Expanding chromospheres of late G and K supergiants

Abstract

The radiative transfer problem in non-LTE moving atmospheres has been explicitly solved for Hα line profiles. These computations have been done for a schematic model of the line-forming region over a wide range of optical depths and velocity gradients in order to cover the observed characteristics in 23 G and K supergiants. The best theoretical fits yield optical depths in the range 10 - 500 and velocity fields in the range 0.5 - 3 Doppler widths. The computed mass-flow rates lie in the range 10-5 - 10-7M_sun;yr-1; the higher the extent of the line-forming region, the lower the mass-loss rates. The effect of the extent on the Hα emission components has also been investigated in some detail. The temperature sensitivity of the mass-loss rates has been considered in an approximate manner.