Spectroscopy across Stellar Surfaces

Abstract: Stars as we observe them are point source objects and their measured spectra are integrated over the stellar disk. Since the beginning of stellar spectroscopy, stellar parameters are calculated from these spectra. However recently, simulations of stellar atmospheres show that it is not possible to determine stellar parameters in a unique way from disk-averaged data. These 3-dimensional simulations are time dependent and follow the relevant laws of hydrodynamics and radiation. Line profiles are obtained from physical parameters of each volume element in each time step. One way to verify these simulations is to resolve the stellar disk and observe stellar surface structures. The most obvious way of observing would be using an interferometer or a big telescope. However the existing telescopes and interferometers are not large enough to resolve the disks of solar-like stars. In this study, another method is suggested. This method uses planetary transits to measure the spectrum of a small area on the stellar surface. In this project a set of line profiles from 3D hydrodynamic models is used to estimated the possibilities of this method. Also we are examining at what can be observed with one of the next generation telescopes (E-ELTs) in terms of resolving the disks of giant stars and the shapes of their line profiles.