College Observatory, 60 Garden Street, Cambridge, MA 02138
Janet A. Mattei
25 Birch Street, Cambridge, MA 02138
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.