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

TL;DR

This study uses Hubble Space Telescope data to precisely measure distances and motions of Y dwarf stars, significantly improving the accuracy of their parallax and distance estimates, which enhances our understanding of these ultracool objects.

Contribution

The paper introduces a method for accurate astrometric measurements of Y dwarfs using HST, providing the first high-precision parallax for a Y0pec dwarf.

Findings

Refined proper motion and parallax for WISE J163940.83-684738.6

Parallax constrained to 211.11 ± 0.56 mas

Distance measured at 4.737 ± 0.013 parsecs

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.