Rotating Loops in the Atmosphere of Rigel (β Orionis A)

Abstract

We discuss time series of Ha profiles of the late B-type supergiant Rigel (s Orionis A). Recent observations indicate the presence of variable and asymmetric outflows and infall of matter. We detected an extraordinary blue-shifted high-velocity absorption (HVA) component almost simultaneously with Kaufer et al. (1996). We found that the blue-shifted HVA disappeared completely in the course of one month, and a strong red-shifted absorption appeared at + 50 km s−1. Based on our observations, as well as those reported in the literature, we propose that extended rotating magnetic structures (closed loops) exist in Rigel. According to our model, the gradual decrease of the blue HVA simultaneous with the increase of the red HVA is not due to variable ejection/accretion rates, but to the variable effective thickness of the part of the loop which crosses our line of sight.