<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Sergio and Fabio,<div><br></div><div>I like to encourage you to use STEREO EUVI data, which would provide</div><div>you the ultimate test to subtract the correct background, because you</div><div>see a loop from two different directions and have two independent</div><div>backgrounds. You can test the self-consistence of background subtraction,</div><div>if you obtain the same EM of the loop from two spacecraft. </div><div>If you look into my recent STEREO paper, you see that one can</div><div>subtract the background with an accuracy of about 10%.</div><div>See Fig.8 therein.</div><div><br></div><div>Cheers,</div><div>Markus</div><div><br></div><div><span class="Apple-style-span" style="font-family: Times; "> Aschwanden,M.J., Nitta,N.V., Wuelser,J.P., and Lemen,J.R. 2008, The Astrophysical Journal, 680, 1477-1495<br><a href="http://www.lmsal.com/~aschwand/eprints/2008_stereo2.pdf">URL1="http://www.lmsal.com/~aschwand/eprints/2008_stereo2.pdf"</a> <br><font size="3"></font><font size="4">First 3D reconstructions of coronal loops with the STEREO A and B spacecraft: II. Electron Density and Temperature Measurements</font></span></div><div><font class="Apple-style-span" face="Times"><span class="Apple-style-span" style="font-size: large;"><br></span></font></div><div><font class="Apple-style-span" face="Times"><span class="Apple-style-span" style="font-size: large;"></span></font></div></body></html>