COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1670 Konkoly Observatory Budapest 1979 September 10 INFRARED LIGHT CURVES OF THE ECLIPSING BINARY VW CEPHEI The VW Cephei system is a contact binary of W UMa type with a W type light curve (Binnendijk 1970). Variable period as well as variable light curve have been reported (Kwee 1966 a,b - Van't Veer 1973). A description of the system in terms of hot spot and shell has recently been suggested by Pustylnik and Sorgsepp (1976), as a tentative explanation for the peculiarities of the light curves. Three infrared light curves at 1.03 and 2.2 micro m are reported here, each of them being obtained during a single night, by continuously alternating variable and comparison observations. Observations The light curve observed during the night April 17-18, 1971 is shown in Figure 1. The measurements were obtained with the [FIGURE 1] Figure 1 17 April 1971 VW Cephei I I light curve of VW Cep in the sense BD +74d 889 - VW. [FIGURE 2-3] [Fig. 2.] 21 January 1976 VW Cephei K [Fig. 3.] 22 January 1976 VW Cephei K Figure 2 and 3: K light curves of VW Cephei in the sense VW - BD + 75d 764 80 cm telescope of the Observatoire de Haute-Provence, a cooled S1 photomultiplier and a filter for the I band at 10 300 A. The star BD +74d889 (G5, m_v =7.9) was used as a comparison star while BD +74d902 (F8, m_v=8.4) was a check star. The epoch for the observed primary minimum was determined by the method described by Kwee and Van Woerden (1956). We obtained: J.D. 2441059.4940 and O-C = -0.0674 in good agreement with the O-C diagram from Van't Veer (1973) and Hopp et al. (1976). The light curves of Figures 2 and 3 were observed at the Cassegrain focus of the 193 telescope of the Observatoire de Haute Provence during the nights January 21-22 and 22-23, 1976. A 77d K/Pb S photometer was used together with a K band-filter (lambda=2.2micro m). The star BD +75d764 (G5, V=6.1) was used as a comparison star, while BD +74d889 was a check star. The following elements were deduced for the primary minimum: 1976 January 21-22 J.D. 2442799.522 and O-C = -0.083 22-23 J.D. 2442800.351 and O-C = -0.089 which gives a mean O-C =-0.086 in good agreement with the diagram of Hopp et al. (1976). Discussion The poor signal to noise ratio of the K observations does not allow to ascertain whether the perturbations of Figures 2 and 3 are intrinsic to the system or due to fast atmospheric variations. Minima I and II display about the same depth at both 1.03 micron and 2.2 micron, with nearly equal maxima. The mean amplitudes are 0.25 mag at lambda=1.03 micro m and 0.22 mag at lambda=2.2 micro m which can be compared to mean value 0.36 mag at lambda=0.44 micro m (B colour) and 0.33 mag at lambda=0.55 micro m (V colour) from Kwee (1966b) and Hopp et al. (1976). The amplitude decrease with increasing wavelength is thus confirmed throughout the infrared domain. M. LUNEL, S. ROUX, J. BERGEAT Observatoire de Lyon 69 230 Saint Genis-Laval, France References: Binnedijk L., 1970, Vistas in Astronomy 12, 217 [BIBCODE 1970VA.....12..217B ] Hopp, U., Witzigmann, S., Kiehl, M., 1976 I.B.V.S. No. 1599 Kwee, K.K., 1966a, Bull.Astron.Inst.Netherl. 18, 448 [BIBCODE 1966BAN....18..448K ] Kwee, K.K., 1966b, Bull.Astron.Inst.Netherl.Suppl. 1, 265 [BIBCODE 1966BANS....1..265K ] Kwee, K.K., Van Voerden, H., 1956, Bull.Astron.Inst.Netherl. 12, 327 [BIBCODE 1956BAN....12..327K ] Pustylnik, I., Sorgsepp, L., 1976, Acta Astron. 26, 319 [BIBCODE 1976AcA....26..319P ] Van't Veer, F., 1973, Astron. and Astrophys. 26, 357 [BIBCODE 1973A&A....26..357V ]