COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2347 Konkoly Observatory Budapest 7 June 1983 HU ISSN 0374-0676 CHANGES IN THE LIGHT CURVE OF W UMa New photometric observations of W UMa were carried out on three nights of February 16, March 12, March 13, 1983. The observations were made at the Ostrowik Station of the Warsaw University Observatory. A single channel photometer with ac; EMI 6256 photomultiplier attached to the 60 cm reflector was used. The comparison star was BD +56d1399 and BD +56d1398 served as a check star. The comparison star was the same as used most often in previous investigations of W UMa. The faint visual companion ADS7494B (V=12.3m, B-V=1.7m, Eggen, 1963), about from W UMa was included in all measurements of the variable. The observations were made in V and B and were reduced to the standard UBV system. 560 individual observations in V and 559 in B were obtained. Times of minima obtained from these data with the Kwee and Van Woerden (1959) method are given in Table I. Table I ------------------------------------------ J.D. Hel Colour E O-C 2440000+ ------------------------------------------ 5382.55723 V 1187.5 -0.0004 6 5382.55688 B 1187.5 -0.0007 5 5406.41124 V 1259 -0.0016 11 5406.41162 B 1259 -0.0012 15 5407.41197 V 1262 -0.0017 12 5407.41279 B 1262 -0.0009 9 5407.58019 V 1262.5 -0.0003 12 5407.57971 B 1262.5 -0.0008 ------------------------------------------ The O-C values in the Table are calculated with the ephemeris (Hamzaoglu et al. 1982): Min I = J.D. Hel.244 4986.3624 + 0.33363808d E One can see that the O-C deviations for the secondary minimum are slightly smaller than those for the primary one. There are no large differences between the light curves obtained on different nights. Therefore all individual observations were phased with the ephemeris: Min I = J.D. Hel.244 5382.5567 + 0.33363808d E and the normal points were calculated. They are presented in Figure 1. [FIGURE 1] Figure 1 The light and colour curves of W UMa made in 1983 It is well known that the light curve of W UMa is variable in the time scale from weeks to years. This behaviour is not unique among W UMa-type systems. Basing on the available publications I have collected 12 V light curves of W UMa obtained between 1965 and 1983. Unfortunately direct intercomparison between them was impossible because some observations were left in the instrumental systems. To investigate the seasonal changes in the light curve of W UMa four parameters were chosen (three of them are linearly independent). Denoting the stellar magnitudes at the primary and secondary minima as Min I and Min II, respectively, and the stellar magnitudes at the maxima following the primary and secondary minima as Max I and Max II, respectively, we can define the parameters: d1 = Min I-Min II, d2 =Min I-Max I, d3 = Min II-Max II, d4 = Max I-Max II. These parameters calculated from 12 light curves are displayed in Figure 2. [FIGURE 2] Figure 2 The changes of the parameters describing the light curve of W UMa in the last 17 years The observations were taken from the following sources: 1. Binnendijk, L., 1966, Astron. J,, 71, 340 2. Binnendijk, L., 1967, Pub. Dom. Astrophys. Obs., 13, 27 3. Breinhorst, R.A., 1971, Astrophys. Space Sci., 20, 411 4. Cester, B. and Gridelli, L,., 1967, Oss Astr. Trieste, No. 371 5. Eaton, J., 1976, I.A.U. Archives of Unpublished Obs. of Var. Stars, file No. 78 6. Evren, S., Tunca, Z., Tumer, 0., 1979, I.B.V.S. No. 1577 7. Guinan, E., Najafi, S.I., 1979, I.B.V.S. No. 1662 8. Linnalouto, S., Piirola., V., 1979., Astron. Astrophys. Suppl. Ser., 36, 33 9. Mikolajewska, J., Mikolajewski, M., 1980, I.B.V.S. No. 1812 10. Rigterink, P.V., 1972, Astron. J., 77, 230 11. present observations The mean errors of the points in Figure 2 are in the range 0.003m-0.02m. From the inspection of Figure 2 we may conclude: 1. The depth difference d1 between minima can change within at least 0.08m and it has some tendency for decreasing during the last 17 years. The primary minimum is always deeper than the secondary one. 2. The amplitude of d2 is about three times greater than the amplitude of d3. 3. The asymmetry of the maxima d4 changes within 0.07m. Usually the Max I is higher than the Max II. JANUSZ KALUZNY Astronomical Observatory of the Warsaw University 00 - 478 Warszawa Al. Ujazdowskie 4 Poland References: Eggen, O.J., 1963, Astron. J., 68, 483 [BIBCODE 1963AJ.....68..483E ] Hamzaoglu, E., Keskin, V., Eker, T., 1982, I.B.V.S. No. 2102 Kwee, K.K., Van Woerden, H., 1956, B.A.N., 12, 327 [BIBCODE 1956BAN....12..327K ]