Journal
ASTROPHYSICAL JOURNAL
Volume 738, Issue 1, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/0004-637X/738/1/50
Keywords
planetary systems; planets and satellites: formation; planet-star interactions; stars: rotation; techniques: spectroscopic
Categories
Funding
- Netherlands Organization for Scientific Research (NWO)
- NASA [NNX09AD36G]
- Grants-in-Aid for Scientific Research [22000005] Funding Source: KAKEN
- NASA [120361, NNX09AD36G] Funding Source: Federal RePORTER
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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 approximate to 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.
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