  Binary systems can evolve into immensely different exotic systems such as
blue straggle stars (BSSs), yellow straggler stars, cataclysmic variables, type
Ia supernovae depending on their initial mass, the orbital parameters and
evolution. The aim of this thesis is to understand the demographics of
post-mass-transfer systems (BSSs, white dwarfs and blue lurkers) present in the
open clusters and how they are formed. First, we identified the cluster members
using Gaia EDR3 data in six open clusters. Two of the clusters, M67 and King2,
were studied in detail using UVIT, Gaia, GALEX, 2MASS and other archival
photometric data. The comprehensive panchromatic study showed that (i) there is
a robust mass-transfer pathway for BSSs, and blue lurkers in M67, (ii) at least
15% of BSSs in King 2 were formed via binary mass transfer. We also created a
homogeneous catalogue of open cluster BSSs using Gaia DR2 data. The analysis of
868 BSSs across 208 clusters showed that (i) BSS frequency increases with age,
(ii) there is a power-law relation between cluster mass and maximum number of
BSSs, (iii) the formation mechanism of BSSs is dominated by binary mass
transfer (54-67%) though there exists a 10-16% chance of BSSs forming through
more than 2 stellar interactions. This study demonstrates that there exists an
extensive variety in the demographics of binary products, and the UV
observations are vital for their detection and characterisation.
