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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