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Start Over Subject stellar evolutionary models Content Level Research
101. Pisa pre-main sequence tracks and isochrones
ID:
ivo://CDS.VizieR/J/A+A/533/A109
Title:
Pisa pre-main sequence tracks and isochrones
Short Name:
J/A+A/533/A109
Date:
21 Oct 2021
Publisher:
CDS
Description:
In recent years new observations of pre-main sequence stars (pre-MS) with Z<Z_{sun}_ have been made available. To take full advantage of the continuously growing amount of data of pre-MS stars in different environments, we need to develop updated pre-MS models for a wide range of metallicity to assign reliable ages and masses to the observed stars. We present updated evolutionary pre-MS models and isochrones for a fine grid of mass, age, metallicity, and helium values. We use a standard and well-tested stellar evolutionary code (i.e. FRANEC), that adopts outer boundary conditions from detailed and realistic atmosphere models. In this code, we incorporate additional improvements to the physical inputs related to the equation of state and the low temperature radiative opacities essential to computing low-mass stellar models. We make available via internet a large database of pre-MS tracks and isochrones for a wide range of chemical compositions (Z=0.0002-0.03), masses (M=0.2-7.0M_{sun}_), and ages (1-100Myr) for a solar-calibrated mixing length parameter alpha (i.e. 1.68). For each chemical composition, additional models were computed with two different mixing length values, namely alpha=1.2 and 1.9. Moreover, for Z>=0.008, we also provided models with two different initial deuterium abundances. The characteristics of the models have been discussed in detail and compared with other work in the literature. The main uncertainties affecting theoretical predictions have been critically discussed. Comparisons with selected data indicate that there is close agreement between theory and observation.
102. PMS tracks at low Z for 0.1<=M<=1.5
ID:
ivo://CDS.VizieR/J/A+A/496/223
Title:
PMS tracks at low Z for 0.1<=M<=1.5
Short Name:
J/A+A/496/223
Date:
21 Oct 2021
Publisher:
CDS
Description:
While MLT-alpha^2D^ models are not available for lower metallicities, we extend to lower Z the NEMO-FST models, under the hypothesis that in such a way we are simulating the results of MLT-alpha^2D^ models also at smaller Z. We use standard stellar computation techniques in which the atmospheric boundary conditions are derived making use of model atmosphere grids. This allows us to take into account the non greyness of the atmosphere, but adds a new parameter to the stellar structure uncertainty, namely the efficiency of convection in the atmospheric structure, if convection is computed in the atmospheric grid by a model different to the model adopted for the interior integration.
103. PopStar I: Evolutionary synthesis models
ID:
ivo://CDS.VizieR/J/MNRAS/398/451
Title:
PopStar I: Evolutionary synthesis models
Short Name:
J/MNRAS/398/451
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new evolutionary synthesis models for Simple Stellar Populations for a wide range of ages and metallicities. The models are based on the Padova isochrones. The core of the spectral library is provided by the medium resolution Lejeune et al. atmosphere models. These spectra are complemented by NLTE atmosphere models for hot stars that have an important impact in the stellar cluster's ionizing spectra: O, B and WR stellar spectra at the early ages, and spectra of post-AGB stars and planetary nebulae, at intermediate and old ages. At young ages, our models compare well with other existing models but we find that, the inclusion of the nebular continuum, not considered in several other models, reddens significantly the integrated colours of very young stellar populations. This is consistent with the results of spectral synthesis codes particularly devised for the study of starburst galaxies. At intermediate and old ages, the agreement with literature model is good and, in particular, we reproduce well the observed colours of star clusters in LMC. Given the ability to produce good integrated spectra from the far-UV to the infrared at any age, we consider that our models are particularly suited for the study of high redshift galaxies. These models are available on the web site http://www.fractal-es.com/SEDmod.htm and also through the Virtual Observatory Tools on the PopStar server.
