On the candidate Thorne Zytkow Object HV 2112: foreground S star.

1 Jan

Thorne and Zytkow and others hypothesised that, when a neutron star sinks inside another star, a stable star like object would be formed.  For decades astronomers have been trying to unambiguously detect this exotic object. Several suggestions were made. By far the most promising candidate appeared to be a red luminous star located in the southern sky HV 2112, as pointed out by Emily Levesque. The star shows evidence for having a strange chemical composition and, if indeed located in the Small Magelanic Cloud, would have been extraordinarily bright.

We show that the object has a large proper motion, meaning that it should be located much closer in the fore ground.  If this measurement is robust, it would exclude its TZO nature.  To explain the abundance patterns we propose a standard binary scenario for extrinsic S stars. Here, the Mo and Rb came from the wind of a former AGB binary companion, Li is made in situ by the star itself as it rises to it’s own AGB phase.  The Ca and K composition are naturally explained by this scenario where the star is part of the very old galactic Halo, where alpha enhanced compositions are normal.