Dynamics of photospheric magnetic flux distribution and variations in solar RVs -- a study using HARPS-N solar and SDO observations

TL;DR

This study investigates how different photospheric magnetic features influence solar radial velocity variations by analyzing high-resolution solar observations, revealing distinct magnetic contributions and evaluating proxies for activity-related RV signals.

Contribution

It demonstrates that strong and weak magnetic fields have distinguishable effects on RV variability and assesses UV intensities as effective proxies for magnetic activity contributions.

Findings

Strong magnetic fields correlate differently with RV than weak fields.

UV intensities at 1600 Å and 1700 Å better trace plage contributions than Ca II H-K indices.

Different magnetic features require tailored proxies for accurate RV modeling.

Abstract

The distribution and evolution of photospheric magnetic field in sunspots, plages and network, and variations in their relative flux content, play key roles in radial velocity (RV) fluctuations observed in Sun-as-a-star spectra. Differentiating and disentangling such magnetic contributions to RVs help in building models to account for stellar activity signals in high precision RV exoplanet searches. In this work, as earlier authors, we employ high-resolution images of the solar magnetic field and continuum intensities from SDO/HMI to understand the activity contributions to RVs from HARPS-N solar observations. Using well observed physical relationships between strengths and fluxes of photospheric magnetic fields, we show that the strong fields (spots, plages and network) and the weak internetwork fields leave distinguishing features in their contributions to the RV variability. We also find that the fill-factors and average unsigned magnetic fluxes of different features correlate differently with the RVs and hence warrant care in employing either of them as a proxy for RV variations. In addition, we examine disk averaged UV intensities at 1600 \r{A} and 1700 \r{A} wavelength bands imaged by SDO/AIA and their performances as proxies for variations in different magnetic features. We find that the UV intensities provide a better measure of contributions of plage fields to RVs than the Ca II H-K emission indices, especially during high activity levels when the latter tend to saturate.