# Three-dimensional Density Structure of a Solar Coronal Streamer Observed by SOHO/LASCO and STEREO/COR2 in Quadrature

## TL;DR

This study models the 3D density structure of a solar coronal streamer using simultaneous observations from two spacecraft, revealing detailed density variations and validating the model against actual data.

## Contribution

It introduces a novel 3D forward modeling approach that fits simultaneous multi-viewpoint coronagraph data to analyze streamer density structures.

## Key findings

- Density contrast between structures up to a factor of 3
- Model fits observational data well
- Densities from polarized and unpolarized data are consistent

## Abstract

Helmet streamers are a prominent manifestation of magnetic structures with current sheets in the solar corona. These large-scale structures are regions with high plasma density, overlying active regions and filament channels. We investigate the three-dimensional (3D) structure of a coronal streamer, observed simultaneously by white-light coronagraphs from two vantage points near quadrature (SOHO/LASCO and STEREO/COR2). We design a forward model based on plausible assumptions about the 3D streamer structure taken from physical models (a plasma slab centered around a current sheet). The streamer stalk is approximated by a plasma slab, with electron density that is characterized by three separate functions describing the radial, transverse and face-on profiles respectively. For the first time, we simultaneously fit the observational data from SOHO and STEREO using a multivariate minimization algorithm. The streamer plasma sheet contains a number of brighter and darker ray-like structures with the density contrast up to about a factor 3 between them. The densities derived using polarized and unpolarized data are similar. We demonstrate that our model corresponds well to the observations.