abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
the x-shooter spectral library (xsl) contains more than 800 spectra of stars across the color-magnitude diagram, that extend from near-uv to near-ir wavelengths (320-2450 nm). we summarize properties of the spectra of o-rich long period variables in the xsl, such as phase-related features, and we confront the data with synthetic spectra based on static and dynamical stellar atmosphere models. we discuss successes and remaining discrepancies, keeping in mind the applications to population synthesis modeling that xsl is designed for. | oxygen-rich long period variables in the x-shooter spectral library |
we have observed a sample of 14 nearby (z∼ 0.03) star-forming blue compact galaxies (bcgs) in the rest-frame far-uv (∼1150-2200 å) using the cosmic origins spectrograph on the hubble space telescope. we have also generated a grid of stellar population synthesis models using the starburst99 evolutionary synthesis code, allowing us to compare observations and theoretical predictions for the si iv_1400 and c iv_1550 uv indices; both are comprised of a blend of stellar wind and interstellar lines and have been proposed as metallicity diagnostics in the uv. our models and observations both demonstrate that there is a positive linear correlation with metallicity for both indices, and we find generally good agreement between our observations and the predictions of the starburst99 models (with the models slightly under-estimating the value of the indices due to contributions from interstellar lines not simulated by a stellar population synthesis code). by combining the rest-frame uv observations with pre-existing rest-frame optical spectrophotometry of our bcg sample, we also directly compare the predictions of metallicity and extinction diagnostics across both wavelength regimes. this comparison reveals a correlation between the uv absorption and optical strong-line diagnostics, offering the first means of directly comparing interstellar medium (ism) properties determined across different rest-frame regimes. finally, using our starburst99 model grid, we determine theoretical values for the short-wavelength uv continuum slope, {{β }18}, which can be used for determining extinction in rest-frame uv spectra of star-forming galaxies. we consider the implications of these results and discuss future work aimed at parameterizing these and other environmental diagnostics in the uv (a suite of diagnostics that could offer particular utility in the study of star-forming galaxies at high redshift) as well as the development of robust comparisons between ism diagnostics across a broad wavelength baseline. | ultraviolet ism diagnostics for star-forming galaxies. i. tracers of metallicity and extinction |
in this paper, we investigate the outer and inner mass distributions of the irregular galaxies ugc 4284 and ugc 11861, taking advantage of published h i and h α high-resolution rotation curves and constraining the stellar disc of both galaxies throughout stellar population synthesis studies. in addition, we take into account the gas content of both galaxies deriving the h i+he rotation curve. the deduced baryonic rotation curves (star+gas) are inadequate to account for the total mass of ugc 4284 and ugc 11861, for that reason we examine the possibility of dark matter (dm) to explain the incongruity between the observed h i and h α rotation curves of ugc 4284 and ugc 11861 and the derived baryonic rotation curves. we consider nfw, burkert, dicintio, einasto, and the stadel dm haloes, to analyse the dm content of ugc 4284 and ugc 11861. the principal results of this work are that cored dm models better reproduce the dm h α and h i rotation curves of ugc 11861 and the dm h i rotation curve of ugc 4284, while the h α rotation curve of ugc 4284 is better reproduced by a cuspy dicintio dm model. in general, cored exponential two-parameter models einasto and stadel give better fits than burkert. this trend, as well as to confirm past results, presents for the first time a comparison between two different exponential dm models, einasto and stadel, in an attempt to better constrain the range of possible exponential dm models applied to real galaxies. | outer and inner mass distributions of the irregular galaxies ugc 4284 and ugc 11861: constraining the baryonic content through stellar population synthesis studies |
in this thesis, the field star initial mass function (imf) and chemical evolution parameters for the milky way (mw) are derived using a forward modelling technique in combination with bayesian statistics. starting from a local mm disc model, observations of stellar samples in the solar neighbourhood are synthesised and compared to the corresponding volume-complete observational samples of hipparcos stars. the resulting imf, derived from observations in the range from 0.5 to 8msun, is a two-slope broken power law with powers of -1.49 +- 0.08 and -3.02 +- 0.06 for the low-mass slope and the high-mass slope, respectively, with a break at 1.39 +- 0.05msun. in order to constrain the imf for stars more massive than 8msun, a fast and flexible chemical enrichment code, chempy, was developed, which is also able to reproduce spatial and stellar population selections of observational samples. the inferred high-mass slope for stellar masses above 6msun is -2.28 +- 0.09, accounting for the systematic effects of different yield sets from the literature. this shows that constraints from chemical modelling, similarly to hydrodynamical simulations of the galaxy, demand a salpeter high-mass index. this is hard to recover from star count analysis given the rareness of high-mass stars. | inference from modelling the chemodynamical evolution of the milky way disc |
various lines of evidence suggest that the cores of a large portion of early-type galaxies (etgs) are virtually evacuated of warm ionised gas. this implies that the lyman-continuum (lyc) radiation produced by an assumed active galactic nucleus (agn) can escape from the nuclei of these systems without being locally reprocessed into nebular emission, which would prevent their reliable spectroscopic classification as seyfert galaxies with standard diagnostic emission-line ratios. the spectral energy distribution (sed) of these etgs would then lack nebular emission and be essentially composed of an old stellar component and the featureless power-law (pl) continuum from the agn. a question that arises in this context is whether the agn component can be detected with current spectral population synthesis in the optical, specifically, whether these techniques effectively place an agn detection threshold in lyc-leaking galaxies. to quantitatively address this question, we took a combined approach that involves spectral fitting with starlight of synthetic seds composed of stellar emission that characterises a 10 gyr old etg and an agn power-law component that contributes a fraction 0 ≤ xagn < 1 of the monochromatic luminosity at λ0 = 4020 å. in addition to a set of fits for pl distributions fν ∝ ν- α with the canonical α = 1.5, we used a base of multiple pls with 0.5 ≤ α ≤ 2 for a grid of synthetic seds with a signal-to-noise ratio of 5-103. our analysis indicates an effective agn detection threshold at xagn ≃ 0.26, which suggests that a considerable fraction of etgs hosting significant accretion-powered nuclear activity may be missing in the agn demographics. | semi-empirical agn detection threshold in spectral synthesis studies of lyman-continuum-leaking early-type galaxies |
we present a detailed spatial analysis of stellar populations based on long-slit optical spectra in a sample of eight luminous early-type galaxies selected from nearby sparse groups and pairs, three of them may have interaction with another galaxy of similar mass. we have spatially measured luminosity-weighted averages of age, [m/h], [fe/h], and [α /fe] in the sample galaxies to add empirical data relative to the influence of galaxy mass, environment, interaction, and agn feedback in their formation and evolution. the stellar population of the individual galaxies were determined through the well-established stellar population synthesis code starlight using semi-empirical simple stellar population models. radial variations of luminosity- weighted means of age, [m/h], [fe/h], and [α /fe] were quantified up to half of the effective radius of each galaxy. we found trends between representative values of age, [m/h], [α /fe], and the nuclear stellar velocity dispersion. there are also relations between the metallicity/age gradients and the velocity dispersion. contributions of 1-4 gyr old stellar populations were quantified in ic 5328 and ngc 6758 as well as 4-8 gyr old ones in ngc 5812. extended gas is present in ic 5328, ngc 1052, ngc 1209, and ngc 6758, and the presence of a liner is identified in all these galaxies. the regions up to one effective radius of all galaxies are basically dominated by α -enhanced metal-rich old stellar populations likely due to rapid star formation episodes that induced efficient chemical enrichment. on average, the age and [α /fe] gradients are null and the [m/h] gradients are negative, although discordant cases were found. we found no correlation between the stellar population properties and the liner presence as well as between the stellar properties and environment or gravitational interaction, suggesting that the influence of progenitor mass cannot be discarded in the formation and evolution of early-type galaxies. | eight luminous early-type galaxies in nearby pairs and sparse groups. i. stellar populations spatially analysed |
nuclear processes not only generate the energy and drive the evolution of stars, but also are responsible for the synthesis of the elements in the universe. helium (4he, or α) is the second most abundant element after hydrogen, thus α-particle induced reactions such as (α , γ) , (α , n) and (α , p) play a crucial role in nuclear astrophysics, especially for understanding stellar helium burning. direct measurement of the cross sections for these α-capture reactions at stellar energies is greatly hindered because of the strong coulomb repulsion. alpha-cluster transfer reaction is a powerful tool for investigation of astrophysical (α , γ) , (α , n) and (α , p) reactions since it can preferentially populate the natural-parity states with an α-cluster structure which dominantly contribute to these astrophysical α-capture reactions during stellar helium burning. in this review we summarize the theoretical scheme, the experimental technique, astrophysical applications and the future perspectives of such approach based on α-cluster transfer reactions. | alpha-cluster transfer reactions: a tool for understanding stellar helium burning |
the core-degenerate (cd) scenario has been suggested to be a possible progenitor model of type ia supernovae (sne ia), in which a carbon-oxygen white dwarf merges with the hot co core of a massive asymptotic giant branch star during their common-envelope phase. however, the sn ia birthrates for this scenario are still uncertain. we conducted a detailed investigation into the cd scenario and then gave the birthrates for this scenario using a detailed monte carlo binary population synthesis approach. we found that the delay times of sne ia from this scenario are ∼70 myr-1400 myr, which means that the cd scenario contributes to young sn ia populations. the galactic sn ia birthrates for this scenario are in the range of ∼7.4 × 10-5 yr-1 - 3.7 × 10-4 yr-1, which roughly accounts for ∼2%-10% of all sne ia. this indicates that, under the assumptions made here, the cd scenario only contributes a small portion of all sne ia, which is not consistent with the results of ilkov & soker. | binary population synthesis for the core-degenerate scenario of type ia supernova progenitors |
improving upon the standard evolutionary population synthesis technique, we present spectrophotometric models of galaxies with morphology going from spherical structures to discs, properly accounting for the effect of dust in the interstellar medium (ism). the models contain three main physical components: the diffuse ism made of gas and dust, the complexes of molecular clouds where active star formation occurs, and stars of any age and chemical composition. these models are based on robust evolutionary chemical description providing the total amount of gas and stars present at any age, and matching the properties of galaxies of different morphological types. we have considered the results obtained by piovan et al. for the properties of the ism, and those by cassarà et al. for the spectral energy distribution (sed) of single stellar populations, both in presence of dust, to model the integral seds of galaxies of different morphological types, going from pure bulges to discs passing through a number of composite systems with different combinations of the two components. the first part of the paper is devoted to recall the technical details of the method and the basic relations driving the interaction between the physical components of the galaxy. then, the main parameters are examined and their effects on the sed of three prototype galaxies are highlighted. the theoretical seds nicely match the observational ones both for nearby galaxies and those at high redshift. | modelling galaxy spectra in presence of interstellar dust - iii. from nearby galaxies to the distant universe |
we present a photometric and spectroscopic study of the polar ring galaxy a0136-0801 in order to constrain its formation history. near-infrared and optical imaging data are used to extract surface brightness and colour profiles of the host galaxy and the wide polar structure in a0136-0801. the host galaxy dominates the light emission in all bands; the polar structure is more luminous in the optical bands and is three times more extended than the main spheroid. the average stellar population in the spheroid is redder than in the polar structure and we use their (b - k) versus (j - k) colours to constraint the ages of these populations using stellar population synthesis models. the inferred ages are 3-5 gyr for the spheroid and 1-3 gyr for the polar structure. we then use long slit spectra along the major axis of the polar structure to derive the emission line ratios and constrain the oxygen abundance, metallicity and star formation rate in this component. we find 12 + log (o/h) = 8.33 ± 0.43 and z ≃ 0.32 z⊙, using emission line ratios. these values are used, together with the ratio of the baryonic masses of the host galaxy and polar structure, to constrain the possible models for the formation scenario. we conclude that the tidal accretion of gas from a gas-rich donor or the disruption of a gas-rich satellite are formation mechanisms that may lead to systems with physical parameters in agreement with those measured for a0136-0801. | surface photometry and metallicity of the polar ring galaxy a0136-0801 |
we present an investigation of the globular cluster population synthesis method of mcwilliam & bernstein, focusing on the impact of non-lte (nlte) modeling effects and color-magnitude diagram (cmd) discretization. johnson-cousins-bessel u - b, b-v, v-i, and j-k colors are produced for 96 synthetic integrated light (il) spectra with two different discretization prescriptions and three degrees of nlte treatment. these color values are used to compare nlte- and lte-derived population ages. relative contributions of different spectral types to the il spectra for different wavebands are measured. il nlte spectra are shown to be more luminous in the uv and optical than lte spectra, but show stronger absorption features in the ir. the main features showing discrepancies between nlte and lte il spectra may be attributed to light metals, primarily fe i, ca i, and ti i, as well as tio molecular bands. main-sequence stars are shown to have negligible nlte effects at ir wavelengths compared to more evolved stars. photometric color values are shown to vary at the millimagnitude level as a function of cmd discretization. finer cmd sampling for the upper main sequence and turnoff, base of the red giant branch, and the horizontal branch minimizes this variation. differences in ages derived from lte and nlte il spectra are found to range from 0.55 to 2.54 gyr, comparable to the uncertainty in gc ages derived from color indices with observational uncertainties of 0.01 mag, the limiting precision of the harris catalog. | non-lte stellar population synthesis of globular clusters using synthetic integrated light spectra. i. constructing the il spectra |
we perform an analysis of the single white dwarf and the double degenerate binary populations in the solar neighbourhood following a population synthesis approach to investigate the effects of unresolved double degenerates in the white dwarf luminosity function. we consider all unresolved synthetic binaries to be associated with fictitious effective temperatures and surface gravities that are obtained in the same way as if these objects were observed as single point sources. we evaluate the effects of unresolved double white dwarfs assuming that the synthetic samples are 'observed' both by the magnitude-limited sdss and volume-limited gaia surveys, the latter limited to a distance of no more than 100 pc. we find that, for our standard model, the impact of unresolved double degenerates in the white dwarf luminosity function derived from the gaia sample is nearly negligible. unresolved double degenerates are hence expected to have no effect on the age of the galactic disc, nor on the star formation history from this population. however, for the sdss sample, the effect of unresolved double degenerates is significant at the brighter bins (mbol < 6.5 mag), with the fraction of such systems reaching ≃40 per cent of the total white dwarf population at mbol = 6 mag. this indicates unresolved double degenerates may influence the constraints on the star formation history derived from the sdss white dwarf sample. | the effects of unresolved double degenerates in the white dwarf luminosity function |
