The “Long Secondary Period (LSP) Variables”: Overview and Some Analysis

Volume 51 number 2 (2023)

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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

Mayank H. Shenoy

Department of Astronomy and Astrophysics, and Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto ON M5S 3H4, Canada

Abstract

We briefly review the phenomenon of “long secondary periods” (LSPs) in red giants, and the “LSP variable stars” classification introduced in the All-Sky Automated Survey for Supernovae (ASAS-SN) variable star catalog; they are red giant Long Period Variables (LPVs) in which their LSP variability is significantly greater than their pulsational variability. We then describe and discuss the results of a period and amplitude analysis of a random sample of 35 LSP variables in the ASAS-SN catalog, using ASAS-SN data and the AAVSO VStar time-series analysis software. The pulsation period and amplitude, and LSP, all increase with increasing luminosity or size of the star, as expected. The behavior of the LSP amplitude is more complicated; it appears to be larger in moderate-luminosity stars, and smaller in low- and high-luminosity stars. In particular, it is relatively small in a sample of 27 Mira stars, analyzed separately using AAVSO visual data. These results are discussed in the context of the current model for the LSP phenomenon, namely that it is caused by eclipses of the red giant star by a dust-enshrouded companion.