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Astronomy & Astrophysics manuscript no. lpref1v2 April 29, 2005 (DOI: will be inserted by hand later)

Summary: Astronomy & Astrophysics manuscript no. lp—ref1—v2 April 29, 2005
(DOI: will be inserted by hand later)
Electron density along a coronal loop observed with CDS/SOHO
I. Ugarte­Urra 1# , J. G. Doyle 1 , R.W. Walsh 2 , and M. S. Madjarska 3,4
1 Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
2 Centre for Astrophysics, University of Central Lancashire, Preston, PR1 2HE, UK
3 Max­Planck­Institut f˜ur Sonnensystemforschung # , Max­Planck­Str. 2, 37191 Katlenburg­Lindau, Germany
4 Department of Solar Physics, Royal Observatory of Belgium, Av. Circulaire 3, B­1180 Bruxelles, Belgium
Received / Accepted
Abstract. The analysis of a coronal loop observed by CDS and EIT on board SOHO is presented. The loop was situated
above the North­East limb at a latitude of #48 # , being clearly visible in the hottest lines of the dataset, Fe ### 360.76 Å, i.e.
greater than 2 000 000 K. The cooler lines in the sample (i.e. O # 629.73 Å and He # 584.35Å) showed only a brightening at the
footpoints location. Based on the Fe ### 353.84/334.17 line ratio, the electron density along the loop was determined following
three di#erent approaches for the background subtraction. No di#erences, within the error bars, can be found between the three
methods. At the apex, the density is 0.9 × 10 9 cm -3 , while at the footpoint it is 50% greater, i.e. 1.4 × 10 9 cm -3 . The inferred
filling factor values along the loop, at the formation temperature of the lines, are in the range 0.2--0.9.
One dimensional hydrodynamic modelling of the loop along a given field line, gravity neglected, was performed. A minimum
# 2 analysis results in a best fit case where the total energy input is directed preferentially to the loop footpoint (the heating rate
is three times larger at the base than at the apex). An isochoric solution can not be ruled out completely. The exercise illustrates
the necessity of accurate spectral diagnostics in order to derive definite conclusions from theoretical models and suggests the


Source: Armagh Observatory


Collections: Physics