Solar Line Asymmetries: Modelling the Effect of Granulation on the Solar Spectrum

TL;DR

This paper presents a parametric model of solar granulation that accurately reproduces observed spectral line asymmetries and velocities, improving understanding of solar photospheric dynamics and elemental abundances.

Contribution

A new simplified granular model that closely matches observed solar spectra and line asymmetries, validated by comparison with observations and damping theory.

Findings

Model reproduces spectral line asymmetries.

Microturbulence and flow velocities decrease exponentially with height.

Photospheric abundances align with meteoric values.

Abstract

A parametric model of granulation employing a small number of parameters was developed. Synthetic spectra calculated using this model closely match observed spectra and, in particular, reproduce the asymmetries observed in spectral lines. Both the microturbulent motions and the large-scale flow velocity decrease exponentially with a scale height of 368 km as the height within the photosphere increases. The model agrees with observations of the solar granulation (from which it was derived). The horizontal motions associated with granulation were found and used to calculate spectra emergent away from disk centre. These calculated spectra were compared to observed spectra, with the agreement supporting the accuracy of the granular model. Also in the course of this work, the Brueckner-O'Mara damping theory was found to predict damping constants accurately. The photospheric abundances of a number of elements were determined. The abundance obtained for iron agrees with the meteoric iron abundance. Astrophysical f-values for some lines were also determined.