Secular Evolution in Mira Variables (Abstract)

Volume 33 number 1 (2005)

Matthew Templeton

Janet A. Mattei

Lee Anne Willson

Abstract

(Abstract only) Stellar evolution theory predicts that stars on the asymptotic giant branch (AGB) undergo a series of short thermal pulses that significantly change the luminosities and masses of these stars on timescales of a few thousand years. These changes may be observable as changes in period for pulsating AGB stars such as the Mira and semiregular variables. It is known that a small fraction of these stars exhibit secular period change. In our project, we examined the light curves of 547 Mira variables from the AAVSO International Database to search for and quantify these secular changes. Approximately 10 percent of stars showed evidence of secular period change at the two-sigma level, and eight stars showed large period changes at the six-sigma level or greater. The largest measured values of dlnP/dt are consistent with those predicted to occur during thermal pulses on the AGB. A number of other stars exhibit non-monotonic period change on long timescales, the cause of which is not yet understood. In the overwhelming majority of cases, the period variations appear to be small and essentially random. [Ed. note: The complete version of this paper has been published in the Astronomical Journal (Vol. 130, p. 776, 2005), and is available from the author upon request.]