COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3022



                                             Konkoly Observatory
                                             Budapest
                                             11 May 1987

                                             HU ISSN 0374-0676


          PHOTOMETRIC OBSERVATIONS OF WR78 = HD 151932


The southern WN7 star WR78 showed no important photometric variations during an observing
run in 1975 by Seggewiss and Moffat (1979) although its spectrum is known to display a complex
behaviour. The star was included in an observing run we made with the Walraven photometer and
the Dutch 91cm telescope on la Silla in 19R6.

Data have been obtained on six nights during the period 23 May - 2 June. Two comparison stars
were chosen : HD 150608 (C1) and HD 155259 (C2). The observing sequence was
W,C1,C2,W,C1,C2,W,C1,C2,W (where W stands for WR78) and took about half an hour to complete. The
reductions were made according to the algorithm published by Manfroid and Heck (1983, 1984).
However no color transformation was attempted and the results are given in the natural system.
Contrarily to the usual practice with the Walraven system, we used conventional magnitudes and
not the decimal log scale. The data were then treated differentially so as to cancel out any trend left
in the extraction of the zero point.

                             [FIGURE 1]

 Figure 1.  V magnitude.: Plot of the differential data relative to WR78
 (filled circles) and to the comparison stars (circles).

                             [FIGURE 2]

 Figure 2.  B magnitude.: Plot of the differential data relative to WR78
 (filled circles) and to the comparison stars (circles).

The most accurate data were obtained in the V and B hands. The scatter of the difference between
both comparison stars is sigma V = 0.004 and sigma B = 0.005 and provides an estimation of the internal ac-
curacy of the data. Plots of W-(C1+C2)/2 and C1-C2 are given in figures 1 (V) and 2 (B).
They clearly show that WR78 was photometrically variable during our observations with a total
amplitude of more than 0.03 i.e. an amplitude which could have been detected by Seggewiss and
Moffat (1979) during their 1975 observations. Unfortunately, due to poor weather conditions, our
data are too scarse to allow the derivation of any periodicity.



                        P. MAGAIN
                        European Southern Observatory
                        Casilla 567
                        La Serena
                        Chile


                        J.M. VREUX and J. MANFROID

                        Institut d'Astrophysique
                        B-4200 Cointe-Ougree
                        Belgium



   References.
   Manfroid, J., Heck. A, 1983, Astron. Astrophys.,  120, 302 [BIBCODE 1983A&A...120..302M ]
   Manfroid, J., Heck. A, 1984, Astron. Astrophys.,  132, 110 [BIBCODE 1984A&A...132..110M ]
   Seggewiss, W., Moffat, A.F.J., Astron. Astrophys., 72, 332 [BIBCODE 1979A&A....72..332S ]