New triple systems in the RasTyc sample of stellar X-ray sources ^*,**,***

¹ Observatoire Astronomique, Université de Strasbourg & CNRS (UMR 7550), 11 rue de l'Université, 67000 Strasbourg, France e-mail: klutsch@astro.u-strasbg.fr
² INAF – Osservatorio Astrofisico di Catania, via S. Sofia, 78, 95123 Catania, Italy
³ Dipartimento di Fisica e Astronomia, Università di Catania, via S. Sofia, 78, 95123 Catania, Italy
⁴ ESO – European Southern Observatory, Karl-Schwarzschild-Str. 3, 85748 Garching bei München, Germany

Received: 6 May 2008
Accepted: 22 July 2008

Abstract

Context. During the study of a large set of late-type stellar X-ray sources, we discovered a high fraction of multiple systems.

Aims. In this paper we investigate the orbital elements and kinematic properties of three new spectroscopic triple systems, along with the spectral types and astrophysical parameters (T_eff, log g, v sin i, log N(Li)) of their components.

Methods. We conducted follow-up optical observations of these systems, both photometric and spectroscopic ones at high resolution. We used a synthetic approach and the cross-correlation method to derive most of the stellar parameters.

Results. We estimated reliable radial velocities and deduced the orbital elements of the inner binaries. The comparison of the observed spectra with synthetic composite ones, obtained as the weighted sum of three spectra of non-active reference stars, allowed us to determine the stellar parameters for each component of these systems. We found all are only composed of main sequence stars.

Conclusions. These three systems are certainly stable hierarchical triples composed of short-period inner binaries plus a tertiary component in a long-period orbit. From their kinematics and/or lithium content, these systems turn out to be fairly young.