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
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.
© ESO, 2002