The variability of DD Mon (HD 202319) was discovered by Hoffmeister
(1934). Later, Ahnert et al. (1947) determined the orbital period
to be 0.567989 days from photographic observations. Wachmann (1968)
gave a photographic light curve and revised the ephemeris. The first
photoelectric photometric and spectroscopic observations were published
by Yamasaki et al. (1990) who assigned the spectral type of the primary
component to be F5. According to Yamasaki et al. (1990), DD Mon is an
almost semidetached system with the primary component almost filling
its critical Roche lobe, while the secondary is not in contact with its
critical lobe. The masses of the components are undermassive for
their radii and luminosities, which was explained by mass loss from
the system during the course of evolution.
These masses of the components and the photometric disturbances
and asymmetries on the light curves make DD Mon a rather interesting
system to study. Our observed plan was to study the structure and
evolutionary state of this system.