Modelling the solar twin 18 Scorpii
Abstract
Context. Solar twins are objects of great interest in that they allow us to understand better how stellar evolution and structure are affected by variations of the stellar mass, age and chemical composition in the vicinity of the commonly accepted solar values.
Aims: We aim to use the existing spectrophotometric, interferometric and asteroseismic data for the solar twin 18 Sco to constrain stellar evolution models. 18 Sco is the brightest solar twin and is a good benchmark for the study of solar twins. The goal is to obtain realistic estimates of its physical characteristics (mass, age, initial chemical composition, mixinglength parameter) and realistic associated uncertainties using stellar models.
Methods: We set up a Bayesian model that relates the statistical properties of the data to the probability density of the stellar parameters. Special care is given to the modelling of the likelihood for the seismic data, using Gaussian mixture models. The probability densities of the stellar parameters are approximated numerically using an adaptive MCMC algorithm. From these approximate distributions we proceeded to a statistical analysis. We also performed the same exercise using local optimisation.
Results: The precision on the mass is approximately 6%. The precision reached on X_{0} and Z_{0} and the mixinglength parameter are respectively 6%, 9%, and 35%. The posterior density for the age is bimodal, with modes at 4.67 Gyr and 6.95 Gyr, the first one being slightly more likely. We show that this bimodality is directly related to the structure of the seismic data. When asteroseismic data or interferometric data are excluded, we find significant losses of precision for the mass and the initial hydrogenmass fraction. Our final estimates of the uncertainties from the Bayesian analysis are significantly larger than values inferred from local optimization. This also holds true for several estimates of the age encountered in the literature.
Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (run ID: 183.D0729(A)).
 Publication:

Astronomy and Astrophysics
 Pub Date:
 November 2018
 DOI:
 10.1051/00046361/201834058
 arXiv:
 arXiv:1810.01387
 Bibcode:
 2018A&A...619A.172B
 Keywords:

 stars: individual: 18 Sco;
 stars: solartype;
 stars: evolution;
 asteroseismology;
 methods: data analysis;
 methods: statistical;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 doi:10.1051/00046361/201834058