Volume 595, November 2016
|Number of page(s)||13|
|Section||Planets and planetary systems|
|Published online||24 October 2016|
Radial velocity observations of the 2015 Mar. 20 eclipse
A benchmark Rossiter-McLaughlin curve with zero free parameters
1 Georg-August Universität Göttingen,
Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
2 Max-Planck Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
Accepted: 31 August 2016
Spectroscopic observations of a solar eclipse can provide unique information for solar and exoplanet research; the huge amplitude of the Rossiter-McLaughlin (RM) effect during solar eclipse and the high precision of solar radial velocities (RVs) allow detailed comparison between observations and RV models, and they provide information about the solar surface and about spectral line formation that are otherwise difficult to obtain. On March 20, 2015, we obtained 159 spectra of the Sun as a star with the solar telescope and the Fourier Transform Spectrograph at the Institut für Astrophysik Göttingen, 76 spectra were taken during partial solar eclipse. We obtained RVs using I2 as wavelength reference and determined the RM curve with a peak-to-peak amplitude of almost 1.4 km s-1 at typical RV precision better than 1 m s-1. We modeled the disk-integrated solar RVs using well-determined parameterizations of solar surface velocities, limb darkening, and information about convective blueshift from 3D magnetohydrodynamic simulations. We confirm that convective blueshift is crucial to understand solar RVs during eclipse. Our best model reproduced the observations to within a relative precision of 10% with residuals lower than 30 m s-1. We cross-checked parameterizations of velocity fields using a Dopplergram from the Solar Dynamics Observatory and conclude that disk-integration of the Dopplergram does not provide correct information about convective blueshift necessary for m s-1 RV work. As main limitation for modeling RVs during eclipses, we identified limited knowledge about convective blueshift and line shape as functions of solar limb angle. We suspect that our model line profiles are too shallow at limb angles larger than μ = 0.6, resulting in incorrect weighting of the velocities across the solar disk. Alternative explanations cannot be excluded, such as suppression of convection in magnetic areas and undiscovered systematics during eclipse observations. To make progress, accurate observations of solar line profiles across the solar disk are suggested. We publish our RVs taken during solar eclipse as a benchmark curve for codes calculating the RM effect and for models of solar surface velocities and line profiles.
Key words: line: formation / line: profiles / methods: observational / techniques: radial velocities / techniques: spectroscopic / Sun: rotation
© ESO 2016
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.