Aperture synthesis using multiple facilities: Keck aperture masking and the IOTA interferometer

As the number of optical interferometers increase, multi-facility observations become both feasible and scientifically interesting. For imaging of complex sources, the capability of increasing (u,v) coverage by using multiple arrays may be necessary for accurately interpreting the fringe visibility and closure phase data. Toward this end, coordinated observations with the IOTA interferometer and Keck aperture masking have been carried out to test techniques for synthesizing images using data from heterogeneous arrays with sparse (u,v) coverage. In particular, we will focus on how the image prior in the Maximum Entropy Method can be used to efficiently incorporate very high spatial frequency information with "low-resolution" data for imaging the generic prototype "Star + Dust Shell" image morphology. Preliminary results using real data for a few dusty evolved stars are presented.