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Obliquity Constraints on an Extrasolar Planetary-Mass Companion

Bryan, Marta L. and Chiang, Eugene and Bowler, Brendan P. and Morley, Caroline V. and Millholland, Sarah and Blunt, Sarah and Ashok, Katelyn B. and Nielsen, Eric and Ngo, Henry and Mawet, Dimitri and Knutson, Heather A. (2020) Obliquity Constraints on an Extrasolar Planetary-Mass Companion. Astronomical Journal, 159 (4). Art. No. 181. ISSN 1538-3881.

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We place the first constraints on the obliquity of a planetary-mass companion outside of the solar system. Our target is the directly imaged system 2MASS J01225093–2439505 (2M0122), which consists of a 120 Myr 0.4 M⊙ star hosting a 12–27 M_J companion at 50 au. We constrain all three of the system's angular-momentum vectors: how the companion spin axis, the stellar spin axis, and the orbit normal are inclined relative to our line of sight. To accomplish this, we measure projected rotation rates (v sin i) for both the star and the companion using new near-infrared high-resolution spectra with NIRSPEC at Keck Observatory. We combine these with a new stellar photometric rotation period from TESS and a published companion rotation period from Hubble Space Telescope to obtain spin-axis inclinations for both objects. We also fitted multiple epochs of astrometry, including a new observation with NIRC2/Keck, to measure 2M0122b's orbital inclination. The three line-of-sight inclinations place limits on the true de-projected companion obliquity and stellar obliquity. We find that while the stellar obliquity marginally prefers alignment, the companion obliquity tentatively favors misalignment. We evaluate possible origin scenarios. While collisions, secular spin–orbit resonances, and Kozai–Lidov oscillations are unlikely, formation by gravitational instability in a gravito-turbulent disk—the scenario favored for brown dwarf companions to stars—appears promising.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bryan, Marta L.0000-0002-6076-5967
Chiang, Eugene0000-0002-6246-2310
Bowler, Brendan P.0000-0003-2649-2288
Morley, Caroline V.0000-0002-4404-0456
Millholland, Sarah0000-0003-3130-2282
Blunt, Sarah0000-0002-3199-2888
Nielsen, Eric0000-0001-6975-9056
Ngo, Henry0000-0001-5172-4859
Mawet, Dimitri0000-0002-8895-4735
Knutson, Heather A.0000-0002-0822-3095
Additional Information:© 2020 The American Astronomical Society. Received 2019 November 21; revised 2020 February 11; accepted 2020 February 14; published 2020 April 1. We thank Ian Czekala, Courtney Dressing, Daniel Fabrycky, Jeffrey Fung, Sivan Ginzburg, and Yifan Zhou for helpful conversations. M.L.B. is supported by her Heising–Simons Foundation 51 Pegasi b Fellowship. E.C. acknowledges support from the Heising–Simons Foundation, NASA, and the National Science Foundation. B.P.B. acknowledges support from the National Science Foundation grant AST-1909209. S.M. is supported by the NSF Graduate Research Fellowship Program under Grant DGE-1122492. S.B. is supported by a National Science Foundation Graduate Research Fellowship. This research made use of Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration, 2018). This paper includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. We extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Maunakea we are privileged to be guests.
Group:Astronomy Department
Funding AgencyGrant Number
Heising-Simons Foundation51 Pegasi b Fellowship
NSF Graduate Research FellowshipDGE-1122492
NASANAS 5-26555
Subject Keywords:Exoplanet systems ; High resolution spectroscopy ; Direct imaging ; Photometry
Issue or Number:4
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanet systems (484); High resolution spectroscopy (2096); Direct imaging (387); Photometry (1234)
Record Number:CaltechAUTHORS:20200309-113347517
Persistent URL:
Official Citation:Marta L. Bryan et al 2020 AJ 159 181
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101782
Deposited By: Joy Painter
Deposited On:09 Mar 2020 20:49
Last Modified:03 Apr 2020 19:17

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