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

Only authorized users are allowed to rename pages.

Only authorized users are allowed to delete pages.

Page revision history

Version Date Modified Size Author Changes ... Change note
7 18-Apr-2021 19:12 7 KB PeterYoung to previous
6 23-Mar-2010 19:19 5 KB PeterYoung to previous | to last
5 19-Nov-2009 18:18 4 KB PeterYoung to previous | to last
4 19-Nov-2009 18:15 4 KB PeterYoung to previous | to last
3 19-Nov-2009 18:14 4 KB PeterYoung to previous | to last
2 19-Nov-2009 18:12 4 KB PeterYoung to previous | to last
1 19-Nov-2009 17:16 3 KB PeterYoung to last

Page References

Incoming links Outgoing links
HeIIOffLimb
HeIIOffLimb

Version management

Difference between version and

At line 1 changed one line
!!He II 256 in off-limb quiet Sun spectra
[{ALLOW edit EISMainUsers}]
[{ALLOW view Anonymous}]
!!!He II 256 in off-limb quiet Sun spectra
At line 16 changed one line
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.
At line 18 changed one line
!Fit to 256 feature
!!Fit to 256 feature
At line 27 changed one line
!Si X 256.366
!!Si X 256.366
At line 33 changed one line
!Fe X 256.398
!!Fe X 256.398
At line 45 changed one line
!Fe XII 256.410
!!Fe XII 256.410
At line 62 changed one line
!Fe XIII 256.422
!!Fe XIII 256.422
At line 66 changed one line
!Summary
!!Summary
At line 73 added 20 lines
----
!!!Variation of He II 256 profile across the limb
To further investigate the He II 256 line, a large raster obtained at the limb has been studied to see how the line profile varies crossing from the disk to the limb.
The raster was obtained on 2007 December 12 at 10:42 (cam_ar_limb) and uses the 2" slit to raster an area of 360" x 512". The observation covers a large active region, but the bottom of the raster covers a relatively quiet region.
He II 256 spectra were generated for 25 positions by averaging Y-pixels 5 to 40 for 25 X-pixels spaced at 7 pixel intervals, beginning with pixel 2 which is inside the limb. I.e., the X-pixels used were 2, 9, 16, 23, etc., up to 170. The spectra were creating using the routine eis_mask_spectrum by creating pixel masks for each position.
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.
[{Image src = 'he2_profiles.png'}]
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
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.
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