COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1599 Konkoly Observatory Budapest 1979 May 8 A NEW B V LIGHTCURVE OF THE ECLIPSING BINARY VW CEPHEI The W UMa star VW Cep is well known to have both a variable period and a variable lightcurve (Kwee, 1966). The older observations show a correlation between the variability of the period and the longtime activities of the lightcurve. VW Cep has a similar period and spectral-type to i 44 Boo which is also well known for variable period and lightcurve disturbances (see, for example, Duerbeck, 1978). For both stars it was suspected that there exist cycles or periods for the observed lightcurve changings. A detailed interpretation of the disturbances of VW Cep by a hot spot and a shell is presented by Pustylnik and Sorgsepp (1976). To carry on the observational work, a new lightcurve of VW Cep was observed on Sept. 23/24 and Sept. 24/25, 1977. 1. The observations The measurements were taken with the 75 cm telescope of the Wilhelm-Foerster Observatory, Berlin, an uncooled RCA 1P21 multiplier, an usual amplifier and Schott filters BG12+GG13 for the B-band and GG11 for the V-band. As comparison star served BD+75d765 (K2) = A, as check star BD+75d755 (G0) = B. Schmidt and Schrick (1955) found that A may be slowly variable, but the difference A-B was found to be constant at DeltaV = -2.143m +-0.008m and DeltaB = - 1.499m +-0.007m between the two nights. The observations of both nights are drawn in Fig. 1 and no systematic differences are found. The observations of Sept. 23/24 cover a primary minimum, the observations of Sept. 24/25 cover the interval from 0.1P to 0.95P. A total of 162 V observations and 146 B observations were obtained. 2. The period The times of the primary and secondary minimum were determined by Pogson's method: Min I_0 2443 410d4180 +- 0.0006d E: 34177 O-C: -0.0949d Min II_0 411.3952 +- 0.0007 34180,5 -0.0918 [FIGURE 1] Fig. 1: B and V lightcurve of VW Cep in the sense VW-BD+75d765 [FIGURE 2] Fig. 2: O-C diagram of VW Cep according to the ephemeris of van't Veer. Table 1 Minima determinations of VW Cep ------------------------------------------------------------------- Epoch Minimum time_0 O-C Reference ------------------------------------------------------------------- 25169 2440903.3557d -0.0693 Pohl, E. Kizilirmak, A. 1972- IBVS 647 26021 1140.4822: -0.0697: 26261 1207.277: -0.071: 26297 1217.298: -0.070: 26408,5 1248.328: -0.072: 27659 1596.364 -0.073 Kizilirmak, A. Pohl, E. 1974-IBVS 937 27953,5 1678.327 -0.074 28442,5 1814.426 -0.073 28496,5 1829.456 -0.072 29071 1989.344 -0.078 31489,5 2662.4519 -0.0816 Patkos, L., 1975-IBVS 1065 31504 2666.4844 -0.0847 31683 2716.3027 -0.0853 Branczewicz, H., Kreiner, J.M., 1976- IBVS 1119 30670 2434.3686 -0.0833 Pohl, E. Kizilirmak, A. 1976-IBVS 1163 30724 2449.3985 -0.0826 31015 2530.388 : -0.084 : 31108,5 2556.407 -0.087 31109 2556.548 -0.086 31130 2562.397 -0.081 31288,5 2606.513: -0.079 : 31550,5 2679.4272 -0.0837 Patkos, L., 1976-IBVS 1200 31554 2680.3996 -0.0854 31601 2693.4799 -0.0860 32664,5 2989.4692 -0.0878 31938,5 2787.4133 -0.0849 Pohl, E. Kizilirmak, A. 1977-IBVS 1358 32301,5 2888.4409: -0.0867: 32391,5 2913.4887: -0.0875: 32883,5 