Period Change in the Semiregular Variable RU Vulpeculae
AAVSO, 49 Bay State Road, Cambridge, MA 02138
Lee Anne Willson
Department of Physics and Astronomy, Iowa State University, Ames, IA 50014
Island Data Corporation, 2386 Faraday Ave., Suite 280, Carlsbad, CA 92008 and AAVSO, 49 Bay State Road, Cambridge, MA 02138
Received September 4, 2007; revised November 30, 2007, accepted January 10, 2008
The well-observed semiregular variable RU Vulpeculae has undergone a substantial change in period over the past fifty-five years. The discovery period of ~155 days has undergone a continuous change to its current value of 108 days. The amplitude and stability of the light curve have changed as well; the pulsations are much less regular and have a lower amplitude now than at the time of RU Vul's discovery and classification. The character of the period change is quantitatively similar to that of the well-studied Mira variable T Ursae Minoris, and we argue that RU Vul may be a semiregular analog of Mira variables undergoing dramatic period changes. We place RU Vul in the context of other AGB stars exhibiting similar behavior, and discuss possible explanations for its period change.