Context and Motivations
The on-going Gaia space mission will provide an exquisite astrometric accuracy and complete 6 dimension census of the sky up to G≈15 mag, and a 5 dimension census up to G≈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 and the core of young associations.
A luminosity of G≈20 mag indeed corresponds to ≈20 MJup at 150 pc and for an age of 3 Myr (typical of young nearby associations), 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 the regions of heavy extinction and bright nebular emission (see animation to the right), where precisely most of the star formation is taking place. Deeper and longer wavelength (infrared, to see "through" the cloud) observations are required.
There is therefore a strong need to complement Gaia:
1. beyond its sensitivity limit to reach the least massive sub-stellar objects, by using deeper images
2. in the embedded cores of young nearby associations, by using infrared images
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© Last Update: 02-05-2017 by H. Bouy