Obliquity Constraints on an Extrasolar Planetary-Mass Companion
Abstract
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.
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.Attached Files
Published - Bryan_2020_AJ_159_181.pdf
Submitted - 2002.11131.pdf
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Additional details
- Eprint ID
- 101782
- Resolver ID
- CaltechAUTHORS:20200309-113347517
- 51 Pegasi b Fellowship
- Heising-Simons Foundation
- AST-1909209
- NSF
- DGE-1122492
- NSF Graduate Research Fellowship
- NAS 5-26555
- NASA
- Created
-
2020-03-09Created from EPrint's datestamp field
- Updated
-
2021-11-16Created from EPrint's last_modified field
- Caltech groups
- Astronomy Department, Division of Geological and Planetary Sciences