AAVSO Estimates and the Nature of Type C Semiregulars: Progenitors of Type II Supernovae (Abstract)

Volume 40 number 1 (2012)

David G. Turner
Saint Mary’s University, Department of Astronomy and Physics, 923 Robie Street, Halifax, NS B3H 3C3, Canada; turner@ap.smu.ca
K. Moncrieff
Saint Mary’s University, Department of Astronomy and Physics, 923 Robie Street, Halifax, NS B3H 3C3, Canada; turner@ap.smu.ca
C. Short
Saint Mary’s University, Department of Astronomy and Physics, 923 Robie Street, Halifax, NS B3H 3C3, Canada; turner@ap.smu.ca
Robert F. Wing
Ohio State University, Department of Astronomy, 140 W. 18th Avenue, Columbus, OH 43210; wing@astronomy.ohio-state.edu
Arne A. Henden
AAVSO Headquarters, 49 Bay State Road, Cambridge, MA 02138; arne@aavso.org

Abstract

(Abstract only) The nature of the variability in the M supergiant type C semiregular (SRC) variables is examined using new and archival spectroscopic and spectrophotometric observations of the stars phased according to AAVSO magnitude estimates. SRC variables appear to be more regular than sometimes suggested, although the nature of their pulsation remains unclear in some cases. Some SRCs appear to undergo irregular fading episodes that may result from dust ejection. But recent light curves of the stars display large scatter that hinders reliable determination of their cycle lengths, a problem that needs to be addressed to improve the usefulness of AAVSO data for learning more about massive stars as they approach the terminal stage of their evolution as Type II supernovae.