in this paper, the orbital evolution of exoplanets at the late stages of stellar evolution was studied using the population synthesis method. stellar evolution was traced from the main sequence stage to the white dwarf stage. the evolutionary tracks were calculated using the mesa package. the statistics of planets that were absorbed, ejected from the system, and surviving by the time of the transformation of parent stars into white dwarfs was calculated considering the variation in the star formation rate over the entire lifetime of the galaxy. we considered planets around stars in the range of initial masses (1-8)${{m}_{ \odot }}$ since less massive stars do not leave the main sequence over the lifetime of the galaxy, and more massive stars do not lead to the formation of white dwarfs. it was found that for the adopted initial distributions of planets on the a-mpl plane, the majority (about 60%) of planets born around stars in the mass range under study are absorbed by parent stars at the giant stage. a small fraction of planets (less than a percent) are ejected out of their systems under the action of the stream of matter escaping the star. the estimated number of "runaway" planets with masses from 0.04 earth masses to 13 jupiter masses in the galaxy is approximately in the 300 million range. | exoplanet population synthesis with account for orbit variation due to stellar evolution |
context. exploring the galactic chemical evolution and enrichment scenarios with open clusters (ocs) allows us to understand the history of the milky way disk. high-resolution spectra of ocs are a crucial tool, as they provide precise chemical information, to combine with precise distances and ages.aims: the aim of the stellar population astrophysics (spa) project is to derive homogeneous and accurate comprehensive chemical characterization of a number of poorly studied ocs.methods: using the harps-n echelle spectrograph at the telescopio nazionale galileo (tng), we obtained high-resolution spectra of giant stars in 18 ocs, 16 of which are chemically characterized for the first time, and two of which are well studied for comparison. the ocs in this sample have ages from a few tens of myr to 4 gyr, with a prevalence of young clusters. we already presented the radial velocities and atmospheric parameters for them in a previous spa paper. here, we present results for the α-elements o, mg, si, ca and ti, and the light elements na and al, all determined by the equivalent width method. we also measured li abundance through the synthesis method.results: we discuss the behaviors of lithium, sodium and aluminum in the context of stellar evolution. for na and al, we compare our findings with models to investigate their behaviors as a function of mass, suggesting that na mixing to the surface might start in masses as low as 2 m⊙. we study the radial, vertical, and age trends for the measured abundance ratios in a sample that combines our results and recent literature for ocs, finding significant (positive) gradients only for [mg/fe] and [ca/fe] in all cases. finally, we compare o and mg in the combined sample with chemo-dynamical models, finding a good agreement for intermediate-age and old clusters. there is a sharp increase in the abundance ratios measured among very young clusters (age < 300 myr), accompanied by a poorer fit with the models for o and mg, likely related to the inadequacy of traditional model atmospheres and methods in the derivation of atmospheric parameters and abundance ratios for stars of such young ages. based on observations made with the italian telescopio nazionale galileo (tng) operated on the island of la palma by the fundación galileo galilei of the inaf (istituto nazionale di astrofisica) at the spanish observatorio del roque de los muchachos. this study is part of the large program titled spa - stellar population astrophysics: the detailed, age-resolved chemistry of the milky way disc (pi: l. origlia), granted observing time with harps-n and giano-b echelle spectrographs at the tng. | stellar population astrophysics (spa) with the tng. α-elements, lithium, sodium and aluminum in 16 open clusters |
the probabilistic value-added bright galaxy survey (provabgs) catalog will provide the posterior distributions of physical properties of >10 million desi bright galaxy survey galaxies. each posterior distribution will be inferred from joint bayesian modeling of observed photometry and spectroscopy using markov chain monte carlo sampling and the hahn et al. stellar population synthesis (sps) model. to make this computationally feasible, provabgs will use a neural emulator for the sps model to accelerate the posterior inference. in this work, we present how we construct the emulator using the alsing et al. approach and verify that it can be used to accurately infer galaxy properties. we confirm that the emulator is in excellent agreement with the original sps model with ≪1% error and is 100× faster. in addition, we demonstrate that the posteriors of galaxy properties derived using the emulator are also in excellent agreement with those inferred using the original model. the neural emulator presented in this work is essential in bypassing the computational challenge posed in constructing the provabgs catalog. furthermore, it demonstrates the advantages of emulation for scaling sophisticated analyses to millions of galaxies. | neural stellar population synthesis emulator for the desi provabgs |
we present a summary of our project that studies galaxies hosting type ia supernova (sn ia) at different redshifts. we present gran telescopio de canarias (gtc) optical spectroscopy of six sn ia host galaxies at redshift z ~ 0.4-0.5. they are joined to a set of sn ia host galaxies at intermediate-high redshift, which include galaxies from surveys sdss and cosmos. the final sample, after a selection of galaxy spectra in terms of signal-to-noise and other characteristics, consists of 680 galaxies with redshift in the range 0.04 < z < 1. we perform an inverse stellar population synthesis with the code fado to estimate the star formation and enrichment histories of this set of galaxies, simultaneously obtaining their mean stellar age and metallicity and stellar mass. after analysing the correlations among these characteristics, we look for possible dependencies of the hubble diagram residuals and supernova features (luminosity, colour and strength parameter) on these stellar parameters. we find that the hubble residuals show a clear dependence on the stellar metallicity weighted by mass with a slope of -0.061 mag dex-1, when represented in logarithmic scale, log ⟨zm/z⊙⟩. this result supports our previous findings obtained from gas oxygen abundances for local and sdss-survey galaxies. comparing with other works from the literature that also use the stellar metallicity, we find a similar value, but with more precision and a better significance (2.08 versus ~ 1.1), due to the higher number of objects and wider range of redshift of our sample. | stellar populations in type ia supernova host galaxies at intermediate-high redshift: star formation and metallicity enrichment histories |
this thesis combines a theoretical model of galaxy formation with a treatment of the radiative transfer in the titular dusty star-forming galaxies. embedding this within the well-established λcdm (lambda cold dark matter) cosmology, the author was able to simulate galaxy populations from which realistic observational images were synthesised. based on further analysis, he shows that there is a good correspondence with observations from new instruments such as the scuba2 bolometric camera and the atacama large millimeter array (alma) interferometer, and reveals some novel aspects of this exciting galaxy population. in particular, he shows that blending of these galaxies in the imaging produces an artificial enhancement in their clustering, which he dubs "blending bias". this implies that the host dark matter halo masses for these galaxies have previously been significantly overestimated. he also presents amongst the first predictions from a galaxy formation model for observations of these galaxies that will be made by the james webb space telescope (the successor to the hubble space telescope). | the nature of dusty star-forming galaxies |
we analyze the spatially resolved star formation history of 300 nearby galaxies from the califa integral field spectroscopic survey to investigate the radial structure and gradients of the present day stellar populations properties as a function of hubble type and galaxy stellar mass. a fossil record method based on spectral synthesis techniques is used to recover spatially and temporally resolved maps of stellar population properties of spheroidal and spiral galaxies with masses 10^9 to 7 × 10^{11} m_⊙. the results show that galaxy-wide spatially averaged stellar population properties (stellar mass, mass surface density, age, metallicity, and extinction) match those obtained from the integrated spectrum, and that these spatially averaged properties match those at r = 1 hlr (half light radius), proving that the effective radii are really effective. further, the individual radial profiles of the stellar mass surface density (μ_star), luminosity weighted ages (agel), and mass weighted metallicity (logzm) are stacked in bins of galaxy morphology (e, s0, sa, sb, sbc, sc and sd). all these properties show negative gradients as a sign 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_star; while mw-like galaxies (sb with m_star ∼ 10^{11} {m}_⊙) show the largest inner age and metallicity gradients. the age and metallicity gradients suggest that major mergers have a relevant role in growing the center (within 3 hlr) of massive early type galaxies; and radial mixing may play a role flattening the radial metallicity gradient in mw-like disks. | califa across the hubble types: spatially resolved properties of the stellar populations |
in this paper, we present the results of a spectroscopic campaign devoted to ascertaining the actual nature of a sample of five objects reported as chemically peculiar stars in the catalogue of ap, hgmn and am stars (2009, a&a, 498, 961). spectroscopic observations were obtained with catania astrophysical observatory spectropolarimeter. for each of the objects, we derive the effective temperature, gravity, rotational and radial velocities, and chemical abundances using the spectral synthesis method. all the targets were found to be sb1 systems. our abundance analysis led us to classify hd 40788 and hd 187959 as marginal am stars and hd 202431 as an am star, and to confirm hd 134793 as an sreucr ap star and, finally, hd 189652 as a normal star. finally, we confirm that am stars can possibly be used as an accurate tool to date stellar populations in galaxies. | spectroscopic study of five sb1 stars with cp components |
the grid of evolutionary tracks of population ii stars with initial masses 0.81 m ⊙ ≤ m zams ≤ 0.85 m ⊙ and chemical composition of the globular cluster m3 is computed. selected models of horizontal branch stars were used as initial conditions for solution of the equations of radiation hydrodynamics and time-dependent convection describing radial stellar oscillations. the boundaries of the instability strip on the herztsprung-russel diagram were determined using ≈100 hydrodynamic models of rr lyr pulsating variables. for each evolutionary track crossing the instability strip the pulsation period was determined as a function of evolutinary time. the rate of period change of most variables is shown to range within -0.02 ≤ \dot{π} ≤ 0.05 day/106 yr. theoretical estimate of the mean period change rate obtained by the population synthesis method is <\dot{π}> = 6.0 × 10-3 day/106 yr and agrees well with observations of rr lyr variables of the globular cluster m3. | evolution and period change in rr lyr variables of the globular cluster m 3 |
methods to recover the fossil record of galaxy evolution encoded in their optical spectra have been instrumental in processing the avalanche of data from mega-surveys along the last decade, effectively transforming observed spectra onto a long and rich list of physical properties: from stellar masses and mean ages to full star formation histories. this promoted progress in our understanding of galaxies as a whole. yet, the lack of spatial resolution introduces undesirable aperture effects, and hampers advances on the internal physics of galaxies. this is now changing with 3d surveys. the mapping of stellar populations in data-cubes allows us to figure what comes from where, unscrambling information previously available only in integrated form. this contribution uses our starlight-based analysis of 300 califa galaxies to illustrate the power of spectral synthesis applied to data-cubes. the selected results highlighted here include: (a) the evolution of the mass-metallicity and mass-density-metallicity relations, as traced by the mean stellar metallicity. (b) a comparison of star formation rates obtained from hα to those derived from full spectral fits. (c) the relation between star formation rate and dust optical depth within galaxies, which turns out to mimic the schmidt-kennicutt law. (d) pca tomography experiments. | spectral synthesis of stellar populations in the 3d era: the califa experience |
context. the super-eddington wind scenario has been proposed as an alternative way for producing type ia supernovae (sne ia). the super-eddington wind can naturally prevent the carbon-oxygen white dwarfs (co wds) with high mass-accretion rates from becoming red-giant-like stars. furthermore, it works in low-metallicity environments, which may explain sne ia observed at high redshifts.aims: in this article, we systematically investigated the most prominent single-degenerate wd+ms channel based on the super-eddington wind scenario.methods: we combined the eggleton stellar evolution code with a rapid binary population synthesis (bps) approach to predict sn ia birthrates for the wd+ms channel by adopting the super-eddington wind scenario and detailed mass-accumulation efficiencies of h-shell flashes on the wds.results: our bps calculations found that the estimated sn ia birthrates for the wd+ms channel are ~0.009-0.315 × 10-3 yr-1 if we adopt the eddington accretion rate as the critical accretion rate. these rates are much lower than those of the observations (<10% of the observed sn ia birthrates). this indicates that the wd+ms channel only contributes a small portion of all sne ia. the birthrates in this simulation are lower than those of previous studies, the main reason for which is that new mass-accumulation efficiencies of h-shell flashes are adopted. we also found that the critical mass-accretion rate has significant influence on the birthrates of sne ia. meanwhile, the results of our bps calculations are sensitive to the values of the common-envelope ejection efficiency. | super-eddington wind scenario for the progenitors of type ia supernovae: binary population synthesis calculations |
we study here, using the mannheim-kazanas solution of weyl conformal theory, the mass decomposition in the representative subsample of 57 early-type elliptical lens galaxies of the sloan lens advanced camera for surveys (slacs) on board the hubble space telescope. we begin by showing that the solution need not be an exclusive solution of conformal gravity but can also be viewed as a solution of a class of f (r ) gravity theories coupled to nonlinear electrodynamics thereby rendering the ensuing results more universal. since lensing involves light bending, we shall first show that the solution adds to schwarzschild light bending caused by the luminous mass (m*) a positive contribution +γ r contrary to the previous results in the literature, thereby resolving a long-standing problem. the cause of the error is critically examined. next, applying the expressions for light bending together with an input equating einstein and weyl angles, we develop a novel algorithm for separating the luminous component from the total lens mass (luminous+dark ) within the einstein radius. our results indicate that the luminous mass estimates differ from the observed total lens masses by a linear proportionality factor across the subsample, which qualitatively agrees with the common conclusion from a number of different simulations in the literature. in quantitative detail, we observe that the ratios of luminous over total lens mass (f*) within the einstein radius of individual galaxies take on values near unity, many of which remarkably fall inside or just marginally outside the specified error bars obtained from a simulation based on the bruzual-charlot stellar population synthesis model together with the salpeter initial mass function favored on the ground of metallicity [grillo et al., astron. astrophys. 501, 461 (2009)]. we shall also calculate the average dark matter density ⟨ρ⟩ av of individual galaxies within their respective einstein spheres. to our knowledge, the present approach, being truly analytic, seems to be the first of its kind attempting to provide a new decomposition scheme distinct from the simulational ones. | mass decomposition of slacs lens galaxies in weyl conformal gravity |
