In this configuration, the field is split, so that two different objects can be observed simultaneously and sent to separate beam
combiners. One of the objects is a bright star used to track the atmospheric piston at a fast rate and stabilize the optical path
difference for the other beam combiner, which can now integrate for much longer times and thus obtain science data for faint objects. The
star used by the AO system can be the bright interferometer reference star, or it can be a third star, as described below. Angle tracking is
done separately for the reference and science stars. Currently fringe tracking is done at K band and angle tracking at H band. As with the
other observing modes, in this configuration observations of the
target/reference pair will be interleaved with observations of the
To maximize the science, performance characterization and engineering benefits of TAC-allocated science during the shared-risk availability, science teams are strongly encouraged to collaborate with the NSF-funded ASTRA development team throughout the science process from planning to publication (contact Julien Woillez, for more information about ASTRA). To recognize their contribution, publications based on DFPR data are strongly encouraged to include ASTRA team co-authors.
As of today, phase-referenced fringe tracking has been demonstrated on a K=12.5 star.
Proposals for DFPR mode MUST include the following items(note that the PI is responsible for identifying appropriate reference and calibrator objects as part of the proposal phase):