Spitzer + HST parallaxes of 13 late T and Y dwarfs

TL;DR

This study combines Spitzer and HST data to measure parallaxes of 13 cold brown dwarfs within 20 parsecs, revealing significant intrinsic scatter in their infrared properties and emphasizing the importance of astrometry for accurate characterization.

Contribution

First combined use of Spitzer and HST data to measure parallaxes of late T and Y dwarfs, highlighting the diversity in their infrared properties.

Findings

Large intrinsic scatter in infrared magnitudes and colors.

Photometric distances are unreliable due to scatter.

Astrometric parallaxes are essential for accurate characterization.

Abstract

We present astrometric measurements for 13 cold brown dwarfs in the solar neighborhood (d < 20pc). By combining archival Spitzer data with our own Hubble Space Telescope (HST) observations, we achieve parallax uncertainties typically around 10%. Using Spitzer and HST photometry we compare our targets with other known late T and Y dwarfs in the Solar neighborhood, confirming that there is large intrinsic scatter in the near- and mid-infrared absolute magnitudes and colors of this population, further highlighting the diversity observed spectroscopically by several James Webb Space Telescope (JWST) programs. This scatter makes photometric distance estimates highly unreliable and, therefore, makes astrometric parallax measurements fundamental for a meaningful characterization of even the nearest cold brown dwarfs.