[Loops] Comments and questions about new AIA Loop Paper

Tue Nov 23 16:09:55 MST 2010

Dear Joan, 
I just would like to point one thing. It might be my imagination, but I think I see another loop crossing your loop of interest precisely where the rectangle happened to be, see the attached PDF. If this is indeed the case, I could easily imagine a background subtraction that would keep in the information of this second loop... and could easily imagine the one that would not. So I'd agree with Marcus that loop profiles, the locations of points where the background was evaluated and explicit explanation of the background subtraction procedure might be extremely beneficial to this discussion. 
-----Original Message-----
From: "Joan T Schmelz (jschmelz)" <jschmelz at memphis.edu>
Sent 11/23/2010 1:54:57 PM
To: "A mailing list for scientists involved in the observation and modeling of solar loop structures" <loops at solar.physics.montana.edu>
Subject: Re: [Loops] Comments and questions about new AIA Loop PaperDear All,I’ll reply privately to Markus since there is no reason why you all have to be involved in this endless discussion. Needless to say, the points he makes are not relevant to the analysis we did. Please don’t let him muddy the waters because he doesn’t like the result. We have subtracted the background as carefully as possible, and the multi-thermal results are for the loop alone.Background subtraction is the x-factor in this analysis. Markus’ method of background subtraction works for an isolated loop, but such a loop is sometimes hard to find in the real coronal. We use this method when it is warranted. However, there could be a higher-T loop sitting right next to the loop you’re trying to analyze. If this is the case, you wouldn’t want to use those pixels for background. Rest assured that we treat the details of background subtraction VERY carefully. Each loop is examined individually and the pixels are selected based on a repeated examination of each filter. We did the same type of analysis with our spectral line data.FYI: Our next paper is almost ready for submission. We analyze 12 171-selected AIA loops and find only 2 where the plasma is consistent with the isothermal case. No matter how often Markus tries to paint me into this corner, I am NOT anti-isothermal. I’ve published results consistent with isothermal plasma, but I’ve always used careful DEM analysis. I’m sure others are working on similar projects, and it may not be too long before we see how all this turns out.Regards,JoanFrom: loops-bounces at solar.physics.montana.edu [mailto:loops-bounces at solar.physics.montana.edu] On Behalf Of Markus J. AschwandenSent: Tuesday, November 23, 2010 1:35 PMTo: A mailing list for scientists involved in the observation and modeling of solar loop structuresSubject: Re: [Loops] Comments and questions about new AIA Loop PaperDear Joan,Thanks for your reply. However, you evaded the crucial point aboutwhat background you subtracted. If you subtracted the backgroundvery close to the loop edges then you should be fine, but if you took thebackground away from the loop then your background-subtracted fluxes are heavily contaminated by the background corona. I wish your paper would quantify what you did. All the paper says is "... we choose 10 pixels from a CLEAN background area...". Since the loop fluxes typically make uponly about 10% of the total flux, the background level is at 90%.If you choose a background in a dark part of the image away from the loop(perhaps this is what you mean with a CLEAN background area ?),say at a 50% level, your background-subracted loop flux is 50% instead of10%, and then the DEM is dominated by the backgroundcorona rather than by the loop-associated flux. This is why I want to knowwhat background you subtracted, so that I can judge whether the resultingDEM is pertinent to the loop or to the corona. It makes all the difference !Looking forward for a clarification. Thanks !Regards,MarkusOn Nov 23, 2010, at 11:10 AM, Joan T Schmelz (jschmelz) wrote:Dear Markus,(2) What are the total fluxes F_tot and background fluxes F_bg that youused in your DEM modeling of the loop fluxes F_loop=F_tot - F_bg in the 6 coronal AIA filters? If the reader knows these 12 numbers, one could verify or reproduce your DEM modeling.>>We’ve already used two quite different DEM methods on these data and gotten very similar results, and personally, I do not want a repeat of what happened after your re-analysis of our CDS loop data. (If anyone is reading this and does not know what I’m talking about, that’s probably a good thing.) I think what might be of greater interest is an entirely independent analysis of your own.Also, you don’t just need 12 numbers; you need the uncertainties as well. These are extremely important, especially for loops that are not visible in all the filters. We always want high- and low-temperature constraints, but we also need to know how strong those constraints are.(3) What are the cross-sectional flux profiles F_tot(x), F_bg(x), F_loop(x)you inferred at the analyzed loop segments. If you show these profiles to thereader, one could inquire or judge whether the same loop or multiple loopsare seen at the analyzed location of the loop, and what the backgroundcontamination in the loop flux could be.>>Same as (2) above.Regards,Joan____________________________________________Dr. Markus J. AschwandenSolar & Astrophysics LaboratoryLockheed Martin Advanced Techology CenterOrg. ADBS, Bldg. 2523251 Hanover St., Palo Alto, CA 94304, USAPhone: 650-424-4001, FAX: 650-424-3994URL: http://www.lmsal.com/~aschwand/e-mail: aschwanden at lmsal.com__________________________________________________________________________________________________________________________
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