binaries (imbhbs), and 3) new methods for directly measuring the neutron-star (ns) equation of state (eos). direct detections of gravitational waves will enrich our current astrophysical knowledge. one such contribution will be through population synthesis of isolated nss. my collaborators and i show that advanced gravitational-wave detectors can be used to constrain the properties of the galactic ns population. gravitational wave detections can also shine light on a currently mysterious astrophysical object: intermediate mass black holes. in developing the imbhb search, we performed a mock data challenge where signals with total masses up to a few hundred solar masses were injected into recolored data from ligo's sixth science run. since this is the first time a matched filter search has been developed to search for imbhbs, i discuss what was learned during the mock data challenge and how we plan to improve the search going forward. the final aspect of my dissertation focuses on important post-detection science. i present results for a new method of directly measuring the ns eos. this is done by estimating the parameters of a 4-piece polytropic eos model that matches theoretical eos candidates to a few percent. we show that advanced detectors will be capable of measuring the ns radius to within a kilometer for stars with canonical masses. however, this can only be accomplished with binary ns waveform models that are accurate to the rich eos physics that happens near merger. we show that the waveforms typically used to model binary ns systems result in unavoidable systematic error that can significantly bias the estimation of the ns eos. | gravitational waves from rotating neutron stars and compact binary systems |
the modality of disc dispersal is thought to be of fundamental importance to planet formation, yet the responsible mechanism is still largely unconstrained. photoevaporation from the central star is currently a promising avenue to investigate, but the models developed to date do not yet have enough predictive power for a piecewise comparison with the observations. we focus on creating new and improved hydrodynamical models of wind profiles from stellar irradiation at different wavelengths (euv, x-rays) in order to have better constraints for current and future observations. we provide several fits of the total mass-loss rate as a function of star's x-ray luminosity, stellar mass, and carbon depletion, which can be used as simple prescriptions in population synthesis models of planet formation, as well as to produce line profiles within the wind for different disc inclinations. we find that the total mass-loss rate is increased by a factor 2 with respect to the previous models and the x-ray photoevaporation can explain a larger fraction of observed transition discs. although these differences are small, they can significantly impact planet formation and their architecture. | the dispersal of planet-forming discs. a new generation of x-ray photoevaporation models. |
light from galaxies is extincted by dust via scattering and absorbtion. studying galaxies without correcting for this extinction could lead to incorrect results. therefore, a careful study of dust correction in the nearby universe should be done first. tamura et al. (2009) developed an approximate method, dubbed the "βv" method, which corrects for dust extinction on a pixel by pixel basis by comparing the observed and the intrinsic flux ratios of optical and mir (l~3.5μm) broadband data. a nasa/adap funded program "magellanic clues to spatially-resolved extinction corrections for distant galaxies in the hst/jwst era" (p.i. : rolf jansen), aims to validate and test the limits of the "βv" method by using imagery of the lmc and smc in various filters and extensive modeling to test assumptions for the intrinsic flux ratios. for the latter, we build spectral energy distribution (sed) models of simple stellar population (ssp), by adopting starburst99 and bc03 models for young (<9myr) and old (>100myr) stellar populations, respectively, and linear combinations of these for intermediate ages. we then construct composite stellar population (csp) seds by combining ssp seds as functions of various star formation histories (sfhs). filter response/throughput curves (v,i,wise w1(3.4μm), spitzer irac-1 (3.6μm) and l-band) were convolved with the model seds to obtain the intrinsic flux ratios (βλ,0). we present the values of βλ,0 as a function of the age and metallicity of stellar populations, and discuss the effect of various sfhs. we also present ranges of βλ,0 values for different types of galaxies. | analysis of the intrinsic βλ,0 ratio using spectral synthesis models of composite stellar populations |
