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 infrom
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.
Original language | English |
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Article number | A127 |
Number of pages | 15 |
Journal | Astronomy and Astrophysics |
Volume | 588 |
Early online date | 30 Mar 2016 |
DOIs | |
Publication status | Published - Apr 2016 |
Keywords
- convection
- methods: data analysis
- planets and satellites: dynamical evolution and stability
- stars: rotation
- techniques: radial velocities
- techniques: spectroscopic