Quantifying Irregularity in Pulsating Red Giants (Poster abstract)

Volume 37 number 2 (2009)

John R. Percy

Samantha Esteves

Alfred Lin

Christopher Menezes

Sophia Wu

Abstract

(Abstract only) Hundreds of red giant variables are classified as type L, which the General Catalogue of Variable Stars 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 is a simple form of time-series analysis which determines the cycle-to-cycle behavior of the star, averaged over all the data; even for stars with no periodicity, it provides a “profile” of the variability, including the average “characteristic time scale” (Percy and Mohammed 2004, J. Amer. Assoc. Var. Star Obs., 32, 9, and references therein). We have applied this method to AAVSO visual observations of several dozen L-type variables, and found a range of behavior: despite their irregularity, most have at least one pulsation period; some also have “long secondary periods” whose cause is unknown. For all of them, we have determined a period, or an equivalent “characteristic time scale.” There seems to be a continuous spectrum of behavior in pulsating red giants, from periodic to irregular. Co-authors SE, AL, CM, and SW were participants in the University of Toronto Mentorship Program which enables outstanding senior high school students to work on research projects at the university. This program will be described briefly. [Ed. note: this paper appears in full in this issue of the Journal, beginning on page 71.]