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The California-Kepler Survey. IV. Metal-rich Stars Host a Greater Diversity of Planets

Petigura, Erik A. and Marcy, Geoffrey W. and Winn, Joshua N. and Weiss, Lauren M. and Fulton, Benjamin J. and Howard, Andrew W. and Sinukoff, Evan and Isaacson, Howard and Morton, Timothy D. and Johnson, John Asher (2018) The California-Kepler Survey. IV. Metal-rich Stars Host a Greater Diversity of Planets. Astronomical Journal, 155 (2). Art. No. 89. ISSN 1538-3881. doi:10.3847/1538-3881/aaa54c.

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Probing the connection between a star's metallicity and the presence and properties of any associated planets offers an observational link between conditions during the epoch of planet formation and mature planetary systems. We explore this connection by analyzing the metallicities of Kepler target stars and the subset of stars found to host transiting planets. After correcting for survey incompleteness, we measure planet occurrence: the number of planets per 100 stars with a given metallicity M. Planet occurrence correlates with metallicity for some, but not all, planet sizes and orbital periods. For warm super-Earths having P = 10–100 days and R_P = 1.0–1.7 R⊕, planet occurrence is nearly constant over metallicities spanning −0.4 to +0.4 dex. We find 20 warm super-Earths per 100 stars, regardless of metallicity. In contrast, the occurrence of warm sub-Neptunes (R_P= 1.7–4.0 R⊕) doubles over that same metallicity interval, from 20 to 40 planets per 100 stars. We model the distribution of planets as df ∝ 10^(βM) dM, where β characterizes the strength of any metallicity correlation. This correlation steepens with decreasing orbital period and increasing planet size. For warm super-Earths β = -0.3^(+0.2)_(-0.2), while for hot Jupiters β = +3.4^(+0.9)_(-0.8). High metallicities in protoplanetary disks may increase the mass of the largest rocky cores or the speed at which they are assembled, enhancing the production of planets larger than 1.7 R⊕. The association between high metallicity and short-period planets may reflect disk density profiles that facilitate the inward migration of solids or higher rates of planet–planet scattering.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Petigura, Erik A.0000-0003-0967-2893
Marcy, Geoffrey W.0000-0002-2909-0113
Winn, Joshua N.0000-0002-4265-047X
Weiss, Lauren M.0000-0002-3725-3058
Fulton, Benjamin J.0000-0003-3504-5316
Howard, Andrew W.0000-0001-8638-0320
Sinukoff, Evan0000-0002-5658-0601
Isaacson, Howard0000-0002-0531-1073
Morton, Timothy D.0000-0002-8537-5711
Johnson, John Asher0000-0001-9808-7172
Additional Information:© 2018 The American Astronomical Society. Received 2017 October 24; revised 2017 December 23; accepted 2017 December 27; published 2018 January 29. The CKS project was conceived, planned, and initiated by A.W.H., G.W.M., J.A.J., H.T.I., and T.D.M. A.W.H., G.W.M., J.A.J. acquired Keck telescope time to conduct the magnitude-limited survey. We thank the many observers who contributed to the measurements reported here. We thank the referee, Lars Buchhave, for his detailed and thoughtful comments on the techniques and interpretations. We also thank Konstantin Batygin, Brendan Bowler, Ian Crossfield, and Eve Lee for enlightening conversations that improved the final manuscript. Kepler was competitively selected as the tenth NASA Discovery mission. Funding for this mission is provided by the NASA Science Mission Directorate. We thank the Kepler Science Office, the Science Operations Center, the Threshold Crossing Event Review Team (TCERT), and the Follow-up Observations Program (FOP) Working Group for their work on all steps in the planet discovery process, ranging from selecting target stars and pointing the Kepler telescope to developing and running the photometric pipeline to curating and refining the catalogs of Kepler planets. The Guoshoujing Telescope (the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST) is a National Major Scientific Project built by the Chinese Academy of Sciences. Funding for the project has been provided by the National Development and Reform Commission. LAMOST is operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences. E.A.P. acknowledges support from 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. L.M.W. acknowledges support from Gloria and Ken Levy and from the Trottier Family. T.D.M. acknowledges NASA grant NNX14AE11G. This work made use of NASA's Astrophysics Data System Bibliographic Services. Finally, the authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Software: All code used in this paper is available at We made use of the following publicly available Python modules: astropy (Astropy Collaboration et al. 2013), isoclassify (Huber et al. 2017), lmfit (Newville et al. 2014), matplotlib (Hunter 2007), numpy/scipy (van der Walt et al. 2011), pandas (McKinney 2010), and pinky (
Group:Infrared Processing and Analysis Center (IPAC), Astronomy Department
Funding AgencyGrant Number
Chinese Academy of SciencesUNSPECIFIED
National Development and Reform Commission (China)UNSPECIFIED
National Astronomical Observatories, Chinese Academy of Sciences (NAOC)UNSPECIFIED
NASA Hubble FellowshipHST-HF2-51365.001-A
NASANAS 5-26555
Gloria and Ken LevyUNSPECIFIED
Trottier Family FoundationUNSPECIFIED
Subject Keywords:methods: statistical – planets and satellites: formation – planets and satellites: general – stars: abundances – stars: fundamental parameters – techniques: spectroscopic
Issue or Number:2
Record Number:CaltechAUTHORS:20180103-141600568
Persistent URL:
Official Citation:Erik A. Petigura et al 2018 AJ 155 89
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84066
Deposited By: George Porter
Deposited On:03 Jan 2018 22:42
Last Modified:15 Nov 2021 20:16

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