Low Metallicity Indicates that the Hypervelocity Star HE 0437-5439 was Ejected from the LMC

TL;DR

This study measures the metallicity and physical properties of hypervelocity star HE 0437-5439, confirming its origin in the Large Magellanic Cloud and suggesting a massive black hole presence there.

Contribution

It provides the first high-resolution spectroscopic metallicity measurement of HE 0437-5439, linking its origin to the LMC and implying a massive black hole in that galaxy.

Findings

Metallicity of HE 0437-5439 is half-solar.

Star's spectral type is B2 IV-III.

Star's properties confirm LMC origin.

Abstract

We measure the metallicity of the unusual hypervelocity star HE 0437-5439 from high resolution spectroscopy to be half-solar. We determine a spectral type of B2 IV-III for the star and derive an effective temperature Teff= 21,500 +/- 1,000 K and a surface gravity log(g) = 3.7 +/- 0.2 (cgs). We also present BV time series photometry and find the star to be non-variable at the 0.02 mag level. We refine the magnitude of the hypervelocity star to V=16.36+/-0.04 mag, with a color B-V=-0.23+/-0.03 mag, confirming its early-type nature. Our metallicity result establishes the origin of HE 0437-5439 in the Large Magellanic Cloud and implies the existence of a massive black hole somewhere in this galaxy.