COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 748 Konkoly Observatory Budapest 1972 December 29 OBSERVATIONS OF SOUTHERN FLARE STARS During the past five years several dMe stars were monitored for flare activity, and some findings have been reported earlier (Kunkel 1968a). This communication presents a second list of stars in which flare activity was noted. Candidates were drawn from Gliese's (1969) catalog of nearby stars, and lists of emission line dwarfs (Bidelman 1954, Haro 1954). Objects found since 1970 were selected on the basis of H_beta photometry which discriminates effectively between flare active and non-active red dwarfs. Flares were considered real if peak U-light (after subtracting the quiescent component), measured in magnitudes, was stronger than faint event detection threshold (Kunkel 1973) given by U_lim = U_sigma + 1.25 log10(T_.5 / Delta t) - 2.03, where U_sigma is the U-magnitude of one standard deviation, Delta t is the time-constant of the data system, and was one second in all cases. The constant corresponds to a detection criterion of five standard deviations, so that the probability of spuriously detecting an event in 30 hours of monitoring should be Less than one percent. Reduction methods have been described elsewhere (Kunkel 1968b, 1973). Table I. Data Summary ----------------------------------------------------------- Gliese Star Aperture Sample No. No. Name M_v Duration U_sigma of Chart cm flares ----------------------------------------------------------- 206 Ross 42 10.7 90 1.34h 16.5 3 G97-47 398 LFT 725 11.7 90 3.68 16.7 1 G44-27 493.1 Wolf 461 13.1: 90 2.16 16.8 3 G60-55 540.2 Ross 845 12.8 150 1.76 18.4 3 A 852A Wolf 1561A 13.6 90 3.04 17.8 2 B 866 L 789-6 14.6 90 3.22 17.5 5 G156-31 871.1B L 574-61 12.5 90 2.03 17.8 1 C ------------------------------------------------------------ Details of individual observations are given in Table 2, following precepts used earlier (Kunkel 1968b, 1973). It should be noted that the photometer used for the first three of these object was not a sensitive as that employed with the other object in the table, as the values of U_sigma indicate. The activity of the first three stars in Table 1 is therefore greater than the number of flares observed might indicate. Had a better detection threshold been achieved, as in the last three object, the number of detected events would have been double that obtained. [FIGURE 1] [FIGURE 2] [FIGURE 3] Table 2. Flare Abstract Ross 42, Gliese 206 25 Nov. 1967, 6h51.6m - 7h46.5m and 7h49.4m - 8h14.9m 3 events k_u = 0.56 ----------------------------------------------------------------- Event U_peak T_0.5 T0.2 T0.1 tau_1 tau_2 Notes U.T. Airmass ----------------------------------------------------------------- 7h03.4m 1.34 15.53 0.19 7 26.7 1.38 16.2 1.3 4.: 7 36.7 1.42 14.22 0.46 1.5 3.1 +.23 -.34 ----------------------------------------------------------------- LFT 725, Gliese 398 7 Feb. 1969 5h09.1m - 6h24.7m no events k_u = 0.52 8 Feb. 1969 3h45.5m - 6h10.5m 1 event k_u = 0.50 ---------------------------------------------------------------- 4h56m 1.29 16.23 2.4 ---------------------------------------------------------------- Wolf 461, Gliese 493.1 9 Feb.1969 7h44.0m - 8h57.8m 2 events k_u = 0.65 ---------------------------------------------------------------- 7h43.35m 1.25 15.70 .17 .8: 8 30.20 1.24 16.16 .28 ---------------------------------------------------------------- 11 Feb.1969 8h10.8m - 9h06.6m 1 event k_u = 0.63 ---------------------------------------------------------------- 8h26.20m 1.24 15.81 0.10 0.35 ---------------------------------------------------------------- Ross 