The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
E Baron - One of the best experts on this subject based on the ideXlab platform.
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the dartmouth Stellar Evolution database
Astrophysical Journal Supplement Series, 2008Co-Authors: Aaron Dotter, Brian Chaboyer, D Jevremovic, Veselin Kostov, E Baron, Jason W FergusonAbstract:The ever-expanding depth and quality of photometric and spectroscopic observations of Stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar Evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved Stellar populations. The Dartmouth Stellar Evolution Database is a collection of Stellar Evolution tracks and isochrones that spans a range of [Fe/H] from –2.5 to +0.5, [α/Fe] from –0.2 to +0.8 (for [Fe/H] ≤ 0) or +0.2 (for [Fe/H] > 0), and initial He mass fractions from Y = 0.245 to 0.40. Stellar Evolution tracks were computed for masses between 0.1 and 4 M☉, allowing isochrones to be generated for ages as young as 250 Myr. For the range in masses where the core He flash occurs, separate He-burning tracks were computed starting from the zero age horizontal branch. The tracks and isochrones have been transformed to the observational plane in a variety of photometric systems including standard UBV(RI)C, Stromgren uvby, SDSS ugriz, 2MASS JHKs, and HST ACS/WFC and WFPC2. The Dartmouth Stellar Evolution Database is accessible through a Web site at http://Stellar.dartmouth.edu/~models/ where all tracks, isochrones, and additional files can be downloaded.
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the dartmouth Stellar Evolution database
arXiv: Astrophysics, 2008Co-Authors: Aaron Dotter, Brian Chaboyer, D Jevremovic, Veselin Kostov, E Baron, Jason W FergusonAbstract:The ever-expanding depth and quality of photometric and spectroscopic observations of Stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar Evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved Stellar populations. The Dartmouth Stellar Evolution Database is a collection of Stellar Evolution tracks and isochrones that spans a range of [Fe/H] from -2.5 to +0.5, [alpha/Fe] from -0.2 to +0.8 (for [Fe/H] 0), and initial He mass fractions from Y=0.245 to 0.40. Stellar Evolution tracks were computed for masses between 0.1 and 4 Msun, allowing isochrones to be generated for ages as young as 250 Myr. For the range in masses where the core He flash occurs, separate He-burning tracks were computed starting from the zero age horizontal branch. The tracks and isochrones have been transformed to the observational plane in a variety of photometric systems including standard UBV(RI)c, Stromgren uvby, SDSS ugriz, 2MASS JHKs, and HST ACS-WFC and WFPC2. The Dartmouth Stellar Evolution Database is accessible through a website at this http URL where all tracks, isochrones, and additional files can be downloaded.
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the acs survey of galactic globular clusters ii Stellar Evolution tracks isochrones luminosity functions and synthetic horizontal branch models
arXiv: Astrophysics, 2007Co-Authors: Aaron Dotter, Brian Chaboyer, D Jevremovic, E Baron, Jason W Ferguson, Ata Sarajedini, Jay AndersonAbstract:The ACS Survey of Galactic Globular Clusters, an HST Treasury Project, will deliver high quality, homogeneous photometry of 65 globular clusters. This paper introduces a new collection of Stellar Evolution tracks and isochrones suitable for analyzing the ACS Survey data. Stellar Evolution models were computed at [Fe/H]= -2.5, -2.0, -1.5, -1.0, -0.5, and 0; [alpha/Fe]= -0.2, 0, 0.2, 0.4, 0.6, and 0.8; and three initial He abundances for masses from 0.1 to 1.8 Msun and ages from 2 to 15 Gyr. Each isochrone spans a wide range in luminosity from Mv~14 up to the tip of the red giant branch. These are complemented by a set of He-burning tracks that extend from the zero age horizontal branch to the onset of thermal pulsations on the asymptotic giant branch. In addition, a set of computer programs are provided that make it possible to interpolate the isochrones in [Fe/H], generate luminosity functions from the isochrones, and create synthetic horizontal branch models. The tracks and isochrones have been converted to the observational plane with two different color-Teff transformations, one synthetic and one semi-empirical, in ground-based B, V, and I, and F606W and F814W for both ACS-WFC and WFPC2 systems. All models and programs presented in this paper are available from this http URL
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the acs survey of galactic globular clusters ii Stellar Evolution tracks isochrones luminosity functions and synthetic horizontal branch models
