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HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities

Yee, Samuel W. and Petigura, Erik A. and Fulton, Benjamin J. and Knutson, Heather A. and Batygin, Konstantin and Bakos, Gáspár Á. and Hartman, Joel D. and Hirsch, Lea A. and Howard, Andrew W. and Isaacson, Howard and Kosiarek, Molly R. and Sinukoff, Evan and Weiss, Lauren M. (2018) HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities. Astronomical Journal, 155 (6). Art. No. 255. ISSN 1538-3881. doi:10.3847/1538-3881/aabfec.

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HAT-P-11 is a mid-K dwarf that hosts one of the first Neptune-sized planets found outside the solar system. The orbit of HAT-P-11b is misaligned with the star's spin—one of the few known cases of a misaligned planet orbiting a star less massive than the Sun. We find an additional planet in the system based on a decade of precision radial velocity (RV) measurements from Keck/High Resolution Echelle Spectrometer. HAT-P-11c is similar to Jupiter in its mass (M_p sin i = 1.6 ± 0.1 M J ) and orbital period (P = 9.3^(+1.0)_(-0.5) year), but has a much more eccentric orbit (e = 0.60 ± 0.03). In our joint modeling of RV and stellar activity, we found an activity-induced RV signal of ~7 m s^(-1), consistent with other active K dwarfs, but significantly smaller than the 31 m s^(-1) reflex motion due to HAT-P-11c. We investigated the dynamical coupling between HAT-P-11b and c as a possible explanation for HAT-P-11b's misaligned orbit, finding that planet–planet Kozai interactions cannot tilt planet b's orbit due to general relativistic precession; however, nodal precession operating on million year timescales is a viable mechanism to explain HAT-P-11b's high obliquity. This leaves open the question of why HAT-P-11c may have such a tilted orbit. At a distance of 38 pc, the HAT-P-11 system offers rich opportunities for further exoplanet characterization through astrometry and direct imaging.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Yee, Samuel W.0000-0001-7961-3907
Petigura, Erik A.0000-0003-0967-2893
Fulton, Benjamin J.0000-0003-3504-5316
Knutson, Heather A.0000-0002-0822-3095
Batygin, Konstantin0000-0002-7094-7908
Bakos, Gáspár Á.0000-0001-7204-6727
Hartman, Joel D.0000-0001-8732-6166
Hirsch, Lea A.0000-0001-8058-7443
Howard, Andrew W.0000-0001-8638-0320
Isaacson, Howard0000-0002-0531-1073
Kosiarek, Molly R.0000-0002-6115-4359
Sinukoff, Evan0000-0002-5658-0601
Weiss, Lauren M.0000-0002-3725-3058
Additional Information:© 2018 The American Astronomical Society. Received 2017 November 9; revised 2018 April 3; accepted 2018 April 17; published 2018 May 25. We thank Joshua Winn for helpful discussions that improved the final manuscript. We thank the many observers who contributed to the measurements reported here including M. Bottom, B. Bowler, P. Butler, J. Brewer, J. Crepp, C. Chubak, K. Clubb, I. Crossfield, D. Fischer, E. Ford, E. Gaidos, M. Giguere, J. Johnson, M. Kao, G. Marcy, T. Morton, G. Mandushev, K. Peek, S. Pineda, G. Torres, S. Vogt, P. Worden, M. Zhao. S.W.Y. acknowledges support from the Caltech Marcella Bonsall Summer Undergraduate Research Fellowship. E.A.P. acknowledges support from a Hubble Fellowship grant HST-HF2-51365.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. for NASA under contract NAS 5-26555. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has long had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Software: Numpy/Scipy (Van Der Walt et al. 2011), Matplotlib (Hunter 2007), Pandas (McKinney 2010), Astropy (Astropy Collaboration et al. 2013), emcee (Goodman & Weare 2010; Foreman-Mackey et al. 2013), RadVel (Fulton et al. 2018a). Facility: Keck:I (HIRES) - .
Group:Astronomy Department
Funding AgencyGrant Number
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
NASA Hubble FellowshipHST-HF2-51365.001-A
NASANAS 5-26555
W. M. Keck FoundationUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Caltech Texaco Postdoctoral FellowshipUNSPECIFIED
Trottier Family FoundationUNSPECIFIED
Subject Keywords:planetary systems – planets and satellites: detection – planets and satellites: dynamical evolution and stability – stars: individual (HAT-P-11)
Issue or Number:6
Record Number:CaltechAUTHORS:20180525-092851253
Persistent URL:
Official Citation:Samuel W. Yee et al 2018 AJ 155 255
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86619
Deposited By: Tony Diaz
Deposited On:25 May 2018 17:03
Last Modified:15 Nov 2021 20:40

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