Stellar Surface Magneto-Convection as a Source of Astrophysical Noise II. Center-to-Limb Parameterisation of Absorption Line Profiles and Comparison to Observations

TL;DR

This paper models how solar surface magneto-convection affects absorption line profiles across the stellar disc, improving understanding of astrophysical noise impacting precise radial velocity measurements for exoplanet detection.

Contribution

It extends the parameterisation of surface magneto-convection effects from the solar centre to the limb, capturing center-to-limb variations in line profiles and radial velocity shifts.

Findings

The model reproduces realistic line profiles across the stellar disc.

It matches observed and simulated radial velocity shifts caused by granulation.

The approach helps quantify astrophysical noise in exoplanet radial velocity surveys.

Abstract

Manifestations of stellar activity (such as star-spots, plage/faculae, and convective flows) are well known to induce spectroscopic signals often referred to as astrophysical noise by exoplanet hunters. For example, setting an ultimate goal of detecting true Earth-analogs demands reaching radial velocity (RV) precisions of ~9 cm/s. While this is becoming technically feasible with the latest generation of highly stabilised spectrographs, it is astrophysical noise that sets the true fundamental barrier on attainable RV precisions. In this paper we parameterise the impact of solar surface magneto-convection on absorption line profiles, and extend the analysis from the solar disc centre (Paper I) to the solar limb. Off disc-centre, the plasma flows orthogonal to the granule tops begin to lie along the line-of-sight and those parallel to the granule tops are no longer completely aligned with the observer. Moreover, the granulation is corrugated and the granules can block other granules, as well as the intergranular lane components. Overall, the visible plasma flows and geometry of the corrugated surface significantly impact the resultant line profiles and induce centre-to-limb variations in shape and net position. We detail these herein, and compare to various solar observations. We find our granulation parameterisation can recreate realistic line profiles and induced radial velocity shifts, across the stellar disc, indicative of both those found in computationally heavy radiative 3D magnetohydrodynamical simulations and empirical solar observations.