This page (revision-7) was last changed on 18-Apr-2021 19:12 by PeterYoung

This page was created on 19-Nov-2009 17:16 by PeterYoung

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HeIIOffLimb
HeIIOffLimb

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The off-limb spectrum being used is from 2007 March 9 20:03. Using the procedure outlined [elsewhere on the wiki|http://msslxr.mssl.ucl.ac.uk:8080/eiswiki/attach/DataProAnalysis/gauss_pixel_masks.pdf] a spatial region has been averaged to produce a single spectrum from which emission lines can be measured. Using standard density diagnostics we find the density is about 10^8.5.
The off-limb spectrum being used is from 2007 March 9 20:03. Using the procedure outlined [elsewhere on the wiki|https://vsolar.mssl.ucl.ac.uk/eiswiki/attach/DataProAnalysis/gauss_pixel_masks.pdf] a spatial region has been averaged to produce a single spectrum from which emission lines can be measured. Using standard density diagnostics we find the density is about 10^8.5.
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The 25 spectra that resulted are plotted in the image below. The limb is found at about X=860.
The 25 spectra that resulted are plotted in the image below. The limb is found at about X=860. The Y-axis is intensity in erg/cm2/s/sr/angstrom, the X-axis gives the wavelength in angstroms but with 256 angstroms subtracted in order to make the plots easier to read.
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[{Image src = 'he2_profiles.png'}]
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If we assume the He II component is on the short wavelength side, then we see it becoming weaker at X=868, which is just above the limb. By X=910 the short wavelength component is about a factor 2 smaller than the long wavelength component which we assume is the blend of the coronal lines. However, as X increases the short wavelength component remains approximately constant relative to the long wavelength component. Both components fall off in intensity with height
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This behavior is not consistent with He II which we expect to drop sharply above the limb, but then remain approximately constant in intensity beyond a certain height due to the scattered light contribution. Instead it actually seems to behave like a coronal line.
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The conclusion from this is that there is likely a coronal line at the wavelength of the He II 256.32 line and this is revealed when we cross the limb. Possibly this line could be one of the Si X, Fe X, Fe XII or Fe XIII lines discussed earlier if one of the lines has an incorrect wavelength. Alternatively it could be a previously unknown transition.
This page (revision-7) was last changed on 18-Apr-2021 19:12 by PeterYoungTop