AAVSO: American Association of Variable Star Observers

ASAS-SN Observations of Long Secondary Periods in Pulsating Red Giants

Volume 48 number 1 (2020)

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John 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
Anthony Mark Wallace
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

Abstract

About a third of all pulsating red giants (PRGs) have long secondary periods (LSPs), an order of magnitude longer than their pulsation periods (P). Although LSPs have been known for many decades, their nature and cause are uncertain. We have analyzed data on 45 PRGs, from the All-Sky Automated Survey for Supernovae (ASAS-SN), and combined the results with data from the literature to draw a few new conclusions about this phenomenon. LSPs have V amplitudes of up to 0.45 mag. The ratio LSP/P has a peak at 10 ± 1, and a broader distribution at 7 ± 1. There is no obvious correlation between LSP/P and LSP itself. Previous studies have suggested that the pulsation amplitude does not vary around the LSP cycle, but varies on longer time scales of 20–45 P. However, we find smaller variations in pulsation amplitude around the LSP cycle, which may be partly due to the effect of the LSP variations on the pulsation amplitude determination, but otherwise appear to be real and common.