the stellar initial mass function (imf) is one of the fundamental pillars in studies of stellar populations. it is the mass distribution of stars at birth, and it is traditionally assumed to be universal, adopting generic functions constrained by resolved (i.e. nearby) stellar populations (e.g., salpeter 1955; kroupa 2001; chabrier 2003). however, for the vast majority of cases, stars are not resolved in galaxies. therefore, the interpretation of the photo-spectroscopic observables is complicated by the many degeneracies present between the properties of the unresolved stellar populations, including imf, age distribution, and chemical composition. the overall good match of the photometric and spectroscopic observations of galaxies with population synthesis models, adopting standard imf choices, made this issue a relatively unimportant one for a number of years. however, improved models and observations have opened the door to constraints on the imf in unresolved stellar populations via gravity-sensitive spectral features. at present, there is significant evidence of a non-universal imf in early-type galaxies (etgs), with a trend towards a dwarf-enriched distribution in the most massive systems (see, e.g., van dokkum & conroy 2010; ferreras et al. 2013; la barbera et al. 2013). dynamical and strong-lensing constraints of the stellar m/l in similar systems give similar results, with heavier m/l in the most massive etgs (see, e.g., cappellari et al. 2012; posacki et al. 2015). although the interpretation of the results is still open to discussion (e.g., smith 2014; la barbera 2015), one should consider the consequences of such a bottom-heavy imf in massive galaxies. | the imf-sfh connection in massive early-type galaxies |
we present the first direct comparison between balmer line and panchromatic sed-based star-formation rates (sfrs) for z ~ 2 galaxies. while dust-corrected sfrs(hα,hβ) using balmer decrements are commonly used at low redshift, it has been argued that balmer lines may miss optically thick star-forming regions at high redshifts. in order to investigate this possible bias, we compare the sfrs(hα,hβ) with independently measured uv-to-far-ir sfrs for star-forming galaxies at z ~ 2. for this comparison we use a sample of galaxies selected from the unique spectroscopic dataset of the mosfire deep evolution field (mosdef) survey. the mosdef survey is a multi-year project that uses the near-ir mosfire spectrograph on the 10-m keck i telescope to characterize the gaseous and stellar contents of ~ 1500 rest-frame optically selected galaxies at 1.37 ≤ z ≤ 3.80. in addition to the rest-frame optical spectra, we use data from spitzer/mips 24 μm, herschel/pacs 100 and 160 μm, and herschel/spire 250, 350, and 500 μm to measure mid- and far-ir fluxes. we fit the uv-to-far-ir seds with the state-of-the-art flexible stellar population synthesis (fsps) models, which utilize energy balance to fit the stellar and dust emission simultaneously. comparing the sfr(hα,hβ) with the robust uv-to-far-ir sed inferrred sfrs, show us how accurately balmer decrements predict the obscuration of the nebular lines in order to robustly calculate sfrs for star-forming galaxies at high redshift. furthermore, we use our data to assess sfr indicators based on modeling the uv-to-mid-ir seds or by adding sfr(uv) and sfr(ir), for which the latter is based on the empirical conversions from mid-ir to total ir luminosity. this study shed light on the validity of various sfr indicators, specifically the nebular emission lines, for galaxies at z ~ 2. | the mosdef survey: the strong agreement between hα and uv-to-fir star formation rates for z ~ 2 star-forming galaxies |
pox 186, a local dwarf starburst galaxy with properties analogous to those expected in reionization-era galaxies, has been the focus of numerous optical spectroscopic studies. extending wavelength coverage to the uv permits a detailed study of the stellar population and outflow in this extraordinary galaxy. we present deep, uv spectra of pox 186 obtained with the hst cosmic origins spectrograph which, when combined with archival data, give coverage from ~1150 - 2000 a. stellar population synthesis models favor a recent burst of star formation that has produced a significant fraction of metal-poor stars. the electron density in the high-ionization zone is in the low-density limit, and the c/o relative abundance is calculated via two methods, both of which result in a c/o ratio (log(c/o) = -0.61) that is consistent with other metal-poor dwarf galaxies. c iv 1548,1550 are observed in emission and are double-peaked, indicating a high escape fraction of ionizing photons. the expected high escape fraction is corroborated by new nuv hst imaging; we observe emission from the resonant mg ii 2796,2803 doublet. the emission is compact, suggesting that there is minimal scattering of the resonant photons and, thus, a low column density of neutral gas. we compare the uv line ratios and ews observed in pox 186 to other galaxies with high escape fractions. along with c iv, he ii 1640 is observed in emission, indicative of a very high-ionization zone in pox 186. gmos ifu data is employed to assess the he ii emission, and we find that 1. he ii emission is centrally located near the ionizing source, and 2. the he ii/o iii] ratio observed in the cos spectrum is in very good agreement with the optical he ii/[o iii] ratio. taken together, we confirm that pox 186 is both an extreme emission line galaxy and an appropriate local analog to the reionization-era galaxies. | hst uv spectroscopy of the dwarf starburst galaxy pox 186 |
