The black hole binary nova Scorpii 1994 (GRO J1655-40): an improved chemical analysis
Résumé
Context: The chemical analysis of secondary stars of low mass X-ray binaries provides an opportunity to study the formation processes of compact objects, either black holes or neutron stars.
Aims: Following the discovery of overabundances of alpha-elements in the Keck I/HIRES spectrum of the secondary star of Nova Scorpii 1994 (Israelian et al. 1999, Nature, 401, 142), we obtained VLT/UVES high-resolution spectroscopy with the aim of performing a detailed abundance analysis of this secondary star.
Methods: Using a chi2-minimization procedure and a grid of synthetic spectra, 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.
Results: The abundances 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 in comparison with Galactic trends of these elements. A comparison with spherically and non-spherically symmetric supernova explosion models may provide stringent constraints to the model parameters as mass-cut and the explosion energy, in particular from the relative abundances of Si, S, Ca, Ti, Fe and Ni.
Conclusions: Most probably the black hole in this system formed in a hypernova explosion of a 30-35 {M}_&sun; progenitor star with a mass-cut in the range 2-3.5 {M}_&sun;. However, these models produce abundances of Al and Na almost ten times higher than the observed values.
Aims: Following the discovery of overabundances of alpha-elements in the Keck I/HIRES spectrum of the secondary star of Nova Scorpii 1994 (Israelian et al. 1999, Nature, 401, 142), we obtained VLT/UVES high-resolution spectroscopy with the aim of performing a detailed abundance analysis of this secondary star.
Methods: Using a chi2-minimization procedure and a grid of synthetic spectra, 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.
Results: The abundances 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 in comparison with Galactic trends of these elements. A comparison with spherically and non-spherically symmetric supernova explosion models may provide stringent constraints to the model parameters as mass-cut and the explosion energy, in particular from the relative abundances of Si, S, Ca, Ti, Fe and Ni.
Conclusions: Most probably the black hole in this system formed in a hypernova explosion of a 30-35 {M}_&sun; progenitor star with a mass-cut in the range 2-3.5 {M}_&sun;. However, these models produce abundances of Al and Na almost ten times higher than the observed values.