Probing the Density Fine Structuring of the Solar Corona with Comet Lovejoy

TL;DR

This study uses observations of Comet Lovejoy's tail in the solar corona to probe local plasma density structures, developing a probabilistic ion beam model that aligns well with observed EUV emission profiles.

Contribution

It introduces a novel probabilistic model of ion beam propagation along magnetic fields to analyze coronal density structures using comet tail observations.

Findings

Coronal density is highly spatially structured.

Model accurately reproduces observed emission intensity profiles.

Inferred densities agree with hydrostatic models.

Abstract

The passage of sungrazing comets in the solar corona can be a powerful tool to probe the local plasma properties. Here, we carry out a study of the striae pattern appearing in the tail of sungrazing Comet Lovejoy, as observed by the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) during the inbound and outbound phases of the comet orbit. We consider the images in EUV in the 171 {\AA} bandpass, where emission from oxygen ions O$^{4+}$ and O$^{5+}$ is found. The striae are described as due to a beam of ions injected along the local magnetic field, with the initial beam velocity decaying because of collisions. Also, ion collisional diffusion contributes to ion propagation. Both the collision time for velocity decay and the diffusion coefficient for spatial spreading depend on the ambient plasma density. A probabilistic description of the ion beam density along the magnetic field is developed, where the beam position is given by the velocity decay and the spreading of diffusing ions is described by a Gaussian probability distribution. Profiles of emission intensity along the magnetic field are computed and compared with the profiles along the striae observed by AIA, showing a good agreement for most considered striae. The inferred coronal densities are then compared with a hydrostatic model of the solar corona. The results confirm that the coronal density is strongly spatially structured.