Author: Dr. Igor Volkov
Sternberg State Astronomical Institute,
Lomonosov Moscow State University, Moscow, Russia 

Title: "Light-time effect in three sourthen eclipsing variables"

Abstract:
    Determination of absolute parameters of the southern eclipsing
binaries with deep eclipses RW CrA, DX Vel, V646 Cen and
explanation of their orbital period changes.
    The data analysis is based on a high quality Walraven photoelectric
photometry, obtained in 1960-70-s, our recent CCD
photometry, ASAS and Hipparcos photometry of the objects. The times of
eclipses were used to construct and analyze the eclipse
time variation diagrams. To extend the timescale of observations, the
older photographic data, were also used. The light curves of the
objects were analyzed using the PHOEBE program.
    We found the reliable absolute parameters of all three objects from
the light curves solutions.We explained the orbital period
changes of RW CrA and DX Vel by a light-time effect and determined
parameters of the third body orbits. In DX Vel semi-detached
binary we found the long term variations of the inclination angle. We
explained the detected orbital period increase in V646 Cen
semi-detached binary by a mass transfer from the less to more massive
component.