COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 307 Konkoly Observatory Budapest 1968 November 2 OBSERVATIONS OF FLARE STARS a) YZ Canis Minoris, b) AD Leo, c) BD +13deg2618 Virginis A few unpublished results from 1966-67 of flare star monitoring and mean colour and magnitude photometry are presented. The material was obtained at the Boyden Observatory with the 16-inch Harvard Nishimura and 60-inch reflectors using equipment previously described (Refs. 1 and 2). In February 1967 photoelectric monitoring of YZ CMi was undertaken by E. Schoffel (Bamberg) as part of the joint optical-radio programme. Results were communicated privately to the radio astronomers at that time. One major flare of more than 2 magnitudes (blue) was well observed at the 16-inch during 23 hours monitoring over 5 nights, and two suspected flares were recorded. The material has been reexamined for small flares occuring during stable sky conditions, and the 3-sigma rule applied together with an arbitrary 'minimum duration' test to aid in the weighting of the observations. Flares accepted on the basis of the 3-sigma rule were judged as possible or doubtful depending on whether the duration was greater or less than 2 minutes. Standard deviations were derived from several 2-minute samples near the flares, where the data points were averages over 12-second tracings. The time constant (half final- deflection) for the tracings was 0.9 second. For the 16-inch continuous-monitoring observations of YZ CMi (B = 12m.88), a typical detection threshold for blue flares is at apparent magnitude 15.4 (for flare alone). An excellent discussion of the detection problem applied to the statistics of flare activity is given by W. Kunkel (Ref.3). Schoffel's hours of coverage and some details of flares are summarized in Tables 1 and 2, and light curves shown in the Figure. Table 1 Monitoring of YZ CMi Coverage U.T. 1967 Feb.2 (2109-2258) 3 1859-2132, 2136-50, 2152-2255, 2257-2304, (2304-2400). 4 (0000-55), 0057-0158,1849-0104. 1854-2009, 2014-21. 13 1814-2000, 2003-06, 2009-2400. 14 0000-35, 0045-0100. Total Coverage 22h45m (parenthesis indicate poor sky conditions) [FIGURE 1] [FIGURE 2] [FIGURE 3] [FIGURE 4] Table 2 Flares of YZ CMi 1967 U.T. Blue Duration sigma Rise Rate Remarks of max. Ampl. >=3(mins) mag/sec Feb.4 18h58.6m 0.24m 3 +/-0.035m 0.005 Possible 4 20 30.6 0.21 1 +/-0.048 0.006 Doubtful 4 22 44.0 2.38 40 +/-0.017 0.092 Definite 13 19 02.3 0.76 2 ? +/-0.044 0.022 Definite The flare star, AD Leo, and the suspected flare star, BD +13deg2618 (Ref. 4), were fragmentarily monitored in 1966 by W. Pretorius (Boyden) and myself. No flares were detected. Coverage is given in Tables 3 and 4, but this material is heterogeneous in that several filters (standard U, B and V) were used for monitoring. Detection thresholds in blue were at 14.8m and 14.6m, for the two stars, respectively. Table 3 Monitoring of AD Leo Coverage U.T. 1966 Jan.24 1954-2027, Feb.16 2144-53, 2155-56, 2202-32, 2236-2400. 17 0000-15 May 8 1933-38, 1941-43, 1958-2000, 2002-13, 2037-42, 2045-52. Total Coverage 3h24m Table 4 Monitoring of BD +13deg2618 Coverage U.T. 1966 Feb.17 0118-24, 0129-0235. Total Coverage 1h12m The photometric data for the three stars in Table 5 is in the standard UBVR system of Johnson et al. (Ref.5). The 60-inch observations were made during the programme mentioned in Ref.2, and the standard errors for AD Leo and its companion at 1.7' NE, in V, V-R, B-V and U-B are +0.01m, +/-0.2m, +/-0.3m and +/-0.4m, respectively. The 16-inch observations of BD +13deg2618 are less accurate, being made by comparison with AD Leo. Mean extinction coefficients were used at air masses of 1.35 and 1.55 for the two stars, respectively, and the small differential colour terms neglected. Except for the red band, results for AD Leo have been published previously by Johnson and Morgan (Ref. 6) and Engelkemeir (Ref.7). Agreement is satisfactory save in the V magnitude. We note that AD Leo is an unresolved astrometric binary (Ref.7), and that small variations in magnitude have been suspected by several workers. Table 5. Photometric Results Star J.D. V V-R B-V U-B Instrument -2439000 AD Leo 486.551d 9.38m 1.63m 1.52 1.03 60-inch Comp. to AD 486.558 10.71 0.98 1.05 0.98 60-inch BD+13deg2618 173.429 9.56 1.54 1.20 16-inch Armagh Observatory October 25, 1968. A.D. ANDREWS REFERENCES 1) A.D. Andrews, Publ.Astr.Soc.Pacific Vol. 78, p. 542, 1966. [BIBCODE 1966PASP...78..542A ] 2) A.D. Andrews, I.B.V.S. No. 265, 1968. 3) W.E. Kunkel, Dissertation, University of Texas, 1967 [BIBCODE 1967PhDT.........1K ] 4) M. Petit and R. Weber, Journ. des Observ. Vol. 39, p. 51, 1956. [BIBCODE 1956JO.....39...51P ] 5) H.L. Johnson et al., Comm. Lunar and Plan.Lab. No. 63, 1966. [BIBCODE 1966CoLPL...4...99J ] 6) H.L. Johnson and W.W. Morgan, Astroph.Journ. Vol. 117, p. 313, 1953. [BIBCODE 1953ApJ...117..313J ] 7) D. Engelkemeir, Publ.Astr.Soc.Pacific Vol. 71, p. 522, 1959. [BIBCODE 1959PASP...71..522E ]