期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 487, 期 1, 页码 1082-1100出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stz1215
关键词
techniques: radial velocities; Sun: activity; Sun: faculae, plages; Sun: granulation; sunspots; planets and satellites: detection
资金
- Prodex Program of the Swiss Space Office (SSO)
- Harvard University Origins of Life Initiative (HUOLI)
- Scottish Universities Physics Alliance (SUPA)
- University of Geneva
- Italian National Astrophysical Institute (INAF)
- University of St Andrews
- University of Edinburgh
- Science and Technology Facilities Council (STFC) [ST/R000824/1]
- UKSA [ST/R003203/1]
- NASA [NNX16AD42G]
- Branco Weiss Fellowship Society in Science
- NASA Heliophysics LWS grant [NNX16AB79G]
- STFC [ST/P000312/1]
- European Union Seventh Framework Programme (FP7/2007-2013) [313014]
- NASA through the Sagan Fellowship Program
- Kepler mission under NASA [NNX13AB58A]
- Smithsonian Astrophysical Observatory
- INAF/Frontiera through the 'Progetti Premiali' funding scheme of the Italian Ministry of Education, University, and Research
- Swiss National Science Foundation
- Swiss National Science Foundation (SNSF) [166227]
- Smithsonian Astrophysical Observatory (SAO)
- Queen's University Belfast
- Lowell Observatory
- NASA [906454, NNX16AD42G] Funding Source: Federal RePORTER
- STFC [ST/R000824/1, ST/P000312/1] Funding Source: UKRI
The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets' masses, obstructing detection of Earth twins. Since 2015 July, we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 yr of observation, interpreting them in the context of spatially resolved solar observations. We describe a Bayesian mixture-model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise-limited radial-velocity precision better than 0.43 m s(-1) per 5-min observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m s(-1). We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m s(-1) and an autocorrelation half-life of 15 min. On longer time-scales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s(-1) and is correlated with the line asymmetry, but leads it by 3 d. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity.
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