MODS1 and MODS2 rotator centers (during cloudy LUCI-AO night)

MODS1 and MODS2 were mounted on 2017 October 21 and 20, respectively, but MODS2 required realignment of the laser launch block and the red grating turret sensors before it could be used on-sky. So while the initial checkout, which included measurement of rotator centers on both blue and red channel cameras, was done on October 30 for MODS1, it was only done tonight for MODS2. MODS1 was used also and the rotator centers measured tonight are consistent with the results from Com20171030, which were, for MODS1B (1539.5,1541) and for MODS1R (1537.0,1547.1).

Image filenames are all: modsNc.20171129.000n.fits where N=1,2, c=b,r and n = 3,4,5,6. Each of these images is a track mode preset at the given position angle.

A version of modsrc (LBTtools.LBC.modsrc) which uses only the source extractor detections within the 3K x 3K field, excluding a 100-pixel buffer zone around the edges. The x,y coordinates of the detected sources for a pair of images were matched with IRAF.immatch.xyxymatch and then geomap was used to determine the mapping between the two images, using only the most basic fit=rotate and order 2 (not much difference for a fit with more free parameters). The fit rms was ~0.6-1.5 pixels. The output of geomap: xshift, yshift, rotation was used to determine the rotator center (xrc,yrc) as follows:

xrc = (a + c*ycor)/(1-b)
yrc = -1*(a*e + d*(1-b))/(c*e - (1-f)*(1-b))

where
   gcos = cos(grot/d2r)
   gsin = sin(grot/d2r)
   b = cos(rotation)
   c = sin(rotation)
   e = -sin(rotation)
   f = cos(rotation)
   a = xshift
   d = yshift

preset	posangle	mods2b	mods2r	mods1b	mods1r
track	0	3	3	3	3
track	180	4	4	4	4
track	270	5	5	5	5
track	90	6	6	6	6

approx avg	180	1513	1511	1506	1535	1537	1538	1536	1545
Rotator Centers
		M2B		M2R		M1B		M1R
pair	dtheta	xrc	yrc	xrc	yrc	xrc	yrc	xrc	yrc
3 & 4	180	1512.34	1512.05	1506.6	1537.1	1536.4	1537.09	1534.6	1544.9
5 & 6	180	1513.02	1509.86	1506	1532	1538.4	1538.4	1537.0	1545.1
4 & 6	90	1517.25	1508.40	1511	1533.8	1542.4	1540.5	1540.4	1549.9
3 & 6	90	1508.7	1507.12	1503.0	1532.5	1539.5	1531.2	1539.6	1539.1
3 & 5	90	1510.07	1514.12	1506.7	1534.4	1531.3	1537.4	1531.0	1542.6
4 & 5	90	1514.28	1514.30	1503.7	1536.8	1536.6	1542.2	1532.3	1548.5
avg	all	1512.6	1511.0	1506.2	1534.4	1537.4	1537.8	1535.8	1545.0
sig(n-1)	pix	3.0	3.0	2.8	2.1	3.7	3.8	3.8	3.9
sig(n-1)	arcsec	0.36	0.36	0.34	0.26	0.44	0.45	0.47	0.48

-- %USERSIG{OlgaKuhn - 2017-11-30}%

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