Dancing in the Dark: New Brown Dwarf Binaries from Kernel Phase Interferometry

TL;DR

This study applies a novel kernel phase interferometry technique to archival Hubble data, revealing five new ultracool dwarf binaries and refining the understanding of their binary fraction, demonstrating improved detection capabilities close to the diffraction limit.

Contribution

The paper introduces a new kernel phase analysis method that significantly enhances the detection of close binary companions in archival space telescope data.

Findings

Revealed five new close binary candidates among ultracool dwarfs.

Achieved detection of companions down to ~1 AU separation.

Estimated a binary fraction of at least 17.2% within 19 parsecs.

Abstract

This paper revisits a sample of ultracool dwarfs in the Solar neighborhood previously observed with the Hubble Space Telescope's NICMOS NIC1 instrument. We have applied a novel high angular resolution data analysis technique based on the extraction and fitting of kernel phases to archival data. This was found to deliver a dramatic improvement over earlier analysis methods, permitting a search for companions down to projected separations of $\sim$1 AU on NIC1 snapshot images. We reveal five new close binary candidates and present revised astrometry on previously-known binaries, all of which were recovered with the technique. The new candidate binaries have sufficiently close separation to determine dynamical masses in a short-term observing campaign. We also present four marginal detections of objects which may be very close binaries or high contrast companions. Including only confident detections within 19 parsecs, we report a binary fraction of at least $\epsilon_b = 17.2^{+5.7}_{-3.7}%$. The results reported here provide new insights into the population of nearby ultracool binaries, while also offering an incisive case study of the benefits conferred by the kernel phase approach in the recovery of companions within a few resolution elements of the PSF core.