Wednesday 26 Feb 2014: Dancing in the Dark: Kernel Phase Interferometry of Ultracool Dwarfs
Ben Pope - University of Oxford
Physics, 4th floor 14:00-15:00
This paper revisits a sample of ultracool dwarfs in the Solar neighbourhood 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. The results reported here provide new insights regarding the population of nearby ultracool binaries, while also offering an incisive case study into the benefits conferred by the kernel phase approach in the recovery of companions within a few resolution elements of the PSF core. The high reported binarity fraction is at odds with the predictions of the embryo ejection model of brown dwarf formation, which predicted a rate closer to ~5%. Moreover, with the additional detections this prediction now lies several sigma away from the observed value.