Study of UV-bright stellar populations in the globular cluster NGC 1261 using <i>Astrosat</i>

ABSTRACT We present UV photometry of the globular cluster NGC 1261 using images acquired with Ultraviolet Imaging Telescope (UVIT) on board Astrosat. performed point-spread function (PSF) four near-UV (NUV) and two far-UV (FUV) constructed colour–magnitude diagrams (CMDs), in combination Hubble Space (HST), Gaia, ground-based optical for member stars. detected full horizontal branch (HB) NUV blue HB FUV identified extreme (EHB) stars have a tight sequence UV–optical CMDs, well fitted isochrones generated (age 12.6 Gyr, [Fe/H] = ?1.27 metallicity) updated BaSTI-IAC models. Effective temperatures (Teff), luminosities, radii bright were estimated spectral energy distribution. As we detect complete sample UV-bright stars, hot end distribution is found to terminate at G-jump ($T_{\rm eff}\, \sim$ 11500 K). The EHB single spectra, Teff 31000 K mass 0.495 M?, follow same Teff–radius relation as constrain formation pathways these loss RGB phase (due either rotation or enhanced helium) early hot-flash scenario.