The Atmospheric Eclipse of 31 Cygni in the Ultraviolet

Abstract

Theoretical spectra have been compared with high-dispersion IUE observations for the 1982 atmospheric eclipse of 31 Cyg (B4 V + K4 Ib). Chromospheric column densities, excitation temperatures, turbulence, and ionization are determined. It is found that temperature increases with height in the chromosphere, showing a range 5000 - 14,400K for four lines of sight. Turbulence remains in the range 20 - 25 km s^-1 throughout the chromosphere. The temperature-minimum region of the upper photosphere has a temperature near 2500K. The velocity structure of wind lines of O I, Si II, Mg II, and Fe II indicates that most of the wind on the side of the K supergiant toward the B dwarf is photoionized to the next higher ionization stage. Abundances of heavy elements are close to solar, but there are anomalies that may result from systematic errors in the oscillator strengths.