TWO UPPER LIMITS ON THE ROSSITER-MCLAUGHLIN EFFECT, WITH DIFFERING IMPLICATIONS: WASP-1 HAS A HIGH OBLIQUITY AND WASP-2 IS INDETERMINATE
- Department of Physics, and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
- California Institute of Technology, Department of Astrophysics, MC249-17, Pasadena, CA 91125 (United States)
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015 (United States)
- Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
- National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Department of Earth and Planetary Sciences, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan)
- Department of Infrared Astrophysics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
- Department of Astronomy, Yale University, New Haven, CT 06511 (United States)
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 {approx}2{sigma} 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.
- OSTI ID:
- 21582934
- Journal Information:
- Astrophysical Journal, Vol. 738, Issue 1; Other Information: DOI: 10.1088/0004-637X/738/1/50; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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