The Long‐Term Behavior of the Semiregular M Supergiant Variable BC Cygni

Abstract

The long-term brightness changes in the M supergiant, type C semiregular variable, Type II supernova progenitor BC Cyg from 1890 to the present are examined using archival data obtained from photographic plates in the collections of Harvard College Observatory and Sternberg Astronomical Institute, in conjunction with AAVSO observations. BC Cyg pulsates with a period close to 700 days but underwent a 0.5 mag increase in brightness between 1900 and 2000, in conjunction with a decrease in pulsation period from 699 to 687 days. Such changes appear to be evolutionary in origin, representing a small contraction of the star associated with a slight decrease in luminosity. Its evolutionary mass is estimated to be ?19 M? from its membership in Berkeley 87, a feature that also permits it to be used to test the M supergiant period-luminosity relation. ? 2006. The Astronomical Society of the Pacific. All rights reserved.