The Sun as a planet-host star: Proxies from SDO images for HARPS radial-velocity variations

R. D. Haywood, A. Collier Cameron, Y. C. Unruh, C. Lovis, A. F. Lanza, J. Llama, M. Deleuil, R. Fares, M. Gillon, C. Moutou, F. Pepe, D. Pollacco, D. Queloz, D. Ségransan

Research output: Contribution to journalArticlepeer-review

127 Citations (Scopus)


The Sun is the only star whose surface can be directly resolved at high resolution, and therefore constitutes an excellent test case to explore the physical origin of stellar radialvelocity (RV) variability. We present HARPS observations of sunlight scattered off the bright asteroid 4/Vesta, from which we deduced the Sun's activity-driven RV variations. In parallel, the Helioseismic and Magnetic Imager instrument on board the Solar Dynamics Observatory provided us with simultaneous high spatial resolution magnetograms, Dopplergrams and continuum images of the Sun in the Fe I 6173 Å line.We determine the RV modulation arising from the suppression of granular blueshift in magnetized regions and the flux imbalance induced by dark spots and bright faculae. The rms velocity amplitudes of these contributions are 2.40 and 0.41 m s-1, respectively, which confirms that the inhibition of convection is the dominant source of activity-induced RVvariations at play, in accordance with previous studies. We find the Doppler imbalances of spot and plage regions to be only weakly anticorrelated. Light curves can thus only give incomplete predictions of convective blueshift suppression. We must instead seek proxies that track the plage coverage on the visible stellar hemisphere directly. The chromospheric flux index R'HK derived from the HARPS spectra performs poorly in this respect, possibly because of the differences in limb brightening/darkening in the chromosphere and photosphere. We also find that the activity-driven RV variations of the Sun are strongly correlated with its full-disc magnetic flux density, which may become a useful proxy for activity-related RV noise.

Original languageEnglish
Pages (from-to)3637-3651
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - Feb 10 2016
Externally publishedYes


  • Planets and satellites: detection
  • Sun: activity
  • Sun: faculae, plages
  • Sun: granulation
  • Sunspots
  • Techniques: radial velocities

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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