COMMISSION 27 OF THE I. A. U.
                  INFORMATION BULLETIN ON VARIABLE STARS
                              Number 3556

                                                       Konkoly Observatory
                                                       Budapest
                                                       19 January 1991

                                                       HU ISSN 0374 - 0676


                CG CYGNI REDUX: MORE 1989 BVR DATA

   Our 1989 July and August BVR light curves of CG Cygni (=BD +34d4217=#142
in the catalog of Strassmeier et al. 1988) exhibited small "waves"
(Beckert et al., 1989). To confirm that these peculiar features were real
(rather than instrumental or weather-generated artifacts), we decided to
re-observe this short-period RS CVn system as soon after as possible on 10 and
11 Sept., 13 Oct., and 11 and 13 Nov., 1989. We note that our earlier data were
obtained on different nights with overlapping phase coverage, yet the
small-scale structure matched smoothly. Also, we tracked the instrumental
magnitude of the comparison star and found it constant within statistical
fluctuations. Finally, observations of RT And done at about the same time
with the same system showed no such small waves. These facts support the claim
that the "waves" originated in the binary system rather than in the
instrumentation or from the observing technique.
   We used our 60-cm Capilla Peak telescope with a CCD camera (Laubscher et
al., 1988) in the mode of a multichannel photometer with our new filter set
(Beckert and Newberry, 1989). Data were reduced with a softward mask for an
effective aperture of 30 arcsec. The orbital phases were calculated from the
ephemeris of Strassmeier et al. (1988).
   Figures 1-3 present the data (converted from instrumental magnitudes to
normalized intensity units) at BVR. As before, the statistical error in each
datum is less than 0.01 mag. In fact, tests of our CCD system indicate that
for V-hand exposures of 30 seconds, the S/N for a system of the magnitude of CG
Cyg is about 500. Hence, our differential photometry is the most precise done
to date and can reliably detect phenomenon at the level of 0.01 mag. To provide
a baseline for comparison, Figures 1-3 also include an optimized binary model
fit (solid line) for i =82.8deg, and photospheric temperatures T_1 = 5300 
K, and T_2 = 4600 K.


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


   We can plainly see that the small "waves" are still visible, though not as
clearly defined as in our previous data. The peaks and troughs on the 90 deg
shoulder match very well those seen before; the fit is not good on the 270 deg
shoulder. The peak-to-peak amplitude is about the same. Hence, we conclude
that these small-scale features arise in the binary system, though we have no
obvious physical mechanism.
   Following Budding and Zeilik (1987), we apply a black, circular spot model
to represent the maculation effect. For V-band, our optimized fit gives:
longitude = 96.2deg +- 4.3deg, radius = 16.2deg +- 2.9deg and latitude = 
60.0deg +- 2.9deg.
Figure 4 shows the results. Within the errors, the longitude is the same as
that for July-August (88.6deg +- 3.5deg) and also the radius (15.6deg +- 
0.5deg). Using 
the B and R band data, we infer a temperature difference between the spotted
region and the photosphere of 1060K +- 170K, similar to that found before
(1140K+-160K).
  This work was supported in part by NSF grant AST-8901374 to MZ.


                              D. BECKERT, S. GORDON, E. JADERLUND,
                                     E. MANN and M. ZEILIK

                                    Capilla Peak Observatory
                                    Institute for Astrophysics
                                   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 1989IBVS.3398....1B ]
Beckert, D., Cox, D., Gordon, S., Ledlow, M., Zeilik, M., 1989,
        Inf.Bull.Var.Stars, No. 3398.
Budding, E. and Zeilik M., 1987, Astrophys. J., 319, 827 [BIBCODE 1987ApJ...319..827B ]
Laubscher, B.E., Gregory, S. Bauer, T.J., Zeilik, M. and Burns, J.O., 1988,
        Pub. Astron Soc. Pac., 100, 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 ]