The "UV-route" to search for Blue Straggler Stars in Globular Clusters: first results from the HST UV Legacy Survey

Abstract

We used data from the HST UV Legacy Survey of Galactic Globular Clusters to select the Blue Straggler Star (BSS) population in four intermediate/high density systems (namely NGC 2808, NGC 6388, NGC 6541 and NGC 7078) through a "UV-guided search". This procedure consists in using the F275W images in each cluster to construct the master list of detected sources, and then force it to the images acquired in the other filters. Such an approach optimizes the detection of relatively hot stars and allows the detection of complete sample of BSSs even in the central region of high-density clusters, because the light from the bright cool giants, which dominates the optical emission in old stellar systems, is sensibly reduced at UV wavelengths. Our UV-guided selections of BSSs have been compared to the samples obtained in previous, optical-driven surveys, clearly demonstrating the efficiency of the UV approach. In each cluster we also measured the parameter A+, defined as the area enclosed between the cumulative radial distribution of BSSs and that of a reference population, which traces the level of BSS central segregation and the level of dynamical evolution suffered by the system. The values measured for the four clusters studied in this paper nicely fall along the dynamical sequence recently presented for a sample of 25 clusters.

30 pages, 9 figures, 4 tables; accepted for publication in ApJ

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• The Peculiar Radial Distribution of Multiple Populations in the massive globular cluster M80
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• A new identity card for the bulge globular cluster NGC 6440 from resolved star counts
• Spectral Energy Distribution of Blue Stragglers in the core of 47 Tucanae
• Slowly cooling white dwarfs in M13 from stable hydrogen burning
• Determination of dynamical ages of open clusters through the A${}^{+}$ parameter -- I
• GlobULeS-IV. UVIT/AstroSat detection of extremely low mass white dwarf companions to blue straggler stars in NGC 362
• UVIT-HST-GAIA view of NGC 288: A census of hot stellar population and their properties from UV
• Globular Clusters UVIT Legacy Survey (GlobULeS) I. FUV-optical Color-Magnitude Diagrams for Eight Globular Clusters
• The First Extensive Exploration of UV-bright Stars in the Globular Cluster NGC 2808
• A young white dwarf orbiting PSR J1835-3259B in the bulge globular cluster NGC 6652
• Slowly cooling white dwarfs in NGC 6752
• A binary-related origin mediated by environmental conditions for blue straggler stars
• Investigating the Blue Straggler Stars radial distribution in globular clusters with Monte Carlo simulations
• AstroSat study of the globular cluster NGC 2298: probable evolutionary scenarios of hot HB stars
• Blue straggler stars beyond the Milky Way. II. A binary origin for blue straggler stars in Magellanic Cloud clusters
• Blue straggler stars beyond the Milky Way. III. Detection of evolved blue straggler candidates in Large Magellanic Cloud clusters
• Inferring the Helium abundance of extragalactic Globular Clusters using Integrated Spectra
• Study of UV bright stellar populations in the globular cluster NGC 1261 using AstroSat
• The dynamical age of the LMC globular cluster NGC 1835 using the "dynamical clock"
• Discovery of an extended Horizontal Branch in the Large Magellanic Cloud globular cluster NGC1835
• The "canonical" White Dwarf Cooling Sequence of M5
• Study of UV bright sources in globular cluster NGC 4590 using Ultraviolet Imaging Telescope (UVIT) observations
• Structural parameters, chronological age and dynamical age of the LMC globular cluster NGC 1754
• A rotation-based census of blue lurker candidates in open clusters
• Study of dynamical status of the globular cluster NGC 1851 using Ultraviolet Imaging Telescope