Author(s): R.A. Harrison (CDS), J.-P. Delaboudiniere (EIT), D. Judge (SEM), J. Kohl (UVCS), P. Lemaire (SUMER)

Progress:

Draft Scheme                            February 15 1994    
Discussion at SPWG/SICWG                June 13/14 1994     


Detailed PlanMinor Revision             June 22             
                                        1994November 4      
                                        1994                

CDS ID: ICAL2

Objective: To transfer SEM observations to an inter-instrument calibration involving EIT, CDS and projecting to SUMER and UVCS.

Synopsis: Using EIT we project SEM calibrated intensities to a small region on the Sun which is being monitored by CDS, UVCS and SUMER. Thus, the CDS intensities for that region, at 304Å will be known. By the use of invariant line ratios we project the calibration to longer wavelengths for comparison to SUMER and UVCS.

Scheme: The actual observation is simple. The five instruments must operate at the same time, with UVCS, SUMER and CDS on the same portion of the solar disc. EIT must record full-Sun images. To cater for the potential influence of transient activity, observations should be made over several tens of minutes at least.

After the operation, the SEM "calibrated" intensity is divided across the Sun's disc using the EIT intensity distribution. The EIT 304Å and CDS 304Å images are compared and this produces a calibration of CDS at this wavelength. To project to longer wavelengths, we may make use of various methods. For example, we may use branching ratios (see CDS Science Report [Blue Book] - version 5.0, 1993, pages 174 and 176) which are invariant intensity ratios due to emission lines orginating from the same upper level. One would want to start from a line near 304Å and this appears to be possible. For example, we could use O VI 318/986Å, N IV 303/1118Å, N IV 323/1446Å, though the shorter wavelength (CDS) lines have yet to be identified in the solar spectrum. Alternatively, there are some invariant ratios suggested by Kastner and Neupert (A & A 128, 181, 1983), though we have not identified a specific means of obtaining measures above 500Å. Finally, one could compare orders - for example, given the 304Å calibration, one might be satisfied that the intensities in the CDS-GI region 331-346Å are sufficiently well understood, and these lines can be compared to identical lines in second order in CDS-GI band 4. From this, we can compare lines in first order from the longest wavelength band of CDS-GI to SUMER.

The precise details of wavelength selection remain to be worked out, although a straight calibration of CDS from SEM is relatively easy at 304Å. The details we need to establish are for the projection to other wavelengths.

Operation:

SEM

Monitor the Sun for a specified period of up to 250 minutes.

EIT

Monitor the full-Sun in 304Å starting at the same time as the SEM observation. Run in survey mode with 5 arcsec resolution, i.e. 512x512 bins, with transmission time of

42 minutes (one band) and accumulation time of 5 minutes. Cycle 5 times, i.e. total =

(5+42)x5 = 235 min.

CDS

Grazing Incidence

Slit 4x4 arcsec

Raster area 2x2 arcmin

30x30 locations, 3.0 sec exposure at each.

Total duration per raster = 2700 sec (45 min).

Start at onset of SEM campaign and repeat 5 times.

Assuming an overhead of 20%, total duration 248 minutes.

Select data from 261-346Å range (2nd GI detector).

No data compression required.

SUMER

Slit 1x300 arcsec

Raster area 120x300 arcsec - centred on CDS field

160 locations - 0.76 arcsec step - accumulate over every 4 steps

20 sec exposure (5 step per sec) - Total duration = 13.33 minutes.

Start at onset of SEM campaign and repeat 18 times. Total duration 240 minutes.

Line selection - TBD - It depends on CDS line identifications and the use of relevant

branching ratios or other invariant line ratios.

UVCS

Slit 14arcsec x 40 arcmin

Raster area 140arcsec x 40 arcmin - centred on CDS field

10 locations - 80 sec exposure at each. Total duration = 13.33 minutes.

Start at onset of SEM campaign and repeat 18 times. Total duration 240 minutes.

Line selection - TBD - See SUMER entry.