A New Planet around an M Dwarf: Revealing a Correlation between Exoplanets and Stellar Mass

Creators: Johnson, John Asher; Butler, R. Paul; Marcy, Geoffrey W.; Fischer, Debra A.; Vogt, Steven S.; Wright, Jason T.; Peek, Kathryn M. G.

Abstract

We report precise Doppler measurements of GJ 317 (M3.5 V) that reveal the presence of a planet with a minimum mass M_P sin i = 1.2 M_(Jup) in an eccentric, 692.9 day orbit. GJ 317 is only the third M dwarf with a Doppler-detected Jovian planet. The residuals to a single-Keplerian fit show evidence of a possible second orbital companion. The inclusion of a second Jupiter-mass planet (P ≈ 2700 days, M_P sin i = 0.83 M_(Jup)) decreases √X_v^2 from 2.02 to 1.23, and reduces the rms from 12.5 to 6.32 m s^(-1). A false-alarm test yields a 1.1% probability that the curvature in the residuals of the single-planet fit is due to random fluctuations, lending additional credibility to the two-planet model. However, our data only marginally constrain a two-planet fit, and further monitoring is necessary to fully characterize the properties of the second companion. To study the effect of stellar mass on giant planet occurrence, we measure the fraction of stars with planets in three mass bins comprised of our samples of M Dwarfs, solar-mass stars, and intermediate-mass subgiants. We find a positive correlation between stellar mass and the occurrence rate of Jovian planets within 2.5 AU. Low-mass K and M stars have a 1.8% ± 1.0% planet occurrence rate compared to 4.2% ± 0.7% for solar-mass stars and 8.9% ± 2.9% for the higher mass subgiants. This result indicates that the former F- and A-type stars with M_* ≥ 1.3 M_☉ in our sample are nearly 5 times more likely than the M dwarfs to harbor a giant planet. Our analysis shows that the correlation between Jovian planet occurrence and stellar mass exists even after correcting for the effects of stellar metallicity.

Additional Information

© 2007 American Astronomical Society. Received 2007 June 15; accepted 2007 July 17. 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 gratefully acknowledge the efforts and dedication of the Lick Observatory and Keck Observatory staff.We are also grateful to the time assignment committees of NASA, NOAO, and the University of California for their generous allocations of observing time. We thank Ben Zuckerman for his thought-provoking conversations regarding M dwarf metallicities. We acknowledge support by NSF grants AST 07-02821 (to J.A. J.) and AST 03-07493 (to S. S. V.); AST 99-88087, NASA grant NAG5-12182, and travel support from the Carnegie Institution of Washington (to R. P. B.); and NASA grant NAG5-8299 and NSF grant AST 95-20443 (to G. W. M.). D. A. F. is a Cottrell Science Scholar of Research Corporation and acknowledges support from NASA grant NNG 05G164G, which made this work possible. This research has made use of the Simbad database operated at CDS, Strasbourg, France, and the NASA ADS database. Finally the authors wish to extend 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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