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You are here: Foswiki>Commissioning Web>RotatorAngle (18 Apr 2019, JohnHill)Edit Attach
Rotator Angle, Position Angle, Parallactic Angle and Doug's Angle
Here are some accumulated facts and issues about angles and rotators on LBT........(perhaps more than you wanted to know)How Rotator Angle, Parallactic Angle and Position Angle are connected at various focal stations
LBC
In LBC, as displayed on the LBC GUI:Rotator Angle = Parallactic Angle - Position Angle
Demand Angle = Rotator Angle + Rotator Offset = Parallactic Angle - Position Angle + Rotator Offset
LUCI1 and IRTC2 at LFBG
Apparently (deduced from the LUCI1 headers):ROTANGLE x LEFTSCALE = POSANGLE - PARANGLE + (180 - LEFTZEROPOINT) In this case ROTANGLE is the demand angle of the Bent Gregorian Rotator, and not exactly the same thing as Rotator Angle in LBC. PARANGLE is the Parallactic Angle. POSANGLE is the Position Angle - image orientation relative to North. LEFTSCALE = 1.0
LEFTZERPOINT = -187.703 (updated to -187.764 on 20100915)
Hidden inside the value of LEFTZEROPOINT (the PCS variable to orient the instrument on the sky) are DSP zeropoints for the physical rotators, and telescope geometry effects. LEFTSCALE (the PCS variable to control rotator direction) accounts for the presence or absence of a tertiary mirror. Filling in LEFTTZEROPOINT and LEFTSCALE, and subtracting 360:
ROTANGLE = POSANGLE - PARANGLE + 7.7
20090213 UT
FITSname TELALT TELAZ PARANGLE POSANGLE ROTANGLE luci_20090213_0001.fits 60.499226 -3.323632 174.0639 210.0000 43.5126 luci_20090213_0002.fits 60.483902 -3.616531 173.5363 210.0000 44.0403 luci_20090213_0003.fits 60.466972 -3.912084 173.0010 210.0000 44.5761 luci_20090213_0004.fits 60.448963 -4.203963 172.4744 210.0000 45.1030 luci_20090213_0005.fits 60.429424 -4.498290 171.9412 210.0000 45.6366 luci_20090213_0006.fits 60.408752 -4.788890 171.4156 210.0000 46.1630 luci_20090213_0007.fits 60.392883 -5.365861 170.3881 210.0000 47.1711 luci_20090213_0008.fits 60.368313 -5.654432 169.8647 210.0000 47.6964 luci_20090213_0009.fits 60.341671 -5.951203 169.3265 210.0000 48.2350 luci_20090213_0010.fits 60.314377 -6.238841 168.8036 210.0000 48.7602 luci_20090213_0011.fits 60.285458 -6.529237 168.2750 210.0000 49.2905 luci_20090213_0012.fits 60.255608 -6.815309 167.7542 210.0000 49.8107 luci_20090213_0013.fits 60.047131 -8.228965 164.9637 210.0000 52.3570 luci_20090213_0014.fits 60.009575 -8.509059 164.4492 210.0000 52.8745 luci_20090213_0015.fits 59.883659 -9.381216 162.8381 210.0000 54.4899 luci_20090213_0016.fits 59.708382 -10.387048 161.0577 210.0000 56.4579 luci_20090213_0017.fits 60.190678 366.456207 -168.3273 210.0000 25.8156 luci_20090213_0018.fits 60.219799 366.170441 -168.8493 210.0000 26.3375
Doug's Angle for LFBG
From Doug's IDL code, the angle to rotate the Zernikes from the frame of the WFS into the frame of the Primary Mirror:Doug's Angle = 9 - ROTANGLE
Where does the 9 come from?
Perhaps the 9 degrees is actually 7.7 degrees to be consistent with LEFTZEROPOINT?
