COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3956 Konkoly Observatory Budapest 25 November 1993 HU ISSN 0374 - 0676 UBV PHOTOMETRY FOR THREE NEW VARIABLE STARS From November 23 to December 3, 1992 and during March 7-11, 1993 UBV photoelectric photometry of several bright M type stars was carried out. The 60 cm reflector of Beijing Astronomical Observatory is equipped with a DC photoelectric photometer. Standard UBV filters are employed by this photoelectric system. During the run of observations differential determination of brightness of the program stars was used. Information about our program, comparison, and check stars is given in Table 1. Table 1. Properties of program (V), comparison (CO), and check (CH) stars. ------------------------------------------------------- Star SAO V Sp. R.A.(1950.0) Dec. ------------------------------------------------------- V 037673 7.9m M8 1h55m37.3s 45d11'33" CO 037668 8.0 K5 1h55m26.1s 44d52'40" CH 037657 8.1 G5 1h55m0.3s 45d15'14" V 056225 7.5 MA 3h 8m11.5s 37d52'53" CO 056202 7.1 K0 3h 6m17.5s 37d 6'44" CH 056178 7.6 G0 3h 4m28.7s 36d25'45" V 024927 6.9 M0 4h52m48.8s 59d20'34" CO 025088 6.4 K0 5h10m47.0s 59d20'57" CH 025003 6.4 K0 5h 1m50.6s 58d57'15" ------------------------------------------------------- At each night three sets of stars listed in Table 1 were observed and UBV photoelectric observations of each set of stars (V, CO, CH) were usually made several times at different zenith distances. Therefore the observations of more than two comparison or check stars can be used for calculation of atmospheric extinction coefficients in UBV bandpasses. Average value of extinction coefficients derived from more than two stars was used to correct for extinction for each observation. For the first and second sets of stars in Table 1, differential magnitude was determined by subtracting the mean magnitude of comparison and check stars from magnitude of program star. For the last set of stars, because check star SAO 025003 is a variable (Wahlgren G., 1992, AJ, 104, 1174) only one comparison star was used in reduction, therefore differential magnitude was magnitude difference between the program and comparison star. The resulting data were reduced to John-on system through transformation equation given later. Light curves in V bandpass for three program stars are shown in Figures 1, 2 and 3. In Figures 1 and 2 filled circles show differential magnitudes of program stars and open circles magnitude differences between comparison and check stars. In Figure 3 filled circles indicate differential magnitudes of program star, open circles magnitudes of the comparison star. The light curves with open [FIGURE 1] Figure 1. V light curve for SAO 037673. [FIGURE 2] Figure 2. V light curve for SAO 056225. [FIGURE 3] Figure 3. V light curve for SAO 024927. Table 2. Photometric data for SAO 037673. JD2448000+ U B V 949.184 9.784 9.043 7.449 949.200 9.786 9.048 7.454 949.213 9.784 9.043 7.449 950.125 9.723 8.991 7.401 950.134 9.793 9.026 7.436 950.142 9.808 9.026 7.446 952.080 9.778 8.986 7.404 952.084 9.753 8.976 7.414 955.196 9.704 8.948 7.359 955.204 9.675 8.973 7.369 955.213 9.695 8.963 7.364 955.992 9.630 8.902 7.317 956.000 9.685 8.922 7.342 956.113 9.809 9.027 7.407 956.121 9.784 9.002 7.392 957.050 9.710 8.946 7.361 957.059 9.709 8.926 7.346 958.009 9.724 8.941 7.356 958.017 9.704 8.941 7.352 960.030 9.710 8.933 7.349 960.038 9.690 8.919 7.329 1053.980 9.732 8.963 7.297 1053.992 9.628 8.938 