Lundi 18 février 2013, 14:00, salle de l'entresol

Complementing Gaia from the ground

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.

Pour plus d'informations : page web de Hervé Bouy