Long-Term VRI Photometry of Small-Amplitude Red Variables. I. Light Curves and Periods

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, h Gem, m Gem, w 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, a Her, V642 Her, R Lyr, V450 Aql, V1293 Aql, d Sge, EU Del, V1070 Cyg, W Cyg, and m 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.