The chromosphere and corona of Procyon (Alf CMi,F5IV-V).

Abstract

Observations are reported of Procyon (alpha CMi), an F5 IV-V star, obtained with the IUE satellite at low and high spectral resolutions as part of a program to study the chromospheres and coronae in late-type stars. Methods for analyzing the fluxes and linewidths of alpha CMi and other near main sequence stars are presented, and applied to alpha CMi to give the emission measure distribution, the electron pressure, and hence a model of the density and temperature as a function of height. Models are made for several boundary values of the electron pressure. The maximum temperature for a model with uniform emission is deduced to be 300,000 K. Higher temperature and pressure models are allowed only if the EUV emission originates from limited areas of the stellar disk. The terms of the energy balance equation are calculated, and the profiles of several lines are analyzed to give the non-thermal motions. A comparison is made between the empirical energy input function and that expected from the dissipation of acoustic and Alfven waves.