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

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. Subject headings: galaxies: individual (LMC) — stellar dynamics — stars: abundances — stars: early type — stars: individual (HE 0437–5439) Based on observations made with the European Southern Observatory telescopes obtained from the ESO/ST-ECF Science Archive Facility and with the 1 meter Henrietta Swope telescope located at Las Campanas Observatory, Chile. Vera Rubin Fellow. Hubble Fellow.