in this work, we study the mass distribution of two irregular galaxies, ugc 6446 and ugc 7524, by means of h i rotation curves derived from high-resolution h i velocity fields obtained through the westerbork synthesis radio telescope data archive. we constrain the stellar and gas content of both galaxies with stellar population synthesis models and by deriving the h i+he+metals rotation curves from the total h i surface density maps, respectively. the discrepancy between the circular velocity maxima of the stellar plus the h i+he+metals rotation curves and the observed h i rotation curves of both galaxies requires the inclusion of a substantial amount of dark matter. we explore the navarro frenk and white, burkert, di cintio, einasto and stadel dark matter halo models. we obtain acceptable fits to the observed h i rotation curves of ugc 6446 and ugc 7524 with the cored burkert, einasto and stadel dark matter haloes. in particular, einasto and stadel models prove to be an appropriate alternative to the burkert dark matter halo. this result should increase the empirical basis that justifies the usage of dark matter exponential models to adjust the observed rotation curves of real galaxies. | mass content of ugc 6446 and ugc 7524 through h i rotation curves: deriving the stellar discs from stellar population synthesis models |
we performed 12co(j = 1-0) (hereafter, co) observations toward 12 normal star-forming galaxies with stellar masses of m⋆ = 1010.6-1011.3 m⊙ at z = 0.1-0.2 with the 45 m telescope at the nobeyama radio observatory. the samples were selected with dn(4000), that is, the strength of the 4000 å break, instead of the commonly used far-infrared (fir) flux. we successfully detected the co emissions from eight galaxies with signal-to-noise ratio larger than three, demonstrating the effectiveness of the dn(4000)-based sample selection. for the first time, we find a tight anti-correlation between dn(4000) and molecular gas fraction (fmol) using literature data of nearby galaxies in which the galaxies with more fuel for star formation have younger stellar populations. we find that our co-detected galaxies at z ∼ 0.1-0.2 also follow the same relation as nearby galaxies. this implies that the galaxies evolve along this dn(4000)-fmol relation, and that dn(4000) seems to be able to be used as a proxy for fmol, which requires many time-consuming observations. based on the comparison with the model calculation with a population synthesis code, we find that star formation from metal enriched gas and its quenching in the early time are necessary to reproduce galaxies with large dn(4000) and non-zero gas fraction. | co emissions from optically selected galaxies at z ∼ 0.1-0.2: tight anti-correlation between molecular gas fraction and 4000 å break strength |
we present the results of determination of the age, helium mass fraction (y), metallicity ([fe/h]), and abundances of the elements c, n, o, na, mg, ca, ti, c and mn for the galactic globular cluster ngc 6652. we use its medium-resolution integrated-light spectrum from the library of schiavon and our population synthesis method to fulfill this task. we select the evolutionary isochrone and stellar mass function for our analysis, which provide the best approximation to the shapes and intensities of the observed balmer line profiles. the determined elemental abundances, age and metallicity are characteristic of stellar populations in the galactic bulge. | age and chemical composition of the globular cluster ngc 6652 |
the extreme ultraviolet (euv) spectra of distant star-forming regions cannot be probed directly using either ground- or space-based telescopes due to the high cross section for interaction of euv photons with the interstellar medium. this makes euv spectra poorly constrained. the millimeter/submillimeter recombination lines of h and he, which can be observed from the ground, can serve as a reliable probe of the euv. here we present a study based on alma observations of three galactic ultracompact h ii regions and the starburst region sgr b2(m), in which we reconstruct the key parameters of the euv spectra using millimeter recombination lines of h i, he i, and he ii. we find that in all cases the euv spectra between 13.6 and 54.4 ev have similar frequency dependence: ${l}_{\nu }\propto {\nu }^{-4.5\pm 0.4}.$ we compare the inferred values of the euv spectral slopes with the values expected for a purely single stellar evolution model (starburst99) and the binary population and spectral synthesis code (bpass). we find that the observed spectral slope differs from the model predictions. this may imply that the fraction of interacting binaries in h ii regions is substantially lower than assumed in bpass. the technique demonstrated here allows one to deduce the euv spectra of star-forming regions, providing critical insight into photon production rates at $\lambda \leqslant 912\mathring{{\rm{a}}}$ , and can serve as calibration to starburst synthesis models, improving our understanding of star formation in the distant universe and the properties of ionizing flux during reionization. | reconstructing the euv spectrum of star-forming regions from millimeter recombination lines of h i, he i, and he ii |
massive early-type galaxies (etgs) show several strong co absorption features in their h- and k-band spectra that cannot be explained by state-of-the-art stellar population models. for many years, the disagreement has been attributed to the presence of intermediate-age stellar components that are dominated by stars in the asymptotic giant branch phase. however, no robust evidence of this scenario has been provided so far. one way to test this claim is by comparison of co indices for etgs and for relic galaxies. lacking the intermediate-age stellar populations, relic galaxies provide us with a unique opportunity to address the origin of strong co absorptions in etgs. here, we utilize the prototype relic galaxy ngc 1277 and compare the co absorption features of this galaxy with the ones of a representative sample of massive etgs. we show that the co lines in both systems have similar strengths, significantly stronger than the predictions of stellar population synthesis models. we conclude that intermediate-age stellar populations in massive etgs are not the culprit of the strong co absorptions. | the relic galaxy ngc 1277 rules out intermediate-age stellar populations origin of co-strong absorptions in massive early-type galaxies |
the population synthesis code sevn (stellar evolution for n-body) includes up-to-date stellar evolution (through look-up tables), binary evolution, and different recipes for core-collapse supernovae. sevn also provides an up-to-date formalism for pair-instability and pulsational pair-instability supernovae, and is designed to interface with direct-summation n-body codes such as starlab (ascl:1010.076) and higpus (ascl:1207.002). | sevn: stellar evolution for n-body |
we study the evolution of the red sequence (rs) scatter in galaxy clusters and groups simultaneously using predictions from our simulations (cosmological hydrodynamic + semi-analytical) as well as observational data from the hawk-i cluster survey (hcs), a sample of galaxy clusters at redshifts $0.8 < z < 1.5$. we analyze the intrinsic scatter of the rs to investigate whether the stellar age can be its main effective driver, at the same time assessing the role of metallicity variations in shaping the rs building at around epoch $z\sim$1 and beyond. to this purpose we rely on various methods to derive the average age and age spread from the rs colour scatter of the hcs sample, with the aid of population synthesis models. the rs scatter predicted by the models at $z< 0.7$ is found to not depend on the star formation history adopted, whilst at $z>the correlation found between age and rest-frame colour scatters is quite robust, although all age scatter estimations ultimately depend on the definition of rs as well as on the completeness limits adopted. we find that the age spread of rs galaxies predicted by both hydrodynamical simulations and sam increases with cosmic epoch, while the ratio between the age spread and the average age remains approximately constant. both trends are in agreement with observational results from both the hcs and other literature samples. | the high-redshift evolution of the red sequence scatter from joint simulations and hawk-i cluster survey |
using the stellar population synthesis tool trilegal, we discuss the expected stellar populations in the kepler and corot fields. | the expected stellar populations in the kepler and corot fields |
we explore the possibility of using uv spectroscopy in combination with broad-band photometry as diagnostic tools for understanding the shape of the initial mass function (imf) in unresolved stellar populations. building on our previous work, we extend the stochastically lighting up galaxies (slug) code to include a high-resolution uv spectral synthesizer and equivalent width calculation capabilities. we first gain a qualitative understanding of how uv spectral features behave as the parameters that define a star cluster in slug (mass, age, extinction, and imf slope α3) are changed. we then exploit bayesian inference techniques to recover the α3 values for clusters simulated with slug, using mock observations of these clusters comprised of broad-band photometry and equivalent width measurements of a selection of uv spectral features. we find some improvement when compared to attempts using broad-band photometry alone (with the interquartile range of the α3 posterior pdf shrinking by ≃ 32%), although we still do not yet fully break the known degeneracy between the cluster mass and α3. finally, we make predictions about how effective real observations will be by quantifying our ability to constrain α3 as a function of limiting equivalent width. we find that observations sensitive to a modest equivalent width of ≃ 9 å are sufficient to improve the recovery of the imf slope parameter by ≃ 32% (interquartile range of posterior pdf median residuals), moving to ≃ 39% when we include all the significant spectral features in the wavelength range 900-3000 å. | theoretical predictions for imf diagnostics in uv spectroscopy of star clusters |
the method for the multicomponent photoionization modelling (mphm) of low-metallicity h ii regions surrounding the starburst region was developed. the internal structure of the h ii region has been determined using the evolutionary modelling of the superwind bubble surrounding the star-forming region. models of chevalier and clegg (1985) and weaver et al.(1977) have been used to determine the radial distribution of the gas density, the velocity of gas layers, and the temperature within internal components (the region of the superwind free expansion and the cavity, respectively). the chemical abundances in region of the superwind free expansion were obtained from the evolutionary population synthesis with including of rotating stars. the chemical abundances within cavity were defined by averaging over mass the chemical compositions of mixture of the abundances of gas from superwind and ones within outer component, because of gas evaporation from external component into the cavity. external components of our models describe a high-density, thin shell of gas formed by superwind shock and a typical undisturbed hydrodynamically h ii region, respectively. evolutionary grids of multicomponent low-metallicity models are calculated. a comparative analysis of the results of their calculation with the observed data has been carried out. the ionic abundances averaged over modelling volume as well as chemical composition assumed in models were used to derive the new expressions for ionization-correction factors that were used to redetermine the chemical compositions of 88 h ii regions in blue compact dwarf galaxies. it must be noticed that we used for this propose the ionic abundances obtained by izotov et al. (2007). in result the primordial helium abundance and its enrichment during stellar chemical evolution of matter were determined. | the primordial helium abundance determination using multicomponent photoionization modelling of low-metallicity h ii regions |
in this paper, we present the properties of 10 halo globular clusters (gcs) with luminosities l ≃ 5-7 × 105 l⊙ in the local group galaxy m33 using images from the hubble space telescope wfpc2 in the f555w and f814w bands. we obtained the ellipticities, position angles, and surface brightness profiles for each gc. in general, the ellipticities of the m33 sample clusters are similar to those of the m31 clusters. the structural and dynamical parameters are derived by fitting the profiles to three different models combined with mass-to-light ratios (m/l values) from population-synthesis models. the structural parameters include core radii, concentration, half-light radii, and central surface brightness. the dynamical parameters include the integrated cluster mass, integrated binding energy, central surface mass density, and predicted line of sight velocity dispersion at the cluster center. the velocity dispersions of the four clusters predicted here agree well with the observed dispersions by larsen et al. the results here showed that the majority of the sample halo gcs are better fitted by both the king model and the wilson model than the sérsic model. in general, the properties of the clusters in m33, m31, and the milky way fall in the same regions of parameter spaces. the tight correlations of cluster properties indicate a “fundamental plane” for clusters, which reflects some universal physical conditions and processes operating at the epoch of cluster formation. | structural parameters for 10 halo globular clusters in m33 |
we have obtained the time and space-resolved star formation history (sfh) of m51a (ngc 5194) by fitting galaxy evolution explorer (galex), sloan digital sky survey and near-infrared pixel-by-pixel photometry to a comprehensive library of stellar population synthesis models drawn from the synthetic spectral atlas of galaxies (ssag). we fit for each space-resolved element (pixel) an independent model where the sfh is averaged in 137 age bins, each one 100 myr wide. we used the bayesian successive priors (bsp) algorithm to mitigate the bias in the present-day spatial mass distribution. we test bsp with different prior probability distribution functions (pdfs); this exercise suggests that the best prior pdf is the one concordant with the spatial distribution of the stellar mass as inferred from the near-infrared images. we also demonstrate that varying the implicit prior pdf of the sfh in ssag does not affect the results. by summing the contributions to the global star formation rate of each pixel, at each age bin, we have assembled the resolved sfh of the whole galaxy. according to these results, the star formation rate of m51a was exponentially increasing for the first 10 gyr after the big bang, and then turned into an exponentially decreasing function until the present day. superimposed, we find a main burst of star formation at t ≈ 11.9 gyr after the big bang. | the resolved star formation history of m51a through successive bayesian marginalization |
the study of ages, helium mass fraction (y) and chemical composition of globular clusters in dwarf galaxies is important for understanding the physical conditions at the main evolutionary stages of the host galaxies and for constraining the build-up histories of large galaxies. we present the analysis of integrated-light spectra of 8 extragalactic and 20 galactic globular clusters (gcs) using our population synthesis method. we calculate synthetic spectra of gcs according to the defined stellar mass functions using model atmospheres and stellar parameters ([fe/h], teff, and logg) set by theoretical isochrones. the main advantage of our method is the ability to determine not only chemical composition but also the age and mean y in a cluster by modelling and analysis of balmer absorption lines. the knowledge of y and anomalies of light elements in star clusters is one of the key points for understanding the phenomenon of multiple stellar populations. | modeling and analysis of medium-resolution integrated-light spectra of globular clusters in dwarf galaxies |
different accretion regimes onto magnetized nss in hmxbs are considered: wind-fed supersonic (bondi) regime at high accretion rates g s-1, subsonic settling regime at lower and supercritical disc accretion during roche lobe overflow. in wind-fed stage, nss in hmxbs reach equilibrium spin periods p * proportional to binary orbital period pb. at supercritical accretion stage, the system may appear as a pulsating ulx. population synthesis of galactic hmxbs using standard assumptions on the binary evolution and ns formation is presented. comparison of the model p * - pb (the corbet diagram), p* - lx and pb - lx distributions with those for the observed hmxbs (including be x-ray binaries) and pulsating ulxs suggests the importance of the reduction of p* in non-circular orbits, explaining the location of be x-ray binaries in the model corbet diagram, and the universal parameters of pulsating ulxs depending only on the ns magnetic fields. | x-ray binaries with neutron stars at different accretion stages |
after a brief review of population synthesis of close-by cooling neutron stars, i focus on the interpretation of the dichotomy of spin periods of near-by coolers. the existence of two well separated groups - short period (∼ 0.1-0.3 s) radio pulsars and long period (∼ 3-10 s) radio quiet sources, aka the magnificent seven, - can not easily be explained by unified models developed recently (popov et al. 2010; gullón et al. 2014). i speculate that the most natural solution of the problem can be in the bimodal initial magnetic-field distribution related to the existence of an additional mechanism of field generation in magnetars. | magneto-rotational and thermal evolution of young neutron stars |
