# Stellar Surface Magneto-Convection as a Source of Astrophysical Noise III. Sun-as-a-star Simulations and Optimal Noise Diagnostics

## TL;DR

This study uses Sun-as-a-star simulations based on 3D magnetohydrodynamic models to identify line profile diagnostics and photometric proxies that can significantly reduce granulation-induced noise in radial velocity measurements, aiding exoplanet detection.

## Contribution

It introduces a method to mitigate stellar granulation noise in radial velocity data using line profile diagnostics and photometry, validated through Sun-like star simulations.

## Key findings

- Line profile characteristics correlate with convection velocities.
- Removing correlations reduces 50-60% of granulation noise.
- Photometry can also mitigate about 50% of the noise.

## Abstract

Stellar surface magnetoconvection (granulation) creates asymmetries in the observed stellar absorption lines that can subsequently manifest themselves as spurious radial velocities shifts. In turn, this can then mask the Doppler-reflex motion induced by orbiting planets on their host stars, and represents a particular challenge for determining the masses of low-mass, long-period planets. Herein, we study this impact by creating Sun-as-a-star observations that encapsulate the granulation variability expected from 3D magnetohydrodynamic simulations. These Sun-as-a-star model observations are in good agreement with empirical observations of the Sun, but may underestimate the total variability relative to the quiet Sun due to the increased magnetic field strength in our models. We find numerous line profile characteristics linearly correlate with the disc-integrated convection-induced velocities. Removing the various correlations with the line bisector, equivalent width, and the V_asy indicator may reduce ~50-60% of the granulation noise in the measured velocities. We also find that simultaneous photometry may be a key diagnostic, as our proxy for photometric brightness also allowed us to remove ~50% of the granulation-induced radial velocity noise. These correlations and granulation-noise mitigations breakdown in the presence of low instrumental resolution and/or increased stellar rotation, as both act to smooth the observed line profile asymmetries.