abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
compared with the evolutionary population synthesis (eps) models without binary interactions, the derived stellar age and metallicity of galaxies of the eps models with binary interactions are larger. but, we do not know how the galaxies evolve if considering binary interactions in the galaxy evolution models.for early-type galaxies with the uv-upturn phenomenon, there are two explanations: recent star formation (rsf) and binary interactions.in this study, we obtain the mass return fraction and yields for stellar populations with and without binary interactions. in combination with the galaxy chemical and photoionization models, we study the effect of binary interactions on the chemical evolution of early-type galaxies, the metallicity evolution for the early-type galaxies with uv-upturn phenomenon under the two popular mechanisms.we find that the inclusion of binary interactions can raise the ejected mass, metallicity, alpha element, and accelerate the gas cooling. these can reasonably explain the conclusions made via the eps models.moreover, we find that the gas cooling is more efficient under the uv-upturn formation mechanism by binary interactions than rsf, and the ratios of metallicity are different for the two mechanisms, which can be further used to distinguish these two mechanisms. | binary interactions on the early-type galaxy chemical evolution and gas cooling function |
in this dissertation we explore how the nature of tidal interactions tear gravitationally bound systems apart into distinct morphological and kinematic structures. we use the properties of these structures, persisting for billions of years, to investigate the potential of the milky way galaxy and to disentangle the baryonic evolution of gas in dwarf galaxy interactions. we approach these problems through a combination of observations, and simulations, as well as comparisons between the two. in particular, we use the properties of the thin, curved stellar stream emerging from the old, milky way globular cluster, palomar 5 (pal 5) to show that its mere existence can rule out a moderately triaxial potential model of our galaxy. pal 5-like streams on appropriate orbits diffuse much further in space from the orbital path (dubbed "stream-fanning") in this triaxial potential than in the oblate case. we further show that torques from the milky way's galactic bar, can create ever-widening gaps in stellar streams. the fact that the bar can create such under densities, demonstrates that we should be careful when interpreting gaps in stellar streams as indirect evidence of the existence of dark matter subhalos in our galaxy. we carry out a systematic study of resolved neutral hydrogen (hi) synthesis maps of 10 interacting dwarf galaxy pairs. the pairs are located in a range of environments and captured at various interaction stages. we find that the neutral gas is extended in the interacting pairs when compared to non-paired analogs, indicating that gas is tidally pre- processed. additionally, we find that dwarf-dwarf interactions enable the "parking" of gas at large distances to serve as a continual gas supply channel to the dwarfs until accretion by a more massive host. we model a specific dwarf pair in our sample, ngc 4490/85, which is an isolated analog of the magellanic clouds and is surrounded by a ∼50 kpc extended hi envelope. we use hybrid n-body and test-particle simulations along with a visualization interface to simultaneously reproduce the observed present-day morphology and kinematics. our numerical results con- firm that encounters between two dwarf galaxies can "park" baryons at very large distances, without the aid of environmental effects. the extended tidal features will continue to evolve over several billion years which will affect the efficiency of gas stripping if such dwarf pairs are accreted by a massive host. in contrast, in isolated environments dwarf-dwarf interactions can create a long-lived supply mode of gas to the merger remnant potentially explaining the population of dwarfs in the field with large gas envelopes, but limited star formation. all of these topics share the common theme of utilizing morphological and kinematic structures left behind from ongoing gravitational interactions on various scales. | stellar streams, dwarf galaxy pairs, and the halos in which they reside |
for the galaxies composed of all kinds of stars, it is important to estimate the parameters of stellar population synthesis quickly and accurately from the massive data of galactic spectra. it is presented in this paper that the genetic-simulated annealing (ga-sa) combined algorithm with a complementary advantage of the good global searching-ability and the fast convergence-ability of ga, as well as the strong local searching-ability of sa. in the aspect of the speed and the accuracy of the parameter estimation of stellar population synthesis, the experimental results show that the presented ga-sa combined algorithm is better than the single sa algorithm. | parameter estimation of stellar population synthesis using genetic algorithm |
we have recently released version 2.0 of the binary population and spectral synthesis (bpass) population synthesis code. this is designed to construct the spectra and related properties of stellar populations built from ~200,000 detailed, individual stellar models of known age and metallicity. the output products enable a broad range of theoretical predictions for individual stars, binaries, resolved and unresolved stellar populations, supernovae and their progenitors, and compact remnant mergers. here we summarise key applications that demonstrate that binary populations typically reproduce observations better than single star models. | binary population and spectral synthesis |
apparent magnitude difference distribution of visual binary is modeled under various assumptions on initial mass function. | population synthesis of visual binary stars |
x-ray binaries (xrbs) are signposts for the remnants of massive stars and thus provide important constraints on massive stellar evolution. additionally, xrbs are key to understanding the progenitor paths for gravitational wave sources. star-forming galaxies are ideal environments in which to find particularly rare systems, such as potential gravitational wave progenitor wolf-rayet xrbs. we present results from a recent 160 ks continuous chandra observation of the candidate wolf-rayet xrb in the nearby starburst galaxy ngc 253. using hubble space telescope photometry we constrain the companion stellar type. incorporating archival chandra and nustar observations, we summarize the properties of variable sources and study the 1-30 kev x-ray luminosity function. we compare the observed x-ray luminosity function to results from population synthesis modeling based on the star formation history of ngc 253. | revealing the x-ray binary population of the starburst galaxy ngc 253 with chandra and nustar |
this contribution aims to study the nature (kinematic, nuclear activity, and stellar population) of a sample of 10 galaxies in the poor cluster abell s0805. as no detailed optical spectroscopy for some members has been published yet, the selected sample makes this study ideal for investigating the properties of the following objects: eso 104- g(002, 006, 007, 008, 009, 010, 013), fairall 0187, and pgc (062384, 062391). our main results were obtained after subtraction of the underlying stellar population with the spectral synthesis code starlight. the residual spectra reveal seven galaxies with only absorption lines [eso 104- g(002, 007, 008, 009), fairall 0187 and pgc (062384, 062391)], and three galaxies with emission lines [eso 104- g(006, 010, 013)]. according to the boundaries in the diagnostic diagrams, the intensities of h α and the low-ionization lines ([n ii] λ6584 å and [s ii] λλ6716,6731 å) suggest the following results: (i) the brightest cluster galaxy (eso 104- g006, an elliptical cd galaxy) shows low-ionization nuclear emission-line region (liner)-like excitation, quite common in `cool core clusters'; (ii) the eso 104- g010 (`x-galaxy' or `crystal frog') shows an excess of the nitrogen emission-line [n ii] λ6584 å not yet reported. we also suggest this object as a liner; (iii) the spiral eso 104- g013 is a star-forming galaxy with typical emission lines. no obvious signs of interaction were observed in this study. the heliocentric velocities agree within 1σ with the most recent values. the stellar population, rotation curves, and velocity dispersions are also discussed for the first time for some objects. | optical long-slit spectroscopy in the cluster abell s0805 |
we first give a short historical overview with some key facts of massive star population synthesis with binaries. we then discuss binary population codes and focus on two ingredients which are important for massive star population synthesis and which may be different in different codes. population simulations with binaries is the third part where we consider the initial massive binary frequency, the rsg/wr and wc/wn and snii/snibc number ratio's, the probable initial rotational velocity distribution of massive stars. | massive star population synthesis with binaries |
recent analyses of lee et al. (2018, 2019) have confirmed that galactic bulge consists of stellar populations originated from milky way globular clusters (mwgcs). motivated by this, here we present the evolutionary population synthesis (eps) for the galactic bulge and early-type galaxies (etgs) with the realistic treatment of individual variations in light elements observed in the mwgcs. we have utilized our model with gc-origin populations to explain the cn spread observed in etgs, and the results show remarkable matches with the observations. we further employ our model to estimate the age of etgs, which are considered as good analogs for the mw bulge. we find that, without the effect of our new treatments, eps models will almost always underestimate the true age of etgs. our analysis indicates that the eps with gc-origin populations is an essential constraint in determining the etg formation epoch and is closely related to understanding the evolution of the universe. | globular cluster — bulge connection: population synthesis models with multiple populations |
aims: the galactic halo likely grew over time in part by assembling smaller galaxies, the so-called building blocks (bbs). we investigate if the properties of these bbs are reflected in the halo white dwarf (wd) population in the solar neighbourhood. furthermore, we compute the halo wd luminosity functions (wdlfs for four major bbs of five cosmologically motivated stellar haloes). we compare the sum of these to the observed wdlf of the galactic halo, derived from selected halo wds in the supercosmos sky survey, aiming to investigate if they match better than the wdlfs predicted by simpler models.methods: we couple the seba binary population synthesis model to the munich-groningen semi-analytic galaxy formation model applied to the high-resolution aquarius dark matter simulations. although the semi-analytic model assumes an instantaneous recycling approximation, we model the evolution of zero-age main sequence stars to wds, taking age and metallicity variations of the population into account. to be consistent with the observed stellar halo mass density in the solar neighbourhood (ρ0), we simulate the mass in wds corresponding to this density, assuming a chabrier initial mass function (imf) and a binary fraction of 50%. we also normalize our wdlfs to ρ0.results: although the majority of halo stars are old and metal-poor and therefore the wds in the different bbs have similar properties (including present-day luminosity), we find in our models that the wds originating from bbs that have young and/or metal-rich stars can be distinguished from wds that were born in other bbs. in practice, however, it will be hard to prove that these wds really originate from different bbs, as the variations in the halo wd population due to binary wd mergers result in similar effects. the five joined stellar halo wd populations that we modelled result in wdlfs that are very similar to each other. we find that simple models with a kroupa or salpeter imf fit the observed luminosity function slightly better, since the chabrier imf is more top-heavy, although this result is dependent on our choice of ρ0. | white dwarfs in the building blocks of the galactic spheroid |
stars with masses more than 10 times that of our sun emit radiation able to completely ionize the interstellar hydrogen surrounding them. these clouds of ionized hydrogen are known as hii regions. they are the brightest objects in the galaxy at infrared and radio wavelengths and can be detected across the entire galactic disk. this makes hii regions invaluable in understanding galactic star formation, structure, and evolution. to get a global picture of these properties in our galaxy, we need a complete sample of hii regions. my thesis work has two main components : (1) completing the catalog of hii regions throughout the milky way, specifically focusing on the extreme outer galaxy, and (2) using this catalog to constrain hii region population synthesis models of the milky way. the hii region discovery survey and its extensions aim at producing a complete sample of hii regions throughout the galaxy. working with dr. loren anderson, i have been part of the team observing hii region candidates, mainly with the green bank telescope (gbt). these surveys have the sensitivity to detect all regions ionized by single o-stars throughout the galaxy and are nearly complete in the first galactic quadrant, where we focused the majority of our gbt observations. thus far, we have discovered 887 hii regions and studied their sizes, distances, electron temperatures, and compositions. focusing on only the brightest candidates, we have missed a significant population of the faintest hii regions throughout the galaxy. fainter regions can be either very distant or produced by lower-mass stars (i.e. b-type stars). sampling regions surrounding less intrinsically luminous stars gives insight on the total number of galactic hii regions, whereas targeting especially distant regions ( 15 kpc from the galactic center) helps delineate an outer boundary for the galaxy. of particular interest here is a population of hii regions discovered in an extension of the scutum-centaurus spiral arm in the first galactic quadrant, deemed the outer scutum-centaurus arm, or osc. discovered by dame and thaddeus in 2011, the osc warps above the plane and was therefore missed by most galactic plane surveys. to match observed hii region populations with predicted galactic structures, i created an hii region population synthesis model. by constraining structural details of the model and showing that we are able to detect hii regions out to the furthest reaches of the galaxy, we will refine global galactic parameters and probe high-mass star formation throughout the entire milky way. | a census of the galactic hii region population |
a model of the evolution of an ensemble of magnetic massive stars on the main sequence is developed. we use our own population synthesis code, which allows us to obtain distributions of stars by radii, ages, masses, temperatures, effective magnetic fields, and magnetic fluxes from the pre-main sequence up to the tams stages. we assume that magnetic fields in massive stars decrease with time. the rate of magnetic field dissipation may depend on the mass of a star on zams. the distribution of magnetic fluxes of the zams stars is assumed to be log-normal. we show that such kind of distribution may be a result of the dynamo action occurring at the pre-ms evolutionary stage of magnetic stars. our model also includes capabilities for statistical simulations and parameter estimation necessary for the analysis of real data. comparison of model magnetic field distributions with those obtained from recent measurements of stellar magnetic fields allows us to conclude that the evolution of magnetic fields of massive stars is very slow if not absent. the shape of the real magnetic field distribution has no indications of the “magnetic desert,” previously suggested by lignieres et al. (2014). based on those findings we argue that the observed fraction of magnetic stars is determined only by physical conditions at early stages of stellar evolution. | magnetic field distribution for massive stars |
