From kaf@cygnus Sun Jan 5 22:42:19 1997 Received: from cygnus.mit.edu by wiwaxia AA09945; Sun, 5 Jan 97 22:42:18 EST Received: by cygnus AA18450; Sun, 5 Jan 97 22:42:17 EST Date: Sun, 5 Jan 97 22:42:17 EST From: Kathryn A. Flanagan To: dd@cygnus Subject: focus checks Status: R Hi Dan, We had a very lengthy meeting here will 4 gratings coves (Jeremy, Herman, Peter and me) discussing the misaligned grating problem. There is now little doubt that is is a misaligned grating. We DO see the blob at 60 pixels above third order showing up at 20 pixels above 1st order. Furthermore, there is a -1st order focus check we will examine, to ascertain that the blob there showels up 20 pixels below the -1 st order. That will confirm that it is not scattering off a mirror, or a detector effect. Given that the data in hand satisfies this question, there are two other benefits that further testing will give. A deep focus check for each shell will isolate which ring the outlying MEG gratings are on. Better staistics will reveal any other outliers we never saw before. By knowing which quadrant and which shell, we can visually examine the 22 or 27 candidates to see if any are damaged, for example, next chance we get. I think this is minimally important to interpret the data we will obtain in high orders. The HEGS are less of a problem, and we can probably wait until Mg for example. We have examined the possibility of a ring focus as well. This has the value of potenetially telling us WHICH gratings are the problems. At third order, typical deviations are 6 arcmins. This is 20 pixels. A facet in the defocused image subtends about 60 pixels. (The worst outlier is 60 pixels above, not 20 pixels.) A test like this might be useful, and we would be looking for gaps of 10 to 20 pixels in individual gratings. Bad gratings top and bottom are easier to find this was. North and south are, unfortunately, harder. The distribution of photons azimuthally will be complicated. In fact, it is important to NOT attempt this at an energy where the individual grating efficiency varies. That leaves out AL, and makes Fe interesting. The problem at the moment is all the litlle nearby xray lines. I did speak with Dick Elder, and there NO post-shake test candidates that exceed two arcmins or so. This means the misalignment occurred later. In the worst case, I am suspicious of a damaged grating, but at least I am guessing it may be obvious to the naked eye which grating is the bad one. Peter will think about Fe L (and the associated statistics) at high orders. He will definitely move the tests up in priority to this test period. Even though the line is broad, it is broad in the dispersion direction, so he could look for similar effects. At this juncture, I have changed my mind about elimination high order HSI pictures, because I fear we will need pictures! OK, that's the news from the front. feel free to share this with the grating coves! Kathy