KINEMATICS, AGES, AND EVOLUTIONARY STATUS OF UV CETI STARS

The kinematic properties of 93 UV Ceti stars of the solar neighborhood are studied, based on a list of flares within 25 pc of the Sun (pi gr eater than or equal to 0.04 ''). With updated values for their distanc es, proper motions and radial velocities, space velocity dispersions a re calculated for these stars. It is found that the total velocity dis persion of the flare stars (sigma = 30 +/- 3 km s(-1)) is similar to t hat of the F5 V stars from the same catalogue, for which the conventio nally estimated mean age is about 3 10(9) yr. Membership of the flare stars to some well-identified kinematic groups and superclusters is st udied. A number of flares are identified as members of the Hyades, Sir ius or Pleiades groups. The velocity dispersions found for the nearby flare stars and the membership of some of them to young kinematic grou ps indicate that they belong to the young disk population. The evoluti onary status of the UV Ceti stars is discussed on the basis of these r esults. It is concluded that they do not differ significantly from the flash stars and that, indeed, they may be identified with the older r emnants of the flash population of galactic clusters long ago disrupte d. A small number (7) of UV Ceti stars have kinematics corresponding t o thick disk or halo population. Their long-lived chromospheric activi ty is interpreted as due to coalescence of old short-period binaries. The question of the age of Proxima Centauri is examined in the context of our results, and found to be compatible with the ages of Alpha Cen tauri A and B.