Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets

Creators: Marcy, Geoffrey W.; Howard, Andrew W.; Ciardi, David; Rogers, Leslie; Morton, Timothy; Johnson, John Asher; Shporer, Avi

Abstract

We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm^(–3), suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than ~2 R_⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H_2O).

Additional Information

© 2014 American Astronomical Society. Received 2013 October 28; accepted 2013 December 12; published 2014 January 13. Based in part on observations obtained at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology. Kepler was competitively selected as the tenth NASA Discovery mission. Funding for this mission is provided by the NASA Science Mission Directorate. Some of 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 Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Some of the asteroseismology analysis was performed by the Stellar Astrophysics Centre which is funded by the Danish National Research Foundation (Grant DNRF106). The research is supported by the ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) funded by the European Research Council (Grant 267864). D.H. is supported by an appointment to the NASA Postdoctoral Program at Ames Research Center, administered by Oak Ridge Associated Universities through a contract with NASA. W.J.C., Y.E., T.L.C., G.R.D, R.H and A.M. acknowledge financial support from the UK Science and Technology Facilities Council (STFC). S.B. acknowledges NSF grant AST-1105930. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant agreement no.: DNRF106). The research is supported by the ASTERISK project (ASTERoseismic Investigations with SONG and Kepler) funded by the European Research Council (Grant agreement no. 267864). S.H. acknowledges financial support from the Netherlands organisation for Scientific Research (NWO). The research leading to the presented results has received funding from the European Research Council under the European Community's Seventh Framewrok Programme (FP7/2007-2013)/ERC grant agreement no. 338251 (StellarAges).W. F.Welsh and J. A. Orosz acknowledge support from NASA through the Kepler Participating Scientist Program and from the NSF via grant AST-1109928. D. Fischer acknowledges support from NASA ADAP12-0172. O. R. Sanchis-Ojeda & J. N. Winn are supported by the Kepler Participating Scientist Program (PSP) through grant NNX12AC76G. E. Ford is partially supported by NASA PSP grants NNX08AR04G & NNX12AF73G. Eric Agol acknowledges NSF Career grant AST-0645416. R.L.G. has been partially supported by NASA co-operative agreement: NNX09AG09A. A. Santerne acknowledges the support by the European Research Council/European Community under the FP7 through Starting Grant agreement number 239953. The authors would like to thank the many people who gave so generously of their time to make this Mission a success. All Kepler data products are available to the public at the Mikulski Archive for Space Telescopes http://stdatu.stsci.edu/kepler and the spectra and their products are made available at the NExSci Exoplanet Archive and its CFOP Web site: http://exoplanetarchive.ipac.caltech.edu. We thank 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, Hien Tran, and Grant Hill for support with HIRES and Greg Wirth for support with remote observing. This work made use of the SIMBAD database (operated at CDS, Strasbourg, France) and NASA's Astrophysics Data System Bibliographic Services. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Finally, the authors wish to extend special thanks to those of Hawai'ian 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.

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