A new pulsating white dwarf - GD 154

Abstract

Additional results are reported for a survey of luminosity variations in white dwarfs. GD 154, a DA white dwarf with B-V = +0.18, is found to vary at either of two dominant periods, 1186 or 780 s. For nine nights the 1186-s period dominated and the light curve was strictly periodic, so that an ephemeris could be constructed which predicted the time of arrival of pulse peaks to + or - 30 s. On a 10th night the 780-s period dominated. The variations are probably caused by nonradial g-mode pulsations, but the extreme length of the 1186-s pulsation period strongly suggests that the white dwarf is pulsating in a very high overtone (k of approximately 10-30). The change in the period on the last night is attributed to transfer of pulsation energy from the 1186-s pulsation mode to the 780-s pulsation mode.