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

 

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John R. Percy

Kaushala Bandara

J. Donald Fernie

University of Toronto, Department of Astronomy and Astrophysics, 60 George Street, Room 1403, Toronto, Ontario, Canada M5S 3H8

 

P. L. Cottrell

Ljiljana Skuljan

University of Canterbury, Department, of Physics and Astronomy, Private Bag 4800, Christchurch, New Zealand

 

Presented at the 93rd Spring Meeting of the AAVSO, July 23, 2004; received January 19, 2005; accepted January 20, 2005

 

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.

 

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