COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 831 Konkoly Observatory Budapest 1973 October 3 PHOTOELECTRIC OBSERVATIONS OF 31 CYGNI DURING THE 1972 ECLIPSE On seventeen nights between April and July, 1972, photoelectric observations of 31 Cygni were obtained in three colors (UBV) by Landis at his observatory in Fast Point, Georgia, with a 20.3 cm reflector. An unrefrigerated 1P21 photomultiplier was used with the cathode at -800 volts. The filters used to reproduce the UBV system are Corning 3384 (4.5 mm) for visual, Corning 5030 (4.9 mm) plus Schott GG13 (2 mm) for blue, and Corning 9863 (3 mm) for ultraviolet. A full description of the photoelectric equipment used has been made elsewhere (PASP 85, 133, 1973). All observations were transformed from the natural instrumental system to the standard UBV system. The transformation coefficients and their mean errors were found to be epsilon = - 0.01 +/-0.01, mu=1.05+/-0.01, and psi=1.00+/-0.02. Mean extinction coeficients for the Atlanta area were determined from standard stars and were found to be 0.364, 0.471 and 0.765 for yellow, blue and ultraviolet respectively. The data reduction was done by Williamon through the facilities available to the Fernbank Science Center. Table I UBV Photoelectric Observations of 31 Cygni J.D. Hel J.D. Hel 2441000+ DeltaV DeltaB DeltaU 2441000+ Delta V DeltaB DeltaU 431.8855 -1.298 -1.122 -1.671 483.7468 -1.188 -0.752 -0.070 .9024 -1.289 -1.120 -1.691 .7683 -1.191 -0.753 -0.091 432.8835 -1.275 -1.126 -1.671 490.7459 -1.174 -0.728 -0.050 .9043 -1.268 -1.110 -1.685 .7616 -1.167 -0.740 -0.061 433.8838 -1.323 -1.133 -1.644 491.7255 -1.191 -0.736 -0.053 .9060 -1.352 -1.153 -1.668 .7417 -1.189 -0.733 -0.046 441.8857 -1.202 -0.757 -0.084 492.7714 -1.188 -0.750 -0.055 .9042 -1.218 -0.786 -0.143 .7888 -1.182 -0.738 -0.042 442.8818 -1.205 -0.779 -0.114 498.7253 - -0.764 -0.092 .8990 -1.202 -0.757 -0.065 .7413 -1.176 -0.742 -0.078 446.8679 -1.191 -0.777 -0.130 .7568 -1.185 -0.756 -0.059 .8852 -1.219 -0.712 -0.099 .7730 -1.175 -0.738 -0.065 447.8566 -1.210 -0.786 -0.089 501.7388 -1.268 -1.003 -1.057 .8760 -1.244 -0.798 -0.137 .7548 -1.279 -0.999 -1.063 469.8031 -1.189 -0.760 -0.097 .7702 - -0.983 -1.065 .8186 -1.166 -0.735 -0.077 504.6875 -1.304 -1.082 -1.528 470.8018 -1.225 -0.739 -0.097 .7019 -1.264 -1.088 -1.551 .8247 -1.176 -0.745 -0.019 519.6520 -1.271 -1.116 -1.728 .6659 -1.271 -1.120 -1.739 All observations of 31 Cygni were made differentially with respect to 26 Cygni. 30 Cygni was used as an early type check star on several nights and gave no indication of any variability of 26 Cygni. The magnitude differences in each of the three colors are listed in Table I. The first column contains the heliocentric Julian date and the second column the differential magnitude for each color. [FIGURE 1] Table II Properties of the Light Curves Delta V Delta B Delta U Light outside eclipse -1.2934(8) -1.1251(8) -1.6870(8) Light during eclipse -1.1935(23) -.07526(24) -0.0797(24) Depth 0.0999 0.3625 1.6073 ( )gives the number of observations From the average values of Delta V, Delta B,and Delta U during totality and outside of eclipse, the corresponding depths of the eclipses were deduced and are given in Table II. The light curve shown in the figure uses the average value of Delta V, Delta B and Delta U for each night. 20 August, 1973 HOWARD E. LANDIS RICHARD M. WILLIAMON 2395 Wood Hill Lane Fernbank Observatory East Point, Georgia 30344 Atlanta, Georgia