COMMISSIONS 27 AND 42 OF THE IAU 
           INFORMATION BULLETIN ON VARIABLE STARS 
                       Number 3719
 
                                        Konkoly Observatory 
                                        Budapest 
                                        30 April 1992 
 
                                        HU ISSN 0374 - 0676 
 
 
 
 
         1991 BV PHOTOELECTRIC OBSERVATIONS OF CG Cyg 
 
 
  Photometric observations for this star have been reported previously 
by Zeilik et al., 1991; Dapergolas et al., 1991; Dapergolas et al., 
1989a and references therein. 
 
  The eclipsing binary CG Cyg was observed for the period 15-26 July 
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.

  The data reduction method is the standard one and as a comparison star 
we used BD +34d4216. 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 I lists the dates of observations and phases covered whereas 
Figures 1 and 2 summarize the results for B and V colours. 
 
  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=2439425.121d + 
0.631141d E given by Milone and Ziebarth (1974). 
 
 
               TABLE I 
Date           Phase 
15 July 1991   .61       .97 
17 July 1991   .76       .14 
19 July 1991   .92       .31 
20 July 1991   .46       .76 
25 July 1991   .98       .76 
26 July 1991   .97       .40 


                           [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     2448455.5163      0.045   2448455.5163   0.046 
          +/-0.0001                 +/-0.0001 
Primary     2448457.4097      0.045   2448457.4099   0.046 
          +/-0.0001                 +/-0.0001 
Secondary   2448458.3563      0.545   2448458.3560   0.545 
          +/-0.0003                 +/-0.0003 
Secondary   2448463.4048      0.545   2448463.4048   0.545 
          +/-0.0002                 +/-0.0003 
Primary     2448464.3527      0.046   2448464.3528   0.046 
          +/-0.0002                 +/-0.0002 
 
 
 
       TABLE III 
    Differences between Primary and Secondary 
    minima for CG Cygni in B and V colours 
  DATE   deltaB(mag)   deltaV(mag) 
  1991   0.46          0.37 
  1990   0.48          0.37 
  1989   0.45          0.39 
  1988   0.34          0.30 
  1987   0.41          0.30 
 
 
 
  From Figures 1 and 2 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), and Zeilik et al. (1991). 
 
  The observed differences between the primary and secondary minima for 
the period 1987 - 1991 are listed in Table III (Dapergolas et al., 1988, 
1989a, 1989b, 1991). 
 
  From the values of Table III 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. 
 
  From the times of minima found here and those published by Milone et 
al. (1979) and Dapergolas et al. (1989a, 1989b, 1991) the O-C 
residuals show large variations which might be due to the continuous 
period variations of the system. 
 
 
 
A. DAPERGOLAS and E. KONTIZAS 
National Observatory of Athens 
Astronomical Institute 
P.O. Box 20048 
GR Athens 118-10 
Greece 
 
M. KONTIZAS 
 
Section of Astrophysics, Astronomy 
  and Mechanics, Dept. of Physics, 
University of Athens 
Panepistimiopolis 
GR-157 83, Zografos Athens, Greece 
 
 
 
References: 
 
Beckert, D., Cox, D., Gordon, S., Ledlow, M. and Zeilik, M.: 1989, 
  I.B.V.S. No. 3398. 
Dapergolas, A., Kontizas, E. and Kontizas, M.: 1988, I.B.V.S. No. 3249. 
Dapergolas, A., Kontizas, E. and Kontizas, M.: 1989a, I.B.V.S. No. 3322. 
Dapergolas, A., Kontizas, E. and Kontizas, M.: 1989b, I.B.V.S. No. 3380. 
Dapergolas, A., Kontizas, E. and Kontizas, M.: 1991, I.B.V.S. No. 3609. 
Dapergolas, A. and Korakitis, R.: 1987, Publ. Nat. Obs. of Athens, Ser II, 
  No.28. 
Kwee, K.K., 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, I.B.V.S. No. 3663.