  Ultraviolet (UV) wavelength observations have made a significant contribution
to our understanding of hot stellar populations of star clusters.
Multi-wavelength spectral energy distributions (SEDs) of stars, including
ultraviolet observations, have proven to be an excellent tool for discovering
unresolved hot companions in exotic stars such as blue straggler stars (BSS),
thereby providing helpful clues to constrain their formation mechanisms.
Melotte 66 is a 3.4 Gyr old open cluster located at a distance of 4810 pc. We
identify the cluster members by applying the ML-MOC algorithm on Gaia EDR3
data. Based on our membership identification, we find 1162 members, including
14 BSS candidates, 2 yellow straggler candidates (YSS), and one subdwarf B
candidate (sdB). We generated SEDs for 11 BSS candidates and the sdB candidate
using Swift/UVOT data combined with other archival data in the optical and IR
wavelengths. We discover a hot companion of one BSS candidate, BSS3, with
temperature of 38000$_{-6000}^{+7000}$ K, luminosity of 2.99$_{-1.86}^{+5.47}$
L$_\odot$, and radius of 0.04$_{-0.005}^{+0.008}$ R$_\odot$. This hot companion
is a likely low-mass WD with an estimated mass of 0.24 $\text{-}$ 0.44
M$_\odot$. We report one BSS candidate, BSS6, as an Algol-type eclipsing binary
with a period of 0.8006 days, based on the Gaia DR3 variability classification.
We suggest that BSS3 is formed via either the Case A or Case B mass-transfer
channel, whereas BSS6 is formed via the Case A mass transfer.
