Line profile variations in γ Equ: A puzzle

Abstract

Abstract. Line profile variations in 7 Equ show the classic blue-to-red travelling bumps of m-modes resolved by rotation, and they have been identified as (. = 2 or 3, m = -H or -£+1 by characterising the line shapes using the moment method. The mode identifications cannot be correct, however, since 7 Equ is an extremely slowly rotating star (P rot > 70 yr). We propose an alternative interpretation, according to which the observed line profile variations are a manifestation of a shock wave in the high atmosphere near the magnetic polar regions; the oscillation mode is then still consistent with the photometric observations.