CO Spectral Line Formation in the Sun: Convective Simulation, Line Profiles and Isotopic Abundance Measures

Abstract

CO spectral line formation in the Sun was modelled using realistic, ab initio, timedependent 3D radiative-hydrodynamical model atmospheres. Three `phases' of 3D model atmospheres were utilised. In Phase 1, strong CO lines formed in very high atmospheric layers were modelled using the established model (Asplund et al. 2000b). This produced less than perfect agreement with observed line asymmetries measured in the ATMOS disc-centre solar atlas. The velocity, temperature and density fields were then manually altered during Phase 2 in order to ascertain the reasons for the disagreement with observation during Phase 1. Following reasonably successful reproduction of observed profiles and bisectors in Phase 2, new self-consistent simulations were performed using an updated version of the hydrodynamical code and an extended simulation domain in Phase 3. In this final phase, excellent agreement between observed and synthesisedline profile shapes, depths and bisectors was achieved.