COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2450 Konkoly Observatory Budapest 23 December 1983 HU ISSN 0374-0676 FLARE LIKE ACTIVITY IN AR LACERTAE The system AR Lac (=BD +45d3813 = HD 210334 = HV 2980 = HR 8448) is an interesting RS CVn binary. The system is known to be a radio source (vide Hjellming and Blankenship, 1973; Gibson and Hjellming, 1974; Spangler et al., 1977; Feldman, 1978; Owen and Gibson, 1978; Walter et al., 1978) showing variable radio emission and also occasionally flaring activity. Ultraviolet observations by Kiziloglu et al. (1983) through IUE show that it is an active star, H and K emission of CaII and H-alpha emission are found to be present in the system, which indicate that this system has an active chromosphere. So far UBV flares have been observed in two RS CVn stars, SV Cam (Patkos, 1981) and XY UMa (Zeilik et al., 1982, 1983). UBV observations of AR Lac were secured during the period October 1975 to January 1976 and some interesting features in the light curves of the system, particularly, an additional light of the order of 0.10m, just preceding primary minimum, and of the order of 0.05m, just preceding secondary minimum, in all the colours were reported (Srivastava, 1981), These appeared as humps on the shoulders of both the eclipses. The nature of these additional lights has been investigated in this communication. The additional lights have been observed on four nights (6 October 1975, 9 October 1975, 14 October 1975 and 15 October 1975) in all the three filters. Two nights (6 October 1975 and 14 October 1975) are related to the ingress part of the primary eclipse, while the remaining two nights (9 October 1975 and 15 October 1975) are concerned with the ingress part of the secondary eclipse. The additional lights observed on all the four nights have been obtained by taking the difference of observed and computed lights of the system from the smoothened light curves. These differences are plotted in Figures 1, 2 and Figures 3, 4 for primary and secondary eclipses, respectively. The figures show that flare-like activity is present in the system. The characteristics of flares are given in Table I. [FIGURE 1] Figures 1-2 Flares of AR Lacertae during primary minimum [FIGURE 3] Figures 3-4 Flares of AR Lacertae during secondary minimum. Filled and open circles represent the first and the second flares, respectively. Table I Characteristics of the flares of AR Lacertae ------------------------------------------------------------------------------ Min. Date Fil- Start time End time Duration Time of Maximum 1975 ter of flare of flare of flare maxima amplitude (UT) (UT) of flare of flare (UT) (mag.) ------------------------------------------------------------------------------ Pr. 6 Oct. U 16h 33.1m 19h 28.9m 02h 55.8m 18h 57.6m 0.12m B 16 36.4 19 28.9 02 52.5 18 12.7 0.04 V 16 40.3 19 28.9 02 48.2 18 42.1 0.07 First flare Sec. 9 Oct. U 16 45.6 18 06.6 01 21.0 17 30.4 0.06 B 17 13.2 18 44.9 01 31.7 18 09.1 0.08 V 16 56.4 18 41.2 01 44.8 17 37.6 0.11 Second flare U 18 44.9 19 36.5 00 51.6 19 36.5* 0.13* B 18 59.1 19 40.4 00 41.3 19 40.4* 0.13* V 18 44.9 19 36.5 00 51.6 19 36.5* 0.12* Pr. 14 Oct. U 15 50.4 19 32.9 03 42.5 16 32.0 0.15 B 16 14.2 19 32.9 03 18.7 16 32.0 0.07 V 15 50.4 19 32.9 03 42.5 16 32.0 0.06 First flare Sec.15 Oct. U 16 25.3 19 22.5 02 57.2 17 44.8 0.05 B 15 51.6 18 52.1 03 00.5 17 15.9 0.05 V 15 23.8 19 03.1 03 39.3 17 30.2 0.04 Second flare U - - - - - B 19 46.1 20 07.8 00 21.7 00 21.7* 0.02* V 19 47.9 20 07.8 00 19.9 00 49.9* 0.02* ---------------------------------------------------------------------------- * These values do not relate to the actual times of maxima, amplitudes of the flares, but are only apparent values as the secondary flares have not been observed fully. The average standard deviation of individual observations of comparison star is 0.02m. In both the flares of secondary minima (Figures 3 and 4), the flares start from the normal light (quiescent) level, rise to the maximum light (flare) level and then subside and return to the quiescent level. However, the flare curves of 9 October 1975 show a sharp rise and a sharp decline while the flare curves of 15 October 1975 show a slow rise and a slow decline. The second flare starts on these nights after the main burst. The rise during the second flare is not conspicuous on 15 October 1975 in the U filter due to considerable scatter present in the observations. The secondary flares seem to be more intense showing steeper rise. The flares of primary minima on 6 October 1975 and 14 October 1975 show declining tendency after the start and then rise to the maximum intensity before the last decline, The flares of 14 October 1975 do not decline to the quiescent levels, but show a tendency to rise before the last decline. The duration of flare on 14 October 1975 is the longest. The pattern of flare of 14 October 1975 indicates that sympathetic flare may have been associated with the preceding flare as is shown in the case of EV Lac (Godoli, 1968). The flares of 6 October 1975 have not been observed fully. This is the first reporting of the flares in the UBV region for AR Lac. The author has interpreted these additional light's phenomena on the plausible basis of flare-like activity. However, the alternative interpretations of these additional lights, if any, would need further investigation. The author is thankful to Drs. C.D. Kandpal and M.C. Pande for their discussions and suggestions. R.K. SRIVASTAVA Uttar Pradesh State Observatory, Manora Peak, Naini Tal-263129, India References: Feldman, P.A., 1978, Bull. American Astron.Soc. 10, No. 2, 418 [BIBCODE 1978BAAS...10..418F ] Gibson, D.M. and Hjellming, R.M., 1974, Publ.Astron.Soc. Pacific 86, 652 [BIBCODE 1974PASP...86..652G ] Godoli, G., 1968, Mass Motion in Solar Flares and Related Phenomena, Nobel Symposium 9, Almqvist and Wiksell, Stockholm, p. 211 [BIBCODE 1968mmsf.conf..211G ] Hjellming, R.M. and Blankenship, L., 1973, Nature (Physical Sci.) 243, No. 127, 81 [BIBCODE 1973NPhS..243...81H ] Kiziloglu, U., Derman, E., Ogelman, H. and Tokdemir, F., 1983, Astron. Astrophys. 123, 17 [BIBCODE 1983A&A...123...17K ] Owen, F.N. and Gibson, D.M., 1978, Astron. J. 83, No. 12, 1488 [BIBCODE 1978AJ.....83.1488O ] Patkos, L., 1981, Astrophys. Lett. 22, 1 [BIBCODE 1981ApL....22....1P ] Spangler, S.R., Owen, F.N. and Hulse, R.A., 1977, Astron. J. 82, 989 [BIBCODE 1977AJ.....82..989S ] Srivastava, R.K., 1981, Astrophys. Space Sci. 78, 123 [BIBCODE 1981Ap&SS..78..123S ] Walter, F.M., Phillip, P. and Bowyer, S., 1978, Astron.J. 83, No. 12, 1539 [BIBCODE 1978AJ.....83.1539W ] Zeilik, M., Elston, R. and Henson, G., 1982, Inf.Bull. Variable Stars No. 2200 Zeilik, M., Elston, R. and Henson, G., 1983, Astron.J. 88, 532 [BIBCODE 1983AJ.....88..532Z ]