COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1686

                                      Konkoly Observatory
                                      Budapest
                                      1979 October 16



             NEW ELEMENTS FOR VW CEPHEI



    For the very complex eclipsing binary system VW Cephei new
elements, both photometric and geometric, are obtained using the
method by Wood (1972). Two sets of solutions are presented here:
for the observations in yellow by Kwee (1966) and for the observations 
in 1977-78 obtained with a 50-cm telescope in Bucharest
(with a V_5500 filter).
    An approximate solution was obtained with a Horak type method. 
From various variants of models, obtained for different
values of limb darkening coefficients and outer contact angle,
was chosen the one with the smallest (O-C)^2. These elements were
improved with the method by Wood, the results being given in
Fig. 1 and Fig. 2 and in the Table. The limb darkening coefficients 
have been fixed x_1=x_2=1, since from all the light curves
the values of these coefficients resulted greater than those


                        [FIGURE 1]


                  Table
                                         
         Model I  Model II               Model III
                  Adjusted parameters

i        66.6d    68.730                69.050
R        0.528    0.598                  0.557
r        0.244    0.222                  0.232        
T_2(eq)  4953dK   4825dK                 4920dK
                
                  Auxiliary parameters

a_1      0.567    0.671                  0.611
b_1      0.533    0.605                  0.562
c_1      0.483    0.519                  0.498
a_2      0.259    0.231                  0.243
b_2      0.241    0.220                  0.230
c_2      0.233    0.215                  0.224
L_1      0.929    0.896                  0.899
L_2      0.071    0.103                  0.100 
1-epsilon_1 0.955 0.903                  0.919
1-epsilon_2 0.931 0.954                  0.947

                  Fixed parameters

T_1(eq)  5500dK   5500dK                 5500dK
beta_1=beta_2 0.25 0.08                  0.08
q=       0.34     0.34                   0.34
w_1=w_2  0        0.5                    0.5
n_1=n_2  5.0      5.0                    5.0
x_1=x_2  1.0      1.0                    1.0

corresponding to the respective spectral classes. In the same
time, the mass ratio was considered constant and equal to q=0.34
though from the 1977-78 light curve it results q ~ 0.6. In Fig. 1
the comparison between theoretical and observed (Kwee) light
curves is represented. The theoretical solution (called Model I)
corresponds to a radiative atmosphere; a convective atmosphere
model (Model II) was also used and the results are slightly 
different mainly during the secondary minimum, where this theoretical 
solution is above the radiative solution with about 0.01 magnitude. 
In Fig. 2 are represented the theoretical and observed
light curves for 1977-78 period; a convective atmosphere model
was used (Model III). The photometric and geometric elements for
the three models are given in Table.


                       [FIGURE 2]



                C. CRISTESCU, G. OPRESCU, M.D. SURAN
                Center for Astronomy and Space Sciences


References:
Wood, D.B., 1972, Goddard Space Flight Center, X-110-72-473
Kwee, K.K., 1966, BAN, Suppl.Ser., 1, 6, 245-264 [BIBCODE 1966BANS....1..245K ]