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As the Worlds Turn: Constraining Spin Evolution in the Planetary-mass Regime

Bryan, Marta L. and Ginzburg, Sivan and Chiang, Eugene and Morley, Caroline and Bowler, Brendan P. and Xuan, Jerry W. and Knutson, Heather A. (2020) As the Worlds Turn: Constraining Spin Evolution in the Planetary-mass Regime. Astrophysical Journal, 905 (1). Art. No. 37. ISSN 1538-4357. doi:10.3847/1538-4357/abc0ef.

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To understand how planetary spin evolves and traces planet formation processes, we measure rotational line broadening in eight planetary-mass objects (PMOs) of various ages (1–800 Myr) using near-infrared high-resolution spectra from NIRSPEC/Keck. Combining these with published rotation rates, we compile 27 PMO spin velocities, 16 of which derive from our NIRSPEC/Keck program. Our data are consistent with spin velocities v scaling with planetary radius R as v ∝ 1/R. We conclude that spin angular momentum is conserved as objects cool and contract over the sampled age range. The PMOs in our sample spin at rates that are approximately an order of magnitude below their break-up values, consistent with the hypothesis that they were spun down by magnetized circum-PMO disks (CPDs) during the formation era at ages ≾a few Myr. There is a factor of 4–5 variation in spin velocity that has yet to be understood theoretically. It also remains to be seen whether spin evolves on timescales ≳1 Gyr for PMOs, as it does for stars and high-mass brown dwarfs emitting magnetized winds.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bryan, Marta L.0000-0002-6076-5967
Chiang, Eugene0000-0002-6246-2310
Morley, Caroline0000-0002-4404-0456
Bowler, Brendan P.0000-0003-2649-2288
Xuan, Jerry W.0000-0002-6618-1137
Knutson, Heather A.0000-0002-0822-3095
Additional Information:© 2020 The American Astronomical Society. Received 2020 August 27; revised 2020 October 1; accepted 2020 October 12; published 2020 December 9. We thank Ian Czekala, Daniel Fabrycky, and Yifan Zhou for helpful conversations. M.L.B. and S.G. are supported by their Heising-Simons Foundation 51 Pegasi b Fellowships. This work benefited from NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by the NASA Science Mission Directorate, and was supported in part by NASA grant NNX15AD95G/NEXSS. We extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Maunakea we are privileged to be guests.
Funding AgencyGrant Number
Heising-Simons Foundation51 Pegasi b Fellowship
Subject Keywords:High resolution spectroscopy ; Exoplanet formation
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: High resolution spectroscopy (2096); Exoplanet formation (492)
Record Number:CaltechAUTHORS:20201215-095747947
Persistent URL:
Official Citation:Marta L. Bryan et al 2020 ApJ 905 37
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107084
Deposited By: Tony Diaz
Deposited On:15 Dec 2020 18:47
Last Modified:16 Nov 2021 18:59

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