COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                              Number 2938

                                                         Konkoly Observatory
                                                         Budapest
                                                         25 September 1986

                                                         HU ISSN 0374 - 0676


              LINEAR POLARIMETRIC MEASUREMENTS OF 55 CYGNI

In the last several years the investigation of Be stars came into
prominence. Their polarimetric measurements may provide additional data
to our understanding of the physics of these stars.
   In the past 20 years I have carried out polarimetric observations of a
number of Be stars. Because these observations may be of some interest I
plan to publish the data in a series of papers.
   55 Cygni (=BD +45d3291= HD 198478) was previously recommended as a 
polarimetric standard star (Serkowski, 1974). Hsu and Breger (1982) showed that
55 Cyg underwent definite polarimetric variations on a short time scale
in the position angle while the amount of the polarization changed only
marginally.
   Our polarimetric observations of 55 Cyg were made in August 1967 and
July-August 1974. The measurements are given in Table I. The observations
obtained in 1967 (J.D. 2439 733-741) were carried out in V light with a
two-channel integrating polarimeter attached to the 50-cm Cassegrain
telescope of Konkoly Observatory. The 1974 observations (J.D. 2442 250-279)
were made with the same polarimeter in UV light at the 60-cm Cassegrain
telescope of the Haute Provence Observatory.
   The 1967 observations in V light did not indicate any noticeable changes
in the polarization values, whereas the 1974 observations in UV light
definitely show small irregular changes in the amount of polarization between
2.0 and 2.6%. Small changes in the position angle were also observed within
only a few days. This result is in accord with that of Hsu and Breger (1982).
   I would like to thank Dr. Marie Therese Martell for her help and
encouragement. I also thank the granted observing time at Haute Provence
Observatory.


     Table I. Polarimetric observations of 55 Cygni

   J.D.             p %            Theta        filter

2439733.344     2.54 +-0.34     169.3 +-1.9       V
    734.333     2.57   0.34     169.4   1.9       V
    735.354     2.53   0.34     169.5   1.9       V
    738.437     2.38   0.32     173.6   1.9       V
    739.385     2.51   0.33     170.9   1.9       V
    741.313     2.44   0.33     171.0   1.9       V
2442250.438     2.57   0.19       0.6   1         UV
    250.465     2.54   0.18       2.0   1         UV
    250.479     2.56   0.17       1.9   1         UV
    250.528     2.52   0.17       2.3   1         UV
    250.542     2.37   0.20       3.3   1         UV
    250.552     2.30   0.22       1.7   1         UV
    251.535     2.44   0.19       0.0   1.1       UV
    251.563     2.40   0.16       1.7   1         UV
    252.542     2.41   0.24       2.1   1.4       UV
    273.500     2.39   0.23       8.1   1.3       UV
    274.514     2.43   0.26       2.7   1.5       UV
    275.493     2.21   0.20       3.7   1.2       UV
    275.521     2.02   0.21     179.9   1.4       UV
    276.507     2.06   0.22       1.2   1.4       UV
    279.507     2.36   0.26       0.5   1.5       UV



                           G. VIRAGHALMY

                         Konkoly Observatory
                      1525 Budapest, P.O. Box 67
                              Hungary



References:

Hsu, Jin-chung, and Breger, Michel, 1982, Astrophys. J., 262, 732. [BIBCODE 1982ApJ...262..732H ]
Serkowski, K., 1974, in: Planets, Stars and Nebulae (ed. T. Gehrels),
   University of Arizona, Tucson, p. 135. [BIBCODE 1974psns.coll..135S ]