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The Sun as a star seen through planet-hunting instruments

Presentation #200.04 in the session RV and Extreme Precision RV.

Published onApr 03, 2024
The Sun as a star seen through planet-hunting instruments

Despite spectacular advances in the stability and precision of radial-velocity spectrometers over the last 3 decades, the detection threshold for the reflex orbital motion of planet-host stars has been stalled at around 1 m/s for the last 15 years. This is an order of magnitude greater than is needed for determining the masses of Earth analogues around solar-type stars. The culprit is stellar activity, whose forms range from p-modes and photospheric granulation to Doppler-shifted flux perturbations by dark spots and bright faculae, to localised magnetic suppression of convective flows at different depths in the photosphere. A small, purpose-built solar telescope has been feeding integrated sunlight into the HARPS-N radial-velocity spectrometer every clear day since July 2015. I will review a selection of the ongoing investigations that are using these Sun-as-a-star data to develop both data-driven and physics-based methods for separating the effects of stellar photospheric physics from true dynamical Doppler shifts. The findings of these investigations offer good prospects for pushing the detection threshold for small planets towards the 10 cm/s needed for the detection of an Earth analogue.

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