Sensitivity of a Ground-Based Infrared Interferometer for Aperture Synthesis Imaging

Sensitivity limits of ground-based infrared interferometers using aperture synthesis are presented. The motivation of this analysis is to compare an interferometer composed of multiple large telescopes and a single giant telescope with adaptive optics. In deriving these limits, perfect wavefront correction by adaptive optics and perfect cophasing by fringe tracking are assumed. We consider the case in which n beams are pairwise combined at n(n− 1)/2 detectors (C2 interferometer) and the case in which all the n beams are combined at a single detector (Cn interferometer). Our analysis covers broadband observations by considering spectral dispersion of interference fringes. In the read noise limit, the Cn interferometer with one dimensional baseline configuration is superior to the C2 interferometer, while in the background limit, the advantage of the one-dimensional Cn interferometer is small. As a case study, we compare the point-source sensitivities of interferometers composed of nine 10-m diameter telescopes and a 30-m diameter single telescope with adaptive optics between 1 and 10 μm for 10-σ detection in one hour. At J and H, the sensitivities of the interferometers are limited to 25 to 24 mag by read noise and OH airglow background, while that of the single telescope is limited to 28 to 26 mag by OH airglow background. Longward of 2 μm, the sensitivities of the interferometers and the single telescope are all limited by instrumental thermal background. At K, the sensitivities of the interferometers are around 23 mag, while that of the single telescope is 27 mag. At N, the sensitivities of the interferometers are around 10.7 mag, while that of the single telescope is 14.4 mag.