COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 654 Konkoly Observatory Budapest 1972 April 6 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR UV CET Continuous photoelectric monitoring of the flare star UV Ceti has been carried out at the Stephanion Astronomical Station (lambda=-22deg49'44" phi=+37deg45'15") during the period of cooperative optical observations of this star proposed by the IAU Working Group on Flare Stars i.e. October 11-27, 1971 (Andrews et al. 1971) using the 30-inch Cassegrain reflector of the Department of Geodetic Astronomy, University of Thessaloniki. Observations have been made with a Johnson dual channel photoelectric photometer in the B color of the international UBV system. The telescope and photometer will be described elsewhere. Here we mention only that the transformation of our instrumental ubv system to the international UBV system is given by the following equations: V=v+2.094+0.022 (b-v), B-V=0.837+1.005 (b-v), U-B=-1.179+0.993 (u-b). The monitoring intervals in UT as well as the total monitoring time for each night are given in Table 1. Any interruption of more than one minute has been noted. During the 29,6 hours of monitoring time 6 flares were observed the characteristics of which are given in Table 2. For each flare following characteristics (Andrews et al. 1971) are given: a) the date and universal time of flare maximum, b) the duration before and after maximum (t_b and t_a respectively) as well as the total duration of the flare, c) the value of the ratio (I_f-I_0)/I_0 corresponding to flare maximum, where I_0 is the intensity deflection less sky background of the quiet star and I_f is the total intensity deflection less sky background of the star plus flare, d) the integrated intensity of the flare over its total duration, including pre-flares, if present, P= Integral (I_f-epsilon_0)/I_0 dt, e) the increase of the apparent magnitude of the star at flare maximum delta m(b)=2.5 log(I_f/I_0), where b is the blue magnitude of the star in our instrumental system, f) the standard deviation of random noise fluctuation sigma mag=2.5 log(I_0+sigma)/I_0 and g) the air mass. The light curves of the observed flares in the b color are shown in Figs. 1-6. TABLE 1 Monitoring intervals (UT) Date Total 1971 Monitoring intervals Monitoring Oct. Time 11-12 22^h11^m-22^h20^m, 2224-2235, 2243-2255, 2258-2309, 2314-2326, 0011-0025, 0033-0037. 1^h13^m 13-14 2055-2106, 2109-2119, 2123-2134, 2145-2157, 2200-2210, 2214-2223, 2326-2333, 2347-2358, 0004-0016, 0019-0030, 0039-0044, 0050-0101, 0103-0115, 0118-0127, 0129-0135, 0139-0151, 0154-0209, 0211-0240. 3^h23^m 15-16 2119-2139, 2143-2157, 2159-2220, 2225-2231, 2232-2242, 2244-2301, 2303-2315, 2318-2321, 2328-2341, 2350-0010, 0014-0024. 2^h26^m 17-18 2113-2130, 2132-2152, 2155-2216, 2221-2239, 2242-2300, 2311-2326, 2331-2345, 2351-0008, 0012-0016, 0047-0103, 0111-0120. 2^h49^m 19 2215-2234, 2239-2250. 30^m 20 2226-2228. 02^m 21-22 2042-2100, 2103-2119, 2124-2130, 2147-2205, 2211-2229, 2233-2252, 2258-2315, 2319-2340, 2344-2350, 0016-0034, 0037-0050, 0102-0120, 0125-0145, 0149-0210, 0213-0232. 4^h02^m 22-23 2047-2105, 2109-2132, 2149-2200, 2214-2225, 2229-2254, 2258-2320, 2327-2339, 2342-2346, 2355-0007. 2^h18^m 23-24 2122-2130, 2136-2156, 2158-2219, 2221-2245, 2249-2311, 2313-2332, 2336-2355, 0008-0023, 0026-0042, 0048-0111, 0125-0127. 3^h09^m 25-26 2036-2100, 2102-2122, 2124-2144, 2154-2215, 2217-2237, 2240-2331, 2337-0000, 0002-0018, 0023-0042, 0047-0107, 0110-0130, 0132-0153, 0157-0220. 4^h58^m 26-27 2016-2037, 2041-2101, 2105-2124, 2129-2151, 2153-2216, 2218-2240, 2246-2310, 2311-2335, 2337-0000, 0004-0049, 0051-0137, 0138-0145. 4^h46^m Total 29^h36^m Table 2. Characteristics of the flares observed Flare Date U.T. t_b t_a Duration (I_f-I_0)/I_0 P delta m sigma Air No. 1971 maximum min. min. min. maximum min. mag. mag. mass Oct. 1 14 01^h23.^m6 0.6 1.0 1.6 1.78 0.85 1.11 0.14 2.65 2 17 22 00.0 0.2 3.7 3.9 3.00 1.94 1.50 0.18 1.79 3 18 00 55.1 0.4 1.8 2.2 3.51 4.15 1.64 0.15 2.48 4 23 22 38.4 0.3 3.6 3.9 2.36 1.63 1.31 0.07 1.81 5 23 22 51.3 0.1 0.6 0.7 1.19 0.35 0.85 0.11 1.84 6 24 01 05.4 0.2 ? ? 4.17 ? 1.78 0.07 3.04 [FIGURE 1] [FIGURE 2] Department of Geodetic Astronomy University of Thessaloniki, Greece March 27, 1972 G. ASTERIADIS, L.N. MAVRIDIS. References: Andrews, A.D., Chugainov, P.H., Gershberg, R.E., and Oskanian, V.S.: 1969, Comm. 27 IAU, Inf. Bull. Var. Stars No. 326. Andrews, A.D., Chugainov, P.F., Kellogg, E.M., and Oskanian, V.S.: 1971, Comm. 27 IAU, Inf. Bull. Var. Stars No. 516.