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SUMMARY:The Rossiter McLaughlin effect reloaded: Convective Problems and N
 ew Solutions - Heather Cegla (Belfast)
DTSTART:20160518T150000Z
DTEND:20160518T160000Z
UID:TALK65070@talks.cam.ac.uk
CONTACT:Dr B.-O. Demory
DESCRIPTION:I will present my recent work exploring the impact of magnetoc
 onvection on the Rossiter-McLaughlin (RM) effect and our new RM modeling t
 echnique. To first investigate the impact of magnetoconvection\, we simula
 ted the transit of a hot Jupiter about a Sun-like star for a variety of ro
 tation rates\, both with and without convective centre-to-limb variations 
 (in net blueshift and line profile asymmetry). We found that ignoring thes
 e convective effects generated residuals that increased with increasing st
 ellar rotation and decreasing intrinsic profile width. Moreover\, I will s
 how that these effects may introduce systematic errors in the projected ob
 liquities 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 mea
 sures 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 sp
 ectra to isolate the starlight behind the planet. We then measure the loca
 l velocity shifts behind the planet\, and model them as a combination of d
 ifferential stellar rotation and position-dependent convective blueshift. 
 I will show our applications of this technique to HD 189733\, where we fou
 nd good agreement with 3D MHD simulations and ruled out rigid body rotatio
 n with high confidence (>99% probability)\; this in turn allowed us to dis
 entangle the equatorial velocity and stellar inclination. As such\, we det
 ermined both the sky-projected (-0.4 +/- 0.2 degrees) and true 3D obliquit
 y (7^+12_-4 degrees). Hence\, our new technique provides a powerful tool t
 hat can probe stellar photospheres\, differential rotation\, determine 3D 
 obliquities\, and remove sky projection biases in planet migration theorie
 s. 
LOCATION:Martin Ryle Seminar Room\, Kavli Institute
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