AU Monocerotis (AU Mon; HD 50846; BD; ) was discovered to be an eclipsing binary of Algol type by Hoffmeister (1931). From their spectroscopic studies, Sahade & Cesco (1945) reported the spectral types of the primary and secondary components to be B5 and about F0, respectively. Lorenzi (1980a) published the first photoelectric light curve, in yellow, of this system in the form of 2616 individual observations. Later he combined these observations into 183 weighted normal points (Lorenzi 1980b; hereafter L80) and corrected them for a suspected intrinsic variation, with a period of about 411 days and amplitude of , in the system. Assuming symmetry for the eclipse light curve, he obtained ten normal points from these corrected 183 normals (L80; Table 3 (click here)). These ten normals were considered by Lorenzi as "representative of an approximate mean light curve of the eclipsing variations''. Giuricin et al. (1982) solved this light curve of ten normal points using Wood's WINK program and obtained photometric elements of the system. Since only a mass function, , of (Sahade & Cesco 1945) and not the mass ratio was available to them, Giuricin et al. (1982) assumed a plausible value for the mass of the B5 primary component and derived a mass ratio of 0.2 for the system and used this value in their analysis.
In a further study of his observations, Lorenzi (1982, Table 1 (click here) and Fig. 1 (click here)) published the light curve of the variation of the unknown source in the system and provided twenty seven corrected normal points (symmetrized) including eight points from his previous study (L80, Table 3 (click here)). Forming an average symmetric light curve from these points, Lorenzi (1982) solved it for elements using Russell-Merrill (1952) method. Recently Popper (1989) obtained spectra of both the components of AU Mon and published the amplitudes and of the radial velocity curves, from which one can get a reliable mass ratio () of the system. Hence we felt it worthwhile to reanalyse the light curve of Lorenzi (L80) using the mass ratio obtained by Popper (1989) and thus obtain improved elements of AU Mon. In the following we give details of our analysis and its results.
Figure 1: AU Mon: The relation between the mass ratio, q, and . The solid line is a free hand drawn curve. The minimum occurs at q=0.1985