Moderate-resolution K-band Spectroscopy of the Substellar Companion VHS 1256 b
Abstract
We present moderate-resolution (R ∼ 4000) K-band spectra of the planetary-mass companion VHS 1256 b. The data were taken with the OSIRIS integral field spectrograph at the W.M. Keck Observatory. The spectra reveal resolved molecular lines from H2O and CO. The spectra are compared to custom PHOENIX atmosphere model grids appropriate for young, substellar objects. We fit the data using a Markov chain Monte Carlo forward-modeling method. Using a combination of our moderate-resolution spectrum and low-resolution broadband data from the literature, we derive an effective temperature of 1240 K, with a range of 1200–1300 K, a surface gravity of log g = 3.25, with a range of 3.25–3.75, and a cloud parameter of log P_(cloud) 6, with a range of 6.0–6.6. These values are consistent with previous studies, regardless of the new, larger system distance from GAIA EDR3 (21.15 ± 0.22 pc). We derive a C/O ratio of 0.590^(+0.280)_(-0.354) for VHS 1256b. Both our OSIRIS data and spectra from the literature are best modeled when using a larger 3 μm grain size for the clouds than used for hotter objects, consistent with other sources in the L/T transition region. VHS 1256 b offers an opportunity to look for systematics in the modeling process that may lead to the incorrect derivation of properties like C/O ratio in the high contrast regime.
Additional Information
The authors thank observing assistant John Pelletier and support astronomer Jim Lyke for their help obtaining these observations. K.K.W.H., Q.M.K, T.S.B, and L.S.B. acknowledge support by the National Aeronautics and Space Administration under Grants/Contracts/Agreements No.NNX17AB63G and 80NSSC21K0573 issued through the Astrophysics Division of the Science Mission Directorate. T.S.B. also acknowledges support by the National Science Foundation under grant No. 1614492. Any opinions, findings, and conclusions or recommendations expressed in this paper are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Portions of this work were conducted at the University of California, San Diego, which was built on the unceded territory of the Kumeyaay Nation, whose people continue to maintain their political sovereignty and cultural traditions as vital members of the San Diego community.Additional details
- Eprint ID
- 117216
- Resolver ID
- CaltechAUTHORS:20221003-756400000.27
- NNX17AB63G
- NASA
- 80NSSC21K0573
- NASA
- AST-1614492
- NSF
- W. M. Keck Foundation
- Created
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2022-10-09Created from EPrint's datestamp field
- Updated
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2022-10-09Created from EPrint's last_modified field