Luminosity change in DQ Herculis.

UBV photometry of DQ Her was obtained in 1975 in order to compare the light curves at the present epoch with those obtained in 1954. Near-IR and Stromgren-Crawford y light curves were also taken. It is found that since 1954, the B light outside eclipse has dimmed by about 0.5 magnitude and the light at primary minimum has dimmed by about 1.3 magnitudes. A simple analysis of the UBV light curves obtained in 1954 and 1975 reveals the occurrence of several light changes, providing indirect evidence that the mass-transfer rate is not constant with time. Specifically, it is shown that the nebula has fallen to about 25% of its 1954 luminosity while the accretion disk has fallen to 80% of its 1954 luminosity. It is concluded that variations in the mass-transfer rate of the order of 20% may occur on times scales of less than 0.7 yr, that much of the IR light at mideclipse may come from the red main-sequence star which eclipses the disk, and that the mass of the red star is no more than 0.4 solar mass.