We have reanalyzed data for the proposed moving group associated with \beta Pictoris in order to determine if the group ( or part of it ) is real , and , if so , to derive an improved age estimate for \beta Pic .
By using new , more accurate proper motions from PPM and Hipparcos and a few new radial velocities , we conclude that on kinematic grounds most of the proposed members of the moving group are not , in fact , associated with \beta Pic .
However , two M dwarfs - or three , actually , since one of them is a nearly equal mass binary - have space motions that coincide with that of \beta Pic to within 1 km/s with small error bars .
Based on a color-magnitude diagram derived from accurate photometry and Hipparcos parallaxes , these two possible proper-motion companions to \beta Pic are very young ; we derive an age of \sim 20 Myr by comparison to theoretical tracks from D ’ Antona & Mazzitelli .
In fact , the proposed \beta Pic companions comprise two of the three youngest M dwarfs in the sample of 160 dM stars for which we have data .
The chromospheric and coronal activity of these two stars also confirm that they are quite young .
We argue that the probability that two of the three youngest nearby M dwarfs would accurately share the space motion of \beta Pic by chance is quite small , and therefore we believe that \beta Pic and the two M dwarfs ( GL 799 and GL 803 ) were formed together .
The estimated age for \beta Pic is then 20 \pm 10 Myr , where the uncertainty in the age arises primarily from possible errors in the PMS isochrones and in the conversion from color to effective temperature .
This young age for \beta Pic supports the contention that the IR-excess for the Vega-like stars is age dependent .