Long-term VRI photometry of small-amplitude red variables. I. Light curvesand periods

We report up to 5000 days of VRI photometry, from a robotic photometric tel escope, of 34 pulsating red giants, namely, TV Psc, EG And, Z Psc, RZ And, 4 Ori, RX Lep, UW Lyn, eta Gem, mu Gem, psi (1) Aur, V523 Mon, V614 Mon, HD 52690, Y Lyn, BC CMi, X Cnc, UX Lyn, RS Cnc, VY UMa, ST UMa, TU CVn, FS Co m, SW Vir, 30 Her, alpha (1) Her, V642 Her, R Lyr, V450 Aql, V1293 Aql, del ta Sge, EU Del, V1070 Cyg, W Cyg, and mu Cep, as well as a few variable com parison stars. V, R, and I variations are generally in phase. The length an d density of the data enable us to look for variations on timescales rangin g from days to years. We use both power-spectrum (Fourier) analysis and aut ocorrelation analysis, as well as light-curve analysis; these three approac hes 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 i s 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 rota tion, or it may be due to a new kind of convectively induced oscillatory th ermal mode, recently proposed by P. Wood.