Dear Ignacio,

Thanks for the preprint. I guess this is the same work we had an interesting
discussion at the Napa meeting back in December. The results are intriguing,
especially the dependence of the loop lifetimes on the temperature. However,
you probably realize (better than we all) how many loops intersect in the
fore- and background of the line-of-sight where you choose a box and plot
a lightcurve to derive the lifetime. I have the impression that most lightcurves
contain emission from multiple loops, but I admit that it is very difficult to
disentangle them. It would be interesting if we could isolate individual loops
by proper geometric (cross-sectional+background) modeling in all filters to
see if your preliminary results hold up. 
Keep us posted about further progress!

Cheers,
Markus



On Jan 9, 2009, at 5:54 AM, Ignacio Ugarte Urra wrote:

Hi all,

Just wanted to let you know about a paper on EIS/XRT observations of
coronal loops just accepted by ApJ.

http://arxiv.org/abs/0901.1075

Title: "Active region transition region loop populations and their
relationship to the corona"
Authors: Ignacio Ugarte-Urra, Harry P. Warren and David H. Brooks

Abstract:
The relationships among coronal loop structures at different
temperatures is not settled. Previous studies have suggested that
coronal loops in the core of an active region are not seen cooling
through lower temperatures and therefore are steadily heated. If loops
were cooling, the transition region would be an ideal temperature regime
to look for a signature of their evolution. The Extreme-ultraviolet
Imaging Spectrometer (EIS) on Hinode provides monochromatic images of
the solar transition region and corona at an unprecedented cadence and
spatial resolution, making it an ideal instrument to shed light on this
issue. Analysis of observations of active region 10978 taken in 2007
December 8 -- 19 indicates that there are two dominant loop populations
in the active region: core multi-temperature loops that undergo a
continuous process of heating and cooling in the full observed
temperature range 0.4-2.5 MK and even higher as shown by the X-Ray
Telescope (XRT); and peripheral loops which evolve mostly in the
temperature range 0.4-1.3 MK. Loops at transition region temperatures
can reach heights of 150 Mm in the corona above the limb and develop
downflows with velocities in the range of 39-105 km/s.

Best,
Ignacio
--
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ Ignacio Ugarte-Urra ~
  Naval Research Laboratory. Code 7673U.                      
  4555 Overlook Ave SW. Washington, DC 20375
  Contractor. Spain.
  phone: (+1) 202 404 1779
  email: iugarte@ssd5.nrl.navy.mil
  http:  http://tcrb.nrl.navy.mil/~iuu
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Dr. Markus J. Aschwanden
Solar & Astrophysics Laboratory
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