AAVSO: American Association of Variable Star Observers

A Note on Bimodal Pulsating Red Giants

Volume 48 number 1 (2020)

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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

Abstract

ASAS-SN data and the AAVSO time-series analysis package vstar have been used to determine the pulsation periods of a sample of 23 bimodal pulsating red giants. The results have been combined with results from the literature to determine period ratios and pulsation modes, and how these vary systematically with the observed pulsation period(s). The results are consistent with previous results, and with theoretical predictions: most longer-period bimodal stars pulsate in the fundamental mode (period P0) and the first overtone mode (period P1), with P1/P0 decreasing slightly with increasing P0; most shorter-period bimodal stars pulsate in the first-overtone mode and the second-overtone mode (period P2), with P2/P1 decreasing slightly with increasing P1. Stars with period 100 to 200 days show a mixture of the two behaviors.