Sparkling extreme- ultraviolet dots observed with Hi-C

Regnier, Stephane, Alexander, Caroline, Walsh, Robert, Winebarger, Amy, Cirtain, Jonathan, Golub, Leon, Korreck, Kelly, Mitchell, Nick, Platt, Simon, Weber, Mark, De Pontieu, Bart, Title, Alan, Kobayashi, Ken, Kuzin, Sergey and DeForest, Craig (2014) Sparkling extreme- ultraviolet dots observed with Hi-C. The Astrophysical Journal, 784 (2). p. 134. ISSN 0004-637X

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Abstract

Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 Å. One of them is the existence of short, small brightenings "sparkling" at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale, trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 1026 erg.

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