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Studies of Mira Stars and Their Small-Amplitude Relatives

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John R. Percy

Erindale College

University of Toronto

Mississauga, Ontario L5L 1C6

Canada

Presented at the AAVSO Session on Mira Stars (part of the 85th Annual Meeting), November 1, 1996

Abstract

Some aspects of the nature and evolution of Mira stars and their small-amplitude relatives are briefly described. As stars ascend the asymbiotic giant branch, it appears that they begin to pulsate when their effective temperature drops below 3800 K. The amplitude tends to increase with decreasing temperature. The stars show appreciable periodicity, perhaps beginning to pulsate in a high radial overtone, then in lower overtones as they approach the Mira stage. Mode-switching is occasionally observed in the small-amplitude variables. There is appreciable irregularitiy in the latter stars, including long-term variability of unknown cause. Our understanding if these stars will certainly increase as a result of new Hipparcos parallaxes and other advances. The observation and analysis of these and other variables provides fruitful projects for students.