  We present the study of four FUV stars in the field of open cluster NGC 2420
using the Ultra Violet Imaging Telescope (UVIT) mounted on AstroSat. The three
stars 525, 527, and 560 are members, while star 646 is a non-member of the
cluster. To characterize and determine the parameters of these stars,
multi-wavelength spectral energy distributions (SEDs) are analyzed using UV,
optical, and IR data sets. For all four FUV bright stars, a two-component SED
model fits well. Our findings indicate that two stars, 525 and 560, are binary
BSS systems. These binary BSS systems may have formed in a tertiary system due
to mass transfer from an evolved outer tertiary companion. Star 527 is a binary
system of a BSS and an extremely low-mass (ELM) white dwarf, while Star 646 is
a binary system of a horizontal branch star and an ELM white dwarf. The
effective temperatures, radii, luminosities and masses of the two ELMs are
(10250, 11500) K, (0.42, 0.12) Rsun, (1.61, 0.23) Lsun, and (0.186, 0.170)
Msun, respectively. The star 527 could be a post-mass transfer system and may
have originated through the Case A/B mass transfer process in a low-density
environment. The cooling age of the ELMs is < 1 Myr, indicating that they have
only recently formed.

Solar and Stellar Astrophysics;Astrophysics of Galaxies