COMMISSION 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3839 Konkoly Observatory Budapest 9 February 1993 HU ISSN 0374 - 0676 NEW PROBABLE ECLIPSING BINARY GSC 1383_600 On December 28-29, 1992, I observed minor planet (4179) Toutatis. The observations were done with 0.18-m, f/5.6 Maksutov and SBIG ST-6 CCD-camera; eleven R and eight V images were taken, each exposure 2 minutes long. Already during the observations I noticed that one 11-magnitude star in the field of view changed its brightness by about 0.6 mag in the course of observing session. The variable star is GSC 1383_600. Observing conditions on December 28-29 were not fully photometric (cirrus clouds interference in a part of the night), so two additional (V and R) images were taken on the photometric night of January 2, 1993, to assure absolute photometric calibration of the images. Results of photometric reduction of the images are presented in Table I and a sparse composite lightcurve is shown in Figure 1. [FIGURE 1] Figure 1: Composite lightcurve of the variable star GSC 1383_600 on December 28-29, 1992. R-points were shifted by +0.48 to meet V-points. Table 1: V and R magnitudes of the variable star GSC 1383_600. UT JD-244800 V R 1992 Dec. 28.9343 985.4343 11.40 +-0.03 -- 28.9430 985.4430 -- 10.86 +-0.03 28.9481 985.4481 -- 10.93 +-0.03 28.9530 985.4530 11.39 +-0.03 -- 28.9808 985.4808 -- 10.57 +-0.03 28.9950 985.4950 -- 10.43 +-0.03 29.0006 985.5006 -- 10.36 +-0.02 29.0041 985.5041 10.84 +-0.03 -- 29.0071 985.5071 10.82 +-0.03 -- 29.0105 985.5105 -- 10.35 ± 0.02 29.0389 985.5389 -- 10.35 +-0.02 29.0725 985.5725 10.82 +-0.02 -- 29.0794 985.5794 -- 10.36 +-0.02 29.1061 985.6061 -- 10.34 +-0.02 29.1095 985.6095 10.82 +-0.03 -- 29.1494 985.6494 -- 10.35 +-0.02 29.1538 985.6538 10.83 +-0.02 -- 29.1919 985.6919 10.84 +-0.02 -- 29.1957 985.6957 -- 10.36 +-0.02 1993 Jan. 02.0345 989.5345 10.84 +-0.02 -- 02.0369 989.5369 -- 10.38 +-0.02 Mean V-R is 0.48 +-0.01, no significant color change was detected. There is no variable star at that position listed in the fourth edition of GCVS (Kholopov et al., 1985). The shape of the lightcurve suggests that the variable star is an eclipsing binary. An amplitude of the brightness change is 0.57 mag in V (10.83-11.40). The brightness is nearly constant during its minimum for at least 27 minutes, and there is rather steep rising branch with maximal duration of 68 minutes (lower limit of the mean rate is 0.50 mag/hour). There is a convenient comparison star for photoelectric and other photometry, GSC 1383_1005, which is located at distance of 99 arcsec approximately in SSE direction. Positions (from GSC, 1989) and photometric parameters (measured, errors 0.01-0.02) of both stars are listed in Table 2. One of the R-images (taken on January 2, 1993) is reproduced in Figure 2. Table 2: The variable star and convenient comparison star. Star R.A. (2000) Decl.(2000) V V-R GSC 1383_600 08h29m39.36s +17d17'01.8" 10.83-11.4 0.4 GSC 1383_1005 08h29m43.00s +17d15'38.1" 11.34 0.2 I conclude that GSC 1383_600 is probably an eclipsing binary with an amplitude of 0.57 (+-0.02) mag and maximal brightness corresponding to 10.83 (+-0.01) mag in V-band. Further studies could confirm the type of variability suggested, determine a period and find a detailed lightcurve. The author is grateful to Dalibor Hanzl for his valuable help. [FIGURE 2] Figure 2: R-image of the field of the variable star GSC 1383_600, taken on January 2, 1993. The size of the area imaged is 31*23 arcmin^2, north is up. The star GSC 1383_1005 is also marked. Petr PRAVEC Astronomical Institute CS-25165 Ondrejov Czech Republic References: Kholopov, P.N., Samus, N.N., Frolov, M.S., Goranskij, V.P., Gorynya, N.A., Kireeva, N.N., Kukarkina, N.P., Kurochkin, N.E., Medvedeva, G.I., Perova, N.B., and Shugarov, S. Yu., 1985, General Catalogue of Variable Stars, the 4th edition, "Nauka", Moscow. The Guide Star Catalog (GSC), 1989, Space Telescope Science Institute, Baltimore.