COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3917 Konkoly Observatory Budapest 30 July 1993 HU ISSN 0374 - 0676 FLARE STAR SEARCH IN THE ALPHA PERSEI CLUSTER Parallel with the programme for the investigation of low-mass members in the open cluster Alpha Persei (~ 8 x 10^7 years) of Prosser (1991, 1992) on the basis of their proper motion determination the monitoring flare star observations were carried out at the Rozhen Observatory, Bulgarian Academy of Sciences. The monitoring has an aim to independently identify new red dwarf members of the cluster and to determine the flare activity of the stars in this intermediate-age cluster. For the monitoring observations we used the 50/70/172 cm Rozhen Schmidt telescope. In the period November 1990 - March 1993, 98 monitoring multiple exposure plates (emulsion ORWO ZU21) with the centre - the star BD +48d920 (03h24m29.1s, 48d53'25" (1950)) were obtained. The total effective observational time is 93h44m. The data of the observing material are given in Table 1. Table 1. Flare Star Monitoring in the Alpha Persei cluster. ----------------------------------------------------------------- Year Number of Total Exp Number of Duration of Light/ plates Time exposures the exposure Filter ----------------------------------------------------------------- 1990 1 1h00m 6 10^min Pg/- 1991 39 38 20 230 10 U/UG1 7 3 54 39 6 Pg/- 1992 26 25 30 153 10 U/UG1 1993 25 25 00 150 10 U/UG1 ----------------------------------------------------------------- Total 98 93 44 578 ----------------------------------------------------------------- After the visual inspection of the observational material with CARL ZEISS blink-comparator we found two new flare stars in the cluster region, different from the known UV Cet type stars (Sediakina 1971 and Wang 1993). The data of the newly discovered flare stars are listed in Table 2. It seems that the low flare activity is charasteristic for this cluster. Table 2. New Flare Stars in the Alpha Persei Cluster. ------------------------------------------------------------ R.A. DEC. Magnitude in Magnitude in No. 1950 1950 Minimum Maximum mag(V) mag(I) mag(U) ------------------------------------------------------------ 1. 3h25m17.6s 50d05`55" 16.17m 13.91m 14.1m 2. 3 23 46.7 47 47 02 18.7 15.3 12.7 ------------------------------------------------------------ The photometric CCD V,I -magnitudes (Kron system) in quiescence of the new flare stars were obtained with the Whipple Observatory 1.2m telescope on Mt. Hopkins, Arizona. The (V, V-I) photometry of both flare stars makes them acceptable for membership in the cluster. Neither FS1 nor FS2 had been previously identified as candidate cluster members from proper motion surveys. Based on their photometry, FS1 appears to be a late K or early M dwarf, while FS2 is probably M5 or later. FS2 is therefore one of the lowest-mass candidate members of the Alpha Persei cluster identified to date. The rough photographic B-magnitude of FS1 in minimum measured on the direct plate obtained with the Rozhen Schmidt telescope is 17.5m (B). The magnitude of FS2 estimated on the Palomar Observatory Sky Survey 0-print is about 20.4m (Bp). The amplitudes of FS1 and FS2 flare events registered, with the correspondence of their standard U-B colours (for spectral types M0 and M5) are 4.6m (U) and ~9.0m (U) magnitudes. The very big amplitude of FS2 seems to be not exception for such active faint M-dwarfs, when we compare with similar flare stars in the Pleiades cluster (Haro et al. 1982). Table 3. Photographic Photometry of the Discovered Flare Events. ---------------------------------------------------------------- FS Plate Exposure J.D. Magnitude No. No. No. mag (U) ---------------------------------------------------------------- 1 5987 1 2448510.4257 > 15.5 1 5987 2 .4330 > 15.5 1 5987 3 .4403 > 15.5 1 5987 4 .4476 > 15.5 1 5987 5 .4549 14.8 1 5987 6 .4622 14.1 1 5988 1 .4716 14.2 1 5988 2 .4789 14.4 1 5988 3 .4861 14.7 1 5988 4 .4934 14.7 1 5988 5 .5007 14.6 1 5988 6 .5080 14.8 1 5989 1 .5174 15.0 1 5989 2 .5247 15.3 1 5989 3 .5320 > 15.5 1 5989 4 .5393 > 15.5 1 5989 5 .5466 > 15.5 1 5989 6 .5539 > 15.5 2 6134 1 2448628.3049 > 15.5 2 6134 2 .3122 12.7 2 6134 3 .3195 13.0 2 6134 4 .3268 13.9 2 6134 5 .3341 13.6 2 6134 6 .3413 13.7 ------------------------------------------------------------- The identification maps of the FS1 and FS2 reproduced from the CCD I-frames (5 arcmin on a side) are given in Figures 1a and 1b. North is on the top, East - on the left. [FIGURE 1] Figures 1a, 1b. Identification maps of the new flare stars. The future digitization of the observational material for an automatic detection of the flare- and other type variable stars is planned. EVGENI H. SEMKOV CHARLES F. PROSSER KATYA P. TSVETKOVA MILCHO K. TSVETKOV Center for Astrophysics 60 Garden St. MS-66 Department of Astronomy and Cambridge, MA 02138, U. S.A. National Astronomical Observatory E.mail: prosser@cfa0.harvard.edu Bulgarian Academy of Sciences Tsarigradsko Shosse # 72 BG-1784, Sofia, Bulgaria E.mail: tsvetkov @ bgearn.bitnet REFERENCES Haro, G., Chavira, E., Gonzales, G.,1982, Boll. Inst. Tonantzintla, 3, No. 1, 3. [BIBCODE 1982BITon...3....3H ] Prosser, Ch. F.,1991, Ph. D. thesis, University of California, Santa Cruz, CA. [BIBCODE 1991PhDT........48P ] Prosser, Ch. F.,1992, AJ, 103, 488. [BIBCODE 1992AJ....103..488P ] Sediakina, A. N., 1971, Perem. Zvezdy, 18, 218. [BIBCODE 1971PZ.....18..218S ] Wang, Jun-jie, 1993, IBVS, No. 3836.