ORBITAL ELEMENTS AND EVOLUTIONARY NATURE OF THE LONG-PERIOD RS CVN TYPE ECLIPSING BINARY RZ ERIDANI

Light curves of the long period RS CVn type eclipsing binary RZ Eri, o btained during the period 1976-1979 with the 1.2 m telescope of the Ja pal-Rangapur Observatory are analysed, using Wilson-Devinney method, b y fixing the two parameters T(h) (7400-degrees-K) and q(0.963), result ing in the following absolute elements: A = 72.5 +/- 1.4R., R(h) = 2.8 4 +/- 0.12R., R(c) = 6.94 +/- 0.20R., M(bol,h) = 1.35 +/- 0.28, M(bol, c) = 1.41 +/- 0.28, m(h) = 1.69 +/- 0.06m. and m(c) = 1.63 +/- 0.13m. . The presence of humps and dips of varying amplitudes at a few phases in the normal UBV light curves is explained as due to residual distor tion wave. The derived (B-V) and (U-B) colours of both the components appear to have been reddened to an extent of 0.20m in (B-V) and 0.16m in (U-B) colours. This reddening is attributed to the presence of an e nvelope around the system, the material of which might have come from the loss of mass experienced by the evolving cooler component. Taking into consideration the dereddened colours and temperatures of the comp onents, spectral types of F0 IV for the primary and G 5-8 III-IV for t he secondary component were derived. The fractional radii of 0.039 and 0.096 of the two components, when compared with the radii of their cr itical Roche lobes of 0.378 and 0.372 suggest that these components ar e well within their critical sizes. From the position of the component s on the isochrones and the evolutionary tracks of stars of Pop I comp osition computed by Maeder & Meynet, it is concluded that the evolutio n of the components of RZ Eri is abnormal. This system is found to be situated at a distance of 185 pc, with an age of about 2.5 x 10(9) yrs .