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The Stellar Obliquity and the Long-period planet in the HAT-P-17 Exoplanetary System

Fulton, Benjamin J. and Howard, Andrew W. and Winn, Joshua N. and Albrecht, Simon and Marcy, Geoffrey W. and Crepp, Justin R. and Bakos, Gáspár Á. and Johnson, John Asher and Hartman, Joel D. and Isaacson, Howard and Knutson, Heather A. and Zhao, Ming (2013) The Stellar Obliquity and the Long-period planet in the HAT-P-17 Exoplanetary System. Astrophysical Journal, 772 (2). Art. No. 80. ISSN 0004-637X.

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We present the measured projected obliquity – the sky-projected angle between the stellar spin axis and orbital angular momentum – of the inner planet of the HAT-P-17 multi-planet system. We measure the sky-projected obliquity of the star to be λ = 19^(+14)_( −16) degrees by modeling the Rossiter- McLaughlin (RM) effect in Keck/HIRES radial velocities (RVs). The anomalous RV time series shows an asymmetry relative to the midtransit time, ordinarily suggesting a nonzero obliquity – but in this case at least part of the asymmetry may be due to the convective blueshift, increasing the uncertainty in the determination of λ. We employ the semi-analytical approach of Hirano et al. (2011) that includes the effects of macroturbulence, instrumental broadening, and convective blueshift to accurately model the anomaly in the net RV caused by the planet eclipsing part of the rotating star. Obliquity measurements are an important tool for testing theories of planet formation and migration. To date, the measured obliquities of ∼50 Jovian planets span the full range, from prograde to retrograde, with planets orbiting cool stars preferentially showing alignment of stellar spins and planetary orbits. Our results are consistent with this pattern emerging from tidal interactions in the convective envelopes of cool stars and close-in planets. In addition, our 1.8 years of new RVs for this system show that the orbit of the outer planet is more poorly constrained than previously thought, with an orbital period now in the range of 10–36 years.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper DOIArticle
Fulton, Benjamin J.0000-0003-3504-5316
Howard, Andrew W.0000-0001-8638-0320
Winn, Joshua N.0000-0002-4265-047X
Marcy, Geoffrey W.0000-0002-2909-0113
Crepp, Justin R.0000-0003-0800-0593
Bakos, Gáspár Á.0000-0001-7204-6727
Johnson, John Asher0000-0001-9808-7172
Hartman, Joel D.0000-0001-8732-6166
Isaacson, Howard0000-0002-0531-1073
Knutson, Heather A.0000-0002-0822-3095
Zhao, Ming0000-0002-4258-9517
Additional Information:© 2013 The American Astronomical Society. Received 2013 January 25; accepted 2013 May 24; published 2013 July 9. We thank the referee for a prompt response, careful reading, and useful comments, Jason Eastman for providing the EXOFAST code to community, and the many observers who contributed to the measurements reported here. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff, especially Scott Dahm, Greg Doppman, Hien Tran, and Grant Hill for support of HIRES and Greg Wirth for support of remote observing. Finally, we extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible. Facilities: Keck:I (HIRES), Keck:II (NIRC2)
Subject Keywords:planets and satellites: fundamental parameters – planets and satellites: individual (HAT-P-17b) – techniques: high angular resolution – techniques: radial velocities
Issue or Number:2
Record Number:CaltechAUTHORS:20130722-104229869
Persistent URL:
Official Citation:The Stellar Obliquity and the Long-period Planet in the HAT-P-17 Exoplanetary System Benjamin J. Fulton et al. 2013 ApJ 772 80
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:39494
Deposited By: Tony Diaz
Deposited On:19 Aug 2013 22:01
Last Modified:09 Mar 2020 13:18

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