THE CHROMOSPHERE AND CORONA OF PROCYON (ALPHA-CMI, F5 IV-V)

Observations of Procyon (a CMi), an F5 IV-V star, have been obtained with the International Ultraviolet Explorer (IUE) satellite at low and high spectral resolution. Emission line fluxes are used to find the emission measure distribution. The range of likely electron pressure is discussed, based in part on consideration of line opacities. Models are made for several boundary values of the electron pressure. The chosen model has Pe = 1.2 x 1014 cm3 K at 2 x 105 K and Pe = 3.6 x 1014 cm3 K at 104 K, the latter being a factor of 3 greater than in the chromospheric model by Ayres, Linsky & Shine. The maximum temperature for a model with uniform emission is deduced to be 3xl05K, much lower than in the solar corona. Higher temperature and pressure models are allowed only if the EUV emission originates from limited areas of the stellar disc. The radiation losses are shown to exceed the net conductive flux, and the energy input required can then be found without knowing the electron pressure/The non-thermal energy content is calculated from the widths of optically thin lines. The energy input is compared with the energy flux carried by acoustic, shock and Alfven waves. Pure acoustic waves cannot account for the required energy flux. A combination of shock dissipation and Alfven waves, of the type proposed by Osterbrock cannot be excluded. © Royal Astronomical Society.