Re: Solar absorption lines
- From: "Thomas Smid" <thomas.smid@xxxxxxxxx>
- Date: 9 Jul 2006 13:39:29 -0700
George Dishman wrote:
"Scott" <ss@xxxxxxxxxxxxxxxx> wrote in message
news:44b10377$0$22123$afc38c87@xxxxxxxxxxxxxxxxxxxxxxx
Hi George,
Thanks for joining in this discussion.
Atoms in the chromosphere can scatter in all
directions but they are only illuminated from
one side, that facing the Sun.
Yes. But I don't see how that can create absorption lines.
If a patch of gas is illuminated by a source at
some brightness covering 2 pi steradians and then
emits the same energy into 4 pi sterardians it
must appear less bright.
The geometrical effect does thus reduce here the absorption lines only
to half the intensity of the continuum (as for subsequent scattering
events the radiation field is practically isotropic).
The explanation for the Fraunhofer lines must thus lie elsewhere. The
primary mechanism should be:
1) In the course of the scatterings, photons are shifted from the line
center into the line wings due to the Doppler effect.
2) Due to multiple scattering, photons within the line stay for such a
long time in the solar atmosphere that they have a high probability of
ionizing excited states of hydrogen (the density of the latter is too
small to affect any radiation that is going straight through (i.e. the
continuum), but for photons within the line the effective pathlength is
several orders of magnitude larger and photoionization of excited
states will be important). The photoionization process leads then
subsequently again to a photon on recombination of the photoelectron,
but this will have a completely different wavelength, i.e. like for
mechanism (1) photons will be lost from the line.
Thomas
.
- References:
- Solar absorption lines
- From: Scott
- Re: Solar absorption lines
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- Re: Solar absorption lines
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- Re: Solar absorption lines
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- Re: Solar absorption lines
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- Re: Solar absorption lines
- From: George Dishman
- Re: Solar absorption lines
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- Re: Solar absorption lines
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