UVIT-HST-GAIA view of NGC 288: A census of hot stellar population and their properties from UV

TL;DR

This study provides a comprehensive UV and optical analysis of NGC 288, identifying and characterizing its hot stellar populations, including BHB and BSS stars, using multi-instrument data to reveal their properties and distributions.

Contribution

It presents the first complete census of BHB and BSS stars in NGC 288 using UVIT, HST, ground, and GAIA data, highlighting their properties and spatial distributions.

Findings

Two peaks in BHB temperature distribution at ~10,300 K and extending to 18,000 K.

Detection of 2 EHB candidates with temperatures 29,000-32,000 K.

Bright BSSs are more centrally concentrated than faint BSSs and BHB stars.

Abstract

A complete census of Blue Horizontal Branch (BHB) and Blue Straggler Star (BSS) population within the 10$'$ radius from the center of the Globular Cluster, NGC 288 is presented, based on the images from the Ultraviolet Imaging Telescope (UVIT). The UV and UV$-$optical Colour-Magnitude Diagrams (CMDs) are constructed by combining the UVIT, HST-ACS and ground data and compared with the BaSTI isochrones generated for UVIT filters. We used stellar proper motions data from GAIA DR2 to select the cluster members. Our estimations of the temperature distribution of 110 BHB stars reveal two peaks with the main peak at $T_{eff}\sim$ 10,300 K with the distribution extending up to $T_{eff}\sim$ 18,000 K. We identify the well known photometric gaps including the G-jump in the BHB distribution which are located between the peaks. We detect a plateau in the FUV magnitude for stars hotter than $T_{eff}\sim$ 11,500 K (G-jump), which could be due to the effect of atomic diffusion. We detect 2 Extreme HB (EHB) candidates with temperatures ranging from 29,000 to 32,000 K. The radial distribution of 68 BSSs suggests that the bright BSSs are more centrally concentrated than the faint BSS and the BHB distribution. We find that the BSSs have a mass range of 0.86 - 1.25 M$_{\odot}$ and an age range of 2 - 10 Gyr with a peak at 1 M$_{\odot}$ and 4 Gyr respectively. This study showcases the importance of combining UVIT with HST, ground, and GAIA data in deriving HB and BSS properties.