COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3915 Konkoly Observatory Budapest 29 July 1993 HU ISSN 0374 - 0676 PHOTOELECTRIC PHOTOMETRY OF THE ECLIPSING BINARY STAR EG CEPHEI EG Cep (BD+76d790=HD 194089=BV 200) was discovered by Strohmeier (1958) as an eclipsing binary with a period of P=0.54d. The star was observed photoelectrically by Geyer (1961), Cochran (Wood, 1971), Van der Wal et al. (1972), Kaluzny and Semeniuk (1984). Kaluzny and Semeniuk analyzed their light curves with the Wilson-Devinney method. They found that EG Cep is most probably a semidetached system in the slow stage of case A mass exchange evolving to a contact configuration. The system was observed photoelectrically at the Ege University Observatory. The observations were performed in the observational seasons of 1991 and 1992. The 48 cm (f/13) Cassegrain reflector equipped with an unrefrigerated EMI 9781A photomultiplier tube was used. All observations were made with the B and V filters of the UBV system. BD+76d791 and BD+76d789 were used as comparison and check stars respectively. The atmospheric extinction coefficients in each colour for every nights were calculated from the observations of the comparison star using conventional methods. Then, all the differential observations (variable minus comparison) were corrected for differential extinction. A total of 550 observational points were obtained in each colour. During the observations moments of six primary and four secondary minima were obtained which are given in Table I. The (O-C)I values were computed using the following light elements given by Mallama (1980): Hel Min I JD=2442594.3825+0.54462183d x E (1) Table I. Times of minima of EG Cep J.D. Hel. Min Method Filter E (O-C)I (O-C)II ------------------------------------------------------------------- 2448483.3901 I pe B 10813 0.01175 0.00206 48483.3904 I pe V 10813 0.01205 0.00236 48489.3805 I pe V 10824 0.01131 0.00161 48489.3819 I pe B 10824 0.01271 0.00301 48495.3696 I pe B 10835 0.00957 -0.00014 48495.3709 I pe V 10835 0.01087 0.00116 48516.3389 II pe B 10873.5 0.01093 0.00117 48516.3395 II pe V 10873.5 0.01153 0.00177 48523.4174 II pe B 10886.5 0.00935 -0.00043 48523.4181 II pe V 10886.5 0.01005 0.00027 48810.4333 II pe V 11413.5 0.00954 -0.00091 48810.4323 II pe B 11413.5 0.00854 -0.00191 48841.4739 II pe V 11470.5 0.00670 -0.00383 48841.4760 II pe B 11470.5 0.00880 -0.00173 48843.3851 I pe V 11474 0.01172 0.00119 48843.3858 I pe B 11474 0.01242 0.00189 48850.4651 I pe V 11487 0.01164 0.00109 48850.4623 I pe B 11487 0.00884 -0.00171 48855.3652 I pe B,V 11496 0.01014 -0.00042 ------------------------------------------------------------------- [FIGURE 1] Figure 1. The O-C diagram for EG Cep [FIGURE 2] Figure 2. Differential B and V light and B-V colour curves of EG Cep for 1991 and 1992 The (O-C)I diagram of EG Cep is shown in Figure 1. This diagram contains other times of minima which can be found from the literature. As it is clearly seen from the figure, EG Cep shows a parabolic variation indicating a continuous increase in the period. The period increase is found to be about 0.55+-0.04 second per century. Using the times of minima plotted in Figure 1, quadratic light elements have been calculated by the least squares method as follows: HJD Min I=2442594.3842+0.54462206d x E+0.473d x 10^-10 x E^2 (2) +-4 +-5 +-35 The (O-C)2 values in the table are calculated with these new light elements. However, the following linear ephemeris can be used in the near future: HJD Min I=2448850.4640+0.54462314d x E +-4 +-5 Our individual differential observations in both colours and the B-V colour curve are plotted in Figure 2. The phases were calculated with the formula (3). The shape of the light curve is typical of beta Lyr type. Kaluzny and Semeniuk (1984) found that the phase of the secondary minima in yellow is earlier than that of the secondary minima in blue, and the light curves of EG Cep are not quite symmetric. We could not see the same effects in our secondary minima nor in the light curves. The primary minimum is an annular eclipse. The amplitudes are about 0.945m and 0.875m at the primary, 0.275m and 0.290m at the secondary minimum in blue and yellow light, respectively. The colour curve in Figure 2 shows that the system is slightly redder at the primary and bluer at the secondary minimum. So, the spectral type of the secondary component is later than that of the primary. The photometric analysis of the light curves is in progress and will be published elsewhere. A. ERDEM B. KILINC O. L. DEGIRMENCI O. GULMEN, C. SEZER and N. GUDUR Ege University Observatory Campus, 35100 Bornova, Izmir, Turkiye References: Geyer, E.: 1961, Z. Astrophys., 51, 79 [BIBCODE 1961ZA.....51...79G ] Kaluzny, J. and Semeniuk, I.: 1984, Acta Astron., 34, 433 [BIBCODE 1984AcA....34..433K ] Mallama, A. D.: 1980, Astrophys. J. Suppl., 44, 241 [BIBCODE 1980ApJS...44..241M ] Strohmeier, W.: 1958, Kl. Veroff. Bamberg, 21, 22 Van der Wal, P. B., Nagel, C., Voordes, H. R., and de Boer, K. S.: 1972, Astron. Astrophys. Suppl., 6, 131 [BIBCODE 1972A&AS....6..131V ] Wood, D. B.: 1971, Astron. J., 76, 701 [BIBCODE 1971AJ.....76..701W ]