the widespread impact of asymptotic giant branch (agb) stars on the observed properties of galaxies is universally accepted. despite their importance, severe uncertainties plague agb models and propagate through to current population synthesis studies of galaxies, undermining the interpretation of a galaxy's basic properties (mass, age, chemical evolution, dust budget). the only reliable path forward is to apply a physically-sound calibration of agb stellar models in which all main physical processes and their interplay are taken into account (e.g., mixing, mass loss, nucleosynthesis, pulsation, molecular chemistry, dust formation). in this context, i will review recent and ongoing efforts to calibrate the evolution of agb stars, which combine an all-round theoretical approach anchored by stellar physics with exceptionally high quality data of resolved agb stars in the milky way and nearby galaxies. | approaching a physical calibration of the agb phase |
massive luminous red galaxies (lrgs) are believed to be evolving passively and can be used as cosmic chronometers to estimate the hubble constant (the differential age method). however, different lrgs may be located in different environments. we investigate the environmental and mass dependence of the formation of `quiescent' lrgs by using the population synthesis software starlight. we derive the stellar populations in each lrg, and obtain the mean age distribution and the mean star formation history (sfh) of those lrgs. we find that there is no apparent dependence of the mean age and the sfh of quiescent lrgs on their environment, while the ages of these quiescent lrgs depend weakly on their mass. we also evaluate the possible uncertainties in estimating the hubble constant by the differential age method when using lrgs as cosmic chronometers. | environmental effects on lrgs as cosmic chronometers |
we present estimates of ages, [fe/h], helium content (y) and abundances of c, n, mg, ca, and several other elements for the following globular clusters (gcs): gc7 in ngc147, and mayall ii, mackey 1 and mackey 6 in m31. medium-resolution integrated-light spectra of the gcs were conducted with the 6m telescope. to derive the ages and abundances for the gcs we carried out their population synthesis using model stellar atmospheres, the padova yzvar isochrones and the chabrier mass function. we compare the results with the corresponding data obtained using the same method for several massive galactic gcs. we show that the differences in the light-element abundances between gcs with similar ages and metallicities may reach 0.5-0.6 dex. the corresponding differences for other elements are usually 2-3 times smaller. we suggest that at least partially the detected differences may be due to light-element abundance variations in the atmospheres of high-luminosity red giant branch stars as a consequence of the transportation of the produced elements to the surface layers. | ages and chemical compositions of massive clusters in ngc147 and m31 |
we resolve spatially the star formation history of 300 nearby galaxies from the califa integral field survey to investigate: a) the radial structure and gradients of the present stellar populations properties as a function of the hubble type; and b) the role that plays the galaxy stellar mass and stellar mass surface density in governing the star formation history and metallicity enrichment of spheroids and the disks of galaxies. we apply the fossil record method based on spectral synthesis techniques to recover spatially and temporally resolved maps of stellar population properties of spheroids and spirals with galaxy mass from 109 to 7×1011 m⊙. the individual radial profiles of the stellar mass surface density (μ*), stellar extinction (a v ), luminosity weighted ages (<logage> l ), and mass weighted metallicity (<log z/z ⊙> m ) are stacked in seven bins of galaxy morphology (e, s0, sa, sb, sbc, sc and sd). all these properties show negative gradients as a sight of the inside-out growth of massive galaxies. however, the gradients depend on the hubble type in different ways. for the same galaxy mass, e and s0 galaxies show the largest inner gradients in μ* and andromeda-like galaxies (sb with log m* (m ⊙) ~ 11) show the largest inner age and metallicity gradients. in average, spiral galaxies have a stellar metallicity gradient ~ -0.1 dex per half-light radius, in agreement with the value estimated for the ionized gas oxygen abundance gradient by califa. a global (m*-driven) and local (μ*-driven) stellar metallicity relation are derived. we find that in disks, the stellar mass surface density regulates the stellar metallicity; in spheroids, the galaxy stellar mass dominates the physics of star formation and chemical enrichment. | the star formation history of galaxies in 3d: califa perspective |
we present a study of stellar population synthesis of a sample of 10 post-starburst quasars (psqs) at z ∼ 0.3. these psgs posses the spectral signatures of massive intermediate-aged stellar populations, making them potentially useful for studying the connections between the galactic nuclear activity and the host galaxy evolution. with the help of the stellar synthesis code starlight, we have determined the stellar population ages, black hole masses, and eddington ratios of their host galaxies. we find that the psqs have the black hole mass mbh ∼ 108 m⊙, the bolometric luminosity of a few percent of eddington luminosity, and the ages of host stellar populations from several hundred myr to a few gyr. the result may support a time delay existed between the merge-induced starburst and the quasar being triggered/becoming visible. the synthetical spectral energy distribution (sed) of the psqs indicates that they are closely related with the ultra luminous infrared galaxies (ulirgs), and for these psqs, the derived infrared luminosity has attained the level of a luminous infrared galaxy, implying that very possibly, these quasars selected by their optical spectra are undergoing the evolution from ulirgs to optical quasars. | a study of stellar population synthesis of post-starburst quasars |
we characterize in detail the radial structure of the stellar population properties of 300 galaxies in the nearby universe, observed with integral field spectroscopy in the califa survey. the sample covers a wide range of hubble types, from spheroidal to spiral galaxies, ranging in stellar masses from m*∼109 to 7×1011 ⊙. we derive the stellar mass surface density (μ⋆), light-weighted and mass-weighted ages («log age»l, «log age»m), and mass-weighted metallicity («logz⋆ »m), applying the spectral synthesis technique. we study the mean trends with galaxy stellar mass, m⋆, and morphology (e, s0, sa, sb, sbc, sc and sd). we confirm that more massive galaxies are more compact, older, more metal rich, and less reddened by dust. additionally, we find that these trends are preserved spatially with the radial distance to the nucleus. deviations from these relations appear correlated with hubble type: earlier types are more compact, older, and more metal rich for a given m⋆, which evidences that quenching is related to morphology, but not driven by mass. | the califa survey across the hubble sequence: how galaxies grow their bulges and disks |
we study dynamical models of the massive spiral galaxy ngc 2841 using both the newtonian models with navarro-frenk-white (nfw) and isothermal dark haloes, as well as various mond (modified newtonian dynamics) models. we use the observations coming from several publicly available data bases: we use radio data, near-infrared photometry as well as spectroscopic observations. in our models, we find that both tested newtonian dark matter approaches can successfully fit the observed rotational curve of ngc 2841. the three tested mond models (standard, simple and, for the first time applied to another spiral galaxy than the milky way, bekenstein's toy model) provide fits of the observed rotational curve with various degrees of success: the best result was obtained with the standard mond model. for both approaches, newtonian and mond, the values of the mass-to-light ratios of the bulge are consistent with the predictions from the stellar population synthesis (sps) based on the salpeter initial mass function (imf). also, for newtonian and simple and standard mond models, the estimated stellar mass-to-light ratios of the disc agree with the predictions from the sps models based on the kroupa imf, whereas the toy mond model provides too low a value of the stellar mass-to-light ratio, incompatible with the predictions of the tested sps models. in all our mond models, we vary the distance to ngc 2841, and our best-fitting standard and toy models use the values higher than the cepheid-based distance to the galaxy ngc 2841, and the best-fitting simple mond model is based on the lower value of the distance. the best-fitting nfw model is inconsistent with the predictions of the λ cold dark matter cosmology, because the inferred concentration index is too high for the established virial mass. | dark matter and mond dynamical models of the massive spiral galaxy ngc 2841 |
the fit of synthetic spectra has proved to be a powerful tool for determining astrophysical parameters of stellar clusters (scs). such methodology is particularly useful to treat integrated spectra of extragalactic scs. in this work, we present the results obtained by applying this technique to a sample of scs belonging to the large magellanic cloud (lmc) observed from casleo, and using the starlight code. the fitting of the data was performed by means of evolutive--synthesis models of simple--stellar populations of different ages and metallicities, based on the milesm stellar libraries. the integrated spectra of 34 scs of the lmc were fitted in order to obtain the age and metallicity of each object. this study also presents a comparison between the properties derived from those fittings and the method of confrontation of our observations with spectral templates of well known ages. | ajuste de espectros integrados de cúmulos estelares de la nube mayor de magallanes mediante el código starlight |
we show that gw150914, the binary black hole merger detected last year by ligo, could easily have been formed dynamically through interactions in the dense core of an old globular cluster. using models of globular clusters with detailed n-body dynamics and stellar evolution, we show that a typical cluster can very naturally form a binary black hole with "heavy" components that will merge at low redshift, like gw150914. we describe in some detail the dynamical interaction processes that could form such a system. finally, we also show that theoretical predictions for this dynamical formation channel are in general far more robust than those from "population synthesis" studies for isolated massive binaries in the field. | dynamical formation of black hole binaries in globular clusters and the origins of gw150914 |
binary evolution pulsator (bep) is an extremely low-mass member of a binary system, which pulsates as a result of a former mass transfer to its companion. bep mimics rr lyrae-type pulsations but has different internal structure and evolution history. we present possible evolution channels to produce beps, and evaluate the contamination value, i.e. how many objects classified as rr lyrae stars can be undetected beps. in this analysis we use population synthesis code startrack. | contamination of rr lyrae stars from binary evolution pulsators |
the period distributions of classical cepheids in the small and large magellanic cloud are quite different. using the trilegal population synthesis code and a theoretical instability strip the ultimate aim is to understand these differences quantitatively. first results are presented for one area in the lmc using vmc nir data. | the period distribution of cepheids: a test of stellar evolution |
a model of the evolution of an ensemble of magnetic massive stars in the galaxy on the main sequence is developed. the population synthesis code allowing to obtain the distribution of stars by radii, ages, masses, temperatures, effective magnetic fields, and magnetic fluxes is created. the distribution of the magnetic flux on the zams is assumed to be the lognormal. it is supposed that with the increasing star age, its magnetic flux exponentially decreases. the rate of decay is controlled by the dissipation parameter, which is the ratio of the magnetic dissipation time to the main sequence lifetime of a star. as a result of simulations, the distribution of stars by magnetic fields is obtained. the shape of the distribution is highly dependent on the dissipation parameter and the adopted value of the threshold magnetic field. it is shown that this distribution function is in agreement with that obtained from the analysis of the measured magnetic fields of the oba stars. | modeling the distribution function of magnetic fields in massive stars |
by means of a population synthesis code and by constructing a simple toy model of dust produced by asymptotic giant branch (agb) stars, common envelope (ce) ejecta and binary merger ejecta, we estimate the dust product rates (dprs) of these processes in the milky way. the total dpr from agb stars is ~ 6.7 × 10-4 msolar yr-1, in which about 73% of dust grains are carbon, 24% are silicates and 3% are iron. the total dpr from ce ejecta is ~ 4.2 × 10-4 msolar yr-1, in which about 83% of dust grains are silicates, about 12% are carbon and 5% are iron. the dpr from binary merger ejecta is less than 1/3 that from agb stars or ce ejecta, and it could even be negligible under certain circumstances. therefore, compared with agb stars and ce ejecta, the contribution of dust produced by binary merger ejecta to total dust grains in the milky way is smaller or can be negligible. | contribution of dust produced by binary merger ejecta |
evolutionary population synthesis (eps) models play an important role in many studies on the formation and evolution of galaxy. the poorly calibration for some stellar evolution stages in eps models can lead to uncertainty of the parameter determinations for galaxies. by means of the hyperz code and a set of theoretical galaxy template, which are built on the eps models with and without binary interactions, we present photometric redshift (photo-z) estimates for passive galaxy sample at redshift z ~ 2.0. the passive galaxy sample is selected from fang et al., and they also provide the redshift for these passive galaxies. by comparing the photo-z determined from eps models with and without binary interactions, we find that the binary interactions have little effect in the photo-z determinations. | the effect of binary stars on photometric redshift for galaxies at z ~ 2.0 |
