COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1974

                                  Konkoly Observatory
                                  Budapest
                                  1981 June 8

                                  HU ISSN 0374-0676


      ECLIPSE IN CI Cyg BINARY-SYSTEM IN 1980


  Photometric observations of the symbiotic eclipsing-binary
star CI Cyg have been continued in 1980 from March, 31 to December
1. (Belyakina, 1976, 1979a,b, 1980)
  These observations were very important because of the next
expected eclipse in CI Cyg binary-system for summer 1980.

                          [FIGURE 1]

  The results of UBV observations in 1980 and those of the end
of 1979 are plotted in Fig. 1. Unfortunately, due to bad weather
conditions the number of the observations for the eclipse ingress
was not sufficient. It is seen in Fig. 1 that all three curves
showed the eclipse effect. The amplitudes of the light variations in
V,B,U-bands are 0.45m, 0.8m, 1.0m, respectively. Considerable U-light
fluctuations are seen in minimum. V magnitude before the eclipse
was 0.1m less than after it. The minimum center was near 1980 June 6.
  Our observations of 1975 (Belyakina, 1976, 1979a) and those
of 1980 are compared in Fig. 2. From Fig. 2 it is seen that as the
durations of both minima as minimum V magnitudes are close to
each other.

                          [FIGURE 2]

  But (B-V) and (U-B) colour indices in 1980 were redder than
in 1975. Moreover the from of the (U-B) curve variations in 1980
changed as compared with 1975. These facts evidence that U-band
radiations in the eclipse minimum decreased considerably from
1975 to 1980. One of the possible causes of this effect might
be the decrease of U-light radiating region.



                           T.S. BELYAKINA
                     Crimean Astrophysical Observatory
                     334413 Nauchny, Crimea, USSR




References:
Belyakina, T.S. 1976, IBVS No. 1169
Belyakina, T.S. 1979, Izv. Krimsk. Astrophys. Obs. 59, 133.
Belyakina, T.S. 1979, IBVS No. 1602
Belyakina, T.S. 1980, IBVS No. 1808.