with the detection of gravitational waves from merging compact objects, a new observational window onto the fates of massive stars has been opened. to explain the observed mergers of compact objects, we need accurate knowledge about the evolution of massive binary stars. yet, current population synthesis calculations often yield puzzling results, as they predict certain types of stellar systems in large numbers, which are rarely observed. whether this is due to observational challenges or due to errors in the underlying evolutionary models, is one of the major open questions in massive star research. in this proposal, we tackle two crucial stages of massive binary evolution that are predicted in large numbers, but so far rarely observed: systems containing an ob-star accompanied by an x-ray-quiet black hole (bh) and systems where a hot, envelope-stripped star is outshined by its ob-type companion. in both cases, the (compact) companion hardly leaves any trace in the optical beyond a suspicious, small he ii disk-like emission. to identify the nature of the companion and distinguish between a bh and a stripped-star companion, uv spectroscopy is the only viable tool. with the unique capabilities of the hst, we will perform a pilot study for two prototypical systems in the galaxy and the lmc that harbor either a bh or a stripped star companion. by determining the presence of tracing ions and the wind parameters of the stars, our study will confirm or deny the existence of the presently only known dormant bh in the milky way, marking an anchor point for our understanding of massive binary evolution and defining a framework for future observations of stripped stars. | smoking guns in massive binary evolution: the hunt for black holes and stripped stars |
the presence of double red clumps (rcs) in the milky way bulge is interpreted as an evidence for the x-shaped structure originated from the disk and bar instabilities. here we show, however, that this double rcs phenomenon is another manifestation of multiple populations observed in globular clusters (gcs) in the metal-rich regime. as in the bulge gc terzan 5, the super-helium rich second generation stars (g2) in the metal-rich bulge are placed on the bright rc, which is about 0.5 mag brighter than the normal rc originated from the first generation stars (g1), producing the observed double rcs. our models can also naturally reproduce key observables, such as the negligible color difference between the two rcs, and the dependence of the double rcs feature on the galactic latitude and metallicity. unlike metal-poor gcs, the formation of g2 in the metal-rich system requires only moderate helium enrichment parameter, dy/dz = 5-6, which would make it possible for g2 to be prevailed in the bulge field. if confirmed by gaia trigonometric parallax distances, this would indicate that bulk of the stars in the milky way bulge originated from disrupted primordial building blocks, such as terzan 5, and that the early-type galaxies would be similarly prevailed by super-he-rich g2. | super-helium-rich stars and the origin of the double red clumps in the bulge: implications on the population synthesis |
the satellites of jupiter are thought to have formed in a circumplanetary disc. here we study their formation and orbital evolution with a population synthesis approach, by varying the dust-to-gas ratio, the disc dispersal timescale and the dust refilling timescale of the cpd. the initial conditions of the disc (density and temperature) are directly drawn from the results of 3d radiative hydrodynamical simulations and the disc evolution is taken into account within the population synthesis. our results show that the moons form fast, often within 10 thousand years, and that many are lost into the planet due to fast migration, polluting jupiter's envelope with typically 15 earth-masses of metals. the last generation of moons can form very late in the evolution of the giant planet and the distribution of the satellite-masses is peaking slightly above galilean masses, up until a few earth-masses, in a regime which is observable with the current instrumentation around jupiter-analog exoplanets orbiting sufficiently close to their host stars. | satellites form fast and late: a population synthesis for the galilean moons |
the correlation between stellar mass and metal abundance (or mzr, the mass-metallicity relation) reflects the balance between galactic feedback and gravitational potential. feedback ejects metals out of galaxies, while gravitational potential retains the produced metals, which enrich later generations of stars. because stellar metallicity indicates the amount of metals incorporated into stars at their formations, it reflects the 'star-formation history average' metal abundance. we present stellar mzrs based on the stellar metallicities of individual quiescent galaxies in the cl0024 and ms0451 galaxy cluster at redshifts 0.4 and 0.54 respectively. the measurements were made via full-spectrum stellar population synthesis modeling. the lower limit of our stellar mass range is 109.7m⊙. to our knowledge, this is the lowest galaxy mass at which individual stellar metallicity has been measured beyond the local universe. we detect an evolution of the stellar mzr with observed redshift when the metal is iron (fe). we do not detect any significant evolution with observed redshift when the metal is magnesium (mg). however, when the relevant redshift is the redshift of the galaxy's formation (not observation), the evolutions of both fe and mg are more easily detectable. we trace these quiescent galaxies back to their star-formation epochs by taking their ages into account. we find that fe abundance strongly depends on galaxy formation epoch; mg abundance has a weaker, but significant, dependence. the stronger evolution of fe than mg can be explained by the difference in their recycling times. fe, mainly produced in type ia supernovae (sn), has a longer recycling time than mg, which is mainly produced in core-collapse sn. fe elements that return to the interstellar medium after quenching would not have been incorporated into stars. the evolution of mg with formation time supports the idea that galaxies have different dominating quenching mechanisms at different redshifts, i.e. the mass-loading factor is redshift dependent. lastly, the gentle slope in the mzrs suggest that the mass-loading factor might be minimally dependent on mass over the observed range of masses. | evolution of the stellar mass - stellar metallicity relation |