The Astronomical Journal, 2007Co-Authors: Aaron Dotter, Brian Chaboyer, D Jevremovic, E Baron, Jason W Ferguson, Ata Sarajedini, Jay AndersonAbstract:The ACS Survey of Galactic Globular Clusters, an HST Treasury Project, will deliver high-quality, homogeneous photometry of 65 globular clusters. This paper introduces a new collection of Stellar Evolution tracks and isochrones suitable for analyzing the ACS survey data. Stellar Evolution models were computed at [Fe/H] = -2.5, -2.0, -1.5, -1.0, -0.5, and 0; [α/Fe] = -0.2, 0, 0.2, 0.4, 0.6, and 0.8; and three initial He abundances for masses from 0.1 to 1.8 M⊙ and ages from 2 to 15 Gyr. Each isochrone spans a wide range in luminosity, from MV ~ 14 up to the tip of the red giant branch. These are complemented by a set of He-burning tracks that extend from the zero-age horizontal branch to the onset of thermal pulsations on the asymptotic giant branch. In addition, a set of computer programs are provided that make it possible to interpolate the isochrones in [Fe/H], generate luminosity functions from the isochrones, and create synthetic horizontal-branch models. The tracks and isochrones have been converted to the observational plane with two different color-Teff transformations, one synthetic and one semiempirical, in ground-based B, V, and I, and F606W and F814W for both ACS WFC and WFPC2 systems. All models and programs presented in this paper are available at the Dartmouth Stellar Evolution Database and the Multimission Archive at the Space Telescope Science Institute.
F Castelli - One of the best experts on this subject based on the ideXlab platform.
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a large Stellar Evolution database for population synthesis studies ii Stellar models and isochrones for an α enhanced metal distribution
The Astrophysical Journal, 2006Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large, new set of Stellar Evolution models and isochrones for an α-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our Stellar model library for a scaled-solar metal distribution already presented by Pietrinferni et al. The effect of the α-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state, and for the first time in the bolometric corrections and color transformations. This allows us to avoid the inconsistent use—common to all α-enhanced model libraries currently available—of scaled-solar bolometric corrections and color transformations for α-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U, B portion of Stellar spectra for Teff ≤ 6500 K are significantly affected by the metal mixture, especially at the higher metallicities. Our models cover both an extended mass range (between 0.5 and 10 M☉, with a fine mass spacing) and a broad metallicity range, including 11 values of the metal mass fraction Z, corresponding to the range -2.6 ≤ [Fe/H] ≤ 0.05. The initial He mass fraction is Y = 0.245 for the most metal-poor models, and it increases with Z, according to ΔY/ΔZ = 1.4. Models with and without the inclusion of overshoot from the convective cores during the central H-burning phase are provided, as well as models with different mass loss efficiencies. We also provide complete sets of Evolutionary models for low-mass, He-burning Stellar structures cover the whole metallicity range. This database, used in combination with our scaled-solar model library, is a valuable tool for investigating both Galactic and extragalactic simple and composite Stellar populations, using Stellar population synthesis techniques.
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a large Stellar Evolution database for population synthesis studies ii Stellar models and isochrones for an alpha enhanced metal distribution
arXiv: Astrophysics, 2006Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:[Abridged] We present a large, new set of Stellar Evolution models and isochrones for an alpha-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our Stellar model library for a distribution already presented in Pietrinferni et al.(2004). The effect of the alpha-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state and, for the first time, the bolometric corrections, and color transformations. This allows us to avoid the inconsistent use - common to all alpha-enhanced model libraries currently available - of scaled-solar bolometric corrections and color transformations for alpha-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U,B portion of Stellar spectra for T_{eff}<=6500K, are significantly affected by the metal mixture, especially at the higher metallicities. We also provide complete sets of Evolutionary models for low-mass, He-burning Stellar structures covering the whole metallicity range, to enable synthetic horizontal branch simulations. We compare our database with several widely used Stellar model libraries from different authors, as well as with various observed color magnitude and color-color diagrams (Johnson-Cousins BVI and near infrared magnitudes, Stromgren colors) of Galactic field stars and globular clusters. We also test our isochrones comparing integrated optical colors and Surface Brightness Fluctuation magnitudes with selected globular cluster data. We find a general satisfactory agreement with the empirical constraints.