we derive detailed dynamical models for two galaxies, the massive spiral galaxy ngc 5055 and the dwarf irregular ddo 154. we used navarro, frenk & white (nfw) and isothermal halo models for the dark matter (dm) distribution, along with the most recent and reliable radio observations of h i to determine the rotation curves of these galaxies. contributions from the neutral gas and the luminous matter were accounted for. for ngc 5055, the latest stellar population synthesis (sps) models, combining metallicity and age as indicators of the stellar mass-to-light ratio (m/l) were used to better constrain both the dm model and the contribution to the total mass from all components. the isothermal dark halo model successfully fitted both observed rotation curves with realistic values for stellar m/l, while the nfw model needed further constraints for m/l to fit the rotation curve of ddo 154. in the case of ngc 5055, we found the best-fitting m/l in the 3.6 μm band (m/l3.6) for stellar disc to be 0.57 ± 0.04 for isothermal, and 0.50 ± 0.05 for nfw dm model. the most probable value for m/l3.6 from sps models is 0.46, which is in agreement within uncertainties with our best-fitting nfw model. in the case of ddo 154, we obtained the stellar disc m/l3.6 of 0.25 ± 0.20 for the isothermal dm model. the stellar disc m/l3.6 for the nfw model was fixed to 0.26, as best reasonable value. for ngc 5055, we derived radial profiles of stellar m/l for our best estimate for a particular dm model. | two regimes of galaxy dynamics: mass models of ngc 5055 and ddo 154 |
we present a new model of the optical nebular emission from hii regions by combining the results of the binary population and spectral synthesis (bpass) code with the photoionization code cloudy (ferland et al. 1998). we explore a variety of emission-line diagnostics of these star-forming hii regions and examine the effects of metallicity and interacting binary evolution on the nebula emission-line production. we compare the line emission properties of hii regions with model stellar populations, and provide new constraints on their stellar populations and supernova progenitors. we find that models including massive binary stars can successfully match all the observational constraints and provide reasonable age and mass estimation of the hii regions and supernova progenitors. | emission-line diagnostics of nearby hii regions including supernova hosts |
we present a spectroscopic analysis of the central disc regions of barred spiral galaxies, concentrating on the region that is swept by the bar but not including the bar itself (the 'star formation desert' or sfd region). new spectroscopy is presented for 34 galaxies, and the full sample analysed comprises 48 sba-sbcd galaxies. these data confirm the full suppression of sf within the sfd regions of all but the latest type (sbcd) galaxies. however, diffuse [n ii] and h α line emission is detected in all galaxies. the ubiquity and homogeneous properties of this emission from sba to sbc galaxies favour post-asymptotic giant branch (p-agb) stars as the source of this line excitation, rather than extreme blue horizontal branch stars. the emission-line ratios strongly exclude any contribution from recent sf, but are fully consistent with recent population synthesis modelling of p-agb emission by other authors, and favour excitation dominated by ambient gas of approximately solar abundance, rather than ejecta from the agb stars themselves. the line equivalent widths are also larger than those observed in many fully passive (e.g. elliptical) galaxies, which may also be a consequence of a greater ambient gas density in the sfd regions. | diffuse liner-type emission from extended disc regions of barred galaxies |
the derivation of accurate stellar populations of galaxies is a non-trivial task because of the well-known age-metallicity degeneracy. we aim to break this degeneracy by invoking a chemical evolution model (cem) for isolated disk galaxy, where its metallicity enrichment history (meh) is modelled to be tightly linked to its star formation history (sfh). our cem has been successfully tested on several local group dwarf galaxies whose sfhs and mehs have been both independently measured from deep colour-magnitude diagrams of individual stars. by introducing the cem into the stellar population fitting algorithm as a prior, we expect that the sfh of galaxies could be better constrained. | stellar population synthesis of galaxies with chemical evolution model |
context. the pressure exerted by the ambient hot x-ray gas on cluster galaxies can lead to the presence of ram pressure stripped (rps) galaxies, characterized by asymmetric shapes, and, in some cases, tails of blue stars and/or x-ray gas, with increased star formation.aims: with the aim of increasing the known sample of rps galaxies at redshift z ∼ 0.5, notably higher than most rps samples presently known, we extended our searches for such galaxies to the cluster ms 0451.6-0305.methods: our study is based on hubble space telescope (hst) imaging in the f814w band (corresponding to a restframe wavelength of 529 nm), covering a region of about 6 × 6 mpc2, an eight magnitude ground-based catalogue with photometric redshifts, and a spectroscopic redshift catalogue. we defined as cluster members a spectroscopic redshift sample of 359 galaxies within ±4σv of the mean cluster velocity, and a photometric redshift sample covering the [0.48, 0.61] range. we searched for rps galaxies in the hst images and tested the error on their classification with a zooniverse collaboration. we also computed the phase space diagram of rps candidates in the spectroscopic sample. finally, we ran the lephare stellar population synthesis code through the gazpar interface to analyze and compare the properties of rps and non-rps galaxies.results: we find 56 and 273 rps candidates in the spectroscopic and photometric redshift samples, respectively. they are distributed throughout the cluster and tend to avoid high density regions. the phase space diagram gives the percentages of virialized, backsplash, and infall galaxies. rps galaxy candidates typically show rather high star formation rates, young ages, and relatively low masses. we compare all our results to those previously obtained for the massive merging cluster macs j0717+3745, at a similar redshift.conclusions: this study increases by at least 56 objects if we only consider galaxies with spectroscopic redshifts, and probably much more if galaxies with photometric redshifts are taken into account. this study increases the number of rps candidates at redshift z > 0.5, and confirms that they host, on average, younger stellar populations and strongly form stars when compared with non-rps counterparts. the fact that rps candidates with spectroscopic and with photometric redshifts have comparable properties shows that large samples of such objects could be gathered based on multi-band photometry only, a promising result in view of the very large imaging surveys planned in the coming years (des, euclid, lsst, etc.). 217 rps galaxy candidates with photometric redshifts are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/662/a84 | ram pressure stripping in the z ∼ 0.5 galaxy cluster ms 0451.6-0305 |
the first directly observed gravitational wave event, gw150914, featuring the merger of two massive black holes, highlighted the need to determine how these systems of compact remnant binaries are formed. we use the binary population synthesis code compact object synthesis and monte carlo investigation code (cosmic) to predict the types of massive stars that will show significant radial velocity (rv) variations, indicative of a potential compact object (i.e. a black hole or neutron star) orbiting the star. we 'observe' the binaries generated in the populations with a similar number of epochs and rv accuracy as planned for the milky way mapper (mwm) survey. in this analysis, we are especially interested in systems where a compact remnant is orbiting a massive o or b star as these systems survived the first supernova and neutron star kick. we test the ability of the milky way mapper observing strategy to distinguish among different mass-loss and kick prescriptions. we find that wolf-rayet stars or hot subdwarfs in binaries could be detectable (i.e. luminous, high δrvmax), viable progenitors of such objects, while the different prescriptions primarily affect the number of sources. | mapping progenitors of binary black holes and neutron stars with binary population synthesis |
cosmic (compact object synthesis and monte carlo investigation code) generates synthetic populations with an adaptive size based on how the shape of binary parameter distributions change as the number of simulated binaries increases. it implements stellar evolution using sse (ascl:1303.015) and binary interactions using bse (ascl:1303.014). cosmic can also be used to simulate a single binary at a time, a list of multiple binaries, a grid of binaries, or a fixed population size as well as restart binaries at a mid point in their evolution. the code is included in cmc-cosmic (ascl:2108.023). | cosmic: compact object synthesis and monte carlo investigation code |
compas (compact object mergers: population astrophysics & statistics) draws properties for a binary star system from a set of initial distributions and evolves it from zero-age main sequence to the end of its life as two compact remnants. evolution prescriptions and model parameters are easily adjustable in the software. compas has been used for inference from observations of gravitational-wave mergers, galactic neutron stars, x-ray binaries, and luminous red novae. | compas: rapid binary population synthesis code |
using a method of population synthesis, we investigate the runaway stars produced by disrupted binaries via asymmetric core collapse supernova explosions (cc-rass) and thermonuclear supernova explosions (tn-rass). we find the velocities of cc-rass in the range of about 30-100 km s -1. the runaway stars observed in the galaxy are possibly cc-rass. due to differences in stellar chemical components and structures, tn-rass are divided into hydrogen-rich tn-rass and helium-rich tn-rass. the velocities of the former are about 100-500 km s -1, while the velocities of the latter are mainly between 600 and 1100 km s -1. the hypervelocity stars observed in the galaxy may originate from thermonuclear supernova explosions. our results possibly cover the us 708 which is a compact helium star and travels with a velocity of 1157 ±53 km s-1 in our galaxy. | velocity distributions of runaway stars produced by supernovae in the galaxy |
we study the dynamical models of two massive nearby early-type galaxies, ngc 4473 and ngc 4697, using globular clusters (gcs) as tracers of their gravitational potential. we use their velocity dispersion to model their dynamics based on solving the spherical jeans equation in both newtonian and modified newtonian dynamics (mond) approaches. we take into account the orbital anisotropies and we model the following three cases: we study isotropic, tangentially and radially anisotropic models interior to ∼12 effective radii for ngc 4473 and interior to ∼3 effective radii for ngc 4697. we analyse these two galaxies that are part of the larger sluggs sample because we obtained photometric data using the new 1.40 m telescope `milanković' for both objects to estimate the contribution of the visible, stellar, component, using several stellar population synthesis models as priors. in addition to three widely analysed mond models (standard, simple, and toy) for the first time in the literature we analyse the zhao mond model on elliptical galaxies. we also analysed several additional mond models found in the literature and we also tested the einasto dark matter models. we find that in the newtonian approach, both galaxies in general may need dark matter to describe their kinematics. the best-fitting results were in both cases obtained with the inclusion of the dark matter halo but we managed to find solutions for which the dark component is not needed. we also find that both galaxies may be well modelled using all the tested mond functions assuming the existence of the visible matter only. | testing mond on two nearby elliptical galaxies: the cases of ngc 4473 and ngc 4697 |
the detailed study of the different stellar populations which can be observed in galaxies is one of the most promising methods to shed light on the evolutionary histories of galaxies. so far, stellar population analysis has been carried out mainly in the optical wavelength range. the infrared spectral range, on the other hand, has been poorly studied so far, although it provides very important insights, particularly into the cooler stellar populations which are present in galaxies. however, in the last years, space telescopes like the spitzer space telescope or the wide-field infrared survey explorer and instruments like the spectrograph x-shooter on the very large telescope have collected more and more photometric and spectroscopic data in this wavelength range. in order to analyze these observations, it is necessary to dispose of reliable and accurate stellar population models in the infrared. only a small number of stellar population models in the infrared exist in the literature. they are mostly based on theoretical stellar libraries and very often cover only the near-infrared wavelength range at a rather low resolution. hence, we developed new single-burst stellar population models between 8150 and 50000å which are exclusively based on 180 spectra from the empirical infrared telescope facility stellar library. we computed our single stellar population models for two different sets of isochrones and various types of initial mass functions of different slopes. since the stars of the infrared telescope facility library present only a limited coverage of the stellar atmospheric parameter space, our models are of sufficient quality only for ages larger than 1 gyr and metallicities between [fe/h] = 0.40 and 0.26. by combining our single stellar population models in the infrared with the extended medium-resolution isaac newton telescope library of empirical spectra in the optical spectral range, we created the first single stellar population models covering the whole optical and infrared wavelength range between 3500 and 50000å which are almost completely based on spectra of observed stars (apart from two gaps which were fitted with theoretical stellar spectra) . we analyze the behaviour of the near-infrared (j - k) and the spitzer ([3.6]-[4.5]) colour calculated from our models. for ages older than 3 gyr, both colours depend only slightly on age and metallicity. however, for younger ages, both colours become redder which is caused by the asymptotic giant branch stars contributing significantly to the light in the infrared at ages between 0.1 and 3 gyr. furthermore, we find a satisfactory agreement between the optical and near-infrared colours measured from our models and the colours observed from various samples of globular clusters and early-type x galaxies. however, our model predictions are only able to reproduce correctly the spitzer ([3.6]-[4.5]) colours of older, more massive galaxies that resemble a single-burst population. younger, less massive and more metal-poor galaxies show redder colours than our models. this mismatch can be explained by a more extended star formation history of these galaxies which includes a metal-poor or/and young population. the spitzer ([3.6]-[4.5]) colours derived from our models also agree very well with those from most other models available in this wavelength range as long as they also correctly take into account a strong co absorption band situated at 4.5 μm. the model predictions for colours in the near-infrared, such as (j - k), differ more between the different sets of models, depending on the underlying prescriptions for the asymptotic giant branch stellar evolutionary phase. compared to other authors, we adopt only a moderate contribution of asymptotic giant branch stars to our models. our stellar population models allow us also to determine mass-to-light ratios in different infrared bands. consequently, we can confirm that the massto- light ratio determined in the spitzer [3.6] μm band changes much less as a function of both age and metallicity than it does in the optical bands. however, it shows a non-negligible sensitivity to the initial mass function. our models are of sufficient resolution to measure line strength indices up to the l-band. hence, we redefined many indices in the near-infrared and identified new indicators for age, metallicity and the slope of the initial mass function. the equivalent widths of many indices which we computed from our stellar population models cannot be used to trace the large indices measured from observed early-type galaxies. while in the literature, this disagreement between the predicted and the observed line strength indices is usually attributed to a much enhanced contribution of asymptotic giant branch stars, we present a number of evidences which are at odds with such a view. therefore, we propose an alternative scenario. we argue that a different abundance pattern in the early-type galaxies compared to that of the milky way which is characterized by an enhanced [c/fe] ratio is able to account for this mismatch. the differences in the carbon enhancement between the galaxies can be attributed to the duration of their episodes of star formation which seem to be driven by galactic environment. in denser environments like in galaxy clusters, star formation takes place on a shorter characteristic timescale than in isolated galaxies. hence, contrary to the situation in clusters, in isolated galaxies, the massive expulsion of carbon into the interstellar medium occurs before star formation has finished. therefore, in the latter ones carbon is incorporated into the new generation of stars leading to enhanced carbon abundances with respect to cluster galaxies of a similar mass. we show that if we additionally include the effect of a bottom-heavy initial mass function in the case of the most massive early-type galaxies and assume enhanced abundance ratios for some other elements like sodium, we are able to simultaneously reproduce all of the studied line strength indices. our analysis also shows that an active galactic nucleus does not seem to have any impact on the line strength indices which we measure for central stellar populations. | understanding the formation and evolution of early-type galaxies based on newly developed single-burst stellar population synthesis models in the infrared |
