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The chemical analysis of secondary stars of low mass X-ray binaries providesan opportunity to study the formation processes of compact objects, eitherblack holes or neutron stars. Following the discovery of overabundances of$\alpha$-elements in the HIRES/Keck spectrum of the secondary star of NovaScorpii 1994 (Israelian et al. 1999), we obtained UVES/VLT high-resolutionspectroscopy with the aim of performing a detailed abundance analysis of thissecondary star. Using a $\chi2$-minimization procedure and a grid of syntheticspectra, we derive the stellar parameters and atmospheric abundances of O, Mg,Al, Ca, Ti, Fe and Ni, using a new UVES spectrum and the HIRES spectrum.Theabundances of Al, Ca, Ti, Fe and Ni seem to be consistent with solar values,whereas Na, and especially O, Mg, Si and S are significantly enhanced incomparison with Galactic trends of these elements. A comparison withspherically and non-spherically symmetric supernova explosion models mayprovide stringent constraints to the model parameters as mass-cut and theexplosion energy, in particular from the relative abundances of Si, S, Ca, Ti,Fe and Ni. Most probably the black hole in this system formed in a hypernovaexplosion of a 30--35 \Msun progenitor star with a mass-cut in the range 2--3.5\Msun. However, these models produce abundances of Al and Na almost ten timeshigher than the observed values.

The Black Hole Binary Nova Scorpii 1994 (GRO J1655-40): An improved chemical analysis