A Note on the Long-Term Light Curves of SRd Variable Stars

Volume 53 number 1 (2025)

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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

Chelsea Willow Taiger

Department of Astronomy and Astrophysics, and Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada; chelsea.taiger@gmail.com

Abstract

We briefly review some recent results on SRd variables—low-mass yellow supergiants with semiregular brightness variability. We then describe some interesting features of the long-term light curves of 19 SRd variables for which there are many decades of sustained visual and photoelectric data in the AAVSO International Database. DE Her, RS Lac, UY CMa, and possibly RX Ret showed a large-amplitude, long-term cyclic variation; TV Per brightened by 2.5 magnitudes in the last 10,000 days; Z Aur switched between dominant periods of 110 and 135 days; UU Her switched between dominant periods of 44 and 72 days, as it is well-known to do; TX Aql showed an unusually short period of 35 days. We have used the AAVSO VStar time-series analysis package to determine the average periods and amplitudes in each of the stars. The amplitudes are strongly variable with time. There is no strong evidence for long secondary periods of the kind found in RV Tauri stars or red giants in any of these stars.