IRTC at LDG
LEFTSCALE = -1.0LEFZEROPOINT = +5.5
rotateZernikes(_rotatorDirection * rotAngle + _probeRotationFactor * probeAngle);
MODS1 at LDG
LEFTZEROPOINT=+27.63LEFTSCALE=-1.0
Apparently (deduced from the MODS headers):
ROTANGLE x LEFTSCALE = POSANGLE - PARANGLE + (180 - LEFTZEROPOINT)
20111030 UT
FILENAME OBJECT TELALT TELAZ PARANGLE(deg) POSANGLE(deg) ROTANGLE(deg) mods1r.20111030.0002.fits "J203642-055300 mask" 51.45634 181.96432 1.94148 19.21280 -169.78001 mods1r.20111030.0006.fits J012156+144823 52.05757 109.02199 -55.22049 0.00000 -207.72548 mods1r.20111030.0054.fits J033854-000521 56.53182 193.41318 11.54500 0.00000 -141.08008 mods1r.20111030.0068.fits J033854-000521 51.25908 216.67310 30.37947 0.00000 -122.17295 mods1r.20111030.0076.fits "Q0805+046 mask" 49.55791 127.43106 -41.94015 -29.07080 -165.36517
Doug's Angle for MODS1
From Doug's IDL code, the angle to rotate the Zernikes from the frame of the WFS into the frame of the Primary Mirror:Doug's Angle = 120 - ROTANGLE
MODS2 at RDG
RIGHTZEROPOINT=-32.45RIGHTSCALE=-1.0
Apparently:
ROTANGLE x RIGHTSCALE = POSANGLE - PARANGLE + (180 - RIGHTZEROPOINT)
PISCES at RFBG
RIGHTZEROPOINT=-2.4 (before 20121229)RIGHTZEROPOINT=177.6 (after 20121229 when AGW2 was rotated)
RIGHTSCALE=1.0
Apparently (deduced from the headers):
ROTANGLE x RIGHTSCALE = POSANGLE - PARANGLE + (180 - RIGHTZEROPOINT)
(seems off by a few tenths of degrees for PISCES)
Filling in RIGHTZEROPOINT and RIGHTSCALE:
ROTANGLE = POSANGLE - PARANGLE + 182.4
(The above equations are correct for the guider image.)
Correcting the Position Angles in the PISCES headers
Warning: ADD 90 deg from the POSANGLE in the PISCES headers to get the true position angle of the PISCES image. This is based on GG Tau image pisces.20111109.11585.fits which shows all 4 components of the quadruple star, and 3 binary stars observed in June. The GG Tau image has an X-flip, but is otherwise actually PA=0 (with header saying POSANGLE = -90 deg). See R.Koehler in A&A 2011. This extra 90 deg rotation is because PISCES is mounted at a different angle to the sky compared to the AGW2 in front of it, and they matched the rotation of the PISCES tilted window because of the incorrect window orientation on IRTC2. All PISCES data from June 2011 to January 2012 needs this correction. CorrectedRotatorPA(the actual PA of image) = RotatorPA(what is in the header) + 90 degStellarPA = ApparentPA + RotatorPA + 90 deg
# Data from above six stars calculating PA as atan2(X2-X1,Y2-Y1)
Filename ApparentPA StellarPA RotatorPA CorrectedRotatorPA pisces.20110612.0063.hdr.fits -60.05 116.8 90.0 180 pisces.20110612.0194.hdr.fits -118.21 151.0 180.0 270 pisces.20110612.0260.hdr.fits -28.18 151.0 90.0 180 pisces.20111109.11585.fits -27.11 331.5 -90.0 0 Aa-Ab pisces.20111109.11585.fits -172.64 185.6 -90.0 0 Aa-Ba pisces.20111109.11585.fits +136.50 135? -90.0 0 Ba-Bb
20110612 UT
FILE PARANGLE(deg) POSANGLE(deg) ROTANGLE(deg) 260 173.78 90.0 98.15 385 32.36 -20.0 130.348
20111109 UT
FILENAME OBJECT PARANGLE(deg) POSANGLE(rad) ROTANGLE(rad) pisces.20111109.10780.fits "PN_HUBBLE_12" 146.690 2.23402 2.85280 pisces.20111109.11580.fits "GG_Tau" 40.1325 -1.57080 0.919788 pisces.20111109.11585.fits "GG_Tau" 41.1014 -1.57080 0.902646 pisces.20111109.11589.fits "GG_Tau" 41.4574 -1.57080 0.896328converting radians to degrees
FILENAME OBJECT PARANGLE(deg) POSANGLE(deg) ROTANGLE(deg) pisces.20111109.10780.fits "PN_HUBBLE_12" 146.690 128.0 163.45 pisces.20111109.11580.fits "GG_Tau" 40.1325 -90.0 52.70 pisces.20111109.11585.fits "GG_Tau" 41.1014 -90.0 51.72 pisces.20111109.11589.fits "GG_Tau" 41.4574 -90.0 51.36Data from the Close et al. (2012) observations of the Trapezium on 16-October-2011 suggest that the real correction to the header should be:
CorrectedRotatorPA(the actual PA of image) = RotatorPA(what is in the header) + 89.1 deg
LUCI2 at RFBG
RIGHTZEROPOINT=178.55 (20131111)RIGHTSCALE=1.0
POSANGLE for ADI Observations
Warning: PISCES header values ROTANGLE and POSANGLE are showing the demand value and are WRONG when the rotator has been stopped for ADI observations. See the MSCPU logs (attached to the Twiki logs in November 2011) to recover the true rotator angle. For data taken prior to November 2011, the MCSPU log data is recorded in a less consistent way. A better observing technique would be to use the rotator in PARALLACTIC mode. Alternately, IDL could read the rotator angle from MCS rather than PCS when making the FITS header. Inverting the equation above:POSANGLE = PARANGLE + ROTANGLE - 182.4
JMH: Does this equation need another 0.9 degrees subtracted to make -183.3 degrees in order to match other telescopes?