type-1 nuclear activity has been thought to be rare in cluster of galaxies since the earliest works in the 1970s. however, clear specimen of type-1 activity have been found in recent spectroscopic surveys of cluster galaxies. seven seyfert 1 and intermediate seyfert nuclei have been discovered in the wide field nearby galaxy cluster survey (wings). we present a focused analysis of their emission line properties, along with refined stellar population synthesis modelling of the host galaxies. some general implications on non-thermal activity in cluster are drawn from the contextualization along the quasar main sequence of the type-1 agn discovered in wings. | seyfert 1 galaxies in wings |
the old metal-rich open cluster ngc 6791 is characterized by a cmd in which the horizontal branch is bimodal and for which canonical stellar models fail to reproduce the requisite number of hb stars and morphology. it is also thought that ngc 6791 has a large binary population. a series of binary population synthesis (bps) simulations have been carried out in order to see if binary interactions can produce a fuller hb population, especially ehb (extreme horizontal branch) stars, that canonical models fail to reproduce. in particular, the han binary population synthesis code (han 2000), together with results from bps studies of the formation channels of sdb/ehb stars (han et al. 2002, 2003) from common envelope (ce), stable roche lobe overflow (rlof), and wd merger events, are applied to ngc 6791. the results provide a good fit to the cmd of ngc 6791 as well as a theoretical fraction of ehb stars of 0.29, which is close to the observed fraction of 0.28 (yong et al. 2000). | ehb stars and ngc 6791 |
sunnynet learns the mapping the between lte and nlte populations of a model atom and predicts the nlte populations based on lte populations for an arbitrary 3d atmosphere. to use sunnynet, one must already have a set of lte and nlte populations computed in 3d, to train the network. these must come from another code, as sunnynet is unable to solve the formal problem. once sunnynet is trained, one can feed it lte populations from a different 3d atmosphere, and obtain predicted nlte populations. the nlte populations can then be used to synthesize any spectral line that is included in the model atom. sunnynet's output is a file with predicted nlte populations. sunnynet itself does not calculate synthetic spectra, but a sample script written in the julia language that quickly computes hα spectra is included. | sunnynet: neural network framework for solving 3d nlte radiative transfer in stellar atmospheres |
understanding how galaxy growth is regulated by gas exchange between galaxies and their surrounding halos is a key priority area highlighted by the astro2020 decadal survey report. the proposed research program aims to probe feeding and feedback in the diffuse circumgalactic medium (cgm) using a legacy sample of h 400 unique galaxy-quasar pairs, which provides a six-fold increase in available sample size at z h 0.002-0.14. it is designed to characterize the dynamic, warm ionized cgm using the ovi absorption doublet as a tracer and to examine how the empirical properties of the gas are connected to galactic properties. the warm ionized cgm is a product of competing feeding and feedback processes in galaxy halos. its dynamic state is dictated by the balance between cooling and heating. at logt /k h 5-5.5, the gas is near the peak of radiative cooling rate with a short cooling time scale, h 100 myr (in comparison to the typical dynamic time of h 1 gyr of the cgm), making it the most active phase in responding to feeding and feedback. with a high ionization potential of 114 ev, o5+ ions and the associated ovi »» 1031, 1037 doublet transitions provide an ideal tracer of this warm ionized gas. however, previous ovi-cgm studies have yielded discrepant results due to limited sample sizes and uncertainties in galaxy properties. the proposed study is enabled by vast public data archives which provide high-quality uv spectra of distant qsos for absorption-line probes and multi-wavelength galaxy imaging data for constraining the stellar population and star formation history over five decades in galaxy mass, from log mstar/msun h 6 to log mstar/msun h 11. additionally, medium-resolution fuv spectra of distant qsos from the fuse archive will provide spectral coverage for ovi and a suite of low and intermediate ionization state transitions covered by fuse spectra, such as ly2, cii » 1036, ciii » 977, nii » 1083, and niii » 989 at z<~0.14. half of the qso sample also have hst cos fuv spectra covering additional ionic transitions at longer