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

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