UOCS. IV. Discovery of diverse hot companions to blue stragglers in the old open cluster King 2

Abstract

King 2, one of the oldest clusters in the Milky Way, with an age of $\sim$ 6 Gyr and distance of $\sim 5700$ pc, has been observed with UVIT payload on the \textit{ASTROSAT}. With membership information derived from {\it Gaia} EDR3, the cluster is found to have 39 blue straggler stars (BSSs). We created multi-wavelength spectra-energy distributions (SED) of all the BSSs. Out of 10 UV detected BSSs, 6 bright ones fitted with double component SEDs and were found to have hotter companions with properties similar to extreme horizontal branch (EHB)/subdwarf B (sdB) stars, with a range in luminosity and temperature, suggesting a diversity among the hot companions. We suggest that at least 15\% of BSSs in this cluster are formed via mass-transfer pathway. When we compared their properties to EHBs and hotter companions to BSS in open and globular clusters, we suggest that EHB/sdBs like companions can form in binaries of open clusters as young as 6 Gyr.

14 pages, 4 figures, Accepted in Journal of Astrophysics and Astronomy

References in corpus (10)

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• UVIT Open Cluster Study. II. Detection of extremely low mass white dwarfs and post-mass transfer binaries in M67
• Metallicities and Radial Velocities of Five Open Clusters Including a New Candidate Member of the Monoceros Stream
• Detection of a White Dwarf companion to a Blue Straggler Star in the outskirts of globular cluster NGC 5466 with the Ultraviolet Imaging Telescope (UVIT)
• The blue-edge problem of the V1093 Her instability strip revisited using evolutionary models with atomic diffusion
• UOCS. III. UVIT catalogue of open clusters with machine learning based membership using \textit{Gaia} EDR3 astrometry
• Mode identification in three pulsating hot subdwarfs observed with TESS satellite
• UVIT/ASTROSAT studies of Blue Straggler stars and post-mass transfer systems in star clusters: Detection of one more blue lurker in M67
• Peculiarities in the horizontal branch stars of globular cluster NGC 1851: Discovery of a Blue straggler companion to an EHB star
• UOCS. V. UV study of the old open cluster NGC 188 using AstroSat

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• UOCS-VIII. UV Study of the open cluster NGC 2506 using ASTROSAT
• Characterization of hot populations of Melotte 66 open cluster using Swift/UVOT
• GlobULeS-IV. UVIT/AstroSat detection of extremely low mass white dwarf companions to blue straggler stars in NGC 362
• Study of Open Star Clusters Using the Gaia DR3: I- Poorly Studied King 2 and King 5
• UOCS-IX. AstroSat/UVIT study of the open cluster NGC 2818: Blue Stragglers, Yellow Stragglers, Planetary Nebula, and their membership
• M67 Blue Stragglers with High-resolution Infrared Spectroscopy
• UVIT Open Cluster Study. X. Rich Collection of Post Mass Transfer Systems in NGC 6791
• UOCS. XIV. Uncovering extremely low mass white dwarfs and blue lurkers in NGC 752
• Field blue straggler stars: Discovery of white dwarf companions to blue metal-poor stars using UVIT/AstroSat
• A rotation-based census of blue lurker candidates in open clusters