COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3663

                                                Konkoly Observatory
                                                Budapest
                                                23 September 1991

                                                HU ISSN 0374 - 0676


                 1991 BVR PHOTOMETRY OF CG CYGNI


We are continuing our long-term program of photometry of
chromospherically-active, short-period binary stars with a new epoch for CG
Cygni (= BD+34d 4217 = #142 in the catalog of Strassmeier et al. [1988]).
Our earlier observations in 1989 (Beckert et al., 1989 and Beckert et al., 1991)
showed peculiar, short-term, small-amplitude fluctuations imposed upon the
eclipsing light curve and maculation wave. Such irregularities outside of
eclipse are visible also in the 1990 BV light curves of Dapergolas et al.
(1991) and those from 1989 (Dapergolas et al., 1989).

We carried out our observations with the 61-cm telescope at Capilla Peak
Observatory equipped with a Photometrics CCD camera (Laubscher et al., 1988).
We used this system as a multichannel photometer to sample sky, variable, and
the comparison star simultaneously. Our filter set (Beckert and Newberry,
1989) is matched to Johnson at B and V and Kron-Cousins at R. Typical
exposures were 15-20 seconds at R, 30-40 seconds at V, and 60-70 seconds at B.
These provided a typical S/N of about 400. Our comparison star is Yü's (1923)
star (a), not BD+34d 4216 used by single-channel observers. The observations
were made on the nights of June 8, 18, 21, 24, and 27, 1991 (UT).

Figures 1-3 show the delta magnitudes in the instrumental system, which are
very close to standard magnitudes. Figure 4 shows a 2-spot information
optimization limit (Budding and Zeilik, 1987) fit to the distortion wave at
V-band. We have assumed T_1 = 5300 K, T_2 = 4600 K, and i = 82.8deg to make
these fits with black (T = 0 K) spotted regions. The derived starspot
parameters were:  longitude = 46deg+-14deg, radius = 5.6deg+-1.4deg for spot #1 and
longitude = 238deg+-11deg, radius = 6.9deg+-1.3deg for spot #2. Both spots 
were fixed at a latitude of 45deg.


                              [FIGURE 1]
                              [FIGURE 2]
                              [FIGURE 3]
                              [FIGURE 4]


The short-term fluctuations are clearly visible again at all wavelengths. (We
carefully monitored a subset of the instrumental magnitudes of the comparison
star; they did not show any periodic variations. We were also careful to keep
the star images on the same pixels from night to night.) About five peaks are
visible in the data at B-band; they are roughly equally-spaced in phase. This
gives an approximate period of 3 hours. The features are unlikely caused by
very small spots, for their amplitudes are too large and widths too narrow for
black, circular spots on either component. We are hard pressed to come up with
a physical explanation; gaseous matter between the components would not explain
the periodic nature of the effect.

This research was supported in part by National Science Foundation Grant
AST-8901374 to MZ.


M. ZEILIK, M. LEDLOW, M. RHODES,       P.A. HECKERT
D.L. SUMMERS, E. JADERLUND,            Dept: Chemistry and Physics
and K. BOUDREAU                        Western Carolina University
Capilla Peak Observatory               Cullowhee, NC 28723
Institute for Astrophysics             U.S.A.
The University of New Mexico
Albuquerque, NM 87131
U.S.A.

References:

Beckert, D.C. and Newberry, M.V., 1989, Pub. Astron. Soc. Pac., 101, 849. [BIBCODE 1989PASP..101..849B ]
Beckert, D., Cox D., Gordon, S., Ledlow, M., and Zeilik, M., 1989, 
   Inf Bull. Var. Stars, No. 3398.
Beckert, D., Gordon, S., Jaderlund, E., Mann, E., and Zeilik, M., 1991, 
   Inf. Bull. Var. Stars, No. 3556.
Budding, E., and Zeilik, M., 1987, Astrophys. J., 319, 827. [BIBCODE 1987ApJ...319..827B ]
Dapergolas, A., Kontizas, E., and Kontizas, M., 1989, 
   Inf. Bull. Var. Stars, No. 3322.
Dapergolas, A., Kontizas, E., and Kontizas, M., 1991, 
   Inf Bull. Var. Stars, No. 3609.
Heckert, P.A. and Zeilik, M., 1989, Inf. Bull. Var. Stars, No. 3294.
Laubscher, B.E., Gregory, S., Bauer, T.J., Zeilik, M., and Buros, J.O., 1988,
   Pub. Astron. Soc. Pac., 110, 131. [BIBCODE 1988PASP..100..131L ]
Strassmeier, K.G., Hall, D.S., Zeilik, M., Nelson, E., Eker, Z., and Fekel,
   F.C., 1988, Astron. Astrophys. Suppl. Ser., 72, 291. [BIBCODE 1988A&AS...72..291S ]
Yu, C.-S., 1923, Astrophys. J., 58, 75. [BIBCODE 1923ApJ....58...75Y ]