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EP: Fachverband Extraterrestrische Physik

EP 9: Poster

EP 9.11: Poster

Wednesday, March 22, 2023, 17:30–19:00, HSZ OG1

Local HD flows at the Apex of an Astropause — •Kuljeet Singh Saddal^1,2 and Dieter H Nickeler¹ — ¹Astronomical Institute AV CR Ondrejov, Fricova 298, 25165 Ondrejov, Czech Republic — ²Charles University, Faculty of Mathematics and Physics, V Holešovickách 2, 180 00 Praha 8, Czech Republic

Astrospheres are the interaction regions between the stellar wind and the ambient interstellar medium, which consists of various HD (or MHD) discontinuities. Astropause is a contact discontinuity that separates the two flows, and its structure is described by one of the separatrices of the fluid flow. In 2D, there must be at least one X-type null point (X-point) close to the apex. This analysis aims to study hydrodynamically the geometrical and topological structures of the streamlines in the vicinity of the X-point. As the flow close to the apex can be considered incompressible, one can make use of stream functions to describe such flows. The definition of streamlines, along with the equations of ideal HD, gives a single, (non-)linear elliptic partial differential equation, known as the Grad-Shafranov equation (GSE). This equation is analysed by approximating the stream function close to the null point as a series of polynomials to various orders, and assuming specific forms for the pressure function. Depending on the choice of the pressure function and the order at which the polynomial is truncated, either the original null point can become an X-point of higher order, or more null points can appear in its vicinity. Moreover, an isotropic pressure might not exist for every choice of stream functions, and hence adding an extra anisotropic term becomes important.