COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2327 Konkoly Observatory Budapest 4 May 1983 HU ISSN 0374 - 0676 ON THE PERIOD OF EG CEPHEI The first photoelectrical measurements of this beta Lyr star were done in 1959/60. They showed some interesting lightcurve instabilities (Geyer, 1961). Therefore, we reobserved this eclipsing binary in the nights of Sept. 1/2, 2/3, 3/4, 1980 with a double beam photometer attached at the Nasmyth focus of the 106 cm Cassegrain telescope of Hoher List Observatory. This photometer which is equipped with usual UBV filters, 1P28B photomultipliers and charge integrators was described by Geyer and Hoffmann (1974, 1975). This instrument allows simultaneous observations of the variable- and the comparison stars with fairly high time resolution. The integration times for the U-measurements were 20 seconds, for the B and V were 10 seconds. A total of 307 U, 614 B and 614 V-observations were obtained on the three nights. We used the same comparison star as Geyer (1961). The reduction of the measurements was done in the usual manner, channel calibrations were done during the second and third night. From our observations, we derived one time instant for the primary and two time instants for the secondary minima by the Pogson method which are listed in Table I. The O-C values were calculated with the light ephemeris given by Strohmeier (1958) (confirmed by Geyer, 1961). From the literature, we collected all photoelectric determinations of minimum time instants and the extensive visual and photographic minimum time instant estimations by AAVSO-, BAV-, BBSAG- and Sonneberg-Observers (Mallama, 1980; Ahnert, 1975; Locher, 1975-1980). The visual and photographic Table I - Determinations of heliocentric Times of Minima for EG Cep -------------------------------------------------- Minimum time m.e. C E O-C -------------------------------------------------- 244 4484.4962d +- 0.0025d V 32233.5 + 0.0252d 4484.4951 0.0014 B 32233.5 + 0.0241 4484.4972 0.0016 U 32233.5 + 0.0262 4485.5820 +- 0.0016 V 32235.5 + 0.0217 4485.584 +- 0.004 B 32235.5 + 0.024 4486.4032 +- 0.0008 V 32237 + 0.0260 4486.4026 +- 0.0006 B 32237 + 0.0254 4486.4022 +- 0.0010 U 32237 + 0.0250 ------------------------------------------------- m.e.: mean error; E: Epoch; O-C calculated with the ephemerides of Strohmeier determinations were binned to normal epochs, all photoelectric results were taken into account individually. These values are listed in Table II. Using Strohmeier's light ephemeris, we calculated the O-C values given in Table II and shown in Figure 1. We investigated the (O-C)'s for the influence of cumulative and observational [FIGURE 1] Fig. 1: The O-C diagram according to the light ephemeris of Strohmeier Table II: Photoelectric minimum time determinations and normal epochs from visual and photographic observations of EG Cephei -------------------------------------------------------- Epoch O-C W Reference --------------------------------------------------------- 17 781 + 0.0065d 10 Geyer, ZfA 51.79 (1961) 17 941 + 0.0032 10 21 373 + 0.0029 5 Normalepoch (NE) 23 244 + 0.0091 5 23 585 + 0.0083 10 Ahnert, MVS 7.65 (1975) 24 092 + 0.0087 10 24 210 + 0.0080 5 NE 24 739 + 0.0099 5 24 795 + 0.0103 10 Ahnert, MVS 7.65 (1975) 24 794 + 0.0130 5 NE 24 887 + 0.0091 10 Ahnert, MVS 7.65 (1975) 25 410 + 0.0093 5 NE 25 388 + 0.0127 5 26 081 + 0.0132 5 26 272 + 0.0108 5 26 751 + 0.0079 5 27 336 + 0.0133 5 27 422 + 0.0153 5 28 092 + 0.0154 5 28 257 + 0.0186 5 28 763 + 0.0156 5 29 051 + 0.0147 5 29 434 + 0.0152 5 29 437 + 0.0169 10 Pohl, IBVS 1358 (1977) 29 612 + 0.0155 5 NE 30 037.5 + 0.0149 10 Ebersberger, IBVS 1449 (1978) 30 104 + 0.0162 5 NE 30 641.5 + 0.0171 10 Pohl, IBVS 1924 (1981) 30 775 + 0.0219 5 NE 30 924 + 0.0222 5 31 869 + 0.0213 5 32 233.5 + 0.0252 10 this paper 32 235.5 + 0.0227 10 32 237 + 0.0255 10 32 755 + 0.0278 5 NE -------------------------------------------------------- errors according to the method described by Sterne (1934) with the result that a cumulative period error of 8.8*10^-5 day is present. Therefore the slight curvature in the (O-C)- diagram is fully explained by this "random walk" effect. Removing the linear trend in the (O-C)-diagram (figures) one yields the improved light elements: t_Min.(J.D.) - 2426 929.4325d + 0.54462159d E. Within the errors this new period agrees well with that found by Mallama (1980) based on the 112 visual determinations of AAVSO observers between 1969 and 1978. It represents all mentioned minima instants very well, indicating that the period was constant during 1959-1980 within 9*10^-5 day. Our new UBV lightcurves which resemble those given by Geyer (1961), show some interesting, wavelength dependent instabilities. They will be discussed in detail elsewhere. The found cumulative period errors may be the result of such light curve variabilities. U. HOPP E.H. GEYER Institut fur Astronomie F.-Th. LENTES und Astrophysik Observatorium Hoher List Technische Universitat D-5568 Daun/Eifel D-1000 Berlin 10 References: Ahnert, P.: 1975, Mitt.f.Veranderliche Sterne 7, 65 [BIBCODE 1975MitVS...7...63A ] Geyer, E.H.: 1961, Zeitschrift f. Astrophys. 51, 79 [BIBCODE 1961ZA.....51...79G ] Geyer, E.H., Hoffmann, M.: 1974, Mitt. Astron. Ges. No. 35, 209 [BIBCODE 1974MitAG..35..209G ] Geyer, E.H., Hoffmann, M.: 1975, Astron. & Astrophys. 38, 359 [BIBCODE 1975A&A....38..359G ] Locher, K.: 1975-1980, BBSAG-Bull. No. 22 - 62 Mallama, A.D.: 1980, Astrophys. J. Suppl. S. 44, 241 [BIBCODE 1980ApJS...44..241M ] Sterne, T.E.: 1934, Harvard Circ. 386, 1 [BIBCODE 1934HarCi.386....1S ] Strohmeier, W.: 1958, Kleine Veroff. Bamberg No. 22, 3