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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