we present a pilot study on the nearby massive galaxy ngc 1291, in which we aim to constrain the dark matter in the inner regions, by obtaining a dynamical determination of the disc mass-to-light ratio (m/l). to this aim, we model the bar-induced dust lanes in the galaxy, using hydrodynamic gas response simulations. the models have three free parameters, the m/l of the disc, the bar pattern speed and the disc height function. we explore the parameter space to find the best fit models, i.e. those in which the morphology of the shocks in the gas simulations matches the observed dust lanes. the best-fit models suggest that the m/l of ngc 1291 agrees with that predicted by stellar population synthesis models in the near-infrared (~ 0.6 m ⊙/l ⊙), which leads to a borderline maximum disc for this galaxy. the bar rotates fast, with corotation radius <= 1.4 times the bar length. additionally, we find that the height function has a significant effect on the results, and can bias them towards lower or higher m/l. | breaking the disc-halo degeneracy in ngc 1291 using hydrodynamic simulations |
the eso public kilo-degree survey (kids) is an optical wide-field imaging survey carried out with the vlt survey telescope and the omegacam camera. kids will scan 1,500 deg2 in four optical filters (u, g, r, i). designed to be a weak lensing survey, it is ideal for galaxy evolution studies, thanks to the high spatial resolution of vst, the excellent seeing and the photometric depth. the surface photometry has provided with structural parameters (e.g. size and sérsic index), aperture and total magnitudes have been used to obtain photometric redshifts from machine learning methods and stellar masses/luminositites from stellar population synthesis. our project aimed at investigating the evolution of the colour and structural properties of galaxies with mass and environment up to redshift z ∼ 0.5 and more, to put constraints on galaxy evolution processes, as galaxy mergers. | galaxy evolution within the kilo-degree survey |
stellar population synthesis based models of the milky way play a crucial role in understanding and interpreting observational data from large surveys of the milky way. we describe the basic theoretical framework for modelling the milky way and discuss algorithms for generating a synthetic sample of stars out of such models. next, we discuss how asteroseismology can be used to test and possibly refine theoretical models of the milky way. as an application we test the ability of galaxia to reproduce the properties of stars observed by the nasa kepler mission. we present some preliminary results. we find that galaxia can reproduce the photometric properties of the sample. additionally, it can also reproduce the distribution of average asteroseismic parameters and radius. in future, comparing the mass distributions will allow us to test the galactic models more rigorously. | modelling the milky way with galaxia and making use of asteroseismology |
we investigate the spatially resolved specific star formation rate (ssfr) in the inner ∼40 pc for a nearby seyfert 2 galaxy, m51 (ngc 5194) by analyzing spectra obtained with the hubble space telescope (hst) space telescope imaging spectrograph (stis). we present 24 radial spectra measured along the stis long slit in m51, extending ∼ 1″ from the nucleus (i.e., -41.5 pc to 39.4 pc). by simple stellar population synthesis, the stellar contributions in these radial optical spectra are modeled. it is found that the mean flux fraction of young stellar populations (younger than 24.5 myr) is about 9%. excluding some regions with zero young flux fraction near the center (from -6 pc to 2 pc), the mean mass fraction is about 0.09%. the young stellar populations are not required in the center inner ∼8 pc in m51, suggesting a possible ssfr suppression in the circumnuclear region (∼ 10 pc) from the feedback of active galactic nuclei (agns). the radial distribution of ssfr in m51 is not symmetrical with respect to the long slit in stis. this unsymmetrical ssfr distribution is possibly due to the unsymmetrical agn feedback in m51, which is related to its jet. supported by the national natural science foundation of china. | the inner ∼ 40 pc radial distribution of the star formation rate for a nearby seyfert 2 galaxy m51 |
it is interesting to ask what fraction of the total available rr lyrae (rrl) sample that falls in the kepler and k2 fields of view (fov) is known or discovered. in order to answer this question we compared the known rrl sam- ple in the kepler and k2 fields with synthetic galactic models. the catalina sky survey rrl sample was used to calibrate our method. we found that a large number of faint rrl stars is missing from kepler and k2 fields. | population synthesis of rr lyrae stars in the original kepler and k2 fields of view |
i present integrated colors and surface brightness fluctuation magnitudes in the mid-ir, derived from stellar population synthesis models that include the effects of the dusty envelopes around tp-agb stars. the models are based on the bruzual & charlot cb* isochrones; they are single-burst, range in age from a few myr to 14 gyr, and comprise metallicities between z = 0.0001 and z = 0.04. i compare these models to mid-ir data of agb stars and star clusters in the magellanic clouds, and study the effects of varying self-consistently the mass-loss rate, the stellar parameters, and the output spectra of the stars plus their dusty envelopes. | mid-ir colors and surface brightness fluctuations as tracers of stellar mass-loss in the tp-agb |
planets form in discs around young stars. many of these discs are expected to experience a phase of gravitational instability at early times. if they are sufficiently cold and massive, they may fragment to form bound clumps. depending on the conditions in the discs during and after fragmentation, as well as a number of physical processes governing the behaviour of the clumps, these may contract and become giant planets. this mechanism, called disc instability, may present a formation pathway for some observed giant planets at large separation, as the ones in the hr8799 system. in order to assess the feasibility of this formation mechanism, we are working on a disc instability population synthesis (dipsy). the first step in this endeavour is to study the conditions in protoplanetary discs during fragmentation. they are dominated by strong mass infall from the collapsing molecular cloud core. for the first time we perform a large parameter study where we self-consistently model the formation of the star-disc system, including the effects of autogravitation and fragmentation on the disc's surface density. we present the distribution of initial mass and initial semi-major axis of fragments, as well as the evolution of disc mass and stellar mass. | influence of cloud collapse on the fragmentation of protoplanetary discs |
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 recovered periods for 20,000 cool dwarfs. the period distribution resembles the kepler and k2 distributions, including periods up to 90 days. using gyrochronology, we estimated masses, ages, and other fundamental stellar parameters for 5,000 tess stars with apogee spectroscopy. we combine this with a similar sample from kepler and show that we can use rotation-based ages to recover galactic chemical evolution trends previously seen only in stars more massive or more evolved than the sun. with rotation periods across the entire sky, we can characterize stars along many more lines of sight than before, enabling detailed study of the galaxy's stellar populations. | rotational characterization of tess stars with deep learning |
massive stars are key components of galaxies. characterized by high luminosities and strong outflows, their evolution is strongly impacted by the amount of mass and angular momentum lost through stellar winds. while previously deemed smooth and spherically symmetric, the outflows of massive stars are now found to be inhomogeneous, i.e. clumpy. this severely hampers earlier estimates of the mass-loss rate of hot massive stars and the validity of mass-loss recipes widely adopted in stellar evolution and population synthesis computations.\nin the context, the maestro (massive star outflows) project aims to achieve a comprehensive analysis of the wind structure by combining ultraviolet and optical observational diagnostics and a new generation of stellar wind models capable of a detailed treatment of clumping structure (including porosity and vorosity).\n \nto derive meaningful results and improve on existing mass-loss recipes, we need to study\nof a representative set of massive stars covering the upper hertzsprung-russell diagram (hrd) and in multiple metallicity environments (as required to investigate the cosmologically important metallicity dependence of the mass-loss rates).\n \nunfortunately, existing fuv archival data do not offer sufficient coverage of the hrd at sub-solar metallicity. we therefore propose to use cos/g140l to obtain fuv spectroscopy of 42 massive stars that have been selected to fill existing gaps in the parameter space. this will provide us with a continuous view of the mass-loss and clumping properties as a function of stellar mass and of metallicity, allowing us to derive modern prescriptions for the ouflows of massive stars. | massive star outflows (maestro) |
combining high-contrast imaging with medium-resolution spectroscopy has recently been shown to significantly boost the direct detection of exoplanets. in this optic, harmoni, one of the first-light instruments to be mounted on eso's elt, will be equipped with a single-conjugated adaptive optics system to reach the diffraction limit of the elt in h and k bands, a high-contrast module dedicated to exoplanet imaging, and a medium-resolution (up to r = 17 000) optical and near-infrared integral field spectrograph. when combined, these systems will provide unprecedented contrast limits at separations between 50 and 400 mas. we will present in this talk the results of extensive simulations of exoplanet observations with the harmoni high-contrast module. we used an end-to-end model of the instrument to simulate observations based on realistic observing scenarios and conditions. we then analyzed these observations with the so-called "molecule mapping" technique, which has shown in recent studies its efficiency to disentangle planetary companions from their host star and boost their signal. although harmoni has not been fully designed for high-contrast imaging, we will show that it should greatly outperform the current dedicated instruments, such as sphere on the vlt. we detect planets above 5σ in 2 hours at contrasts up to 16 mag and separations down to 75 mas in several spectral configurations of the instrument. simulating planets from population synthesis models, we could image in this amount of time companions as close as 1 au from a host star at 30 pc and as light as 2 mjup. we show that taking advantage of the combination of high-contrast imaging and medium-resolution spectroscopy through molecule mapping allows us to access much fainter planets (up to 2.5 mag) than the standard high-contrast imaging techniques. we also demonstrate that harmoni should be available for near-critical exoplanet observations with this method during 60 to 70% of telescope time at the elt. | direct imaging and spectroscopy of exoplanets with the elt/harmoni high-contrast module |
a longstanding question in stellar evolution is which massive stars produce black holes (bhs) rather than neutron stars (nss) upon death. it has been common practice to assume that a given zero-age main sequence (zams) mass star (and perhaps a given metallicity) simply produces either an ns or a bh, but this fails to account for a myriad of other variables that may effect this outcome, such as spin, binarity, or even stochastic differences in the stellar structure near core collapse. we argue that instead a probabilistic description of ns versus bh formation may be better suited to account for the current uncertainties in understanding how massive stars die. using the observed bh mass distribution from galactic x-ray binaries, we investigate the probability that a star will make a bh as a function of its zams mass. although the shape of the black hole formation probability function is poorly constrained by current measurements, we believe that this framework is an important new step toward better understanding bh formation. we also consider some of the implications of this probability distribution, from its impact on the chemical enrichment from massive stars, to its connection with the structure of the core at the time of collapse, to the birth kicks that black holes receive. a probabilistic description of bh formation will be a useful input for future population synthesis studies that are interested in the formation of x-ray binaries, the nature and event rate of gravitational wave sources, and answering questions about chemical enrichment. | the black hole formation probability |
the standard model of evolution of cataclysmic variables has been around for over 3 decades. within this time, both theoretical and observational progress has deliver a robust description of the overall population properties of cvs. however, several discrepancies between predictions and properties of the observed cv population remain. in the last few years, efforts have concentrated in forming an observational picture from the youngest systems (post-common envelope systems) to the oldest (period bouncers). this has allowed to probe the evolution of cvs in a wider time-scale and directly test our assumptions implemented in the theory. in parallel, the advent of new stellar evolution codes and binary population synthesis codes have allowed to trace the different outcomes and shortcomings of the standard model, such as common envelope physics and influence of nova eruptions, and its impact in the present-day cv population.in this review talk, i will provide the current state of our knowledge of cv evolution and present the recent theoretical and observational breakthroughs of the past years. in particular, i will focus on the impact of these results on the space densities of the present cv population. the next decade will deliver a deeper and rich multi-wavelength all-sky dataset which will enable us to probe both ends of the evolution (as well as everything in between) and will provide firmer limits to the true space density of the cv population. | secular evolution of cvs and associated space densities |
high mass x-ray binaries (hmxbs) are a natural by-product of recent massive star formation in normal galaxies. not surprisingly, the number of hmxbs and their typical x-ray luminosities (lx) tend to increase in galaxies with higher star formation rates (sfrs). however, to take the qualitatively observed lx-sfr relationship and extract meaningful constraints on the evolutionary processes by which massive binaries survive compact object formation and establish mass transfer, the lx-sfr relationship must be properly calibrated. hmxbs are inherently x-ray variable, and different techniques for measuring the sfr can yield results that are discrepant by up to an order of magnitude. in this presentation, we illustrate how the inferred sfr on sub-kiloparsec scales varies dramatically when different sfr prescriptions (uv+ir emission from galex and spitzer, respectively, vs. stellar population synthesis modeling of resolved stellar populations from hubble) are used. we find that the commonly used, uv+ir prescriptions tend to over-estimate sfrs on sub-kiloparsec scales when compared to resolved stellar population modeling with hubble. if verified, this could imply that hmxbs are being formed more efficiently and in lower-sfr environments than previously suggested. | revisiting the lx-sfr relationship in nearby galaxies: dependence on sfr indicator |
we attempt to characterise statistically the evolutive parameters of the stellar populations in the milky way galaxy using multi band photometry (gaia, tyco 2, sdss, wise y 2mass). towards this goal, we perform a comparison between the color magnitude diagrams obtained from the observations and from a stellar population synthesis model. finally, we apply these results to build up a model of the stellar populations of our galaxy, which will be necessary for further investigations related to the detection of satellite galaxies in the galactic halo. | characteristic parameters of the stellar populations in the milky way galaxy |
