LOW STELLAR OBLIQUITIES IN COMPACT MULTIPLANET SYSTEMS
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Author(s)
Albrecht, Simon H.
Marcy, Geoffrey W.
Howard, Andrew W.
Isaacson, Howard
Johnson, John Asher
Winn, Joshua Nathan
Date Issued
June 2013
Journal
The Astrophysical Journal
Publisher
IOP Publishing
Citation
Albrecht, Simon, Joshua N. Winn, Geoffrey W. Marcy, Andrew W. Howard, Howard Isaacson, and John A. Johnson. “LOW STELLAR OBLIQUITIES IN COMPACT MULTIPLANET SYSTEMS.” The Astrophysical Journal 771, no. 1 (June 10, 2013): 11.
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Author's final manuscript
Abstract
We measure the sky-projected stellar obliquities (λ) in the multiple-transiting planetary systems KOI-94 and Kepler-25, using the Rossiter-McLaughlin effect. In both cases, the host stars are well aligned with the orbital planes of the planets. For KOI-94 we find λ = –11° ± 11°, confirming a recent result by Hirano and coworkers. Kepler-25 was a more challenging case, because the transit depth is unusually small (0.13%). To obtain the obliquity, it was necessary to use prior knowledge of the star's projected rotation rate and apply two different analysis methods to independent wavelength regions of the spectra. The two methods gave consistent results, λ = 7° ± 8° and –0[° over .]5 ± 5[° over .]7. There are now a total of five obliquity measurements for host stars of systems of multiple-transiting planets, all of which are consistent with spin-orbit alignment. This alignment is unlikely to be the result of tidal interactions because of the relatively large orbital distances and low planetary masses in the systems. In this respect, the multiplanet host stars differ from hot-Jupiter host stars, which commonly have large spin-orbit misalignments whenever tidal interactions are weak. In particular, the weak-tide subset of hot-Jupiter hosts has obliquities consistent with an isotropic distribution (p = 0.6), but the multiplanet hosts are incompatible with such a distribution (p ~ 10[superscript –6]). This suggests that high obliquities are confined to hot-Jupiter systems, and provides further evidence that hot-Jupiter formation involves processes that tilt the planetary orbit.
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1088/0004-637X/771/1/11