cmc-cosmic models dense star clusters using hénon's method using orbit-averaging collisional stellar dynamics. it includes all the relevant physics for modeling dense spherical star clusters, such as strong dynamical encounters, single and binary stellar evolution, central massive black holes, three-body binary formation, and relativistic dynamics, among others. cmc is parallelized using the message passing interface (mpi), and is pinned to the cosmic (ascl:2108.022) package for binary population synthesis, which itself was originally based on the version of bse (ascl:1303.014). cosmic is currently a submodule within cmc, ensuring that any cluster simulations or binary populations are integrated with the same physics. | cmc-cosmic: cluster monte carlo code |
nitellopsis obtusa (starry stonewort) is a green macroalga (family characeae) native to europe and asia that is of conservation concern in its native range but expanding in north america. we synthesize current science on n. obtusa and identify key knowledge gaps. nitellopsis obtusa is able to reproduce sexually or asexually via fragments and bulbils. native populations reproduce primarily asexually; sexual fertility increases with longer growing seasons and in shallower waters. in north america, only males have been observed. nitellopsis obtusa has been known from north america for four decades and confirmed in seven u.s. states and two canadian provinces. it is typically associated with low-flow areas of lakes with alkaline to neutral ph and elevated conductivity. nitellopsis obtusa has ecological benefits in its native range, contributing to food webs and water clarity. in its invaded range, n. obtusa could negatively influence native macrophytes and habitat quality, but there has been little research on impacts. there have been many efforts to control n. obtusa through physical removal or chemical treatments, but little systematic evaluation of outcomes. substantial areas of uncertainty regarding n. obtusa include controls on reproduction, full distribution in north america, ecological impacts, and control strategies. | biology, ecology, and management of starry stonewort (nitellopsis obtusa; characeae): a red-listed eurasian green alga invasive in north america |
in this work, we have developed a new approach to form stars from clusters first, where massive stars are formed from fractions of mass of small stellar clusters. this new approximation is based on the empirical power law found in recent years and the maximum stellar mass that can be formed in a cluster. to produce the new models we have used the most recent version of starburst99 that incorporates the most recent stellar evolution models with rotation. at the verge of solving nearby stellar populations and observing small stellar populations across the universe, this new approach brings a new scope on trying to disentangle the nature of hyper and supermassive stars in small stellar populations. models for ngc 3603 and ngc 604 are presented. our most important result is a strong ionizing power from small clusters by forming enough supermassive stars in a cluster of ~ 104 m⊙. | modeling small stellar populations using starburst99 |
interstellar extinction is critical when studying stellar populations and galactic structure. by taking into account all informations on stellar populations on a given line of sight, the population synthesis approach is an efficient tool to derive the distribution of extinction. this approach has been shown to give reliable estimates in regions where the stars are numerous enough and well distributed in distance. this method has some limits due to dependency on model hypotheses. with other methods, some biases can appear close to the limiting magnitude, and to the maximum distance of detection, due to detection limits of the stars which depend on the extinction itself. we present the successes of this method as well as its limitations and compare with results of other methods. | making of 3d extinction maps from population synthesis approach |
based both on observations and simulations, recent works propose that the speed of the spiral pattern in disk galaxies may decrease with increasing radius; the implications are that patterns are actually short-lived, and that the azimuthal color/age gradients across spiral arms predicted by density wave theory could not be produced. we, however, have consistently found such gradients, and measured spiral pattern speeds by comparing the observations with stellar population synthesis models (gonzález & graham 1996; martínez-garcía et al. 2009a, b; martínez-garcía & gonzález-lópezlira 2011). here, we summarize our previous results in non-barred and weakly barred spirals, together with six new, as yet unpublished, objects. on the other hand, we have indeed found a trend whereby pattern speeds at smaller radii are larger than expected from a model that assumes purely circular orbits (cf. figure 1), likely due to the effect of spiral shocks on the orbits of newborn stars. the results suggest that spirals may behave as steady long-lived patterns. | signatures of long-lived spiral patterns: the color gradient trend |
we apply a new statistical analysis technique, the mean field approach to independent component analysis (mf-ica) in a bayseian framework, to galaxy spectral analysis. this algorithm can compress a stellar spectral library into a few independent components (ics), and the galaxy spectrum can be reconstructed by these ics. compared to other algorithms which decompose a galaxy spectrum into a combination of several simple stellar populations, the mf-ica approach offers a large improvement in efficiency. to check the reliability of this spectral analysis method, three different methods are used: (1) parameter recovery for simulated galaxies, (2) comparison with parameters estimated by other methods, and (3) consistency test of parameters derived with galaxies from the sloan digital sky survey. we find that our mf-ica method can not only fit the observed galaxy spectra efficiently, but can also accurately recover the physical parameters of galaxies. we also apply our spectral analysis method to the deep2 spectroscopic data, and find it can provide excellent fitting results for low signal-to-noise spectra. | spectral synthesis via mean field approach to independent component analysis |
we investigate the relationship between host galaxies’ stellar content and active galactic nuclei (agns) for optically selected qsos with z < 0.5. there is a total of 82 qsos that we select from the sloan digital sky survey. these 82 qsos have both wide-field infrared survey explorer data and measurable stellar content. with the help of the stellar population synthesis code starlight, we determine the luminosity fractions of agns, stellar population ages, and star formation histories (sfhs) of host galaxies. we find that there is a correlation between the sfh and agn properties, which suggests a possible delay from star formation to agn. this probably indicates that the agn activity correlates with the star formation activity, which consistent with a coevolution scheme for black hole and host galaxies. | a systematic analysis of stellar populations in the host galaxies of sdss type i qsos |
for more than 100 years, humanity (both specialists and enthusiastic laics) has been searching for extraterrestrial life hoping we are not alone. the first step in the quest for extraterrestrial life is to define what and where exactly to look for. thus, the basic definition of living matter is a conditio sine qua non for the quest. the diversity of species on earth is so large that our quest for extraterrestrial life cannot be limited to forms and shapes present and known to us from our environment. however, there are two formal conditions that must be fulfilled in order for something to be assumed as living matter. first, it should represent a growing open thermodynamic system (in biological terms - a cell), and thus be a system out of equilibrium. second, it must perform synthesis, self-assembly and accumulation processes (in biological terms to grow, maintain homeostasis, respond to environment, reproduce, exchange matter and energy, evolve). populated planets are consisted of two components: biosphere and its environment (geosphere, hydrosphere and atmosphere). living matter and its environment are out of equilibrium. thus, the candidate planets are dynamic inhomogeneous systems for two reasons. first, a planet receives energy from its star, which leads to disequilibrium for external reasons. animate matter contributes to disequilibrium for internal reasons: accumulation of matter and self-assembly. in practice, for a screening, an astrobiologist should search for increase in inhomogeneity on a candidate planet. | wanted dead or alive extraterrestrial life forms (thermodynamic criterion for life is a growing open system that performs self-assembly processes) |
we aim to investigate the connections existing between the density profiles of the stellar populations used to define a gravitationally bound stellar system and their star formation history: we do this by developing a general framework accounting for both classical stellar population theory and classical stellar dynamics. we extend the work of pasetto et al. (2012) on a single composite-stellar population (csp) to multiple csps, including also a phase-space description of the csp concept. in this framework, we use the concept of distribution function to define the csp in terms of mass, metallicity, and phase-space in a suitable space of existence e of the csp. we introduce the concept of foliation of e to describe formally any csp as sum of disjointed simple stellar populations (ssp), with the aim to offer a more general formal setting to cast the equations of stellar populations theory and stellar dynamics theory. in doing so, we allow the csp to be object of dissipation processes thus developing its dynamics in a general non-hamiltonian framework. furthermore, we investigate the necessary and sufficient condition to realize a multiple csp consistent with its mass-metallicity and phase-space distribution function over its temporal evolution, for a collisionless csp. finally, analytical and numerical examples show the potential of the result obtained. | theory of multiple-stellar population synthesis in a non-hamiltonian setting |
this paper uses population synthesis to investigate the possible origin of isolated millisecond pulsars as born from the coalescence of a neutron star and a white dwarf. results show that the galactic birth rate of isolated millisecond pulsars is likely to lie between 5.8×10-5 yr-1 and 2.0×10-4 yr-1, depending on critical variables, such as the stability of mass transfer via the roche lobe and the value of kick velocity. in addition to this, this paper estimates that the solar mass of isolated millisecond pulsars can range from 1.5 and 2.0 mʘ, making them more massive than other `normal' pulsars. finally, the majority of isolated millisecond pulsars in our simulations have spin periods ranging from several to 20 ms, which is consistent with previous observations. | on isolated millisecond pulsars formed by the coalescence of neutron stars and massive white dwarfs |
double-peaked emission-line galaxies have long been perceived as objects related to merging galaxies or other phenomenawith disturbed dynamical activities, such as outflows and disk rotation. in order to find the connection between the unique activities happening in these objects and their stellar population physics, we study the stellar populations of the stacked spectra drawn from double-peaked emission-line galaxies in the large sky area multi-object fiber spectroscopic telescope (lamost) data release 4 (dr4) and the sloan digital sky survey (sdss) data release 7 (dr7) databases. we group the selected double-peaked emission-line objects into 10 different types of pairs based on the baldwin-phillips-terlevich (bpt) diagnosis for each pair of blueshifted and redshifted components, and then stack the spectra of each group for analysis. the software starlight is employed to fit each stacked spectrum, and the contributions of stars at different ages and metallicities are quantified for subsequent comparative study and analysis. to highlight the commonality and uniqueness in these double-peaked emitting objects, we compare the population synthesis results of the stacked spectra of double-peaked emission-line galaxies with those of their counterpart reference samples displaying single-peaked emission features. the reference samples are also selected from the lamost dr4 and sdss dr7 databases. from the comparison results, we confirm the strong correlations between stellar populations and their spectral classes, and find that the double-peaked emitting phenomenon is more likely to occur in an ‘older’ stellar environment and the subgroups hosting different bpt components will show an obvious heterogeneous star formation history. | stellar population analysis on the stacked spectra of double-peaked emission-line galaxies |
binary population synthesis is the method by which predictions of varied observables of stellar populations can be made from theoretical models of binary stellar evolution. binary stars have many more possible evolutionary outcomes compared to single stars and the relative rates of the different pathways, such as the rates of different supernova types, depend on uncertain or poorly constrained physics. in this chapter, we describe population synthesis, outline the major uncertainties, and discuss the relevant predictions for core-collapse supernovae. after we overview single-star evolution, we outline the important physical processes that occur in binaries including roche-lobe overflow, common-envelope evolution, and supernova kicks. we also discuss how a synthetic stellar population incorporating interacting binaries can be constructed and how uncertainties, such as the strength of supernova kicks, affect any predictions. we illustrate the process by comparing predictions for the stellar populations in two young star clusters. we then discuss the important predictions from population synthesis for understanding core-collapse supernovae, their delay-time distribution, and their progenitor stars. finally we discuss how we can predict the rate of mergers of compact remnants and thus predict the initial parameters of gravitational wave sources. | population synthesis of massive close binary evolution |
it is well-known that fitting color-magnitude diagrams (cmds) to theoretical isochrones is the main method to determine star cluster ages. however, when cmds are not available, the spectral energy distribution (sed)-fitting technique is the only other approach, although it suffers the age-metallicity-reddening degeneracy. in this work, we gather the ages, metallicities, and masses of dozens of m31 star clusters from the cmd-fitting with hubble space telescope images from the literature for comparison. we check the reliability of the sed-fitting results with different models, i.e., bruzual & charlot model (bc03), galaxy evolutionary synthesis models (galev), and advanced stellar population synthesis (asps) for the simple stellar populations (ssps) with single stars (ss)-ssp/binary-star (bs)-ssps models. the photometry bands includes the galaxy evolution explorer galex fuv/nuv bands, optical/near-infrared ubvrijhk bands, as well as the wide-field infrared survey explorer (wise) w1/w2 bands. the comparisons show that the sed-fitting ages agree well with the cmd-fitting ages, either with the fixed metallicity or with the free metallicity for both the bc03 and the galev model. however, for the asps models, it seems that sed-fitting results are systematically older than the cmd ages, especially for the ages log t < 9.0 (year). the fitting also shows that the galex fuv/nuv-band are more important than the wise w1/w2 for constraining the ages, which confirms the previous findings. we also derived the masses of our sample star clusters from the bc03 and galev models and it is found that the values agree well with those in the literature. | the ages of m31 star clusters: spectral energy distribution versus color-magnitude diagram |
