Howard, Andrew W. and Johnson, John Asher and Marcy, Geoffrey W. and Fischer, Debra A. and Wright, Jason T. and Henry, Gregory W. and Isaacson, Howard and Valenti, Jeff A. and Anderson, Jay and Piskunov, Nikolai E. (2011) The NASA-UC Eta-Earth Program. II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses. Astrophysical Journal, 726 (2). Art. No. 73. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110201-145242900
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We report the discovery of HD 156668 b, an extrasolar planet with a minimum mass of M_P sin i = 4.15 M_⊕. This planet was discovered through Keplerian modeling of precise radial velocities from Keck-HIRES and is the second super-Earth to emerge from the NASA-UC Eta-Earth Survey. The best-fit orbit is consistent with circular and has a period of P = 4.6455 days. The Doppler semi-amplitude of this planet, K = 1.89 m s^(−1), is among the lowest ever detected, on par with the detection of GJ 581 e using HARPS. A longer period (P ≈ 2.3 years), low-amplitude signal of unknown origin was also detected in the radial velocities and was filtered out of the data while fitting the short-period planet. Additional data are required to determine if the long-period signal is due to a second planet, stellar activity, or another source. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 156668 (an old, quiet K3 dwarf) is photometrically constant over the radial velocity period to 0.1 mmag, supporting the existence of the planet. No transits were detected down to a photometric limit of ~3 mmag, ruling out transiting planets dominated by extremely bloated atmospheres, but not precluding a transiting solid/liquid planet with a modest atmosphere.
|Additional Information:||© 2011 The American Astronomical Society. Received 2010 March 16; accepted 2010 October 29; published 2010 December 16. 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 both NASA and the University of California. We thank the many observers who contributed to the velocities reported here. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff, especially Scott Dahm, Hien Tran, and Grant Hill for support of HIRES and Greg Wirth for support of remote observing. We thank Heather Knutson, Doug Lin, Shigeru Ida, Jeff Scargle, and Ian Howard for helpful discussions. We are grateful to the time assignment committees of the University of California, NASA, and NOAO for their generous allocations of observing time. Without their long-term commitment to RV monitoring, these long-period planets 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. gratefully acknowledges support from a Townes Post-doctoral Fellowship at the U. C. Berkeley Space Sciences Laboratory. G.W.M. acknowledges the NASA Grant NNX06AH52G. G.W.H. acknowledges support from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence program. J.T.W. was partially supported by funding from the Center for Exoplanets and Habitable Worlds. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. 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.|
|Subject Keywords:||planetary systems – stars: individual (HD 156668) – techniques: radial velocities|
|Classification Code:||PACS: 97.82.-j; 97.10.Kc; 97.20.Jg; 95.75.De|
|Official Citation:||Andrew W. Howard et al. 2011 ApJ 726 73 doi: 10.1088/0004-637X/726/2/73|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Benjamin Perez|
|Deposited On:||02 Feb 2011 00:07|
|Last Modified:||26 Dec 2012 12:53|
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