7.282 1057.988 9.717 8.933 7.297 1057.996 9.663 8.948 7.302 Table 3. Photometric data for SAO 056225. JD2448000+ U B V 949.309 10.885 9.028 7.309 949.321 10.880 9.033 7.314 949.334 10.980 9.033 7.299 950.184 10.790 9.018 7.301 950.196 10.790 9.008 7.286 950.209 10.979 9.028 7.282 952.200 11.053 9.040 7.295 952.209 11.063 9.025 7.290 952.329 10.914 9.000 7.275 952.363 10.825 8.990 7.294 955.238 10.826 9.004 7.254 955.250 10.959 9.004 7.264 955.292 10.840 8.984 7.239 955.300 10.850 8.949 7.224 955.363 10.826 8.974 7.254 955.371 10.850 8.964 7.249 956.046 10.844 8.924 7.200 956.059 10.884 8.968 7.240 956.205 10.924 9.018 7.255 956.217 10.969 9.063 7.300 956.280 10.904 9.023 7.260 956.288 10.874 8.968 7.240 957.155 10.931 9.000 7.249 957.171 10.921 9.020 7.299 958.096 10.953 8.992 7.259 958.109 10.978 8.987 7.249 960.129 10.758 8.989 7.247 960.142 11.045 8.999 7.262 1056.050 9.156 7.390 1056.092 9.262 7.510 1058.050 10.981 9.179 7.464 1058.059 11.055 9.190 7.474 Table 4. Photometric data for SAO 024927. JD2448000+ U B V 950.246 10.235 8.369 6.696 950.259 10.205 8.349 6.681 950.272 10,225 8.344 6.681 952.221 10.058 8.304 6.636 952.230 10.093 8.294 6.660 955.259 10.098 8.335 6.694 955.267 10.088 8.320 6.679 955.338 10.023 8.259 6.614 955.342 10.008 8.245 6.604 956.159 9.995 8.254 6.601 956.167 10.035 8.244 6.597 956.254 10.080 8.294 6.646 956.259 10.115 8.324 6.666 957.184 10.079 8.268 6.625 957.196 10.063 8.272 6.610 958.117 10.052 8.254 6.611 958.125 10.067 8.250 6.606 958.155 10.087 8.270 6.611 960.155 9.991 8.204 6.543 960.163 10.051 8.254 6.583 1053.150 10.206 8.258 6.599 1053.163 10.072 8.213 6.578 1053.188 9.845 8.238 6.574 1053.200 10.012 8.208 6.573 1058.071 10.112 8.209 6.535 1058.079 10.147 8.209 6.521 circles in all figures were shifted vertically to compare clearly with light curves of program stars. For scientific analysis of photoelectric observations from different observers it is necessary to reduce the observations of these variables with longer timescales to the standard system. In the run of our observations 12 Johnson standard stars in Praesepe were also observed on three nights. After correcting for extinction, least squares fit was applied to the observations of these 12 standard stars. The following equations were obtained. V=v+(0.012+-0.018)(B-V)+(7.823+-0.012) B-V=(0.985+-0.006)(b-v)+(0.552+-0.002) U-B=(0.991+-0.011)(u-b)-(1.105+-0.017), where U, B and V are magnitudes in the standard system, u, b and v instrumental magnitudes after correction for extinction. Our photometric observations were finally reduced to Johnson system by the above equations. The UBV magnitudes are listed in Tables 2, 3 and 4 respectively. Our limited observations have well indicated that stars SAO 037673, SAO 056225 and SAO 024927 are variable stars. The standard error of a typical observation in V bandpass is about 0.01 mag., however, the observations in U show larger scatter than that in B and V. The UBV light curves of stars SAO 037673, SAO 056225 and SAO 024927 derived from our observations show significant variations. They are small-amplitude red variables with period probably greater than 30 days. We would like to thank Wang Hung and Chang Hungching for their participation in the observations. We thank Hu Jingyao who provided us with data of photometric standard stars. YANG TINGGAO CAO MING JIANG SHIYANG Shaanxi Astronomical Observatory Beijing Astronomical Observatory Chinese Academy of Sciences Chinese Academy of Sciences