star formation rates in early-type galaxies are notoriously hard to determine because of their very low specific star formation rates. for this project, we use hubble space telescope photometric data in 4-5 visible and near-uv filters to measure the young stellar clusters in nine early-type galaxies. aperture photometry colors were compared to colors from synthetic photometry produced by the flexible stellar population synthesis code (conroy et. al, apj 699, 486-506 (2009)), using a chi-squared likelihood method to estimate the age, metallicity and extinction for each cluster. masses were determined using the best-fit model, the distance to each galaxy and the measured fluxes. young clusters were selected below a cutoff age of 100 myr, and star formation rates for each galaxy were then calculated as the combined mass of the young clusters divided by the cutoff age. star formation rates computed in this way are far below those computed using the 22 micron emission. while some completeness effects are biasing the cluster-estimated sfrs low, the extreme difference (two orders of magnitude) may also point to sfr overestimation due to contamination from older stars in the 22 micron sfrs. | star clusters in early-type galaxies |
a binary evolution pulsator (bep) is a low-mass (0.26 m_⊙) member of a binary system, which pulsates as a result of a former mass transfer to its companion. the bep mimics rr~lyrae-type pulsations, but has completely different internal structure and evolution history. although there is only one known bep (ogle-blg-rrlyr-02792), it has been estimated that approximately 0.2% of objects classified as rr lyrae stars can be undetected binary evolution pulsators. in the present work, this contamination value is re-evaluated using the population synthesis method. the output falls inside a range of values dependent on tuning the parameters in the startrack code, and varies from 0.06% to 0.43%. | contamination of rr lyrae stars from binary evolution pulsators |
the astrophysical origin of the heaviest elements made by rapid neutron-capture (the r-process) is unknown, though neutron star mergers (nsms) are strong possible candidates. metal-poor stars enhanced with these elements provide some basis of comparison with nucleosynthesis model yields, such as that from nsms. currently, many theoretical r-process studies take this route of comparing individual model results to observed stellar abundances. however, we take the opposite approach in a way that has so far not been accomplished in literature; we use the observed abundances of metal-poor stars themselves to reconstruct properties of the progenitor neutron star binaries that would have merged to produce those elements. we will present the results of this new analysis and comment on whether the predicted binary systems agree with present-day galactic populations of neutron stars. we also explore the effect that the nuclear equation of state (eos) has on our results and if metal-poor stars can provide an additional, indirect eos constraints. | which neutron star mergers synthesized the r-process elements? |
studying the lives of exoplanets formed inside star clusters, where the majority of stars are born, provides deeper insight into the vast diversity of planetary systems observed in the galaxy. due to the dense gas that surrounds star clusters, though, direct observation is often difficult, making computational simulations useful for studying these environments. however, modeling the full life-cycle of these clusters in a single simulation is currently computationally unrealistic. we propose a piece-wise approach: using torch, which creates physically accurate stellar clusters from a given molecular gas cloud, and bridging the gas-ejection end-state with tycho, which models the effects of stellar close encounters on planetary systems within clusters. this produces a fully realized stellar and planetary population which mimics the formation environments commonly believed to be the galactic norm. in this work, we detail one such realization (referred to as the valoo cluster), simulated on a single moderate-level hpc node over the course of a few weeks, as a proof-of-concept for the power of this methodology. | exoplanetary population synthesis via coupled mhd stellar formation and n-body stellar dynamics simulations |
local brightest cluster galaxies (bcgs) are the most massive galaxies in the local universe and have had the full age of the universe to build. we present the radial profile of ages, metallicities, and dynamics of 23 bcgs observed using the sparsepak instrument on wiyn by running the starlight stellar population synthesis models. preliminary results of the stellar populations for different regions of the bcg, such as its core and outskirts, the intracluster light (icl), and close companions of the bcg, are presented. the bcg core is found to host an older, more metal-rich population of stars than those found within the icl. analysis of the velocity dispersion as a function of the distance from the galactic center yields a rising or flat profile for 70 percent of our x-ray selected sample. | the distribution of ages, metallicities and dynamics of stellar populations in 23 bcgs using the sparsepak ifu |
asymptotic giant branch (agb) stars represent one of the main stellar sources for production of dust in the universe. we provide a description of the formation and growth of dust particles in the circumstellar envelope of agbs, starting from 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. | dust from agbs: understanding the spitzer observations of evolved stars in the large magellanic cloud |
the millihertz gravitational wave band, covered by the lisa observatory, will be replete with signals from ultra-compact binaries comprised of two stellar remnants — white dwarfs, neutron stars, and stellar mass black holes in any combination. with ~107 such binaries in the stellar graveyard of the milky way, the composite signal will be a merged confusion noise of most of the signals overlapping together; there will be ~104 that will be individually distinguishable. while this signal is generally regarded as noise that competes with other signals in the signal-rich millihertz band, there is astrophysical information about the populations of the stellar graveyard buried in the shape and amplitude of the confusion foreground. here will illustrate the use of the cosmic population synthesis package to examine sub-populations in the foreground as a precursor to making inferences about the galaxy from lisa measurements. | gravitational wave observations of the galaxy using ultra-compact binaries |
high redshift galaxies permit the study of the formation and evolution of x-ray binary populations on cosmological timescales, probing a wide range of metallicities and star-formation rates. here, i will present results from a large scale population synthesis study that models the x-ray binary populations from the first galaxies of the universe until today. we use as input to our modeling the millennium ii cosmological simulation and the updated semi-analytic galaxy catalog by guo et al. (2011) to self-consistently account for the star formation history and metallicity evolution of the universe. our modeling, which is constrained by the observed x-ray properties of local galaxies and compared to the most recent chandra surveys of distant galaxies, gives predictions about the global scaling of emission from x-ray binary populations with properties such as star-formation rate and stellar mass, and the evolution of these relations with redshift, as well as the evolution of the galaxy x-ray luminosity function with redshift. our simulations show that the x-ray luminosity density (x-ray luminosity per unit volume) from x-ray binaries in our universe today is dominated by low-mass x-ray binaries, and it is only at z>2.5 that high-mass x-ray binaries become dominant. we also find that there is a delay of ~1.1 gyr between the peak of x-ray emissivity from low-mass xray binaries (at z~2.1) and the peak of star-formation rate density (at z~3.1). the peak of the x-ray luminosity from high-mass x-ray binaries (at z~3.9), happens ~0.8 gyr before the peak of the star-formation rate density, which is due to the metallicity evolution of the universe. finally, i will discuss the possible energy feedback of x-ray binaries in the re-ionization and thermal evolution of the universe at early times, providing prescriptions for the x-ray binary feedback that can be directly incorporated into cosmological simulations. | evolution of x-ray binaries across cosmic time and energy feedback at high redshift |
posydon (population synthesis with detailed binary-evolution simulations) incorporates full stellar structure and evolution modeling for single and binary-star population synthesis. the code is modular and allows the user to specify initial population properties and adopt choices that determine how stellar evolution proceeds. populations are simulated with the use of mesa (ascl:1010.083) evolutionary tracks for single, non-interacting, and interacting binaries organized in grids. machine-learning methods are incorporated and applied on the grids for classification and various interpolation calculations, and the development of irregular grids guided by active learning, for computational efficiency. | posydon: single and binary star population synthesis code |
hii regions are the archetypical tracers of high-mass star formation. because of their high luminosities, they can be seen across the entire galactic disk from mid-infrared to radio wavelengths. a uniformly sensitive survey of galactic hii regions across the disk would allow us to constrain the properties of galactic structure and star formation. we have cataloged over 8000 hii regions and candidates in the wise catalog of galactic hii regions (astro.phys.wvu.edu/wise), but only 2000 of these are confirmed hii regions. the work is ongoing, but from our survey completeness limits and population synthesis modeling, we predict there are nearly 10,000 hii regions in the milky way created by a central star of type b2 or earlier. a population of especially interesting hii regions trace the outer scutum-centaurus spiral arm (osc), the most distant molecular spiral arm in the milky way. these regions represent star formation at low densities and low metallicities, similar to the conditions in galaxies like the large magellanic cloud or a much younger milky way. to date, we have detected high-mass star formation at 17 locations in the osc, with the most distant source at 23.5 kpc from the sun and 17 kpc from the galactic center. they have molecular cloud masses up to 105 msol and central stellar types as early as o4. by comparing molecular and stellar masses, we can begin to put constraints on the star formation efficiency of these distant outer galaxy sources. we map the ionized gas using the very large array at x-band in the d-configuration. we map the 13co, hcn, and hco+ molecular gas emission using the argus array on the green bank telescope, producing individual 5 arcmin maps with 8 arcsec resolution and 0.5 k sensitivity in 20 minutes. | high-mass star formation in the far outer galaxy |
over the past 20 years, we have learned that exoplanets are ubiquitous throughout our galaxy and show a diverse set of demographics, yet there is much work to be done to understand this diversity. determining the distributions of the fundamental properties of exoplanets will provide vital clues regarding their formation and evolution. this is a difficult task, as exoplanet surveys are not uniformly sensitive to the full range of planet parameter space. various observational biases and selection effects intrinsic to each of the different discovery techniques constrain the types of planets to which they are sensitive. herein, i record a collection of the first studies to develop and apply the methodology of synthesizing results from multiple detection techniques to construct a statistically-complete census of planetary companions to m dwarfs that samples a wide region of their parameter space. i present a robust comparison of exoplanet discoveries from microlensing and radial velocity (rv) surveys of m dwarfs which infer giant planet frequencies that differ by more than an order of magnitude and are, prima facie, in direct conflict. i demonstrate that current, state-of-the-art rv surveys are capable of detecting only the high-mass tail of the population of planets beyond the ice line inferred by microlensing studies, engendering a large, apparent difference in giant planet frequency. this comparison further establishes that results from these types of surveys are, in fact, consistent over the region of parameter space wherein their sensitivities overlap. a synthesis of results from microlensing and rv surveys yields planet occurrence rates for m dwarfs that span several orders of magnitude in mass and orbital period. on average, each m dwarf hosts about two planets, and while jupiter and super-jupiter companions are relatively rare ( 3%), gas giants, in general, are quite common ( 15%). these occurrence rates are significantly lower than those inferred around fgk stars and are thus, at least qualitatively, consistent with the predictions of core accretion theory. finally, i present a synthesis of results from microlensing, rv, and direct imaging surveys that improve constraints on the demographics of long-period, massive planetary companions to m dwarfs. i demonstrate that the results of five different surveys for exoplanets employing these three independent techniques are consistent with a single population of planets described by a simple, joint power-law distribution function in mass and semimajor axis, and provide constraints on the parameters of such a population. the final result is the most statistically-complete census of exoplanets that has hitherto been constructed for a given type of host star, spanning a mass range of 1-104 m⊕ and an orbital period range of 1-105 days. this work represents an important benchmark for all future exoplanet population studies, and the methodologies developed herein are applicable to new and larger data sets of forthcoming "next-generation" surveys. | the demographics of exoplanetary companions to m dwarfs: synthesizing results from microlensing, radial velocity, and direct imaging surveys |
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 the hard (e > 12 kev) x-ray sensitivity of nustar, we are able to differentiate between the accretion states and compact object types of x-ray binaries (xrbs) in the andromeda galaxy (m31), the nearest milky way-mass galaxy to us. we combine 10 shallow (~50 ks each) observations across the disk of m31 with a previous deep, three-field (500 ks per field) survey of a smaller region of andromeda's disk. the shallow survey adds 20 sources detected at 3-sigma in the 4-25 kev bandpass to the ~60 sources detected in the deep survey, crucially increasing the number of sources detected at higher luminosities. using hardness diagrams that compare our source colors to those of known milky way xrb compact object type and states, we classify 12 (29) of these sources in the shallow (deep) surveys and contrast these results with that of m31's bulge, which is dominated by old (non-magnetized) neutron star accretors. in addition, we construct a luminosity function (lf) of sources detected in the 12-25 kev bandpass for the combined survey. this lf is directly compared to that of the high mass xrb lf found in the milky way through hard x-ray surveys conducted by swift bat and integral, which are dominated by sources of similar (or lower) luminosity. at present, comparison of extragalactic xrbs with those of the milky way at these luminosities is only feasible for m31; we also discuss how a future hard x-ray observatory could revolutionize our understanding of xrb populations in the universe. | characterizing the hard x-ray binary population of the disk of m31 |
