[Loops] EM loci

[Markus J. Aschwanden]

On Sep 23, 2010, at 8:43 AM, Harry Warren wrote:

> 
> Markus,
> 
> I thought that your papers on the early STEREO data indicated that
> background subtraction was reasonably well understood. You obtained similar
> intensities from the two different vantage points.
> 
	Dear Harry,
        Good point, with STEREO we have a double-check of the background,
	which gives us more confidence on background definition methods.
	However I find a high sensitivity of the DEM width on the background definition
	using 6 coronal AIA filters. With 3 filters from STEREO it is easier in a
	more restricted temperature range.

> Also, you've stressed the importance of computing the cross-correlation of
> the emission at different temperatures. Considering only highly correlated
> data removes many spurious broad DEM results.

	In principle, yes, but I there are more near-cospatial loops in 6 AIA filters
	than in 3 filter data from TRACE or STEREO.
> 
> I think that the most significant problem is our bias toward bright loops
> that we can measure easily. They might not be representative.

	I fully agree with this bias. On the other side, bright loops have a higher
	probability of multi-strand structuring, so finding near-isothermal bright
	loops is even a stronger argument than near-isothermal week strands.
	
        Cheers,
	Markus
> 
> Finally, a quick comment on the paper. I was expecting to see some Monte
> Carlo simulations and least-square fits to the resulting data. Isn't the
> real question how many lines and what level of uncertainty do we need to
> determine the emission measure.
> 
> Best wishes,
> 
> Harry
> 
> On 9/23/10 10:20 AM, "Markus J. Aschwanden" <aschwanden at lmsal.com> wrote:
> 
>> Friends,
>> 
>> I'm glad to see that the EM loci method is put on a more quantitative basis,
>> especially in relationship to Gaussian DEM functions with variable temperature
>> spread. While the two methods can now being used interchangably thanks to
>> this recent nice study of Landi and Klimchuk, the biggest diagnostic problem
>> for 
>> coronal loops is (in my view) still the proper background subtraction.
>> Every contaminations from background fluxes introduces always a bias
>> towards broader multi-thermal DEMs. This problem is even worse for AIA
>> data, because more filters involve more confusion.
>> 
>> Looking forward to a patented background subtraction technique.
>> 
>> Cheers,
>> Markus
>> 
>> 
> 
> -- 
> // ---------------------------------------------------------------------
> // Harry P. Warren             phone : 202-404-1453
> // Naval Research Laboratory   fax   : 202-404-7997
> // Code 7673HW                 email : hwarren at nrl.navy.mil
> // Washington, DC 20375        www   : http://tcrb.nrl.navy.mil/~hwarren
> // ---------------------------------------------------------------------
> 
> 
> 
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____________________________________________
Dr. Markus J. Aschwanden
Solar & Astrophysics Laboratory
Lockheed Martin Advanced Techology Center
Org. ADBS, Bldg. 252
3251 Hanover St., Palo Alto, CA 94304, USA
Phone: 650-424-4001, FAX: 650-424-3994
URL: http://www.lmsal.com/~aschwand/
e-mail: aschwanden at lmsal.com
_______________________________________
____________________________________



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