Astronomy and Astrophysics – Astrophysics – Earth and Planetary Astrophysics
Scientific paper
2010-09-26
Astronomy and Astrophysics
Astrophysics
Earth and Planetary Astrophysics
4 pages, 3 figures, accepted for publication in ApJ Letters
Scientific paper
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 6.5m Magellan Telescope at Las Campanas Observatory. By modeling the Rossiter-McLaughlin effect, we find the sky-projected spin-orbit angle to be lambda = 167.4 \pm 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 lambda differs by 45 \pm 13 deg from the previously announced value, and we also find that the spectroscopic transit occurs 15 \pm 5 min 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.
Bayliss Daniel D. R.
Mardling Rosemary A.
Sackett Penny D.
Winn Joshua N.
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