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M. Opher, P.C. Liewer (Jet Propulsion Laboratory), M. Velli (Dept. of Astronomy and Space Science, Univ. of Firenzi), T.I. Gombosi, W. Manchester, D.L. DeZeeuw, G. Toth, I.V. Sokolov (Space Physics Research Lab., Univ. of Michigan)
Stars have winds which interact with the interstellar medium. The intensity of the winds can be 10 million times greater than that of the solar wind. The magnetic fields of these stars can be orders of magnitude greater than that of the Sun. The rotation periods can be appreciably different from that of the Sun. A detailed description of the interaction of stellar winds with the interstellar winds has never been made. The interaction between the Sun and Interstellar Medium creates three major structures: Termination Shock, Heliopause and Bow Shock. Recently, we found (Opher et al. 2003, 2004) that beyond the region where the solar wind become subsonic, the Termination Shock, a jet-sheet structure forms in the equatorial plane of the Sun rotation axis. This structure forms due to the compression of the solar magnetic field by the interstellar wind. The structure of the jet-sheet resembles a the "brim of a baseball cap"- it extends beyond the Termination Shock for 150 AU (almost touching the Bow Shock) and has a width of 10AU. This result is due to a novel application of a state-of-art 3D Magnetohydrodynamic (MHD) code with a highly refined grid (0.75 AU~ 4 orders of magnitude smaller than the physical dimensions of the system). The jet-sheet is unstable and oscillates up and down due to a velocity shear instability. We showed that the sinuous mode is the dominant mode that develops into a velocity-shear-instability with a growth rate of 0.027 years-1. We are the first to predict the formation of this structure at the equatorial region in the interaction of magnetized rotating star and an external wind (for a stellar rotation and magnetic field axis aligned). In this work, we extend our previous solar studies and investigate the effect in other solar-like stars. We present the dependence of the jet-sheet structure and the velocity-shear instability on the star mass-loss rate and magnetic field. We discuss further applications to other stellar wind interactions and the observational limits for the detection of this structure.
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Bulletin of the American Astronomical Society, 36 #2
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