COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                              Number 2973

                                                         Konkoly Observatory
                                                         Budapest
                                                         6 January 1987

                                                         HU ISSN 0374 - 0676


           NEW PHOTOMETRY OF THE WOLF-RAYET STAR HD191765

A small photometric and spectral variability of the star HD191765 (WN6)
with the period 7d.44 was discovered by Antokhin et al. (1982). The amplitude
of the photometric variability was equal to 0.04m. It was suggested that this
is a binary system consisting of a WR star and a neutron star (so-called "WR+
compact companion" system, see Moffat, 1983). Antokhin and Cherepashchuk
(1984) improved the value of the period of the light variability (P=7d.483)
and reported about discovering the narrow, "eclipse-like", secondary minimum
on a light curve. This argues for a binary nature of this star.
   Recently the paper of Vreux and Manfroid (1985) has been published which
is devoted to photometric observations of HD191765 during 14 days in August
1985. These observations have been made with the purpose of searching the fast
variability of HD191765. Vreux and Manfroid report that no light changes greater 
than 0.02m have been found in filters 4060A (Delta lambda=70A) and 4260A
(Delta lambda=65A) from night to night.
   Our observations of HD 191765 were carried out at the 48-cm telescope of
the Alma-Ata Station of the Shternberg State Astronomical Institute in October
December 1984, September-October 1985, April-May and June-July 1986. The UBV-
photometer in the regime of photon counting was used. Two comparison stars
were observed: HD 191917 (V=7m.8, B1)=C1 and the star K (Cherepashchuk,
1972)=C2.
   Figures 1-4 show the results of these observations in B,V filters.
Each point is the average value of 3-19 individual light observations.
   The value m_c2-m_c1 is also shown. One can see that the value m_c2-m_c1 is
stable within the accuracy +-0m.006.
   Our observations in a time interval 1984-1986 show that the character of
the light variability of HD 191765 after 1983 changed significantly:
    1. The average light of the star is variable on a long timescale.
       In a time interval of ~3 months in 1984 it changed by 0m.02
       (Fig. 1, the straight line is drawn using the least-square method).
       The average light in 1986 is also variable (Fig. 3, 4).
    2. The shape of the light curve is also variable. The variability became
       less regular in 1984 (Fig. 1 ) and irregular - in 1985 and probably 1986
       (Figs. 2-4).
    3. The amplitude of the variability decreased to 0.02 in B,V filters.
       in 1985 and increased again in 1986. It must be pointed out that the
       results of our observations in 1985 (Fig. 2) being practically 
       simultaneous with the observations of Vreux and Manfroid (1985) are 
       consistent fully with their results.

   Thus, light curves of HD 191765 are variable in shape, amplitude and
average light level on a long timescale. Similar variations in the light curve
were observed in the case of another suspected "WR + compact companion" system,
HD 50896 (Lamontagne et al., 1986). Such variations can be explained by 
precession effects arising from a nonsymmetric SN-explosion in a binary system.


                            [FIGURE 1]

               Fig. 1  V-observations of HD191765 in 1984.

                            [FIGURE 2]

               Fig. 2  B-observations of HD191765 in 1985.

                            [FIGURE 3]

               Fig. 3  B-observations of HD191765 in April-May 1986.

                            [FIGURE 4]

               Fig. 4  V-observations of HD191765 in June-July 1986.


   As a result of such explosion the rotational axis or the formed neutron star
can align oblique to the orbital plane. Further observations of this interesting 
star are nesessary.


                   I.I. ANTOKHIN
                    I.M. VOLKOV

                  Shternberg State
               Astronomical Institute
                   Moscow, USSR



References :

Antokhin I.I., Aslanov A.A., Cherepashchuk A.M., 1982, Pis'ma Astron. Zh.,
     8, 290, [BIBCODE 1982SvAL....8..156A ]
Antokhin I.I., Cherepashchuk A.M., 1984, Pis'ma Astron. Zh. 10, 370. [BIBCODE 1984PAZh...10..370A ]
Cherepashchuk A.M., 1972. Astron. Zirk., No. 682, 1. [BIBCODE 1972ATsir.682....1C ]
Lamontagne R., Moffat A.F.J., Lamarre A., 1986, Astron. J., 91, 925. [BIBCODE 1986AJ.....91..925L ]
Moffat, A.F.J., 1983, In: "WR Stars: Progenitors of Supernovae" Proc. of the
     Workshop held at the Observatoire de Paris-Meudon. [BIBCODE 1983wrsp.conf...13M ]
Vreux J.M., Manfroid J., 1985, Inf. Bull. Var. Stars, No. 2821, 1.