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a large Stellar Evolution database for population synthesis studies i scaled solar models and isochrones
The Astrophysical Journal, 2004Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large and updated Stellar Evolution database for low-, intermediate-, and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite Stellar populations using population synthesis techniques. The Stellar mass range is between � 0.5 and 10 Mwith a fine mass spacing. The metallicity (Fe/H) comprises 10 values ranging from � 2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y ¼ 0:245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Y =Z � 1:4. For each adopted chemical composition, the Evolutionary models have been computed without (canonical models) and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. Semiconvection is included in the treatment of core convection during the He-burning phase. The whole set of Evolutionary models can be used to compute isochrones in a wide age range, from � 30 Myr to � 15 Gyr. Both Evolutionary models and isochrones are available in several observational planes, employing an updated set of bolometric corrections and color-TeA relations computed for this project. The number of points along the models and the resulting isochrones is selected in such a way that interpolation for intermediate metallicities not contained in the grid is straightforward; a simple quadratic interpolation produces results of sufficient accuracy for population synthesis applications.We compare our isochrones with results from a series of widely used Stellar Evolution databases and perform some empirical tests for the reliability of our models. Since this work is devoted to scaled solar chemical compositions, we focus our attention on the Galactic disk Stellar populations, employing multicolor photometry of unevolved field main-sequence stars with precise Hipparcos parallaxes, well-studied open clusters, and one eclipsing binary system with precise measurements of masses, radii, and (Fe/H) of both components. We find that the predicted metallicity dependence of the location of the lower, unevolved main sequence in the color magnitude diagram (CMD) appears in satisfactory agreement with empirical data. When comparing our models with CMDs of selected, well-studied, open clusters, once again we were able to properly match the whole observed Evolutionary sequences by assuming cluster distance and reddening estimates in satisfactory agreement with empirical evaluations of these quantities. In general, models including overshooting during the H-burning phase provide a better match to the observations, at least for ages below � 4 Gyr. At (Fe/H) around solar and higher ages (i.e., smaller convective cores) before the onset of radiative cores, the selected efficiency of core overshooting may be too high in our model, as well as in various other models in the literature. Since we also provide canonical models, the reader is strongly encouraged to always compare the results from both sets in this critical age range. Subject heading gs: galaxies: Stellar content — Galaxy: disk — open clusters and associations: general — stars: Evolution — stars: horizontal-branch
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a large Stellar Evolution database for population synthesis studies i scaled solar models and isochrones
arXiv: Astrophysics, 2004Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large and updated Stellar Evolution database for low-, intermediate- and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite Stellar populations using population synthesis techniques. The Stellar mass range is between \sim0.5Mo and 10Mo with a fine mass spacing. The metallicity [Fe/H] comprises 10 values ranging from -2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y=0.245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Delta Y/Delta Z\sim 1.4. For each adopted chemical composition, the Evolutionary models have been computed without and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. The whole set of Evolutionary models can be used to compute isochrones in a wide age range, from \sim30 Myr to \sim15Gyr. Both Evolutionary tracks and isochrones are available in several observational planes, employing updated set of bolometric corrections and color-Te relations computed for this project. The number of points along the models and the resulting isochrones is selected in such a way that interpolation for intermediate metallicities not contained in the grid is straightforward. We compare our isochrones with results from different Stellar Evolution databases and perform some empirical tests for the reliability of our models. Since this work is devoted to scaled solar compositions, we focus our attention on the Galactic disk populations, employing multicolor photometry of unevolved field MS stars with precise Hipparcos parallaxes, well-studied open clusters and one eclipsing binary system with precise measurements of masses, radii and [Fe/H] of both components.
S Cassisi - One of the best experts on this subject based on the ideXlab platform.
