Long‐Term<i>VRI</i>Photometry of Small‐Amplitude Red Variables. I. Light Curves and Periods

Abstract

We report up to 5000 days of VRI photometry, from a robotic photometric telescope, of 34 pulsating red giants, namely, TV Psc, EG And, Z Psc, RZ And, 4 Ori, RX Lep, UW Lyn, η Gem, μ Gem, ψ1 Aur, V523 Mon, V614 Mon, HD 52690, Y Lyn, BC CMi, X Cnc, UX Lyn, RS Cnc, VY UMa, ST UMa, TU CVn, FS Com, SW Vir, 30 Her, α1 Her, V642 Her, R Lyr, V450 Aql, V1293 Aql, δ Sge, EU Del, V1070 Cyg, W Cyg, and μ Cep, as well as a few variable comparison stars. V, R, and I variations are generally in phase. The length and density of the data enable us to look for variations on timescales ranging from days to years. We use both power‐spectrum (Fourier) analysis and autocorrelation analysis, as well as light‐curve analysis; these three approaches are complementary. The variations range from regular to irregular, but in most of the stars, we find a period in the range of 20–200 days, which is probably due to low‐order radial pulsation. In many of the stars, we also find a period which is an order of magnitude longer. It may be due to rotation, or it may be due to a new kind of convectively induced oscillatory thermal mode, recently proposed by P. Wood.