COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2821

                                        Konkoly Observatory
                                        Budapest
                                        21 November 1985

                                        HU ISSN 0374 - 0676




         PHOTOMETRY OF THE WOLF-RAYET STAR HD191765




The star HD191765 (WN6) is known to be a photometric and
spectroscopic variable with a period of 7d.44 (Antokhin et al.,
1982). It has been suggested that it is a binary system
consisting of a WR and a neutron star (Antokhin et al. 1982) i.e.
is one of the so-called WR+ compact companion (Moffat, 1983). In
a recent paper one of us (Vreux, 1985) has drawn the attention on
the peculiar distribution of the published periods of the members
of that family and has suggested that some of these periods could
be aliases of the true ones which would be much shorter and would
have been missed due to the distribution of the observations.
HD191765 is one of the candidate to be reinvestigated in search
of shorter periods.
 Observations spanning an interval of 14 days were carried out in
August 85 at the 1 m. telescope of the Mont Chiran station of the
Haute Provence Observatory (France). The photometer (PAM II) was
used in a classical one-channel configuration.
The photomultiplier was not cooled.


   In an attempt to separate the respective contributions of
the lines and of the continuum, three filters were used.
1 - central wavelength 4060 A, Delta lambda = 70 A (= IHW C3 filter)
   isolating the NIV line (the reason for the choice of
   that line is given in Vreux et al., 1985);
2 -C.W. 4100 A, Delta lambda = 180 A (= Stromgren v) covering lines of
   HeII, NIV, NIII...;
3 -C.W. 4260 A, Delta lambda = 65 A (IHW CO+ filter) practically line
   free.


                         [FIGURE 1]

 Fig. 1. Phase diagram of HD191765 with a period of
 7.44 days. The comparison stars are HD192536 and
 HD192537. The y axis is m4060.

                           
   3 comparison stars were observed: HD192020 (G8V), HD192536
(Am) and HD192537 (B8V) with the hope that at least the Am star
would prove to be constant. The observations were made in rapid
sequences so as to cancel as much as possible instrumental and
atmospheric variations.

The comparison HD192020 has shown small variations. On the other
hand, the pair HD192536, HD192537 remained quite constant.


All measurements were therefore compared to those stars in a
differential manner.
Instrumental problems prevented us to observe more than five
nights with all three filters. The remaining of the observing run


                           [FIGURE 2]

 Fig. 2. Same as Fig. 1. for the color index m4260 - m4060.


had to be done with the 4060 A filter only. The residual noise of
the data was much higher than expected, again because of
instrumental reasons. Nevertheless, the data relative to the
comparison stars demonstrated that night to night variations as
small as 0.01 magn. could be detected.
The data presented in Figures 1 and 2 are plotted as a function of
the phase for a period of 7.44 days. (Period suggested by
Antokhin, Aslanov and Cherepashchuk, 1982).
Fig. 1 shows the 4060 A (NIV) magnitude compared to 1/2 (HD192536
+ HD192537). The magnitudes of the comparison stars were smoothed
with a time scale of 30 minutes. The resulting differences were
binned in intervals of about 30 minutes. If one forgets the noise
within each night, our data suggest variations not larger than
0.01 or 0.02. The color index (m4260 - m4060) plotted in Fig. 2,
and based on only five nights, indicates variations of about 0.02
magn.



Although the sampling is less than complete, we have to conclude
that our data do not support the light curve determined by
Antokhin et al. (1982). Unfortunately we are not able to suggest
another period: our time base is not sufficient due to the
instrumental problems encountered.






                          J.M. VREUX
                          J. MANFROID
                          Institut d'Astrophysique
                          B-4200 Liege
                          BELGIUM





 References:


 Antokhin, I.I., Aslanov, A.A., Cherepashchuk, A,M., 1982,
            Pis'ma Astron. Zh. 8, 290. 

 Moffat, A.F.J.,   1983, in WR Stars: Progenitors of Supernova,
            Proceedings of the Workshop held at the
            Observatoire de Paris-Meudon, April 20-22,
            111, 13. [BIBCODE 1983wrsp.conf...13M ]

 Vreux, J.M., 1985, Publ. Astron. Soc. Pac., 97, 274-279. [BIBCODE 1985PASP...97..274V ]

 Vreux, J.M., Andrillat, Y., Gosset, E., 1985, Astron,
            Astrophys., 149, 337-342. [BIBCODE 1985A&A...149..337V ]