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XTE J1118+480: A Metal-Rich Black Hole Binary in the Galactic Halo

Jonay I. Gonzalez Hernandez·Rafael Rebolo·Garik Israelian·Emilios T. Harlaftis·Alexei V. Filippenko·Ryan Chornock
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Abstract

We present medium-resolution optical spectra of the secondary star in the high Galactic latitude black hole X-ray binary XTE J1118+480 and determine the abundance of Mg, Al, Ca, Fe, and Ni in its atmosphere. For all the elements investigated we find supersolar abundances; thus, we reject the hypothesis that the black hole came from the direct collapse of an ancient massive halo star. The compact primary most likely formed in a supernova event of a massive star whose nucleosynthetic products polluted the secondary star. The observed element abundances and their ratios can be explained using a variety of supernova models with a wide range of metallicities. While an explosive origin in the Galactic halo or thick disk cannot be discarded, a metal-rich progenitor is clearly favored by the observed abundance pattern. This suggests that the black hole was produced in the Galactic thin disk with a violent natal kick, propelling the X-ray binary to its current location and orbit.

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Jonay I. Gonzalez Hernandez, Rafael Rebolo, Garik Israelian, Emilios T. Harlaftis, Alexei V. Filippenko, Ryan Chornock. 2006-05-03. XTE J1118+480: A Metal-Rich Black Hole Binary in the Galactic Halo. https://doi.org/10.1086/505391

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