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

Abstract: The All-Sky Automated Survey for Supernovae (ASAS-SN) has recently used over 2000 days of 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. In this paper, we analyze ASAS-SN 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 2, 3, or 4 times the actual period, or the ASAS-SN period is a "long secondary period" with a shorter pulsation present, or the star is multi-periodic or otherwise complex, or the star's data 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 actually 2 or more times the actual period. Our results are not surprising, given the very complex behavior of PRGs.