Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime

TL;DR

This study constructs comprehensive spectral energy distributions for a large sample of ultracool dwarfs, deriving fundamental parameters and analyzing the effects of age, gravity, and clouds on their spectral properties.

Contribution

It provides the largest dataset to date of fundamental parameters for ultracool dwarfs across a wide age and mass range, including new bolometric corrections and age-sensitive relationships.

Findings

Young L dwarfs are systematically cooler by up to 300K compared to field age counterparts.

Bolometric corrections in J-band differ by up to a magnitude between young and old objects.

Spectral morphology is influenced by degeneracies among temperature, gravity, and clouds.

Abstract

We combine optical, near-infrared and mid-infrared spectra and photometry to construct expanded spectral energy distributions (SEDs) for 145 field age (\textgreater 500 Myr) and 53 young (lower age estimate \textless 500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group (NYMG). We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities ($L_\text{bol}$) and radius estimates from evolutionary models give semi-empirical effective temperatures ($T_\text{eff}$) for the full range of young and field age late-M, L and T dwarfs. We construct age-sensitive relationships of luminosity, temperature and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as $T_\text{eff}$, surface gravity, and clouds on spectral morphology. We report bolometric corrections in $J$ for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in $Ks$ shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR-MIR reddening of low gravity L dwarfs and identify a systematically cooler $T_\text{eff}$ of up to 300K from field age objects of the same spectral type and 400K cooler from field age objects of the same $M_H$ magnitude.