ORBITAL PERIOD VARIATION STUDY OF THE ALGOL ECLIPSING BINARY DI PEGASI

Abstract

We discuss the orbital period changes of the Algol semi-detached eclipsing binary DI Peg by con-structing the (O.C) residual diagram via using all the available precise minima times. We conclude that the period variation can be explained by a sine-like variation due to the presence of a third body orbiting the binary, together with a long-term orbital period increase (dP/dt = 0.17 sec/century) that can be interpreted to be due to mass transfer from the evolved secondary component (of rate 1.52×10 -8 M ⊙ /yr) to the primary one. The detected low-mass third body (M 3 min. = 0.22±0.0006 M ⊙ ) is responsible for a periodic variation of about 55 years light time effect. We have determined the orbital parameters of the third component which show a considerable eccentricity e 3 = 0.77± 0.07 together with a longitude of periastron ? 3 = 300° ± 10°.