[Loops] EIS AR Loops - Tripathi et al, 2009, ApJ

[Joan T Schmelz (jschmelz)]

Hi Helen,

The paper on fuzzy TRACE 284 structures that Leon was referring to is:
	
The Transparency of Solar Coronal Active Regions
Brickhouse & Schmelz
ApJ, 636, L53

Abstract: Resonance scattering has often been invoked to explain the disagreement between the observed and predicted line ratios of Fe XVII λ15.01 to Fe XVII λ15.26 (the ``3C/3D'' ratio). In this process photons of λ15.01, with its much higher oscillator strength, are preferentially scattered out of the line of sight, thus reducing the observed line ratio. Recent laboratory measurements, however, have found significant inner-shell Fe XVI lines at 15.21 and 15.26 Å, suggesting that the observed 3C/3D ratio results from blending. Given our new understanding of the fundamental spectroscopy, we have reexamined the original solar spectra, identifying the Fe XVI λ15.21 line and measuring its flux to account for the contribution of Fe XVI to the λ15.26 flux. Deblending brings the 3C/3D ratio into good agreement with the experimental ratio; hence, we find no need to invoke resonance scattering. Low opacity in Fe XVII λ15.01 also implies low opacity for Fe XV λ284.2, ruling out resonance scattering as the cause of the fuzziness of TRACE and SOHO-EIT 284 Å images. The images must, instead, be unresolved due to the large number of structures at this temperature. Insignificant resonance scattering implies that future instruments with higher spatial resolution could resolve the active region plasma into its component loop structures.

Here is the link:

http://adsabs.harvard.edu/abs/2006ApJ...636L..53B

I look forward to reading your new paper!

Happy New Year,
Joan

________________________________________
From: loops-bounces at solar.physics.montana.edu [loops-bounces at solar.physics.montana.edu] On Behalf Of H.E.Mason at damtp.cam.ac.uk [H.E.Mason at damtp.cam.ac.uk]
Sent: Wednesday, January 07, 2009 3:22 AM
To: Leon Golub
Cc: loops at mithra.physics.montana.edu; H.E.Mason at damtp.cam.ac.uk
Subject: Re: [Loops] EIS AR Loops - Tripathi et al, 2009, ApJ

Hi Leon,

thanks for your comment.

I agree that we are looking at fine threads making up a loop
like structure. The question is why the lower temperature structures
are spatially more defined than the higher temperature structures.
We are providing evidence from EIS that this is indeed the case.
Obviously more work needs to be done, studying other active
regions. This is something we discussed at the Napa workshop.
Your interpretation is not inconsistent with our findings.
Is there a ref for your paper with Joan?

I look forward to seeing (and working with) new data in this
regard.

Best wishes,
helen

On Jan 6 2009, Leon Golub wrote:

>Helen et al.,
>
>I can't let this go uncommented. Even though this paper was
>accepted (I know, I was the editor) I disagree with the conclusion
>that hot loops are fuzzier. Yes, that's what you see, but it is
>also explainable if the hot parts of the AR have many fine threads
>(unresolved at present resolution) with a large filling factor.
>That as the conclusion Joan and I came to from analyzing 284A
>data.
>
>Anyway, this won't be settled until we fly an imager with higher
>resolution. We're proposing one this year and I'm hoping we get
>the chance to clear this up, finally.
>Cheers,
>
>Leon
>
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