we present an expanded investigation of the library of globular cluster (gc) synthetic integrated light (il) spectra of young & short, focusing on the impact of non-local thermodynamic equilibrium (nlte) modeling effects on cluster parameters derived from photometric colors and sensitivity of near-ir spectral features to cluster age and metallicity. johnson-cousins-bessel ubvijk photometric colors are produced for 910 synthetic il spectra with two degrees of α enhancement, in both nlte and local thermodynamic equilibrium (lte). these color values are used to investigate the gc age-metallicity degeneracy and compare nlte and lte derived [m/h] values for ngc 104, ngc 5139, and ngc 6205. for a given age, derived [m/h] values are shown to increase by up to 0.05 dex when modeled in nlte. a total of 86 spectral lines in the range λ = 12000-22000 å, representing 14 different atomic species, were identified as sensitive to either cluster age or metallicity, 12 of which were identified as sensitive to both. equivalent widths of the lines are measured in nlte and lte spectra, with nlte effects changing the widths by up to {}-0.15+0.25 å depending on the atomic species. | nlte stellar population synthesis of globular clusters using synthetic integrated light spectra. ii. expanded photometry and sensitivity of near-ir spectral features to cluster age and metallicity |
for the galaxies composed of different 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 combination of the genetic algorithm (ga) with the simulated annealing (sa) algorithm has the complementary advantages of the good global search ability and fast convergence of ga, as well as the strong local search ability of the sa algorithm. in both the speed and accuracy of the parameter estimation of stellar population synthesis, the ga-sa combined algorithm is superior to the single sa algorithm. | parameter estimation of stellar population synthesis using a combined genetic algorithm |
the x-shooter spectral library (xsl) contains more than 800 spectra of stars across the color-magnitude diagram, that extend from near-uv to near-ir wavelengths (320-2450 nm). we summarize properties of the spectra of o-rich long period variables in xsl, such as phase-related features, and we confront the data with synthetic spectra based on static and dynamical stellar atmosphere models. we discuss successes and remaining discrepancies, keeping in mind the applications to population synthesis modeling that xsl is designed for. | oxygen-rich long period variables in the x-shooter spectral library |
we use the grids of geneva stellar evolution models and the new population synthesis code (syclist) to produce synthetic stellar populations, fully accounting for stellar rotation effects, and study their evolution in time. we show how the fraction of rapidly-rotating stars and of surface-enriched stars evolve with time and show how our theoretical results compare with some results in the literature for rotating populations, in particular with that of single be stars. we propose to search among early b populations of the same age to look for differences in nitrogen enrichment effects. | evolution of intermediate-mass rotating stellar populations: rotational properties, nitrogen surface abundances, and their link to the be-phenomenon. |
in recent years the stellar populations of the milky way have been investigated from large scale surveys in different ways, from pure star count analysis to detailed studies based on spectroscopic surveys. while in the former case the data can constrain the scale height and scale length thanks to completeness, they suffer from high correlation between these two values. on the other hand, spectroscopic surveys suffer from complex selection functions which hardly allow to derive accurate density distributions. the scale length in particular has been difficult to be constrained, resulting in discrepant values in the literature. here, we investigate the thick disc characteristics by comparing model simulations with large scale data sets. the simulations are done from the population synthesis model of besançon. we explore the parameters of the thick disc (shape, local density, age, metallicity) using a monte carlo markov chain method to constrain the model free parameters (robin et al. 2014). correlations between parameters are limited due to the vast spatial coverage of the used surveys (sdss + 2mass). we show that the thick disc was created during a long phase of formation, starting about 12 gyr ago and finishing about 10 gyr ago, during which gravitational contraction occurred, both vertically and radially. moreover, in its early phase the thick disc was flaring in the outskirts. we conclude that the thick disc has been created prior to the thin disc during a gravitational collapse phase, slowed down by turbulence related to a high star formation rate, as explained for example in bournaud et al. (2009) or lehnert et al. (2009). our result does not favor a formation from an initial thin disc thickened later by merger events or by secular evolution of the thin disc. we then study the in-plane distribution of stars in the thin disc from 2mass and show that the thin disc scale length varies as a function of age, indicating an inside out formation. moreover, we investigate the warp and flare and demonstrate that the warp amplitude is changing with time and the node angle is slightly precessing. finally, we show comparisons between the new model and spectroscopic surveys. the new model allows to correctly simulate the kinematics, the metallicity, and α-abundance distributions in the solar neighbourhood as well as in the bulge region. | clues on the milky way disc formation from population synthesis simulations |
snapdragons (stellar numbers and parameters determined routinely and generated observing n-body systems) is a simplified version of the population synthesis code galaxia (ascl:1101.007), using a different process to generate the stellar catalog. it splits each n-body particle from the galaxy simulation into an appropriate number of stellar particles to create a mock catalog of observable stars from the n-body model. snapdragon uses the same isochrones and extinction map as galaxia. | snapdragons: stellar numbers and parameters determined routinely and generated observing n-body systems |
isolated millisecond pulsars (imsps) are a topic of academic contention. there are various models to explain their formation. we explore the formation of imsp via quark novae (qn). during this formation process, low-mass x-ray binaries (lmxbs) are disrupted when the mass of the neutron star (ns) reaches 1.8m_⊙. using population synthesis, this work estimates that the galactic birthrate of qn-produced imsps lies between {∼ }9.5× 10^{-6} and {∼ }1.7× 10^{-4} yr^{-1}. the uncertainties shown in our experiment model is due to the qn's kick velocity. furthermore, our findings not only show that qn-produced imsps are statistically more significant than those produced by mergers, but also that millisecond pulsar binaries with a high eccentricity may originate from lmxbs that have been involved in, yet not disrupted by, a qn. | quark novae: an alternative channel for the formation of isolated millisecond pulsars |
abell 1767 is a dynamically relaxed, cd cluster of galaxies with a redshift of 0.0703. among 250 spectroscopically confirmed member galaxies within a projected radius of 2.5r200, 243 galaxies (∼ 97%) are spectroscopically covered by the sloan digital sky survey. based on this homogeneous spectral sample, the stellar evolutionary synthesis code starlight is applied to investigate the stellar populations and star formation histories of galaxies in this cluster. the star formation properties of galaxies, such as mean stellar ages, metallicities, stellar masses, and star formation rates, are presented as functions of local galaxy density. a strong environmental effect is found such that massive galaxies in the high-density core region of the cluster tend to have higher metallicities, older mean stellar ages, and lower specific star formation rates (ssfrs), and their recent star formation activities have been remarkably suppressed. in addition, the correlations of the metallicity and ssfr with stellar mass are confirmed. | star formation properties of galaxy cluster a1767 |
context. researching the properties of the brightest globular cluster (referred to as gc1) in m 81 can provide a fossil record of the earliest stages of galaxy formation and evolution. the beijing-arizona-taiwan-connecticut (batc) multicolour sky survey has carried out deep exposures of m 81.aims: we derive the magnitudes in intermediate-band filters of the batc system for gc1 and determine its age, mass, and structural parameters.methods: gc1 was observed by batc using 14 intermediate-band filters covering a wavelength range of 4000-10 000 å. based on photometric data in batc and two micron all sky survey near-infrared jhks filters, we constructed an extensive spectral energy distribution of gc1, spanning the wavelength range from 4000 to 20 000 å. by comparing multicolour photometry with theoretical single stellar population synthesis models, we derived the age and mass of gc1. in addition, we obtained ellipticities, position angles, and surface brightness profiles for gc1 based on the images of deep observations with the advanced camera for surveys on the hubble space telescope. gc1 is better fitted by the wilson model than by the king and sérsic models in the f606w filter, and it is better fitted by the sérsic model than by the king and wilson models in the f814w filter. the `best-fit' half-light radius of gc1 obtained here is 5.59 pc, which is larger than the majority of normal globular clusters (gcs) of the same luminosity.results: the age and mass of gc1 estimated here are 13.0 ± 2.90 gyr and 1.06 − 1.48 × 107 m⊙, respectively. the rh versus mv diagram shows that gc1 occupies the same area as extended star clusters. therefore, we suggest that gc1 is more likely an accreted former nuclear star cluster than a classical gc similar to most of those in the milky way. full table 4 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/649/ a138 | properties of the brightest globular cluster in m 81 based on multicolour observations |
the aim of this work is to explore the potential of surface brightness fluctuations (sbf) for studying composite stellar populations (csp). to do so, we have computed the standard (mean) and sbf spectra with e-miles stellar population synthesis code. we have created a set of models composed by different mass fractions of two single stellar populations, as a first approximation of a csp scenario. with these models we present an ensemble of sbf colour-colour diagnostic diagrams that reveal different secondary populations depending on the bands used. for this work we focus on those colours capable of unveiling small fractions of metal-poor components in elliptical galaxies, which are dominated by old metal-rich stellar populations. we fit a set of synthetic models and a selection of nearby elliptical galaxies to our csp models using both mean and sbf colours. we find that the results are highly improved and return small secondary components when mean and sbf values are applied simultaneously, instead of employing them separately or as a constraint. finally, we explore the possibility of tracking chemical enrichment histories by including in the analysis a variety of sbf colours. for this purpose we present an example where, with two different sbf colour-colour diagrams, we untangle a small contribution of a young solar population and an old metal-poor component from an old solar principal population. the results we have found are promising, but limited by the available data. we highlight the urgent need for new, better, and more consistent sbf observations. | surface brightness fluctuations to constrain secondary stellar populations: revealing very low-metallicity stars in massive galaxies |
galaxy evolution is generally affected by tidal interactions. first, in this series, we reported several effects that suggest that tidal interactions contribute to the regulation of star formation (sf). to confirm this, we now compare stellar mass assembly histories and sf look-back time annular profiles between califa survey tidally and non-tidally perturbed galaxies. we pair their respective star-forming regions at the closest stellar mass surface densities to reduce the influence of stellar mass. the assembly histories and annular profiles show statistically significant differences so that higher star-formation rates characterize regions in tidally perturbed galaxies. these regions underwent a more intense (re)activation of sf in the last 1 gyr. varying shapes of the annular profiles also reflect fluctuations between suppression and (re)activation of sf. since gas-phase abundances used to be lower in more actively than in less actively star-forming galaxies, we further explore the plausible presence of metal-poor gas inflows able to dilute such abundances. the resolved relations of oxygen (o) abundance with stellar mass density and with total gas fraction show slightly lower o abundances for regions in tidally perturbed galaxies. the single distributions of o abundances statistically validate this. moreover, from a metallicity model based on stellar feedback, the mass rate differentials (inflows-outflows) show statistically valid higher values for regions in tidally perturbed galaxies. these differentials, and the metal fractions from the population synthesis, suggest dominant gas inflows in these galaxies. this dominance and the differences in sf through time confirm the previously reported effects of tidal interactions on sf. | star formation in califa survey perturbed galaxies - ii. star-formation histories and oxygen abundances |
very recently, wind roche-lobe overflow (wrlof) has been suggested as a possible mass transfer mechanism for ultra-luminous x-ray sources (ulxs) and, to date, two neutron-star (ns) ulxs (i.e., ngc 7793 p13 and ngc 300 ulx-1) are remarkable and hard to understand in the current, usual rlof picture. in this work, we test if the two sources could fit into the wrlof paradigm. by using an evolutionary population synthesis method, we modeled the population of ns ulxs with (super)giant donors, taking the wrlof accretion mode into account. we find that the population of wind-fed ns ulxs in the wrlof mode is distinct in numbers and binary parameters from that in the traditional bondi-hoyle-lyttleton mode, and it is strongly metallicity dependent. the number of ns ulxs with (super)giant donors can be enhanced greatly, by one or two orders of magnitude, depending on the metallicity adopted. sources with massive (∼15−40 m⊙) (super)giant donors dominate wind-fed ns ulxs in the very low metallicities, while sources in near solar cases are dominated by a red supergiant with a lower mass m2 < 10 m⊙ instead. moreover, the two ns ulxs can be well reproduced in the wrlof paradigm, which significantly enriches our understanding of the nature of ulxs and the population. we also present the current distributions of binary parameters of wind-fed ns ulxs, which may be further testified by future high-resolution optical and x-ray observations of these populations. | population synthesis on ultra-luminous x-ray sources with an accreting neutron star: wind roche-lobe overflow cases |
short-grb progenitors could come in various flavors, depending on the nature of the merging compact stellar objects (including a stellar-mass black hole or not) or depending on their ages (millions or billions of years). at a redshift of z = 0.122, the nearly face-on spiral host of the short grb 080905a is one of the closest short-grb host galaxies identified so far. this made it a preferred target to explore spatially resolved star formation and to investigate the afterglow position in the context of its star formation structures. we used vlt/muse integral-field unit observations, supplemented by atca 5.5/9.0 ghz radio-continuum measurements and publicly available hst data, to study the star formation activity in the grb 080905a host galaxy. the muse observations reveal that the entire host is characterized by strong line emission. using the hα line flux, we measure for the entire galaxy an sfr of about 1.6 m ⊙ yr-1, consistent with its non-detection by atca. several individual star-forming regions are scattered across the host. the most luminous region has a hα luminosity that is nearly four times as high as the luminosity of the tarantula nebula in the large magellanic cloud. even though star-forming activity can be traced as close to about 3 kpc (in projection) distance to the grb explosion site, stellar population synthesis calculations show that none of the hα-bright star-forming regions is a likely birthplace of the short-grb progenitor. | vlt/muse and atca observations of the host galaxy of the short grb 080905a at z = 0.122 |
magnetic fields generated by a dynamo mechanism due to differential rotation during stellar mergers are often proposed as an explanation for the presence of strong fields in certain classes of magnetic stars, including high field magnetic white dwarfs (hfmwds). in the case of the hfmwds, the site of the differential rotation has been variously proposed to be the common envelope itself, the massive hot outer regions of a merged degenerate core or an accretion disc formed by a tidally disrupted companion that is subsequently incorporated into a degenerate core. in the present study i explore the possibility that the origin of hfmwds is consistent with stellar interactions during the common envelope evolution (cee). in this picture the observed fields are caused by an $\alpha-\omega$ dynamo driven by differential rotation. the strongest fields would arise when the differential rotation equals the critical break up velocity and would occur from the merging of two stars during cee or double degenerate (dd) mergers in a post common envelope (ce) stage. those systems that do not coalesce but emerge from the ce on a close orbit and about to initiate mass transfer will evolve into magnetic cataclysmic variables (mcvs), the population synthesis calculations carried out in this work have shown that the origin of high fields in isolated white dwarfs (wds) and in wds in mcvs is consistent with stellar interaction during common envelope evolution. i compare the calculated field strengths to those observed and test the correlation between theory and observation by means of the kolmogorov--smirnov (k--s) test and show that the resulting correlation is good for values of the ce energy efficiency parameter, $\alpha{_{\rm{ce}}}$, in the range 0.1--0.3. | the genesis of magnetic fields in white dwarfs |