104. PopStar II. Giant HII regions models
ID:
ivo://CDS.VizieR/J/MNRAS/403/2012
Title:
PopStar II. Giant HII regions models
Short Name:
J/MNRAS/403/2012
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the second paper of a series reporting the results from the popstar evolutionary synthesis models. Here, we present synthetic emission-line spectra of HII regions photoionized by young star clusters, for seven values of cluster masses and for ages between 0.1 and 5.2Myr. The ionizing spectral energy distributions (SEDs) are those obtained by the popstar code for six different metallicities, with a very low-metallicity set, Z=0.0001 , not included in previous similar works. We assume that the radius of the HII region is the distance at which the ionized gas is deposited by the action of the mechanical energy of the winds and supernovae from the central ionizing young cluster.
105. POPSTAR models. III. Young star clusters
ID:
ivo://CDS.VizieR/J/MNRAS/432/2746
Title:
POPSTAR models. III. Young star clusters
Short Name:
J/MNRAS/432/2746
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the third paper of a series reporting the results from the POPSTAR evolutionary synthesis models. The main goal of this work is to present and discuss the synthetic photometric properties of single stellar populations resulting from our POPSTAR code. Colours in the Johnson and Sloan Digital Sky Survey (SDSS) systems, H{alpha} and H{beta} luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicity (Z=0.0001-0.05) and age (0.1Myr to 20Gyr). We calculate the evolution of the cluster and the region geometry in a consistent manner. We demonstrate the importance of the contribution of emission lines to broader band photometry when characterizing stellar populations, through the presentation of both contaminated and non-contaminated colours (in both the Johnson and SDSS systems). The tabulated colours include stellar and nebular components, in addition to line emission. The main application of these models is the determination of physical properties of a given young ionizing cluster, when only photometric observations are available; for an isolated star-forming region, the young star cluster models can be used, free from the contamination of any underlying background stellar population. In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometric properties result from the combination of a young star-forming burst and the underlying older population of the host. Therefore, the second objective of this paper is to provide a grid of models useful in the interpretation of mixed regions where the separation of young and old populations is not sufficiently reliable. We describe the set of popstar spectral energy distributions (SEDs), and the derived colours for mixed populations where an underlying host population is combined in different mass-ratios with a recent ionizing burst. These colours, together with other common photometric parameters, such as the H{alpha} radius of the ionized region, and Balmer line equivalent widths and luminosities, allow one to infer the physical properties of star-forming regions even in the absence of spectroscopic information.
106. Population model of binary stars in the Galaxy
ID:
ivo://CDS.VizieR/J/AZh/79/738
Title:
Population model of binary stars in the Galaxy
Short Name:
J/AZh/79/738
Date:
21 Oct 2021
Publisher:
CDS
Description:
A comparative study of the population of the galactic binary stars is performed for two modes of star formation: star formation at a constant rate over 10^+10^yrs, and a burst of star formation that reprocesses the same mass of gas into stars over 10^+9^yrs. Estimates are presented for the star formation rates and populations of about 100 types of binaries and the products of their evolution.
107. Population synthesis in the blue. IV
ID:
ivo://CDS.VizieR/J/ApJS/171/146
Title:
Population synthesis in the blue. IV
Short Name:
J/ApJS/171/146
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new set of model predictions for 16 Lick absorption line indices from H{delta} through Fe5335 and UBV colors for single stellar populations with ages ranging between 1 and 15Gyr, [Fe/H] ranging from -1.3 to +0.3, and variable abundance ratios. The models are based on accurate stellar parameters for the Jones library stars and a new set of fitting functions describing the behavior of line indices as a function of effective temperature, surface gravity, and iron abundance. The abundances of several key elements in the library stars have been obtained from the literature in order to characterize the abundance pattern of the stellar library, thus allowing us to produce model predictions for any set of abundance ratios desired. We develop a method to estimate mean ages and abundances of iron, carbon, nitrogen, magnesium, and calcium that explores the sensitivity of the various indices modeled to those parameters. The models are compared to high-S/N data for Galactic clusters spanning the range of ages, metallicities, and abundance patterns of interest. Essentially all line indices are matched when the known cluster parameters are adopted as input. Comparing the models to high-quality data for galaxies in the nearby universe, we reproduce previous results regarding the enhancement of light elements and the spread in the mean luminosity-weighted ages of early-type galaxies.
