Limits on Planetary Companions from Doppler Surveys of Nearby Stars

Creators: Howard, Andrew W.; Fulton, Benjamin J.

Abstract

Most of our knowledge of planets orbiting nearby stars comes from Doppler surveys. For spaced-based, high-contrast imaging missions, nearby stars with Doppler-discovered planets are attractive targets. The known orbits tell imaging missions where and when to observe, and the dynamically determined masses provide important constraints for the interpretation of planetary spectra. Quantifying the set of planet masses and orbits that could have been detected will enable more efficient planet discovery and characterization. We analyzed Doppler measurements from Lick and Keck Observatories by the California Planet Survey. We focused on stars that are likely targets for three space-based planet imaging mission concepts studied by NASA—WFIRST-AFTA, Exo-C, and Exo-S. The Doppler targets are primarily F8 and later main sequence stars, with observations spanning 1987–2014. We identified 76 stars with Doppler measurements from the prospective mission target lists. We developed an automated planet search and a methodology to estimate the pipeline completeness using injection and recovery tests. We applied this machinery to the Doppler data and computed planet detection limits for each star as a function of planet minimum mass and semimajor axis. For typical stars in the survey, we are sensitive to approximately Saturn-mass planets inside of 1 au, Jupiter-mass planets inside of ~3 au, and our sensitivity declines out to ~10 au. For the best Doppler targets, we are sensitive to Neptune-mass planets in 3 au orbits. Using an idealized model of Doppler survey completeness, we forecast the precision of future surveys of non-ideal Doppler targets that are likely targets of imaging missions.

Additional Information

© 2016 The Astronomical Society of the Pacific. Received 2015 December 18; accepted 2016 May 12; published 2016 September 27. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology. Keck time has been granted by NASA, the University of California, and the University of Hawaii. We thank Karl Stapelfeldt and Sara Seager for instigating us and the JPL Program Office to make this study happen. Thanks to Steve Unwin for cheerfully and skillfully shepherding our work on this study and to Margaret Turnbull for providing target lists and associated stellar properties and for helpful conversations. We thank the many observers who contributed to the measurements reported here, including Geoff Marcy, Debra Fischer, Jason Wright, John Johnson, R. Paul Butler, and Steve Vogt. We gratefully acknowledge the efforts and dedication of the staffs of Lick Observatory and Keck Observatory and the time assignment committees of the University of Hawaii, the University of California, NASA, the California Institute of Technology, and Yale University for their generous allocations of observing time over the past two decades that enabled these measurements. We thank Geoff Marcy for helpful comments. We acknowledge NASA-JPL award #1505707. This work made use of the SIMBAD database (operated at CDS, Strasbourg, France), NASA's Astrophysics Data System Bibliographic Services, the NASA Star and Exoplanet Database (NStED), the Exoplanet Orbit Database and the Exoplanet Data Explorer at exoplanets.org. Finally, we extend special thanks to those of Hawai'ian ancestry on whose sacred mountain of Maunakea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible. Facilities: Lick (Hamilton Spectrograph) - , Keck (HIRES).

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