Complementing Gaia from the ground
Le jeudi 14 février à 14h dans la salle de conférences de l’observatoire
par Herve Bouy, Center for Astrobiology, Madrid
Abstract : The galaxy includes large structures such as clusters, star forming regions, and OB associations. Understanding the formation and evolution of these components has been one of the greatest challenges of modern astrophysics. The future Gaia mission will provide an exquisite accuracy and complete 6-D census of the sky up to V 15 mag, and a 5 dimension census up to V 20 mag. Although it represents a tremendous improvement with respect to its predecessor Hipparcos, Gaia will unfortunately not be sensitive enough to study the least massive objects. V 20 mag indeed corresponds to 25 MJup at 100 pc and for an age of 1 Myr, when the mass function is known to extend at least down to 3∼4 MJup. Additionally, young stellar clusters and associations are very often deeply embedded and contain bright H II regions. Since it will operate in the visible part of the spectrum, Gaia will be mostly blind in these regions, where precisely most of the star formation is taking place. Deeper kinematic surveys at longer wavelengths are therefore needed. Taking advantage of the wide field surveys performed in the early 2000, the DANCe survey (Dynamical Analysis of Nearby ClustErs) is performing a comprehensive study of kinematics in a large number of nearby associations and clusters. The initial surveys reached sensitivities well beyond the substellar limit at the age and distance of these associations. Complementing archival data with new sensitive wide field observations, we are compiling a multi-epoch panchromatic database encompassing large (several tens of square degrees) areas of young nearby associations. This database is used to derive accurate transverse motions for all sources with multi-epoch detections, using a new set of tools and algorithm optimized for precision astrometry. Depending on the magnitude and observational history, our new algorithms allow us to achieve an estimated accuracy as good as 0.5 mas/yr, but at longer wavelength and well beyond Gaia’s limit of sensitivity (up to i=22 23mag). The applications and scientific cases that can be addressed using this unprecedented database are numerous and include, among others, the study of mass function and internal dynamics, the search for solar system bodies, the search for white dwarfs and nearby brown dwarfs and the study of the galactic dynamics and galactic populations in the corresponding line of sight.