The Long-term Spectroscopic and Photometric Behavior of the Carbon Star RS Cygni

Abstract

RS Cygni is a semiregular variable carbon star that has a distinctive light curve. Twenty-one years of optical spectroscopic and photometric observations of this star made at Grinnell College have been used not only to produce a comprehensive survey of the behavior of this star but also to compare these two sets of data. A number of spectral features vary in strength with the cycle of the star and some, but not all, of this variation is correlated with the dips that often occur near the maxima of the light curve. In particular, the strengths of the Balmer emission lines often have two peaks per cycle. Such correlation might be consistent with a mechanism for producing the dips, such as dust formation, that reduces the brightness in a way that does not involve rapid changes in photospheric characteristics. The large amount of data and the precision of the photometry presented give an unusually detailed view of how the light of RS Cyg varies over time.