HD 206893 B at High Spectral Resolution with the Keck Planet Imager and Characterizer

Creators: Sappey, Ben¹; Konopacky, Quinn¹; Ó, Clarissa R. Do¹; Barman, Travis²; Ruffio, Jean-Baptiste¹; Wang 王, Jason 劲飞³; Theissen, Christopher A.¹; Finnerty, Luke⁴; Xuan, Jerry⁵; Hortsman, Katelyn⁵; Mawet, Dimitri⁵; Zhang, Yapeng⁵; Inglis, Julie⁵; Wallack, Nicole L.⁶; Sanghi, Aniket⁵; Baker, Ashley⁵; Bartos, Randall⁷; Blake, Geoffrey A.⁵; Bond, Charlotte Z.⁸; Calvin, Benjamin^{4, 5}; Cetre, Sylvain⁹; Delorme, Jacques-Robert⁹; Doppmann, Greg⁹; Echeverri, Daniel⁵; Fitzgerald, Michael P.⁴; Hsu, Chih-Chun³; Jovanovic, Nemanja⁵; Liberman, Joshua^{5, 2}; López, Ronald A.⁴; Martin, Emily C.¹⁰; Morris, Evan¹⁰; Pezzato-Rovner, Jacklyn⁵; Phillips, Caprice L.¹¹; Ruane, Garreth⁷; Schofield, Tobias⁵; Skemer, Andrew¹⁰; Venenciano, Taylor¹²; Wallace, J. Kent⁷; Wang 王, Ji 吉¹¹; Wizinowich, Peter⁹; Xin, Yinzi⁵

1. University of California, San Diego
2. University of Arizona
3. Northwestern University
4. University of California, Los Angeles
5. California Institute of Technology
6. Carnegie Institution for Science
7. Jet Propulsion Lab
8. UK Astronomy Technology Centre
9. W.M. Keck Observatory
10. University of California, Santa Cruz
11. The Ohio State University
12. Pomona College

Abstract

We present an atmospheric characterization and orbital analysis of HD 206893 B, an exceptionally red, L/T-transition substellar companion in a multiplanetary system, via Keck Planet Imager and Characterizer (KPIC) high-resolution (R ∼ 35,000) K-band spectroscopy. Using PHOENIX atmospheric models in a forward-model framework that fits the spectrum of the companion and diffracted starlight simultaneously, we detect HD 206893 B at >8σ significance via cross correlation in two epochs. We find an effective temperature for the companion of 1634_(−38)^(+72) K and a logg of 4.55_(−0.22)^(+0.17). Only accounting for statistical uncertainties, we measure the carbon-oxygen ratio (C/O) of this companion to be 0.57 ± 0.02, or near-solar while assuming solar metallicity. The C/O ratio we measure fits the tentative trend of >4 M_Jup companions having near-solar C/O ratios while less massive companions have greater-than-solar C/O ratios. Using substellar evolution models, we find an age of 112_(−22)^(+36) Myr, a mass of 22.7_(−1.7)^(+2.5) M_Jup, and a radius of 1.11 ± 0.03 R_Jup for this companion. We also use KPIC radial velocity data to fit the orbit of HD 206893 B and analyze the orbital stability of this system. We find that the orbital stability is relatively independent of the mass of HD 206893 B, and favors an orbital configuration where B and its interior planetary companion, HD 206893 c, are coplanar. The measured C/O ratio coupled with the current architecture of the system cannot rule out the core accretion scenario, nor the disk fragmentation scenario regarding the formation pathway of HD 206893 B.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

B.S and Q.K. acknowledge support from NSF grant AST-2046883.

C.D.O. is supported by the National Science Foundation Graduate Research Fellowship Program under grant No. DGE-2038238.

K.H. is supported by the National Science Foundation Graduate Research Fellowship Program under grant No. 2139433.

J.X. is supported by the NASA Future Investigators in NASA Earth and Space Science and Technology (FINESST) award #80NSSC23K1434.

Funding for KPIC has been provided by the California Institute of Technology, the Jet Propulsion Laboratory, the Heising-Simons Foundation (grants #2015-129, #2017-318, #2019-1312, and #2023-4598), the Simons Foundation, and the NSF under grant AST-1611623.

Some of 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 W. M. Keck Observatory was made possible by the financial support of the W. M. Keck Foundation. The authors wish to acknowledge the significant cultural role that the summit of Maunakea has always had within the indigenous Hawaiian community. The authors are extremely fortunate 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.

Facilities

Keck:II - KECK II Telescope, Exoplanet Archive - .

Software References

astropy (Astropy Collaboration et al. 2013, 2018, 2022), breads (https://github.com/jruffio/breads/tree/main), corner (D. Foreman-Mackey 2016), efit5 (L. Meyer et al. 2012), emcee (D. Foreman-Mackey et al. 2013), h5py (https://www.h5py.org), KPIC Data Reduction Pipeline (https://github.com/kpicteam /kpic_pipeline), matplotlib (J. D. Hunter 2007), numpy (https://numpy.org), orbitize! (S. Blunt et al. 2020), pandas (The pandas development team 2020), petitRADTRANS (P. Mollière et al. 2019), scipy (P. Virtanen et al. 2020), smart (C.-C. Hsu et al. 2021).

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Resource type: Journal Article
Publisher: American Astronomical Society
Published in: Astronomical Journal, 169(3), 175, ISSN: 0004-6256.
Languages: English