  We present a study of Far Ultraviolet (FUV) bright horizontal branch (HB)
stars to understand the peculiarities seen in the HB sequence of the Globular
Cluster NGC 1851, using ground and space based multi-wavelength data. Optical
and UV color magnitude diagrams are used to classify HB stars and their
membership from HST and Gaia DR2 data. The Spectral energy distributions (SEDs)
of the hot HB stars located from the core to tidal radii are constructed. The
SEDs reveal that the HB stars near the G-jump show a decrease in the FUV flux
when atmospheric models of cluster metallicity are used for fitting, but a
better fit is found with higher metallicity models, as expected due to
atmospheric diffusion. We report on four particularly interesting extreme HB
(EHB) stars, two each in inner and outer regions. We detect a sub-luminous EHB
and a "blue-Hook" candidates with temperatures Teff ~ 25,000 K and 31,000 K,
respectively. We found an EHB star (Teff ~ 17,000 K) with the radius lies
between the BHB and normal EHB stars. The most peculiar of our EHB stars (Teff
~ 28,000 K) is found to be a photometric binary to a Blue Straggler star (BSS)
(Teff ~ 7,000 K), which is an important target for spectroscopic study. This
discovery of the candidate EHB+BSS binary system, could help to explain the
mass loss in the RGB phase, leading to the formation of EHB stars.
