A line-profile analysis of the large-amplitude beta Cephei star xi1 Canis Majoris

Abstract

We present a detailed line-profile study of the beta Cephei star xi1 Canis Majoris, for which we have assembled numerous high-resolution spectra over a period of 4.5 years. It is the first time that the line-profile variations of this star have been analysed. We focused on the Si III line profiles centered on 4560 A. We searched for oscillation frequencies in different line diagnostics and find the star to be monoperiodic with frequency f=4.77153 c/d. By means of the moment method and from amplitude and phase variations across the line profiles we identified the oscillation mode of the star as radial. xi1 CMa is among the very few beta Cephei stars with a radial-velocity amplitude larger than the local speed of sound and profile variations that clearly deviate from those predicted by linear oscillation theory.