COMMISSION 27 OF THE I. A. U.
                INFORMATION BULLETIN ON VARIABLE STARS
                             Number 2410


                                                      Konkoly Observatory
                                                      Budapest
                                                      12 October 1983

                                                      HU ISSN 0374-0676

                   ON THE PERIOD OF BW VULPECULAE


  BW Vul was observed at the Wroclaw Observatory for the World-wide Observing 
Campaign on BW Vulpeculae organized in 1982 by M.S. Snowden and C. Sterken.
The observations were carried out with a 60-cm Cassegrain reflector and a
photoelectric photometer equipped with an EMI 6256S photomultiplier tube and
a Stromgren b filter. The weather conditions were relatively poor. Our data
are, however, sufficiently accurate and numerous to derive a mean epoch of
maximum light.
  Taking the period of BW Vul as equal to P_0 = 0.20103d, and assuming an 
initial epoch T_0 = 2428000.5, a mean light-curve was derived. It is shown in
Figure 1. The points are the individual observations and the solid line,
drawn by hand, represents the mean curve.


                               [FIGURE 1]

 Figure 1  The mean b light-curve of BW Vul. Delta _b_ is the magnitude
 difference "BW Vul minus a mean of HD 198820 and HD 198527"


  The following epoch of maximum of BW Vul was derived from the above-
mentioned light-curve:

       Hel. JD (max. light) = 2445228.482d + 0.002d

The (O-C) residuals obtained from this epoch of maximum and from the quadratic
ephemerides of Valtier (1976) and Margrave (1979) are 0.036d and 0.014d, 
respectively. On the other hand, the linear ephemeris of Tunca (1978) yields (O-C)=
0.005d. This results indicates that Tunca's two linear ephemerides fit the 
observations better than the quadratic ephemeris of either Valtier or Margrave.
Our observations provide, therefore, another argument in favour of a 
discontinuous increase of the period of BW Vul.





            E. SZUSZKIEWICZ AND S. RATAJCZYK

            Wroclaw University Observatory
            ul. Kopernika 11
            51-622 Wroclaw
            Poland





References:

Margrave, T.E., 1979, Publ. A.S.P. 91, 666 [BIBCODE 1979PASP...91..666M ]
Tunca, Z., 1978, Inf. Bull. Var. Stars No. 1386
Valtier, J.-C., 1976, Astron. Astrophys. 51, 465 [BIBCODE 1976A&A....51..465V ]