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updated electron conduction opacities the impact on low mass Stellar models
The Astrophysical Journal, 2007Co-Authors: S Cassisi, A Y Potekhin, A Pietrinferni, M Catelan, M SalarisAbstract:We review the theory of electron-conduction opacity, a fundamental ingredient in the computation of low-mass Stellar models; shortcomings and limitations of the existing calculations used in Stellar Evolution are discussed. We then present new determinations of the electron-conduction opacity in Stellar conditions for an arbitrary chemical composition that improve over previous works and, most importantly, cover the whole parameter space relevant to Stellar Evolution models (i.e., both the regime of partial and high electron degeneracy). A detailed comparison with the currently used tabulations is also performed. The impact of our new opacities on the Evolution of low-mass stars is assessed by computing Stellar models along both the H- and He-burning Evolutionary phases, as well as main sequence models of very low-mass stars and white dwarf cooling tracks.
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a large Stellar Evolution database for population synthesis studies ii Stellar models and isochrones for an α enhanced metal distribution
The Astrophysical Journal, 2006Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large, new set of Stellar Evolution models and isochrones for an α-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our Stellar model library for a scaled-solar metal distribution already presented by Pietrinferni et al. The effect of the α-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state, and for the first time in the bolometric corrections and color transformations. This allows us to avoid the inconsistent use—common to all α-enhanced model libraries currently available—of scaled-solar bolometric corrections and color transformations for α-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U, B portion of Stellar spectra for Teff ≤ 6500 K are significantly affected by the metal mixture, especially at the higher metallicities. Our models cover both an extended mass range (between 0.5 and 10 M☉, with a fine mass spacing) and a broad metallicity range, including 11 values of the metal mass fraction Z, corresponding to the range -2.6 ≤ [Fe/H] ≤ 0.05. The initial He mass fraction is Y = 0.245 for the most metal-poor models, and it increases with Z, according to ΔY/ΔZ = 1.4. Models with and without the inclusion of overshoot from the convective cores during the central H-burning phase are provided, as well as models with different mass loss efficiencies. We also provide complete sets of Evolutionary models for low-mass, He-burning Stellar structures cover the whole metallicity range. This database, used in combination with our scaled-solar model library, is a valuable tool for investigating both Galactic and extragalactic simple and composite Stellar populations, using Stellar population synthesis techniques.
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a large Stellar Evolution database for population synthesis studies ii Stellar models and isochrones for an alpha enhanced metal distribution
arXiv: Astrophysics, 2006Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:[Abridged] We present a large, new set of Stellar Evolution models and isochrones for an alpha-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our Stellar model library for a distribution already presented in Pietrinferni et al.(2004). The effect of the alpha-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state and, for the first time, the bolometric corrections, and color transformations. This allows us to avoid the inconsistent use - common to all alpha-enhanced model libraries currently available - of scaled-solar bolometric corrections and color transformations for alpha-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U,B portion of Stellar spectra for T_{eff}<=6500K, are significantly affected by the metal mixture, especially at the higher metallicities. We also provide complete sets of Evolutionary models for low-mass, He-burning Stellar structures covering the whole metallicity range, to enable synthetic horizontal branch simulations. We compare our database with several widely used Stellar model libraries from different authors, as well as with various observed color magnitude and color-color diagrams (Johnson-Cousins BVI and near infrared magnitudes, Stromgren colors) of Galactic field stars and globular clusters. We also test our isochrones comparing integrated optical colors and Surface Brightness Fluctuation magnitudes with selected globular cluster data. We find a general satisfactory agreement with the empirical constraints.
