The Keck-HGCA Pilot Survey – II. Direct imaging discovery of HD 63754 B, a ∼20 au massive companion near the hydrogen burning limit

Yiting Li*, Timothy D. Brandt*, Kyle Franson, Qier An, Taylor Tobin, Thayne Currie, Minghan Chen, Lanxuan Wang, Trent J. Dupuy, Rachel Bowens-Rubin, Maïssa Salama, Briley L. Lewis, Aidan Gibbs, Brendan P. Bowler, Rebecca Jensen-Clem, Jacqueline Faherty, Michael P. Fitzgerald, Benjamin A. Mazin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

We present the joint astrometric and direct imaging discovery, mass measurement, and orbital analysis of HD 63754 B (HIP 38216 B), a companion near the stellar-substellar boundary orbiting ∼20 au from its Sun-like host. HD 63754 was observed in our ongoing high-contrast imaging survey targeting stars with significant proper-motion accelerations between Hipparcos and Gaia consistent with wide-separation substellar companions. We utilized archival High Resolution Echelle Spectrograph and High Accuracy Radial Velocity Planet Searcher radial velocity (RV) data, together with the host star’s astrometric acceleration extracted from the Hipparcos–Gaia Catalog of Accelerations, to predict the location of the candidate companion around HD 63754 A. We subsequently imaged HD 63754 B at its predicted location using the Near Infrared Camera 2 (NIRC2) in the L band at the W. M. Keck Observatory. We then jointly modelled the orbit of HD 63754 B with RVs, Hipparcos–Gaia accelerations, and our new relative astrometry, measuring a dynamical mass of 81.9+−56.84MJup, an eccentricity of 0.260+−00.059065, and a nearly face-on inclination of 174.81+−00.5048. For HD 63754 B, we obtain an L-band absolute magnitude of L = 11.39 ± 0.06 mag, from which we infer a bolometric luminosity of log(Lbol/L) = −4.55 ± 0.08 dex using a comparison sample of L and T dwarfs with measured luminosities. Although uncertainties linger in age and dynamical mass estimates, our analysis points towards HD 63754 B’s identity as a brown dwarf on the L/T transition rather than a low-mass star, indicated by its inferred bolometric luminosity and model-estimated effective temperature. Future RV, spectroscopic, and astrometric data such as those from JWST and Gaia Data Release 4 will clarify HD 63754 B’s mass, and enable spectral typing and atmospheric characterization.

Original languageEnglish
Pages (from-to)3501-3516
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume533
Issue number3
Early online date6 Aug 2024
DOIs
Publication statusPublished - 1 Sept 2024

Keywords / Materials (for Non-textual outputs)

  • astrometry
  • methods: data analysis
  • techniques: high angular resolution
  • techniques: image processing

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