Closing of the astrotail

Abstract

Context. The structure of astrospheres depends on the interaction between the host star and the surrounding interstellar medium (ISM). Observations of astrospheres offer new opportunities to learn about the details of this interaction. Aims. The aim of this work is to study the global structure of astrospheres, concentrating on the case of strong interstellar magnetic field and low relative velocity between the star and the ISM. Methods. We used a simple magnetohydrodynamical numerical code to simulate the interaction between the stellar wind and the ISM, using different assumptions about the interstellar magnetic field strength, the velocity of the star, and the parameters of the interstellar medium. From the resulting time-stationary solutions, we derived the mass flux distribution of the stellar plasma inside the astrosphere, with particular attention to the flow topology. Results. We find that the tube-like topology of the astrosphere can occur for an interstellar magnetic field strength of 7 µG (a realistic value in the Galactic disk region), provided that the velocity of the star relative to the ISM is low enough (0.5 km s−1 ). The two-stream structure of the stellar wind mass flow appears to some extent in all our models.