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Session 102 - Pulsating Stars.
Display session, Thursday, January 18
North Banquet Hall, Convention Center
Repeated PC HST exposures of the core of the globular cluster 47 Tucanae have revealed U band (F336W) variability among stars on a narrow section of the asymptotic giant branch (AGB) limited to stars fainter than the tip of the red giant branch. Since the periods of the variable stars are longer than the time span of the observations (1.6 days) the variability is poorly characterized, however the periods are as short as \sim2--3 days and the amplitude a few percent. The position of the variable stars in the CMD, and their small amplitudes and periods show they are a population distinct from the brighter and redder Mira and semi-regular variables already known in 47 Tuc. The variations could represent high overtone pulsations and further study may enhance our understanding of stellar evolution along the start of the AGB.
