COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3398

                                          Konkoly Observatory
                                          Budapest
                                          1 December 1989

                                          HU ISSN 0374 - 0676


              1989 BVR PHOTOMETRY OF CG CYGNI


CG Cygni (=BD +34d4217 = #142 in the catalog of Strassmeier et al. 1988) is a
member of the short-period RS CVn group as defined by Hall (1976). Since the
discovery of its variability by Williams (1922), CG Cyg has been observed
intensely at frequent intervals. Heckert and Zeilik (1989) presented 1987
V-band photometry; Dapergolas et al. (1989) collected complete 1987 light
curves at B and V. We report here on 1989 BVR data, where the R-band allows us
to estimate the temperature of the spotted regions.

Our observations were carried out at Capilla Peak Observatory (CPO) the nights
of 18 July and 3-5 August 1989 UT. Our CCD camera (Laubscher et al., 1989) was
used in a multichannel mode to measure CG Cyg, the companion star (BD +34d
4216), and the sky simultaneously. Our new filter set (Beckert and
Newberry, 1989) matches closely Johnson BV and Kron-Cousins R-band response.
The data were reduced with an effective aperture of 21 arcsec. Phases were
calculated from the ephemeris in Strassmeier et al. (1988).

Figures 1-3 present the observational data in the instrumental system at BVR;
note the coverage is complete and accomplished within a month. The statistical
error in each datum is less than 0.01 magnitude. Note the small-scale "bumps"
that appear on the shoulders of the light curve. They are clearly visible at
all wavelengths.  The weather was photometric on all nights, so we consider
these features to be real, not observational artifacts. Such "bumps' are just
discernable in Jassur's 1978 data (Jassur, 1980); they are no apparent in our
1987 light curve (Heckert and Zeilik, 1989).

Figure 4 presents an optimized binary model fit (solid line) to the V-band data
(open circles). This comparison clearly reveals the maculation effect (near
90deg), as well as the smaller variations. This fit follows the procedures of
Budding and Zeilik (1987) and uses a temperature of 5200 K for the primary star
and 4400 K for the secondary. We fitted a single black, circular spot to the
distortion wave and found these following optimized starspot parameters:
longitude = 86.0deg+-3.4deg, radius = 15.6+-0.5deg, and latitude = 41.7deg. (The
latitude fit was an indeterminate solution and so has no formal errors).
Compared to our 1987 results, we find that the spotted region has moved to a
lower longitude but stayed at about the same latitude. Its area has increased
roughly 40%. Using the V and R data together, we estimate that the temperature
difference of the spotted region compared to primary star's photosphere is 1140
K+-160K, or T_spot=4060K for T_primary=5200K.


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


This work was supported in part by NSF grant AST-8901374 to MZ.


D. BECKERT, D. COX, S. GORDON, M. LEDLOW
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 1989PASP..101..849B ]
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
Hall, D.S., 1976, in Multiple Periodic Variable Stars, edited W. S. Fitch
   (Reidel: Dortrecht) p. 278. [BIBCODE 1976ASSL...60..287H ]
Heckert P.A. and Zeilik, M., 1989, Inf. Bull. Var. Stars, No. 3294.
Jassur, D.M.Z., 1980, Astrophys. Space Sci., 67, 19. [BIBCODE 1980Ap&SS..67...19J ]
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 ]
Williams, A.S., 1922, Mon. Not. Roy. Astr. Soc., 82, 300. [BIBCODE 1922MNRAS..82..300W ]