binary population synthesis models predict that ~30% of massive stars will have their hydrogen envelopes removed via interaction with a binary companion. the resulting "stripped" helium cores are relatively long-lived, hot, compact, and emit extreme ultraviolet radiation. as a result, they represent a critical piece in our understanding of the ionizing radiation from stellar populations as well as the nature of supernova and gravitational wave progenitors. however, despite their importance and predicted ubiquity, observations have remained elusive. this is now changing. using uv maps of the magellanic clouds, a sample of candidate systems has been identified. optical spectroscopy reveals stars with temperatures in excess of 60,000 k, but luminosities intermediate between wolf-rayet and subdwarf stars. a lack of strong emission line features indicates their mass loss rates must be more than an order of magnitude lower than previously assumed based on extrapolations from higher luminosity stars. here, we propose to obtain hst/cos spectra of a sample of 7 of these helium stars in the magellanic clouds. uv observations are necessary to measure their mass loss and wind parameters, and this sample was chosen to allow the first observational constraints of these parameters as a function of both luminosity and metallicity. precise mass loss parameters will have a large impact on the stellar radii, ionizing radiation, and final surface composition of stripped helium stars. these hst/cos observations will therefore provide vital constraints for models of binary evolution, impacting our understanding of supernova progenitors, gravitational wave sources, and ionizing radiation. | from supernova progenitors to ionizing radiation - hst/cos spectroscopy of stripped helium stars |
the "galaxy model" (galmod) is a theoretical population synthesis model able to simulate synthetic surveys of the milky way, m31, and able to generate initial conditions for quasi-equilibrium collisionless models. galmod assumes the galaxy to be a discrete superposition of several composite stellar populations (csps) representing a few nominal significant stellar populations: the thin disk, the thick disk, the stellar halo, and the bulge. galmod immerses these csps in a single dark matter (dm) halo component and a hot coronal gas component (hcg). a parametric model for the modeled galaxy gravitational potential is computed to secure consistency with the density profiles by solving the poisson equation. these density profiles generate synthetic hertzsprung-russell and color-magnitude diagrams (cmds) in several photometric bands, including updated gaia dr2 photometry and subaru hyper suprime-cam. finally, the gravitational potential is used to realize the stellar kinematics. a global model for the milky way's gravitational potential is built to secure consistency with the density profiles by solving the poisson equation. in turn, these density profiles are used to generate synthetic probability distribution functions (pdfs) for the allocation of stars in the cmds. finally, the gravitational potential is used to constrain the stellar kinematics using the moment method on phase-space distribution functions. galmod contains non-axisymmetric galactic components such as the spiral arms, bar, and photometric extinction. the realization of the f.o.v. has no size limit; even full-sky synthetic surveys are possible. | the galaxy model — galmod 2021 |
we present a deep chandra acis-i survey of m81 (4 fields, ~200 ks each, total 800 ks) sampling the entire optical, and a large fraction of the extended uv, disks. we detected about 600 point sources down to a sensitivity limit of ~ 6 x 10^35 erg/s. our x-ray point sources comprise x-ray binary stars, background active galactic nuclei, foreground stars, and supernova remnants (snrs). we classify the detected x-ray point sources by cross-correlating with several multi-wavelength source catalogs (ir: wise, spitzer; optical: pan-starrs), as well as published snr and globular cluster catalogs. we construct x-ray binary luminosity functions for galactic substructures such as the bulge, disk, spiral arms, halo, extended uv disk and globular clusters, which can then be compared to state-of-the-art x-ray binary population synthesis models. | deep chandra observations of the grand design spiral m81: a first look |
observational studies of field stars and globular clusters over the past few decades have revealed a wide range of rotational velocities for hb stars along the extent of the horizontal branch. globular cluster horizontal branch stars with hot hb stars ( teff > 11000 k; hot end of bhb) tend to show lower rotational velocities (v sin i < 8-10 km s-1) than cooler hb stars (teff < 11000 k; cooler end of bhb), whose rotational velocities can approach 10 < v sin i < 30-40 km s-1, with most having more modest velocities of v sin i ~15-20 km s-1 (peterson 1983a, 1983b; peterson1985a, 1985b; peterson et 1995; behr et al. 2000a, 2000b). the notable difference in rotational velocities between hot and cool hb stars across the 11000 k transition point is also accompanied by a very big difference in surface abundances for such stars. moreover, the higher masses of red hb stars on the zahb (in comparison to the hotter, bluer hb stars) suggests that their higher angular momenta reflect the smaller amounts of mass lost from their progenitor rgb stars due to mass losses (e.g. stellar wind or binary processes) which takes away angular momentum. greater clarity of the implied coupling between hb rotational velocities, envelope masses spanning the hb, and surface abundances across the teff ~11000 k divide could be obtained by studying the rotational properties and abundances of field sdb stars, corresponding to globular cluster ehb stars, in particular because most sdb stars are known to be slow rotators. here, a binary population synthesis study is performed, based on the sdb formation channels discussed by han et al. (2002, 2003), in order to investigate the role of binary interactions in affecting the rotational rates of sdb stars and how this can contribute to the bimodality in rotational velocities in field bhb stars as in globular cluster bhb stars, also possibly indicating that cluster environment might not be a large factor in such observations, also serving to constrain sdb/ehb formation channels. | rotational properties of sdb stars |
hst has invested thousands of orbits imaging extragalactic deep fields with the goal of understanding the structural evolution of galaxies. determining how galaxies grow requires transforming the distribution of light we observe into maps of stellar mass and star formation through cosmic time. this is challenging because a significant fraction of the light from young stars is absorbed and radiated further into the infrared, beyond hubble's wavelength coverage. deriving reliable estimates of physical quantities requires a modeling framework that can synthesize resolved and unresolved data. here we propose the development of a next generation tool: pirate. pirate is built within prospector, a bayesian inference framework designed to constrain high-dimensional, self-consistent models of galaxies using broad-band photometry. pirate extends prospector to a resolved framework with an innovative hierarchical model to optimally constrain spatially resolved physical properties of galaxies from data with heterogeneous resolutions. with the ability to map stellar mass and star formation in galaxies at 0.5 | pirate: walking the plank to spatially resolved stellar populations in candels |
binary systems containing a compact object may exhibit periodic brightening episodes due to gravitational lensing of the nondegenerate companion by the compact object as it transits. such self-lensing systems provide a new means of discovering noninteracting compact binaries, providing mass measurements as well as constraints on the formation and evolution of compact objects. we present early results from a systematic search for self-lensing signatures in galactic stellar-mass binaries using data from the zwicky transient facility (ztf). thanks to its extensive optical variability coverage of the northern hemisphere sky, ztf provides an ideal dataset for this search; population synthesis suggests that thousands of self-lensing systems may be detectable. ztf's sparse cadence and ground-based photometric precision pose challenges to discovery; we outline the potential for new search approaches. | searching for gravitational self-lensing binaries with the zwicky transient facility |
binary systems containing a compact object may exhibit periodic brightening episodes due to gravitational lensing of the nondegenerate companion by the compact object as it transits. such self-lensing systems provide a new means of discovering noninteracting compact binaries, providing mass measurements as well as constraints on the formation and evolution of compact objects. we present first results from a systematic search for self-lensing signatures in galactic stellar-mass binaries using data from the zwicky transient facility (ztf). thanks to its extensive optical variability coverage of the northern hemisphere sky, ztf provides an ideal dataset for this search; population synthesis suggests that thousands of self-lensing systems may be detectable. ztf's spare cadence and ground-based photometric precision pose challenges to discovery; we outline the potential for new search approaches. | first results from a search for gravitational self-lensing binaries with the zwicky transient facility |
population synthesis models aim to reproduce the spectral energy distributions of stellar systems ranging from single clusters to entire massive galaxies. model atmospheres play a crucial role in realistic models, as empirical spectral libraries are often incomplete and/or cover limited wavelength ranges. the goal of the modeling is to learn about structural parameters, star-formation histories, chemical evolution, and more. this review covers recent results and current challenges. the emphasis will be on stellar aspects but some processes related to the interstellar medium will be addressed as well. | stellar population synthesis |
artpop (artificial stellar populations) synthesizes stellar populations and simulates realistic images of stellar systems. the code is modular, making it possible to use each of its functionalities independently or together. artpop can build stellar populations independently from generating mock images, as one might want to do when interested only in calculating integrated photometric properties of the population. the code can also generate stellar magnitudes and artificial galaxies, which can be inject into real imaging data. | artpop: artificial stellar populations generator |
how many hii regions are in the milky way? even with the success of recent surveys, we still do not have an adequate answer to this fundamental question. hii regions are the archetypical tracers of galactic high-mass star formation, but population synthesis modeling indicates that their detection throughout the galaxy is incomplete, biased toward the most luminous and nearby complexes. using mid-infrared (mir) data from the wise satellite, we identified over 8000 hii regions and candidates, all of which share the characteristic morphology of 12 micron emission enveloping a core of 22 micron emission. of these, nearly 4000 candidates have no detectable radio continuum emission from galactic plane surveys and therefore their classification is unknown. these “radio quiet” candidates could represent a significant population of faint hii regions which are ionized by b-stars and/or are especially distant, or they might not be hii regions at all.we present here a survey of radio quiet hii regions in the second and third galactic quadrants with the very large array. this was the first systematic study of radio quiet hii region candidates. nearly 60% of the 145 sources observed were detected by the vla at x-band (10 ghz) to sub-mjy sensitivities. coupled with their mir morphologies, detection of continuum strongly indicate they are hii regions. if 60% of radio quiet candidates throughout the galaxy prove to be hii regions, the number of expected hii regions in the milky way would more than double. constraining the total number of hii regions within the milky way will feed back into stellar population synthesis modeling, informing both the high-mass tail of the galactic star formation rate and the role of high-mass stars in the evolution of the ism. we estimate there are between 6500 and 7000 hii regions in milky way created by a star of type b2 or earlier. | a complete vla census of the ~7000 milky way hii regions |
we have applied for a jwst ers first transients survey, flare to answer empirically how the universe made its first stars. to quest the epoch of reionization we target what happened to these first stars by observing the most luminous events, supernovae. these transients provide direct constraints on star formation rates and the initial mass function.these very rare events can be reached by jwst at 27 mag ab in 2 micron and 4.4 micron over a field of 0.1 square degree visited multiple times each year.the survey may detect massive pop iii sne at redshifts up to 10, pinpointing the redshift of first stars, a key scientific goal of jwst.we explore all models of star formation history (derived from uv luminosity densities and ir data), dtd, top heavy imf of early, low metallicity stars, and normalizations to data of sn ia, ii rates (snls, clash, candels, sdss, sviss), as well as slsn (rotse, snls) to estimate the expected sn rates as function of redshift.population synthesis of double degenerate and single degenerate scenarios of sn ia shows that the shape of the dtd is rather insensitive to the assumptions (common envelope prescription and metallicities, or retention efficiency of accreted h to white dwarf core and mass transfer rate).indeed goods high z sn ia rates imply substantial delay in their progenitor model, and hubble higher z sn search constrains delay time distribution models as well.slsn (i, ii /h/ and extreme rare pulsational pair instability) are magnetars (ulgrb) in high local star formation rate, faint, low metallicity galaxies. | detecting first supernovae with jwst |
the history of the galaxy is captured in the population of dead stars in the galaxy. a particularly interesting population are the ultra-compact binaries (ucb) which emit detectable gravitational waves (gw); 95% of this population is comprised by doubly degenerate white dwarf binaries, which are good sources for lisa. we use the population synthesis code cosmic to simulate the lives of ucbs. we evaluate the stellar evolutionary history of each binary to discern how the end state properties of a given binary are connected to its initial state and the ensuing evolutionary history. we find binaries evolve through parameter space together, so groupings in the lisa catalog of observed binaries are tracers for stellar evolution. in this paper, we illustrate how the evolution history and zams properties of binary systems would affect the properties of the stellar population in the galaxy today that can be observed by lisa. | imprint of binary evolution on the lisa ultra-compact binary catalogue |