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a large Stellar Evolution database for population synthesis studies i scaled solar models and isochrones
The Astrophysical Journal, 2004Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large and updated Stellar Evolution database for low-, intermediate-, and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite Stellar populations using population synthesis techniques. The Stellar mass range is between � 0.5 and 10 Mwith a fine mass spacing. The metallicity (Fe/H) comprises 10 values ranging from � 2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y ¼ 0:245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Y =Z � 1:4. For each adopted chemical composition, the Evolutionary models have been computed without (canonical models) and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. Semiconvection is included in the treatment of core convection during the He-burning phase. The whole set of Evolutionary models can be used to compute isochrones in a wide age range, from � 30 Myr to � 15 Gyr. Both Evolutionary models and isochrones are available in several observational planes, employing an updated set of bolometric corrections and color-TeA relations computed for this project. The number of points along the models and the resulting isochrones is selected in such a way that interpolation for intermediate metallicities not contained in the grid is straightforward; a simple quadratic interpolation produces results of sufficient accuracy for population synthesis applications.We compare our isochrones with results from a series of widely used Stellar Evolution databases and perform some empirical tests for the reliability of our models. Since this work is devoted to scaled solar chemical compositions, we focus our attention on the Galactic disk Stellar populations, employing multicolor photometry of unevolved field main-sequence stars with precise Hipparcos parallaxes, well-studied open clusters, and one eclipsing binary system with precise measurements of masses, radii, and (Fe/H) of both components. We find that the predicted metallicity dependence of the location of the lower, unevolved main sequence in the color magnitude diagram (CMD) appears in satisfactory agreement with empirical data. When comparing our models with CMDs of selected, well-studied, open clusters, once again we were able to properly match the whole observed Evolutionary sequences by assuming cluster distance and reddening estimates in satisfactory agreement with empirical evaluations of these quantities. In general, models including overshooting during the H-burning phase provide a better match to the observations, at least for ages below � 4 Gyr. At (Fe/H) around solar and higher ages (i.e., smaller convective cores) before the onset of radiative cores, the selected efficiency of core overshooting may be too high in our model, as well as in various other models in the literature. Since we also provide canonical models, the reader is strongly encouraged to always compare the results from both sets in this critical age range. Subject heading gs: galaxies: Stellar content — Galaxy: disk — open clusters and associations: general — stars: Evolution — stars: horizontal-branch
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a large Stellar Evolution database for population synthesis studies i scaled solar models and isochrones
arXiv: Astrophysics, 2004Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large and updated Stellar Evolution database for low-, intermediate- and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite Stellar populations using population synthesis techniques. The Stellar mass range is between \sim0.5Mo and 10Mo with a fine mass spacing. The metallicity [Fe/H] comprises 10 values ranging from -2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y=0.245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Delta Y/Delta Z\sim 1.4. For each adopted chemical composition, the Evolutionary models have been computed without and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. The whole set of Evolutionary models can be used to compute isochrones in a wide age range, from \sim30 Myr to \sim15Gyr. Both Evolutionary tracks and isochrones are available in several observational planes, employing updated set of bolometric corrections and color-Te relations computed for this project. The number of points along the models and the resulting isochrones is selected in such a way that interpolation for intermediate metallicities not contained in the grid is straightforward. We compare our isochrones with results from different Stellar Evolution databases and perform some empirical tests for the reliability of our models. Since this work is devoted to scaled solar compositions, we focus our attention on the Galactic disk populations, employing multicolor photometry of unevolved field MS stars with precise Hipparcos parallaxes, well-studied open clusters and one eclipsing binary system with precise measurements of masses, radii and [Fe/H] of both components.
A Pietrinferni - One of the best experts on this subject based on the ideXlab platform.
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a large Stellar Evolution database for population synthesis studies ii Stellar models and isochrones for an α enhanced metal distribution
The Astrophysical Journal, 2006Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large, new set of Stellar Evolution models and isochrones for an α-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our Stellar model library for a scaled-solar metal distribution already presented by Pietrinferni et al. The effect of the α-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state, and for the first time in the bolometric corrections and color transformations. This allows us to avoid the inconsistent use—common to all α-enhanced model libraries currently available—of scaled-solar bolometric corrections and color transformations for α-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U, B portion of Stellar spectra for Teff ≤ 6500 K are significantly affected by the metal mixture, especially at the higher metallicities. Our models cover both an extended mass range (between 0.5 and 10 M☉, with a fine mass spacing) and a broad metallicity range, including 11 values of the metal mass fraction Z, corresponding to the range -2.6 ≤ [Fe/H] ≤ 0.05. The initial He mass fraction is Y = 0.245 for the most metal-poor models, and it increases with Z, according to ΔY/ΔZ = 1.4. Models with and without the inclusion of overshoot from the convective cores during the central H-burning phase are provided, as well as models with different mass loss efficiencies. We also provide complete sets of Evolutionary models for low-mass, He-burning Stellar structures cover the whole metallicity range. This database, used in combination with our scaled-solar model library, is a valuable tool for investigating both Galactic and extragalactic simple and composite Stellar populations, using Stellar population synthesis techniques.
