EDP Sciences
Free access
Volume 397, Number 2, January II 2003
Page(s) 747 - 756
Section Formation and evolution of planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20021536

A&A 397, 747-756 (2003)
DOI: 10.1051/0004-6361:20021536

The photospheric abundances of active binaries

I. Detailed analysis of HD 113816 (IS Vir) and HD 119285 (V851 Cen)
D. Katz1, 2, F. Favata1, S. Aigrain1, 3 and G. Micela4

1  Astrophysics Division - Research and Science Support Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
2  Observatoire de Paris, GEPI, Place Jules Janssen, 92195 Meudon, France
3  Institute of Astronomy, Madingley Road, Cambridge, UK
4  Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

(Received 8 March 2002 / Accepted 15 October 2002 )

The high-resolution optical spectra of the two X-ray active binaries RS CVn stars HD 113816 (IS Vir) and HD 119285 (V851 Cen) are analysed and their Na, Mg, Al, Si, Ca, Sc, Ti, Co and Ni contents determined, in the framework of a larger program of chemical analysis of RS CVn stellar atmosphere. The analysis of IS Vir and V851 Cen is performed with three different LTE methods. In the first one, abundances are derived for a large set of transitions (among which 28 Fe I lines, spanning a broad interval in excitation potential and equivalent width, and 6 Fe II transitions) using measured equivalent widths and Kurucz LTE model atmospheres as input for the MOOG software package. The input atmospheric parameters and abundances are iteratively modified until (i) the Fe I abundances exhibit no trend with excitation potential or equivalent width, (ii) Fe I and Fe II average abundances are the same and (iii) Fe and Alpha elements average abundances are consistent with the input values. The second method follows a similar approach, but uses a restricted line list (without the Fe I "low excitation potential" transitions) and relies on the B-V and V-I colour indices to determine the temperature. The third method uses the same restricted line list as the second method and relies on fitting the 6162 Å Ca I line wing profiles to derive the surface gravity. The reliability of these methods is investigated in the context of single line RS CVn stars. It is shown that the V-I photometric index gives, on a broader sample of stars, significantly cooler estimates of the effective temperature than the B-V index. All approaches give results in good agreement with each other, except the V-I based method. The analysis of IS Vir and V851 Cen results in both cases in their primaries being giant stars of near-solar metallicity. Their parameters as derived with the first method are respectively $T_{\rm eff} = 4720$ K, $\log g = 2.65$, ${\rm [Fe/H]} = +0.04$ and $T_{\rm eff} = 4700$ K, $\log g =
3.0$ and ${\rm [Fe/H]} = -0.13$. In the case of V851 Cen the derived iron content is significantly higher than a previous determination in the literature. Both stars exhibit relative overabundances of several elements (e.g. Ca) with respect to the solar mix.

Key words: stars: fundamental parameters -- stars: abundances -- stars: individual: HD 113816, HD 119285

Offprint request: D. Katz, david.katz@obspm.fr

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