Synthesis Imaging detection limits with the Space Interferometry Mission

The Space Interferometry Mission (SIM) will be the next mission of NASA's ORIGINS program designed primarily for microarcsecond level astrometry. SIM is a double baseline ( ∼ 9 and ∼ 8 m) spaceborne optical interferometer also capable of synthesis imaging. In this paper we present numerical simulations of the dynamic range limits for close (<1^") binaries using the synthesis imaging mode of SIM as a function of the primary magnitude, integration time, angular separation of the companion and phase noise in the instrument. The limiting dynamic range was obtained by subtracting a noiseless instrumental PSF from a reconstructed noisy image of the primary star and the residual was searched for the secondary signal. For bright stars (V < 12 mag) the dynamic range for synthesis imaging is limited by the minimum instrumental phase noise of SIM: with a 1^o phase noise a dynamic range of 4,000 is achievable. The dynamic range was found to be independent of the angular separation which gives SIM advantage over the ACS camera aboard Hubble Space Telescope for fields smaller than 0.25^" radius around the primary star. SIM offers 40 times higher dynamic range than ACS in such small fields and is thus ideally suited for detection and studies of close separation multiple stars, debris disks and active galactic nuclei.