Five New Extrasolar Planets

Creators: Marcy, Geoffrey W.; Butler, R. Paul; Vogt, Steven S.; Fischer, Debra A.; Henry, Gregory W.; Laughlin, Greg; Wright, Jason T.; Johnson, John A.

Abstract

We report multiple Doppler measurements of five nearby FGK main-sequence stars and subgiants obtained during the past 4-6 yr at the Keck Observatory. These stars, namely, HD 183263, HD 117207, HD 188015, HD 45350, and HD 99492, all exhibit coherent variations in their Doppler shifts consistent with a planet in Keplerian motion. The five new planets occupy known realms of planetary parameter space, including a wide range of orbital eccentricities, e = 0-0.78, and semimajor axes, 0.1-3.8 AU, that provide further statistical information about the true distributions of various properties of planetary systems. One of the planets, HD 99492b, has a low minimum mass of 0.112M_(Jup) = 36M_(Earth). Four of the five planets orbit beyond 1 AU. We describe two quantitative tests of the false alarm probability for Keplerian interpretations of measured velocities. The more robust of these involves Monte Carlo realizations of scrambled velocities as a proxy for noise. Keplerian orbital fits to that "noise" yield the distribution of χ^2_v to compare with χ^2_v from the original (unscrambled) velocities. We establish a 1% false alarm probability as the criterion for candidate planets. All five of these planet-bearing stars are metal-rich, with [Fe/H] > +0.27, reinforcing the strong correlation between planet occurrence and metallicity. From the full sample of 1330 stars monitored at Keck, Lick, and the Anglo-Australian Telescope, the shortest orbital period for any planet is 2.64 days, showing that shorter periods occur less frequently than 0.1% in the solar neighborhood. Photometric observations were acquired for four of the five host stars with an automatic telescope at Fairborn Observatory. The lack of brightness variations in phase with the radial velocities supports planetary-reflex motion as the cause of the velocity variations. No transits were observed, but their occurrence is not ruled out by our observations.

Additional Information

© 2005 American Astronomical Society. Received 2004 June 25; accepted 2004 September 24. 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 A. Cumming, J. Scargle, E. Ford, and P. Stark for valuable discussions about false alarm probability. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff. We appreciate support by NASA grant NAG5-75005 and by NSF grant AST 03-07493 (to S. S. V.); also support by NSF grant AST 99-88087, by NASA grant NAG5-12182, and travel support from the Carnegie Institution of Washington (to R. P. B.). G. W. H. acknowledges support from NASA grant NCC5-511 and NSF grant HRD-9706268. We are also grateful for support by Sun Microsystems. We thank the NASA and UC Telescope assignment committees for allocations of telescope time toward the planet search around M dwarfs. This research has made use of the Simbad database, operated at CDS, Strasbourg, France. The authors wish to extend special thanks to those of Hawaiian 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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