COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2753

                                       Konkoly Observatory
                                       Budapest
                                       27 June 1985

                                       HU ISSN 0374 - 0676


       AN INTERESTING EPISODE IN THE HISTORY OF CH CYGNI


  Periods of activity of CH Cyg observed so far lasted from September 1963
till August 1965, then from June 1967 till the end of 1970, and the
latest outburst began in May 1977 and has not ended yet, In the quiet
state CH Cyg has a usual spectrum of the M6III type. During outbursts this
late type spectrum is veiled by a blue continuum extending far into ultraviolet,
and numerous emission lines of hydrogen and ionized metals appear. In all
the three observed outbursts forbidden lines were seen belonging to FeII,
OI (lambda6300), SII (lambda4069), and only once, in 1968, the line lambda5007 [OIII]
appeared (Hack, Selvelli). When the star returned to its normal phase in
December 1970 it showed a normal M6III spectrum with weak emissions in Halpha
and Hbeta (Faraggiana and Hack). We began our observations of CH Cyg in 1974,
more than 3 years after the end of the previous active period. That year 4
spectrograms were obtained on August 15 and 17 with a grating spectrograph
attached to the 70 cm reflector of the Main Astronomical Observatory of the
Ukrainian Academy of Sciences. The spectrograms have dispersion 1.68*10^5 and
cover the wavelength range 6800 - 3800 angstrom. They revealed the presence of 
several emissions in the otherwise quite normal M6III spectrum without any trace
of the blue continuum. Table I gives laboratory wavelengths of the emission
lines, their identification and intensities relative to the intensity of the
underlying continuum. Such a spectrum has not been observed in CH Cyg, the
more so in quiet periods. The line lambda3869 of double ionized neon has never been
observed in this star either. Apart from lambda5007 no other lines of the multiplet
OIII 1F are seen on our spectrograms, though it would be very difficult to
notice the line lambda4959 in a very sharp intensity leap in TiO alpha(1.0) band

                       Table I

        Emission lines in the spectrum of CH Cyg in 1974

  lambda lab angstrom   Identification Intensity

    6562.82             Halpha            1.74
    6300.23             OI 1F             1.18
    5006.84             OIII 1F           1.45:*
    4861.33             Hbeta             2.18:*
    4340.47             Hgamma            1.19
    4068.62             SII 1F            1.33
    3868.74             NeIII 1F          1.62:






      *lines lambda5007 and lambda14861 are situated in strong absorption
       bands of TiO, and the local continuum for them is traced
       with great uncertainty because of low photographic density
       in those bands.



head at lambda=4957A. Thus, taking into account the photographic plate noise
the ratio of intensities of OIII auroral and nebular lines can be
evaluated; I4363/(I5007+I4959)<0.06. This ratio is ~0.3 for symbiotic stars
(Boyarchuk) while it is of the order of 0.01 for planetary nebulae
(Aller and Liller).





                       M.H. RODRIGUEZ

                       Main Astronomical Observatory
                       of the Ukrainian Academy of Sciences
                       Goloseevo
                       252127 Kiev-127,
                       U.S.S.R.





References:

Aller, L., Liller, W., 1968, In "Stars and Stellar Systems", vol. VII,
      "Nebulae and Interstellar Matter", chap. 9, p. 527.
Boyarchuk, A., 1970, In "Eruptive Stars", Moscow: Nauka Press, p. 151.
Faraggiana, R., Hack, M., 1971, Astron. and Astrophys., 15, 55. [BIBCODE 1971A&A....15...55F ]
Hack, M., Selvelli, P.L. 1981, "The Nature of Symbiotic Stars" Proc. IAU
      Colloq. No. 70, ed. by Friedjung and R. Viotti, p. 131. [BIBCODE 1982ASSL...95..131H ]