Albrecht, Simon and Winn, Joshua N. and Johnson, John Asher and Butler, R. Paul and Crane, Jeffrey D. and Shectman, Stephen A. and Thompson, Ian B. and Narita, Norio and Sato, Bun'ei and Hirano, Teruyuki and Enya, Keigo and Fischer, Debra (2011) Two Upper Limits on the Rossiter-Mclaughlin Effect, with Differing Implications: WASP-1 has a High Obliquity and WASP-2 is Indeterminate. Astrophysical Journal, 738 (1). Art. No. 50. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110908-120943442
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We present precise radial-velocity (RV) measurements of WASP-1 and WASP-2 throughout transits of their giant planets. Our goal was to detect the Rossiter-McLaughlin (RM) effect, the anomalous RV observed during eclipses of rotating stars, which can be used to study the obliquities of planet-hosting stars. For WASP-1, a weak signal of a prograde orbit was detected with ≈2σ confidence, and for WASP-2 no signal was detected. The resulting upper bounds on the RM amplitude have different implications for these two systems because of the contrasting transit geometries and the stellar types. Because WASP-1 is an F7V star, and such stars are typically rapid rotators, the most probable reason for the suppression of the RM effect is that the star is viewed nearly pole-on. This implies that the WASP-1 star has a high obliquity with respect to the edge-on planetary orbit. Because WASP-2 is a K1V star, and is expected to be a slow rotator, no firm conclusion can be drawn about the stellar obliquity. Our data and our analysis contradict an earlier claim that WASP-2b has a retrograde orbit, thereby revoking this system's status as an exception to the pattern that cool stars have low obliquities.
|Additional Information:||© 2011 American Astronomical Society. Received 2011 May 19; accepted 2011 June 10; published 2011 August 11. The data presented herein were collected with the Magellan (Clay) Telescope located at Las Campanas Observatory, Chile; the Subaru telescope, which is operated by the National Astronomical Observatory of Japan; and the Keck I telescope at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. We thank G. Marcy and M. Holman for help gathering some of the data presented here. We are grateful to the anonymous referee for a prompt and insightful report, and to Amaury Triaud for comments on the manuscript. S.A. acknowledges support by a Rubicon fellowship from the Netherlands Organization for Scientific Research (NWO). J.N.W. acknowledges support from a NASA Origins grant (NNX09AD36G). This research has made use of the Simbad database located at http://simbad.u-strasbg.fr/. Facilities: Keck:I, Subaru, Magellan:Clay|
|Subject Keywords:||planetary systems; planets and satellites: formation; planet–star interactions; stars: rotation; techniques: spectroscopic|
|Classification Code:||PACS: 95.75.Fg; 97.82.Cp; 95.30.Gv|
|Official Citation:||Two Upper Limits on the Rossiter-Mclaughlin Effect, with Differing Implications: WASP-1 has a High Obliquity and WASP-2 is Indeterminate Simon Albrecht et al. 2011 ApJ 738 50|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||08 Sep 2011 23:14|
|Last Modified:||26 Dec 2012 13:40|
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