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The Rossiter-McLaughlin effect reloaded : probing the 3D spin-orbit geometry, differential stellar rotation, and the spatially-resolved stellar spectrum of star-planet systems

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Cegla, H. M., Lovis, C., Bourrier, V., Beeck, B., Watson, C. A. and Pepe, F. (2016) The Rossiter-McLaughlin effect reloaded : probing the 3D spin-orbit geometry, differential stellar rotation, and the spatially-resolved stellar spectrum of star-planet systems. Astronomy & Astrophysics, 588 . A127. doi:10.1051/0004-6361/201527794

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Official URL: http://dx.doi.org/10.1051/0004-6361/201527794

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Abstract

When a planet transits its host star, it blocks regions of the stellar surface from view; this causes a distortion of the spectral lines and a change in the line-of-sight (LOS) velocities, known as the Rossiter-McLaughlin (RM) effect. Since the LOS velocities depend, in part, on the stellar rotation, the RM waveform is sensitive to the star-planet alignment (which provides information on the system’s dynamical history). We present a new RM modelling technique that directly measures the spatially-resolved stellar spectrum behind the planet. This is done by scaling the continuum flux of the (HARPS) spectra by the transit light curve, and then subtracting the in- from the out-of-transit spectra to isolate the starlight behind the planet. This technique does not assume any shape for the intrinsic local profiles. In it, we also allow for differential stellar rotation and centre-to-limb variations in the convective blueshift. We apply this technique to HD 189733 and compare to 3D magnetohydrodynamic (MHD) simulations. We reject rigid body rotation with high confidence (>99% probability), which allows us to determine the occulted stellar latitudes and measure the stellar inclination. In turn, we determine both the sky-projected (λ ≈ −0.4 ± 0.2°) and true 3D obliquity (ψ ≈ 7+12-4°). We also find good agreement with the MHD simulations, with no significant centre-to-limb variations detectable in the local profiles. Hence, this technique provides a new powerful tool that can probe stellar photospheres, differential rotation, determine 3D obliquities, and remove sky-projection biases in planet migration theories. This technique can be implemented with existing instrumentation, but will become even more powerful with the next generation of high-precision radial velocity spectrographs.

Item Type: Journal Article
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Faculty of Science > Physics
Library of Congress Subject Headings (LCSH): Astronomical spectroscopy, Planets -- Spectra, Light curves , Stellar photospheres
Journal or Publication Title: Astronomy & Astrophysics
Publisher: EDP Sciences
ISSN: 0004-6361
Official Date: April 2016
Dates:
DateEvent
April 2016Published
30 March 2016Available
31 January 2016Accepted
Date of first compliant deposit: 14 January 2021
Volume: 588
Article Number: A127
DOI: 10.1051/0004-6361/201527794
Status: Peer Reviewed
Publication Status: Published
Access rights to Published version: Restricted or Subscription Access
Copyright Holders: © ESO, 2016
RIOXX Funder/Project Grant:
Project/Grant IDRIOXX Funder NameFunder ID
UNSPECIFIED[SNSF] Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschunghttp://dx.doi.org/10.13039/501100001711
RPG-249Leverhulme Trusthttp://dx.doi.org/10.13039/501100000275
ST/L000709/1[STFC] Science and Technology Facilities Councilhttp://dx.doi.org/10.13039/501100000271
SFB 963/1 (A16)[DFG] Deutsche Forschungsgemeinschafthttp://dx.doi.org/10.13039/501100001659
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