COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3189 Konkoly Observatory Budapest 20 May 1988 HU ISSN 0374-0676 PHOTOGRAPHIC UBV PHOTOMETRY OF FLARE STARS IN THE GAMMA CYGNI REGION The observations in the investigated 4dx4d area in Cygnus (central star BD+ 40 4165 with coordinates R.A. 1950 = 20h24m35s and D 1950 = 41d12'52" were initiated in view of the presence of some young objects appearing as active star formation indicators. The close relationship between the T Tau stars, H-alpha emission stars and flare stars is already well established. Thus one can expect the presence of flare stars in every group containing T Tau stars and related objects. In the investigated region only two probable UV Cet type stars were known - V 1381 Cyg and LD21 (Dahlmark, 1982) up to our special searches for flare stars. Fifteen new flare stars were discovered (Melikian et al., 1980, Tsvetkova, 1980, 1982, Tsvetkova et al., 1983). The identification charts of the discovered flare stars obtained from the E-print of the Palomar Observatory Sky Survey Atlas are presented in Figure 1. Where the nebulae worsen the visibility of the stars the O-print is used. On these charts, north is at the top, east is to the left. The photometric observations were made with the 40"/52" Schmidt telescope of the Byurakan Astrophysical Observatory in September, 1980. The photometry was carried out with an Ascania iris photometer. Doing the photometry, we adopted the existing photoelectric standards in the association Cygnus OB2 and the photographic standards in the region of the nebula IC 5070. The second photographic standards in this region are in the interval 11.6 - 18.3 (V). The presence of dark and emission nebulae in the investigated region requires to determine the influence of the uneven background. The mean quadratic errors are respectively +/-0.10m(V), +/-0.09m(B), +/-0.10m(U). In Table I the results from the UBV photographic photometry of the flare stars in quiet state (minimum of the brightness) are given. The designation of the flare stars is according to the General Catalogue of Variable Stars (Kholopov et al., 1985a) and to the 67th Name-List of Variable Stars (Kholopov et al., 1985b). [FIGURE 1] Table I Name V B-V U-B V1695Cyg 16m03 1m23 1m02 V1750Cyg 17.39 0.76 0.14 V1752Cyg 17.90 - - V1753Cyg 17.74 - - V1754Cyg 17.60 0.85 - V1755Cyg 15.44 1.37 0.99 V1756Cyg 17.79 - - V1757Cyg 18.02 - - V1772Cyg 15.76 2.17 - V1778Cyg 16.42 0.87 0.33 V1779Cyg 16.61 0.97 0.73 V1780Cyg 17.82 1.31 - V1781Cyg 15.19 1.09 0.71 V1785Cyg 15.52 1.34 0.92 Table II Name B POSS B-V POSS V1752Cyg 20m00 2m10 V1753Cyg 19.55 1.75 V1756Cyg 21.00 3.20 V1757Cyg 21.00 3.00 V1777Cyg 21.00 2.20 Table III Name Date of flare-up Telescope *(min) V1695Cyg 12 Sept. 1977 40"/52" 18m28 2m16 V1750Cyg 13 Sept. 1980 - - 18.29 3.34 V1752Cyg 29 Oct. 1980 20"/28" 21.00* 5.40 V1753Cyg 18 June 1980 - - 20.55* 4.78 V1754Cyg 12 Sept. 1980 40"/52" 19.45* 3.33 V1755Cyg 15 Aug. 1980 20"/28" 17.80* 1.50 V1756Cyg 16 Aug. 1980 " 22.00* 6.24 V1757Cyg 17 July 1980 " 22.00* 6.10 V1772Cyg 19 Sept. 1981 " 18.93* 2.13 V1777Cyg 17 Sept. 1982 " 22.00* 6.32 V1778Cyg 27 Aug. 1981 " 17.62 1.50 V1779Cyg 03 Aug. 1981 " 18.31 3.05 " 20 Sept. 1981 " " 3.19 V1780Cyg 03 June 1981 " 20.13* 4.22 V1781Cyg 31 July 1981 " 16.99 1.31 V1785Cyg 29 Aug. 1981 " 17.78 1.62 * The stellar magnitudes are obtained on the basis of the approximate relation (U-B)min = +1. The magnitudes of the flare stars fainter than the limit of the photometric plates were obtained by measuring the diameters of the stellar images on the POSS prints with a mean quadratic error of +/-0.17 in the magnitude interval mag. 17-21(B POSS) (Table II). A summary of the flare-ups is given in Table III. In some cases there are differences reaching one magnitude between the stellar magnitudes in the maximum brightness given earlier and estimated now. The reason is in the higher accuracy of the estimation of stellar magnitudes with an iris photometer and in the determination of the influence of the uneven background. We obtained V- and B-magnitudes of V1381 Cyg, a probable UV Cet type star Romano, 1969). The star shows rapid changes in the V-light from 16.95m to 18.30m and in the B light with a smaller amplitude from 18.33m to 18.97m.It is not clear whether these are short time scale irregular changes of the brightness or flare-ups because the star is below the limit on our patrol U-plates. KATYA P. TSVETKOVA, M.K. TSVETKOV Department of Astronomy and National Astronomical Observatory blvd. Lenin 72, Sofia-1784 Bulgaria References: Dahlmark, L. 1982, IBVS, No. 2157. Kholopov, P.N. et al., 1985a,General Catalogue of Variable Stars, 4th Ed., Vol. II., Nauka, Moscow. Kholopov, P.N. et al., 1985b,IBVS, No. 2681. Melikian, N.D., Jankovics, I., Tsvetkova, K.P., and Tsvetkov, M.K., 1980, IBVS, No. 1750. Romano, G., 1969, Pubbl. Oss. Astron. Padova, No. 156. Tsvetkova, K.P., 1980, IBVS, No. 1887. Tsvetkova, K.P., 1982, IBVS, No. 2131. Tsvetkova, K.P., Hambarian, V.V., Brutian, G.H., 1983, IBVS, No. 2365.