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Similarity Models of Interstellar Loop Structures

W. W. Zuzak

Department of Astronomy, University of Manchester

Received December 11, 1970,  revised June 18, 1971
Astronomy and Astrophysics,  15, 95-109 (1971)


ABSTRACT

It is hypothesized that the interstellar loop structures are continuously driven by means of cosmic rays emitted by some source near the centre. Spherical similarity solutions, in which the shock position varies with time according to R = Atα, are obtained in the approximation that all fluid motion is radial, u = (ur, 0, 0), the magnetic field is tangential, B = (0, 0, Bφ), and the diffusion coefficient η is zero. Any derived shell thicknesses may be obtained by considering radiation losses to occur at the shock and thereafter treating the shocked gas adiabatically. The total energy of the shell and the rate of energy input are given by ε ~ t5α-2 and δε/δt ~ t5α-3 respectively. The solutions show that the magnetic field near the contact surface at the inside of the shell is sharply peaked to a maximum value which is approximately independent of the value of the initial magnetic field. Sharp steps in the radio synchrotron emission are to be expected in scanning across such regions. Information available on Loops I and II (North Polar Spur and Cetus Arc) indicate that these have undergone relatively large cooling and are driven by a relatively small energy input.

Key words: interstellar loop structures -- magnetic fields -- similarity solutions -- energy input