The Palomar kernel-phase experiment: testing kernel phase interferometry for ground-based astronomical observations

Abstract

At present, the principal limitation on the resolution and contrast of astronomical imaging instruments comes from aberrations in the optical path, which may be imposed by the Earth's turbulent atmosphere or by variations in the alignment and shape of the telescope optics. These errors can be corrected physically, with active and adaptive optics, and in post-processing of the resulting image. A recently-developed adaptive optics post-processing technique, called kernel phase interferometry, uses linear combinations of phases that are self-calibrating with respect to small errors, with the goal of constructing observables that are robust against the residual optical aberrations in otherwise well-corrected imaging systems. Here we present a direct comparison between kernel phase and the more established competing techniques, aperture masking interferometry, point spread function (PSF) fitting and bispectral analysis. We resolve the α Ophiuchi binary system near periastron, using the Palomar 200-Inch Telescope. This is the first case in which kernel phase has been used with a full aperture to resolve a system close to the diffraction limit with ground-based extreme adaptive optics observations. Excellent agreement in astrometric quantities is found between kernel phase and masking, and kernel phase significantly outperforms PSF fitting and bispectral analysis, demonstrating its viability as an alternative to conventional non-redundant masking under appropriate conditions.

Kernel phase imaging with VLT/NACO: high-contrast detection of new candidate low-mass stellar companions at the diffraction limit

“…However, kernel phase uses the light collected by the entire pupil and should perform better in the high Strehl regime and the bright limit (e.g. Pope et al 2016;Sallum & Skemer 2019).…”

Mid-infrared photometry of the T Tauri triple system with kernel phase interferometry

“…The kernel phase technique was developed by Martinache (2010), who was able to achieve an angular resolution of ∼ 0.6 λ/D on the known low-contrast binary GJ 164 with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope (HST). Later, Pope et al (2013) used the technique to detect brown dwarf companions, also with HST/NICMOS, and Pope et al (2016) and Sallum & Skemer (2019) showed that kernel phase should outperform sparse aperture masking under appropriate seeing conditions longward of ∼ 3 µm from the ground given the reduced sensitivity to sky background noise. Recently, Kammerer et al (2019) used the kernel phase technique to detect eight stellar companions in an archival VLT/Nasmyth Adaptive Optics System (NAOS) nearinfrared imager and spectrograph (NACO) high-contrast imaging survey, two of which are below the classical diffraction limit at angular separations of ∼ 0.8 and ∼ 1.2 λ/D.…”

High-resolution survey for planetary companions to young stars in the Taurus Molecular Cloud

“…The kernel phase technique was first used by Martinache (2010) who demonstrated the detection of a 10:1 companion at 0.5 λ/D in HST/NICMOS data, clearly showing the improved speckle calibration capabilities with respect to image plane data reduction techniques. More recently, Pope et al (2016) applied kernel phase to ground-based observations of α Oph with the 5.1 m Hale Telescope and showed that it outperforms PSF fitting and bispectral analysis under appropriate conditions (i.e., high Strehl). Kammerer et al (2019) further developed the technique including a principal component calibration based on Karhunen-Loève decomposition (Soummer et al 2012) for the subtraction of the residual kernel phase signal measured on calibrator stars and detected Here, we use the same kernel phase data reduction pipeline as Kammerer et al (2019), with slight modifications and improvements explained below.…”