COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1020 Konkoly Observatory Budapest 1975 July 22 PHOTOELECTRIC OBSERVATIONS OF THE STAR UV Cet IN 1972 Continuous photoelectric monitoring of the flare star. UV Cet has been carried out at the Stephanion Observatory (lambda = -22d49'44", phi = +37d45'15") during the period of cooperative optical observations of this star proposed by the IAU Working Group on Flare Stars i.e. October 1-15, 1972 (Chugainov, 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 colour of the international UBV system. The telescope and photometer will be described elsewhere. Here we option only that the transformation of our instrumental ubv system to the international UBV system is given by the following equations: V = v_0+0.018(b-v)_0 + 1.788, B-V = 0.814+0.930(b-v)_0, U-B = -0.951+0.864(u-b)_0. The monitoring intervals in UT as well as the total monitoring time for each night are given in Table I. Any interruption of more than one minute has been noted. In the fourth column of Table I the standard deviation of random noise fluctuation sigma(mag)=2.5log(I_0+sigma)/I_0 for different times (UT) of the corresponding monitoring interval is given. During the 10.61 hours of monitoring time 7 flares were observed the characteristics of which are given in Table II. For each flare following characteristics (Andrews et al. 1969) 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 If is the total intensity deflection less sky background of the plus flare, d) the integrated intensity of the flare over its total duration, including pre-flares, if present, P=Integral(I_f-I_0)/I_0 dt, e) the increase of the apparent magnitude of the star at flare maximum Deltam(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 during the quiet- state phase immediately preceding the beginning of the flare and g) the air mass at flare maximum. The light curves of the observed flares in the b colour are shown in Figs. 1-4. Following remarks should be added: 1) The characteristics of flare No. 5 given in Table II refer to the v colour instead of the b, because this flare occurred when the v magnitude of the star was measured. For the same reason the value of sigma(mag) given for this flare in Table II is smaller than the values of sigma(mag) given in Table I for the corresponding monitoring interval which also refer to the b colour. 2) Flare No. 7 has been also observed by B. Lovell using the Mk 1A radio telescope at Jodrell Bank working on a frequency of 408MHz. A joint discussion of both the radio and optical observations for this flare has been published already (Lovell et al. 1974). 3) During the time interval October 7, 1972 UT = 00h50m10s-00h50m41s an interruption of the monitoring at Stephanion was made, in order to check the position of the star in the field of view of the telescope. For this reason no confirmation of the small flare observed by Cristaldi and Rodono (1973) at October 7, 1972 UT = 00h50m39s can be made. M.E. CONTADAKIS and L.N. MAVRIDIS University of Thessaloniki References: Andrews, A.D., Chugainov, P.F., Gershberg, R.E. and Oskanian, V.S.: 1969, I.B.V.S. No. 326 Chugainov, P.F.: 1971, I.B.V.S. No. 605 Cristaldi, S., Rodono, M.: 1973, I.B.V.S. No. 760 Lovell, B., Mavridis, L.N., Contadakis, M.E.: 1974, Nature 250, 124 [BIBCODE 1974Natur.250..124L ] Table I ----------------------------------------------------------------------------------- Date Monitoring interval (U.T) Total Monitoring sigma(U.T) 1972 Time Oct. ----------------------------------------------------------------------------------- 4 21h31m-21h35m,2137-2147,2150-2158, 0h55m 0.11(21b35m) 2200-2232. 0.13(22h22m) 6-7 2121-2132,2133-2148,2150-2208, 0.14(21h25m) 2209-2229,2231-2247,2250-2309 0.11(22h00m) 0.11 2320-2348,2349-0019,0021-0100, (22h35m) 0102-0116,0117-0131,0133-0146 0.13(24h00m),0,10(00h30m) 0149-0202,0204-0213,0216-0224 4h27m 0.12(00h55m),0.11(01h20m) 0.18(01h58m),0.27(2h21m) 10-11 2049-2102,2103-2125,2126-2131,2133-2150 0.14(20h50m),0.13(21h30m) 2152-2206,2207-2222,2223-2243,2249-2302 0.12(22h00m),0.12(22h30m) 2342-2348,0010-0022,0024-0034. 2h28m 0.10(23h00m),0.08(23h40m) 0.12(00h24m) 11-12 2118-2128,2130-2136,2138-2232,2234-2243, 0.11(21h20m),0.14(22h00m) 2244-2257,0049-0100,0103-0135. 2h24m 0.14(22h45m),0.14(00h52m) 0.14(01h23m) 12 2320-2332,2335-2346 023m 0.10(21h25m), ----------------------------------------------------------------------------------- Total 10h37m Table II Characteristics of the Flares Observed ------------------------------------------------------------------------------- Date Duration Flare 1972 U.T. t_b t_a (I_f-I_o)/I_o P Deltam sigma Air No. Oct.max. min. min. min. max. min. mag mag mass. ------------------------------------------------------------------------------- 1 7 00h53m32.4 0.64 0.80 1.49 1.02 0.65 0.76 0.12 2.10 2 7 00 55 1.0 0.08 1.14 1.22 1.53 0.59 1.01 0.12 2.10 3 7 01 20 32.8 0.32 1.58 1.90 3.28 1.57 1.58 0.11 2.32 4 7 01 23 27.0 0.20 2.00 2.20 1.30 0.90 1.33 0.11 2.33 5 10 23 42 27.0 0.05 1.00 1.05 0.62 0.05 0.53 0.07 1.85 6 10 23 44 13.3 0.16 1.08 1.24 1.03 0.46 0.77 0.08 1.85 7 11 21 18 53.3 0.67 65.11 65.78 > 47.78 > 29.46> 4.55 0.11 1.95 ------------------------------------------------------------------------------- [FIGURE 1] [FIGURE 2] [FIGURE 3] [FIGURE 4]