3050.4218 -0.0869 28735 1895.8309 -0.0758 Scarfe, C.D. Barlow. D.J., 1979- 29823,5 2198.7773 -0.0785 IBVS 1379 30031 2256.8019 -0.0832 30075 2268.7702 -0.0825 30078,5 2269.7467 -0.0802 30154 2290.7587 -0.0812 30154,5 2290.8973 -0.0817 31113,5 2557.8039 -0.0820 31135 2563.7854 -0.0843 32622,5 2977.7824 -0.0853 34137 3399.2870 -0.0932 Cristescu, C., 1978-IBVS 1383 34202 3417.3786 -0.0922 34216 3421.2737 -0.0936 34216,5 3421.4126 -0.0939 34227 3424.3332 -0.0956 34270 3436.3029 -0.0936 34288 3441.3090 -0.0972 34313 3448.2663 -0.0978 34352,5 3459.2635 -0.0942 35140,5 3678.5786 -0.0936 Niarchos, P.G., 1979-IBVS 1576 35144 3679.5510 -0.0953 35148 3680.6646 -0.0950 33825 3312.4522 -0.0928 Ebersberger, J., Pohl, E.,Kizilirmak, 34062 3378.4148 -0.0915 A., 1978-IBVS 1449 34177 3410.4180 -0.0949 this paper 34180,5 3411.3952 -0.0918 -------------------------------------------------------------------- The given values of minima times are means of the value obtained from the B and V lightcurve. The given O-C value for Min II is calculated under the premises that Min II lies at 0.5P. The ephemeris are adopted from van't Veer (1973): Min I_0 = J.D.2433898.4410d + 0.27831793d E. Fig. 2 shows van't Veer's O-C diagram completed by minima determinations given in Table 1. The figure clearly shows that the period shortening still goes on. Kreiner (1977) showed that all good observed W UMa variable stars change their periods in rather short time and than remain constant. Using all minima of Table 1 with E > 28000, one can find by a linear last square fit the actual value of the photometric period to be 0.27831481d or 0.270 seconds less than van't Veer's value. 3. The lightcurve Schmidt and Schrick determined three values to describe the lightcurve variability around the extrema: Delta_1 m = m_Min I^-m_Min II B + 0.10m V + 0.086m Delta_2 m = m_Max I^-m_Min II - 0.31 - 0.312 Delta_3 m = m_Max II^-m_Min II - 0.33 - 0.296 The actual values from our observations are tabulated. A shoulder appears at 0.64P in the V-band, but it is not detected in the B- band. In the light curve of i Boo and W UMa (Duerbeck), shoulders are found which are interpreted by Breinhorst and Reinhardt (1974) as light absorption of a gaseous stream. Except the pronounced feature at 0.64P in the V-band, no similar disturbances are detected. An unusual great scatter in B and V is observed around 0.95P. A small asimmetry of Min II may be possible in the bottom of the V lightcurve. U. HOPP, S. WITZIGMANN, M. KIEHL Wilhelm Foerster Sternwarte Munsterdamm 90, D 1000 Berlin - 41 References: Breinhorst, R.A., Reinhardt, M., 1974 - Acta Astron. 24, 377 [BIBCODE 1974AcA....24..377B ] Duerbeck, H.W., 1978 - Astron.Astrophys. 32, 361 [BIBCODE 1978A&AS...32..361D ] Kwee, K.K., 1966 - Bull.Astron.Inst.Netherl. 18, 448 [BIBCODE 1966BAN....18..448K ] Kreiner, J.M., 1977,- in: Kippenhahn, R., Rahe, J., Strohmeier, W., Veroff.Remeis Sternw. Bd. XI Nr. 121 Pustylnik, I., Sorgsepp, L., 1976 - Acta Astron. 26, 319 [BIBCODE 1976AcA....26..319P ] Schmidt, H., Schrick, K.W., 1955 - Zeitschrift f.Astrophys. 37, 73 [BIBCODE 1955ZA.....37...73S ] van't Veer, F., 1973 - Astron. Astrophys. 26, 357 [BIBCODE 1973A&A....26..357V ]