COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3474

                                        Konkoly Observatory
                                        Budapest
                                        7 June 1990

                                        HU ISSN 0374 - 0676


  CH CYGNI: A VERY DEEP MINIMUM ACCOMPANIED BY AN EPISODE OF ACTIVITY

   CH Cygni is known as a semiregular variable star of spectral
type M6 - M7III (Kholopov, 1985), occasionally exhibiting symbiotic 
features. The last conspicuous active phase, which took
place from 1977 to 1987, has been extensively studied (e.g. Luud
et al., 1986, Mikolajewska et al., 1987, Mikolajewski et al.,
1990a,b etc.). Since 1987 the star has been in an inactive state
showing semiregular variations in V magnitude and color index B-V
about 1.5 - 1.8 mag. A short-time episode of activity occurred in
summer 1989 with the appearance of flickering in U filter and
changes in the spectrum (Skopal, 1989, Tomov et al., 1989, Mikolajewski 
et al., 1990b).
   Photoelectric UBV observations of CH Cyg with a 0.5m telescope 
have been carried out at Tartu Observatory since 1968 (see
Luud et al., 1977 for the description of observational equipment
and methods). Latest observations in 1990 have revealed that the
star has become fainter than ever in this century. There is no
evidence of V brightness below the 9th magnitude (Mikolajewski et
al., 1990a), but now, on JD 2448025 we have measured V=9.19m and
on JD 2447941, with some uncertainty V=9,21. In the table we
present our UBV observations since September 1989. U, B and V
magnitudes are presented in the figure as well. HD 182691 is used
as a comparison star with V=6.54m, B-V=-0.05m, U-B=-0.24m. For
every night the mean of 4-8 measurements is given. Errors of those
mean values may be about 0.02m - 0.05m (increasing from V to U).

                   TABLE 1

UBV observations of CH Cyg at Tartu Observatory

      JD          V     B-V       U-B

2447791.340      7.53  1.68       0.83
    806.255      7.71  1.68       0.81
    814.349      7.92  1.79       0.90
    815.313      7.96  1.72       0.91
    851.417      8.50: 1.44:      0.32:
    858.292      8.48  1.52       0.27
    864.166      8.34: 1.60:      0.42:
    866.210      8.30  1.60       0.57
    876.319      8.14  1.76       0.66
    895.251      8.30  1.73       0.69
    906.193      8.58  1.67       0.76
    941.238      9.21: 1.56:      -
    945.242      9.15  1.59       0.56
    957.428      9.06  1.61       0.32
    964.423      8.95  1.64       0.38:
    969.574      8.81  1.69       0.68
    978.564      8.69  1.71       0.63
    987.435      8.73  1.70       0.49
    990.539      8.79  1.71       0.52
    994.424      8.82  1.56      -0.01
    999.417      8.80  1.38      -0.19
   8005.425      8.80  1.22:     -0.34:
    006.417      8.93  1.43      -0.20
    010.447      9.06  1.56       0.00
    014.407      9.15  1.46      -0.05
    018.419      9.16  1.28:     -0.24:
    021.435      9.18  1.35      -0.33
    025.427      9.19  1.34      -0.45


                         [FIGURE 1]

 Figure 1. U, B and V magnitudes of CH Cyg from September, 1989
 to May, 1990. Vertical bars mark moments when spectra with emission 
 lines have been observed. Thin bars mark emission line of Halpha, thick 
 bars - Hbeta and Hgamma.

 
 In the figure variations in V magnitude can be detected with
a characteristic time of about 100 days. This time coincides with
the dominant period which has been observed over the whole photometric 
history of CH Cyg (Muciek and Mikolajewski, 1989, Mikolajewski 
et al., 1990a), but now variations take place on a very low
level of brightness. Variations in B are similar to those in V,
but not so prominent. In U we can find a rapid brightening by ~1m
at about JD 2447992. After a short-time decrease the U brightness
has again attained the 10th magnitude. There are some hints that
flickering in U filter may be present, but our equipment does not
enable to fix it firmly. At the same time emission lines have
reappeared in the spectrum of CH Cyg. Our observations with a 1.5m
telescope and a Cassegrain spectrograph have revealed one-component 
emission lines of H-alpha, H-beta and H-gamma. The moments of 
spectroscopic observations are shown in the figure.

    Hence, CH Cyg has again surprised observers. Further analysis
of the described events remains for forthcoming papers. Continuing
observations of CH Cyg in all spectral regions are urgently 
needed.


                           L. LEEDJARV
                    Tartu Astrophysical Observatory
                        Toravere 202444
                             Estonia





REFERENCES


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