The galactic orbits of nearby, high-velocity stars.

. We have used a recently developed model for the galactic mass distribution (Allen and Martos 1986, Rev. Mex. Astron. Astrof. in press, and this conference) to numerically integrate the galactic orbits of 10 nearby stars. The stars were chosen for their intrinsic interest, as well as for the fact that, since their space velocities are large, the usual approxiination to the galactic orbits is likely to be poor for them. The orbits were integrated backwards in time for 1.2x101O years. Errors in the total energy and in the of the angular momentum were of the order of Ah/h < AE/E < at the end of a run. The computed orbits do indeed strongly deviate from circular orbits. The stars undergo very large excursions in the radial coordinate (of up to 9 kpc), but they reach in general only moderately high distances from the galactic plane (not more than 1.5 kpc). Their galactic periods of revolution are between 1.3 and 2.3 Gy, a'0d thus sane- what longer than those expected for nearby stars. The most eccentric orbit computed corresponds to Gl 191 (Kapteyn' S star); it is also retrograde. Gl 699 (Barnard' s star) reaches the largest apogalactic distance (15.6 kpc), and G1 445 the largest height above and below the galactic plane. As a rule, the computed orbits are of box type; there are two exceptions: the orbits of the triple system G1 166 (40 Eridani) and of Gl 699 (Barnard's star), which are of shell type. On the basis of their orbits, these nearby, high-velocity stars can be classified as belonging to a very old, thisk disk population. Their observed spectra and colors are, on the whole, not inconsistent with this classification. Further details about this work can be found in Allen and Martos 1986, Rev. MexicanaAstron. Astrof., Vol. 13,137. KeU wo)t : STARS-DYNAMICS