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a large Stellar Evolution database for population synthesis studies ii Stellar models and isochrones for an alpha enhanced metal distribution
arXiv: Astrophysics, 2006Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:[Abridged] We present a large, new set of Stellar Evolution models and isochrones for an alpha-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our Stellar model library for a distribution already presented in Pietrinferni et al.(2004). The effect of the alpha-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state and, for the first time, the bolometric corrections, and color transformations. This allows us to avoid the inconsistent use - common to all alpha-enhanced model libraries currently available - of scaled-solar bolometric corrections and color transformations for alpha-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U,B portion of Stellar spectra for T_{eff}<=6500K, are significantly affected by the metal mixture, especially at the higher metallicities. We also provide complete sets of Evolutionary models for low-mass, He-burning Stellar structures covering the whole metallicity range, to enable synthetic horizontal branch simulations. We compare our database with several widely used Stellar model libraries from different authors, as well as with various observed color magnitude and color-color diagrams (Johnson-Cousins BVI and near infrared magnitudes, Stromgren colors) of Galactic field stars and globular clusters. We also test our isochrones comparing integrated optical colors and Surface Brightness Fluctuation magnitudes with selected globular cluster data. We find a general satisfactory agreement with the empirical constraints.
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a large Stellar Evolution database for population synthesis studies i scaled solar models and isochrones
The Astrophysical Journal, 2004Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large and updated Stellar Evolution database for low-, intermediate-, and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite Stellar populations using population synthesis techniques. The Stellar mass range is between � 0.5 and 10 Mwith a fine mass spacing. The metallicity (Fe/H) comprises 10 values ranging from � 2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y ¼ 0:245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Y =Z � 1:4. For each adopted chemical composition, the Evolutionary models have been computed without (canonical models) and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. Semiconvection is included in the treatment of core convection during the He-burning phase. The whole set of Evolutionary models can be used to compute isochrones in a wide age range, from � 30 Myr to � 15 Gyr. Both Evolutionary models and isochrones are available in several observational planes, employing an updated set of bolometric corrections and color-TeA relations computed for this project. The number of points along the models and the resulting isochrones is selected in such a way that interpolation for intermediate metallicities not contained in the grid is straightforward; a simple quadratic interpolation produces results of sufficient accuracy for population synthesis applications.We compare our isochrones with results from a series of widely used Stellar Evolution databases and perform some empirical tests for the reliability of our models. Since this work is devoted to scaled solar chemical compositions, we focus our attention on the Galactic disk Stellar populations, employing multicolor photometry of unevolved field main-sequence stars with precise Hipparcos parallaxes, well-studied open clusters, and one eclipsing binary system with precise measurements of masses, radii, and (Fe/H) of both components. We find that the predicted metallicity dependence of the location of the lower, unevolved main sequence in the color magnitude diagram (CMD) appears in satisfactory agreement with empirical data. When comparing our models with CMDs of selected, well-studied, open clusters, once again we were able to properly match the whole observed Evolutionary sequences by assuming cluster distance and reddening estimates in satisfactory agreement with empirical evaluations of these quantities. In general, models including overshooting during the H-burning phase provide a better match to the observations, at least for ages below � 4 Gyr. At (Fe/H) around solar and higher ages (i.e., smaller convective cores) before the onset of radiative cores, the selected efficiency of core overshooting may be too high in our model, as well as in various other models in the literature. Since we also provide canonical models, the reader is strongly encouraged to always compare the results from both sets in this critical age range. Subject heading gs: galaxies: Stellar content — Galaxy: disk — open clusters and associations: general — stars: Evolution — stars: horizontal-branch
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a large Stellar Evolution database for population synthesis studies i scaled solar models and isochrones
arXiv: Astrophysics, 2004Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large and updated Stellar Evolution database for low-, intermediate- and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite Stellar populations using population synthesis techniques. The Stellar mass range is between \sim0.5Mo and 10Mo with a fine mass spacing. The metallicity [Fe/H] comprises 10 values ranging from -2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y=0.245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Delta Y/Delta Z\sim 1.4. For each adopted chemical composition, the Evolutionary models have been computed without and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. The whole set of Evolutionary models can be used to compute isochrones in a wide age range, from \sim30 Myr to \sim15Gyr. Both Evolutionary tracks and isochrones are available in several observational planes, employing updated set of bolometric corrections and color-Te relations computed for this project. The number of points along the models and the resulting isochrones is selected in such a way that interpolation for intermediate metallicities not contained in the grid is straightforward. We compare our isochrones with results from different Stellar Evolution databases and perform some empirical tests for the reliability of our models. Since this work is devoted to scaled solar compositions, we focus our attention on the Galactic disk populations, employing multicolor photometry of unevolved field MS stars with precise Hipparcos parallaxes, well-studied open clusters and one eclipsing binary system with precise measurements of masses, radii and [Fe/H] of both components.
