SCExAO/CHARIS Spectroscopic Characterization of Cloudy L/T Transition Companion Brown Dwarf HIP 93398 B

TL;DR

This study uses high-resolution infrared spectroscopy to reclassify a brown dwarf companion, HIP 93398 B, revealing it as a late-L dwarf near the L/T transition with implications for brown dwarf evolution models.

Contribution

The paper provides new spectroscopic data and analysis that revise the classification and physical parameters of HIP 93398 B, resolving previous inconsistencies with evolution models.

Findings

HIP 93398 B is a late-L dwarf near the L/T transition.

Revised temperature and luminosity resolve model-observation tension.

Spectroscopy suggests the presence of moderate to thick clouds in its atmosphere.

Abstract

Brown dwarfs with measured dynamical masses and spectra from direct imaging are benchmarks that anchor substellar atmosphere cooling and evolution models. We present Subaru SCExAO/CHARIS infrared spectroscopy of HIP 93398 B, a brown dwarf companion recently discovered by Li et al. 2023 as part of an informed survey using the Hipparcos-Gaia Catalog of Accelerations. This object was previously classified as a T6 dwarf based on its luminosity, with its independently-derived age and dynamical mass in tension with existing models of brown dwarf evolution. Spectral typing via empirical standard spectra, temperatures derived by fitting substellar atmosphere models, and J-H, J-K and H-L' colors all suggest that this object has a substantially higher temperature and luminosity, consistent with classification as a late-L dwarf near the L/T transition (T = 1200$^{+140}_{-119}$ K) with moderate to thick clouds possibly present in its atmosphere. When compared with the latest generation of evolution models that account for clouds with our revised luminosity and temperature for the object, the tension between the model-independent mass/age and model predictions is resolved.