V-Band, Near-IR, and TiO Photometry of the Semi-Regular Red Supergiant TV Geminorum: Long-Term Quasi-Periodic Changes in Temperature, Radius, and Luminosity

Seventeen years of V-band and intermediate Wing near-IR TiO (lambda 719-nm to lambda 1024-nm) time-series photometry of the M1-4 Jab supergiant TV Geminorum are presented. The observations were conducted from 1997 to 2014 with the primary goals of deteimining both long-term (years) and short-term (months) periodicities and estimating temporal changes in temperature, luminosity, and radius as the star varies in brightness. Our results suggest a dominant short-term V-band period of similar to 411 days (similar to 1.12 years) that is superimposed on a long-term cycle of similar to 3137 days (similar to 8.59 years). Over this long-term cycle, the effective temperature varies between similar to 3500 K to similar to 3850 K and, at an adopted distance of 1.5 +/- 0.2 kpc, the luminosity varies from similar to 6.2 x 10(4) L-circle dot to similar to 8.9 x 10(4) L-circle dot and the radius varies from similar to 620 R-circle dot to similar to 710 R-circle dot. Variations in temperature and luminosity are indicative of a semi-regular long-term pulsation with imposed short-term periods similar to the V-band variations. However, the calculated radius variations are apparently not generally inversely correlated with respect to the long-term temperature and luminosity changes as typically found in Cepheids and Mira-type variables. This observation suggests other undetermined mechanisms, such as the formation and subsequent dissipation of supergranules or possible complex pulsations, are taking place in this evolved red supergiant to account for these variations. Like other young, massive luminous red supergiants such as Betelgeuse (alpha Orionis) and Antares (alpha Scorpii), TV Gem shows complicated light variations on time scales that range from months to several years. These evolved high massive stars are important to study because they are nearby, bright progenitors of core-collapsed Type II supernovae.