| Abstract : | We present the multi-wavelength study of the hot stellar population in Galactic Globular Clusters (GGCs). We targeted six GGCs in this thesis i.e., NGC 6656, NGC 1851, NGC 4590, NGC 6218, NGC 6838, and NGC 7078. In the thesis, we have extensively made use of Indian multi-wavelength space- and ground-based facilities like UVIT onboard AstroSat and 1.3m Devasthal fast optical telescope i.e., 1.3m DFOT. We have taken observations and reduced and calibrated data sets taken from these Indian facilities and other major international facilities including UVOT on-board Swift and 2.2m ESO/MPI, etc. To select the genuine cluster members, we used HST and Gaia DR2/DR3 astro-photometric catalogs. This allows us to select the hot stellar population from the center to the outskirts of the GCs. We have obtained the dynamical status of these six GCs using high-resolution and multi-wavelength data by studying the radial distribution of blue straggler star (BSS) with respect to the reference population. Based on the BSS radial distribution, we found that GCs can be classified into three different categories as Family I, Family II, and Family III, respectively. We also study the spectral energy distributions (SEDs) of the Far UV bright stars of the cluster NGC 1851, using multi-wavelength data extending from far UV to near IR to identify the peculiarities in the HB sequence stars. We found four extreme horizontal branch (EHB) stars which are classified as blue-hook, sub-luminous EHB, BHB/EHB, and one with a blue straggler companion to an EHB. We also studied the HB morphology of these six clusters having different pairs of metallicities (i,e., high, intermediate, and low) and age. We found a strong dependency of age and mass-loss parameter on the HB morphology, which suggest that age and mass-loss along RGB could be the possible "second parameter". |
