Confirmation of a Retrograde Orbit for Exoplanet WASP-17b
Abstract
We present high-precision radial velocity observations of WASP-17 throughout the transit of its close-in giant planet, using the MIKE spectrograph on the 6.5 m Magellan Telescope at Las Campanas Observatory. By modeling the Rossiter-McLaughlin effect, we find the sky-projected spin-orbit angle to be λ = 167.4 ± 11.2 deg. This independently confirms the previous finding that WASP-17b is on a retrograde orbit, suggesting it underwent migration via a mechanism other than just the gravitational interaction between the planet and the disk. Interestingly, our result for λ differs by 45 ± 13 deg from the previously announced value, and we also find that the spectroscopic transit occurs 15 ± 5 minutes earlier than expected, based on the published ephemeris. The discrepancy in the ephemeris highlights the need for contemporaneous spectroscopic and photometric transit observations whenever possible.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2010
- DOI:
- 10.1088/2041-8205/722/2/L224
- arXiv:
- arXiv:1009.5061
- Bibcode:
- 2010ApJ...722L.224B
- Keywords:
-
- planets and satellites: dynamical evolution and stability;
- planets and satellites: individual: WASP-17b;
- stars: individual: WASP-17;
- techniques: radial velocities;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 4 pages, 3 figures, accepted for publication in ApJ Letters