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Discovery of a Thorne-Żytkow object candidate in the Small Magellanic Cloud

Published online by Cambridge University Press:  23 January 2015

Emily M. Levesque ,
Philip Massey ,
Anna N. Żytkow  and
Nidia Morrell
Emily M. Levesque
Affiliation:
Center for Astrophysics & Space Astronomy, University of Colorado UCB 389, Boulder, CO 80309, USA; Hubble Fellow email: Emily.Levesque@colorado.edu
Philip Massey
Affiliation:
Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001, USA
Anna N. Żytkow
Affiliation:
Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
Nidia Morrell
Affiliation:
Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile
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Abstract

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Thorne-Żytkow objects (TŻOs) are a theoretical class of star in which a compact neutron star is surrounded by a large, diffuse envelope. Supergiant TŻOs are predicted to be almost identical in appearance to red supergiants (RSGs), with their very red colors and cool temperatures placing them at the Hayashi limit on the H-R diagram. The only features that can be used at present to distinguish TŻOs from the general RSG population are the unusually strong heavy-element and lithium lines present in their spectra. These elements are the unique products of the stars fully convective envelope linking the photosphere with the extraordinarily hot burning region in the vicinity of the neutron star core. We have recently discovered a TŻO candidate in the Small Magellanic Cloud. It is the first star to display the distinctive chemical profile of anomalous element enhancements thought to be characteristic of TŻOs; however, up-to-date models and additional observable predictions (including potential asteroseismological signatures) are required to solidify this discovery. The definitive detection of a TŻO would provide the first direct evidence for a completely new model of stellar interiors, a theoretically predicted fate for massive binary systems, and never-before-seen nucleosynthesis processes that would offer a new channel for heavy-element and lithium production in our universe.

Keywords

stars: peculiarsupergiantsvariables
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 9 , Issue S307: New windows on massive stars: asteroseismology, interferometry, and spectropolarimetry , June 2014 , pp. 57 - 63
Copyright
Copyright © International Astronomical Union 2015 

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