845, Gliese 540.2 22 Mar.1969 6h37.7m - 8h23.5m 3 events k_u = 0.5 ---------------------------------------------------------------- 7h13.1m 1.00 17.45 0.17 8 07.3 1.02 17.38 0.65 2.4: 7 38.7 1.00 17.9: 1.8 ---------------------------------------------------------------- Wolf 1561A, Gliese 852A 29 Sep.1971 1h02.0m - 4h04.6m 2 events k_u = 0.46 ---------------------------------------------------------------- 3h00.9m 1.08 16.79 1.30 2.8: 3 45.90 1.11 15.51 .24 .47 .90 +.69 ---------------------------------------------------------------- L 789-6, Gliese 866 30 Sep. 1971 1h10.0m - 1h44.9m and 1h46.8m - 4h19.2m 7 events k_u = 0.55 ------------------------------------------------------------------------- 1h26.60m 1.09 14.62 .085 .13 .17 +1.41 +1.30 T_0.05 = .4 1 40.31 1.08 16.13 .5 1.7 2 38.65 1.04 16.58c .08 .15c Double 3 11.13 1.04 16.66 .18 3 23.55 1.05 16.44 .4 2.2 4 00.1: 1.08< 13.34 <.3 lost peak 4 11.58 1.10 15.68 .05 .11 ------------------------------------------------------------------------- L 574-61, Gliese 871.1B 29 Sept.1971 4h41.0m - 6h43.8m 1 event k_u = 0.46 ------------------------------------------------------------------------- 4h57.02m 1.11 16.34 0.44 1.7 3.7 .3b -.36 ------------------------------------------------------------------------- At the luminosity of Ross 42 few flare stars are known of comparable activity. The present data are insufficient to form a reliable incidence statistic. However, an estimate based on the three recorded events points to an activity of M_u,o ~~ 14.6, greater than that of any flare star of similar luminosity. As the star is a spectroscopic binary, an assumption of activity divided equally between like components yields a level of activity similar to that of CoD-32d16135, with M_u,o ~~ 15.3 per component. The space motion of Ross 42 is similar to that of YZ CMi, CoD-32d16135 and CoD-31d17815, the stars that define the upper envelope of flare activity in the solar neighborhood Thus a possibly common origin for these stars appears likely. Gliese gives space motions for five of the stars in Table 1. The largest space motion is that of Number 866, with U = -67, V = -2, and W = +41 km/s. Numbers 493.1 and 852 likewise have large motions with components perpendicular to the plane significantly greater than those commonly associated with solar neighborhood flare stars. It is becoming clear that flare activity far more common among stars of the old disk population than had once been belived. Lastly, Shakhovskaya and Sofina (1972) have recently reported flare activity on Ross 858 (Gliese 669A), of which the fainter companion is known as a flare star (Kunkel 1967). Wolf 1561A is a second example of a situation in which the brighter component of a binary flares. No flare activity has been reported on the fainter component, which is one magnitude fainter. The conclusion, implicit in Kunkel's (1973) discussion of flare visibility, is that the preponderance of observed flare activity in the fainter components of binaries is likely to be a selection effect. WILLIAM E. KUNKEL Cerro Tololo Inter-American Observatory La Serena, Chile. References: Bidelman, W.P. 1954, Ap.J. Suppl. 1, 175. [BIBCODE 1954ApJS....1..175B ] Gliese, W. 1969, Verof.Astr.Rechen-Inst.Heidelberg, No. 22. [BIBCODE 1969VeARI..22....1G ] Haro, G. 1954, Bol.Ton. y Tac. No. 11, 11. [BIBCODE 1954BOTT....2k..11H ] Kunkel, W.E. 1967, Dissertation, University of Texas, Austin. [BIBCODE 1967PhDT.........1K ] Kunkel, W.E. 1968a, I.B.V.S. No. 294. Kunkel, W.E. 1968b, I.B.V.S. No. 315. Kunkel, W.E. 1973, Ap.J.Suppl. 25, 213. [BIBCODE 1973ApJS...25....1K ] Shakhovskaya, N.I. and Sofina, W. 1972, I.B.V.S. No. 730.