Do Yellow Semiregular (SRd) Variables Show Long Secondary Periods?

Volume 34 number 2 (2006)

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John R. Percy

Claudia Ursprung

Department

Abstract

Semiregular pulsating variable supergiants of spectral types F, G, and K (SRd variables in the General Catalogue of Variable Stars), and RV Tauri (RV) stars share many similarities in their physical properties, evolutionary status, and light curve properties. A significant fraction of RV variables (called RVb stars) show long secondary photometric periods, an order of magnitude longer than the primary (pulsation) period. We have searched for long secondary periods in 8 well-studied SRd variables in the AAVSO visual observing program, using light curve analysis, and especially self-correlation analysis. We first tested the procedure on 4 RVa variables, and on 4 RVb variables, and derived new values for the long secondary periods in the latter. We find no compelling evidence for long secondary photometric periods in the RVa or SRd variables. Since the RVb phenomenon is believed to be due to binarity, it is not clear why SRd variables could not also be binary members which show long secondary periods