Filament Study
observed by SUMER 28.Jul.96

SUMER performed four consecutive scans in alternating directions within a region in the Solar north-west containing a filament. (To identify the filaments, please compare a full disk picture made by Big Bear Solar Observatory 1 hour earlier.) The images shown below cover a region 406 to 519 arcsec west and 413 to 713 arcsec north of the Solar center.

Each scan consisted of 101 raster steps of approx. 1.13 arsec with an exposure time of 8 seconds each, leading to approx. 14 minutes per scan. The scans were taken in four emission lines simultaneously, namely 

Neon VIII    770.41 Å   Corona              600 000 K
Neon VIII    780.32 Å
Carbon IV   1548.20 Å   Transition Region   100 000 K
Carbon IV   1550.77 Å
for the first and second scan, and 
Silicon IV  1393.76 Å   Transition Region   140 000 K
Silicon IV  1402.77 Å
Oxygen IV   1401.16 Å   Transition Region   170 000 K
Oxygen IV   1404.81 Å   (blend with Sulfur IV)
for the third and fourth scan.

An on-board compression scheme ("Method 11") was used for this study, resulting in the transmission of just two values per spatial pixel: (a) the total intensity, and (b) and estimated line position within the spectral window, which is calculated by fitting the profile to a Gaussian and taking the centroid. The spectral window is approx. 1.05 Å in second order (Ne VIII) and 2.1 Å in first order (C IV, Si IV, O IV) around the commanded wavelength.

The intensities in the pictures below are not on the same scale, whereas the Doppler pictures all show velocities between +/- 50 km/s on the same scale. A mixture of dark red and blue pixels here is usually an indication for noise due to low intensity, which is clearly to be observed e.g. in the filament's absorption of the Ne VIII line. - The last O IV Doppler picture shows mainly noise, due to the line blend with S IV (a situation that Method 11 is not suited for); the significant redshift in the region of the filament is probably due to a stronger influence of the (colder) O III line at 702.8 Å (second order), pushing the spectral window's center of gravity to a longer wavelength.

First Scan (east-west, 15:54 UT):
Ne VIII 770, Ne VIII 780, C IV 1548, C IV 1550

Ne VIII Ne VIII C IV C IV Ne VIII Ne VIII C IV C IV

Second Scan (west-east, 16:08 UT):
Ne VIII 770, Ne VIII 780, C IV 1548, C IV 1550

Ne VIII Ne VIII C IV C IV Ne VIII Ne VIII C IV C IV

Third Scan (east-west, 16:22 UT):
Si IV 1393, Si IV 1402, O IV 1401, O IV / S IV 1404

Si IV Si IV O IV O IV/S IV Si IV Si IV O IV O IV/S IV

Fourth Scan (west-east, 16:36 UT):
Si IV 1393, Si IV 1402, O IV 1401, O IV / S IV 1404

Si IV Si IV O IV O IV/S IV Si IV Si IV O IV O IV/S IV

IED, 08.May.97