See also Issue 3952. The explanation for the parallactic angle errors at high elevations (fixed in TCS build of 15-Nov-2013) was that the parallactic angle was being calculated for the "FK5 meridian" and not the "Apparent meridian".
HR8799 on 20111109 UT
The MCSPU log reports that the rotator was at 150:35:14 (150.587 deg) from 03:03:44 to 04:24:31 UT on 20111109 (HR8799).The MCSPU log reports that the rotator was at 170:52:59 (170.883 deg) from 06:31:47 to 09:03:19 UT on 20111109 (HD15115).
which evaluates for the HR 8799 data to:
POSANGLE = PARANGLE - 31.81
The following table shows the corrected values of the Position Angle using the actual fixed rotator angle (not the values from the headers) (and -182.4).
FILENAME OBJECT PARANGLE(deg) POSANGLE(TBD) ROTANGLE(deg)from MSCPU pisces.20111109.10360.fits HR_8799 4.30316 -27.51 150.587 pisces.20111109.10423.fits HR_8799 13.2049 -18.61 150.587 pisces.20111109.10573.fits HR_8799 30.8977 -0.91 150.587 pisces.20111109.10688.fits HR_8799 40.6208 +8.81 150.587 pisces.20111109.11500.fits HD_15115 47.1660 +35.65 170.883These POSANGLEs are still wrong for the PISCES images (June-November 2011) because of how PISCES is mounted to AGW2.
Add 90 degrees to the POSANGLE in the header to get the true positon angle of the image (see above).
Doug's Angle for RFBG
From Doug's IDL code, the angle to rotate the Zernikes from the frame of the WFS into the frame of the Primary Mirror:Doug's Angle = 180 - ROTANGLE
FLAO CCD47 at LFBG and RFBG
For FLAO CCD47s on both LFBG and RFBG with PositionAngle=0 and ParallacticAngle=0, then Increasing IE move the telescope to a lower elevation and moves the star image straight up on the CCD47. Increasing CA moves the telescope to a larger azimuth and moves the star image to the left on the CCD47. As the ParallacticAngle becomes more positive, the IE/CA vectors above rotate counterclockwise on CCD47 (while PositionAngle is fixed by the moving rotator). For FLAO: PositionAngle=0 puts North to the top and East to the Left.LMIRcam at LBTI
LMIRCam on LBTI is fixed to the telescope without an instrument rotator, resulting in sky rotation during an observation. For a value of 0 parallactic angle, the top of the detector corresponds to North on the sky. East is to the left for this configuration. Thus, as the parallactic angle increases, the orientation of North appears to rotate clockwise on the detector. The exact orientation was measured during the May 2011 observations. Another binary star was measured at the end of 15-Nov-2011. from http://zero.as.arizona.edu/groups/lmircam/wiki/9bbcb/Pixel_Scale_and_Orientation.html POSANGLE = PARANGLE + CONSTANTCCD47 for LBTI
For SX LBTI, Increasing IE moves the telescope to a lower elevation and moves the star image to the Right on the CCD47. Increasing CA moves the star image down on the CCD47. For DX LBTI, Increasing IE moves the star image to the Left on the CCD47. Increasing CA moves the star image up on the CCD47. For LBTI, there is no rotator, so PositionAngle = ParallacticAngle. Therefore SX LBTI has North to the left and East to the bottom at PositionAngle = ParallacticAngle = 0, and DX LBTI has North to the Right and East to the top.Decoding LBT TCS nomenclature about instrument rotator modes
Here's how the funny astronomer nomenclature works (independent of telescope)
The Vertical Angle is the angle from the source to the zenith along a great circle (always aligned to the elevation direction for an ideal Alt-Az telescope). The Parallactic Angle is the angle from the source to the North Celestial Pole along a great circle. The Position Angle is the angular offset of the image of the sky relative to North (Is North up on the picture?). Position Angle is also used to specify the angle of the second component of a binary star relative to the primary component.Here's the jargon for the LBT Telescope Control System (PCS)
Position Mode
In rotator Position Mode , we track the rotator so that the Position Angle (orientation of the sky) on the detector is the one requested (including offsets such as LEFT/RIGHTZEROPOINT which calibrate the orientation of the detector).Vertical Angle Mode = Parallactic Mode
In rotator Vertical Angle Mode (what LBT TCS calls Parallactic Mode ), the rotator is fixed so the slit or detector is stationary relactive to the vertical angle. (The drawback is that this trails the sky on the detector in rotation as the telescope tracks.)PEPSIPFU (without a rotator)
- PFUguider.pdf: PEPSIPFU guider orientation from Ilya
| I | Attachment | Action | Size | Date | Who | Comment |
|---|---|---|---|---|---|---|
 pdf |
PFUguider.pdf | manage | 650 K | 18 Apr 2019 - 01:35 | JohnHill | PEPSIPFU guider orientation from Ilya |
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Topic revision: r17 - 18 Apr 2019, JohnHill
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