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We present a study of Far Ultraviolet (FUV) bright horizontal branch (HB)stars to understand the peculiarities seen in the HB sequence of the GlobularCluster NGC 1851, using ground and space based multi-wavelength data. Opticaland UV color magnitude diagrams are used to classify HB stars and theirmembership 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. TheSEDs reveal that the HB stars near the G-jump show a decrease in the FUV fluxwhen atmospheric models of cluster metallicity are used for fitting, but abetter fit is found with higher metallicity models, as expected due toatmospheric diffusion. We report on four particularly interesting extreme HB(EHB) stars, two each in inner and outer regions. We detect a sub-luminous EHBand 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 liesbetween 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. Thisdiscovery of the candidate EHB+BSS binary system, could help to explain themass loss in the RGB phase, leading to the formation of EHB stars.

Peculiarities in the horizontal branch stars of globular cluster NGC 1851: Discovery of a Blue straggler companion to an EHB star