COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2176 Konkoly Observatory Budapest 1982 July 16 HU ISSN 0374-0676 A 2.2 micron LIGHT CURVE OF THE ECLIPSING BINARY VW CEPHEI The star VW Cephei is a triple system (Hershey 1975) with a W UMa type eclipsing binary (components A and B; subclass W according to Binnendijk 1970) and a remote companion (C) of estimated spectral type K7V, while G8 is obtained for (A+B). Due to a 0.64" separation between (A+B) and (C), the three lights are included in photometric measurements. Variable period as well as variable light curve have been reported (Kwee 1966 a, b - Van't Veer 1973 - Rovithis and Rovithis-Livaniou 1980 - Niarchos 1980). Various models have been proposed for the latter phenomenon (Kwee 1966 a - Leung and Jurkevich 1969 - Van't Veer 1973 - Pustylnik and Sorgsepp 1976) in term of spots and/or circumstellar gas. The observed period shortening possibly contradicts the thermal oscillation theory (Linnell 1980). See also Walter 1979 for a precessional model. Since the infrared observations we reported for VW Cephei (Lunel et al. 1979) the 77dK PbS photometer was abandoned for a more sensitive InSb version. New observations at Lambda = 2.2 micron (K window) were made at the Cassegrain focus of the 80 cm telescope of the Observatoire de Haute-Provence (CNRS France) during the night of 1980 October 25 (Fig. 1). The star BD +75d764 was used as a comparison star. No strong perturbation can be ascertained in the light curve, despite the improved signal to noise ratio. The mean amplitude of 0.22 mag. at lambda = 2.2 micron as precedently quoted (Lunel et al. 1979) is confirmed. The total flux of the system at maximum light is the same as the one observed in January 1976. The difference between maxima heights is only 0.01 mag. while the difference between minima is about 0.024 mag. According to Heinz (1975) component C is 2.9 mag. fainter than (A+B) at maximum in visual light. Assuming for C the spectral distribution for a K7V star, a F(A+B)/F(C) = 4.4 light ratio is deduced at 2.2 micron to be compared to 14.4 in visual light. The observations of Fig. 1 can then be corrected for the third light, using the former ratio. The mean amplitude then becomes 0.28 mag. [FIGURE 1] [FIGURE 2] The epoch of the primary minimum has been determined by the method of Kwee and Van Woerden (1956). We obtained : J.D. 2 444 538. 4223 and O - C = - 0.1131 in good agreement with the O-C diagram as established by Van't Veer (1973) and Hopp et al. (1979). See Fig. 2 . LUNEL, M., GARNIER, R., BERGEAT, J. Observatoire de Lyon 69230 St-Genis-Laval France VAN'T VEER, F. Institut d'Astrophysique 98bis, Boulevard Arago 75014 Paris Observatoire de Haute-Provence St-Michel l'Observatoire References: Binnendijk, L., 1966, Vistas in Astronomy 12, 217 [BIBCODE 1970VA.....12..217B ] Heinz, W.D., 1975, IAU Inf. Circ. Vis. Double Stars No. 64 Hershey, J.L., 1975, Astron. J. 80, 662 [BIBCODE 1975AJ.....80..662H ] Hopp, U., Witzigmann, S. and Kiehl, M., 1979, IBVS No. 1599 Kwee, K.K., 1966a, Bull. Astron. Inst. Netherl. 18, 448 [BIBCODE 1966BAN....18..448K ] Kwee, K.K., 1966 b, Bull. Astron. Inst. Netherl. Suppl. 1, 265 [BIBCODE 1966BANS....1..265K ] Kwee, K.K. and Van Woerden, H., 1956, Bull. Astron. Inst. Netherl. 12, 217 [BIBCODE 1956BAN....12..327K ] Leung, K.C and Jurkevich, I., 1969, B.A.A.S. 1, 251 [BIBCODE 1969BAAS....1T.251L ] Linnell, A.P., 1980, P.A.S.P. 92, 202 [BIBCODE 1980PASP...92..202L ] Lunel, M., Roux, S., and Bergeat, J., 1979, IBVS No. 1670 Niarchos, P.G., 1980, IBVS No. 1729 Pustylnik, I. and Sorgsepp, L., 1976, Acta. Astron. 26, 319 [BIBCODE 1976AcA....26..319P ] Rovithis, P. and Rovithis-Livaniou, H., 1980 IBVS No 1736 Rovithis, P. and Rovithis-Livaniou, H., 1980 Astrophys. and Space Science, 73, 27 [BIBCODE 1980Ap&SS..73...27R ] Van't Veer, F., 1973, Astron. and Astrophys. 26, 357 [BIBCODE 1973A&A....26..357V ] Walter, K., Astron.and Astrophys., 1979, 80, 27 [BIBCODE 1979A&A....80...27W ]