The California Legacy Survey. IV. Lonely, Poor, and Eccentric: A Comparison between Solitary and Neighborly Gas Giants

Creators: Rosenthal, Lee J.; Howard, Andrew W.¹; Knutson, Heather A.¹; Fulton, Benjamin J.

1. California Institute of Technology

Abstract

We compare systems with single giant planets to systems with multiple giant planets using a catalog of planets from a high-precision radial velocity survey of FGKM stars. Our comparison focuses on orbital properties, planet masses, and host-star properties. We use hierarchical methods to model the orbital eccentricity distributions of giant singles and giant multiples, and find that the distributions are distinct. The multiple giant planets typically have moderate eccentricities and their eccentricity distribution extends to e = 0.47 (90th percentile), while the single giant planets have a pileup of nearly circular orbits and a long tail that extends to e = 0.77. We determine that the stellar hosts of multiple giants are distinctly more metal rich than the hosts of solitary giants, with respective mean metallicities of 0.228 ± 0.027 versus 0.129 ± 0.019 dex. We measure the distinct occurrence distributions of single and multiple giants with respect to orbital separation, and find that single gas giants have a ∼2.3σ significant hot Jupiter (a < 0.06) pileup not seen among multigiant systems. We find that the median mass (M sin i) of giants in multiples is nearly double that of single giants (1.71 M_J versus 0.92 M_J). We find that giant planets in the same system have correlated masses, analogous to the "peas in a pod" effect seen among less-massive planets.

Copyright and License

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

L.J.R. led the construction of this paper, including performing all analysis, generating all of the figures, and writing this article. H.A.K. and A.W.H. advised substantially on the scientific direction of this work. B.J.F. collaborated on occurrence analysis.

A.W.H. acknowledges NSF grant 1753582. H.A.K. acknowledges NSF grant 1555095.

We thank Fei Dai, Lauren Weiss, and Konstantin Batygin for valuable discussions.

This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.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.

Software References

All code used in this paper is available at https://github.com/California-Planet-Search/rvsearch and github.com/leerosenthalj/CLSIV. 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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