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

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.