• Winn, Joshua N.
;
• Howard, Andrew W.
;
• Johnson, John Asher
;
• Marcy, Geoffrey W.
;
• Isaacson, Howard
;
• Shporer, Avi
;
• Bakos, Gáspár Á.
;
• Hartman, Joel D.
;
• Holman, Matthew J.
;
• Albrecht, Simon
;
• Crepp, Justin R.
;
• Morton, Timothy D.

Abstract

We present observations of the Rossiter-McLaughlin effect for two exoplanetary systems, revealing the orientations of their orbits relative to the rotation axes of their parent stars. HAT-P-4b is prograde, with a sky-projected spin-orbit angle of λ = -4.9 ± 11.9 deg. In contrast, HAT-P-14b is retrograde, with λ = 189.1 ± 5.1 deg. These results conform with a previously noted pattern among the stellar hosts of close-in giant planets: hotter stars have a wide range of obliquities and cooler stars have low obliquities. This, in turn, suggests that three-body dynamics and tidal dissipation are responsible for the short-period orbits of many exoplanets. In addition, our data revealed a third body in the HAT-P-4 system, which could be a second planet or a companion star.