ASTRA: ASTrometry and phase-Referencing Astronomy on the Keck   interferometer
  ASTRA (ASTrometric and phase-Referencing Astronomy) is an upgrade to the existing Keck Interferometer which aims at providing new self-phase referencing (high spectral resolution observation of YSOs), dual-field phase referencing (sensitive AGN observations), and astrometric (known exoplanetary systems characterization and galactic center general relativity in strong field regime) capabilities. With the first high spectral resolution mode now offered to the community, this contribution focuses on the progress of the dual field and astrometric modes. 
J. Woillez, R. Akeson, M. Colavita, J. Eisner, A. Ghez, J. Graham, L.   Hillenbrand, R. Millan-Gabet, J. Monnier, J.-U. Pott...
astro-ph.IM