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Seeing Double with K2: Testing Re-inflation with Two Remarkably Similar Planets around Red Giant Branch Stars

Grunblatt, Samuel K. and Huber, Daniel and Gaidos, Eric and Lopez, Eric D. and Howard, Andrew W. and Isaacson, Howard T. and Sinukoff, Evan and Vanderburg, Andrew and Nofi, Larissa and Yu, Jie and North, Thomas S. H. and Chaplin, William and Foreman-Mackey, Daniel and Petigura, Erik and Ansdell, Megan and Weiss, Lauren and Fulton, Benjamin and Lin, Douglas N. C. (2017) Seeing Double with K2: Testing Re-inflation with Two Remarkably Similar Planets around Red Giant Branch Stars. Astronomical Journal, 154 (6). Art. No. 254. ISSN 1538-3881. doi:10.3847/1538-3881/aa932d.

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Despite more than 20 years since the discovery of the first gas giant planet with an anomalously large radius, the mechanism for planet inflation remains unknown. Here, we report the discovery of K2-132b, an inflated gas giant planet found with the NASA K2 Mission, and a revised mass for another inflated planet, K2-97b. These planets orbit on ≈9 day orbits around host stars that recently evolved into red giants. We constrain the irradiation history of these planets using models constrained by asteroseismology and Keck/High Resolution Echelle Spectrometer spectroscopy and radial velocity measurements. We measure planet radii of 1.31 ± 0.11 R J and 1.30 ± 0.07 R_J, respectively. These radii are typical for planets receiving the current irradiation, but not the former, zero age main-sequence irradiation of these planets. This suggests that the current sizes of these planets are directly correlated to their current irradiation. Our precise constraints of the masses and radii of the stars and planets in these systems allow us to constrain the planetary heating efficiency of both systems as 0.03%^(+0.03%)_(-0.02%). These results are consistent with a planet re-inflation scenario, but suggest that the efficiency of planet re-inflation may be lower than previously theorized. Finally, we discuss the agreement within 10% of the stellar masses and radii, and the planet masses, radii, and orbital periods of both systems, and speculate that this may be due to selection bias in searching for planets around evolved stars.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Grunblatt, Samuel K.0000-0003-4976-9980
Huber, Daniel0000-0001-8832-4488
Gaidos, Eric0000-0002-5258-6846
Howard, Andrew W.0000-0001-8638-0320
Isaacson, Howard T.0000-0002-0531-1073
Sinukoff, Evan0000-0002-5658-0601
Vanderburg, Andrew0000-0001-7246-5438
Chaplin, William0000-0002-5714-8618
Foreman-Mackey, Daniel0000-0002-9328-5652
Petigura, Erik0000-0003-0967-2893
Ansdell, Megan0000-0003-4142-9842
Weiss, Lauren0000-0002-3725-3058
Fulton, Benjamin0000-0003-3504-5316
Lin, Douglas N. C.0000-0001-5466-4628
Additional Information:© 2017 The American Astronomical Society. Received 2017 June 19; revised 2017 September 15; accepted 2017 October 10; published 2017 November 27. The authors would like to thank Jonathan Fortney, Ruth Angus, Ashley Chontos, Travis Berger, Allan Simeon, Jr., Jordan Vaughan, and Stephanie Yoshida for helpful discussions. This research was supported by the NASA Origins of Solar Systems grant NNX11AC33G to E.G. and by the NASA K2 Guest Observer Award NNX16AH45G to D.H. D.H. acknowledges support by the Australian Research Council's Discovery Projects funding scheme (project number DE140101364) and support by the National Aeronautics and Space Administration under grant NNX14AB92G issued through the Kepler Participating Scientist Program. W.J.C. and T.S.H.N. acknowledge support from the UK Science and Technology Facilities Council (STFC). A.V. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1144152. This research made use of the Exoplanet Orbit Database and the Exoplanet Data Explorer at This work benefited from the Exoplanet Summer Program in the Other Worlds Laboratory (OWL) at the University of California, Santa Cruz, a program funded by the Heising-Simons Foundation. This work was based on observations at the W. M. Keck Observatory granted by the University of Hawaii, the University of California, and the California Institute of Technology. We thank the observers who contributed to the measurements reported here and acknowledge the efforts of the Keck Observatory staff. We extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Maunakea we are privileged to be guests. Some/all of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. This research made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research made use of the SIMBAD and VIZIER Astronomical Databases, operated at CDS, Strasbourg, France (, and of NASAs Astrophysics Data System, of the Jean-Marie Mariotti Center Search service (, co-developed by FIZEAU and LAOG/IPAG. E.D.L. received funding from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement number 313014 (ETAEARTH). Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
Group:Astronomy Department
Funding AgencyGrant Number
Australian Research CouncilDE140101364
Science and Technology Facilities Council (STFC)UNSPECIFIED
NSF Graduate Research FellowshipDGE-1144152
Heising-Simons FoundationUNSPECIFIED
European Research Council (ERC)313014
Subject Keywords:planet–star interactions – planets and satellites: detection – planets and satellites: gaseous planets – planets and satellites: physical evolution – stars: fundamental parameters – stars: oscillations
Issue or Number:6
Record Number:CaltechAUTHORS:20171128-073236272
Persistent URL:
Official Citation:Samuel K. Grunblatt et al 2017 AJ 154 254
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83482
Deposited By: Tony Diaz
Deposited On:28 Nov 2017 17:04
Last Modified:15 Nov 2021 19:58

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