Nulling at short wavelengths: theoretical performance constraints and a demonstration of faint companion detection inside the diffraction limit with a rotating-baseline interferometer

Abstract

ABSTRACT The Palomar Fiber Nuller (PFN) is a rotating-baseline nulling interferometer that enables high-accuracy near-infrared (NIR) nulling observations with full azimuth coverage. To achieve NIR null-depth accuracies of several x 10−4, the PFN uses a common-mode optical system to provide a high degree of symmetry, single-mode-fibre beam combination to reduce sensitivity to pointing and wavefront errors, extreme adaptive optics to stabilize the fibre coupling and the cross-aperture fringe phase, rapid signal calibration and camera readout to minimize temporal effects, and a statistical null-depth fluctuation analysis to relax the phase stabilization requirement. Here, we describe the PFN’s final design and performance and provide a demonstration of faint-companion detection by means of nulling-baseline rotation, as originally envisioned for space-based nulling interferometry. Specifically, the Ks-band null-depth rotation curve measured on the spectroscopic binary η Peg reflects both a secondary star 1.08 ± 0.06 × 10−2 as bright as the primary, and a null-depth contribution of 4.8 ± 1.6 × 10−4 due to the size of the primary star. With a 30 mas separation at the time, η Peg B was well inside both the telescope’s diffraction-limited beam diameter (88 mas) and typical coronagraphic inner working angles. Finally, we discuss potential improvements that can enable a number of small-angle nulling observations on larger telescopes.