wavelengths, including sii, siii-iv, and civ. together, these uv spectra provide the most detailed constraints possible of the thermodynamic state of the diffuse cgm. in parallel, multi-bandpass images of the galaxies from uv (galex), to optical (ground-based all sky surveys), to ir (wise) enable the construction of broad-band spectral energy distributions (seds) necessary for stellar population synthesis analysis to determine star formation rate, mstar, dust properties, and possible agn presence. at z<~0.1,these imaging data provide sufficient spatial resolution to reveal detailed galaxy morphologies, providing critical constraints both for the relative alignment between the qso sightline and the star-forming disk, and for the possible presence of disturbed morphologies or tidal features that are indicative of recent mergers (or close encounters). the proposed study will (1) obtain a robust characterization of how the dynamic, warm ionized cgm traced by ovi depends on galaxy properties and environment, (2) resolve the tensions between (i) existing cgm ovi surveys and (ii) between observations and model predictions; and (3) expand the current cgm survey limit to include both low- mass dwarf and high-mass halos. it will advance a deeper understanding of the physical processes that drive feeding and feedback in galaxy halos. this study will also serve as a pathfinder for the study of the warm hot cgm by targeting [ne v] and [ne vi] in emission using the jwst. | probing feeding and feedback in the circumgalactic medium using ovi as a tracer |
in 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. however, recent observations of planetary nebulae with binary cores (bpne), believed to be the immediate products of ce evolution, indicate orbital periods that are significantly shorter than predicted by population synthesis models using this standard prescription. in this talk, i explore a modified treatment of the ce phase, in which the final orbital separation is dictated by the dynamical condition that the spiral-in of the secondary will be halted when the frictional torque on the secondary is reduced to approximately zero. i crudely estimate this separation as a function of core mass based upon existing stellar models of agb stars between 1 and 7 solar masses. i calculate a theoretical orbital period distribution of bpne using a population synthesis code that incorporates this modified prescription and find it is in much better agreement with observations. | the post-ejection evolution of the orbital components during a common envelope phase |
young, extremely metal-poor stellar populations are central to our quest to characterize the faintest star-forming galaxies in the universe at all redshifts. ongoing efforts to model the nebular and stellar wind lines in extremely metal-poor (< 10% zsun) star-forming galaxies have revealed substantial disagreements with current stellar models. a primary source of this tension is a lack of calibration at low-metallicites: no uv spectrum of an individual o star at z/zsun < 0.1 has ever been taken. we propose to target the brightest two o stars in the extremely metal-poor (z/zsun<0.1) dwarf galaxy leo a (d 700 kpc) with deep hst/cos fuv spectroscopy. leo a is the nearest galaxy with a population of massive stars at these metallicities, making these the most efficient observations possible. with these cos observations, we will (i) directly constrain the stellar metallicity (independent of the gas phase) by accessing faint photospheric lines of iron and (ii) for the first time, make a precise measurement of the wind strengths these massive low-metallicity stars drive. our results have significant implications for massive stellar models in this metallicity regime, and consequently for population synthesis techniques applied to galaxies throughout the universe. this experiment relies entirely on fuv spectra to access crucial massive stellar features inaccessible at other wavelengths, and cannot be conducted in the optical. this will constitute the first observational test of stellar models at the metallicities we expect to encounter regularly in reionization-era galaxies with jwst. | uncovering extremely metal-poor massive stars in leo a |
the first glimpse of the spectra of z 7-10 galaxies has revealed intense nebular emission that has proven challenging to interpret owing to shortcomings in our understanding of low metallicity stellar populations. recent work with hst/cos in the local universe has provided a way forward, characterizing the uv spectra that are common in metal poor galaxies. attention to date has focused on the strongest civ emitting galaxies found locally, as these appear most similar to the few detections known at z>6. but it has recently become clear that the majority of metal poor galaxies exhibit much weaker civ. nothing is known about the nature of the massive stars in these systems, resulting in an extremely biased view of the range of radiation fields powered by low metallicity stars in metal poor galaxies. here we propose to combat this problem by providing the first study of the massive stars in the dominant population of metal poor galaxies in the local universe. via deep (5 orbit) cos/g160m spectra of two of the z<0.02 metal poor galaxies with weak civ emission, we will deliver quantitative constraints on the metallicity of massive stars through measurement of photospheric absorption lines and test stellar wind prescriptions in the poorly calibrated low metallicity regime. using new spectral tools, we will test whether existing population synthesis models can simultaneously reproduce the metallicity and radiation field, providing a powerful stress test for models. if this uv database is not completed soon, the interpretation of reionization era galaxy spectra will be jeopardized throughout the jwst era. | ultra-deep hst/cos spectroscopy of extremely metal-poor galaxies |
