COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3380 Konkoly Observatory Budapest 5 October 1989 HU ISSN 0374 - 0676 1989 BV PHOTOELECTRIC OBSERVATIONS OF CG Cyg The eclipsing binary CG Cyg was observed from 24 July through 1 August with the 1.2m Kryonerion telescope and a single channel photon counting photometer described by Dapergolas and Korakitis (1987). The photometer employs a high gain 9789QB phototube and conventional BV filters. Its output is fed directly to a microcomputer enabling rapid data access. Photometric observations for this star have been reported by us in 1988 and 1989 and other investigators listed by Dapergolas et al. (1989). The data reduction method is the standard one and the BD+34d4216 was used as a comparison star. The constancy of the comparison star was verified by Milone et al. (1979). The data were obtained with an accuracy of +-0.015 mag. Table I lists the dates of observations and phases covered whereas Figures 1 and 2 summarize the results for B and V colours. Table I Date Phase 24 July 1989 .16 .53 25 July 1989 .83 .14 26 July 1989 .31 .73 27 July 1989 .96 .14 30 July 1989 .78 .08 31 July 1989 .22 .65 1 Aug 1989 .05 .22 In Table II the times of minima and the O-C values are listed for the V and B bands respectively. Times of minima are calculated using the method described by Kwee and van Woerden (1956) whereas the O-C values were determined from the linear ephemeris T=2439425.1221d+0.631141d*E given by Milone and Ziebarth (1974). From Figures 1 and 2 it can be seen that there are irregularities outside the eclipse already reported by Milone et al. (1979) and ten years later by Dapergolas et al. (1989). [FIGURE 1] [FIGURE 2] Table II V COLOUR B COLOUR Type of Heliocentric (O-C) Heliocentric (O-C) minima Jul. Day phase Jul. Day phase Primary 2447733.4867 0.039 2447733.4865 0.038 +-0.0001 +-0.0001 Secondary 2447734.4335 0.539 2447734.4331 0.538 +-0.0001 +-0.0002 Primary 2447735.3801 0.039 2447735.3798 0.038 +-0.0001 +-0.0001 Primary 2447738.5353 0.038 2447738.5355 0.038 +-0.0003 +-0.0003 Secondary 2447739.4826 0.539 2447739.4826 0.539 +-0.0001 +-0.0001 The observed difference between the primary and secondary minima is 0.45 mag for the B and 0.39 mag for V whereas these values for 1988 are 0.34 mag and 0.30 mag respectively (Dapergolas et al., 1988) and for the year 1987 0.41 mag and 0.30 mag (Dapergolas et al., 1989). These values indicate that the differential variation of the two minima depths is similar for both colours (0.11 mag for B and 0.09 mag for V) for the years 1988 - 1989 but are quite different (-0.07 mag for B and 0.0 mag for V) for the years 1987 - 1988. From the times of minima found here and those published by Dapergolas et al. (1989) and Milone et al. (1979) the O-C residuals show large variations which might be due to the continuous period variation of the system. A. DAPERGOLAS and E. KONTIZAS M. KONTIZAS National Observatory of Athens University of Athens Astronomical Institute Laboratory of Astrophysics P.O. Box 20048 Panepistimiopolis GR Athens 118-10 GR Athens 151-71 Greece Greece References: Dapergolas, A., Kontizas, E. and Kontizas, M.: 1988, Inf. Bull. Var. Stars, No. 3249. Dapergolas, A., Kontizas, E. and Kontizas, M.: 1989, Inf. Bull. Var. Stars, No. 3322. Dapergolas, A. and Korakitis, R.: 1987, Publ. Nat. Obs. of Athens, Ser II. No. 28. Kwee, K.K. and van Woerden, H.: 1956, Bull. Astr. Inst. Netherlands, 12, 327. [BIBCODE 1956BAN....12..327K ] Milone, E.F. and Ziebarth, K.E.: 1974, Publ. Astron. Soc. Pacific, 86, 684. [BIBCODE 1974PASP...86..684M ] Milone, E.F., Castle, K.G., Swadrom, D., Burke, E.W., Hall, D.S., Michlovic, J.E. and Zissell, R.E.: 1979, Astron. J., 84, 417. [BIBCODE 1979AJ.....84..417M ]