UBVRI Photometry of the Recurrent Nova T Coronae Borealis

Differential UBVRI photometry of this bright recurrent nova at three different observatories in 1981, 1982, and 1983 reveals variability on three different timescales. By Fourier analysis the amplitude of the ellipticity effect at UBVRI is determined and used to find the prolateness coefficient z = 0.14 + or - 0.01. Times of minimum light equated with times of conjunction and combined with previously published times yield 227.67 d + or - 0.02 d for a refined orbital period. Continuous photometry on one night confirms short-term variability reported earlier. Residuals from the Fourier fits reveal an additional variability with a period of about 55 days and an amplitude that in 1983 was 0.35 mag in V, 0.5 mag in B, and 0.8 mag in U. It is concluded that the gM3 primary is probably a semiregular red variable.