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Quantifying Irregularity in Pulsating Red Giants

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John R. Percy
Samantha Esteves
Alfred Lin
Christopher Menezes
Sophia Wu

Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON Canada M5S 3H4

Based on a paper presented at the 98th Spring Meeting of the AAVSO, Big Bear Lake, CA, May 19–21, 2009

Received July 20, 2009; revised August 9, 2009; accepted August 17, 2009

Hundreds of red giant variable stars are classified as "type L," which the General Catalogue of Variable Stars (GCVS) defines as "slow irregular variables of late spectral type...which show no evidence of periodicity, or any periodicity present is very poorly defined..." Self-correlation (Percy and Muhammed 2004) is a simple form of time-series analysis which determines the cycle-to-cycle behavior of a star, averaged over all the available data. It is well suited for analyzing stars which are not strictly periodic. Even for non-periodic stars, it provides a “profile” of the variability, including the average “characteristic time” of variability. We have applied this method to twenty-three L-type variables which have been measured extensively by AAVSO visual observers. We find a continuous spectrum of behavior, from irregular to semiregular.

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