COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1120 Konkoly Observatory Budapest 1976 April 2 THREE-COLOUR PHOTOGRAPHIC PHOTOMETRY OF V 1057 CYGNI According to a program of investigation of flare stars and other nonstable objects in the 16 square degrees region of Cygnus (RA_1950=20h52; D_1950=+42d40') a great number of u, pg and some b, v patrol plates were taken between 1972 August 4 and 1974 August 30 (1121 days) with the 40 inch/50 inch and 21 inch/21 inch telescopes of the Byurakan Astrophysical Observatory. On 89 of our plates we measured the magnitudes of V 1057 Cyg in u, b (pg) and v colours and compared them with the results of Gieseking (1) obtained for the period 1970-1975. In order to obtain a good approximation to the UBV system we used the following telescope and plate-filter combinations: u - 40 in. telescope, Kodak 103aO or ZU-2 + Schott UG2 or UG1 b - 40 in. telescope, Kodak 103aO or ZU-2 + Schott GG13 pg - 21 in. telescope, Kodak 103aO or ZU-2 without filter v - 40 in. telescope, Kodak 103aD + Schott GGII Our investigation (2) shows that the used u,b,v system is a good approximation of Johnson's photographic system and that pg- magnitudes are equal to b. The measurements were carried out with an "ASKANIA" irisphotometer. Characteristic curves were derived for each plate using a group of 5 stars of photoelectric UBV - standard of Bigay and Garnier (3) and 7 stars of our secondary UBV photographic standard in the region of IC 5070 according to (2). As in this region the background is very inhomogenous the iris readings for V 1057 Cyg were corrected according to the method of Argue (4). The nebula around V1057 Cyg influenced our measurements in the sense that our u,b, (pg), v magnitudes of this star were systematically brighter. The results of our three-colour photographic photometry are given in the Table. In the Figure we present the light curve of V 1057 Cyg in three colours. With dots and solid lines are presented our u,b(pg), J.D.244... v b/pg u J.D.294... v b/pg u 1534,28 12,05 2251,42 11.78 1537,30 10,90pg 2251,43 11,60 1538,43 12,03 2251,44 11,67 1547,42 11,98 2251,49 12,61 1550,46 11,06pg 12,07 2252,38 12,79 1567,24 11,95 2252,42 12,74 1597,30 11,00pg 2254,37 12,73 1621,17 11,95 2254,40 12,76 1631,19 11,01pg 2254,49 12,70 1810,46 11,32pg 2255,30 12,68 1843,47 11,46pg 2269,28 11,80 1860,40 12,67 2272,31 10,03 1866,43 11,52 2272,47 12,83 1868,41 12,62 2273,30 12,68 1888,30 11,52 2273,33 12,90 1889,42 12,42 2273,36 12,69 1891,26 12,70 2275,30 11,68 1891,31 12,55 2275,31 10,13 1893,50 12,66 2278,47 12,87 1914,29 12,39 2279,33 12,71 1919,34 12,65 2299,30 12,89 1920,33 12,40 2300,31 12,70 1921,29 12,32 2304,32 11,70pg 1922,24 12,65 2312,40 11,85pg 1923,32 11,28 2331,25 11,88pg 1923,34 11,30 2337,21 11,87pg 1923,42 12,55 2337,22 13,08 1925,31 12,45 2337,30 13,11 1927,48 9,90 2339,18 13,12 1946,26 11,28 2339,23 13,03 1946,30 12,59 2622,29 10,04 1947,41 9,80 2628,35 13,16 1949,29 11,42pg 2628,38 11,90 2162,54 9,95 2628,39 11,95 2222,48 11,61 2628,40 10,15 2223,48 12,56 2631,30 13,08 2225,38 12,78 2631,40 11,80 2240,34 12,85 2631,41 10,05 2242,28 12,65 2652,22 10,22 2242,38 12,62 2652,23 11,80 2247,40 10,02 2652,25 13,20 2247,40 9,92 2655,34 10,21 2247,45 10,07 2655,35 11,83 2250,50 12,68 2655,36 13,12 2251,42 11,53 v measurements, with crosses and dashed lines - the data of Gieseking obtained in the period 1972-1973, according to (1). The slopes of the brightness decrease per 100 days in the time interval 1973-1975 are: for u - 0.080m+-0.009m for b - 0.066m+-0.008m for v - 0.038m+-0.008m For the time interval of 750 days (from JD = 2441900 to JD= 2442650) we get the following changes of v and colours (u-b) and (b-v): v = 0.3m; (b-v) = 0.2m; (u-b) = 0.1m From the Figure it can be seen that, starting from the summer 1973, the slope diminished approximately twice. [FIGURE 1] M.K. TSVETKOV Byurakan Astrophysical Observatory Department of Astronomy, Bulgarian Academy of Sciences References: 1) Gieseking, F., Astron. and Astrophys.,31, 117, 1974 [BIBCODE 1974A&A....31..117G ] 2) Tsvetkov, Dissertation, 1975, Yerevan 3) Bigay, J.H., Garnier, R., Astr.Astrophys.Suppl., 1, 15, 1970 [BIBCODE 1970A&AS....1...15B ] 4) Argue, A.N., Vistas Astronomy, Pergamon Press, Ed. A. Beer, vol. 3, 184, 1960. [BIBCODE 1960VA......3..184A ]