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

Abstract

It has been argued in the literature that the star HV~2112 in the Small Magellanic Cloud is the first known example of a TŻO, a Red Supergiant with a degenerate neutron core. This claim is based on the star having a high luminosity ($\log (L/L_{\odot })$~> 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-IR for HV~2112 and integrating under it's spectral energy distribution we find a bolometric luminosity in the range of $\log (L/L_{\odot })$=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($\sim$5M${}_{\odot }$) 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.

arXiv commentAccepted for publication in MNRAS, 5 pages, 4 figures

References in corpus (20)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Spitzer Space Telescope Mission
• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• MESA Isochrones and Stellar Tracks (MIST) 0: Methods for the construction of stellar isochrones
• A Quantitative Comparison of SMC, LMC, and Milky Way UV to NIR Extinction Curves
• The Effective Temperature Scale of Galactic Red Supergiants: Cool, But Not As Cool As We Thought
• The Magellanic Clouds Photometric Survey: The Small Magellanic Cloud Stellar Catalog and Extinction Map
• Spectral synthesis including massive binaries
• The Effective Temperatures and Physical Properties of Magellanic Cloud Red Supergiants: The Effects of Metallicity
• The temperatures of Red Supergiants
• The DENIS Point Source Catalogue towards the Magellanic Clouds
• The luminosities of cool supergiants in the Magellanic Clouds, and the Humphreys-Davidson limit revisited
• Radiative hydrodynamics simulations of red supergiant stars. IV gray versus non-gray opacities
• Luminosities and mass-loss rates of Local Group AGB stars and Red Supergiants
• Discovery of a Thorne-Zytkow object candidate in the Small Magellanic Cloud
• HV2112, a Thorne-Zytkow Object or a Super Asymptotic Giant Branch Star
• Large proper motion of the Thorne-Żytkow object candidate HV 2112 reveals its likely nature as foreground Galactic S-star
• The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. IV. Long-Period Variables in the Large Magellanic Cloud
• Gaia DR2 confirms that candidate Thorne-Żytkow object HV 2112 is in the SMC

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