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2. Analysis

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 tex2html_wrap_inline1193 K (Allen 1976; Popper 1980; Schmidt-Kaler 1982) for this component. As regards the other important parameter, tex2html_wrap_inline1195, the mass ratio, Popper (1989) reported two values for tex2html_wrap_inline1153: one of tex2html_wrap_inline1199 obtained from He and Mg II lines and the other of tex2html_wrap_inline1201 obtained from H lines. However, he obtained a unique value of tex2html_wrap_inline1203 for tex2html_wrap_inline1155 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 tex2html_wrap_inline1159 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 tex2html_wrap_inline1215 treated it as a fixed parameter. In addition, the limb darkening coefficients tex2html_wrap_inline1217 and tex2html_wrap_inline1219, the albedos, tex2html_wrap_inline1221 and tex2html_wrap_inline1223; the gravity darkening coefficients, tex2html_wrap_inline1225 and tex2html_wrap_inline1227 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; tex2html_wrap_inline1231, the surface potential of the hotter component; tex2html_wrap_inline1233, the relative monochromatic luminosity of the hotter component; tex2html_wrap_inline1235, 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 tex2html_wrap_inline1159 showed a minimum and the corrections to the parameters became smaller than their probable errors. The values of tex2html_wrap_inline1159 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 tex2html_wrap_inline1159 (Fig. 1 (click here)) showed a minimum at q=0.1985. Hence we obtained another solution, as before, with q=0.1985 and tex2html_wrap_inline1215 as fixed parameters. In this solution, we treated tex2html_wrap_inline1255, tex2html_wrap_inline1257 and tex2html_wrap_inline1259 also as adjustable parameters. The results are given in Table 2 (click here). One can notice that l3 is absent in the solution.


tex2html_wrap_inline1267 tex2html_wrap_inline1193
tex2html_wrap_inline1271 tex2html_wrap_inline1273
*q 0.1985
tex2html_wrap_inline1279 tex2html_wrap_inline1281
pole tex2html_wrap_inline1283
point tex2html_wrap_inline1285
tex2html_wrap_inline1287 sidetex2html_wrap_inline1289
back tex2html_wrap_inline1285
pole tex2html_wrap_inline1293
point tex2html_wrap_inline1295
tex2html_wrap_inline1297 side tex2html_wrap_inline1299
back tex2html_wrap_inline1301
tex2html_wrap_inline1303 tex2html_wrap_inline1305
tex2html_wrap_inline1307 0.3410
l3 tex2html_wrap_inline1313
tex2html_wrap_inline1257 tex2html_wrap_inline1317
tex2html_wrap_inline1259 tex2html_wrap_inline1321
tex2html_wrap_inline1323 1.0
tex2html_wrap_inline1255 tex2html_wrap_inline1329
tex2html_wrap_inline1331 0.25
tex2html_wrap_inline1335 0.08
tex2html_wrap_inline1339 1.0
tex2html_wrap_inline1343 1.0
* Fixed parameters.
Table 2: AU Mon: Results obtained from the analysis using tex2html_wrap_inline1263 and q=0.1985 as 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
tex2html_wrap_inline1351 tex2html_wrap_inline1353 tex2html_wrap_inline1353
tex2html_wrap_inline1357 tex2html_wrap_inline1359 tex2html_wrap_inline1361
tex2html_wrap_inline1363 tex2html_wrap_inline1365 tex2html_wrap_inline1367
tex2html_wrap_inline1369 tex2html_wrap_inline1371 tex2html_wrap_inline1373
tex2html_wrap_inline1375 tex2html_wrap_inline1377 tex2html_wrap_inline1379
tex2html_wrap_inline1381 tex2html_wrap_inline1383 tex2html_wrap_inline1385
tex2html_wrap_inline1387 tex2html_wrap_inline1389 tex2html_wrap_inline1391
Table 3: AU Mon: Absolute elements derived from the values of tex2html_wrap_inline1347 and tex2html_wrap_inline1349 and other parameters from Table 2 (click here)


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