[Paper Review] Stellar mass and age determinations - I. Grids of stellar models from Z=0.006 to 0.04 and M=0.5 to 3.5 Msun

N. Mowlavï, P. Eggenberger+6 more|arXiv (Cornell University)|Jan 17, 2012

Stellar, planetary, and galactic studiesPhysics and Astronomy1 references75 citations

TL;DR

This paper presents dense, high-precision grids of non-rotating stellar evolution models for masses 0.5–3.5 M⊙ and metallicities Z = 0.006 to 0.04 (corresponding to [Fe/H] = −0.33 to +0.54), with advanced interpolation techniques enabling accurate determination of stellar mass and age from observed Hertzsprung-Russell diagram positions. The key contribution is a 1% accuracy in radius and effective temperature for interpolated models, validated against detached binaries and open clusters, with new iso-surface metallicity (Z_surf) lines accounting for atomic diffusion effects in low-mass stars.

ABSTRACT

We present dense grids of stellar models suitable for comparison with observable quantities measured with great precision, such as those derived from binary systems or planet-hosting stars. We computed new Geneva models without rotation at metallicities Z=0.006, 0.01, 0.014, 0.02, 0.03 and 0.04 (i.e. [Fe/H] from -0.33 to +0.54) and with mass in small steps from 0.5 to 3.5 Msun. Great care was taken in the procedure for interpolating between tracks in order to compute isochrones. Several properties of our grids are presented as a function of stellar mass and metallicity. Those include surface properties in the Hertzsprung-Russell diagram, internal properties including mean stellar density, sizes of the convective cores, and global asteroseismic properties. We checked our interpolation procedure and compared interpolated tracks with computed tracks. The deviations are less than 1% in radius and effective temperatures for most of the cases considered. We also checked that the present isochrones provide nice fits to four couples of observed detached binaries and to the observed sequences of the open clusters NGC 3532 and M67. Including atomic diffusion in our models with M<1.1 Msun leads to variations in the surface abundances that should be taken into account when comparing with observational data of stars with measured metallicities. For that purpose, iso-Zsurf lines are computed. These can be requested for download from a dedicated web page together with tracks at masses and metallicities within the limits covered by the grids. The validity of the relations linking Z and FeH is also re-assessed in light of the surface abundance variations in low-mass stars.

Motivation & Objective

• To provide dense, high-precision stellar evolution models for accurate stellar mass and age determination from modern high-precision observations.
• To address the limitations of previous model grids by improving interpolation accuracy across mass and metallicity in the 0.5–3.5 M⊙ range.
• To account for atomic diffusion effects in low-mass stars (M < 1.1 M⊙), which alter surface abundances and affect metallicity indicators.
• To construct reliable isochrones and interpolated tracks using a robust interpolation procedure that preserves morphological features across mass and metallicity.
• To provide downloadable data, including tracks, isochrones, and iso-Z_surf lines, for direct use in observational comparisons.

Proposed method

• Computation of non-rotating Geneva stellar evolution models using updated input physics, including Asplund et al. (2005) solar abundances and atomic diffusion for M < 1.1 M⊙.
• Use of a dense grid in mass (0.5–3.5 M⊙ in small steps) and metallicity (Z = 0.006, 0.01, 0.014, 0.02, 0.03, 0.04) to enable high-accuracy interpolation.
• Development of a specialized interpolation procedure between evolutionary tracks to maintain accuracy in radius and effective temperature, with deviations <1%.
• Construction of isochrones via interpolation across the mass-metallicity grid, validated against observed detached binaries and open clusters (NGC 3532, M67).
• Computation of iso-surface metallicity (Z_surf) lines to account for surface abundance changes due to atomic diffusion, especially in low-mass stars.
• Use of asteroseismic parameters (ν_max, Δν, A_max) to enhance model comparison with observational data.

Experimental results

Research questions

• RQ1 How accurately can interpolated stellar models predict radius and effective temperature across a dense mass-metallicity grid?
• RQ2 To what extent do atomic diffusion effects alter surface abundances in low-mass stars (M < 1.1 M⊙), and how does this affect metallicity indicators?
• RQ3 Can the new interpolation method produce isochrones that accurately fit observed detached binary systems and open cluster sequences?
• RQ4 How do the relations between Z and [Fe/H] break down in low-mass stars due to surface abundance variations from atomic diffusion?
• RQ5 What is the impact of numerical treatment of convection on the morphology of isochrones, particularly in the 1.15–1.25 M⊙ transition mass range?

Key findings

• The interpolation procedure achieves deviations of less than 1% in radius and effective temperature for most interpolated models, validating its high accuracy.
• The isochrones constructed from the grids provide excellent fits to observed detached binary systems and to the sequences of open clusters NGC 3532 and M67.
• Atomic diffusion in stars with M < 1.1 M⊙ causes measurable surface abundance changes, necessitating the use of iso-Z_surf lines for accurate metallicity comparisons.
• The relation between Z and [Fe/H] becomes inaccurate to within about 5% in low-mass stars due to surface abundance variations from atomic diffusion.
• In the transition mass range 1.15–1.25 M⊙ at solar metallicity, isochrones may display more than two hooks due to convective core development, with morphology sensitive to convection treatment.
• The model grids and associated data products (tracks, isochrones, iso-Z_surf lines) are available for download at http://obswww.unige.ch/Recherche/evol/-Base-de-donnees-.