A conceptually novel model - one in which stimulated (i.e. induced) resonance Rayleigh scattering causes ions of select species to become accelerated to very high terminal velocities in the solar winds of high mass-losing stars - is proposed to explain the general appearance of so-called P Cygni profiles that often dominate the vacuum ultraviolet (VUV) spectra of such stars. In the unit step of the proposed scattering process, a radially outgoing photon (frequency ) that is arbitrarily blueshifted with respect to the rest frame frequency
of the resonance line associated with a P Cygni profile is absorbed from the illuminating star's continuum, a new photon (frequency
) that is very close to
and that propagates in the backwards direction (i.e. towards the star) is created, and the outwardly directed velocity v of the ion being accelerated is increased by an amount
with all three events occurring simultaneously. A monochromatic wave at
initially forms at some distance from the star, and becomes enormously amplified via the stimulated scattering process as it propagates radially inwards towards the star, all the while retaining a relatively high degree of monochromaticity. The high rate of stimulated scattering enables ions of the resonant species in the solar wind to become accelerated to terminal velocities as high as ~ 1000 km/sec. Since stimulated scattering processes are characterized by pump power thresholds, the model readily explains why only select species are accelerated to very high velocities in a given star's solar wind, and also why a dramatic P Cygni profile for a given ion species can often discontinuously be present or absent when spectra of stars varying only slightly in spectral type are compared.
By: P. P. Sorokin, J. H. Glownia
Published in: RC23260 in 2004
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