Using the light curve of variation of the unknown source in the system as given by Lorenzi (1982, Table 1 (click here) and Fig. 1 (click here)) we corrected the 183 weighted normals of Lorenzi (L80; Table 1 (click here)) for the intrinsic brightness variations and analysed them for elements using Wilson-Devinney (W-D) (1971) method. The number of points in each of the 183 normals was taken as its weight. For initiating the W-D method, we used the elements derived by Giuricin et al. (1982) as preliminary elements. Since the semi detached nature of this system was confirmed by Giuricin et al. (1982) and Popper (1989), we used code-5 of the W-D method meant for such systems and a circular orbit (e=0) was assumed for the analysis. Since the spectral type of the primary component was reported to be B5 (Sahade & Cesco 1945; Giuricin et al. 1982; Popper 1989) we assumed a temperature of K (Allen 1976; Popper 1980; Schmidt-Kaler 1982) for this component. As regards the other important parameter, , the mass ratio, Popper (1989) reported two values for : one of obtained from He and Mg II lines and the other of obtained from H lines. However, he obtained a unique value of for from the D lines. Hence the value of q is ambiguous: it can be either 0.190 (H lines) or 0.213 (He and Mg II lines). In order to find the value of q that gives minimum from the light curve analysis, we analysed the data using a range of q values viz.: 0.190, 0.195, 0.1975, 0.20, 0.21 and 0.22, and along with treated it as a fixed parameter. In addition, the limb darkening coefficients and , the albedos, and ; the gravity darkening coefficients, and of the primary and secondary components were also treated as fixed parameters. The following parameters were treated as adjustable: i, the inclination of the orbit; , the surface potential of the hotter component; , the relative monochromatic luminosity of the hotter component; , the mean effective temperature of the cooler component and l3, the third light. With these fixed and adjustable parameters, a number of runs of the program (code-5) were made till the sum of the residuals showed a minimum and the corrections to the parameters became smaller than their probable errors. The values of obtained from the analysis for different q values are given in Table 1 (click here). A free hand drawn curve through a plot of q versus (Fig. 1 (click here)) showed a minimum at q=0.1985. Hence we obtained another solution, as before, with q=0.1985 and as fixed parameters. In this solution, we treated , and also as adjustable parameters. The results are given in Table 2 (click here). One can notice that l3 is absent in the solution.
|* Fixed parameters.|
The theoretical light curve obtained from the parameters given in Table 2 (click here) is shown as solid line in Fig. 2 (click here).
Figure 2: AU Mon: Light curve in yellow.The solid line is the theoretical curve obtained from the parameters given in Table 2 (click here). The filled circles represent the 183 corrected normal points used in the present analysis. The 27 normal points of Lorenzi (1982) are shown as squares
Here the filled circles represent the corrected 183 normal points. The 27 normal points of Lorenzi (1982, Table 3 (click here)) are shown as squares. Keeping in view the sparse observational coverage at some phases of the light curve, we conclude that the fit of the theoretical curve to the observations is quite satisfactory except in the phase range of 0.88 to 0.96 and 0.04 to 0.12. We attribute this misfit to the presence of gases or gas streams in the system that are favourably situated to absorb some of the light during these phases. The presence of gases or gas streams in AU Mon was evidenced by the spectroscopic studies of Sahade and Cesco (1945), Sahade & Ferrer (1982), Popper (1962), Peters & Polidan (1984) and Peters (1994). Similar misfits and distortions of light curves due to the presence of gases in the semi detached systems of TT Hya (Vivekananda Rao & Sarma 1994), HU Tau (Parthasarathy et al. 1995), R CMa (Sarma et al. 1996), EU Hya (Vivekananda Rao et al. 1996) and RY Gem (Sarma & Vivekananda Rao 1997) were already reported.
|Parameter||Hot Component||Cool Component|