Self-Correlation Analysis of R Coronae Borealis Stars: A Pilot Project

Volume 33 number 1 (2005)

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John R. Percy

Kaushala Bandara

J. Donald Fernie

University

P. L. Cottrell

Ljiljana Skuljan

University

Abstract

R. Coronae Borealis (RCB) stars are peculiar yellow supergiant stars which suddenly and unpredictably decrease in brightness by up to several magnitudes, then slowly return to normal. Most (perhaps all) RCB stars also pulsate, and the pulsations may be related to the ejection of the dust clouds which produce the fadings. As a pilot project, we have applied self-correlation analysis to two datasets: long-term photometry of R CrB itself by J. D. Fernie, and long-term photometry of several southern RCB stars by P. L. Cottrell, L. Skuljan, and their colleagues. Self-correlation is a simple form of time series analysis which displays the cycle-to-cycle behavior of a variable star, averaged over a dataset. It is especially useful for semi-regular variables. Generally, the seasonal pulsation time scales and amplitudes which we derive are in agreement with Fourier analysis of the same datasets. In the case of R CrB, we confirm that there is apparent mode-switching from season to season.