UVIT study of UV bright stars in the globular cluster NGC 4147

TL;DR

This study uses UVIT on AstroSat to observe UV bright stars in NGC 4147, identifying multiple stellar populations, their properties, and spatial distributions through UV-optical CMDs and Gaia data.

Contribution

It provides the first detailed UV study of NGC 4147's stellar populations, revealing sub-populations and their characteristics using UVIT data combined with Gaia proper motions.

Findings

Identified 37 BHBs, 1 BSS, and 15 variable stars in NGC 4147.

Discovered two sub-populations, BHB1 and BHB2, among UV-bright BHBs.

BHB1 stars are more centrally concentrated than BHB2 stars.

Abstract

We present far ultraviolet (FUV) observations of globular cluster NGC 4147 using three FUV filters, BaF2 (F154W), Sapphire (F169M), and Silica (F172M) of Ultra-Violet Imaging Telescope (UVIT) on-board the \mbox{{\em AstroSat}} satellite. We confirmed the cluster membership of the UVIT observed sources using proper motions from Gaia data release 2 (GAIA DR2). We identified 37 blue horizontal branch stars (BHBs), one blue straggler star (BSS) and 15 variable stars using UV-optical color magnitude diagrams (CMDs). We find that all the FUV bright BHBs are second generation population stars. Using UV-optical CMDs, we identify two sub-populations, BHB1 and BHB2, among the UV-bright BHBs in the cluster with stars count ratio of 24:13 for BHB1 and BHB2. The effective temperatures (T$_{\mathrm{eff}}$) of BHB1 and BHB2 were derived using color-temperature relation of BaSTI-IAC zero-age horizontal branch (ZAHB). We found that BHB1 stars are more centrally concentrated than BHB2 stars. We also derive physical parameters of the detected FUV bright BSS by fitting younger age BaSTI-IAC isochrones on optical and UV-optical CMDs.