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.