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The black hole binary nova Scorpii 1994 (GRO J1655-40): an improved chemical analysis
Context: The chemical analysis of secondary stars of low mass X-raybinaries provides an opportunity to study the formation processes ofcompact objects, either black holes or neutron stars. Aims:Following the discovery of overabundances of ?-elements in theKeck I/HIRES spectrum of the secondary star of Nova Scorpii 1994(Israelian et al. 1999, Nature, 401, 142), we obtained VLT/UVEShigh-resolution spectroscopy with the aim of performing a detailedabundance analysis of this secondary star. Methods: Using a?2-minimization procedure and a grid of synthetic spectra, we derivethe 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 consistentwith solar values, whereas Na, and especially O, Mg, Si and S aresignificantly enhanced in comparison with Galactic trends of theseelements. A comparison with spherically and non-spherically symmetricsupernova explosion models may provide stringent constraints to themodel parameters as mass-cut and the explosion energy, in particularfrom the relative abundances of Si, S, Ca, Ti, Fe and Ni. Conclusions: Most probably the black hole in this system formed in ahypernova explosion of a 30-35 {M}_&sun; progenitor star with a mass-cutin the range 2-3.5 {M}_&sun;. However, these models produce abundancesof Al and Na almost ten times higher than the observed values.Basedon observations obtained with UVES at VLT Kueyen 8.2 m telescope inprogramme 073.D-0473(A).
| Precise positions in the FK4 system for 120 radio source reference stars
Positions are given in the FK4 system for 120 primary reference starsgrouped around the optical counterparts of 11 extragalactic radiosources. The observations were made in 1979 and 1980 with the 6-in.transit circle of the U.S. Naval Observatory. The results reported hererepresent the first step in a three-tiered process to determineastrometric positions of the optical counterparts referred to the systemof the FK4. One application of such positions is the determination of anearly inertial optical reference frame, which eventually may becompared to a reference frame at radio wavelengths.
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