M Salaris - One of the best experts on this subject based on the ideXlab platform.
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updated electron conduction opacities the impact on low mass Stellar models
The Astrophysical Journal, 2007Co-Authors: S Cassisi, A Y Potekhin, A Pietrinferni, M Catelan, M SalarisAbstract:We review the theory of electron-conduction opacity, a fundamental ingredient in the computation of low-mass Stellar models; shortcomings and limitations of the existing calculations used in Stellar Evolution are discussed. We then present new determinations of the electron-conduction opacity in Stellar conditions for an arbitrary chemical composition that improve over previous works and, most importantly, cover the whole parameter space relevant to Stellar Evolution models (i.e., both the regime of partial and high electron degeneracy). A detailed comparison with the currently used tabulations is also performed. The impact of our new opacities on the Evolution of low-mass stars is assessed by computing Stellar models along both the H- and He-burning Evolutionary phases, as well as main sequence models of very low-mass stars and white dwarf cooling tracks.
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a large Stellar Evolution database for population synthesis studies ii Stellar models and isochrones for an α enhanced metal distribution
The Astrophysical Journal, 2006Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large, new set of Stellar Evolution models and isochrones for an α-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our Stellar model library for a scaled-solar metal distribution already presented by Pietrinferni et al. The effect of the α-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state, and for the first time in the bolometric corrections and color transformations. This allows us to avoid the inconsistent use—common to all α-enhanced model libraries currently available—of scaled-solar bolometric corrections and color transformations for α-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U, B portion of Stellar spectra for Teff ≤ 6500 K are significantly affected by the metal mixture, especially at the higher metallicities. Our models cover both an extended mass range (between 0.5 and 10 M☉, with a fine mass spacing) and a broad metallicity range, including 11 values of the metal mass fraction Z, corresponding to the range -2.6 ≤ [Fe/H] ≤ 0.05. The initial He mass fraction is Y = 0.245 for the most metal-poor models, and it increases with Z, according to ΔY/ΔZ = 1.4. Models with and without the inclusion of overshoot from the convective cores during the central H-burning phase are provided, as well as models with different mass loss efficiencies. We also provide complete sets of Evolutionary models for low-mass, He-burning Stellar structures cover the whole metallicity range. This database, used in combination with our scaled-solar model library, is a valuable tool for investigating both Galactic and extragalactic simple and composite Stellar populations, using Stellar population synthesis techniques.
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a large Stellar Evolution database for population synthesis studies ii Stellar models and isochrones for an alpha enhanced metal distribution
arXiv: Astrophysics, 2006Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:[Abridged] We present a large, new set of Stellar Evolution models and isochrones for an alpha-enhanced metal distribution typical of Galactic halo and bulge stars; it represents a homogeneous extension of our Stellar model library for a distribution already presented in Pietrinferni et al.(2004). The effect of the alpha-element enhancement has been properly taken into account in the nuclear network, opacity, equation of state and, for the first time, the bolometric corrections, and color transformations. This allows us to avoid the inconsistent use - common to all alpha-enhanced model libraries currently available - of scaled-solar bolometric corrections and color transformations for alpha-enhanced models and isochrones. We show how bolometric corrections to magnitudes obtained for the U,B portion of Stellar spectra for T_{eff}<=6500K, are significantly affected by the metal mixture, especially at the higher metallicities. We also provide complete sets of Evolutionary models for low-mass, He-burning Stellar structures covering the whole metallicity range, to enable synthetic horizontal branch simulations. We compare our database with several widely used Stellar model libraries from different authors, as well as with various observed color magnitude and color-color diagrams (Johnson-Cousins BVI and near infrared magnitudes, Stromgren colors) of Galactic field stars and globular clusters. We also test our isochrones comparing integrated optical colors and Surface Brightness Fluctuation magnitudes with selected globular cluster data. We find a general satisfactory agreement with the empirical constraints.
