Observation of the Onset of an Emission Episode in the Be Star MU Centauri

Abstract

A series of recent CCD observations which shows the rapid development of Hα emission in the pulsating, transient Be star μ Cen in only 2 days and thus establishes a time scale for the physical changes in the photosphere that lead to the outburst, are presented. On 1985 March 25, Hα was in pure absorption in μ Cen but by 1985 March 27 a centrally reversed emission feature was observed. Postoutburst observations revealed that the Hα emission increased slightly in strength and then waned within a period 1 month. Complementary observations of He I 6678 as well as UV spectra from IUE are used to discuss the extent of photospheric activity associated with the outburst and line-of-sight mass flow into the circumstellar envelope.