Solar Radiative Recombination Spectrum

Research Fig.14:

Theoretical flux densities due to recombination (thick solid curve, displaced upwards by 8 orders of magnitude) and cascading (thin solid curve) within (half) a spherical shell (R=7*105km, ΔR=100 km) of a plasma of density Np=1014cm-3, an average electron energy of 0.5 Ry and an ion temperature of T=6000 oK at a distance from the earth D=1.5*108 km for frequencies from 1010 to 1015 Hz. The dashed curve (which is shown here displaced upwards by 8 orders of magnitude) gives the cascade emission if no radiative enhancement due to level broadening by plasma field fluctuations is assumed.
It is evident that for these parameters (which are generally assumed to be appropriate for the solar photosphere) the theoretical curve is not consistent with the observed solar spectrum as the former becomes discrete for infrared and shorter wavelenghts. At least a density of Np=1020cm-3 would be required to make the spectrum continuous well into the visible region (see also the page regarding Coronal Heating in this context). In addition, the actual differential height structure of the solar atmosphere might have to be taken into account to yield the actual solar 'Planck-type' spectrum. The overall theoretical radiation excess could be explained by the neglection of radiative transfer effects for the present model.

Solar Radiative Recombination Spectrum

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Thomas Smid (M.Sc. Physics, Ph.D. Astronomy)