A determination of the spin-orbit alignment of the anomalously dense planet orbiting HD 149026

Creators: Wolf, Aaron S.; Laughlin, Gregory; Henry, Gregory W.; Fischer, Debra A.; Marcy, Geoffrey W.; Butler, Paul; Vogt, Steve

Abstract

We report 35 radial velocity measurements of HD 149026 taken with the Keck Telescope. Of these measurements, 15 were made during the transit of the companion planet HD 149026b, which occurred on 2005 June 25. These velocities provide a high-cadence observation of the Rossiter-McLaughlin effect, the shifting of photospheric line profiles that occurs when a planet occults a portion of the rotating stellar surface. We combine these radial velocities with previously published radial velocity and photometric data sets and derive a composite best-fit model for the star-planet system. This model confirms and improves previously published orbital parameters, including the remarkably small planetary radius, the planetary mass, and the orbital inclination, found to be Rp/RJup = 0.718 ± 0.065, Mp/MJup = 0.352 ± 0.025, and I = 86.1° ± 1.4°, respectively. Together the planetary mass and radius determinations imply a mean planetary density of 1.18(-0.30)(+0.38)g cm(-3). The new data also allow for the determination of the angle between the apparent stellar equator and the orbital plane, which we constrain to be λ = -12° ± 15°.

Additional Information

© 2007. The American Astronomical Society. Received 2005 November 1; accepted 2006 February 11. We thank Peter Bodenheimer, David Charbonneau, and Josh Winn for useful discussions. Aaron Wolf's research on this project was supported by the NASA Astrobiology Institute through grant NNA 04-CC99A (to G.L.). This research was also supported by NASA grant NNG 04-GK19G and NSF grant AST 04-49986 (to G.L.); NASA grant NNG 05-G164G (to D.A.F.); NASA grant NCC 5-511 and NSF grant HRD 97-06268 (to G.W.H.); NSF grant AST 03-07493 (to S.S.V.); NSF grant AST 99-88087 and travel support from the Carnegie Institution of Washington (to R.P.B.); NASA grant NAG5-8299 and NSF grant AST 95-20443 (to G.W.M.); and by Sun Microsystems. This research has made use of the Simbad database, operated at CDS, Strasbourg, France. 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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