Chromospheric Structure of Cool Carbon Stars

Abstract

A semiempirical chromospheric model is proposed for TX Psc which is a prototype for the N-type carbon stars. Observational data imply that the chromospheric temperature rise must begin at a low density, that the temperature gradient in the lower chromosphere must be steep, that partial redistribution must be employed in the Mg II calculation, and that the lower chromosphere is expanding away from the photosphere with a velocity of close to 50 km/s. The present model also shows that the microturbulent velocity is about 7 km/s at the temperature minimum region, dropping to 5 km/s in the chromosphere, and that the Lyman lines are optically thick in the chromosphere.