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UVIT Open Cluster Study. I. Detection of a White Dwarf Companion to a Blue Straggler in M67: Evidence of Formation through Mass Transfer

Sindhu, N. and Subramaniam, Annapurni and Jadhav, Vikrant V and Chatterjee, Sourav and Geller, Aaron M and Knigge, Christian and Leigh, Nathan and Puzia, Thomas H and Shara, Michael and Simunovic, Mirko (2019) UVIT Open Cluster Study. I. Detection of a White Dwarf Companion to a Blue Straggler in M67: Evidence of Formation through Mass Transfer. In: ASTROPHYSICAL JOURNAL, 882 (1).

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Official URL: https://dx.doi.org/10.3847/1538-4357/ab31a8

Abstract

The old open cluster M67, populated with blue straggler stars (BSSs), is a well-known test bed to study the BSS formation pathways. Here, we report the first direct detection of a white dwarf (WD) companion to a BSS in M67, using far-UV images from the Ultra-Violet Imaging telescope on ASTROSAT. Near-simultaneous observations in three far-UV bands combined with Galaxy Evolution Explorer, International Ultraviolet Explorer, and ground and space-based photometric data covering a 0.14-11.5 mu m range for WOCS1007 were found to require a binary fit to its spectral energy distribution (SED), consisting of a BSS and a hot companion. On the other hand, a single spectral fit was found to be satisfactory for the SEDs of two other BSSs, WOCS1006 and WOCS2011, with the latter showing a deficient far-UV flux. The hot companion of WOCS1007 is found to have a T-eff similar to 13,250-13,750 K and a radius of 0.09 +/- 0.01 R-circle dot. A comparison with WD models suggests it to be a low-mass WD (similar to 0.18M(circle dot)), in agreement with the kinematic mass from the literature. As a low-mass WD (<0.4M(circle dot)) necessitates formation through mass transfer in close binaries, WOCS1007 with a known period of 4.2 days along with its fast rotation, is likely to be formed by a case A or case B binary evolution.

Item Type: Journal Article
Additional Information: copyright for this article belongs to IOP PUBLISHING LTD
Keywords: open clusters and associations: individual (M67); stars: individual (blue stragglers, white dwarfs); ultraviolet: stars
Department/Centre: Division of Physical & Mathematical Sciences > Astronomy and Astrophysics Programme
Depositing User: Id for Latest eprints
Date Deposited: 24 Sep 2019 06:27
Last Modified: 24 Sep 2019 06:27
URI: http://eprints.iisc.ac.in/id/eprint/63636

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