Further Studies of "Irregularity" in Pulsating Red Giants
John R. Percy
Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada;
Received March 5, 2010; accepted March 16, 2010
In a previous paper (JAAVSO 37, 2009, p. 71) we used self-correlation to analyze AAVSO visual observations of twenty-three L-type (irregular) pulsating red giants, and found that they exhibited a continuous spectrum of behavior, from truly irregular to semiregular. In this paper, we carry out Fourier analysis of the same stars, partly to investigate whether some of their irregularity might be due to multiperiodicity, and partly to look for evidence of possible spurious periods of one year and one month, due to the methodology of visual observing. We find evidence of such spurious periods in many stars. We have also analyzed an additional seventeen L-type pulsating red giants, using both self-correlation and Fourier techniques. Several show evidence of spurious one-month or one-year periods. Only XY Lyr, VY UMa, and possibly DY Vul and BU Gem show evidence of intrinsic periodicity. Several show little or no variability. The rest vary irregularly on time scales of a few hundred days. We find no evidence that irregularity in L-type variables is due to multiperiodicity.