Measurement of the Rossiter–McLaughlin Effect in the Transiting Exoplanetary System TrES-1

Abstract

Abstract We report a measurement of the Rossiter–McLaughlin effect in the transiting extrasolar planetary system TrES-1, via simultaneous spectroscopic and photometric observations with the Subaru and MAGNUM telescopes. By modeling the radial velocity anomaly that was observed during a transit, we determine the sky-projected angle between the stellar spin axis and the planetary orbital axis to be $\lambda = 30^{\circ}\pm 21^{\circ}$. This is the third case for which $\lambda$ has been measured in a transiting exoplanetary system, and the first demonstration that such measurements are possible for relatively faint host stars ($V \sim$ 12, as compared to $V \sim$ 8 for the other systems). We also derive a time of mid-transit, constraints on the eccentricity of the TrES-1b orbit ($e =$ 0.048$\pm$0.025), and upper limits on the mass of the Trojan companions ($\lesssim$ 14 $M_{\oplus}$) at the 3$\sigma$ level.