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

TL;DR

This study investigates the timing of fadings in R Coronae Borealis stars and their relation to stellar pulsations, revealing that fadings are closely linked to pulsation cycles and that pulsation periods exhibit random fluctuations.

Contribution

It provides new observational evidence connecting fadings to pulsation phases and models pulsation period wandering as random fluctuations in R CrB stars.

Findings

Fadings are synchronized with pulsation periods, with some scatter.

Pulsation periods show random cycle-to-cycle fluctuations.

Pulsation amplitude varies non-periodically over about 20 cycles.

Abstract

We have measured the times of onset of recent fadings in four R CrB 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.