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Dear all,<br>
<br>
Just wanted to let you know about our new paper just published in
the Astrophysical Journal.<br>
<br>
<br>
Is Active Region Core Variability age dependent?<br>
<br>
Ignacio Ugarte-Urra and Harry P. Warren<br>
<br>
The presence of both steady and transient loops in active region
cores has been reported from soft X-ray and extreme-ultraviolet
observations of the solar corona. The relationship between the
different loop populations, however, remains an open question. We
present an investigation of the short-term variability of loops in
the core of two active regions in the context of their long-term
evolution. We take advantage of the nearly full Sun observations of
<i>STEREO</i> and <i>Solar Dynamics Observatory</i> spacecraft to
track these active regions as they rotate around the Sun multiple
times. We then diagnose the variability of the active region cores
at several instances of their lifetime using EIS/<i>Hinode</i>
spectral capabilities. We inspect a broad range of temperatures,
including for the first time spatially and temporally resolved
images of Ca <span class="sml">XIV</span> and Ca <span class="sml">XV</span>
lines. We find that the active region cores become fainter and
steadier with time. The significant emission measure at high
temperatures that is not correlated with a comparable increase at
low temperatures suggests that high-frequency heating is viable. The
presence, however, during the early stages, of an enhanced emission
measure in the "hot" (3.0-4.5 MK) and "cool" (0.6-0.9 MK) components
suggests that low-frequency heating also plays a significant role.
Our results explain why there have been recent studies supporting
both heating scenarios.<br>
<br>
<br>
<a class="moz-txt-link-freetext" href="http://iopscience.iop.org/0004-637X/761/1/21/">http://iopscience.iop.org/0004-637X/761/1/21/</a><br>
<br>
<br>
Best regards,<br>
Ignacio<br>
<br>
<pre class="moz-signature" cols="72">--
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ Ignacio Ugarte-Urra ~
Naval Research Laboratory. Code 7681.
4555 Overlook Ave SW. Washington, DC 20375
phone: (+1) 202 404 1779
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
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