EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 413/2 Article
Free access article

Issue A&A
Volume 413, Number 2, January II 2004
Page(s) 643 - 655
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20034045



A&A 413, 643-655 (2004)
DOI: 10.1051/0004-6361:20034045

X-ray spectroscopy of the Hertzsprung-gap giant star 31 Com, observed with XMM-Newton

L. Scelsi1, A. Maggio2, G. Peres1 and Ph. Gondoin3

1  Dipartimento di Scienze Fisiche ed Astronomiche, Sezione di Astronomia, Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
2  INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
3  Research and Scientific Support Department, ESA-ESTEC, Noordwijk, The Netherlands

(Received 3 July 2003 / Accepted 29 September 2003)

Abstract
We have analysed the XMM-Newton X-ray spectra of the yellow giant 31 Com with the aim of deriving information on the coronal structures of this archetypical Hertzsprung-gap star. To determine the emission measure distribution vs. temperature, EM(T), and the elemental abundances of the coronal plasma, with an accurate line-based approach, we have developed a new method for simple and accurate line measurements, based on rebinning and co-adding the two RGS spectra. We have reconstructed the  EM(T) independently with both APED and CHIANTI atomic databases in order to investigate possible differences in the final outcome of the analysis, and we have obtained consistent results. The derived emission measure distribution has a well defined peak at $T \sim 10^{7}$ K and a significant amount of plasma at higher temperatures; there is also evidence for plasma at temperatures below ~ 106.5 K, with a mean electron density of ~ $3 \times 10^{10}$ cm -3, as inferred from the line ratio of the $\ion{O}{vii}$ triplet. We have made a global fitting of the EPIC spectra, using multi-component isothermal (3-T) model, and then compared the results with the EM(T), looking for a consistent multi-temperature description of both the RGS and EPIC spectra, over the whole spectral range. While the EM(T) and the 3-T models individually provide a good description of the data set on which they are based, none of them describes adequately the data of all the other instruments; the disagreements may be related, at least in part, to cross-calibration problems. Finally, we have used the EM(T) to derive information about the properties of the coronal structures. Our results indicate that the corona of 31 Com is dominated by a class of magnetic loops with peak temperature ~ 107 K and apparently more isothermal than the solar ones.


Key words: X-rays: stars -- techniques: spectroscopic -- stars: activity -- stars: coronae -- stars: individual: 31 Com

Offprint request: L. Scelsi, scelsi@oapa.astropa.unipa.it

SIMBAD Objects in preparation



© ESO 2004


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.