Parallaxes of Cool Objects with WISE: Filling in for Gaia

TL;DR

This paper presents a WISE-based method to measure proper motions and parallaxes of low-mass stars and brown dwarfs, surpassing Gaia's limits for faint objects, demonstrated on nearby dwarfs with promising results.

Contribution

It introduces a novel WISE multi-epoch astrometry technique using MCMC, enabling measurements of faint low-mass objects beyond Gaia's detection capabilities.

Findings

Achieved ~4 mas/yr proper motion precision.

Achieved ~7 mas parallax precision.

Measured parallaxes for 20 nearby low-mass dwarfs.

Abstract

This paper uses the multi-epoch astrometry from the Wide-field Infrared Survey Explorer (WISE) to demonstrate a method to measure proper motions and trigonometric parallaxes with precisions of $\sim$4 mas yr$^{-1}$ and $\sim$7 mas, respectively, for low-mass stars and brown dwarfs. This method relies on WISE single exposures (Level 1b frames) and a Markov Chain Monte Carlo method. The limitations of Gaia in observing very low-mass stars and brown dwarfs are discussed, and it is shown that WISE will be able to measure astrometry past the 95% completeness limit and magnitude limit of Gaia (L, T, and Y dwarfs fainter than $G\approx19$ and $G=21$, respectively). This method is applied to WISE data of 20 nearby ($\lesssim17$ pc) dwarfs with spectral types between M6-Y2 and previously measured trigonometric parallaxes. Also provided are WISE astrometric measurements for 23 additional low-mass dwarfs with spectral types between M6-T7 and estimated photometric distances $<17$ pc. Only nine of these objects contain parallaxes within Gaia Data Release 2.