type ia supernovae (sn ia) are excellent distance indicators that require an empirical model to be standardized. the resulting standardization cannot be redshift dependent or sn ia cosmology would be biased. recently the residuals from the best fit cosmology show a correlation with host galaxy properties; a systematic limitation to improving future measurements. rose et al. 2019 used flexible stellar population synthesis (fsps) via pyfsps to estimate the age of the stellar population around the location of the sn ia to investigate these observed correlations. | estimating the average age of stellar populations to understand type ia supernova systematics |
silicon- and oxygen-containing species such as silicon monoxide (sio) and silicon dioxide (sio2) represent basic molecular building blocks connected to the growth of silicate grains in outflows of oxygen-rich asymptotic giant branch (agb) stars like r doradus. yet the fundamental mechanisms of the formation of silicate grains and the early processes that initiate the coupling of the silicon with the oxygen chemistries in circumstellar envelopes have remained obscure. here, in a crossed molecular beams experiment combined with ab initio electronic structure calculations, we reveal that at least the d2-silaformaldehyde (d2sio) and d2-hydroxysilylene (dsiod) molecules-proxies for the astronomically elusive silaformaldehyde (h2sio) and hydroxysilylene (hsioh) molecules-can be synthesized via the reaction of the d1-silylidyne radical (sid; x2π) with d2-water (d2o) under single-collision conditions. this system represents a benchmark of a previously overlooked class of reactions, in which the silicon-oxygen bond coupling can be initiated by a reaction between the simplest silicon-bearing radical (silylidyne) and one of the most abundant species in the circumstellar envelopes of evolved oxygen-rich agb stars (water). as supported by novel astrochemical modeling, considering that silicon- and oxygen-containing species like h2sio and hsioh might be photolyzed easily, they ultimately connect to simple molecular precursors such as sio that drive a chain of reactions conceivably forming higher molecular weight silicon oxides and, ultimately, a population of silicates at high temperatures. | gas-phase synthesis of silaformaldehyde (h2sio) and hydroxysilylene (hsioh) in outflows of oxygen-rich asymptotic giant branch stars |
we investigate the stellar populations and ionised gas properties of a sample of central spheroidal galaxies in order to better constrain their history of star formation and gas excitation mechanism. we select galaxies from spheroids panchromatic investigation in different environmental regions (spider) catalogue and separate these galaxies in different regimes of halo and galaxy mass. to characterise the stellar population properties of these galaxies we use the stellar population synthesis method with the starlight code, and the presence of ionised gas is identified by measurements of the hα equivalent width. we analyse how these properties behave as a function of the galaxy stellar mass and the parent halo mass. a trend is observed in the sense of increased ionised gas emission for low-mass centrals in high-mass halos. we interpret this trend in a scenario of intracluster medium (icm) cooling versus active galactic nuclei (agn) feedback in a bondi accretion context. | stellar populations and ionised gas in central spheroidal galaxies |
it is believed that type ia supernovae (sne ia) are thermonuclear explosions of carbon-oxygen white dwarfs (wds) that accrete mass from a binary companion, which can be either an other carbon-oxygen wd that merges with the first one (double-degenerate scenario) or a non-degenerate star such as a main sequence star or a giant that transfers part of its mass to the wd (single-degenerate scenario). both scenarios have severe problems in explaining the observed properties of sne ia. one of these problems is that population-synthesis models typically predict rates of sne ia explosions several times lower than the observations. in these models, the contribution of asymptotic giant branch (agb) stars is marginal, for two reasons. first, because roche-lobe overflow from agb donor stars is mostly unstable, agb stars do not efficiently transfer mass on to wds in the single-degenerate channel. second, in the double-degenerate scenario only an agb star in a narrow range of separations can form a wd in such a close-enough orbit that the two wds merge within a hubble time. consequently, binary systems with an agb companion of a carbon-oxygen wd are considered unlikely progenitors of sne ia. however, most population-synthesis models assume spherically-symmetric winds and low wind accretion efficiencies, as predicted by the canonical bondi-hoyle-lyttleton model. in contrast, recent hydrodynamical simulations of binary systems with agb donors show that agb winds can be very efficiently accreted by the companions, and that the expelled material can carry a significant amount of angular momentum, in some cases shrinking the orbit significantly.in my presentation i will show the results of a population-synthesis study which investigates the impact of these two effects, namely the high wind-accretion efficiencies and the strong angular-momentum losses, on the sne ia rate, and i will discuss the role of agb stars as progenitors of sne ia. | what is the role of wind mass transfer in the progenitor evolution of type ia supernovae? |
the process of binary stellar evolution is a complex tapestry of initial stellar evolutionary parameters convolved with a lifetime of orbital and mass evolution that leave imprints in the observational properties of the large population of binaries in the milky way galaxy. even beyond the conventional end of stellar life, when main sequence stars have evolved into stellar remnants, binary systems continue to evolve through interactions with their stellar-mass partner. the stellar graveyard of the milky way, comprised of highly evolved stars and stellar remnants, encodes a record of the physical processes that drive the evolution of these systems throughout their lives. our current ability to probe and disentangle this evolutionary history is built on three interlinked probes of the population: electromagnetic surveys, numerical simulation and population synthesis, and forthcoming gravitational wave surveys. this proposal outlines a concerted effort to tightly link these three probes in a comprehensive multi-messenger observation program. we are specifically interested in how electromagnetic observations define the current boundaries of possible model inputs for population synthesis, how electromagnetic observations will quantitatively inform gravitational wave searches, how gravitational wave observations will seed electromagnetic follow-up (particularly in large-scale time-domain transient surveys), how joint em-gw analyses of ultra-compact binaries can be conducted in the lisa era, and how joint em-gw data will be used in model selection analyses to constrain binary evolution scenarios. | multi-messenger constraints on close binary evolution in the milky way |
hubble space telescope (hst) optical imaging of resolved stellar populations has been used to constrain the star formation history (sfh) and chemical evolution of many nearby dwarf galaxies. however, even for dwarf galaxies, the angle subtended by nearby systems can be greater than the hst field of view. thus, estimates of stellar mass from the hst footprint do not accurately represent the total mass of the system, impacting how sfh results can be used in holistic comparisons of galaxy properties. here, we use the sfhs of dwarfs combined with stellar population synthesis models to determine mass-to-light ratios for individual galaxies, and compare these values with measured infrared luminosities from spitzer irac data. in this way, we determine what fraction of mass is not included in the hst field of view. to test our methodology, we focus on dwarfs whose stellar disks are contained within the hst observations. then, we also apply this method to galaxies with larger angular sizes to scale the stellar masses accordingly. | scaling stellar mass estimates of dwarf galaxies |
creating spectral energy distributions (sed) of galaxies with known age and metallicity parameters can be done computationally using standard python simulations, such as conroy's fsps model. however, doing the inverse accurately has been a problem for current models; because of age-metallicity and mass degeneracies, galaxies with different characteristics can have seds that are extremely similar, making it hard to fit to a given sed and return the parameters that define that galaxy. like prospector, we have developed a computational model that uses bayesian statistics and markov chain monte carlo (mcmc) framework to accurately determine the age, metallicity, and mass of a galaxy given the galaxy's sed. unlike prospector, which can only fit models using one value for metallicity, we have developed a model that can predict multiple different metallicities of stellar populations within synthesized galactic seds accurately. our model has been tested on spectral data taken from conroy's fsps and can accurately fit randomly generated gaussian galactic seds with up to 30 different age-metallicity stellar population combinations, returning accurate mass-to-light-ratios as a metric of the accuracy of the fit. along with this, the model can accurately predict ten different age bins of stellar populations within the galaxy as well as three different metallicity bins, with some degree of uncertainty. this makes it a more flexible model than prospector in this regard, as prospector can only fit to a single metallicity. determining the unknown masses of galaxies in are universe is essential for accurately determining the dark matter fraction of the universe, as well as for galaxy formation and evolution. along with this we hope to discover unknown degeneracies between age, metallicity, and mass when it comes to galactic seds. | a flexible approach to fitting galactic spectral energy distributions |
using a hybrid binary population synthesis approach, we modelled the formation and evolution of populations of accreting white dwarfs (wds) for differing star formation histories. we found that the delay time distribution of sne ia in the single degenerate scenario is inconsistent with observations. additionally, we found that our predicted x-ray and uv emission of populations of accreting wds are consistent with the x-ray luminosities of early-type galaxies observed by chandra and the heii 4686 å/hβ line ratio measured in stacked sdss spectra of passively evolving galaxies. moreover, we found that the majority of current novae in elliptical-like galaxies have low-mass wds, long decay times, long recurrence periods and are relatively faint. in contrast, the majority of current novae in spiral-like galaxies have massive wds, short decay times, short recurrence periods and are relatively bright. our predicted distribution of mass-loss timescales in an m31-like galaxy is consistent with observations for andromeda. | populations of accreting white dwarfs |
in the years preceding lisa, milky way compact binary population simulations can be used to inform the science capabilities of the mission. galactic population simulation efforts generally focus on high fidelity models that require extensive computational power to produce a single simulated population for each model. each simulated population represents an incomplete sample of the functions governing compact binary evolution, thus introducing variance from one simulation to another. we present a rapid monte carlo population simulation technique that can simulate thousands of populations in less than a week, thus allowing a full exploration of the variance associated with a binary stellar evolution model. | variance in binary stellar population synthesis |
planet formation is sensitive to the environment in protoplanetary disks, for which scaling laws as a function of stellar mass are known. can the observed population of planets around low-mass stars be explained by these trends or is there evidence for separate formation channels? we explored this question by confronting state-of-the-art planet formation theory with a sample of planets observed by the harps and carmenes radial velocity (rv) surveys. to account for detection biases, we performed injection-and-retrieval experiments on the actual rv data to produce synthetic observations of planets that we simulated following the core accretion paradigm. we find that these simulations robustly reproduce the observed high occurrence of rocky worlds around low-mass stars. on the other hand, while planet formation theories consistently predict a strong stellar mass-giant planet occurrence correlation, we observe a population of giant planets around stars less massive than 0.4 solar masses that can not be reconciled with theory. this may point to a different giant planet formation channel around very low-mass stars. | giant planets around low-mass stars: a challenge for core accretion theory |
utilizing data from the mapping nearby galaxies at apache point observatory (manga) survey, of the latest generation of the sloan digital sky survey (sdss-iv), we identified 30 post-starburst, e+a systems that lie within the green valley transition zone. first identified by their single-fiber spectra and (u-r) colour from the sdss dr15, these galaxies were then put through numerous integral field spectroscopic testing methods, to prove the galaxies exhibited e+a properties throughout the entirety of the system, and not only in their central regions. we provide maps of gaussian fitted fluxes, spatially resolved spectral line ratios, and stellar age, metallicity and kinematic maps, to better understand the content and star formation history of e+a galaxies. this e+a sample, assembled with these refined criteria to establish a well-defined population within the broader post-starburst galaxy population, will be used to further study stellar population properties, spectral energy distributions and quenching properties in e+a galaxies, and to investigate their role in galaxy evolution. | refining the e+a galaxy: a spatially resolved spectral analysis and synthesis of nearby post-starburst systems in sdss-iv manga (mpl-5) |
we present a novel galaxy population synthesis model: galmod (pasetto et al. 2016, 2017a,b) is the only star-count model featuring an asymmetric bar/bulge as well as spiral arms as directly obtained by applying linear perturbative theory to self-consistent distribution function of the galaxy stellar populations. compared to previous literature models (e.g., besancon, trilegal), galmod allows to generate full-sky mock catalogue, m31 surveys and provides a better match to observed milky way (mw) stellar fields.the model can generate synthetic mock catalogs of visible portions of the mw, external galaxies like m31, or n-body simulation initial conditions. at any given time, e.g., a chosen age of the galaxy, the model contains a sum of discrete stellar populations, namely bulge/bar, disk, halo. the disk population is itself the sum of subpopulations: spiral arms, thin disk, thick disk, and gas component, while the halo is modeled as the sum of a stellar component, a hot coronal gas, and a dark matter component. the galactic potential is computed from these subpopulations' density profiles and used to generate detailed kinematics by considering the first few moments of the boltzmann collisionless equation for all the stellar subpopulations. the same density profiles are then used to define the observed color-magnitude diagrams within an input field of view from an arbitrary solar location. several photometric systems have been included and made available on-line, e.g., sdss, gaia, 2mass, hst wfc3, and others. finally, we model the extinction with advanced ray tracing solutions.the model's web page (and tutorial) can be accessed at www.galmod.org. | galmod: the last frontier of galaxy population synthesis models |
