Emission from the transition regions and coronae of three cool dwarf stars.

Abstract

An analysis is presented of the outer atmospheres of three cool dwarf stars (Tau Cet, Delta Pav, and 61 Cyg A) observed with the IUE, for which Einstein X-ray observations are available. The ultraviolet emission line fluxes are used to derive the distribution of the emission measure as a function of temperature, and from these distributions the structure of a uniformly emitting region in hydrostatic equilibrium is derived as a function of electron pressure at 200,000 degrees. In the two models for Tau Cet the net conductive flux is less than the radiation losses at all temperatures. However, for Delta Pav and 61 Cyg A the model with the upper boundary value of the electron pressure has a temperature range where the radiative losses are less than the net conductive fluxes. Measured X-ray fluxes are used to test the coronal temperature values derived from the ultraviolet observations.