A Study of Pulsation and Fadings in some R Coronae Borealis (RCB) Stars

Volume 46 number 2 (2018)

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John R. Percy

Department of Astronomy and Astrophysics, and Dunlap Institute of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada; john.percy@utoronto.ca

Kevin H. Dembski

Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON, M5S 3H4, Canada; kevin.dembski@mail.utoronto.ca

Abstract

We have measured the times of onset of recent fadings in four R Coronae Borealis (RCB) stars—V854 Cen, RY Sgr, R CrB, and S Aps. These times continue to be locked to the stars’ pulsation periods, though with some scatter. In RY Sgr, the onsets of fading tend to occur at or a few days after pulsation maximum. We have studied the pulsation properties of RY Sgr through its recent long maximum using (O–C) analysis and wavelet analysis. The period “wanders” by a few percent. This wandering can be modelled by random cycle-to–cycle period fluctuations, as in some other types of pulsating stars. The pulsation amplitude varies between 0.05 and 0.25 in visual light, non-periodically but on a time scale of about 20 pulsation periods.