Type C Semiregulars and Irregulars: the Forgotten Pulsating Luminous Stars (Abstract)

Volume 44 number 2 (2016)

David G. Turner

St. Mary’s University, Department of Astronomy and Physics, 56 Shalimar Crescent, Dartmouth, NS B2W 4L8, Canada; turner@ap.smu.ca

Abstract

(Abstract only) Variable M supergiants, comprising the SRC and LC classes of semiregular and irregular variables, represent late stages of evolution for stars of about 20–25 solar masses, and the likely progenitors for many core collapse supernovae. Most have escaped dedicated study, either long-term photometry or detailed spectroscopy, primarily because of lengthy pulsation periods of 100–1000 days. Yet they appear to share many of the characteristics of classical Cepheids, and their high luminosities make them just as valuable, if not more so, for calibrating the extragalactic distance scale. Many are double-mode, and possibly triple-mode, pulsators, much like Cepheids, which complicates estimates for their periods of variability. Demonstrated here are some of the techniques used for studying such stars, and what has been learned so far about their characteristics. AAVSO observers have a wonderful opportunity to contribute to the field through observations of the forthcoming 2016 maximum of m Cephei.