The Rossiter McLaughlin effect reloaded: Convective Problems and New Solutions

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• Heather Cegla (Belfast)
• Wednesday 18 May 2016, 16:00-17:00
• Martin Ryle Seminar Room, Kavli Institute.

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 Seminars series.

This talk is included in these lists:

• Cambridge Astronomy Talks
• Combined External Astrophysics Talks DAMTP
• Cosmology, Astrophysics and General Relativity
• Exoplanet Seminars
• Institute of Astronomy Talk Lists
• LCLU Departmental Talks
• Martin Ryle Seminar Room, Kavli Institute

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