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A critical re-evaluation of the Thorne-Zytkow object candidate HV 2112

Beasor, ER, Davies, B, Cabrera-Ziri, I and Hurst, G (2018) A critical re-evaluation of the Thorne-Zytkow object candidate HV 2112. Monthly Notices of the Royal Astronomical Society, 479 (3). pp. 3101-3105. ISSN 0035-8711

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Abstract

It has been argued in the literature that the star HV 2112 in the Small Magellanic Cloud (SMC) is the first known example of a Thorne–Żytkow object (TŻO), a red supergiant with a degenerate neutron core. This claim is based on the star having a high luminosity (log (L/L⊙) ≳ 5), an extremely cool effective temperature, and a surface enriched in in lithium, calcium, and various irp-process elements. In this paper we re-examine this evidence, and present new measurements of the stellar properties. By compiling archival photometry from blue to mid-infrared for HV 2112 and integrating under its spectral energy distribution, we find a bolometric luminosity in the range of log (L/L⊙) = 4.70–4.91, lower than that found in previous work and comparable to bright asymptotic giant branch (AGB) stars. We compare a VLT+XSHOOTER spectrum of HV 2112 to other late-type, luminous SMC stars, finding no evidence for enhancements in Rb, Ca, or K, though there does seem to be an enrichment in Li. We therefore conclude that a much more likely explanation for HV 2112 is that it is an intermediate mass (∼5 M⊙) AGB star. However, from our sample of comparison stars we identify a new TŻO candidate, HV 11417, which seems to be enriched in Rb but for which we cannot determine a Li abundance.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 16 Oct 2018 12:11
Last Modified: 18 Oct 2018 14:12
DOI or Identification number: 10.1093/mnras/sty1744
URI: http://researchonline.ljmu.ac.uk/id/eprint/9489

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