COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2530

                                        Konkoly Observatory
                                        Budapest
                                        5 June 1984

                                        HU ISSN 0374-0676

                A NEW LIGHT CURVE OF CG Cyg

    The unusual eclipsing binary CG Cyg has a distortion wave, which
seems to be advancing through the light curve at an increasing rate.
Because significant variations in the light curve occur over a period of
months (Zeilik 1982), a new light curve was obtained by combining data
from four of five consecutive nights.
    These observations were made from the Climenhaga Observatory of the
University of Victoria on 17-18, 18-19, 20-21, and 21-22 August 1982. A
50 cm reflector and photometric system closely matching the V and B
filters of the Johnson system was used. Unfortunately due to equipment
problems the sky brightness in the V band was not adequately subtracted,
rendering the V data useful only for colour transformations. The
observations of the variable star were bracketed by observations of the
comparison star BD+34d 4216, whose constant brightness was checked at
least nightly with observations of BD+34d 4213. The difference in B
magnitude was 1.57+/-.02 indicating that the comparison star has
remained constant since 1965 (Milone et al 1979). Mean extinction and
transformation coefficients were used to correct the differential
magnitudes to the Johnson system.
   The differential B magnitudes are plotted in the figure against
heliocentric phase calculated from the ephemeris of Milone and Zeibarth
(1974). The phases of minimum light were 0.0174p +/-.0011 and
0.5168p +/-.0019 as found from all the data points within 0.03p of the
minimum using a computer program based on the method of Kwee and Van


                          [FIGURE 1]


Worden (1956). A truncated five-term Fourier series was fit to the
intensity data excluding the points within +/-0.08p of the observed
minima. The constant term A0 is 0.3600+/-.0016 which indicates that CG
Cyg is dimmer now than in 1977 and 1982. The cosine terms normalized by
A0 are A1=+0.0113+/-.0061 and A2=-0.0128+/-.0067 and the normalized sine
terms are B1=-0.0407+/-.0040 and B2=+0.0022+/-.0044. Following the
definitions of Milone et al. (1979), the phase of the distortion wave is
calculated to be 286+/-8 degrees and the amplitude is 0.0422+/-.0041.
   In comparison with the past behaviour of this system, as reported
by Milone et al. (1979), Zeilik et al. (1982), and Jassur (1978), the
light curve seems most similar to that of 1965; so similar that the
corresponding coefficients of the Fourier series of the two years are
nearly within the errors of one another. Since the system experienced a
change of period between 1965 and 1967, further observations may be
rewarding.
   The value of this light curve lies in the fact that it is unlikely
that significant variations occurred during the five nights of
observations. Phases of overlap, 0.05 to 0.08 and 0.54 to 0.57, were
examined for significant differences and none were found. The amplitude
and timescale of short term variations might be determined by comparing
this light curve with others observed at nearly the same epoch. To
assist other observers in making this comparison, the data have been
deposited in the I.A.U. Archives of Unpublished Observations of
Variable Stars, File No. 135 (Breger 1981).


             R.M. ROBB
             Physics Department
             University of Victoria
             Victoria, BC Canada V8W 2Y2

References:
Breger, M. 1981, Pub. Astron. Soc. Pacific, 93, 528. [BIBCODE 1981PASP...93..528B ]
Jassur, D.M. 1978, Inf. Bull. Var. Stars No. 1458.
Kwee, K.K., and van Woerden, H. 1956, Bull. Astr. Inst. Netherlands 12,
   327. [BIBCODE 1956BAN....12..327K ]
Milone, E.F. and Zeibarth, K.E. 1974, Pub. Astron. Soc. Pacific 86, 684. [BIBCODE 1974PASP...86..684M ]
Milone, E.F., Castle, K.G., Robb, R.M., Swadron, 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., Elston, G., Henson, P., Schmolke, P., Smith, P. 1982, 
   Inf. Bull. Var. Stars, No. 2138.


                       [DATAFILE 1]