Characterizing Solar Center-to-Limb Radial-Velocity Variability with SDO

TL;DR

This study analyzes how solar surface features and limb angle affect radial velocity measurements, revealing complex and feature-specific variability crucial for detecting Earth-like exoplanets.

Contribution

It provides a detailed characterization of the center-to-limb radial velocity variability caused by various solar surface inhomogeneities using SDO data, highlighting their complex signatures.

Findings

Distinct CLV signatures for different solar features.

Magnetic activity influences convective blueshift suppression.

Feature-specific RV variability impacts exoplanet detection.

Abstract

Stellar photospheric inhomogeneities are a significant source of noise which currently precludes the discovery of Earth-mass planets orbiting Sun-like stars with the radial-velocity (RV) method. To complement several previous studies which have used ground- and spaced-based facilities to characterize the RV of the Sun, we here characterize the center-to-limb variability (CLV) of solar RVs arising from various solar-surface inhomogeneities observed by SDO/HMI and SDO/AIA. By using various SDO observables to classify pixels and calculate line-of-sight velocities as a function of pixel classification and limb angle, we show that each identified feature type, including the umbrae and penumbrae of sunspots, quiet-Sun magnetoconvective cells, magnetic network, and plage, exhibit distinct and complex CLV signatures, including a notable limb-angle dependence in the observed suppression of convective blueshift for magnetically active regions. We discuss the observed distributions of velocities by identified region type and limb angle, offer interpretations of the physical phenomena that shape these distributions, and emphasize the need to understand the RV signatures of these regions as astrophysical signals, rather than simple (un)correlated noise processes.