Letter to the Editor

Direct detection of the companion of Orionis

¹ Max-Planck-Institut für extraterrestrische Physik, Gießenbachstraße 1, 85748 Garching, Germany
² California Institute of Technology, 105-24 (Astronomy) 1200 E. California Blvd., Pasadena, CA 91125, USA
³ Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA

Corresponding author: B. König, bkoenig@mpe.mpg.de

Received: 28 August 2002
Accepted: 18 September 2002

Abstract

We present an H-band image of the companion of  Orionis taken with the Keck adaptive optic system and NIRC 2 camera equipped with a 300 mas-diameter coronographic mask. The direct detection of this companion star enables us to calculate dynamical masses using only Kepler's laws (, ), and to study stellar evolutionary models at a wide spread of masses. The application of Baraffe et al. ([CITE]) pre-main-sequence models implies an age of 70–130 Myrs. This is in conflict to the age of the primary, a confirmed member of the Ursa Major Cluster with a canonical age of 300 Myrs. As a consequence, either the models at low masses underestimate the age or the Ursa Major Cluster is considerably younger than assumed.