The NASA-UC-UH ETA-Earth Program. IV. A Low-mass Planet Orbiting an M Dwarf 3.6 PC from Earth

Creators: Howard, Andrew W.; Marcy, Geoffrey W.; Fischer, Debra A.; Isaacson, Howard; Muirhead, Philip S.; Henry, Gregory W.; Boyajian, Tabetha S.; von Braun, Kaspar; Becker, Juliette C.; Wright, Jason T.; Johnson, John Asher

Abstract

We report the discovery of a low-mass planet orbiting Gl 15 A based on radial velocities from the Eta-Earth Survey using HIRES at Keck Observatory. Gl 15 Ab is a planet with minimum mass M sin i = 5.35 ± 0.75 M_⊕, orbital period P = 11.4433 ± 0.0016 days, and an orbit that is consistent with circular. We characterize the host star using a variety of techniques. Photometric observations at Fairborn Observatory show no evidence for rotational modulation of spots at the orbital period to a limit of ~0.1 mmag, thus supporting the existence of the planet. We detect a second RV signal with a period of 44 days that we attribute to rotational modulation of stellar surface features, as confirmed by optical photometry and the Ca ii H & K activity indicator. Using infrared spectroscopy from Palomar-TripleSpec, we measure an M2 V spectral type and a sub-solar metallicity ([M/H] = −0.22, [Fe/H] = −0.32). We measure a stellar radius of 0.3863 ± 0.0021 R_☉ based on interferometry from CHARA.

Additional Information

© 2014 The American Astronomical Society. Received 2013 June 13; accepted 2014 August 13; published 2014 September 23. 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, Greg Doppman, Hien Tran, and Grant Hill for support of HIRES and Greg Wirth for support of remote observing. We thank Kevin Apps, Andrew Mann, Evan Sinukoff, and Calla Howard for helpful discussions.We are grateful to the time assignment committees of the University of Hawaii, the University of California, and NASA for their generous allocations of observing time. Without their long-term commitment to RV monitoring, this planet would likely remain unknown. We acknowledge R. Paul Butler and S.S. Vogt for many years of contributing to the data presented here. A.W.H. acknowledges NASA grant NNX12AJ23G. G.W.H. acknowledges support fromNASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence program. J.A.J. gratefully acknowledges support from generous grants from the David & Lucile Packard and Alfred P. Sloan Foundations. This work made use of the SIMBAD database (operated at CDS, Strasbourg, France), NASA's Astrophysics Data System Bibliographic Services, and the NASA Star and Exoplanet Database (NStED). 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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Submitted - 1408.5645v1.pdf

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