COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2889 Konkoly Observatory Budapest 16 April 1986 HU ISSN 0374 - 0676 PHOTOELECTRIC OBSERVATIONS OF BY Dra IN 1984-85 Photoelectric monitoring of BY Dra was carried out in 7 nights during 1984-85 using the 60 cm telescope of the National Astronomical Observatory, Rozhen, Bulgaria and the 1 m and the 50 cm telescopes of the Piszkesteto mountain station of the Konkoly Observatory, Hungary. The observations in Rozhen were obtained in U light using 1 to 10 sec integration times. Alternating UBV measurements at Piszkesteto were made with 20 sec integrations in each colour. The total monitoring time was 7h51m10s. The time intervals covered are given in Table I. The comparison star used was BD + 51deg2408 = HD 172268 (K5). Table I Colour Time intervals U 2445919.3606-.3705, .3834-.4007, .4037-.4066, .4107-.4299, .4342- .4438, .4465-.4489 U 2445923.4084-.4112, .4134-.4209, .4229-.4325, .4342-.4418, .4435- .4548, .4648-.4736, .4757-.4874 U 2445925.4617-.4693, .4711-.4803, .4820.-4891 UBV 2445932.3666-.3700, .3752-.3786, .3841-.3875, .4070-.4131, .4182- .4243, .4298-.4358, .4409-.4470, .4521-.4556, .4673-.4733, .4791- .4852, .4905-.4965, .5045-.5075 UBV 2446211.4440-.4505, .4566-.4631, .4694-.4758, .4830-.4894 U 2446214.4348-.4369, .4379-.4408, .4422-.4447, .4467-.4490, .4499- .4522, .4530-.4559, .4566-.4588, .4596-.4624, .4632-.4661, .4668- .4688, .4696-.4726, .4739-.4763, .4771-.4794, .4801-.4826, .4835- .4859, .4880-.4900, .4908-.4932, .4938-.4963, .4973-.4993, .5001- .5006 UBV 2446271.4287-.4359, .4438-.4482, .4491-.4532, .4604-.4692, .4767- .4854, .4929-.5015, .5088-.5129 [FIGURE 1] Figure 1: Flare of BY Dra [FIGURE 2] Figure 2: UBV observations of BY Dra One flare event was recorded in 19/20 August, 1984 at Konkoly Observatory in UBV light. The intensity curves of the flare are drawn in Figure 1 together with the preceding one hour quiescent light. The flare showed the following characteristics: Time of maximum: 2445932.4905 I/I0 (max.): 1.28 (U), 1.09 (B), 1.035 (V) Max. amplitudes in magn.: 0.26m (DeltaU), 0.12m (DeltaB), 0.04m (DeltaV) Standard deviations of the observations: 0.032m (U), 0.012m (B), 0.007m (V) Since no observation was made after the flare declined the duration of the flare event =36 min. is probably underestimated. On an other night, 24/25 July, 1985 = 2446271, when 32 U,B and V measurements were taken, the observations had the following standard deviations; 0.031 (U), 0.006 (B), 0.005 (V). Similarly to those observations taken at 19/20 August, 1984; the scatter in the ultraviolet light is extremely high. At the mountain station of the Konkoly Observatory when the sky is reasonably good, in the case of a similar bright star (but without chromospheric activity) the typical scatter in the ultraviolet light is under 0.02 magn. Therefore we concluded that we observed some intrinsic variation (see Figure 2). Butler et al. (1986) observed UV Cet in LE X-ray (EXOSAT) and in Hgamma and found almost continuous microflaring in both wavelengths, on timescales from tens of seconds to several minutes. Our observations of BY Dra show similar features in the ultraviolet light which, similarly to those events observed in UV Cet by Butler et al. (1986), is very probably a manifestation of the continuous chromospheric activity, namely microflaring. Acknowledgement: One of us (K.O.) thanks to J. Marton for making some of the observations. KATALIN OLAH Konkoly Observatory 1525 Budapest, P.O. Box 67 Hungary MARGARITA IVANOVA and L. ILIEV National Astronomical Observatory 4700 Smoljan, P.O. Box 136 Bulgaria Reference: Butler, C.J., Rodono, M., Foing, B.H., Haisch, B.H., 1986, Armagh Observatory Preprint Series No. 24, submitted to Nature [BIBCODE 1986Natur.321..679B ]