V725 Sagittarii: Unique, Important, Neglected

Volume 48 number 2 (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

During the last century, V725 Sgr gradually changed from a 12-day Cepheid to an 85-day yellow semiregular giant. This paper presents wavelet analysis of AAVSO visual observations from 1982 to 2020, and Fourier analysis of ASAS-SN observations from 2016 to 2018. The results confirm that the previously-identified pulsation period has increased from about 50–60 days to 80–90 days since 1982. In the ASAS-SN data, there appear to be both a 82.6-day period and a possible 160.0-day period, though the latter is not prominent after pre-whitening. If it is real, however, the two periods could be interpreted as a first overtone period and a fundamental period, respectively. Evidence for two (or more) periods can also be seen in the ASAS-SN light curve, and in the visual data. The total V range is 1.1 magnitude. Since recent results in the literature indicate that V725 Sgr is a K4 yellow giant, it should be classified as a SRd variable. In view of its continuing changes, it needs and deserves to be monitored more systematically.