PHOTOMETRIC STUDIES OF BY DRA

An exact analytical expression for the light variations of a star with a spot is used to analyze the photometric data obtained fur the varia ble BY Dra over the last 28 years. The photometric period of this star , P = 3.829(d), was found to be constant to within 0.005(d). We propos e a method for determining the magnitude and color of an unspotted sta r and a method Tor deriving the spot temperature from the mean light i n different bands, which yields more accurate spot temperatures, For t he primary component of the star, we obtained V-0 = 8.355, B-0 - V-0 = 1.18, and V-0 - R-0 = 1.08; the temperature difference between the st ar and the spot ranges from 400 to 700 K. For the adopted mathematical model of a star with a spot, a group of spots lying along the latitud e circle is required to explain the light curve of BY Dra. Within the accuracy of our data, we found no correlation between the period and t he latitude of the spot.