Determining Parameters of Cool Giant Stars by Modeling Spectrophotometric and Interferometric Observations Using the SAtlas Program

TL;DR

This study tests the SAtlas stellar atmosphere model against interferometric and spectrophotometric data for giant stars, finding it robust and consistent with other models like Phoenix, with some temperature and luminosity differences.

Contribution

It demonstrates the robustness of the SAtlas program for modeling extended stellar atmospheres using combined observational data.

Findings

SAtlas provides effective temperature estimates 100-200 K lower than other models.

Best-fit parameters align with Phoenix model predictions within observational uncertainties.

SAtlas effectively models the interferometric and spectrophotometric observations of evolved giant stars.

Abstract

Context: Optical interferometry is a powerful tool for observing the intensity structure and angular diameter of stars. When combined with spectroscopy and/or spectrophotometry, interferometry provides a powerful constraint for model stellar atmospheres. Aims: The purpose of this work is to test the robustness of the spherically symmetric version of the Atlas stellar atmosphere program, SAtlas, using interferometric and spectrophotometric observations. Methods: Cubes (three dimensional grids) of model stellar atmospheres, with dimensions of luminosity, mass, and radius, are computed to fit observations for three evolved giant stars, \psi Phoenicis, \gamma Sagittae, and \alpha Ceti. The best-fit parameters are compared with previous results. Results: The best-fit angular diameters and values of \chi^2 are consistent with predictions using Phoenix and plane-parallel Atlas models. The predicted effective temperatures, using SAtlas, are about 100 to 200 K lower, and the predicted luminosities are also lower due to the differences in effective temperatures. Conclusions: It is shown that the SAtlas program is a robust tool for computing models of extended stellar atmospheres that are consistent with observations. The best-fit parameters are consistent with predictions using Phoenix models, and the fit to the interferometric data for \psi Phe differs slightly, although both agree within the uncertainty of the interferometric observations.