Atlas of the solar intensity spectrum and its center to limb variation

TL;DR

This paper presents a spectral atlas of the solar intensity spectrum and its variation from center to limb, based on systematic spectrally resolved measurements across different angles, aiding solar atmosphere modeling.

Contribution

It provides the first systematic spectrally resolved measurements of the solar limb darkening function across multiple angles and wavelengths, creating a spectral atlas for improved solar atmosphere models.

Findings

Spectral data covering 439-666 nm at 10 heliocentric angles.

Enhanced understanding of the anisotropy of solar radiation.

Constraints for modeling the Second Solar Spectrum.

Abstract

The solar limb darkening function is well known and is widely employed in models of the solar atmosphere. However, there has been a lack of systematic spectrally resolved measurements. Therefore we recently decided to start an observing campaign with the Gregory Coud\'e Telescope at IRSOL in Locarno in order to produce a spectral atlas obtained at 10 different heliocentric angles $\theta$, chosen so that $\mu = \cos\theta$ covers the interval from 0.1 to 1.0 in step of 0.1. The measurements carried out till now include the spectral range from 439 nm to 666 nm. The collected data provide information about the anisotropy of the emergent radiation field on the solar surface, allowing a better modeling of the Second Solar Spectrum. In addition the data give observational constraints that should be taken into account when modeling the solar atmosphere.