COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 2907 Konkoly Observatory Budapest 12 June 1986 HU ISSN 0374 - 0676 VARIATIONS OF THE LIGHT CURVE OF VW Cep VW Cep (HD 197433 :G5: 7.2) is an eclipsing binary system of the W UMa type. This system shows some peculiar light variations, like asymmetries on both sides of the maximum, sporadic changes of the level of two consecutive maxima (see Fig. 2) small humps on both sides of both minima, asymmetry of the (B-V) curve, and finally intrinsic light variations. The system also shows the Kwee effect (that is a delay or advance of the primary minimum according to which maximum, II or I, is the higher). This effect was interpreted by Kwee (1966) as produced by an inhomogeneous and absorbing cloud of circumstellar matter, rotating around the double star with a period of little longer than the orbital period of the binary system. Van't Veer (1973) has proposed that the Kwee effect is originated by gas flows from regions in the neighbourhood of the first Lagrangian point L_1 to the outer envelope of the system. Walter (1979) has associated this. event with the precessional periods of the rotational axes of the components. Pustylnik and Sorgsepp (1976) proposed a model for VW Cep which consisted of a thin gas shell in the form of a disk and a hot spot produced by a gas stream, impacting on a circumstellar shell. Linnel (1980) reported X-ray emissions for this system. In same way, this one could be the origin for the cited humps near the minima of our measurements during the night 12/13 August, 1985, It was observed like two small humps, near the secondary minimum, at phases 0.45 and 0.53 (see Fig.3). During these nights, the colour index (b-v) was unusually elevated, as it is shown by the dispersion of the points of the observation carried out in the Mojon de Trigo Observatory, Sierra Nevada (see Fig. 1), The photometric observations were obtained at the Mojon de Trigo Observatory at 2616m height, during the nights of 30/31 July, 10/11 August, ad 12/13, 13/14 October 1985. We have employed the 32 cm Cassegrain telescope (f/14) equipped with photoelectric photometer using an EMI 6256A photomultiplier. We used the B, V Johnson filters. The 450 points obtained in each colour are plotted in Figure 1. The acquisition system used was a voltage-frequency converter linked to a Vic 20 personal computer, using a pulse counting program. [FIGURE 1] [FIGURE 2] [FIGURE 3] Additionally a second set of observations was made at Calar Alto Observatory in Almeria (Spain) employing the 1.23m telescope (f/8) and one photometer using the RCA 3134 photomultiplier, during the nights of 30/31 August, 31 August to 1 September and 1/2 September. We used the standard UBV Johnson filters. Figure 2 shows the 285 points measured at Calar Alto in each colour. We always used HD 197665, SAO 9836 as comparison star. In total, using the Mojon de Trigo plus Calar Alto observations, we determined 14 times of minima, of which 8 are primary and 6 are secondary ones listed in Table I. The O-C residuals and the epoch are also given in this Table. The O-C residuals have been calculated using Kwee's ephemeris : Min. I = HJD 2433898.4410 + 0d.2731793 x E or Min II with E+O.5. The epoch was evaluated with the ephemeris given by Hopp et al. (1979) Min. I = HJD 2443410.4180 + 0d.2783148 x E Table I HJD 2446000+ EPOCH O-C TYPE MIN. 277.5912 44479 -0.1530 I 287.6104 44515 -0.1533 I 288.4439 44518 -0.1547 I 288.5885 44518.5 -0.1493 II 289.4221 44521.5 -0.1507 II 289.5565 44522 -0.1554 I 308.6248 44590.5 -0.1519 II 309.4612 44593.5 -0.1505 II 309.5963 44597 -0.1545 I 310.5768 44597.5 -0.1481 II 350.5087 44741 -0.1548 I 351.4888 44744.5 -0.1489 II 351.6213 44745 -0.1555 I 352.4563 44748 -0.1555 I SANTIAGO, F., QUESADA, J. A., PALACIOS, F., SANCHEZ, J. A., and COBO, M. Grupo Astrofisico de Granada C/ Albahaca 1 Bloque 2, 1 G. Granada 18006 - Spain - References: Hopp, U., Witzigmann, S., and Kiehl, M.: 1979, IBVS, No 1599. Kwee, K. K.: 1966, Bull. Astron. Inst. Netherl. 18, 448. [BIBCODE 1966BAN....18..448K ] Linnell, A. P.: 1980, Pub. A.S.P. 92, 202. [BIBCODE 1980PASP...92..202L ] Pustylnik, I., Sorgsepp, L.: 1976, Acta Astron. Vol. 26, 319. [BIBCODE 1976AcA....26..319P ] Van't Veer, F.: 1973, Astron. Astrophys. 26, 357. [BIBCODE 1973A&A....26..357V ] Walter, K.: 1979, Astron. Astrophys. 80, 27. [BIBCODE 1979A&A....80...27W ]