UBV photometric study of MR Cyg.

Photoelectric UBV observations of MR Cygni were obtained and the resulting three light curves solved. The eclipses are complete but very nearly grazing. Values of k derived six different ways (depth and shape k in three colors) agree well; the resulting elements represent all observations very faithftilly. The (U- B), (B- V) indices imply a spectral type of B3 for the primary; the old classification A0 is apparently wrong. Several lines of reasoning lead to a spectral type of B8 I 1 for the secondary. The spectroscopic orbit of Harper et ci., leads to unreasonably small absolute dimensions. A mass ratio of 1.8, typical of B3 and B8 main-sequence stars, leads to 7.5 "o, 5.1 Ho and 4.2 9.)? , 3.7 R0 respectively. MR Cyg is probably a system of two main-sequence stars, quite close, but normal and uncomplicated.