Light, velocity, and Hα variations in the pulsating red giant V CVn

Abstract

W e have analyzed the visual light variations of the pulsating red giant, V CVn (M4M6me, Joy and Merrill 1937), monitored by the A.A.V.S.O. since the mid I920's [Figure I]. Although similar to the more luminous long-period Mira variables, V CVn was classified as a semi-regular variable because of its relatively short 192 day period and great cycle-to-cycle variation. The light variations may not be as irregular as they appear. A Fourier transform (Horne and Baliunas lg86) of all the data indicates a strong 102 day period plus a weaker 187.5 day secondary period, possibly a low order, non-radial pulsation. Fourier transforms of 15 year intervals reveal different secondary periods which are always close to but shorter than the primary period [Table 1]. The secondary period definitely exists. It does not result from small phase changes in the 192 day pulsation because a 192-day sine wave fits the light curve well over all 50 years. Filtering (Home and Baliunas 1986) demonstrates that the secondary period is not an alias of the 192 day period. The secondary period is also not an artifact of a long ~5 year period such as those previously seen in the light curves of other semi-regular variables (Glasby 1969). Such a long period cannot produce the observed cycle-to-cycle variation in the phases of the extra "humps" in the light curve of V CVn.