the vast majority of all massive stars are born in binaries. the binarity of a star may influence its life drastically via a large variety of interactions with its companion star. several astrophysical events, like the recently detected gravitational wave mergers, have a binary origin. to investigate the possible paths of binary evolution, a new stellar grid-based binary populations synthesis code combine is developed. during binary evolution, many uncertain phases, including one or more mass-transfer phases, a common-envelope phase and kicks during a supernova explosion, have to be considered. the least understood among them is the common-envelope phase. a detailed analysis of the consequences of the conversion of available energy reservoirs into the ejection of the gas of the common envelope is performed at two metallicities, that of the milky way (z = 0.0088) and that of the dwarf galaxy izwicky18 (z = 0.0002). the most crucial aspect is the bifurcation point which separates the remaining core from the lost material. combine is applied to investigate a variety of parameters of the binary evolution phases and their effects on observable stages during the evolution leading to a final gravitational wave driven merger. the simulations performed with combine are able to reproduce the observed galactic double neutron star population with respect to their orbital parameters and, to some extend, their measured mass distributions. in addition, the simulations can reproduce the progenitor systems of all published merger events of double black hole mergers and the double neutron star merger, gw170817, for appropriate metallicities. merger-rate densities in the local universe are obtained from the simulations. statistical uncertainties are discusses as well as predictions made for future observations and ligo-virgo detections. finally, using combine, the nature of the unseen companion star in the radio pulsar binary psr j1755-2550 is probed to narrow the search window for the companion. | binary star population synthesis - progenitors of gravitational wave driven mergers |
the formation of protoplanetary discs is central to planet formation because it sets its initial conditions. planet formation may also occur while the star-and-disc system is still being formed.in this work we perform an extensive parameter study of the formation and evolution of protostellar and protoplanetary discs that includes many key physical processes and produces a population of stars in agreement with the initial mass function.we constrain physical quantities like mass, radius, lifetime and gravitational instabilities of protostellar and protoplanetary discs by studying their evolution from formation to dispersal.we perform a total of 50'000 simulations using a 1d vertically-integrated viscous evolution code, studying a parameter space of final stellar masses from 0.05 to 5 msol. each star-and-disc system is set up shortly after the formation of the protostar and fed by infalling material from the parent molecular cloud core. initial conditions are chosen based on the results from the radiation hydrodynamics population synthesis of circumstellar discs by bate (2018). we also consider a different infall prescription based on the results of hennebelle et al. (2016) in order to assess the influence of magnetic fields on the disc formation.we find that protoplanetary discs are very massive early in their lives. when averaged over the entire stellar population, we find ~0.3 and ~0.1 msol for systems based on hydrodynamic or mhd initial conditions, respectively. around stars of mass ~ 1 msol, we find disc masses of ~0.7 and ~0.2 msol for "hydro"/"mhd", respectively. furthermore, the inferred total disc lifetimes are long, ~5 - 7 myr on average. this is despite our choice of a high value of 10-2 for the background viscosity α-parameter.in addition, we find fragmentation is common in systems based on hydrodynamic simulations, with more fragments of larger mass formed in more massive systems. in contrast, magnetic fields may suppress fragmentation completely. | the influence of infall on the properties of protoplanetary disks |
individual galactic globular clusters (gcs) harbour two coeval generations of stars: the first one born with the ``standard'' $\alpha$-enhanced metal mixture, observed in field halo objects; and the second one characterized by an anticorrelated cnona abundance pattern overimposed on the first generation. previous works have investigated the effect that such phenomena would have on the integrated properties of populations, for a metal-rich gc ($\mathrm{[fe/h]} = -0.7$). they have found that some spectral indices were appreciably affected by the abundance anticorrelations. to study the effect of the cnona anticorrelation on gcs, we calibrated our synthetic stellar spectra using high spectral resolution observations of the sun and arcturus, as references, from 372 to 930~nm. to produce our synthetic spectra, we used the spectral synthesis program synthe and atlas12. calculating the mean absolute deviation of the predictions of different opacity lists, we produced two atomic line lists, one calibrated with the sun and the other with arcturus. we used our new list calibrated with the sun to compute a grid of synthetic stellar spectra to study the gc 47~tuc (ngc~104), using the empirical stellar library based on the work by martins and the stellar models by coelho. the performance of our two new atomic opacity line lists enhance the representation of the observed spectra by 15 to 25% in comparison to the other lists from the literature. using the line list calibrated with the sun to compute the stellar spectra grid for 47~tuc, we investigated the impact of cnona anticorrelations on the integrated spectrum. it shows that when de cnona variation mixture is applied, the regions sensitive to those atomic lines change: c and o decrease whereas n and na increase, as expected by the anticorrelation patterns of these abundances on gcs. | atomic/molecular opacities and globular cluster spectra |
we investigate interaction effects in the stellar and gas kinematics, stellar population, and ionized gas properties of the interacting galaxy pair am 1204-292,composed of ngc 4105 and ngc 4106. the data consist of long-slit spectra in the range 3000-7050 å. the massive e3 galaxy ngc 4105 presents a flat stellar velocity profile, while the ionized gas is in strong rotation, suggesting an external origin. its companion, ngc 4106, shows asymmetries in the radial velocity field, likely due to the interaction. the dynamics of the interacting pair were modelled using the p-gadget3 treepm/sph code, from which we show that the system has just passed the first perigalacticum, which triggered an outbreak of star formation, currently at full maximum. we characterized the stellar population properties using the stellar population synthesis code starlight and, on average, both galaxies are predominantly composed of old stellar populations. ngc 4105 has a slightly negative age gradient, comparable with that of the most massive elliptical galaxies, but a steeper metallicity gradient. the sb0 galaxy ngc 4106 presents smaller radial variations in both age and metallicity in comparison with intermediate-mass early-type galaxies. these gradients have not been disturbed by interaction, since the star formation happened very recently and was not extensive in mass. electron density estimates for the pair are systematically higher than those obtained in isolated galaxies. the central o/h abundances were obtained from photoionization models in combination with emission-line ratios, which resulted in 12 + log(o/h) = 9.03 ± 0.02 and 12 + log(o/h) = 8.69 ± 0.05 for ngc 4105 and ngc 4106, respectively. | the physical properties and evolution of the interacting system am 1204-292 |
keystone species structure ecological communities and are major determinants of biodiversity. a synthesis of research on keystone species is nonetheless missing a critical component – the sensory mechanisms for behavioral interactions that determine population- and community-wide attributes. here, we establish the chemosensory basis for keystone predation by sea stars (pisaster ochraceus) on mussels. this consumer-resource interaction is prototypic of top-down driven trophic cascades. each mussel species (mytilus californianus and m. galloprovincialis) secretes a glycoprotein orthologue (29.6 and 28.1 kda, respectively) that acts, singularly, to evoke the sea star predatory response. the orthologues (named "keystonein") are localized in the epidermis, extrapallial fluid, and organic shell coating (periostracum) of live, intact mussels. thus, keystonein contacts chemosensory receptors on tube feet as sea stars crawl over rocky surfaces in search of prey. the complete nucleotide sequences reveal that keystonein shares 87% (m. californianus) or 98% (m. galloprovincialis) homology with a calcium-binding protein in the shell matrix of a closely related congener, m. edulis. all three molecules cluster tightly within the complement component 1 domain containing (c1qdc) protein family; each exhibits a large globular domain, low complexity region(s), coiled coil, and at least four of five histidine-aspartic acid tandem motifs. collective results support the hypothesis that keystonein evolved ancestrally in immunological, and later, in biomineralization roles. more recently, the substance has become exploited by sea stars as a contact cue for prey recognition. as the first identified compound to evoke keystone predation, keystonein provides valuable sensory information, promotes biodiversity, and shapes community structure and function. without this molecule, there would be no predation by sea stars on mussels. | keystone predation and molecules of keystone significance |
in evolutionary population synthesis (eps) models, we need to convert stellar evolutionary parameters into spectra via interpolation in a stellar spectral library. for theoretical stellar spectral libraries, the spectrum grid is homogeneous on the effective-temperature and gravity plane for a given metallicity. it is relatively easy to derive stellar spectra. for empirical stellar spectral libraries, stellar parameters are irregularly distributed and the interpolation algorithm is relatively complicated. in those eps models that use empirical stellar spectral libraries, different algorithms are used and the codes are often not released. moreover, these algorithms are often complicated. in this work, based on a radial basis function (rbf) network, we present a new spectrum interpolation algorithm and its code. compared with the other interpolation algorithms that are used in eps models, it can be easily understood and is highly efficient in terms of computation. the code is written in matlab scripts and can be used on any computer system. using it, we can obtain the interpolated spectra from a library or a combination of libraries. we apply this algorithm to several stellar spectral libraries (such as miles, elodie-3.1 and stelib-3.2) and give the integrated spectral energy distributions (iseds) of stellar populations (with ages from 1 myr to 14 gyr) by combining them with yunnan-iii isochrones. our results show that the differences caused by the adoption of different eps model components are less than 0.2 dex. all data about the stellar population iseds in this work and the rbf spectrum interpolation code can be obtained by request from the first author or downloaded from http://www1.ynao.ac.cn/∼zhangfh. | a new stellar spectrum interpolation algorithm and its application to yunnan-iii evolutionary population synthesis models |
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 a non-degenerate star (a main-sequence star or a giant) or an other wd in a binary merger (single- and double-degenerate scenario, respectively). in population-synthesis studies of sne ia the contribution of asymptotic giant branch (agb) stars to either scenario is marginal. however, most of these studies adopt simplified assumptions to compute the effects of wind mass loss and accretion in binary systems. this work investigates the impact of wind mass transfer on a population of binary stars and discusses 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? |
we introduce the ongoing mastar project, which is going to construct a large, well-calibrated, high quality empirical stellar library with more than 8000 stars covering the wavelength range 3,622 - 10,354å at a resolution of r∼2000, and with better than 3% relative flux calibration. the spectra are taken using hexagonal fibre bundles feeding the boss spectrographs on the 2.5m sloan foundation telescope, by piggybacking on the sdss-iv/apogee-2 observations. compared to previous efforts of empirical libraries, the mastar library will have a more comprehensive stellar parameter coverage, especially in cool dwarfs, low metallicity stars, and stars with different [α/fe]. this is achieved by a target selection method based on large spectroscopic catalogs from apogee, lamost, and segue, combined with photometric selection. this empirical library will provide a new basis for calibrating theoretical spectral libraries and for stellar population synthesis. in addition, with identical spectral coverage and resolution to the ongoing integral field spectroscopy survey of nearby galaxies -- sdss-iv/manga (mapping nearby galaxies at apo). this library is ideal for spectral modelling and stellar population analysis of manga data. | sdss-iv mastar: a large, comprehensive, and high quality empirical stellar library |
despite intensive searches, the only pulsar within 0.1 pc of the central black hole in our galaxy, sgr a*, is a radio-loud magnetar. since magnetars are rare among the galactic neutron star population, and a large number of massive stars are already known in this region, the galactic centre (gc) should harbour a large number of neutron stars. population syntheses suggest several thousand neutron stars may be present in the gc. many of these could be highly energetic millisecond pulsars which are also proposed to be responsible for the gc gamma-ray excess. we propose that the presence of a neutron star within 0.03 pc from sgr a* can be revealed by the shock interactions with the disc around the central black hole. as we demonstrate, these interactions result in observable transient non-thermal x-ray and gamma-ray emission over time-scales of months, provided that the spin-down luminosity of the neutron star is lsd ∼ 1035 erg s-1. current limits on the population of normal and millisecond pulsars in the gc region suggest that a number of such pulsars are present with such luminosities. | flares from galactic centre pulsars: a new class of x-ray transients? |
using population synthesis, we study a double-degenerate (dd) scenario for sne ia, aiming to estimate the maximum possible contribution to the rate of sne from this scenario and the dependence of the delay-time distribution (dtd) on it. we make an extreme assumption that all mergers of super-chandrasekhar pairs of co white dwarfs (wds) and mergers of co wds more massive than 0.47 $m_\odot$ with hybrid or helium wds more massive than 0.37$m_\odot$ produce sne ia. the models are parametrized by the product of the common envelope efficiency and the parameter of binding energy of stellar envelopes $\alpha_{ce}\lambda$, which we vary between 0.25 and 2. the best agreement with observations is obtained for $\alpha_{ce}\lambda$=2. a substantial contribution to the rate of sne ia is provided by the pairs with a hybrid wd. the estimated galactic rate of sne ia is $6.5 10^{-3}$ per yr (for the mass of the bulge and thin disk equal to $7.2 10^{10} m_\odot$), which is comparable to the observational estimate $(5.4\pm0.12) 10^{-3}$ per yr. the model dtd for 1 to 8 gyr range satisfactorily fits dtd for sne ia in the field galaxies (maoz et al. 2012). for this epoch, model dtd is a power low with an index -1.64. at earlier and later epochs our dtd has a deficit of events, as in other studies. marginal agreement with observational dtd is achieved even if only co+co wd with $m_1\geq0.8\,m_\odot$ and $m_2\geq0.6\,m_\odot$ produce sne ia. a better agreement of observed and model dtd may be obtained if tidal effects are weaker than assumed and/or metallicity of population is much lower than solar. | merging white dwarfs and sn ia |
