Non-radial pulsations in the extreme helium star HD 160641.

Abstract

Mean periods of 0.35±0.01, 0.71±0.05, 1.12±0.13 and 1.77±0.34 day are identified from separately analysed photometric observations (obtained in 1979 and 1982) of the extreme helium star HD 160641. Radial velocities were obtained simultaneously with photometry on three nights in 1982. Optical variations are not accompanied by detectable colour changes, and radial velocities are not characteristic of radial pulsation. HD 160641 is therefore regarded as a non-radial pulsator. Radial velocity and light variations are tentatively interpreted as l = 4 mode pulsation, corresponding to a Wesselink radius of 7.9±1.0 R_sun;. The consequent luminosity of log (L/L_sun;) = 4.7±0.3 would be consistent with Schönberner's evolution model for a 1 M_sun; extreme helium star.