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The Rossiter McLaughlin effect reloaded: Convective Problems and New Solutions

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If you have a question about this talk, please contact Dr B.-O. Demory.

I will present my recent work exploring the impact of magnetoconvection on the Rossiter-McLaughlin (RM) effect and our new RM modeling technique. To first investigate the impact of magnetoconvection, we simulated the transit of a hot Jupiter about a Sun-like star for a variety of rotation rates, both with and without convective centre-to-limb variations (in net blueshift and line profile asymmetry). We found that ignoring these convective effects generated residuals that increased with increasing stellar rotation and decreasing intrinsic profile width. Moreover, I will show that these effects may introduce systematic errors in the projected obliquities on the order of ~20 degrees, given moderate rotation (e.g. 6 km/s). To avoid such biases, we pioneered a new technique that directly measures the spatially-resolved stellar spectrum behind the planet. We do so by scaling the continuum flux from high precision ground-based spectra by a transit light curve, and subtracting the in- from the out-of-transit spectra to isolate the starlight behind the planet. We then measure the local velocity shifts behind the planet, and model them as a combination of differential stellar rotation and position-dependent convective blueshift. I will show our applications of this technique to HD 189733 , where we found good agreement with 3D MHD simulations and ruled out rigid body rotation with high confidence (>99% probability); this in turn allowed us to disentangle the equatorial velocity and stellar inclination. As such, we determined both the sky-projected (0.4 +/ 0.2 degrees) and true 3D obliquity (7^+12_-4 degrees). Hence, our new technique provides a powerful tool that can probe stellar photospheres, differential rotation, determine 3D obliquities, and remove sky projection biases in planet migration theories.

This talk is part of the Exoplanet Meetings series.

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