The Y dwarf population with HST: unlocking the secrets of our coolest neighbours -- I. Overview & First astrometric results

Abstract

In this paper we present our project that aims at determining accurate distances and proper motions for the Y brown dwarf population using the Hubble Space Telescope. We validate the program with our first results, using a single new epoch of observations of the Y0pec dwarf WISE J163940.83$-$684738.6. These new data allowed us to refine its proper motion and improve the accuracy of its parallax by a factor of three compared to previous determinations, now constrained to $\varpi =211.11\pm 0.56$ mas. This newly derived absolute parallax corresponds to a distance of $4.737\pm 0.013$ pc, an exquisite and unprecedented precision for faint ultracool Y dwarfs.

arXiv commentAccepted for publication in MNRAS. 6 pages, 2 figures, 2 tables

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• HST astrometry of the closest Brown Dwarfs -- II. Improved parameters and constraints on a third body
• Enhanced thermal radiation from a tidally heated exomoon with a single hot spot