Ultracool Spectroscopic Outliers in Gaia DR3

TL;DR

This study identifies outliers among ultracool dwarfs in Gaia DR3 data using spectral and kinematic analysis, discovering new subdwarf candidates and demonstrating a method for future Gaia data releases.

Contribution

Introduces a spectral type-specific color ratio to identify ultracool dwarf outliers in Gaia DR3, including new subdwarf classifications, as a proof-of-concept for future data releases.

Findings

Identified 58 Gaia RP spectra outliers among ultracool dwarfs.

Deemed 7 outliers as prime candidates, including 2 new subdwarf classifications.

Discovered 1 likely young stellar object among the outliers.

Abstract

Gaia DR3 provided a first release of RP spectra and astrophysical parameters for ultracool dwarfs. We used these Gaia RP spectra and astrophysical parameters to select the most outlying ultracool dwarfs. These objects have spectral types of M7 or later and might be young brown dwarfs or low metallicity objects. This work aimed to find ultracool dwarfs which have Gaia RP spectra significantly different to the typical population. However, the intrinsic faintness of these ultracool dwarfs in Gaia means that their spectra were typically rather low signal-to-noise in Gaia DR3. This study is intended as a proof-of-concept for future iterations of the Gaia data releases. Based on well studied subdwarfs and young objects, we created a spectral type-specific color ratio, defined using Gaia RP spectra; this ratio is then used to determine which objects are outliers. We then used the objects kinematics and photometry external to Gaia to cut down the list of outliers into a list of 'prime candidates'. We produce a list of 58 Gaia RP spectra outliers, seven of which we deem as prime candidates. Of these, six are likely subdwarfs and one is a known young stellar object. Four of six subdwarf candidates were known as subdwarfs already. The two other subdwarf candidates: 2MASS J03405673+2633447 (sdM8.5) and 2MASS J01204397+6623543 (sdM9), are new classifications.