California Legacy Survey. II. Occurrence of Giant Planets beyond the Ice Line

Creators: Fulton, Benjamin J.; Rosenthal, Lee J.; Hirsch, Lea A.; Isaacson, Howard; Howard, Andrew W.; Dedrick, Cayla M.; Sherstyuk, Ilya A.; Blunt, Sarah C.; Petigura, Erik A.; Knutson, Heather A.; Behmard, Aida; Chontos, Ashley; Crepp, Justin R.; Crossfield, Ian J. M.; Dalba, Paul A.; Fischer, Debra A.; Henry, Gregory W.; Kane, Stephen R.; Kosiarek, Molly; Marcy, Geoffrey W.; Rubenzahl, Ryan A.; Weiss, Lauren M.; Wright, Jason T.

Abstract

We used high-precision radial velocity measurements of FGKM stars to determine the occurrence of giant planets as a function of orbital separation spanning 0.03–30 au. Giant planets are more prevalent at orbital distances of 1–10 au compared to orbits interior or exterior of this range. The increase in planet occurrence at ~1 au by a factor of ~4 is highly statistically significant. A fall-off in giant planet occurrence at larger orbital distances is favored over models with flat or increasing occurrence. We measure 14.1^(+2.0)_(-1.8) giant planets per 100 stars with semimajor axes of 2–8 au and 8.9^(+3.0)_(-2.4) giant planets per 100 stars in the range 8–32 au, a decrease in occurrence with increasing orbital separation that is significant at the ~2σ level. We find that the occurrence rate of sub-Jovian planets (0.1–1 Jupiter masses) is also enhanced for 1–10 au orbits. This suggests that lower-mass planets may share the formation or migration mechanisms that drive the increased prevalence near the water–ice line for their Jovian counterparts. Our measurements of cold gas giant occurrence are consistent with the latest results from direct imaging surveys and gravitational lensing surveys despite different stellar samples. We corroborate previous findings that giant planet occurrence increases with stellar mass and metallicity.

Additional Information

© 2021. The American Astronomical Society. Received 2021 March 19; revised 2021 April 22; accepted 2021 April 27; published 2021 July 9. We thank Jay Anderson, Gáspár Bakos, Mike Bottom, John Brewer, Christian Clanton, Jason Curtis, Fei Dai, Steven Giacalone, Sam Grunblatt, Michelle Hill, Lynne Hillenbrand, Rebecca Jensen-Clem, John A. Johnson, Chris McCarthy, Sean Mills, Teo Močnik, Ben Montet, Jack Moriarty, Tim Morton, Phil Muirhead, Sebastian Pineda, Nikolai Piskunov, Eugenio Rivera, Julien Spronck, Jonathan Swift, Guillermo Torres, Jeff Valenti, Sharon Wang, Josh Winn, Judah van Zandt, Ming Zhao, and others who contributed to the observations and analysis required for the CLS project. We acknowledge R. P. Butler and S. S. Vogt for many years of contributing to this data set. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. We acknowledge RVs stemming from HIRES data in KOA with principal investigators from the LCES collaboration (S. S. Vogt, R. P. Butler, and N. Haghighipour). We gratefully acknowledge the efforts and dedication of the Keck Observatory staff for support of HIRES and remote observing. We are grateful to the time assignment committees of the Caltech, the University of California, the University of Hawaii, NASA, and NOAO for their generous allocations of observing time. Without their long-term commitment to radial velocity monitoring, these planets would likely remain unknown. We thank Ken and Gloria Levy, who supported the construction of the Levy Spectrometer on the Automated Planet Finder, which was used heavily for this research. We thank the University of California and Google for supporting Lick Observatory, and the UCO staff as well as UCO director Claire Max for their dedicated work scheduling and operating the telescopes of Lick Observatory. G.W.H. acknowledges long-term support from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence program. A.W.H. acknowledges NSF grant 1753582. H.A.K. acknowledges NSF grant 1555095. P.D. gratefully acknowledges support from a National Science Foundation (NSF) Astronomy & Astrophysics Postdoctoral Fellowship under award AST-1903811. The Center for Exoplanets and Habitable Worlds and the Penn State Extraterrestrial Intelligence Center are supported by the Pennsylvania State University and the Eberly College of Science. This research has made use of NASA's Astrophysics Data System. This work has made use of data from the European Space Agency (ESA) mission Gaia (cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Finally, the authors wish to recognize and acknowledge the 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. Facility: Keck:I (HIRES) - . Software: All code used in this paper is available at github.com/California-Planet-Search/rvsearch and github.com/leerosenthalj/CLSII. This research makes use of GNU Parallel (Tange 2011). We made use of the following publicly available Python modules: astropy (Astropy Collaboration et al. 2013), matplotlib (Hunter 2007), numpy/scipy (van der Walt et al. 2011), pandas (McKinney 2010), emcee (Foreman-Mackey et al. 2013), and RadVel (Fulton et al. 2018).

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