The first light curve of the system was obtained by
Menzies & Marang (1986).
Assuming that the temperature of the primary star is
K they found that *T _{2}*=4500 K,

Although it has already been stated, we feel compelled to repeat again
that since the system is very faint and the photometer we used is insensitive to short
wavelengths, our observations in *U* band were scattered, as we expected.

In the analysis of the light curves the normal points were performed in each band. The , and light curves were represented by 51, 65 and 69 normal points, respectively.

The mass of sdB stars is given as by
Saffer et al. (1994).
If we use
this value in the mass function obtained by
Hilditch et al. (1996),
the mass of the
companion star is found to be around as noted earlier by Hilditch et al.
For this reason we adopt the value of 0.28 for the mass ratio. Limb darkening
coefficients play a very important role in light curve analysis. These coefficients
depending on the temperatures of the stars are theoretically evaluated for the stars
hotter than 5500 K. To the best knowledge of the authors of the present study there
is no reference giving those coefficients for stars cooler than 5500 K. In the
previous analysis of HW Vir, limb darkening coefficients of the cooler component are
taken as those of a star with an effective temperature of 5500 K. In the present
paper, limb darkening coefficients of sdB star for *B*, *V* and *R* colour are taken
from
Rucinski (1985)
as 0.240, 0.199 and 0.162, respectively. Corresponding values for cooler low mass
star are derived from light curve analysis. Gravity darkening coefficients for hotter
star for all three colours are taken as 1.0 and for cooler star as 0.32. Bolometric
albedo for hotter star for all three colours is assumed to be 1.0. If the mass of the
cooler component is taken as then its effective temperature should
be 3300 K
(Dorman et al. 1989).
In the solution the above values are kept fixed.

The initial values of the parameters were performed by means of LC (Light
Curve) program till a good approach to the observational data was obtained. Then
the DC (Differential Corrections) was run iteratively until an acceptable stability
of the solution was reached. The adjustable parameters were: orbital inclination
(*i*), surface temperature of the hotter component (*T _{1}*), non-dimensional potentials
of both components, luminosity of hotter star, the limb darkening
coefficient and the albedo of the cooler star. The results are given in
Table 3.

The computed light curves using the parameters given in Table 3 were plotted in Fig. 4 with those of the normal points.

Figure 4:
The observed normal points in B, V and R are plotted against
the orbital phase and compared with the computed curves. Note that the
ordinate is intensity |

Using the results of the radial velocity curve analysis we obtained the radius of the orbit as . The three - colour light curves were analysed simultaneously to obtain the radii of the components. The mean fractional radius of hotter and cooler component stars are 0.218 and 0.201, respectively. The mass, radius and luminosity of the hotter primary star were calculated as 0.50, 0.21 and 55.628 solar units, whilst these parameters are 0.14, 0.20 and 0.0003 for the cooler secondary star. The critical Roche lobes of the components were calculated using the mass ratio of 0.28 and are shown in Fig. 5.

Copyright The European Southern Observatory (ESO)