An expanding circumstellar cloud of Zeta Aurigae

Abstract

Strong absorption satellite lines of CaI λ 6572 were found on spectrograms taken on three successive days just after the fourth contact of the 1971–72 eclipse of Zeta Aurigae. The radial velocities of the satellite lines are −88 km s⁻¹, −74 km s⁻¹, and −180 km⁻¹, respectively, relative to the K-type primary star (K4 Ib). These absorptions should be due to a circumstellar cloud in which the column density of neutral calcium atoms is 1×10¹⁷ cm⁻² and the turbulent velocities come to 20–50 km s⁻¹. It is suggested that the cloud may be formed by the rocket-effect of the Lyman quanta of the B-type component (B6 V). We estimate the density in the cloud to be 2×10¹¹ atoms cm⁻³ fors=10R _K and 2×10¹⁰ atoms cm⁻³ fors=10² R _K, wheres denotes the distance of the cloud from the K star andR _K the K star's radius. The mass loss rate of the K-type component is also estimated to be about 10⁻⁷ M _⊙ yr⁻¹, assuming that the expansion of the K star occurs isotropically.