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A Rotation Rate for the Planetary-mass Companion DH Tau b

Xuan, Jerry W. and Bryan, Marta L. and Knutson, Heather A. and Bowler, Brendan P. and Morley, Caroline V. and Benneke, Björn (2020) A Rotation Rate for the Planetary-mass Companion DH Tau b. Astronomical Journal, 159 (3). Art. No. 97. ISSN 1538-3881. doi:10.3847/1538-3881/ab67c4.

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DH Tau b is a young planetary-mass companion orbiting at a projected separation of 320 au from its ~2 Myr old host star DH Tau. With an estimated mass of 8–22 M_(Jup) this object straddles the deuterium-burning limit, and might have formed via core or pebble accretion, disk instability, or molecular cloud fragmentation. To shed light on the formation history of DH Tau b, we obtain the first measurement of rotational line broadening for this object using high-resolution (R ~ 25,000) near-infrared spectroscopy from Keck/NIRSPEC. We measure a projected rotational velocity (v sin i) of 9.6 ± 0.7 km s⁻¹, corresponding to a rotation rate that is between 9% and 15% of DH Tau b's predicted breakup speed. This low rotation rate is in good agreement with scenarios in which magnetic coupling between the companion and its circumplanetary disk during the late stages of accretion reduces angular momentum and regulates spin. We compare the rotation rate of DH Tau b to published values for other planetary-mass objects with masses between 0.3 and 20 M_(Jup) and find no evidence of a correlation between mass and rotation rate in this mass regime. Finally, we search for evidence of individual molecules in DH Tau b's spectrum and find that it is dominated by CO and H₂O, with no evidence of the presence of CH₄. This agrees with expectations given DH Tau b's relatively high effective temperature (~2300 K).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Xuan, Jerry W.0000-0002-6618-1137
Bryan, Marta L.0000-0002-6076-5967
Knutson, Heather A.0000-0002-0822-3095
Bowler, Brendan P.0000-0003-2649-2288
Morley, Caroline V.0000-0002-4404-0456
Benneke, Björn0000-0001-5578-1498
Additional Information:© 2020 The American Astronomical Society. Received 2019 September 27; revised 2020 January 2; accepted 2020 January 3; published 2020 February 10. 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. This work was funded, in part, by a Summer Undergraduate Research Fellowship (SURF) from California Institute of Technology. M.L.B. is supported by the Heising-Simons Foundation 51 Pegasi b Fellowship. B.P.B. acknowledges support from the National Science Foundation grant AST-1909209. Facility: Keck II/NIRSPEC. - Software: emcee (Foreman-Mackey et al. 2013), PyAstronomy (
Group:Astronomy Department
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
Heising-Simons Foundation51 Pegasi b Fellowship
Subject Keywords:Exoplanet formation; Exoplanet atmospheres; High resolution spectroscopy; Brown dwarfs
Issue or Number:3
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet formation (492); Exoplanet atmospheres (487); High resolution spectroscopy (2096); Brown dwarfs (185)
Record Number:CaltechAUTHORS:20200210-134152724
Persistent URL:
Official Citation:Jerry W. Xuan et al 2020 AJ 159 97
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101207
Deposited By: Tony Diaz
Deposited On:10 Feb 2020 21:53
Last Modified:16 Nov 2021 18:00

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