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Discerning Exoplanet Migration Models Using Spin–Orbit Measurements

Morton, Timothy D. and Johnson, John Asher (2011) Discerning Exoplanet Migration Models Using Spin–Orbit Measurements. Astrophysical Journal, 729 (2). Art. No. 138. ISSN 0004-637X.

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We investigate the current sample of exoplanet spin-orbit measurements to determine whether a dominant planet migration channel can be identified, and at what confidence. We use the predictions of Kozai migration plus tidal friction and planet-planet scattering as our misalignment models, and we allow for a fraction of intrinsically aligned systems, explainable by disk migration. Bayesian model comparison demonstrates that the current sample of 32 spin-orbit measurements strongly favors a two-mode migration scenario combining planet-planet scattering and disk migration over a single-mode Kozai migration scenario. Our analysis indicates that between 34% and 76% of close-in planets (95% confidence) migrated via planet-planet scattering. Separately analyzing the subsample of 12 stars with T_(eff)>6250 K—which Winn et al. predict to be the only type of stars to maintain their primordial misalignments—we find that the data favor a single-mode scattering model over Kozai with 85% confidence. We also assess the number of additional hot star spin-orbit measurements that will likely be necessary to provide a more confident model selection, finding that an additional 20-30 measurement has a >50% chance of resulting in a 95% confident model selection, if the current model selection is correct. While we test only the predictions of particular Kozai and scattering migration models in this work, our methods may be used to test the predictions of any other spin-orbit misaligning mechanism.

Item Type:Article
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Morton, Timothy D.0000-0002-8537-5711
Johnson, John Asher0000-0001-9808-7172
Additional Information:© 2011 American Astronomical Society. Received 2010 September 3; accepted 2010 December 6; published 2011 February 22. We acknowledge very helpful suggestions on the structure and content of this paper from Josh Winn and Dan Fabrycky, and useful comments from an anonymous referee. T.D.M. thanks his office mate Krzysztof Findeisen for helpful suggestions and feedback throughout the course of this project, and also acknowledges the Penn State Astrostatistics Summer School, which helped clarify his thinking about model selection. J.A.J. thanks Jon Swift, Michael Cushing, Brendan Bowler, Justin Crepp, and Ed Turner for illuminating discussions over the years on topics related to data analysis and statistical methods.
Subject Keywords:planets and satellites: formation; stars: statistics
Issue or Number:2
Classification Code:PACS: 97.82.-j; 97.10.Wn
Record Number:CaltechAUTHORS:20110414-105442000
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Official Citation:Discerning Exoplanet Migration Models Using Spin–Orbit Measurements Timothy D. Morton and John Asher Johnson 2011 ApJ 729 138
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23339
Deposited By: Jason Perez
Deposited On:14 Apr 2011 20:03
Last Modified:09 Mar 2020 13:18

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