Are Active Region Loops Isothermal?

Details Are Active Region Loops Isothermal? Are Active Region Loops Isothermal?

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh41b02s&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SH41B-02

Other

7509 Corona, 7554 X Rays, Gamma Rays, And Neutrinos

Scientific paper

Recent results from both EIT and TRACE data suggest that active region loops may be isothermal. The analysis of these observations uses an isothermal approximation derived from narrow-band filter ratios - either 171 (Fe IX; T = .63 MK) to 195 (Fe XII; T = 1.6 MK) angstroms or 195 (Fe XII; T = 1.6 MK) to 284 (Fe XV; T = 2.0 MK) angstroms. These findings imply that the loops cannot be in quasi-static equilibrium unless very strict, possibly unphysical restrictions are met. These results are in sharp contrast to the multi-thermal loops obtained from the analysis of: (a) SXT data, which also uses an isothermal approximation, but one derived from a broad-band filter ratio; (b) CDS data, where individual spectral lines have been used to produce a differential emission measure distribution at multiple pixels along several loops. One possible reason for the discrepancy is the larger pixel size of both SXT and CDS - it is possible that neither instrument is observing a single, isolated loop, but rather a loop bundle which is not resolved. Each individual loop could be isothermal, but the unresolved collection could mimic a multi-thermal loop that is both hydrostatic and in quasi-static equilibrium. To test this idea, we do two related analyses: we do the EIT and TRACE analysis with bigger pixels that match the size of SXT and CDS pixels; and we do an isothermal approximation with different iron line ratios from CDS.

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