CORONAL FUZZINESS MODELED WITH PULSE-HEATED MULTI-STRANDED LOOP SYSTEMS

Journal Article · Tue Aug 10 04:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/719/1/576· OSTI ID:21455002

Guarrasi, Massimiliano; Reale, Fabio; Peres, Giovanni ^[1]

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1. Dipartimento di Scienze Fisiche and Astronomiche, Universita di Palermo, Sezione di Astronomia, Piazza del Parlamento 1, 90134 Palermo (Italy)

Coronal active regions are observed to get increasingly fuzzy (i.e., increasingly confused and uniform) in increasingly hard energy bands or lines. We explain this as evidence of fine multi-temperature structure of coronal loops. To this end, we model bundles of loops made of thin strands, each heated by short and intense heat pulses. For simplicity, we assume that the heat pulses are all equal and triggered only once in each strand at a random time. The pulse intensity and cadence are selected so as to have steady active region loops ({approx}3 MK) on average. We compute the evolution of the confined heated plasma with a hydrodynamic loop model. We then compute the emission along each strand in several spectral lines, from cool ({<=}1 MK), to warm (2-3 MK) lines, detectable with Hinode/Extreme-ultraviolet Imaging Spectrometer, to hot X-ray lines. The strands are then put side by side to construct an active region loop bundle. We find that in the warm lines (2-3 MK) the loop emission fills all the available image surface. Therefore, the emission appears quite uniform and it is difficult to resolve the single loops, while in the cool lines the loops are considerably more contrasted and the region is less fuzzy. The main reasons for this effect are that, during their evolution, i.e., pulse heating and slow cooling, each strand spends a relatively long time at temperatures around 2-3 MK and it has a high emission measure during that phase, so the whole region appears more uniform or smudged. We predict that fuzziness should be reduced in the hot UV and X-ray lines.

• OSTI ID: 21455002
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 719; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ATMOSPHERES
ELECTROMAGNETIC RADIATION
EVOLUTION
EXTREME ULTRAVIOLET RADIATION
FUZZY LOGIC
MAIN SEQUENCE STARS
MATHEMATICAL LOGIC
MEASURING INSTRUMENTS
PLASMA
RADIATIONS
SOLAR ATMOSPHERE
SOLAR CORONA
SOLAR SYSTEM EVOLUTION
SPECTROMETERS
STARS
STELLAR ATMOSPHERES
STELLAR CORONAE
SUN
ULTRAVIOLET RADIATION