Simulating observable structures due to a perturbed interstellar medium in front of astrospheric bow shocks in 3D MHD

TL;DR

This study uses 3D MHD simulations to explore how different perturbations in the interstellar medium affect the observable structures of astrospheric bow shocks, revealing complex morphological variations.

Contribution

It introduces a novel approach by applying various perturbations to 3D MHD models to explain observed bow shock structures and their diversity.

Findings

Perturbations cause significant changes in shock morphology.

Different perturbation types produce diverse observable features.

Viewing angles influence the appearance of shock structures.

Abstract

Context. While the shapes of many observed bow shocks can be reproduced by simple astrosphere models, more elaborate approaches have recently been used to explain differing observable structures. Aims. By placing perturbations of an otherwise homogeneous interstellar medium in front of the astrospheric bow shock of the runaway blue supergiant $\lambda$ Cephei, the observable structure of the model astrosphere is significantly altered, providing insight into the origin of perturbed bow shock images. Methods. Three-dimensional single-fluid magnetohydrodynamic (MHD) models of stationary astrospheres were subjected to various types of perturbations and simulated until stationarity was reached again. As examples, simple perturbations of the available MHD parameters (number density, bulk velocity, temperature, and magnetic field) as well as a more complex perturbation were chosen. Synthetic observations were generated by line-of-sight integration of the model data, producing H$\alpha$, $70\,\mu$m dust emission, and bremsstrahlung maps of the perturbed astrosphere's evolution. Results. The resulting shock structures and observational images differ strongly depending on the type of the injected perturbation and the viewing angles, forming arc-like protrusions or bifurcations of the bow shock structure, as well as rings, arcs, and irregular structures detached from the bow shock.