Effects of velocity laws on line formation

Abstract

We calculated the spectral line profiles in a spherically symmetric expanding medium. Complete redistribution of photons in the line for a two level atom is assumed with Doppler profile function in a purely scattering medium. Using transfer equation we have calculated the source functions in the comoving frame and this is employed to simulate the line profiles observed at infinity. We have characterized the envelope of the star by three functions namely (1) Geometrical extension of the medium; (2) Optical depth law; (3) and Velocity law. For various optical depths and velocities we have considered the different ratios of outer to inner radii of the atmosphere to study the effect of sphericity on line formation. We describe the profiles in terms of fluxes integrated over the whole disc versus the normalized frequency. We obtained several P-Cygni type profiles