Details

Autor(en) / Beteiligte

• Collier Cameron, A
• Mortier, A
• Phillips, D
• Dumusque, X
• Haywood, R D
• Langellier, N
• Watson, C A
• Cegla, H M
• Costes, J
• Charbonneau, D
• Coffinet, A
• Latham, D W
• Lopez-Morales, M
• Malavolta, L
• Maldonado, J
• Micela, G
• Milbourne, T
• Molinari, E
• Saar, S H
• Thompson, S
• Buchschacher, N
• Cecconi, M
• Cosentino, R
• Ghedina, A
• Glenday, A
• Gonzalez, M
• Li, C-H
• Lodi, M
• Lovis, C
• Pepe, F
• Poretti, E
• Rice, K
• Sasselov, D
• Sozzetti, A
• Szentgyorgyi, A
• Udry, S
• Walsworth, R

Titel

Three years of Sun-as-a-star radial-velocity observations on the approach to solar minimum

Ist Teil von

• Monthly notices of the Royal Astronomical Society, 2019-07, Vol.487 (1), p.1082-1100

Erscheinungsjahr

2019

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• Abstract 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.