The image above (TRW ID D-HXH-AL-27.001, run id 107934, taken 1/7/97, logged as 1/8/97) is MEG 3rd order Al-K defocussed to 65.54 mm. The main K-alpha line, satellite line, and K-beta/O-K lines are visible. The image used is the raw HSI image and HSI "gaps" are visible.
Each MEG grating creates an image in one of the shells around the rings. If a grating is mis-aligned in roll ("alignement") its image will move roughly in the +/- Z direction. The 3rd order MEG Al-K is diffracted ~ 55 mm in the dispersion direction, so a 30 arc minute grating roll results in a 0.48 mm Z shift.
The events in each sector (A through FF) of each shell (1 and 3) have been converted from facility Y,Z values into R, theta about the ring center. The events for shell-sector can be view by plotting the appropriate anglular range (0 degrees is along the +Y axis, south; positive angles are right-hand rule about X, e.g., towards +Z) and radial (shell) range. The gaps between facets are generlly visible.
In this theta-R space the cross-dispersion direction is indicated with an arrow of length 30 arc minutes of grating roll and pointing in the direction of "unscrewing" (+ righthand about +X). A histogram of counts vs theta helps identify the gratings, gaps, etc.
The links in the table below are for the given shell-sector image and histogram. The orientation of these images is as if standing in the center of the HESS HRMA-side looking radially out towords the sector: grating 1 of the sector is to the right and grating 7/9 to the left (larger angles.)
| 1A | 1B | 1C | 1D | 1E | 1F | 1AA | 1BB | 1CC | 1DD | 1EE | 1FF |
| 3A | 3B | 3C | 3D | 3E | 3F | 3AA | 3BB | 3CC | 3DD | 3EE | 3FF |
The following is a list of gratings which appear to be highly-rolled. Herman Marshall identified 4 spots in the Focus Check MEG +3 image in his memo and they are here as well as two others: one in the Top quadrant (3EE2) that may be visible in the Top image and one (1E4) that is not clearly visible in South or Bottom but is is on their boundary and so may be blocked by either shutter.
| run id | Quadrant | hlm feature | fraction of quadrant | spot roll | HESS ID | Grating | NE80 Entry | Fab ID | X-GEF Al-K 3rd order | X-GEF Al-K 1st order |
|---|---|---|---|---|---|---|---|---|---|---|
| 107463 | Top | -?- (see in image?) | . | ~+5 arc minutes | 3EE2 | ME1411 | 189 | F07M012 | 1.8-2.0 % | 17-19% |
| 107464 | North | Spot 1 | 5.6 % | -8 arc minutes | 3FF4 | MD1312 | 201 | F07M027 | 2.3-4.9 % | 6.9-7.8 % |
| 107464 | North | Spot 2 | 2.3 % | +23 arc minutes | 3FF5 | MD1307 | 195 | F07M020 | 1.3-1.6 % | 15-17 % |
| 107465 | Bottom | Spot 1 | 3.0 % | +8 arc minutes | 3E1 | ME1405 | 185 | F07M008 | 1.5-1.7 % | 18 % |
| . | South/Bottom | -?- (shutter blocked?) | . | ~+5 arc minutes | 1E4 | ME1402 | 187 | F07M010 | 1.5-1.8 % | 15-18 % |
| 107466 | South | Spot 1 | 4.0 % | -6 arc minutes | 1F4 | MF1502 | 192 | F07M017 | 1.4-1.6 % | 18 % |
Note that all of these gratings are from Lot F07M ! In fact these are 6 of the (only) 11 lot F07M gratings that are on the flight unit. The other five are: 3EE3, 1FF5, 1F1, 3F5, 3F2. Now with suspicion on them the first few of these look like they could have small alignment errors too!
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