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arXiv · 2102.13375

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

Vikrant V. Jadhav·Sindhu Pandey·Annapurni Subramaniam·Ram Sagar
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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.

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Vikrant V. Jadhav, Sindhu Pandey, Annapurni Subramaniam, Ram Sagar. 2021-02-26. UOCS. IV. Discovery of diverse hot companions to blue stragglers in the old open cluster King 2. https://doi.org/10.1007/s12036-021-09746-y

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