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a large Stellar Evolution database for population synthesis studies i scaled solar models and isochrones
The Astrophysical Journal, 2004Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large and updated Stellar Evolution database for low-, intermediate-, and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite Stellar populations using population synthesis techniques. The Stellar mass range is between � 0.5 and 10 Mwith a fine mass spacing. The metallicity (Fe/H) comprises 10 values ranging from � 2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y ¼ 0:245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Y =Z � 1:4. For each adopted chemical composition, the Evolutionary models have been computed without (canonical models) and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. Semiconvection is included in the treatment of core convection during the He-burning phase. The whole set of Evolutionary models can be used to compute isochrones in a wide age range, from � 30 Myr to � 15 Gyr. Both Evolutionary models and isochrones are available in several observational planes, employing an updated set of bolometric corrections and color-TeA relations computed for this project. The number of points along the models and the resulting isochrones is selected in such a way that interpolation for intermediate metallicities not contained in the grid is straightforward; a simple quadratic interpolation produces results of sufficient accuracy for population synthesis applications.We compare our isochrones with results from a series of widely used Stellar Evolution databases and perform some empirical tests for the reliability of our models. Since this work is devoted to scaled solar chemical compositions, we focus our attention on the Galactic disk Stellar populations, employing multicolor photometry of unevolved field main-sequence stars with precise Hipparcos parallaxes, well-studied open clusters, and one eclipsing binary system with precise measurements of masses, radii, and (Fe/H) of both components. We find that the predicted metallicity dependence of the location of the lower, unevolved main sequence in the color magnitude diagram (CMD) appears in satisfactory agreement with empirical data. When comparing our models with CMDs of selected, well-studied, open clusters, once again we were able to properly match the whole observed Evolutionary sequences by assuming cluster distance and reddening estimates in satisfactory agreement with empirical evaluations of these quantities. In general, models including overshooting during the H-burning phase provide a better match to the observations, at least for ages below � 4 Gyr. At (Fe/H) around solar and higher ages (i.e., smaller convective cores) before the onset of radiative cores, the selected efficiency of core overshooting may be too high in our model, as well as in various other models in the literature. Since we also provide canonical models, the reader is strongly encouraged to always compare the results from both sets in this critical age range. Subject heading gs: galaxies: Stellar content — Galaxy: disk — open clusters and associations: general — stars: Evolution — stars: horizontal-branch
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a large Stellar Evolution database for population synthesis studies i scaled solar models and isochrones
arXiv: Astrophysics, 2004Co-Authors: A Pietrinferni, S Cassisi, M Salaris, F CastelliAbstract:We present a large and updated Stellar Evolution database for low-, intermediate- and high-mass stars in a wide metallicity range, suitable for studying Galactic and extragalactic simple and composite Stellar populations using population synthesis techniques. The Stellar mass range is between \sim0.5Mo and 10Mo with a fine mass spacing. The metallicity [Fe/H] comprises 10 values ranging from -2.27 to 0.40, with a scaled solar metal distribution. The initial He mass fraction ranges from Y=0.245, for the more metal-poor composition, up to 0.303 for the more metal-rich one, with Delta Y/Delta Z\sim 1.4. For each adopted chemical composition, the Evolutionary models have been computed without and with overshooting from the Schwarzschild boundary of the convective cores during the central H-burning phase. The whole set of Evolutionary models can be used to compute isochrones in a wide age range, from \sim30 Myr to \sim15Gyr. Both Evolutionary tracks and isochrones are available in several observational planes, employing updated set of bolometric corrections and color-Te relations computed for this project. The number of points along the models and the resulting isochrones is selected in such a way that interpolation for intermediate metallicities not contained in the grid is straightforward. We compare our isochrones with results from different Stellar Evolution databases and perform some empirical tests for the reliability of our models. Since this work is devoted to scaled solar compositions, we focus our attention on the Galactic disk populations, employing multicolor photometry of unevolved field MS stars with precise Hipparcos parallaxes, well-studied open clusters and one eclipsing binary system with precise measurements of masses, radii and [Fe/H] of both components.
