AstroSat study of the globular cluster NGC 2298: probable evolutionary
  scenarios of hot HB stars
  We present the far-UV (FUV) photometry of images acquired with UVIT on
AstroSat to probe the horizontal branch (HB) population of the Galactic
globular cluster NGC 2298. UV-optical color-magnitude diagrams (CMDs) are
constructed for member stars in combination with HST UV Globular Cluster Survey
(HUGS) data for the central region and Gaia and ground-based photometric data
for the outer region. Blue HB (BHB) sequence with a spread and four hot HB
stars are detected in all FUV-optical CMDs and are compared with theoretical
updated BaSTI isochrones and synthetic HB models with a range in helium
abundance, suggesting that the hot HB stars are helium enhanced when compared
to the BHB. The estimated effective temperature, radius, and luminosity of HB
stars, using best SED fits, were compared with various HB models. BHB stars
span a temperature range from 7,500-12,250 K. The three hot HB stars have
35,000-40,000 K, whereas one star has around 100,000K. We suggest the following
evolutionary scenarios: two stars are likely to be the progeny of extreme HB
(EHB) stars formed through an early hot-flasher scenario; one is likely to be
an EHB star with probable helium enrichment, the hottest HB star is about to
enter the WD cooling phase, could have evolved from BHB phase. Nevertheless,
these are interesting spectroscopic targets to understand the late stages of
evolution.
