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Geo Coronal Absorption Frequency

  1. Jun 25, 2015 #1
    From this article on the monitoring of the solar Lyman Alpha emission line, a diagram (attached below) shows the 'mother of all absorption wavelength measurements': namely the geo coronal absorption of solar Lyman Alpha radiation at 1215.664 A or 121.5664 nm.

    Is this still the most accurate measure of geo coronal absorption of solar Lyman Alpha ?

    More recent related scientific articles are more concerned with trying to 'factor out' geo coronal absorption so they can see the 'true' profile of solar Lyman Alpha emission. So they don't pay much attention to the geo coronal absorption frequency itself. And yet I would say it is a very important frequency reference which should be measured as accurately as possible. It's value appears to be a tad lower than 121.56701 nm (NIST) which seems to result from a terrestrial emission (rather than absorption) measurement.

    A more recent (1978) solar Lyman Alpha profile is this one from Artzner. But for some reason he does not specifically state a wavelength for the central geo-coronal absorption mininum. So the only data I am able to find on that is from the above 1969 article whence the graphic below originates.

    Lyman Alpha profile.png
     
  2. jcsd
  3. Jun 26, 2015 #2

    Drakkith

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    Staff: Mentor

    That article looks like its from 1969, so I seriously doubt it. Try searching arxiv.org and see if you can find any recent papers.
     
  4. Jun 27, 2015 #3
    Believe me I have dredged the Internet looking for relevant data and really it's all very sketchy. As far as solar Lyman Alpha emission/absorption is concerned I cannot find anything better than Artzner's 1978 article on the solar Lyman Alpha profile linked above. Post OSO-8 , the only studies in solar uv seem to be from specially adapted Sumer measurements. The Sumer spacecraft (it would seem) was not designed for Lyman Alpha monitoring and therefore any Lyman Alpha studies (that I can find anyway) seem to have required special modifications to the measuring equipment. Also it's at a La Grange point outside the geo-corona so doesn't measure geo coronal absorption. Albeit there being some debate about exactly what constitutes geo-coronal absorption - some of the absorption is apparently by colder layers of hydrogen in the solar vicinity.

    I'm hoping to find a more recent and more accurate value for what should be a fairly exact absorption frequency measurement. I have estimated 1215.66592 A from Artzner's profile but I don't know whether the assumptions I've made about his scale are correct.
     
  5. Jun 27, 2015 #4
    - that should read absorption wavelength measurement
     
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