A Study of Some Pulsating Red Giants Showing Unusual Behavior

Volume 53 number 2 (2025)

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John R. Percy

Department of Astronomy and Astrophysics, and Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada; john.percy@utoronto.ca

Malaika Malik

Department of Astronomy and Astrophysics, and Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada; malaika.malik@mail.utoronto.ca

Abstract

We describe unusual and/or interesting behavior in 54 long period variables (LPVs) in the AAVSO LPV observing program. The usual behavior of LPVs includes slightly “meandering” periods, variable amplitudes, and, in about a third of the stars, long secondary periods which are believed to be caused by eclipses of the LPV by a low-mass, dust-enshrouded companion. In about half the stars in our sample, the “unusual” behavior may be an extreme version of usual behavior. We describe and categorize the unusual behavior of the LPVs in the other half of our sample. The categories are: large, rapid, approximately linear changes in period; multiple pulsation periods, with variable amplitudes; non-sinusoidal (including double-peaked) phase curves; very slow, cyclic variability of unknown nature and cause; long-term eclipse-like variability (as in V Hya); significant changes in the mean brightness level (as in L2 Pup); and “nature and cause unknown.” In several stars, there is an apparent long-period (thousands of days) variability in mean magnitude which is an observational effect, entirely due to the closeness of the pulsation period to a year, and the tendency for the observations to be made when the star is at or near opposition. It is a long-period alias of the pulsation period.