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The short-period eclipsing binary system TY Boo was observed on five consecutive nights with the facilities at Lowell Observatory. The observations covering the eclipse portions of the light curves yielded five epochs of minimum light. A period study gives no indication of the cyclic period variation indicated by Szafraniec. The light curves, defined by 348 observations with the B filter and 353 with the V filter, are of the W Ursae Majoris type and are symmetric. The system becomes redder during each eclipse with a momentary dereddening at phase 0.0. The depths of the eclipse curves are about the same as those in the light curves published by Carr. However, the system appears to have undergone a slight reddening.

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The very short-period eclipsing binary system AD Cnc was observed on three nights with the facilities at Kitt Peak National Observatory. Standard magnitudes have been derived for AD Cnc and for the check and comparison stars. The observations covering the eclipse portions of the light curve yielded five epochs of minimum light. An improved ephemeris is presented. The light curves, defined by 735 observations with both the B and R filter, 733 with the V filter, and 730 with the I filter, are fairly symmetric. The magnitude differences in the maxima are slightly more than the probable errors of the observations. The difference in the depths of the eclipse curves is small (~ 0 m 03-0706) with the depth of the primary eclipse curve averaging 074.

V523 Cassiopeiae is a dwarf contact binary with one of the shortest orbital periods among the nondegenerate systems. Its orbital history is marked by large period changes. The photometrically determined mass ratios have historically been inconsistent with those calculated from radial velocity curves. In 1998 we acquired highprecision and standardized Johnson-Cousins UBV light curves. Our simultaneous BV light curve/radial velocity curve solutions provided good fits to both the light curves and the radial velocity curves using standard gravity darkening coefficients with a mass ratio of $0.5. Seven precision mean epochs of minimum light were determined from these observations. We combine these with all available published times of minimum light, along with 50 times of low light found from a search of the archival Harvard plate stacks in the interval 1901-1942 to give us 567 eclipse timings. Our period study covers nearly 160,000 orbits, or $102 yr. We find a high-amplitude sinusoidal variation with a period of 101 AE 7 yr, overlaid on a strong continuous period increase. The quadratic term is common in contact binaries, but a sinusoidal one is not. This suggests a hierarchical three-star system. Assuming that this is the case and that the inclination from our orbital solution for the close pair is the same as the larger orbit, we obtain a mass for the third star of 0.41 M . This is similar to the masses of the stars that comprise the contact binary. If this scenario is correct, V523 Cas consists of a trio of late K and early M-type dwarfs having a total mass of $1.6 M . We show that high-resolution imaging can confirm this suggestion.

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