The galactic orbits of nearby UV Ceti stars

The galactic orbits of 93 UV Ceti stars of the solar neighborhood have been numerically integrated. The UV Ceti stars studied are those of the working list for which Poveda et al. (1996) determined kinematic properties and ages. All stars are contained within 25 pc of the sun, and values for their distances, proper motions and radial velocities are available for them (Gliese & Jahreiss 1991). The galactic potential model of Allen & Santillan (1991) was used, and the orbits were integrated for times similar to the age of the old disk. The galactic orbital parameters are obtained. The orbits are all regular, and the values found for the orbital parameters are similar to those characteristic of the classic young thin disk. The vertical scale height found for the whole sample is 115 pc. However, the orbital parameters found for the 7 objects with extreme kinematic characteristics recognized in Poveda et al. are markedly different from those of the rest of the flare stars; in particular, their orbital eccentricities are larger than 0.3. The vertical scale height of the sample excluding the anomalous objects is just 103 pc. Consequently, we propose that the anomalous objects belong to the thick disk, which may be characterized by either e >= 0.3 or |z max| > 400 pc.