COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                       Number 2812

                                         Konkoly Observatory
                                         Budapest
                                         23 October 1985

                                         HU ISSN 0374 - 0676


         PHOTOMETRIC AND POLARIMETRIC VARIATIONS OF THE
                   SYMBIOTIC STAR CI CYGNI


 After the outburst in June 1971 (Lowder, 1971) the star CI Cygni exhibited a
transformation in the optical range. The lines of high excitation disappeared
together with a weakening of TiO bands. In December 1971 a P Cygni profile
for HI, HeI predominated. In November 1975 near the minimum (V=11.05) emission
lines of high excitation and TiO bands reappeared. Numerous spectra were taken
by Audouze et al. (1981) when the star (V=8.6) exhibited an F type spectrum.
  Photometric and polarimetric observations were made at the Observatoire de
Haute-Provence in October 1975 and July 1976 with the polarimeter II of
Martel (Chevreton et al. 1977) attached to the 193 cm Cassegrain telescope.
The results are given in Table I.
  The broad-band filters accounted are U (lambda 3200 - 3900 A), B 
(lambda 3800 - 4700 A), V (lambda 5000 - 5900 A). An E.M.I. type 9789 QA tube 
with an S11 photocathode was utilized. All the observations were made obtained
with a diaphragm of angular aperture 14 arcsec. The instrumental polarization 
was determined from the observations of standard stars in the Hiltner 
catalogue. The most significant variations in the polarization of CI Cygni 
were observed after the minimum (V = 9.4). The position of the vibration plane
does not change notably during the polarization variations contrary to 
R Aquarii. Fig.1 shows the dependence of the polarization rate with 
lambda^(-1) quite typical of linear polarizations.
Szkody et al. (1982) have obtained U : 0.70%, B : 0.50%, V : 0.30% for the
ratio of linear polarization of CI Cygni in January 1977 between two minima
(V = 9.9) and show that the source of the polarization is explained by
Rayleigh scattering.
  The strong polarization discovered in July 1976 cannot be attributed entirely
to Rayleigh scattering of nebular emission lines.
  The maximum polarization found in the blue region might come from the
absorption resonance line lambda 4227 A.
  The drop in polarization in the V band is certainly due to the strong TiO 
bands (Aspin et al., 1985).


                                  [FIGURE 1]


                                    Table I

                  Photometric and polarimetric data for CI Cygni
                         
                              V                                          B                                    U
  J.D.      V      P+-DeltaP    theta+-Delta theta      B      P+-DeltaP    theta+-Delta theta       P+-DeltaP    theta+-Delta theta
2442714   11.05     2.73             114.7d
                  +-0.15            +-0.8d

2442980   9.40      2.82             100.0d         10.18       5.22          104.4d                   3.05          104.8d
                  +-0.19             +-1.0d                   +-0.14          +-0.3d                 +-0.17          +-0.8d
 
2442982   9.41      3.17             104.3d         10.23       4.84          106.9d
                  +-0.09             +-0.4d                   +-0.48          +-1.4d

2442985   9.43      2.86             103.6d         10.24       4.88          108.6d                   3.06          105.0d
                  +-0.12             +-0.6d                   +-0.13          +-0.4d                 +-0.19          +-0.9d




 The existence of correlations between the polarization and other parameters
should help to explain the nature of symbiotic stars.



                      R. GRAVINA and M.T. MARTEL
                      Observatoire de Lyon
                      69230 Saint-Genis-Laval
                      France



References:

Aspin, C., Schwarz, H.E., McLean, I.S., Boyle, R.P., 1985, Astron. 
      Astrophys. 149, L 21 - L 23. [BIBCODE 1985A&A...149L..21A ]
Audouze, J., Bouchet, P., Fehrenbach, Ch., Woszczyck, A., 1981, Astron, 
      Astrophys. 93, (1-7). [BIBCODE 1981A&A....93....1A ]
Chevreton, M., Gravina, R., Martel, M.T., Vanderiest, Ch., 1977, Astron. 
      Astrophys. 54, 627. [BIBCODE 1977A&A....54..627C ]
Lowder, W.R. 1971, I.A.U. Circ. No. 2335 [BIBCODE 1971IAUC.2335....1L ]
Szkody, P., Michalsky, J., Stockes, G.M., 1982, Publ. Astron. Soc. Pac., 
      94, 137. [BIBCODE 1982PASP...94..137S ]