Masses and age of the chemically peculiar double-lined binary χ Lupi^⋆,⋆⋆

¹ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, France
e-mail: jean-baptiste.lebouquin@obs.ujf-grenoble.fr
² European Organisation for Astronomical Research in the Southern Hemisphere (ESO), Casilla 19001, Santiago 19, Chile
³ CNRS/Univ. de Chile, Laboratoire Franco-Chilien d’Astronomie (LFCA), UMI 3386, Santiago, Chile

Received: 27 September 2012
Accepted: 8 January 2013

Abstract

Aims. We aim at measuring the stellar parameters of the two chemically peculiar components of the B9.5Vp HgMn + A2 Vm double-lined spectroscopic binary HD 141556 (χ Lup), whose period is 15.25 days.

Methods. We combined historical radial velocity measurements with new spatially resolved astrometric observations from PIONIER/VLTI to reconstruct the three-dimensional orbit of the binary, and thus obtained the individual masses. We fit the available photometric points together with the flux ratios provided by interferometry to constrain the individual sizes, which we compared to predictions from evolutionary models.

Results. The individual masses of the components are M_a = 2.84 ± 0.12 M_⊙ and M_b = 1.94 ± 0.09 M_⊙. The dynamical distance is compatible with the Hipparcos parallax. We find linear stellar radii of R_a = 2.85 ± 0.15 R_⊙ and R_b = 1.75 ± 0.18 R_⊙. This result validates a posteriori the flux ratio used in previous detailed abundance studies. Assuming coevality, we determine a slightly sub-solar initial metallicity Z = 0.012 ± 0.003 and an age of (2.8 ± 0.3) × 10⁸ years. Finally, our results imply that the primary rotates more slowly than its synchronous velocity, while the secondary is probably synchronous. We show that strong tidal coupling during the pre-main sequence evolution followed by a full decoupling at zero-age main sequence provides a plausible explanation for these very low rotation rates.