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We present a chemical abundance analysis of the secondary star in the blackhole binary V404 Cygni, using Keck I/HIRES spectra. We adopt a$\chi^2$-minimization procedure to derive the stellar parameters, taking intoaccount any possible veiling from the accretion disk. With these parameters wedetermine the atmospheric abundances of O, Na, Mg, Al, Si, Ca, Ti, Fe, and Ni.The abundances of Al, Si, and Ti appear to be slightly enhanced when comparingwith average values in thin-disk solar-type stars. The O abundance, derivedfrom optical lines, is particularly enhanced in the atmosphere of the secondarystar in V404 Cygni. This, together with the peculiar velocity of this system ascompared with the Galactic velocity dispersion of thin-disk stars, suggeststhat the black hole formed in a supernova or hypernova explosion. We exploredifferent supernova/hypernova models having various geometries to studypossible contamination of nucleosynthetic products in the chemical abundancepattern of the secondary star. We find reasonable agreement between theobserved abundances and the model predictions. However, the O abundance seemsto be too high regardless of the choice of explosion energy or mass cut, whentrying to fit other element abundances. Moreover, Mg appears to beunderabundant for all explosion models, which produces Mg abundances roughly 2times higher than the observed value.

Chemical Abundances of the Secondary Star in the Black Hole X-Ray Binary V404 Cygni