Period Analysis of All-Sky Automated Survey for Supernovae (ASAS-SN) Data on Pulsating Red Giants

Volume 47 number 2 (2019)

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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

Lucas Fenaux

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

The All-Sky Automated Survey for Supernovae (ASAS-SN) has recently used over 2,000 days of sustained photometric data to identify more than 50,000 variable stars, automatically classify these, determine periods and amplitudes for those that are periodic—part of a remarkable project to classify 412,000 known variable stars and determine their basic properties. This information about the newly-discovered variables, along with the photometric data, is freely available on-line, providing an outstanding resource for both science and education. In this paper, we analyze ASAS-SN V data on two small random samples of pulsating red giants (PRGs) in detail, and compare our results with those found by ASAS-SN. For the majority of a sample of 29 mostly semi-regular (SR) PRGs, the ASAS-SN results are incorrect or incomplete: either the ASAS-SN periods are exactly 2, 3, or 4 times the actual period, or the ASAS-SN period is a “long secondary period” with a shorter pulsation period present, or the star is multi-periodic or otherwise complex, or the star’s data and analysis are contaminated by instrumental effects. For almost all of a sample of 20 of the longest-period Mira stars (period 640 days or more), the ASAS-SN period is exactly 2 or more times the actual period. The results are not surprising, given the very complex behavior of PRGs.