A THREE-COLOR PHOTOELECTRIC INVESTIGATION OF THE ECLIPSING BINARY SYSTEM AR LACERTAE.

Abstract

ABSTRACT AR Lac was observed on 22 nights during the autumns of 1972, 1973, and 1974. Totals of 650-700 observations each were obtained in yellow, blue, and ultraviolet. The period of AR Lac, which is 1d9832, has undergone substantial changes during the past 40 years. Residuals are calculated for all published times of minimum light using three different least squares procedures. The light curves of AR Lac indicate that the intrinsic variation has a total amplitude of about . The eclipses are complete, the primary being an occultation. The primary minimum displays less scatter than does the secondary minimum, and this is consistent with the hypothesis that the intrinsic variation arises chiefly from star A. Star B may well be nonvariable. Photometric elements are obtained using the method of Russell and Merrill. Good agreement was found between the observed light curves and the theoretical light curves for primary minimum, but the agreement was poor for secondary minimum. Orbital eccentricity is considered, but it is found to be very small, if present at all. Radii of 1.54 R0 and 2.81 R0 are obtained for star A and star B, respectively. The masses of the components are nearly identical. Their effective temperatures are estimated to be 5600 K and 4700 K, respectively, and these are in agreement with their spectral types of G2 IV and KO IV. AR Lac is one of very few eclipsing binaries which have been observed to show pronounced flare activity at radio wavelengths. The radio outbursts do not appear to be correlated with phase or with instabilities in the light curves at optical wavelengths. Key words - eclipsing binaries - intrinsic variables - subgiants - radio sources