Thermodynamic quantities for evolutionary and pulsational calculations

Stolzmann, W.; Blöcker, T.

doi:10.1007/3-540-59157-5_178

Cited by 12 publications

(14 citation statements)

References 10 publications

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“…At low temperatures, we use the latest release of the opacity tables by Ferguson et al (2005), completed for T ≥ 10000K by the OPAL opacities, in the version documented by Iglesias & Rogers (1996). The EOS adopted in most of the T − P plane is the latest release of the OPAL EOS 1 , overwritten in the pressure ionization regime by the EOS from Saumon et al (1995), and extended to the high-density, high temperature domain according to the treatment by Stolzmann & Blöcker (2000). The formal borders of the convective regions were found by means of the classic Schwartzschild criterium.…”

Section: The Aton Codementioning

confidence: 99%

Updated pre-main sequence tracks at low metallicities for 0.1 $\mathsf \le\ M/M _\odot\ \le 1.5$

Criscienzo¹,

Ventura²,

D’Antona³

2009

A&A

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Context. Young populations at Z < Z are being examined to understand the role of metallicity in the first phases of stellar evolution. For the analysis it is necessary to assign mass and age to Pre-Main Sequence (PMS) stars. While it is well known that the mass and age determination of PMS stars is strongly affected by the convection treatment, extending any calibration to metallicities different from solar is very artificial, in the absence of any calibrators for the convective parameters. For solar abundance, Mixing Length Theory models have been calibrated by using the results of 2D radiative-hydrodynamical models (MLT-α 2D ), that are very similar to those computed with non-grey ATLAS9 atmosphere boundary conditions and a full spectrum of turbulence (FST) convection model both in the atmosphere and in the interior (NEMO-FST models). Aims. While MLT-α 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-α 2D models also at smaller Z. Methods. 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.Results. We present PMS models for low mass stars from 0.1 to 1.5 M for metallicities [Fe/H] = −0.5, −1.0 and −2.0. The calculations include the most recent interior physics and the latest generation of non-grey atmosphere models. At fixed luminosity more metal poor isochrones are hotter than solar ones by Δ log T eff /Δ log Z ∼ 0.03−0.05 in the range in Z from 0.02 to 0.0002 and for ages from 10 5 to 10 7 yr.

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Section: The Aton Codementioning

confidence: 99%

Updated pre-main sequence tracks at low metallicities for 0.1 $\mathsf \le\ M/M _\odot\ \le 1.5$

Criscienzo¹,

Ventura²,

D’Antona³

2009

A&A

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“…Note that the regions of very high temperature and very low pressure are never used, and are filled up with simple formulations of the EOS, only to provide more convenient interpolation. The tables are filled up in three steps: first the thermodynamic quantities are computed according to the formulation by Stolzmann & Blöcker (1996, 2000) for fully ionized gas. This EOS allows one to consider explicitly different mixtures of elements.…”

Section: Modellingmentioning

confidence: 99%

85 Peg A: what age for a low-metallicity solar-like star?

D’Antona

Cardini

Mauro

et al. 2005

Monthly Notices of the Royal Astronomical Society

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We explore the possible evolutionary status of the primary component of the binary 85 Pegasi, listed as a target for asteroseismic observations by the MOST satellite. In spite of the assessed ‘subdwarf’ status, and of the accurate distance determination from the Hipparcos data, the uncertainties in the metallicity and age, coupled with the uncertainty in the theoretical models, lead to a range of predictions on the oscillation frequency spectrum. Nevertheless, the determination of the ratio between the small separation in frequency modes, and the large separation as suggested by Roxburgh, provides a very good measure of the star age, quite independent of the metallicity in the assumed uncertainty range. In this range, the constraint on the dynamical mass and the further constraint provided by the assumption that the maximum age is 14 Gyr limits the mass of 85 Peg A to the range from 0.75 to 0.82 M⊙. This difference of a few hundredths of a solar mass leads to well detectable differences both in the evolutionary stage (age) and in the asteroseismic properties. We show that the age determination which will be possible through the asteroseismic measurements for this star is independent either of the convection model adopted or the microscopic metal diffusion. The latter conclusion is strengthened by the fact that, although metal diffusion is still described in an approximate way, recent observations suggest that real stars suffer a smaller metal sedimentation compared with the models.

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“…When this occurs, the ionic contribution to the specific heat decreases as T 3 , thus depleting the main thermal reservoir of the star: it is called Debye cooling phase. For this term we adopted the analytical expression described by Stolzmann & Blocker (2000), which is based on the free energy of a Coulomb crystal studied by Chabrier, Ashcroft, & De Witt (1992). The various thermodynamic quantities for pure carbon and pure oxygen have been obtained by analytically deriving the corresponding free energy.…”

Section: Equation Of Statementioning

confidence: 99%

Calibration of White Dwarf Cooling Sequences: Theoretical Uncertainty

Moroni

Straniero

2002

ApJ

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White Dwarf luminosities are powerful age indicators, whose calibration should be based on reliable models. We discuss the uncertainty of some chemical and physical parameters and their influence on the age estimated by means of white dwarf cooling sequences. Models at the beginning of the white dwarf sequence have been obtained on the base of progenitor evolutionary tracks computed starting from the zero age horizontal branch and for a typical halo chemical composition (Z=0.0001, Y=0.23). The uncertainties due to nuclear reaction rates, convection, mass loss and initial chemical composition are discussed. Then, various cooling sequences for a typical white dwarf mass (M=0.6 M ⊙ ) have been calculated under different assumptions on some input physics, namely: conductive opacity, contribution of the ion-electron interaction to the free energy and microscopic diffusion. Finally we present the evolution of white dwarfs having mass ranging between 0.5 and 0.9 M ⊙ . Much effort has been spent to extend the equation of state down to the low temperature and high density regime. An analysis of the latest improvement in the physics of white dwarf interiors is presented. We conclude that at the faint end of the cooling sequence (logL/L ⊙ ∼ −5.5) the present overall uncertainty on the age is of the order of 20%, which correspond to about 3 Gyr. We suggest that this uncertainty could be substantially reduced by improving our knowledge of the conductive opacity (especially in the partially degenerate regime) and by fixing the internal stratification of C and O.

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Thermodynamic quantities for evolutionary and pulsational calculations

Cited by 12 publications

References 10 publications

Updated pre-main sequence tracks at low metallicities for 0.1 $\mathsf \le\ M/M _\odot\ \le 1.5$

Updated pre-main sequence tracks at low metallicities for 0.1 $\mathsf \le\ M/M _\odot\ \le 1.5$

85 Peg A: what age for a low-metallicity solar-like star?

Calibration of White Dwarf Cooling Sequences: Theoretical Uncertainty

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