A model for stellar surface convection and photospheric line asymmetrics

Abstract

A model for stellar convection zones based on linear convective modes using a nonlocal mixing length theory is developed to study the spectral line asymmetries resulting from convective motions in the stellar photospheric region. The amplitudes of these linear convective modes is estimated by demanding that the convective flux due to a linear superposition of such modes should reprodeuce the convective flux required by the mixing length model. The mode with the largest amplitude in the photospheric line formation region is chosen to represent the stellar surface structure. Synthetic spectral line profiles are obtained by summing locally symmetric profiles over the stellar disk according to the local Doppler velocity and intensity fluctuations. Four stars, i.e., the sun, α Cen A, Arcturus, and Procyon, which have characteristically different observed line bisector shapes are chosen for the study. It is found that the simple model considered here can explain the gross features of the observed bisector shapes for these stars of different spectral types.