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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