massive stars play a critical role in the evolution of galaxies and star clusters. recent observations of the latter have highlighted the need for systematic studies dedicated to probing the impact of massive stellar evolution on the properties of stellar populations. while the use of fitting formulae to stellar tracks remains a popular choice for modelling stellar evolution in population synthesis codes, these formulae are not adaptable to changes. in this talk, i will discuss and present results from an alternative approach, one that is more adaptable: method of interpolation for single star evolution (metisse). it can readily make use of stellar models computed with different stellar evolution codes and compare their predictions for populations of stars. using metisse with data from different stellar evolution codes, i will show how various physical ingredients used in the evolution of massive stars, such as the treatment of their radiation dominated envelopes, can lead to differences in their evolutionary properties. i will discuss the implications of these differences on the evolution and interaction of stars in binaries, and how they can impact compact binary mergers and the properties of gravitational wave events. | can uncertainties in the evolution of massive stars explain properties of gravitational wave progenitors? |
the physical processes governing the formation of the seeds of supermassive black holes, as well as how they grow in the early universe, are two fundamental unanswered questions in galaxy formation and cosmology. the unprecedented sensitivity of jwst's instruments hold exciting potential for probing the growth of galaxies and black holes (bhs) in the very early universe. however, detailed theoretical models are essential for interpreting these observations. with the goal of establishing a connection between the "ground-level", small-scale physical processes and the "top-level" observable signatures, we propose to construct an efficient, physics-based modeling pipeline that self-consistently simulates the co-evolution of bhs and galaxies, and produces predictions of their physical and observable properties over a wide redshift and halo mass range. this will be done by incorporating two essential new components into a well-established galaxy formation framework: 1) a suite of models representing different scenarios for bh seed formation and bh accretion, and 2) population synthesis and nebular line emission models that account for radiation from both stars and accreting bh. with this novel modeling pipeline, we will be able to 1) explore the implications of different bh seeding and accretion models for physical bh and host properties at high redshift, as well as observable quantities such as emission line luminosity functions, colors, and line ratios; 2) identify observables that can optimally constrain seeding and accretion models; and 3) create mock catalogs containing synthetic spectra and photometry, which can guide the design of future jwst observational programs. | constraining the seeding and growth of first black holes via observable signatures from the early universe |
mechanical feedback from massive stars is strongly metallicity-dependent, and therefore low metallicity feedback should vary dramatically from that at solar. we examine the following effects relevant at low metallicity: reduced stellar winds, core-collapse supernovae starting at ages much later than 3 myr, feedback from high-mass x-ray binaries, and dynamical mechanisms that remove massive stars from clusters. we use the starburst99 population synthesis code to compare the mechanical luminosity predicted by the classical feedback model at solar metallicity to models at subsolar metallicity. the subsolar models incorporate the effect of weak stellar winds and restrict supernova progenitor masses to 8-23 msol. we find that the onset of mechanical feedback is effectively delayed until an age of ~10 myr, and the total integrated energy of the cluster is reduced by > 30% relative to the classical model at solar metallicity. this has a number of consequences, most notably that radiative feedback dominates over mechanical feedback during the first 10 myr. since this implies that the early mechanical luminosities of metal-poor clusters likely have been overestimated, it may explain the discrepancy between observed and theoretical growth rates of large magellanic cloud superbubbles, and some may be older than previously estimated. furthermore, early superwinds may not be strong enough to clear gas remaining after star formation, leading to gas retention and continued star formation. this scenario may also promote the escape of lyman continuum radiation and may affect galactic chemical evolution. | mechanical feedback starts later in low metallicity starbursts |
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