COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1180 Konkoly Observatory Budapest 1976 September 20 PHOTOELECTRIC OBSERVATIONS OF THE FLARE STAR YZ CMi Continuous B-band photometry of flare activity of YZ CMi was carried out as a collaborative observing programme of the flare stars. The star was monitored on the Sampurnanand 104-cm reflector equipped with a refrigerated EMI 6094S photomultiplier, for a total of 24h39m spread over 7 nights during December 1975. The stellar intensity was measured against sky back ground only, without observing any comparison star. The actual monitoring intervals are given in Table I and the flare characteristics of all the 12 recorded flares are given in Table II. The light curves in relative intensity scales versus Universal Time are given in Figs. 1-12. All the flares are combinations of spike and slow events. In case of flare No. 3, which is a very rapid event, the peak could not be covered for a small interval due to instrumental limitations. Flare No. 6 is a combination of two spike events which could not be separated. The areas under the light curves were planimetered to derive a measure of the total energy radiated by a flare. The quiescent state luminosity in B band is taken to be 2.061 x 10^29 ergs/sec. The author is thankful to Dr. S.D. Sinvhal for suggestions and guidance. Part of this work was carried out with financial assistance with PL-480 funds under Smithsonian Institution Project No. SFG-O-6425. B.B. SANWAL Uttar Pradesh State Observatory, Manora Peak, Naini Tal-263129 India Reference: Cristaldi, S. and Rodono, M., 1973, Astron.Astrophys.Suppl. 10, 47 [BIBCODE 1973A&AS...10...47C ] Table I Monitoring Intervals (Times rounded off to nearest minute of U.T.) Date Dec.1975 2 20h01m- 22h48m, except for 6 breaks totalling 10 minutes. 4 18 53 - 22 52, except for 5 breaks totalling 6 minutes. 6 19 02 - 21 11, except for 4 breaks totalling 7 minutes. 7 18 54 - 23 27, except for 8 breaks totalling 30 minutes. 8/9 18 51 - 19 23, except for 1 break totalling 1 minute. 19 39 - 20 26 20 41 - 20 51, except for 1 break totalling 1 minute. 21 08 - 00 02, except for 5 breaks totalling 10 minutes. 9/10 18 51 - 22 03, except for 4 breaks totalling 6 minutes. 22 19 - 23 04, except for 1 break totalling 3 minutes. 23 18 - 00 12, except for 2 breaks totalling 4 minutes. 10/11 18 54 - 00 22, except for 12 breaks totalling 16 minutes. Table II Characteristics of the Flares on YZ CMi (dm 4.5e: V=11.24; B-V=1.58) Flare Date Flare duration I_0+f/I_0 Energy Total No. Dec. U.T. (in minutes) deltam_B P F(z) released emission 1975 max. Before After sigma/X_S (min) at max. max. flare during t_b t_a max 10^29 the ergs/s event 10^30ergs 1 2 20h13m54s 0.55 5.25 1.277 .265 .013 0.243 1.192 2.63 3.01 2 2 22 12 00 0.70 8.00 1.196 .194 .001 0.516 1.119 2.46 6.39 3 6 19 53 00 0.85 22.00 1.915 .705 .045 2.575 1.203 3.94 31.84 4 8 18 59 40 1.30 3.80 1.150 .151 .012 0.450 1.330 2.37 5.56 5 8 23 31 40 1.13 6.53 1.194 .192 .010 0.773 1.320 2.46 9.56 6 9 20 08 51 0.27 4.00 1.183 .182 .010 0.925 1.15 2.43 11.43 20 13 20 0.25 6.00 1.267 .256 .010 - 1.15 2.61 7 9 20 58 45 0.25 2.10 1.243 .236 .012 0.112 1.24 2.56 1.38 8 9 21 22 30 0.65 7.50 1.125 .127 .025 0.331 1.11 2.32 4.09 9 9 23 46 10 0.80 1.15 1.121 .124 .013 0.092 1.39 2.30 1.13 10 10 18 00 25 0.57 8.6 1.985 .746 .015 1.070 1.30 4.09 13.31 11 10 21 58 05 0.45 3.9 1.194 .192 .012 0.875 1.134 2.46 10.82 12 10 22 19 45 0.15 1.15 1.328 .307 .012 0.193 1.164 2.73 2.39 [FIGURE 1] [FIGURE 2] [FIGURE 3]