COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2056

                                  Konkoly Observatory
                                  Budapest
                                  1981 December 11

                                  HU ISSN 0374-0676




           PHOTOELECTRIC OBSERVATIONS OF CI Cyg




  From July 11 to October 20, 1980 (JD 2444432 - 2444541) a
series of photoelectric observations of the symbiotic star CI Cyg
was accomplished on the 50 cm telescope of the Byurakan Astrophysical 
Observatory. The observations were made close to the,
standard u,b,v bands and in the r and Halpha bands, characterized
by the following data:


                                          r        H_alpha

Halfwidth                               270 A        12 A
lambda_max                             6563 A      6563 A    
Transmission coefficient at lambda_max   42%         60%



  HD 226117 = BD +35d3828 and HD 226172 = BD +35d3834 served
as comparison stars.
  Due to bad weather conditions a part of the final phase of the
eclipse was missed. In Figure 1 the results of our observations
are presented.Each point in this figure presents the mean value of
2-4 comparisons with both comparison stars. The corresponding
values of 3 sigma (the bars on the right hand side in Fig. 1) are 
presented as well.

  On the light curves one can discern four phases.
  During the first interval (JD 2444432-455) the brightness of
CI Cyg increased continuously in all the observed bands. On the
Halpha curve a relatively short lived brightness decrease was well
noticeable. The Delta(u-b), Delta(b-v) and Delta(v-r) colour values decreased
i.e. the star became bluer.

                        [FIGURE 1]

  During the second interval (JD 2444455-473) the brightness
increase continued in general at a smaller rate and with some
irregularities in all the bands except in r. The brightness in
r decreased by 0.1 magnitude. The colours of the star continued
to decrease but at a smaller rate, as well.

  During the third interval (JD 2444473-497) the brightness in
Halpha remained constant on its maximum level. In the bands, r,v,b
and u the brightness increased by small amounts, the greatest
increase being in the b band - 0.15 magnitudes, In the u band a
short lived brightness increase of the order of 3 sigma (Delta m=0.17 mag.)
was noticed. During this interval the colours of the star remained
on a constant minimum level.
  During the fourth interval (JD 2444497-542) a systematic
brightness decrease in all the bands was observed the amplitudes
being Delta u = 0.20, Delta b = 0.17, Delta v = 0.21, Delta r = 0.20 and Delta H_alpha=0.30
magnitudes. It should be noticed that, except maybe in the H_alpha
band, the amplitude of brightness decrease in all the bands was
the same. At the end of this interval the brightness levels of
the star in the bands Halpha and r are almost equal to those observed
in these bands at the beginning of our observations, i.e. to
those corresponding to a phase close to minimum. In this interval
the colours Delta(v-r) and Delta(u-b) increased a little, indicating a
slight reddening of the star. The colour Delta(b-v) increased as well
at the beginning of this interval, but went back to its normal
value at the end.
  The above presented data allow to conclude:
1. During the minimum the hot component was eclipsed.
2. The fact that the amplitude of brightness decrease after
  the maximum is almost the same in all the bands allows to
  admit that the decrease is due to a neutrally absorbing agent.
3. The short lived brightness changes in Halpha and u can be due to
  an interaction between the hot component of CI Cyg and the
  surrounding nebula.





             G.H. GEVORKIAN
             Byurakan Astrophysical Observatory
             Byurakan, Armenian SSR
             USSR