COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 712 Konkoly Observatory Budapest 1972 August 31 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STARS BD+13d2618 and BD+16d2708 Continuous photoelectric monitoring of the flare stars BD+13d2618 and BD+16d2708 has been carried out at the Stephanion Astronomical Station (Lambda = -22d49'44", phi = +37d45'15") during the period May 7-14, 1972 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-0.001(b-v)+2.040, B-V = 0.844+1.031(b-v), U-B = -1.182+0.966(u-b). 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. During the 9.45 hours of monitoring time of the star BD+16d2708 one flare was observed. Only one flare was also observed during the 12.44 hours of monitoring time of the star BD+13d2618. The characteristics of these two flares are given in Table 2. For each flare following characteristic (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 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 - I_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. 1-2. Department of Geodetic Astronomy University of Thessaloniki, Greece July 31, 1972 G. ASTERIADIS and L.N. MAVRIDIS References Andrews, A.D., Chugainov, P.F., Gershberg, R.E., and Oskanian, V.S. 1969, Comm. 27 IAU, Inf.Bull.Var.Stars No. 326. TABLE 1 Monitoring intervals(UT) --------------------------------------------------------------------------------------- Total Star Date Monitoring intervals Total Monitoring 1972 Time MAY --------------------------------------------------------------------------------------- BD+16d2708 7-8 20h46m-20h54m,2056-2109, 2112-2138,2140-2206, 2212-2243,2245-2313, 2315-2336,2342-2345, 2347-0013,0015-0042,0044-0115,0117-0200, 4h43m 11-12 2324-2331,2344-0007,0009-0028. 49m 13-14 1923-1936,1937-1957,1958-2040,2045-2202, 2204-2302,2304-2340,2357-0044,0046-0106 4h13m Total 9h45m BD+13d2618 9-10 2059-2122,2124-2156,2157-2226,2231-2301, 2303-2330,2333-2358,0000-0005,0007-0011, 0017-0031,0034-0102,0103-0158. 4h32m 11 1953-2022,2024-2053,2055-2127,2133-2147, 2203-2230,2232-2300,2304-2307. 2h42m 12-13 1941-2007,2008-2035,2037-2103,2106-2150, 2202-2300,2304-0000,0007-0059,0104-0145. 5h30m Total 12h44m --------------------------------------------------------------------------------------- TABLE 2 Characteristics of the flares observed ----------------------------------------------------------------------------- Star Date (I_f-I_0)/I_0 sigma BD 1972 UT t_b t_a Duration P Delta m Air May max. min. min. min. max. min. mag. mag. Mass ----------------------------------------------------------------------------- +13d2618 12 22h00.3m 0.4 4.0 4.4 0.15 0.17 0.15 0.01 1.24 +16d2708 13 22h34.0m 0.5 4.9 5.4 0.26 0.38 0.25 0.01 1.09 ----------------------------------------------------------------------------- [FIGURE 1] [FIGURE 2]