COMMISSION 27 OF THE I. A. U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 3372

                                           Konkoly Observatory
                                           Budapest
                                           12 September 1989

                                           HU ISSN 0374 - 0676


            A NEW SHORT PERIOD IN THE WR STAR HD 191765


The Wolf - Rayet star HD 191765 is classified in the sixth catalog (Van der
Hucht et al.  1981) as a "single" WN6 star. It is centered in ring nebula S109
and connected with it.  It has been investigated by Antohin et al. (1982) and
a variation in brightness and radial velocity with a period of 7.44d was
found. The authors have concluded that this is a binary WR with a compact
companion.

Having in mind that Vreux et al. (1985) and Vreux (1985) have found periods
less than 1.0d at some WR stars, we searched for such a period in HD 191765.
Applying Lafler - Kinman technique to data used by Antohin et al., we obtained
a period of 0.935d for B and V bands. In comparison with the 7.44d period,
the light curve with the new period (Fig. 1) has lower dispersion. This points
out to its higher reliability. The same analysis of radial velocity, 
using He II 4686 line, shows a period of 0.9d (Fig. 2).


                            [FIGURE 1]
                            [FIGURE 2]


Let us assume that HD 191765 is a binary system with 20M_sun for WR and 1M_sun
for the compact object. In this case the semimajor axis is 11R_sun and the
eccentricity is 0.24. This large eccentricity does not agree with the rather
rapid circularization of such a contact system. The optical depth of this
value of semimajor axis (if we assume that mass loss rate is 10^-5 M_sun/yr) is
1.7. This value is insufficient to explain the absence of X-ray emission of
this star (Sanders et al. 1981).

Finally, we may conclude that these data are insufficient to reliably identify
HD 191765 as a binary WR with a compact companion. But the points with phases
around 0.75 (Fig. 1) look like a second minimum and do not support the pulsation
hypothesis. Further investigation should possibly concentrate on confirming
their existence.


LEONID NIKITOV GEORGIEV
Department of Astronomy
University of Sofia
5 Anton Ivanov str.
Sofia 1126
Bulgaria

References:

Antohin, I.I., Aslanov, A.A., Cherepashchuk, A.M., 1982, Sov. Astron. Lett.
    8, 156.  [BIBCODE 1982SvAL....8..156A ]
Sanders, W.T., Cassinelli, J.P., Van der Hucht, K.A., 1981. IAU Symp., No.
    99., 589. [BIBCODE 1982IAUS...99..589S ]
Van der Hucht, K.A., Conti, P.S., Lundstrom, I., Stenholm, B., 1981, Space
    Sci. Rev., 28, 227. [BIBCODE 1981SSRv...28..227V ]
Vreux, J.-M., 1985, P.A.S.P., 97, 279. [BIBCODE 1985PASP...97..274V ]
Vreux, J.-M., Andrillat, Y., Gosset, E., 1985, Astron. Astrophys., 149, 342. [BIBCODE 1985A&A...149..337V ]