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Astron. Astrophys. 345, 137-148 (1999) 4. Photometric light-curves and their analysis4.1. Normal points and Fourier analysis of the mean light-curvesAll our individual observations of AW UMa were used to construct 250 normal points of the mean light-curve (henceforth LC) in each passband. Each normal point is the mean value of brightness in ranges of 0.004 of the orbital phase and was calculated using 12 individual observations in average. The numbers of individual points coming into one normal point were used as weights. The mean UBV LCs were used for a Fourier analysis. The resulting Fourier coefficients are given in Table 4. Table 4. Fourier coefficients of the mean light-curves Due to the fact that AW UMa is an A-type contact binary with a
slightly hotter (and more massive) primary, the coefficient
The rough estimate of the main photometric elements from Fourier
coefficients fails in systems with
4.2. Photometric elementsThe UBV LCs were analyzed using the synthetic LCs and the
differential corrections code developed by Wilson & Devinney
(1971) (W&D). Particular numbers of individual points coming into
one normal point were used as weights. Mode 3 of the W&D code was
employed assuming synchronous rotation and blackbody radiation. We
have assumed The LC analysis of contact systems is complicated by strong
correlations between some elements (see Wilson & Biermann, 1976).
Moreover, a LC solution is usually insensitive to bolometric albedo
and, to a smaller extent to gravity and limb darkening. Our solution
of the LC of AW UMa was aimed at detection of the third light which
could be ascribed to a possible third component (see Sect. 7). In
previous studies (Hrivnak, 1982; Mochnacki & Doughty, 1972; Wilson
& Devinney, 1973) the third light was set to zero. In solution 1
(see Table 5) we have fixed several parameters
( Table 5. Photometric elements of AW UMa and their probable errors We have also tried to adjust all parameters (except
The normal points as well as the LC from solution 2 are depicted in Fig. 3. Although the fits of the B and V LCs are quite good, there is a significant difference between the fit and the mean U LC around the maximum II. Furthemore, there are difficulties with exact fitting of the minima. A non-uniform distribution of the temperature on the surface of the components, caused by spot(s) as well as the presence of circumstellar matter can be responsible for these differences. Since Maceroni & van't Veer (1993) demonstrated that the determination of the position of spots is not unique, we have not tried to improve the solutions by spots.
The most interesting result of our analysis is the detection of the
third light, which increases from V to U (solution 2). It is hard to
know if the derived values of L3 tell us something physical
about the system, or if they are parameters which adjusted to fit some
of the complications in the LCs. In Sect. 7 we derived the mass of the
third body as In further calculations we have adopted
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