the upper mass limit for stars is unknown. recent uv observations of young (< 3 myr), massive star clusters (>5 x10^4 m_sun) suggest that stars substantially more massive than 100 m_sun exist. these very massive stars (vms) are not properly accounted for in current stellar population synthesis (sps) codes, even though they will dominate the ionization and mechanical feedback in star-forming regions for the first few myr. vms have been detected as resolved stars in the nearby lmc cluster r136 and in the integrated light of two young super star clusters in two nearby starburst galaxies. since jwst will obtain numerous uv rest-frame spectra of young high redshift galaxies, it is essential that we investigate whether vms are common in local, low metallicity analogs, while we still have access to the uv domain. we propose to obtain fuv stis spectroscopy of young (< 3 myr) super star clusters in 4 starbursting galaxies with the aim of establishing if vms are commonly formed in dense star-forming events at low metallicity. the crucial spectral diagnostics for vms are only available in the fuv, and we will use the spectroscopy together with new sps models to constrain the upper mass limit to the initial mass function, and to test the importance of vms for feedback. these spectra will form an important part of the uv legacy of hst and will provide an excellent local-universe analog to the rest-frame uv spectra of high-z galaxies to be obtained with jwst. | very massive stars in the local universe |
we present gemini multi-object spectrograph integral field unit (gmos-ifu) observations of the inner 1.1 kpc of the interacting seyfert galaxy ngc 2992. from full spectral synthesis we found that the stellar population is mainly (up to 80 per cent of the total light) composed by an old (t ≥ 1.4 gyr) metal-rich (z ≥ 2.0) populations with a smaller but considerable contribution (up to 30 per cent) from young (t ≤ 100 myr) metal-poor (z ≥ 1.0) populations. the gas kinematics presents two main components: one from gas in orbit in the galaxy disk and an outflow with mass outflow rate of ∼2 mʘ yr-1 and a kinematic power of ∼ 2 × 1040 erg s-1. | mapping the inner kpc of the interacting seyfert galaxy ngc 2992: stellar populations and gas kinematics |
sengi enables online viewing of the spectral outputs of stellar population synthesis (sps) codes. typical sps codes require significant disk space or computing resources to produce spectra for simple stellar populations with arbitrary parameters, making it difficult to present their results in an interactive, web-friendly format. sengi uses non-negative matrix factorisation (nmf) and bilinear interpolation to estimate output spectra for arbitrary values of stellar age and metallicity; this reduces the disk requirements and computational expense, allowing sengi to serve the results in a client-based javascript application. | sengi: interactive viewer for spectral outputs from stellar population synthesis models |
the development of tunable dye lasers and a simple atomic and ionic beam source for all elements were critical in establishing a reliable absolute scale for atomic transition probabilities in the optical to near uv regions. the laboratory astrophysics program at the university of wisconsin - madison (uw) concentrates on neutral and singly-ionized species transitions that are observable in astronomical spectra of cool stars, emphasizing the rare earth n(eutron)-capture elements and the fe-group elements that are important inputs to early galactic nucleosynthesis studies. the uw program is one of several productive efforts on atomic transition probabilities. these programs generally use time-resolved laser-induced-fluorescence (tr-lif) to accurately measure total decay rates and data from high resolution fourier transform spectrometers (ftss) to determine emission branching fractions (bfs). the uw laboratory results almost always are directly linked to astronomical chemical composition efforts. there are good opportunities to extend similar research to other wavelength regions. | quantitative atomic spectroscopy, a review of progress in the optical-uv region and future opportunities |
the 2-10 kev emission from normal galaxies is dominated by x-ray binary (xrb) populations. the formation of xrbs is sensitive to galaxy properties like stellar age and metallicity---properties that have evolved significantly in the broader galaxy population throughout cosmic history. the 6 ms chandra deep field-south (cdf-s) allows us to study how xrb emission has evolved over a significant fraction of cosmic history (since z ~ 4), without significant contamination from agn. using constraints from the cdf-s, i will show that the x-ray emission from normal galaxies from z = 0-7 depends not only on star-formation rate (sfr), but also on stellar mass (m) and redshift. our analysis shows the that low-mass x-ray binary emission scales with stellar mass and evolves as lx(lmxb)/m ~ (1+z)^3, and high-mass x-ray binaries scale with sfr and evolve as lx(hmxb)/sfr ~ (1+z), consistent with predictions from population synthesis models, which attribute the increase in lmxb and hmxb scaling relations with redshift as being due to declining host galaxy stellar ages and metallicities, respectively. these findings have important implications for the x-ray emission from young, low-metallicity galaxies at high redshift, which are likely to be more x-ray luminous per sfr and play a significant role in the heating of the intergalactic medium. | cosmic evolution of x-ray binary populations: probes of changing chemistry and aging stellar populations in the universe |
we present estimates of ages, [fe/h], helium contents (y) and abundances of c, n, mg, ca, ti, cr, mn, co and ni for the following globular clusters (gcs): 7 in ngc147, and mayall ii, mackey 1 and mackey 6 in m31. medium-resolution integrated-light spectra of the gcs were conducted with the 6m telescope. to derive the ages and abundances for the gcs we carried out their population synthesis using model stellar atmospheres, the padova yzvar isochrones and the chabrier mass function. we compare the results with the corresponding data obtained using the same method for several massive galactic gcs. we show that the differences in the mg and c abundances between gcs with similar ages and metallicities may reach 0.5-0.6 dex. the corresponding differences for other elements are usually ∼2-3 times smaller. we suggest that at least partially the detected differences may be due to mg and c abundance variations in the atmospheres of high-luminosity red giant branch stars as a consequence of the transportation of the produced elements to the surface layers. | ages and chemical compositions of massive globular clusters in ngc147 and m31 |
stellar evolution and galactic evolution have both been greatly advanced by the study of star clusters. in addition the elemental abundance results from clusters have revealed information about galactic chemical evolution and nucleosynthesis. the cluster, ngc 6791, has a number of bizarre properties that make it especially interesting for comparative cluster studies. it is old (8.3 gyr) yet metal-rich ([fe/h] = +0.30). it has a heliocentric distance of 4 kpc and a galactic latitude of +11 degrees which makes it 1 kpc above the galactic plane. its boxy orbit has a high eccentricity (~0.5) with a perigalactic distance of 3 kpc and an apogalactic distance of 10 kpc. the orbital period of ~130 myr indicates that it has crossed the galactic plane several times yet has remained as an intact cluster. we have determined abundances from high-resolution (r = 46,000) keck/hires spectra of turn-off stars in this open cluster ngc 6791. we have a solid determination of [fe/h] = +0.30 +/-0.02 from measurements of some 40 unblended, unsaturated lines of both fe i and fe ii in eight turn-off stars. our o abundances come from the o i triplet near 7774 å and are corrected for small nlte effects. we find consistent ratios of [o/fe]n with a mean of -0.06 +/-0.02, indicating a single population of stars. our results for the alpha elements [mg/fe], [si/fe], [ca/fe] and [ti/fe] are near solar and compare well with those of old, metal-rich field stars. the fe-peak elements, cr and ni, have values of [cr/fe] = +0.05 +/-0.02 and [ni/fe] = +0.04 +/-0.01. determinations of upper limits were found for li by spectrum synthesis; this is consistent with the upper limits in this temperature range for turn-off/subgiant stars in the relatively old, super-metal-rich cluster ngc 6253. we speculate that no stars in ngc 6791 have retained the li with which they formed. | the old, super-metal-rich open cluster, ngc 6791 |
the calcium infrared triplet (cat) is one of the prominent absorption features in the infrared wavelength regime. recently, these absorption features have been getting attention in the prediction of metallicity of globular clusters (gcs) in early-type galaxies (etgs) because of its strong sensitivity to the metallicity and calcium abundance of a star. however, based on our population synthesis model for cat, we find that measuring metallicity directly from cat is inaccurate because the formation mechanism of ca ii ionised line is very inefficient in the cool stars which are abundant in metal-rich stellar populations. this characteristics of ca ii ionised line make the cat-metallicity relation to converge around 8 angstrom in the metal-rich regime. this is why the metallicity of simple stellar populations, such as gcs, greater than [fe/h]~-0.5 is unreliable when the linear conversion between cat and metallicity is applied to derive metallicity. in addition, we have successfully simulated the metal-rich cat peaks found in gcs in etgs by using the nonlinear cat-metallicity relation in the metal-rich regime. this can also explain the difference between color and cat distributions of gcs in various etgs. based on these results, we suggest that cat is not a good metallicity indicator for the metal-rich stellar populations. | does the linear conversion between calcium infrared triplet and metallicity of globular clusters in early-type galaxies hold in the whole range of metallicity? |
accurate determination of physical conditions of interstellar molecular clouds is a crucial step to better understand the life cycle of the interstellar matter and particularly the formation of stars and planets as well as the synthesis of organic molecules that may lead to emergence of life in the universe. a key parameter for the determination of these conditions from interstellar spectra is the calculation of accurate collisional rate coefficients of interstellar molecules with the most abundant species. this information is embedded in the observational spectra of interstellar molecules. in radio- astronomy, it is known that the molecular energy level populations are rarely at local thermodynamic equilibrium (lte). indeed, the gas density is usually such that the rate of collisions is neither negligible nor large enough to maintain lte in the interstellar medium (ism). therefore, analysing observational spectra to derive molecular abundances and physical conditions of molecular clouds requires prior calculations of collisional rate coefficients with the most abundant interstellar species and also einstein radiative coefficients since collisional and radiative processes are in competition. the einstein coefficients are usually available in the literature whereas collisional rate coefficients are system dependent and their calculation is time consuming. | collisional excitation of interstellar molecules: constraining the physical conditions of astrophysical environments |
we present new population synthesis models (chung et al. 2011) for quiescent early-type galaxies (etgs) with uv-upturn phenomenon using relatively metal-poor and helium-enhanced subpopulations in the model. we find that the presence of helium-enhanced subpopulations in etgs can naturally reproduce the strong uv-upturns observed in giant elliptical galaxies (figure 1. left panel), without invoking unrealistically old ages (park & lee 1997). our models with helium-enhanced subpopulations also predict that the well-known burstein relation can be explained by the fraction of helium-enhanced subpopulation, the mean age, and the mean metallicity of the underlying stellar populations (figure 1. right panel). | the effect of helium-enhanced stellar populations on the ultraviolet upturn phenomenon of early-type galaxies |
the present single stellar populations (ssp) models are derived from my ph.d.'s thesis and this paper. the following nomenclature is used throughout the paper and the website (http://smg.astro-research.net/ssp-models/the-models/) to describe the models, e.g. mars models use the m08 isochrones (mar) and the salpeter (s) imf. general information about the models is given in table1. for further information, please refer to the paper. each set of models and their corresponding predictions are available in the website and vizier. the spectral energy distributions (seds) can be downloaded in a zip-file from those pages in ascii format . the spectral energy distributions (seds) can be downloaded in a zip-file from t hose pages in ascii format . the nomenclature of each sed is as follows: isochroneimfsedxxxxhzx.xxxxxxxxxtgxx.xxxxxxxe+xx - where xxxx tells whether those models contain c-stars or no (combo or nocs respectively) h is the spectral band in which normalization occurred z_x.xxxxxxxxx is the metallicity in terms of z tg_xx.xxxxxxxe+xx is the age in years. each set of models contains mars - 96 seds girs - 96 seds bass - 116 seds we have also included in the websites the integrated colours and line-strength indices from all our models (mars, girs and bass). the seds were convolved to a velocity dispersion of 350km/s before calculating indices. (5 data files). | vizier online data catalog: ssp in nir. ii. synthesis models (meneses-goytia+, 2015) |
stellar population synthesis is an important method in galaxy and star-cluster studies. in stellar population synthesis models, a stellar spectral library is necessary for the integrated spectra of the stellar population. usually, the stellar spectral library is utilized for the transformation between the stellar atmospheric parameters and stellar spectrum. the empirical stellar spectral library has distinct advantages over the theoretical library. however, for the empirical spectral library, the distribution of stars is irregular in the stellar atmospheric parameter space, which makes the traditional interpolator difficult to get accurate results. in this work, we will provide an improved radial basis function interpolator which is implemented to obtain the interpolated stellar spectra based on the empirical stellar spectral library. for this interpolator, we use the relation between the standard variance σ in the gaussian radial basis function and the density distribution of stars in the stellar atmospheric parameter space to give the prior constraint on this σ. moreover, we also consider the anisotropic radial basis function by the advantage of the local dispersion of stars in the stellar atmospheric parameter space. furthermore, we use the empirical stellar spectral library miles to test this interpolator. on the whole, the interpolator has a good performance except for the edge of the low-temperature region. at last, we compare this interpolator with our work in 2018, and the interpolation result shows an obvious improvement. users can apply this interpolator to retrieve the interpolated spectra based on the stellar spectral library quickly and easily. | an upgraded interpolator of the radial basis function network for spectral calculation based on empirical stellar spectral library |
