[Loops] More Hinode AR loops - Ugarte-Urra et al. 2009, ApJ

[Ignacio Ugarte Urra]

Thanks Markus and Hugh for your inputs.

To Markus:
The lightcurves I present are from loops identified at transition region
temperatures. These loops are relatively easy to isolate. Then I track
them up in temperature and the fact that the cool loops result from
cooling of the hot component is easy to spot. It is not as
straightforward to do it the other way around because there is more
contamination in the line-of-sight at higher temperatures. The plot with
the temperature decay is for a particular loop very well isolated from
the rest.

To Hugh:
I am aware that, at least a subset of active regions, have a hot steady
component and I agree with you that both populations seem to contribute
to the active region X-ray emission in general. The literature insists,
however, on the fact that hot loops are steady. Here, I do not discuss
this component. As I said before, I start from the lower temperatures up
and it seems to me that a subset of active regions (perhaps it is
associated with the evolutionary stage) do have a non-negligible hot
impulsive component that is seen cooling down to transition region
temperatures. I don't think either that the peripheral loops reach
several million K.

Cheers,
Ignacio

On Fri, 2009-01-09 at 16:12 +0000, Hugh Hudson wrote:
> Dear Ignacio et al.
> 
> 
> I've always suspected that even the cores of active region had both
> kinds of loop population. This is based on what SXT saw, but also from
> the elementary fact that GOES light curves clearly have a flare-like
> and steady component that somehow compete. I don't think the steady
> part could come from peripheral loops below 1.3 MK.
> 
> 
> That said, now I'll read the paper!
> 
> 
> Hugh
> 

> 
On Fri, 2009-01-09 at 08:03 -0800, Markus J. Aschwanden wrote:
> 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 at ssd5.nrl.navy.mil
> >   http:  http://tcrb.nrl.navy.mil/~iuu
> > ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 
> > 
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