COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4051 Konkoly Observatory Budapest, 15 July 1994 HU ISSN 0374 - 0676 1992, 1993 BV PHOTOELECTRIC OBSERVATIONS OF CG Cyg Photometric observations for this star have been reported previously by Zeilik et al. (1991), Dapergolas et al. (1992), Dapergolas et al. (1989a) and references therein. The eclipsing binary CG Cyg was observed for the periods 19-27 July 1992, 29-30 September 1992, 15-22 July 1993 and 23-25 August 1993 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 RV filters. Its output is fed directly to a microcomputer enabling rapid data access. The data reduction method is the standard one and as a comparison star BD +34d4216 was used. The constancy of the comparison star was verified by Milone et al. (1979). The data presented here were obtained with an accuracy of +/-0.015 mag. Table 1 lists the dates of observations and phases covered whereas Figure 1, 2, 3 and 4 summarize the results for July 1992, September 1992, July 1993 and August 1993 respectively. From the times of minima found here and those published by Milone et al. (1979) and Dapergolas et al. (1989a, 1989b, 1991, 1992) the O-C residuals show large variations which might be due to the continuous period variations of the system. In Table 2 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 x E given by Milone and Ziebarth (1974). Table 1 Date Phase Date Phase 19 July 1992 .80 .00 15 July 1993 .77 .20 20 July 1992 .37 .43 16 July 1993 .36 .79 .54 .80 17 July 1993 .96 .37 21 July 1992 .95 .39 18 July 1993 .52 .94 24 July 1992 .73 .08 19 July 1993 .11 .54 25 July 1992 .31 .53 20 July 1993 .73 .13 27 July 1992 .47 .66 21 July 1993 .29 .70 29 Sep. 1992 .79 .16 22 July 1993 .93 .14 30 Sep. 1992 .35 .75 23 Aug. 1993 .57 .99 24 Aug. 1993 .12 .58 25 Aug. 1993 .75 .19 Table 2 V colour B colour Date Type of Heliocentric O-C Heliocentric O-C minima Julian Day phase Julian Day Phase 21/7/1992 Primary 2448825.3666 0.048 24448825.3669 0.049 +/-0.0002 +/-0.0001 24/7/1992 Primary 2448828.5222 0.048 2448828.5223 0.048 +/-0.0002 +/-0.0003 27/7/1992 Secondary 2448831.3629 0.549 2448831.3632 0.549 +/-0.0003 +/-0.0005 29/9/1992 Primary 2448895.4236 0.049 2448895.4236 0.049 +/-0.0001 +/-0.0001 30/9/1992 Secondary 2448896.3711 0.550 2448896.3709 0.550 +/-0.0002 +/-0.0003 15/7/1993 Primary 2449184.4875 0.051 2449184.4873 0.051 +/-0.0001 +/-0.0001 16/7/1993 Secondary 244185.4321 0.548 2449185.4324 0.548 +/-0.0001 +/-0.0002 17/7/1993 Primary 2449186.3808 0.051 2449186.3808 0.051 +/-0.0002 +/-0.0001 20/7/1993 Primary 2449189.5366 0.051 2449189.5366 0.051 +/-0.0001 +/-0.0001 22/7/1993 Primary 2449191.4298 0.051 2449191.4299 0.051 +/-0.0001 +/-0.0001 24/8/1993 Secondary 2449224.5631 0.548 2449224.5631 0.548 +/-0.0004 +/-0.0003 25/8/1993 Primary 2449225.5114 0.051 2449225.5115 0.051 +/-0.0001 +/-0.0001 [FIGURE 1] From Figures 1, 2, 3 and 4 it can be seen that there are irregularities outside the eclipse already reported previously by Milone et al. (1979), Dapergolas et al. (1989b), Beckert et al. (1989), Dapergolas et al. (1991), Zeilik et al. (1991), Dapergolas et al. (1992) and Zeilik et al. (1994). From the Figures 1 and 2 it can be seen that there is a significant difference in the light curves outside the eclipses for the phases 0.6-0.95 whereas there is no difference for the phases 0.1-0.45 whereas from Figures 3 and 4 of the year 1993 it can be seen that there is no significant difference in the light curves. The observed differences between the primary and secondary minima for the period 1987-1993 are shown in Table III (Dapergolas et al.,1988,1989a,1989b,1991,1992). [FIGURE 2] [FIGURE 3] [FIGURE 4] Table 3 Differences between primary and secondary minima for CG Cygni in B and V colours Date deltaB(mag) deltaV(mag) 1987 July 0.41 0.30 1988 Sept. 0.34 0.30 1989 July 0.45 0.39 1990 July 0.48 0.37 1991 July 0.46 0.37 1992 July 0.38 0.30 1992 Sept. 0.43 0.36 1993 July 0.50 0.40 1993 Aug. 0.49 0.42 From the values of Table 3 it can be seen that there is a variation in the difference of both minima depths and for both colours probably due to the photospheric activity of the system. A. DAPERGOLAS M. KONTIZAS E. KONTIZAS Section of Astrophysics, National Observatory of Athens Astronomy and Mechanics, Astronomical Institute Department of Physics, P.O. Box 20048 University of Athens GR Athens 118-10 Panepistimiopolis Greece GR-157 83, Zografos Athens Greece References: Beckert, D., Cox, D., Gordon, S., Ledlow, M. and Zeilik, M., 1989, Inf. Bull. Var. Stars, No. 3398 Dapergolas, A., Kontizas, E. and Kontizas, M., 1988, Inf. Bull. Var. Stars, No. 3249 Dapergolas, A., Kontizas, E. and Kontizas, M., 1989a, Inf. Bull. Var. Stars, No. 3322 Dapergolas, A., Kontizas, E. and Kontizas, M., 1989b, Inf. Bull. Var. Stars, No. 3380 Dapergolas, A., Kontizas, E. and Kontizas, M., 1991, Inf. Bull. Var. Stars, No. 3609 Dapergolas, A., Kontizas, E. and Kontizas, M., 1992, Inf. Bull. Var. Stars, No. 3719 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 ] Zeilik, M., Ledlow, M., Rhodes, M., Summers, D. L., Jaderlund, E., Boudreau, K. and Heckert, P. A., 1991, Inf. Bull. Var. Stars, No. 3663 Zeilik, M., Gordon, S., Jaderlund, E., Ledlow, M., Summers, D. L., Heckert, P. A., Budding E. and Banks, T., 1994, Astrophys. J., 421, 303 [BIBCODE 1994ApJ...421..303Z ]