Paper: astro-ph/0605107
Date: Wed, 3 May 2006 20:16:22 GMT (33kb)

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

Authors: Jonay I. Gonzalez Hernandez, Rafael Rebolo, Garik Israelian, Emilios
T. Harlaftis, Alexei V. Filippenko and Ryan Chornock

Comments: Accepted for publication as a letter in The Astrophysical Journal
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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.

\\ ( http://arXiv.org/abs/astro-ph/0605107 , 33kb)