Testing spherical, expanding, line-blanketed model atmospheres of giant stars with interferometry

Abstract

We show examples of PHOENIX stellar atmosphere model simulations for data obtained by long-baseline optical interferometers. A single spherical, hydrostatic model atmosphere for the M-type giant star γ Sagittae is shown to be in good agreement with interferometric, spectrophotometric, and high-dispersion spectroscopic data sets. In particular we show that the interferometric triple products and wavelength-dependent uniform disk diameters measured by the Navy Prototype Optical Interferometer (NPOI) are well matched by our model. With expanding atmosphere models for the A-type supergiant α Cygni we predict that the center-to-limb intensity profile is sensitive to the mass-loss rate of its stellar wind. For one possible NPOI configuration we show the sensitivity of the squared visibility amplitudes to the model mass-loss rate at spatial frequencies beyond the first null. The importance of hot star photospheric interferometry is discussed.