COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3998 Konkoly Observatory Budapest 23 February 1994 HU ISSN 0374 - 0676 PHOTOELECTRIC PHOTOMETRY OF THE ECLIPSING BINARY STAR CQ CEPHEI CQ Cephei (HD 214419=BD+56d2818) is an eclipsing binary system with a period of ~1.64 days. The binary nature of CQ Cep was discovered by McLaughlin and Hiltne (1941). First photoelectric light curves were obtained by Hiltner (1950). Leung et al. (1983) analyzed Hiltner's V light curve and their NIV 4058 A radial velocity curve with the Wilson - Devinney method. Their analysis showed that the system has a contact configuration. One component is a WN7 and the other is probably a massive early type star (O7). This eclipsing binary was observed photoelectrically at the Ege University Observatory on 19 nights in 1991 and 12 nights in 1992. The observations were made with the 48 cm Cassegrain reflector. An unrefrigerated EMI 9781 A photomultiplier tube and B, V filters which are very close to the standard UBV system were used. BD+56d2815 was selected as comparison and BD +56d2813 as check star. The comparison star was found to be constant in brightness during the period of observations. A total 1511 observational points were obtained in each colour. All the differential magnitudes (in the sense variable minus comparison) were corrected for the atmospheric extinction. Gaposchkin (1944) discovered the changes of period and analysed photographic observations made in the years 1901 to 1942. He interpreted the shortening of period as the effect of a third body. Semeniuk (1968) proved the shortening of period, however, she pointed out the linear light elements which satisfy the observations made in the interval 1945-65. The period variation and possible causes of it was discussed and interpreted due to the mechanism of mass transfer and loss from the WR component by several authors (Kreiner and Tremko, 1983, 1985). According to their analyses, the period of C(a Cep was decreasing over a long time. During the observations 7 primary and 3 secondary times of minima were obtained which are given in Table I. These primary times of minima with other photographic and photoelectric ones taken from Kreiner and Tremko (1983,1985) are used in O-C analysis. The (O-C)_1 values were computed using the following light elements given by Kreiner and Tremko (1983): Hel. Min. I J.D. = 2432456.668d + 1.6412438d * E ( 1 ) The (O-C)_1 diagram of CQ Cep is shown in Figure 1. As it is clearly seen from the figure, CQ Cep shows a parabolic variation indicating a continuous decrease in the period. Using the times of minima plotted in Figure 1, quadratic light elements have been calculated by the weighted least squares method as follows: Hel. Min. I J.D. = 2432456.694d + 1.6412481d * E-9.29 * 10^-10 * E2 (2) +-2 +-2 +-36 [FIGURE 1] Figure 1. O_C diagram for CQ Cep [FIGURE 2] Figure 2. Differential B and V light and B-V colour curves of CQ Cep Table I Times of minima of CQ Cephei ------------------------------------------------------------------- J.D. Hel.2400000+ Method Min E (O-C)_1 (O-C)_2 ------------------------------------------------------------------- 48437.4352 pe I 9737 -0.0437 -0.0026 48506.3667 pe I 9779 -0.0444 -0.0027 48515.4053 pe II 9784.5 - - 48524.4189 pe I 9790 -0.0459 -0.0040 48826.4066 pe I 9974 -0.0471 -0.0026 48844.4651 pe I 9985 -0.0422 0.0023 48849.3938 pe I 9988 -0.0373 0.0073 48872.3633 pe I 10002 -0.0452 -0.0003 48876.4868 pe II 10004.5 - - 48881.4112 pe II 10007.5 - - --------------------------------------------------------------------- Table II. B and V magnitudes of comparison and check stars ----------------------------------------------------------------- Star V B Spectral T. BD+56d2815 (comparison) 8.66m+-0.01 8.66+-0.01 A0 BD+56d2813 (check) 8.26m+-0.01 8.66m+-0.01 A3 ----------------------------------------------------------------- Table III. B and V magnitudes of CQ Cep --------------------------------------- Colour Min.I. Max.I Min.II Max.II --------------------------------------- V 9.09m 8.68m 9.05m 8.64m B 9.51m 9.09m 9.45m 9.06m --------------------------------------- The period of the system is decreasing with the amount of 0.0036+-0.001 second per year. The light and colour curves are given in Figure 2. The phases in Figure 2 were calculated with the following linear light elements: Hel Min. I J.D.= 2448524.423d+ 1.6412299d*E (3) +-2 +-2 These elements were obtained from quadratic light elements and may be used in near future. The shape of light curve is typical of beta Lyrae type. The magnitudes of comparison, check and variable stars were transformed to standard UBV system and given in Tables ' II and III. There are large asymmetries in the light curves. The primary and secondary maxima occur at phases ~0.27 and ~0.81, respectively. Primary eclipse is narrower than the secondary. Secondary minimum occurs at phase ~0.511. In 1992 observations, the primary minimum is deeper by ~0.02m than that of the 1991 observations. In Figure 1, the scattering of our observations near the primary is ~0.05m. The photometric analysis of the V light curve is in progress and will be published elsewhere. Bekir KILINC Ege University Observatory Campus, 35100 Bornova, Izmir, Turkiye References: Gaposchkin, S.: 1944, Astrophys. J., 110, 242 [BIBCODE 1944ApJ...100..242G ] Hiltner, W. A.: 1950, Astrophys. J., 112, 477 [BIBCODE 1950ApJ...112..477H ] Kreiner, J. M., Tremko, J.: 1983, Bull. Astron. Inst. Czech., 34, No. 6, 341 [BIBCODE 1983BAICz..34..341K ] Kreiner, J. M., Tremko, J.: 1985, Abastumani Astrophysical Observatory Bull., 58, 35 [BIBCODE 1985AbaOB..58...35K ] Leung, K. C., Moffat, A. F. J., Seggewiss, W.: 1983, Astrophys. J., 265, 961 [BIBCODE 1983ApJ...265..961L ] McLaughlin, D. B., Hiltner, W. A.: 1941, Publ. Astron. Soc. Pacific., 53, 328 [BIBCODE 1941PASP...53..328M ] Semeniuk, I.: 1968, Acta Astron., 18, No. 2, 314 [BIBCODE 1968AcA....18..313S ] ERRATUM In the No. 3950 issue of the IBVS one of the references was incorrectly given. On page 2, the third ephemeris is based on Oprescu et al. (1991) and the correct reference is: Oprescu, G., Suran, D. M., and Popescu, N., 1991, Inf. Bull. Var. Stars, No. 3560 G. OPRESCU