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

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 ∼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 ǫ 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.

Trigonometric Parallaxes and Proper Motions of 134 Southern Late M, L, and T Dwarfs From the Carnegie Astrometric Planet Search Program

“…This also reduces the inferred radius of the planet by the same amount and increases the planetary density by 10% to 0.79 g cm −3 . 2MASS J20282035+0052265: This is an L-dwarf binary system that was not resolved in Hubble Space Telescope (HST)/NICMOS observations analyzed in Reid et al (2008) but was resolved using new analysis techniques of the same data in Pope et al (2013). The latter work found it to be a nearly equal spectral type binary (L3+L4) and estimated a new spectrophotometric distance of 26.1 ± 3.9 pc.…”

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

“…There are several differences between the application of kernel phase to this dataset and to the previously-published HST sample in Pope et al (2013). In particular, each observation consists of a datacube of 100 frames, yielding excellent experimental diversity so that the statistics on each kernel phase can be readily recovered, as opposed to the case with the HST snapshot data where an ensemble average over many different targets was required.…”

“…The next steep is to fit a parametric model to these kernel phase data, defined by the binary parameters separation (mas), position angle (deg) and contrast, proceeding in a similar fashion to Pope et al (2013). We estimate these parameters using two Bayesian inference algorithms, namely MULTINEST (Feroz et al 2009), an implementation of multi-modal nested sampling, and EMCEE (Foreman-Mackey et al 2013), an affine-invariant ensemble Markov Chain Monte Carlo sampler.…”

“…Pope et al (2013) first applied kernel phase interferometry to a sample of brown dwarf systems imaged by Reid et al (2006) and Reid et al (2008) using the HST-NICMOS NIC1 camera. Where the original papers found a total of ten binary systems out of 72 studied, Pope et al (2013) recovered all of these and found five additional systems with high confidence, as well as four other new more marginal candidates at lower confidence or higher contrast.…”

The Asymmetric Pupil Fourier Wavefront Sensor

“…To build the actual matrix, the pupil is modeled into a discrete grid of subapertures that follow a regular hexagonal grid. Other options (e.g., square grid) remain possible, and have been used so far for kernel-phase analysis (Martinache 2010;Pope et al 2012). The density of the grid should in practice be matched to the density of actuators the deformable mirror that controls the incoming wavefront.…”