Globular Cluster UVIT Legacy Survey (GlobULeS) $-$ II. Evolutionary status of hot stars in M3 and M13

Abstract

We present a far-ultraviolet (FUV) study of hot stellar populations in the second parameter pair globular clusters (GCs) M3 and M13, as a part of the Globular cluster UVIT Legacy Survey program (GlobULeS). We use observations made with F148W and F169M filters of the Ultraviolet Imaging Telescope (UVIT) onboard {\em AstroSat} along with ground-based data (UBVRI filters), {\em Hubble Space Telescope (HST)} GC catalogue, and {\em Gaia} EDR3 catalogue. Based on the FUV-optical colour-magnitude diagrams, we classify the sources into the horizontal branch (HB) stars, post-HB stars, and hot white dwarfs (WDs) in both the GCs. The comparison of synthetic and observed colours of the observed HB stars suggests that the mass-loss at the red giant branch (RGB) and He spread in both clusters have a simultaneous effect on the different HB distributions detected in M3 and M13, such that, HB stars of M13 require a larger spread in He ($0.247-0.310$) than those of M3 ($\mathrm{Y}=0.252-0.266$). The evolutionary status of HB stars, post-HB stars, and WDs are studied using SED fit parameters and theoretical evolutionary tracks on the H-R diagram. We found that the observed post-HB stars have evolved from zero-age HB (ZAHB) stars of the mass range $0.48-0.55$ \Msun\ in M3 and M13. We detect 24 WD candidates in each cluster having $\log ({\mathrm{L}}_{\mathrm{bol}}/{\mathrm{L}}_{\odot })$ in the range $-0.8$ to $+0.6$ and $\log ({\mathrm{T}}_{\mathrm{eff}}/K)$ in the range of 4.2 to 5.0. Placing the WDs on the H-R diagram and comparing them with models suggest that M13 has a population of low-mass WDs, probably originating from binary evolution.

Accepted for publication in MNRAS main journal

References in corpus (19)

• VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. IX. The Atlas of Multiple Stellar Populations
• The updated BaSTI stellar evolution models and isochrones: II. alpha-enhanced calculations
• Homogeneous photometry VII. Globular clusters in the Gaia era
• The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XIX. A Chemical Tagging of the Multiple Stellar Populations Over the Chromosome Maps
• White dwarf evolutionary sequences for low-metallicity progenitors: The impact of third dredge-up
• Mass loss along the red giant branch in 46 Globular Clusters and their multiple populations
• Constraints on the distance moduli, helium and metal abundances, and ages of globular clusters from their RR Lyrae and non-variable horizontal-branch stars. II. Multiple stellar populations in 47Tuc, M3, and M13
• Hot UV-bright stars of galactic globular clusters
• Multiple populations in massive star clusters under the magnifying glass of photometry: Theory and tools
• Is helium the key parameter in the extended color spread of the first generation stars in M3?
• Slowly cooling white dwarfs in M13 from stable hydrogen burning
• A possible formation channel for blue hook stars in globular cluster
• A grid of Synthetic Spectra for Hot DA White Dwarfs and Its Application in Stellar Population Synthesis
• A possible formation channel for blue hook stars in globular cluster - II. Effects of metallicity, mass ratio, tidal enhancement efficiency and helium abundance
• The First Extensive Exploration of UV-bright Stars in the Globular Cluster NGC 2808
• A Census of Above-Horizontal-Branch Stars in Galactic Globular Clusters
• Ultraviolet Imaging Telescope (UVIT) observation of the Galactic Globular Cluster NGC 7492
• Study of UV bright sources in globular cluster NGC 4590 using Ultraviolet Imaging Telescope (UVIT) observations