## 4. Results## 4.1. PointingBefore evaluating the different electron density diagnostics, it is important to establish the relative pointings of both instruments. The pointing for the s3477r01 dataset was X=537, Y=-205 while for the 165749 dataset it was X=530, Y=-200 (see Table 1). Thus the solar Y location of the slit for dataset 165749 is 5 arc sec above that for dataset s3477r01. It is necessary however to also take into account the slit sizes of the two instruments. The slit of SUMER is 117 arc sec in length while that of CDS is 119 arc sec. (The spatial pixel size of SUMER is 0.97 arc sec while that of CDS is 1.68 arc sec). Thus, it may be seen that position 8 to 49 arc sec in dataset 165749 corresponds in absolute terms along the Y-axis to the region 14 to 55 arc sec in dataset s3477r01. However, the start times for dataset s3477r01 from the CDS data and dataset 165749 from the SUMER data differ by 68 minutes (see Table 1). Taking solar rotation into account there is a distance in X of 16 arc sec between the starting locations of each slit. In dataset s3477r01, a summed region from 14 to 55 was used, while in dataset 165749 the summed region from 8 to 49 arc sec was measured, which correspond to similar Y locations. Results from each of these datasets are shown separately below and the results discussed in Sect. 5. The start times of datasets s3479r00 and 173109 are separated by 37 minutes, but they observe the same spatial location, taking solar rotation into account. Region 10 to 55 arc sec in dataset s3479r00 and 4 to 49 arc sec in dataset 173109 are therefore observing the same spatial region, within 1 arc sec. ## 4.2. s3477r01In the Fe XIII 359/348 ratio it was found that due to blending of the Fe XIII 359.64Å line with a Ne V line at 359.37Å (Thomas & Neupert 1994, Dere 1978), it was necessary to use two Gaussians in the fit in order to successfully de-blend these lines. The Ne V component in the blend contributed 10-15% of the total flux. The Fe XIII 348.18Å line also suffered blending, in this case with a high temperature line of Fe XVII at 347.406Å. This was again taken into account by fitting two Gaussians to the Fe XIII /Fe XVII line profile. Because the lines of interest are strong and close together in wavelength we assume that any errors due to line fitting and instrument calibration will be small. In this case errors in the line ratio are estimated to be approximately or 0. 3. This corresponds to errors in the derived density from the Fe XIII ratio of approximately 0.3 dex. In Fig. 2, the derived electron densities are shown for the Fe XIII 359/348 ratio in summed region 14 to 55 arc sec. The theoretical line ratios used may be seen in Fig. 3.
The average measured electron density over the observation time in
this region, from the QUB results, is Log
N These compare well with the values of Log N The average electron density calculated along the whole slit
(i.e.0-118 arc sec) for the QUB results is Log
N ## 4.3. s3479r00In Fig. 4, results are shown for the region 10 to 55 arc sec.
The average electron density for this region over the observation time
is Log N
The average electron density over the whole slit
(0-118 arcsec) has a value of Log
N ## 4.4. 165749For this dataset we choose to observe the region from 8-49 arc sec.
This corresponds to the whole of a bright region at the bottom of the
slit. The theoretical O IV curves used to derive
Log N
Errors in the line ratio are estimated to be approximately or 0.03. This corresponds to errors, in the derived density from the O IV ratio, of approximately 0.25 dex. The electron density, based on the QUB atomic data begins at a
maximum value (in this case Log N Along the whole slit (i.e. summing over the full
117 arc sec) the average electron density was
found to be Log N ## 4.5. 173109The region 4 to 49 arc sec comprises a bright region at the bottom
of the slit. The derived electron densities for this region are shown
in Fig. 7. A clear upsurge in density is visible here in the QUB
results towards the end of the observation with Log
N
The average value over the observation time is Log
N Along the whole slit (i.e. summing over the full
117 arc sec) the average electron density was
found to be Log N
© European Southern Observatory (ESO) 1998 Online publication: September 17, 1998 |