| Authors : | Ranjan Kumar,
Ananta C. Pradhan,
M. Parthasarathy,
Sonika Piridi,
Santi Cassisi,
Devendra K. Ojha,
Abhisek Mohapatra,
and Jayant Murthy |
| Abstract : | The late stages of stellar evolution of low mass stars in globular cluster depends on the mass-loss mechanism during He-flash (at the tip of the red giant branch, RGB-tip). Based upon the remaining envelope mass, their progeny become red-horizontal branch stars (RHBs, effective temperature (Teff) ~6,000K), blue-horizontal branch (BHBs, 7,500 K < Teff < 20,000 K), extreme-horizontal branch stars (EHBs, 20,000 K < Teff < 30, 000 K) or blue-hook stars (BHks, Teff > 30, 000 K). The further evolution of EHBs and BHks never reach the AGB phase instead they evolve through AGB-manqu\'e phase and cool down to become white dwarf. We investigate such hot stellar populations of Galactic globular cluster M68 (NGC 4590) using Ultraviolet Imaging Telescope (UVIT) observations. We find two new hot sources with Teff 28,000+-500 K and 57,500+-7,500 K and surface gravity (logg) 3.5+-0.5 dex and 6.0+-1.0 dex, respectively along-with BHBs and RHBs in the cluster. We investigate their evolutionary status using various evolutionary tracks of BHks, EHBs, BHBs, etc. on the Teff vs. logg and Teff vs. luminosity plane. We find one of the newly detected source is in the EHB phase and another one has evolved from BHk phase and about to become a white dwarf. |
