Abstract
For the first time, BVIc observations of the Cepheid V811 Oph were obtained by using a new 60‑cm telescope at the Caucasus Mountain Observatory, Sternberg Astronomical Institute, Moscow State University (SAI MSU). An \(O{-}C\) diagram covering a time span of 124 years was plotted using photometry from old photographic and modern sky surveys. The diagram has a parabola shape, which made it possible to determine for the first time the quadratic elements of the brightness variations. Furthermore, it made it possible to calculate the rate of an evolutionary decrease in the period of V811 Oph \(dP{\text{/}}dt = - 0.00375( \pm 0.00177)\) s/year, which is consistent with the theoretical calculation results for the second intersection of the instability strip if this Cepheid is a classical one. The pulsation stability test proposed by Lombard and Koen confirmed the actual decrease in the period.
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ACKNOWLEDGMENTS
The authors would like to thank the specialists of the SAI MSU V.A. Senik and I.A. Gorbunov for the assistance in setting up the RC-600 telescope equipment.
Funding
This study was supported by the Russian Foundation for Basic Research (project nos. 18-02-00890 and 19-02-00611). N.I. Shatskii is in part supported by the Russian Scientific Foundation grant no. 17-12-01241. A.A. Belinskii, E.O. Mishin, and D.V. Cheryasov are supported by the grant from the Moscow State University Development Program “Leading Scientific School ‘Physics of Stars, Relativistic Objects, and Galaxies.’” The study was carried out using the equipment purchased at the expense of the Moscow State University Development Program.
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Translated by M. Chubarova
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Berdnikov, L.N., Belinskii, A.A., Shatskii, N.I. et al. BVIc Observations and Search for Evolutionary Variations in the Cepheid V811 Oph Period. Astron. Rep. 64, 310–318 (2020). https://doi.org/10.1134/S1063772920040010
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DOI: https://doi.org/10.1134/S1063772920040010