Absence of a metallicity effect for ultra-short-period planets

Creators: Winn, Joshua N.; Sanchis-Ojeda, Roberto; Rogers, Leslie; Petigura, Erik A.; Howard, Andrew W.; Isaacson, Howard; Marcy, Geoffrey W.; Schlaufman, Kevin C.; Cargile, Phillip; Hebb, Leslie

Abstract

Ultra-short-period (USP) planets are a newly recognized class of planets with periods shorter than one day and radii smaller than about 2 R⊕. It has been proposed that USP planets are the solid cores of hot Jupiters that have lost their gaseous envelopes due to photo-evaporation or Roche lobe overflow. We test this hypothesis by asking whether USP planets are associated with metal-rich stars, as has long been observed for hot Jupiters. We find the metallicity distributions of USP-planet and hot-Jupiter hosts to be significantly different (p = 3 × 10^(−4)) based on Keck spectroscopy of Keplerstars. Evidently, the sample of USP planets is not dominated by the evaporated cores of hot Jupiters. The metallicity distribution of stars with USP planets is indistinguishable from that of stars with short-period planets with sizes between 2 and 4 R⊕. Thus, it remains possible that the USP planets are the solid cores of formerly gaseous planets that are smaller than Neptune.

Additional Information

© 2017 The American Astronomical Society. Received 2017 April 1; Accepted 2017 June 21; Published 2017 July 20. We thank the anonymous referee for a prompt and helpful report. We thank Simon Albrecht, Eugene Chiang, Brian Jackson, Eve Lee, Peter McCullough, Saul Rappaport, Amaury Triaud, and Francesca Valsecchi for helpful discussions. We also thank Enric Palle for sharing his results for KIC 5955905. J.N.W. acknowledges the support from a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. A.W.H. acknowledges the support from NASA grant NNX12AJ23G. Data presented herein were obtained at the W.M. Keck Observatory from telescope time allocated to the National Aeronautics and Space Administration through the agency's scientific partnership with the California Institute of Technology and the University of California. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. 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 was granted by NASA, the University of California, the California Institute of Technology, and the University of Hawaii.

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Submitted - 1704.00203.pdf

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