The 23rd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (Tokyo, June 15-19, 2026)
Published June 6, 2026 | Version v1
Poster Open

Kinematics and Spins of Ultracool Dwarfs: Toward Substellar Galactic Archaeology and Gyrochronology

Description

Ultracool dwarfs are low-mass stars and brown dwarfs with masses below 0.1 Msun. I highlight our recent efforts to understand their formation and evolution using kinematics and spins from ground-based high-resolution spectroscopy.

Along with the BDKP team, over the last few years, we developed the package SMART to measure robust RV and vsini for UCDs with 10+ spectrometers, including Keck/NIRSPEC, SDSS/APOGEE, and Gemini/IGRINS. Our survey highlights with the BDKP Team include (1) first kinematic evidence of the stellar/substellar boundary at L4-L6 subtypes, (2) first RV-verified T dwarf binaries and the shortest-period UCD binary and dozens of RV variable candidates, and (3) radius inflation up to 25% was identified in 26 out of 41 isolated young brown dwarfs (0.05–0.1 Msun).

Along with the KPIC spin survey, our novel analysis of specific angular momentum versus age of 221 stellar/substellar objects below 0.1 Msun with literature spin measurements indicates that substellar objects between 5-40 Mjup retain much higher angular momenta compared to stellar and substellar objects between 40-100 Mjup after 10 Myr, when their initial angular momenta were set.

Along with the JWST Arcana team, we conduct the first JWST NIRSpec metal-poor brown dwarf kinematic survey with the JWST Arcana Team (GO-4668; PI Burgasser). We employ a fitting method to fit JWST/NIRSpec G395H spectra (R~3,000) and show that our G395H RVs can achieve a systematic uncertainty of 5 km/s (vs objects with high-resolution RVs).
Our kinematic analysis indicates the possible first brown dwarf associated with the Gaia Enceladus merger remnant, and another brown dwarf associated with the Thamnos stream.

 

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Additional details

Related works

References
Publication: 2021ApJS..257...45H (Bibcode)
Publication: 2023ApJ...945L...6H (Bibcode)
Publication: 2024ApJ...971....9H (Bibcode)
Publication: 2024ApJS..274...40H (Bibcode)
Publication: 2026AJ....171..224H (Bibcode)

Funding

U.S. National Science Foundation
AST-1517177
National Aeronautics and Space Administration
NNX15AI75G
National Aeronautics and Space Administration
HST-HF2- 51447.001-A
U.S. National Science Foundation
DGE-1762114
Heising-Simons Foundation
2015-129
Heising-Simons Foundation
2017- 318
Heising-Simons Foundation
2019-1312
Heising-Simons Foundation
2023-4598
NSF National Geophysical Facility
AST-1611623
National Aeronautics and Space Administration
80NSSC23K1434
Heising-Simons Foundation
2025-5887
U.S. National Science Foundation
2139433

Dates

Submitted
2026-06-05

Software

Repository URL
https://github.com/chihchunhsu/smart
Programming language
Python