AAVSO: American Association of Variable Star Observers

HD 121620: A Previously Unreported Variable Star with Unusual Properties

Volume 48 number 1 (2020)

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Roy A. Axelsen
AAVSO; Astronomical Association of Queensland; Variable Stars South, P.O. Box 706, Kenmore, Queensland 4069, Australia; reaxelsen@gmail.com

Abstract

During a study of the δ Scuti star V1393 Centauri by digital single lens reflex photometry, it was found that two of the chosen comparison stars were variable. This paper reports the subsequent investigation of one of them, HD 121620, which revealed irregular light variations of 0.8 magnitude in V within a time frame of approximately 24 hours. Photometry in the Hipparcos and Tycho databases from December 1989 to February 1993 revealed an average VT magnitude of 7.25 and little scatter in the data, indicating that the star was then either constant or only slightly variable. Photometry in the ASAS-3 V database between January 2001 and September 2009 showed a similar pattern, with an average magnitude of 7.1. Variability is documented in the ASAS-SN V database from February 2016 to September 2019, and in the ASAS-SN g database from June 2018 to September 2019. Inspection of the author’s light curves and Fourier analysis of the author’s data show a time frame of one day, but no regular periodicity. Since HD 121620 has a spectral type of G6/8III, it belongs to a population of stars which are least likely to be variable. The nature of its variability has not been determined.