A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups

摘要

Context. Nearby late-type stars are excellenttargets for seeking young objects in stellar associations and movinggroups. The origin of these structures is still misunderstood, andlists of moving group members often change with time and also fromauthor to author. Most members of these groups have been identified bymeans of kinematic criteria, leading to an important contamination ofprevious lists by old field stars. Aims. We attempt to identify unambiguous movinggroup members among a sample of nearby-late type stars by studyingtheir kinematics, lithium abundance, chromospheric activity, and otherage-related properties. Methods. High-resolution echelle spectra ()of a sample of nearby late-type stars are used to derive accurateradial velocities that are combined with the precise Hipparcosparallaxes and proper motions to compute galactic-spatial velocitycomponents. Stars are classified as possible members of the classicalmoving groups according to their kinematics. The spectra are also usedto study several age-related properties for young late-type stars,i.e., the equivalent width of the lithium Li I6707.8?lineor the index. Additional information like X-ray fluxes from the ROSAT All-SkySurvey or the presence of debris discs is also taken into account. Thedifferent age estimators are compared and the moving group membershipof the kinematically selected candidates are discussed. Results. From a total list of 405nearbystars, 102 have been classified as moving group candidates according totheir kinematics. i.e., only 25.2% of the sample. Thenumber reduces when age estimates are considered, and only26moving group candidates (25.5% of the102candidates) have ages in agreement with the star havingthe same age as an MGmember. Key words: stars: late-type - stars:kinematics and dynamics - open clusters and associations: general