COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3190 Konkoly Observatory Budapest 20 May 1988 HU ISSN 0374-0676 FLARE STAR OBSERVATIONS IN ORION BY THE METHOD OF PHOTOGRAPHIC STELLAR TRACKS The purpose of our study was the application of the method of photographic stellar tracks (Chavushian, 1986) at the National Astronomical Observatory, Rozhen, Bulgaria. The stellar aggregate Orion (M 42) was chosen for its relatively high flare activity. The observations were carried out in the period 1 November - 3 December, 1986 with the 50/70/172 cm Schmidt telescope of the Rozhen Observatory using ORWO ZU 21 plates without filter, and exposure time of 30 minutes. The average limit of the plates was 15.2m (pg). The effective observational time was 13 hours. The plates were analysed with a Carl Zeiss Jena blink-comparator (16 x magnification, then the detected events were measured with a G2 schnell photometer. After surveying the material, 3 flares were found. The data obtained are listed in Table I. The successive columns of the table contain the following data: 1.- the serial number of the event 2.- other designations 3.- the date of observation 4-6.- U.T. of the beginning of the flare (U.T.b), U.T. of the maximum (U.T. max) and the duration 7.- the magnitude in the quiet state and the amplitude delta m_pg during the flare 8.- the standard deviation of random noise fluctuations sigma(mag). We used photometric sequence No. 2 in Orion according to Andrews (1970) for our photometry. Flare event No. 1 took place in the star Tonantzintla No. 26. This is the second flare observed in this star. The first was observed on 15 December 1963 with an amplitude Delta_mU=2.0m by the multiexposure method (Haro and Chavira, 1964). Flare. event No. 2 was observed in the In type variable star PZ Ori. Table I No. Other Date U.T. U.T. Dura- mpg mpg sigma(mag) design. begin. max tion min max 1. T 26 1 Dec.1986 2h12m06s 2h15m35s >55m36s 17.7 3.8 0.15 2. PZ Ori 1 Dec.1986 1 49 36 1 51 45 3 13 14.6 1.2 0.15 3. Anon 2 Dec.1986 1 45 07 1 48 41 ~10 :21.5 :6.7 0.10 [FIGURE 1] This flare was observed when the star was in a state of increased activity. Usually, this star is near the plate limit on our plates (m_Pg_limit=15.2m) but in the period 2-10 November the star increased its brightness to mpg =14.6m and remained with this magnitude up to the end of our observations. In the General Catalogue of Variable Stars (Kholopov et al., 1985) it is mentioned that this star has m_pg_min = 15.7m. PZ Ori is unknown as a star exhibiting flares. Flare event No. 3 belongs to a very faint star which has not been known to be variable. On the chart No. J-3828 from the U.K.S.T.U. Atlas of the Royal Observatory, Edinburgh, we identified this event with a star of mB~/=21.5m. The [FIGURE 2] identification chart is given in Figure 1. The coordinates of the star are RA(1950)= 5h 34m 05s, D(1950)= -7deg 01.3'. The light curves of the observed flares are given in Figure 2. Thanks are due to the relevant authorities of the ROE for the UKSTU observational material offered by them for the programme. RENADA K. KONSTANTINOVA-ANTOVA M.K. TSVETKOV Department of Astronomy and National Astronomical Observatory 72 Lenin Blvd., Sofia-1784 Bulgaria References: Andrews, A.D., 1970., Bulletin Tonantzintla y Tacubaya Obs. 5, No. 34, p. 195. [BIBCODE 1970BOTT....5..195A ] Chavushian, H.S., 1986, Proc. Symp. "Flare Stars and Related Objects", Byurakan, ed. L.V. Mirzoyan, p. 125 [BIBCODE 1986fsro.conf..125C ] Haro, G., Chavira, E., 1964, The Galaxy and the Magellanic Clouds, IAU - URSI Symposium No. 20. ed. F.G. Kerr and A.W. Rodgers, Canberra, p. 30. [BIBCODE 1964IAUS...20...30H ] Kholopov, P.N. et al., 1985, General Catalogue of Variable Stars, vol. II., Moscow, Nauka, p. 288.