COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4082 Konkoly Observatory Budapest 13 September 1994 HU ISSN 0374 - 0676 PHOTOELECTRIC OBSERVATIONS OF GR TAURI GR Tau (=BD+20d0685) was discovered as an eclipsing binary by Strohmeier et al. (1957). Yamasaki and Okazaki (1984) published the first photoelectric light curves and the radial velocity curves with the revised spectral type A5 V and the orbital period P=0.4298525 days for the system. The remarkable characteristics of GR Tau are its short orbital period and asymmetric light curve with total eclipse. The photometric solution obtained by Yamasaki and Okazaki (1984) showed that the system might be a noncontact but near-contact detached binary. The new photoelectric BV observations were carried out with the single-channel photon- counting photometer at the 60 cm telescope of Beijing Astronomical Observatory during the 1985 and 1993 seasons. The stars BD+20d0684 and BD+19d0642 were used as the comparison and check star, respectively. All the observations were corrected for differential extinction and transformed into the standard Johnson UBV system. Two sets of complete BV light curves and three primary minima were obtained. Using the new times of minima, together with all published p.e. minima as listed in Table 1, a new linear ephemeris was derived as follows: Min.I.= HJD 2446415.0208 + 0.42985142d x E (1) +/-3 +/-7 The O-C values in Table 1 are calculated from new ephemeris (1) and are all plotted in Figure 1. It shows that the period of GR Tau appears to have appreciable long-term changes. Therefore, a quadratic fitting of minima is carried out by the least squares method, which gives the following ephemeris: Min. I=HJD 2446415.0216 + 0.42985146d x E - 6.26d x 10^-11 x E^2 (2) +/-4 +/-6 +/-2.12 The fit of the quadratic ephemeris (2) to the observations is also shown in Figure 1. The rate of the period decrease of GR Tau turns out to be DeltaP/P=-2.91 x 10^-10(~0.0092 sec/yr). By using the linear ephemeris (1), the observations in 1993 were combined into B and V normal light curves as shown in Figure 2. The light; curves exhibit obviously asymmetry with the Max I brighter than the Max II by about 0.05 in V and 0.07 in B. The behaviour of the light curve remains almost the same as that observed in 1980 by Yamasaki and Okazaki (1984) and in 1989 by Hanzl (1990) and no migration of the distortion on the light curves was found yet. The asymmetry of the light curve is probably due to the mass transfer in the system. [FIGURE 1] Figure 1. O-C diagram of minimum times for GR Tau. [FIGURE 2] Figure 2. BV light curves of GR Tau in 1993. Table 1 The times of minima and their O-C values JD(Hel.)2440000+ E O-C Source 4544.3075 -4352 0.0001 Yamasaki and Okazaki (1984) 4573.1074 -4285 0.0000 " 4578.2643 -4273 -0.0014 " 4579.1252 -4271 -0.0002 " 6414.1619 -2 0.0008 This paper 6415.0209 0 0.0001 " 6438.6622 55 -0.0004 Mullis and Faulkner (1991) 7821.4944 3272 -0.0002 Wunder et al.(1992) 7827.5148 3286 0.0023 Hanzl (1990) 7849.4363 3337 0.0013 " 7881.6752 3412 0.0014 Mullis and Faulkner (1991) 7889.4089 3430 -0.0023 Hanzl (1990) 7945.2937 3560 0.0019 Hanzl (1991) 8288.3122 4358 -0.0011 Agerer (1991) 9334.1394 6791 -0.0024 This paper The further photometric analysis of the light curves will be published in a forthcoming paper. Min-jun FANG, Di-sheng ZHAI, Zhen-don GAO, Rong-xian ZHANG, Ji-tong ZHANG, Xiao-bin ZHANG Beijing Astronomical Observatory Chinese Academy of Sciences Beijing, 100080 China References: Agerer, F., 1991, BAV-Mitteilungen, No. 59 Hanzl, D., 1990, Inf. Bull. Var. Stars, No. 3423 Hanzl, D., 1991, Inf. Bull. Var. Stars, No. 3615 Mullis, C. R., Faulkner, D. R., 1992, Inf. Bull. Var. Stars, No. 3593 Strohmeier, W., Knigge, R. and Ott, H., 1963, Veroff. Remeis-Sternw. Bamberg, 5, No. 17 Wunder, E., Wieck, M., Kilinc, B., Gulmen, O., Tunca, Z., Evren, S., 1992, Inf. Bull. Var. Stars, No. 3760 Yamasaki, A., Okazaki, A., 1984, Publ. Astron. Soc. Japan, 36, 175 [BIBCODE 1984PASJ...36..175Y ]