Issue |
A&A
Volume 518, July-August 2010
Herschel: the first science highlights
|
|
---|---|---|
Article Number | A42 | |
Number of page(s) | 10 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361/200913883 | |
Published online | 01 September 2010 |
Active region moss
Basic physical parameters and their temporal variation
1
DAMTP, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK e-mail: D.Tripathi@damtp.cam.ac.uk
2
Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
3
George Mason University, 4400 University Drive, Fairfax, VA 22030, USA
Received:
16
December
2009
Accepted:
10
May
2010
Context. Active region moss are transition region phenomena, first noted in the images recorded by the Transition Region and Coronal Explorer (TRACE) in λ171. Moss regions are thought to be the footpoints of hot loops (3–5 MK) seen in the core of active regions. These hot loops appear “fuzzy” (unresolved). Therefore, it is difficult to study the physical plasma parameters in individual hot core loops and hence their heating mechanisms. Moss regions provide an excellent opportunity to study the physics of hot loops. In addition, they allow us to study the transition region dynamics in the footpoint regions.
Aims. To derive the physical plasma parameters such as temperature, electron density, and filling factors in moss regions and to study their variation over a short (an hour) and a long time period (5 consecutive days).
Methods. Primarily, we have analyzed spectroscopic observations recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. In addition we have used supplementary observations taken from TRACE and the X-Ray Telescope (XRT) aboard Hinode.
Results. The moss emission is strongest in the and
lines. Based
on analyses using line ratios and emission measure we found that moss regions have a characteristic temperature of log T[K] = 6.2.
The temperature structure in moss region remains almost identical from one region to another and it does not change with time.
The electron densities measured at different locations in the moss regions using
ratios are about
1–3 × 1010 cm-3 and about 2–4 × 109 cm-3 using
and
. The densities in the
moss regions are similar in different places and show very little variation over short and long time scales. The derived electron
density substantially increased (by a factor of about 3–4 or even more in some cases) when a background subtraction was performed.
The filling factor of the moss plasma can vary between 0.1–1 and the path length along which the emission originates is from a few
100 to a few 1000 kms long. By combining the observations recorded by TRACE, EIS and XRT, we find that the moss regions correspond to
the footpoints of both hot and warm loops.
Key words: Sun: atmosphere / Sun: activity / Sun: corona / Sun: UV radiation / Sun: transition region / Sun: magnetic topology
© ESO, 2010
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