2018MNRAS.479.3101B -
Mon. Not. R. Astron. Soc., 479, 3101-3105 (2018/September-3)
A critical re-evaluation of the Thorne-Zytkow object candidate HV 2112.
BEASOR E.R., DAVIES B., CABRERA-ZIRI I. and HURST G.
Abstract (from CDS):
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-Zytkow object (TZO), 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 TZO candidate, HV 11417, which seems to be enriched in Rb but for which we cannot determine a Li abundance.
Abstract Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Journal keyword(s):
stars: abundances - stars: individual: HV 2112 - stars: peculiar - supergiants
Simbad objects:
10
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