COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3707 Konkoly Observatory Budapest 3 April 1992 HU ISSN 0374 - 0676 LIGHT CURVE AND COLOR VARIATIONS OF V2101 Oph IN 1991 During observations of the variable stars IX and KK Oph using the 0.6m Zeiss reflector equipped with a pulse - counting photometer at Mt. Maidanak Expedition on 27 June 1991 we detected a rise in the light of the neighbouring U Gem-type star V2101 Oph (Khruzina and Shugarov, 1991). UBVR- monitoring of this star was continued with the same telescope up to September. The results of the photoelectric photometry are listed in Table I. [FIGURE 1] Table 1. UBVR photometry of V2101 Oph in 1991 JD(2448..) V U-B B-V V-R 435.340 11.88 1.32 2.16 2.10 435.397 11.93 2.12 2.17 435.405 11.93 2.15 436.324 11.92 2.19 437.336 11.74 1.89 2.03 438.346 11.67 1.84 2.00 439.329 11.69 1.84 440.300 11.60 1.82 1.90 1.97 443.286 11.54 1.83 1.96 444.276 11.48 0.97 1.82 1.96 445.282 11.47 1.81 1.96 446.276 11.38 0.99 1.83 1.94 448.269 11.40 0.99 1.91 1.95 449.339 11.42 1.92 450.287 11.31 1.84 1.92 451.253 11.38 1.90 1.92 453.267 11.43 1.01 1.89 1.98 454.283 11.45 1.87 1.99 455.313 11.42 1.25 1.91 1.98 456.313 11.41 1.20 1.91 457.312 11.47 1.93 2.05 458.269 11.43 0.83 1.77 1.98 462.263 11.55 1.73 2.02 463.230 11.51 1.86 1.97 465.202 11.59 0.90 1.88 2.02 466.195 11.63 1.97 2.12 2.06 467.200 11.65 1.89 2.06 471.215 11.77 1.94 2.10 472.225 11.76 1.92 2.10 JD(2448..) V U-B B-V V-R 473.199 11.85 1.93 2.14 474.228 11.92 1.86 2.23 477.190 11.97 0.58 2.02 2.19 478.199 12.02 1.49 2.03 2.21 480.186 12.12 2.07 2.25 481.220 12.15 2.05 2.30 482.227 12.15 2.02 2.29 484.185 12.22 1.95 2.30 485.169 12.29 1.94 2.31 486.159 12.32 1.86 2.33 487.164 12.33 2.01 2.32 489.165 12.43 2.28 2.38 490.190 12.46 2.19 2.37 491.191 12.51 2.30 2.39 493.195 12.67: 2.58 494.191 12.67 2.36 2.44 498.199 12.93 2.14 2.59 499.157 12.94 0.43 2.08 2.54 503.162 13.17 1.95 2.64 504.159 13.28 1.76 2.71 505.147 13.27 2.07 2.67 506.158 13.30 2.11 507.161 13.38 1.92 508.160 13.45 0.52 1.89 2.75 509.161 13.51 2.01 510.156 13.59 1.93 2.83 511.140 13.72 1.93 2.89 512.141 13.66 1.97 2.79 513.141 13.67 2.11 2.77 CoD-27d 10844 was used as the comparison star (V=7.800, U-B=-0.07, B-V= 0.415, V-R=0.423). The light curves of the variable in V and in color (V-R) are presented in Figure 1 a, b, V - (V-R) diagram is shown in Figure 2. The light maximum in V band corresponds to JD = 2448451.5. Our photographic estimates of V2101 Oph for 1985-1988 obtained using the plates exposed on the Zeiss Double Astrograph with the limiting magnitude about 17 pg are collected in Table 2. One of the 8 plates shows the star of 13.8 pg (16 August 1987), but on the other plates the magnitude of the star varies near its minimum. Table 2. JD(244...) m(pg) 6295.3 15.4 7024.3 13.8 7323.3 15.9 7327.3 16.0 7330.3 16.0 7331.3 16.1: 7349.3 16.4 7354.3 >16.5 [FIGURE 2] The shape of the light curve during the observational interval, color variations, as well as extremely red color of V2101 Oph are not typical of U Gem-type variables. Moreover, the brightness increase reaches its maximum in B and decreases to R. Therefore we suspect V2101 Oph to be a Mira-type or late type semiregular variable. S.D. YAKUBOV M.A. IBRAGIMOV Astronomical Institute, Tashkent, Uzbekistan S.A. SKORNYAKOVA Saratov State University, Russia Reference: Khruzina, T.S., Shugarov, S.Yu.: 1991, Atlas of Cataclysmic U Gem-type variables, Part 2, Moscow St. Univ. Publ., Moscow