EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 464/ 3 Article

Free access article

Issue A&A
Volume 464, Number 3, March IV 2007
Page(s) L61 - L64
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20077106



A&A 464, L61-L64 (2007)
DOI: 10.1051/0004-6361:20077106

Letter

On the abundances of GRO J1655-40

C. Foellmi1, 2, T. H. Dall3, and E. Depagne1, 4

1  European Southern Observatory, 3107 Alonso de Cordova, Casilla 19001, Vitacura, Santiago, Chile
    e-mail: cfoellmi@eso.org
2  Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
3  Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720, USA
4  Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Campus San Joaquín, Vicuña Mackenna 4860, Casilla 306, Santiago 22, Chile

(Received 16 January 2007 / Accepted 1 February 2007 )

Abstract
Context.The detection of overabundances of $\alpha$-elements and lithium in the secondary star of a black-hole binary provides important insights about the formation of a stellar-mass black-hole. $\alpha$-enhancement might theoretically also be the result of pollution by the nucleosynthesis occurring during an outburst, or through spallation by the jet.
Aims.We study the abundances, and their possible variations with time, in the secondary star of the runaway black-hole binary GRO J1655-40, in order to understand their origin.
Methods.We present a detailed comparison between a Keck spectrum obtained in 1998 found in the literature, archival VLT-UVES data taken in 2004 and new VLT-UVES spectra obtained early 2006. We carefully determine the equivalent widths of different $\alpha$-elements (Mg, O, Ti, S and Si) with their associated uncertainty. We use the well-studied comparison star HD 156098 as well as synthetic spectra to match the spectrum of GRO J1655-40 in order to determine the abundances of these elements.
Results.We see no significant variations of equivalent widths with time. Our fit using HD 156098 reveals that there is significant overabundance of oxygen in all our spectra, but no overabundances of any of the other $\alpha$-elements. Finally, we do not detect the lithium line at 6707 Å.
Conclusions.We show that there is no detected pollution in GRO J1655-40 after the burst in 2005. Moreover, we argue that uncertainties in the equivalent widths were previously underestimated by a factor of ~3. Consequently, our results challenge the existence of general overabundances of $\alpha$-elements observed in this galactic black-hole binary, and thus the accepted interpretation that they are of supernova origin. The physical cause of the overabundance of oxygen remains unclear.


Key words: stars: abundances -- X-rays: binaries -- stars: binaries: spectroscopic -- stars: individual: GRO J1655-40



© ESO 2007

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.