[Loops] New active region paper.

[Ignacio Ugarte]

Dear all,

Just wanted to let you know about our new paper just published in the 
Astrophysical Journal.


Is Active Region Core Variability age dependent?

Ignacio Ugarte-Urra and Harry P. Warren

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 /STEREO/ and /Solar 
Dynamics Observatory/ 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//Hinode/ spectral capabilities. We inspect a broad range of 
temperatures, including for the first time spatially and temporally 
resolved images of Ca XIV and Ca XV 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.


http://iopscience.iop.org/0004-637X/761/1/21/


Best regards,
Ignacio

-- 
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  ~ Ignacio Ugarte-Urra ~
    Naval Research Laboratory. Code 7681.
    4555 Overlook Ave SW. Washington, DC 20375
    phone: (+1) 202 404 1779
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