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Period Changes in the Mira Variable TY Cassiopeiae

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Martha L. Hazen

Harvard College Observatory, 60 Garden Street, Cambridge, MA 02138

Janet A. Mattei

AAVSO, 25 Birch Street, Cambridge, MA 02138

Presented at the 91st Spring Meeting of the AAVSO, July 2, 2002

Abstract  We studied the period changes from 1888 to mid-2002 in the long period, Mira-type variable star TY Cassiopeiae by combining 275 photographic magnitudes and useful upper limits of brightness from the Harvard College Observatory plate collection with more than 1750 visual, photovisual, and CCD(V) magnitude measurements and upper limits from the AAVSO International Database. The star is shown to have a period decrease from 645 to 550 days during the early years of the 1900s, then the period steadily increased to 645 days until the 1980s, and then it stabilized. These changes are qualitatively similar to the predictions of helium-shell flash models of Wood and Zarro (1981). Thus, TY Cas may be an excellent candidate for a star undergoing a helium-shell flash.

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