Field Brown Dwarfs & GAIA

Abstract

Because of their very red colours and intrinsic faintness, field browndwarfs will represent a small but valuable subset of the GAIAcatalogue. The return of the astrometric satellite is expected to beimportant because of the inherent difficulty of obtaining goodparallaxes in general and for this class of objects in particular. Ourfirst estimates show that, due to the photometric sensitivity of theastrometric CCD (ASM1) towards relatively blue objects, GAIA isunlikely to detect field brown dwarfs that have not been already seenis previous near-IR surveys, to the notable exception of the galacticplane region. The real advantage of GAIA over ground-based surveyswill be the very accurate (to within a few percents) astrometric datafor a few thousands brown dwarfs. These data should permit a detailedmapping of the transition region between stellar and substellarregimes, together with the kinematical and density patterns of theyoungest brown dwarfs in our neighbourhood.