108. Population Synthesis Models at very low metallicities
ID:
ivo://CDS.VizieR/VI/109
Title:
Population Synthesis Models at very low metallicities
Short Name:
VI/109
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using new sets of stellar evolution models at very low metallicities (Z=10^-7^; 10^-5^) and previously published grids we examine spectral properties of the ionising continua, the Lyman-break, and the Ly{alpha} and He1640 recombination lines in starbursts. The metallicity dependence of these properties, especially the transition from primordial galaxies (Population III) to currently observed metallicities, is examined for various IMFs and star formation histories.
109. Post-AGB and CSPNe evolutionary models
ID:
ivo://CDS.VizieR/J/A+A/588/A25
Title:
Post-AGB and CSPNe evolutionary models
Short Name:
J/A+A/588/A25
Date:
21 Oct 2021
Publisher:
CDS
Description:
The post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The two grids of models presently available are based on outdated micro- and macrophysics and do not agree with each other. Studies of the central stars of planetary nebulae (CSPNe) and post-AGB stars in different stellar populations point to significant discrepancies with the theoretical predictions of post-AGB models. We study the timescales of post-AGB and CSPNe in the context of our present understanding of the micro- and macrophysics of stars. We want to assess whether new post-AGB models, based on the latter improvements in TP-AGB modeling, can help us to understand the discrepancies between observation and theory and within theory itself. In addition, we aim to understand the impact of the previous AGB evolution for post-AGB phases. We computed a grid of post-AGB full evolutionary sequences that include all previous evolutionary stages from the zero age main sequence to the white dwarf phase. We computed models for initial masses between 0.8 and 4M_{sun}_ and for a wide range of initial metallicities (Z_0_= 0.02, 0.01, 0.001, 0.0001). This allowed us to provide post-AGB timescales and properties for H-burning post-AGB objects with masses in the relevant range for the formation of planetary nebulae (~0,5-0,8M_{sun}_). We included an updated treatment of the constitutive microphysics and included an updated description of the mixing processes and winds that play a key role during the thermal pulses (TP) on the AGB phase.
110. Post-AGB evolution
ID:
ivo://CDS.VizieR/J/ApJS/92/125
Title:
Post-AGB evolution
Short Name:
J/ApJS/92/125
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this paper, we present the results for the post-AGB phases of stellar evolutionary sequences, complete from the main-sequence phase, through the AGB phase, and on into the planetary nebula and white dwarf regimes. Mass loss has been included using an empirical formalism derived from observed mass-loss rates of planetary nebula nuclei available in the literature and from radiation-pressure-driven stellar wind theory. Models are calculated for initial masses 0.89, 0.95, 1.0, 1.5, 2.0, 2.5, 3.5, and 5.0M_{sun}_, and metallicities 0.016, 0.008, 0.004, and 0.001. These abundance and mass values were chosen to allow comparison with Galactic, and Magellanic Cloud planetary nebulae and their nuclei. The post-AGB evolutionary sequences fall into two distinct groups depending on when the planetary nebula nuclei leave the AGB: one group where helium-shell burning is dominant, and the other group where hydrogen-shell burning is dominant. Of the 27 computed sequences: 17 are hydrogen-burners, and 10 are helium-burners. In only five cases was any effort made to control the phase of departure from the AGB. Lower mass models are more likely to leave the AGB burning helium, as the preceding AGB evolution has a mass-loss rate which is greatest immediately prior to a helium-shell flash. The calculations are compared with the large observational database that has developed over recent years for the Large Magellanic Cloud. These calculations will be useful for determining the planetary nebula luminosity function, and for the study of the ultraviolet excess observed in elliptical galaxies.

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