We present an H-band image of the companion of \chi ^ { 1 } 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 ( M _ { A } = 1.01 \pm 0.13 { M } _ { \odot } , M _ { B } = 0.15 \pm 0.02 { M } _ { \odot } ) , and to study stellar evolutionary models at a wide spread of masses .
The application of [ Baraffe et al .
( 1998 ) ] 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 .