in this paper, we derive a novel circular velocity relation for a test particle in a 3d gravitational potential applicable to every system of curvilinear coordinates, suitable to be reduced to orthogonal form. as an illustration of the potentiality of the determined circular velocity expression, we perform the rotation curves analysis of ugc 8490 and ugc 9753 and we estimate the total and dark matter mass of these two galaxies under the assumption that their respective dark matter haloes have spherical, prolate, and oblate spheroidal mass distributions. we employ stellar population synthesis models and the total h i density map to obtain the stellar and h i+he+metals rotation curves of both galaxies. the subtraction of the stellar plus gas rotation curves from the observed rotation curves of ugc 8490 and ugc 9753 generates the dark matter circular velocity curves of both galaxies. we fit the dark matter rotation curves of ugc 8490 and ugc 9753 through the newly established circular velocity formula specialized to the spherical, prolate, and oblate spheroidal mass distributions, considering the navarro, frenk, and white, burkert, di cintio, einasto, and stadel dark matter haloes. our principal findings are the following: globally, cored dark matter profiles burkert and einasto prevail over cuspy navarro, frenk, and white, and di cintio. also, spherical/oblate dark matter models fit better the dark matter rotation curves of both galaxies than prolate dark matter haloes. | general circular velocity relation of a test particle in a 3d gravitational potential: application to the rotation curves analysis and total mass determination of ugc 8490 and ugc 9753 |
apertif is a phased-array feed for the westerbork synthesis radio telescope (wsrt), increasing the field of view of the telescope by a factor of twenty-five to 6.8 square degrees. in 2018, three legacy surveys will commence: a shallow imaging survey, a medium-deep imaging survey, and a pulsars and fast transients survey. the imaging surveys will be done in full polarization over the frequency range 1130-1430 mhz, which corresponds to redshifts of z=0-0.256 for neutral hydrogen (hi). the spectral resolution is 12.2 khz, or an hi velocity resolution of 2.6 km/s at z=0 and 3.2 km/s at z=0.256. the full resolution images will have a beam size of 15"x15"/sin(declination), and tapered data products (i.e., 30" resolution images) will also be available. the footprints of the imaging surveys are chosen to maximize coverage of multi-wavelength datasets, including the herschel atlas north galactic pole field, hetdex region, plus coordination with manga and planned weave follow-up. the survey footprints were also chosen to probe different regions of interest, including the cvn region, coma cluster, and perseus-pisces supercluster. the key science cases for the imaging surveys include understanding how galaxy properties depend on environment, the role of interactions and gas accretion and removal, understanding the smallest gas-rich galaxies, connecting cold gas to agn, understanding the history of star formation and agn activity in the faint radio continuum population, and studying magnetic fields in galaxies and large-scale structure. after a proprietary period, the survey data products will be publicly available through the apertif long term archive (alta). up-to-date information on apertif and the planned surveys can be found at www.apertif.nl.commissioning of the apertif instrument is underway. here we will present results from the imaging commissioning, highlighting the capabilities of the instrument as related to the key science cases of the imaging surveys. | apertif: a new phased-array feed for wsrt |
12c is synthesised in stars by fusion of three α particles. this process occurs through a resonance in the 12c nucleus, famously known as the hoyle state. in this state, the 12c nucleus exists as a cluster of α particles. the state is the band-head for a rotational band with the 2+ rotational excitation predicted in the energy region 9 - 11 mev. this rotational excitation can affect the triple-α process reaction rate by more than an order of magnitude at high temperatures (109 k). depending on the energy of the resonance, the knowledge of the state can also help determine the structure of the hoyle state. in the work presented here, the state of interest is populated by beta decay of radioactive 12n ion beam delivered by the igisol facility at jyfl, jyväskylä. | rotational excitation of the hoyle state in 12c |
small organic molecules of the push-pull architecture are rapidly gaining their status in the organic electronics applications. in densely packed molecular films, both intra- and intermolecular interactions play an essential role for the device performance. here we study two different molecules, a highly symmetric star-shaped one and its newly synthesized single arm analogue, for their photophysical properties. both chromophores were dissolved in a solid matrix at different concentrations to vary their separation and therefore intermolecular coupling. we show that in both molecules the population relaxation accelerates by more than a factor of 10 at shorter intermolecular distances due to self-quenching thereby reducing the exciton survival time. the transient anisotropy dynamics are also quite similar, with their substantial acceleration at shorter interchromophore distances due to exciton diffusion caused by the förster-like resonance energy transfer. however, the anisotropy values are noticeably lower for the star-shaped molecule because of intramolecular mixing of different polarization states. finally, a model is presented that accounts for the observed results. | visualization of molecular excitons diffusion |
gamma ray lines are expected to be emitted as part of the afterglow of supernova explosions, because radioactive decay of freshly synthesised nuclei occurs. significant radioactive gamma ray line emission is expected from 56ni and 44ti decay on time scales of the initial explosion (56ni, τ ~days) and the young supernova remnant (44ti,τ ~90 years). less specific, and rather informative for the supernova population as a whole, are lessons from longer lived isotopes such as 26al and 60fe. from isotopes of elements heavier than iron group elements, any interesting gamma-ray line emission is too faint to be observable. measurements with space-based gamma-ray telescopes have obtained interesting gamma ray line emissions from two core collapse events, cas a and sn1987a, and one thermonuclear event, sn2014j. we discuss integral data from all above isotopes, including all line and continuum signatures from these two objects, and the surveys for more supernovae, that have been performed by gamma ray spectrometry. our objective here is to illustrate what can be learned from gamma-ray line emission properties about the explosions and their astrophysics. | gamma-ray line measurements from supernova explosions |
with the launch of jwst and the upcoming installation of extremely large telescopes, the first galaxies in our universe will finally be revealed. their light will be dominated by massive stars, which peak in in the ultra-violet (uv) part of the electromagnetic spectrum. star formation is the key driver of the evolution of our universe. at young ages, within 10 million years, both high and low mass stars generate complex uv emission processes which are poorly understood yet are vital for interpreting high red-shift line emission. for these reasons, the hubble space telescope (hst) will devote 1000 orbits to obtaining a uv legacy library of young stars as essential standards (ullyses). the purpose of this overview is to outline the basic physical principles driving uv emission processes from local (within 100 parsecs of) star formation, ranging from huge star-forming complexes containing hundreds of massive and very-massive stars (vms), such as 30 doradus (the tarantula nebula) in the neighboring magellanic clouds (only 50 kpc away), to galaxies near and far, out to the epoch of cosmic reionization. | star formation in the ultraviolet |
we present vlt/muse observations of ngc 2070, the dominant ionizing nebula of 30 doradus in the lmc, plus hst/stis spectroscopy of its central star cluster r136. integral field spectroscopy (muse) and pseudo ifs (stis) together provides a complete census of all massive stars within the central 30×30 parsec2 of the tarantula. we discuss the integrated far-uv spectrum of r136, of particular interest for uv studies of young extragalactic star clusters. strong he iiλ1640 emission at very early ages (1-2 myr) from very massive stars cannot be reproduced by current population synthesis models, even those incorporating binary evolution and very massive stars. a nebular analysis of the integrated muse dataset implies an age of ~4.5 myr for ngc 2070. wolf-rayet features provide alternative age diagnostics, with the primary contribution to the integrated wolf-rayet bumps arising from r140 rather than the more numerous h-rich wn stars in r136. caution should be used when interpreting spatially extended observations of extragalactic star-forming regions. | the tarantula nebula as a template for extragalactic star forming regions from vlt/muse and hst/stis |
the origin of dust in a galaxy is poorly understood. recently, surveys of the large magellanic cloud (lmc) have provided astrophysical laboratories for dust studies. using a method of population synthesis, we investigate the contributions of dust produced by asymptotic giant branch (agb) stars, common envelope (ce) ejecta and type ii supernovae (sne ii) to the total dust budget in the lmc. based on our models, the dust production rates (dprs) of agb stars in the lmc are between about 2.5 × 10-5 and 4.0 × 10-6 m⊙ yr-1. the uncertainty mainly results from different models for the dust yields of agb stars. the dprs of ce ejecta are about 6.3 × 10-6 (the initial binary fraction is 50 per cent). these results are within the large scatter of several observational estimates. agb stars mainly produce carbon grains, which is consistent with observations. most of the dust grains manufactured by ce ejecta are silicate and iron grains. the contributions of sne ii are very uncertain. compared with sne ii without reverse shock, the dprs of agb stars and ce ejecta are negligible. however, if only 2 per cent of dust grains produced by sne ii can survive after reverse shock, the contributions of sne ii are very small. the total dust masses produced by agb stars in the lmc are between 2.8 × 104 and 3.2 × 105 m⊙, and those produced by ce ejecta are about 6.3 × 104. they are much lower than the values estimated by observations. therefore, there should be other dust sources in the lmc. | a new dust budget in the large magellanic cloud |
spectral energy distribution (sed) fitting of stellar population synthesis models is an important and popular way to constrain the physical parameters—e.g., the ages, metallicities, masses for stellar population analysis. the previous works suggest that both blue-bands and red-bands photometry works for the sed-fitting. either blue-domained or red-domained sed-fitting usually lead to the unreliable or biased results. meanwhile, it seems that extending the wavelength coverage could be helpful. since the galaxy evolution explorer ( galex) and wide-field infrared survey explorer (wise) provide the fuv/nuv and mid-infrared w1/w2 band data, we extend the sed-fitting to a wider wavelength coverage. in our work, we analyzed the effect of adding the fuv/nuv and w1/w2 band to the optical and near-infrared ubvrijhk bands for the fitting with the (bruzual and charlot in mon. not. r. astron. soc. 344, 1000, 2003) (bc03) models and galev models. it is found that the fuv/nuv bands data affect the fitting results of both ages and metallicities much more significantly than that of the wise w1/w2 band with the bc03 models. while for the galev models, the effect of the wise w1/w2 band for the metallicity fitting seems comparable to that of galex fuv/nuv bands, but for age the effect of the w1/w2 band seems less crucial than that of the fuv/nuv bands. thus we conclude that the galex fuv/nuv bands are more crucial for the sed-fitting of ages and metallicities, than the other bands, and the high-quality uv data (with high photometry precision) are required. | the effects of the wise/ galex photometry for the sed-fitting with m31 star clusters and candidates |
the recent full sky large data surveys (e.g. gaia data release 2) represents a challenge for the galaxy modelling and requires new frameworks and tools to deal with huge amounts of data. we developed a new strategy to infer, all at once, the parameters describing the local star formation history (sfh), the initial mass function (imf) and the density laws of the galactic thin disc component by comparing synthetic versus observed colour-magnitude diagrams. the developed framework combines both the generation of besançon galaxy model fast approximate simulations (bgm fast; te{mor2018}) and approximate bayesian computation methods, to obtain a posterior probability distribution function of the inferred parameters. a robust mathematical development and the adequate codification, using apache spark and apache hadoop environments, make bgm fast about 10^4 times faster than the standard besançon galaxy model and specially suited to deal with huge data sets. from the analysis of tycho-2 colour-apparent magnitude diagrams we want to spotlight the resulting thin disc sfh with a decreasing trend and a present rate of star formation of 1.2 ± 0.2 m_⊙/yr. it is known that in the colour-apparent magnitude diagrams, as the distance of the star is not taken into account, the position of giants and main sequence stars are degenerated . additionally we estimate, using the besançon galaxy model, that the position of old stars (ages > 8 gyr) is mixed with stars with masses larger than 1.53 m_⊙. this lack of information of the intrinsic brightness of the stars is a clear handicap when aiming to derive the local imf and sfh from the population synthesis side. gaia parallaxes are very valuable to infer the intrinsic brightness of the stars and brake some of this degeneracies. gaia parallaxes, colours and magnitudes represents an unprecedented opportunity to constrain the imf and the sfh using bgm fast. | decoding the local star formation scenario with the besanc{c}on galaxy model |
the first stars in the universe (population iii) are thought to be responsible for synthesizing the first heavy elements, thereby creating the chemical conditions from which the second generation of stars has formed. one of the aims of current investigations is to better constrain the initial mass function of population iii stars from the observed abundance patterns of extremely metal poor stars, which is essential to model their influence on cosmic history. we present a set of predictions for the abundance ratios of carbon and europium yields, assuming different types of initial mass function, parametrized by the index , and the upper and lower mass cutoff. we will briefly discuss the parameter space that is consistent with the extremely metal poor stars known so far. | expected abundance patterns from the first generation of stars |
we model the evolution of massive magnetic stars in the galaxy using our own population synthesis code. a comparison of our model magnetic field distribution with that obtained from an analysis of measurements of magnetic fields shows that both model and real distributions can be approximated by a log-normal law with a mean log(b) = 2.5. based on this comparison we conclude that the magnetic flux variations of oba stars on the main sequence (ms) are very slow. the shape of the magnetic field distribution for o, b and a stars appeared to be similar. this means that the mechanisms of the generation of their magnetic field are probably identical. | evolution of magnetic field of massive stars |
the thermally pulsing asymptotic giant branch (tp-agb) phase is still the most uncertain phase among the main evolutionary phases of single stars, due to complicated processes involved, such as third dredge-up (3du) and mass loss. these processes significantly affect the lifetime, luminosity, colors and chemical yields of tp-agb stars. with hst high resolution imaging data from the panchromatic hubble andromeda treasury (phat) survey, tp-agb stars are resolved in m31. this enables us to study the color-magnitude diagram and luminosity functions of tp-agbs of different metallicity and mass within different environments (from the bulge to the disk) of m31. therefore, phat data provides strong constraints for tp-agb models. in this preliminary work, we calibrate tp-agb evolutionary tracks with phat data using stellar population synthesis approach. by adjusting the parameters regulating the third dredge-up occurrence and efficiency as well as the prescription of mass-loss in the model, we are able to satisfactorily reproduce the observed luminosity function (f160w) and color-magnitude diagram (f110w-f160w vs. f160w). | modelling tp-agb stars in m31 with phat data |
we present the first results from a new set of linear, radial, non-adiabatic pulsation models of long-period variables (lpvs), widely covering the space of stellar parameters corresponding to evolution along the asymptotic giant branch (agb). this coverage includes several values of metallicity and carbon-enhanced compositions consistent with the occurrence of repeated third dredge-up events. updated atomic and molecular opacity data were included consistently with chemical composition in order to produce realistic pulsation properties of both o-rich and c-rich variables. we combined the pulsation models with a stellar population synthesis tool in order to study the population of lpvs in the large magellanic cloud (lmc). we found the models to be reasonably good at reproducing the observed period-luminosity (pl) sequences, as well as the distribution of observed amplitudes. we provide a new interpretation of the pl sequences of lpvs that can bring into alignment previously discordant interpretations. | long-period variables in the large magellanic cloud |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.