COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2690 Konkoly Observatory Budapest 22 March 1985 HU ISSN 0374 - 0676 BD+37d2641, A POSSIBLE ECLIPSING BINARY SYSTEM In 1982 we carried out a photometric study of the Delta Scuti star YZ Boo, aimed principally at determining its period of pulsation. Since the method of photometry followed was that of differential photoelectric photometry, the reference stars chosen satisfied the following conditions: The same apparent magnitude of the variable star and in its neighborhood, less than two degrees apart to minimize the effects of atmospheric extinction. Therefore, although most studies on YZ Boo utilized BD+37d2639 or BD+37d2634 as reference stars (Szeidl and Mahdy 1981) we chose BD+37d2640 as a reference and BD+37d2641 as a check star on the nights of 16-17 and 17-18 of April, 1982. The use of at least one check star has been systematically considered in our observations since there is always the chance of utilizing a variable star as reference, thus making the obtention of the periodic content of the problem star impossible. Even more, the "quality" of the night can be directly measured by subtracting the two standard stars and evaluating their corresponding dispersion. When this last procedure was done on the night of April 16-17 we obtained a of the difference of the two comparison stars, of 0.01 mag, but when the same evaluation was done on the following night, that of April 17-18, an exceedingly large scatter was obtained due, as can be seen in Figure 1, to the drop in the magnitude of the BD+37d2641 star. Of course, when one finds a new variable or eclipsing star one cannot be sure of which star has changed, and the variation could be attributed to any of the observed stars. In this particular case, it is hard to believe that the change can be attributed to BD+37d2640 because both this and the variable star YZ Boo, didn't change their magnitude so abruptly. Even more, on continuing the study of the variability of YZ Boo, it was observed this time utilizing not only BD+37d2640, but two more reference stars, mainly BD+37d2634 (which has also been extensively utilized as reference for YZ Boo) and a faint star, which has not been listed in the BD catalogue and that is located next to YZ Boo to the north of it; none of them changed their magnitude during four consecutive nights that were observed one month later from May 6, to 9, 1982, establishing the constancy of BD+37d2640. [FIGURE 1] Figure 1: Light curve of BD+37d2641. The upper part shows the difference between this star and BD+37d2640 on the night of April 17, 1982; the lower the same difference on the following night, April 18, 1982. The observations were carried out using two telescopes. On the first night, April 17, they were carried out with the two-meter telescope whereas on the second one, April 18, the 1.5 m telescope was utilized. Both telescopes are at the Observatorio de San Pedro Martir, Mexico. In both cases a 1P21 cooled phototube was utilized in Johnson's V filter. Each point is an average of five ten-second integrations of the star minus one ten-second integration of the sky. Therefore, the accuracy of each point is of 0.003 mag and of 0.007d in time. The difference in magnitude between BD+37d2641 and BD+37d2640 and the corresponding heliocentric Julian Days are listed in Table I. One can see from the light curve of BD+37d2641, Figure 1, that it experiences a drop in magnitude of at least 0.5 mag in a time span of about two hours, showing the characteristics of a binary system. We plan and encourage further observations of this binary system which, as far as we know, has not been previously reported. Table I : Photometry of BD+37d2641 in the V filter -------------------------------------------------- HEL JD D MAG HEL JD D MAG 2445000.0+ 2445000.0+ -------------------------------------------------- 76.853 -0.215 77.747 -0.193 76.856 -0.192 77.755 -0.198 76.861 -0.205 77.762 -0.207 76.866 -0.190 77.768 -0.191 76.871 -0.188 77.771 -0.191 76.875 -0.192 77.775 -0.195 76.879 -0.182 77.780 -0.198 76.884 -0.195 77.784 -0.193 76.888 -0.201 77.788 -0.182 76.893 -0.205 77.792 -0.190 76.896 -0.200 77.797 -0.192 76.903 -0.201 77.803 -0.196 76.908 -0.198 77.807 -0.194 76.913 -0.185 77.812 -0.189 76.921 -0.199 77.816 -0.194 76.925 -0.195 77.821 -0.189 76.934 -0.193 77.827 -0.179 76.938 -0.197 77.832 -0.180 76.943 -0.195 77.839 -0.183 76.947 -0.195 77.845 -0.173 76.951 -0.188 77.851 -0.189 76.955 -0.190 77.856 -0.177 76.959 -0.197 77.863 -0.188 76.964 -0.191 77.869 -0.182 76.968 -0.201 77.873 -0.163 76.972 -0.195 77.879 -0.123 76.976 -0.192 77.884 -0.102 76.981 -0.186 77.889 -0.063 76.985 -0.182 77.896 -0.004 76.989 -0.188 77.904 0.088 76.993 -0.189 77.909 0.118 76.998 -0.179 77.914 0.168 77.002 -0.174 77.925 0.268 77.005 -0.175 77.930 0.359 77.742 -0.193 ----------------------------------------------------- We would like to thank. the staff of the Observatorio de San Pedro Martir, Mexico, for the assistance provided, to D. Flores for the heliocentric correction evaluation, and to A. Garcia for the drawing. J.A. Miller proofread the manuscript. The plots were carried out utilizing the Technical Report No 11 by J.F. Barral. R. PENICHE, S.F. GONZALEZ and J.H. PENA Instituto de Astronomia Universidad Nacional Autonoma de Mexico Apdo. Postal 70-264-04510 Mexico, D.F., Mexico Reference : Szeidl, B., and Mahdy, H.A., 1981 Communications from the Konkoly Observatory of the Hungarian Academy of Sciences No 75. [BIBCODE 1981CoKon..75....1S ]