we present high signal-to-noise spectra for six early-type galaxies with keck/lris, covering 350-1050 nm and probing spatial scales from 100 pc to several kpc. some of our objects exhibit steep absorption-line gradients within the central ~300 pc, indicating a rapid increase in [na/fe] and [n/fe] toward the galaxy center. while stellar population synthesis (sps) modeling may address whether the stellar initial mass function (imf) varies as a function of radius, we caution that the competing effects of chemical abundance variations and imf variations demands extreme care in interpreting sps models of integrated-light spectra. the steep abundance variations themselves may offer insight to star formation and gas retention in progenitors of today's early-type galaxies, including the possible overabundance of stars above ~3 msun. | imf or abundance variations? steep gradients at the centers of elliptical galaxies |
the dust attenuation law models how the dimming of background light due to dust varies with wavelength. it has been discussed that the measurement of this relationship within the milky way galaxy is not necessarily representative of all attenuation curves, both within and across galaxies. at optical wavelengths, suspected variations of attenuation curves would be largely observed in the slope, rv. the potential variation of this parameter calls into question the many astrophysical observations and measurements which currently rely on the assumed reddening correction being rv= rmw = 3.1. studying this variation should provide a better understanding into the systematics of such procedures. to shed light on the spatial variation of rv within galaxies, we use stellar population synthesis (sps) fitting on the localized integral field unit (ifu) spectra provided by the manga survey in sdss dr17. we discuss the effect of star formation history (sfh) parameterization on the fitted parameters, the correlation of rv to morphological features in our sample galaxies, and similarities/differences in such features across different types of galaxies. | spatially mapping rv in galaxies: stellar population analysis of ifu data for dust attenuation law |
binaries play a key role in understanding star formation and evolution and in the studies of the stellar population synthesis. using the recently re-calibrated (to a precision of a few mmag) stripe 82 photometry, we demonstrate that the intrinsic widths of metallicity-dependent stellar loci of main-sequence stars are essentially zero. based on this fact, we propose a stellar locus outlier (slot) method to determine binary fraction of main-sequence stars statistically. the method is sensitive to neither the period nor mass-ratio distributions of binaries, and applicable to large survey volumes that contain different stellar populations. applying the method to stripe 82, we find an average binary fraction for field fgk stars of 41 per cent. the fraction decreases toward stars of redder colors and probably higher metallicities. | a model-free estimate of binary fraction in the field fgk stars |
our galaxy is composed of different stellar populations which are characterized by different chemical abundances. they are thought to imprint the composition of small bodies formed together with planets : planet building blocks (pbb), asteroids and interstellar objects.we investigated the expected pbb composition in different galactic regions using the ground-based spectroscopic surveys galah and apogee ; and the stoichiometric condensation model from bitsch & battistini (2020). this study has revealed the potential link between the pbb composition and the stellar populations across the galaxy (cabral et al, submitted). interestingly, the pbb compositions determined from large observational surveys reveal common trends determined previously with synthetic models. we confirm the pbb composition valley separating the thin disk stars from the thick disk stars (i.e. a bimodal distribution of compositions) already highlighted in our previous study (cabral et al. 2019) using the besançon stellar population synthesis model of the milky way.moreover, we find that metal-poor stars both in the thin and thick disks should host water-rich pbb. given the importance of water abundance in planet formation simulations (morbidelli et al. 2015, ros et al. 2013, 2019), we discuss in a galactic context the potential impact for the early phases of planet formation.overall we find that the chemical abundances of host stars should impact the composition of exoplanets, as well as small body populations found around these stars. our results imply that thick disk stars (which are rather alpha-rich, metal-poor stars) are suitable hosts for ice-rich small bodies (cf. figure). whether thick disk stars are suitable for water worlds or/and hycean planets (madhusudhan et al. 2021) remains matter of debate. | how does the origin of stars in the milky way affects the composition of planet building blocks? |
we propose a comprehensive survey of 12 fields (each 100 ks) in the lmc probing young (<100 myr) stellar populations of different ages down to lx~2e32 erg/s, and matching the ages sampled in the similar depth smc survey. this lx limit reaches well into the regime of quiescent accreting binaries and x-ray emitting normal stars. the proposed observations will provide the deepest x-ray luminosity functions (xlf) for x-ray binaries ever recorded, enabling us to: (a) directly measure their formation efficiency as a function of age and metallicity; (b) address the evolution of the xlf in the 10-100 myr range, and in particular the influence of the propeller effect; (c) by comparison with x-ray binary population synthesis models, constrain parameters relevant to their formation and evolution. | using the lmc to understand x-ray binary evolution: mind the metallicity gap |
increasingly better observations of resolved protoplanetary disks show a wide range of conditions in which planets can be formed. many transitional disks show gaps in their radial density structure, which are usually interpreted as signatures of planets. it has also been suggested that observed inhomogeneities in transitional disks are indicative of dust traps which may help the process of planet formation. however, it is yet to be seen if the configuration of fully evolved exoplanetary systems can yield information about the later stages of their primordial disks. we use synthetic exoplanet population data from monte carlo simulations of systems forming under different density perturbation conditions, which are based on current observations of transitional disks. the simulations use a core instability, oligarchic growth, dust trap analytical model that has been benchmarked against exoplanetary populations. | transitional disk archeology from exoplanet population synthesis |
we analyze five broad band photometry (nuv, u, b, v and i) from young (< 10 myr) low mass (< 104 msun) clusters, on the spiral galaxy ngc 7793. our sample of clusters were obtained with the hubble space telescope. for this analysis we use stochastically-sampled population synthesis models as an input to generate photoionization models. by generating a library of synthetic magnitudes from our photoionization models we investigate: i) the effect that including the gas and dust has on the absolute magnitudes of our models and ii) the impact that an stochastic sampling of the imf introduces on the calculated photometries. at last, we use this library, and a bayesian analysis method, to estimate physical properties (such as age and extinction) on our sample of observed low mass clusters. | stochastically sampled imfs: contributions of the ionized gas on modelling photometry for low mass star clusters and analysis of hst observations of ngc 7793 |
despite significant progress over the past decades, all state-of-the-art population synthesis (ps) codes suffer from deficiencies limiting their potential of gaining sharp insights into the star formation history (sfh) and chemical enrichment history (ceh) of star-forming galaxies, i.e. the neglect of nebular continuum and, the lack of a mechanism to ensure consistency between the best-fitting sfh and the observed nebular characteristics (onc; balmer-lines, balmer/paschen jumps). these introduce biases in their recovered physical properties (stellar mass m* and ssfr). fado is a novel self-consistent ps code employing genetic optimization, publicly available (<uri xlink:href="http://www.spectralsynthesis.org">http://www.spectralsynthesis.org</uri>), capable of identifying the sfh & ceh that reproduce the onc of a galaxy, alleviating degeneracies in the spectral fits. the current version of fado (v1.b) uses standard bpt emission-line ratios for the classification of low redshift (z) galaxies. whereas this permits a reliable distinction between star-forming, composite, seyfert and liners, it is inapplicable to many intermediate-z galaxies. we present an adaptation of fado (version v1.c) to classify higher z galaxies employing the "blue diagram" (e.g., lamareille <xref rid="r16" ref-type="bibr">2010</xref>) for which the most prominent blue emission-lines (< [oiii]5007å) are observable while the hα and [nii] are inaccessible. fado v1.c was applied to synthetic spectra simulating the evolution of galaxies formed at higher-z with different sfhs. fado can recover the physical and evolutionary properties of galaxies, such as m* and mean age/metallicity, with an accuracy significantly better than purely-stellar codes. an outline of fado v1.c and applications to local and intermediate-z galaxies will be presented. | fado: a novel self-consistency spectral population synthesis tool for the exploration of galaxy evolution at high redshift |
we have identified 12227 thin disc, 1410 thick disc, and 95 halo white dwarf candidates belonging to the gaia 100pc sample (jimenez-esteban et al. 2018mnras.480.4505j, cat. j/mnras/480/4505) by means of an accurate random forest algorithm (breiman 2001machl..45....5b). the unprecedented wealth of valuable information provided to the scientific community by the gaia-dr2 (gaia collaboration 2018a&a...616a...1g, cat. i/345) and, in particular, the quantity and quality of their data related to the white dwarf population requires the application of novel artificial intelligence matching learning algorithms in order to extract the maximum information. to this aim we used a supervised random forest algorithm to disentangle the different white dwarf galactic populations given its flexibility and low number of input parameters. the algorithm has been applied to an 8d space that includes astrometric as well as photometric values for each object. with the aid of a thorough population synthesis model, we accurately reproduce the characteristics of a standard three-component galactic model. the synthetic population is used for the training of the classification algorithm as well as a testbed for assessing its accuracy. (2 data files). | vizier online data catalog: gaia-dr2 100pc white dwarf population (torres+, 2019) |
understanding the gravitational wave (gw) sources in the local universe is significant to several fields in astrophysics. constructing a complete map of the potential gw sources for the nearby universe to the extent of around 100 mpc is specifically critical for the studies and developments of gravitational wave obsevatories like the laser interferometer space antenna (lisa). we focus on the most numerous and one of the most important type of sources of lisa - ultra-compact binaries, which exist mostly in galaxies. we use population synthesis software - cosmic to simulate the stellar populations appropriate to each of the 50,000 galaxies in the gravitational wave galaxy catalogue (gwgc), accounting for the galaxy type, mass, galactic metallcity, and distance to estimate the resulting contribution to the confusion foreground from nearby extragalactic galaxies. | simulating the extragalactic binary confusion foreground for the lisa mission |
our understanding of x-ray binary (xrb) formation and evolution have been revolutionized by hst and chandra by allowing us to study in detail xrbs in extragalactic environments. theoretically, xrb formation is sensitive to parent stellar population properties like metallicity and stellar age. these dependencies not only make xrbs promising populations for aiding in the measurement of galaxy properties themselves, but also have important astrophysical implications. for example, due to the relatively young stellar ages and primordial metallicities in the early universe (z > 3), it is predicted that xrbs were more luminous than today and played a significant role in the heating of the intergalactic medium. unlocking the potential of xrbs as useful probes of galaxy properties and understanding in detail their evolutionary pathways critically requires empirical constraints using well-studied galaxies that span a variety of evolutionary stages. in this adap, we will use the combined power of archival observations from hubble and chandra data of 16 nearby early-type galaxies to study how low-mass xrbs (lmxbs) populations evolve with age. lmxbs are critically important since they are the most numerous xrbs in the mw and are expected to dominate the normal galaxy xray emissivity of the universe out to z ~ 2. understanding separately lmxbs that form via dynamical interactions (e.g., in globular clusters; gcs) versus those that form in-situ in galactic fields is an important poorly constrained area of xrb astrophysics. we are guided by the following key questions: 1. how does the shape and normalization of the field lmxb x-ray luminosity function (xlf) evolve as parent stellar populations age? using theoretical population synthesis models, what can we learn about the evolution of contributions from various lmxb donor stars (e.g., red-giant, main-sequence, and white dwarf donors)? 2. is there any evidence that globular cluster (gc) lmxbs seeded field lmxb populations through the dissolving of gcs or lmxbs being kicked out of their parent gcs? 3. what implications do our results have for the evolution of lmxbs throughout cosmic history and x-ray emission observed in distant galaxy populations (e.g., in the chandra deep field surveys)? the combination of hst and chandra are critical for addressing these questions, as hst can be used to decipher between gc and field lmxbs and chandra can detect the sources. we will make public hst and chandra data and catalogs of x-ray sources and gcs, and will include basic properties (eg.., gc sizes, colors, lmxb spectral shapes, fluxes, luminosities). | a first robust measurement of the aging of field low mass x-ray binary populations from hubble and chandra |
the kepler main field contains stars with a wide range of masses and metallicities. these properties correlate with the amount of building blocks available for planet formation, and leave an imprint on the planet population. we derive planet occurrence rates as a function of stellar mass and metallicity. in contrasts to giant planets, whose occurrence scales positively with both quantities, the occurrence of smaller planets is anti-correlated with stellar mass and shows complex behavior as a function metallicity dependening on planet radius and orbital period.the higher average mass of planetary systems around low-mass stars compared to sun-like stars indicates migration of planetary building blocks is stellar-mass dependent and plays a prominent role in the planet formation process. the trends with stellar metallicity provide new constraints for planet formation and population synthesis models. | the dependence of the kepler planet population on host star properties |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.