Indirect Planet Detection with Ground-based Long-baseline Interferometry

Narrow-angle astrometry with long-baseline infrared interferometers can provide extremely Klgh accuracies as required for indirect planet detection. Narrow-angle astrometric interferom~ try exploits the propertim of atmospheric turbulence over fieldn smaller than the interferometer bmeline divided by the atmospheric scale height. For such fields, wcuracy is linear with star separation, and nearly inversely proportional to baseline length. To exploit these properties, the interferometer observes a relatively bright (<13 ma~ ) target in the near infrared at 2.2 pm, and uses phase referencing to find a reference star withh the 2.2 pm iaoplanatic patch. With this technique faint references can be found for most targets. With bwdinea >100 m, whkh also minimize photon-noise errors, and with careful control of systematic errom by ueing laaer metrology, accuracies of tens of microarcaecon&/ = should be possible.