Abstract:
We have studied ultraviolet (UV) bright sources in the Galactic globular cluster (GGC) NGC 4590 using Ultraviolet Imaging
Telescope onboard the AstroSat satellite. Using UV-optical colour–magnitude diagrams (CMDs), we have identified and
characterized the sources of different evolutionary stages i.e. blue horizontal branch stars (BHBs), extremely blue horizontal
branch stars (EHBs), blue straggler stars (BSs), variable stars, etc. We estimated effective temperature (Teff), gravity (log (g)),
luminosity (Lbol), and hence the radius (R) of these hot stars by fitting spectral energy distribution with the help of stellar
atmosphere models. Two new far-UV bright cluster member stars situated near the core of the cluster have been detected; one of
them is an EHB star and the other one is either in its post-blue hook evolutionary phase or in white dwarf phase. The evolutionary
status of all the hot stars, identified in the cluster, has been investigated by using various evolutionary models. We find the
massive and younger BSs are concentrated at the centre of the cluster whereas the older and less massive BSs are distributed
throughout the cluster. The BSs normalized radial distribution seems to be bi-modal with a minimum located at rmin = 4.3 rc. We
calculated A+ parameter of the cluster which is obtained using cumulative normalized radial distribution of horizontal branch
stars (HBs) and BSs. We measured this value up to half-mass radius of the cluster to be +0.13, which indicates that NGC 4590
is one of the youngest clusters among dynamically intermediate age GGCs with a dynamical age of 0.423 ± 0.096 Gyr
