Indicators of Mass in Spherical Stellar Atmospheres

TL;DR

This paper demonstrates that stellar mass can be inferred from spectral features and surface-brightness distributions in spherical stellar atmosphere models, enabling mass determination from observable parameters for red giants and supergiants.

Contribution

It introduces a method to estimate stellar mass using spectral and surface-brightness features derived from spherical atmosphere models, based on observable luminosity and radius.

Findings

Spectral features vary with stellar mass in model atmospheres.

Surface-brightness distributions show mass-dependent signatures.

Method allows mass estimation from spectroscopy and observed stellar parameters.

Abstract

Mass is the most important stellar parameter, but it is not directly observable for a single star. Spherical model stellar atmospheres are explicitly characterized by their luminosity ($L_\star$), mass ($M_\star$) and radius ($R_\star$), and observations can now determine directly $L_\star$ and $R_\star$. We computed spherical model atmospheres for red giants and for red supergiants holding $L_\star$ and $R_\star$ constant at characteristic values for each type of star but varying $M_\star$, and we searched the predicted flux spectra and surface-brightness distributions for features that changed with mass. For both stellar classes we found similar signatures of the star's mass in both the surface-brightness distribution and the flux spectrum. The spectral features have been use previously to determine $\log_{10} (g)$, and now that the luminosity and radius of a non-binary red giant or red supergiant can be observed, spherical model stellar atmospheres can be used to determine the star's mass from currently achievable spectroscopy. The surface-brightness variations with mass are slightly smaller than can be resolved by current stellar imaging, but they offer the advantage of being less sensitive to the detailed chemical composition of the atmosphere.