A study of the close binary star TU Monocerotis

New photometric elements,i=89°.5,r_a=0.24,r_b=0.25 andL_a=0.82(Y), 0.88(B), 0.94(U), are deduced for the eclipsing system TU Mon, using the incomplete Fourier method for the analysis of its light curve. They are based upon three-colour photoelectric observations obtained in 1966–68 with the 36-inch reflector of the Okayama Astrophysical Observatory. From discussion combined with the spectroscopic data byDeutsch (1945) and byPopper (1967), it seems fair to conclude that TU Mon is an ordinary semi-detached close binary system consisting of a detached brighter B5V star and an A5 subgiant in contact at its Roche limit.