PEPSIPOL AGW3/4 alignment UT 20190119

OSA: J. C. Williams (LBTO)

Observers/ISA: J. Hill (Tucson) plus team PEPSI on the mountain

Software: S. Hooper/P. Kubanek (on-call)

ISp:G. Bechetti

Mtn Manager: M. Wagner


We were on-sky with PEPSIPOL for about 25 minutes in twilight. We were not able to locate a 12 mag off-axis guide star. Humidity closed us before we could evaluate the robustness/cause of that result. They sky may have still been too bright.

Gustavo deployed the ARGOS calibration arms (with the light on!) on both sides, and I was able to spend 3 hours of closed dome time sorting out wfs correction of coma with IDL. The rot_offset angle for coma was off by 90 degrees from what we had measured for astigmatism in Sep 2017, so I'm worried that we still have a sign discrepancy somewhere. In the meantime, I'm confident that we'll be able to correct focus and coma with IDL analyzing the wfs.

We'll want to try this on-sky during twilight on Saturday night.

We also found that the AGW4 guide probe at 0,612.5 seems to be 11 mm off from the location of the DX PEPSIPOL fiber. I've not yet figured out an explanation for that. The agreement is within ~1 mm on the SX side.


Start PEPSIPOL activities in twilight of an ARGOS night

01:02 UT Ilya's ACTIVE preset didn't find the off-axis star - still too bright? so send an ACQUIRE preset to same field and manually move probe to center to adjust pointing.

01:20 UT Can't see 12 mag off-axis guide star. Is there a problem? Or was the sky still too bright?

Close for humidity

Verified that rotator angles are the same on both sides to a small fraction of a degree, but the angle on the right hasn't been calibrated for PEPSIPOL at all.

Closed-dome work SX PEPSIPOL with AGW3

SX Total Collimation to put ARGOS source on-axis X=+4.737 Y=+4.212 Z=-0.5 RX=-147 RY=+59 which is similar to the FLAO position, but not exactly the same.

02:30 UT Running IDL collimate_once in closed-dome with the ARGOS source. John is manually guiding the source on the hotspot as things change temperature. These measurements are using Doug's pupil_on-axis and lenslet_center from last night's data.

            agw_params[i].wfsc.pupil_x_on_axis = 158.
            agw_params[i].wfsc.pupil_y_on_axis = 230.

            agw_params[i].wfsc.lenslet_x_center = 48.
            agw_params[i].wfsc.lenslet_y_center = 122.

            agw_params[i].wfsc.pupil_x_on_axis = 150.0
            agw_params[i].wfsc.pupil_y_on_axis = 235.0

            agw_params[i].wfsc.lenslet_x_center = 45.0
            agw_params[i].wfsc.lenslet_y_center = 117.0

WFS images were originally taken in /home/lbto/, but they have been moved to /home/lbto/data/20190119_idl/. All except the very first images were 2.0 second exposures on the wfs.

02:44 0007 is the coma reference -118 -245 (the measured Z7, Z8 corrections)

send +1000 Z7

  1. drifted in guiding

0009 -355 37

send -1000 Z7 (back to zero)

0010 -122 -210

send +1000 Z8

0011 -1159 -625

send -1000 Z8

0012 -105 -188

At rotator angle 117 +RX moves star UP, and +RY moves star RIGHT

02:54 UT send +1000 Z7

0013 -337 +30

send another +1000 Z7

0014 -86 234

make guiding adjustment

0015 -67 231

send another +1000 Z7

0016 -33 464

send +1365 Z4 (what IDL suggested)

0017 -259 +73 (bright edge at 2 o'clock, and spots out of boxes - why don't they vignette at field stop? )

send -1000 Z7

0018 -172 +758 (bright edge at 3 o'clock)

send +1000 Z8

0019 -294 +254

send another +1000 Z8

0020 -511 +251

SX Total Collimation M2: X=2.879 Y=2.068 Z=-0.684 RX=+68 RY=-137

03:14 changed IDL rot_offset for LPOL from +34.0 deg (above) to +124.0 deg (below). +34 had been previously measured for astigmatism in Fall 2017, so this seems to imply some sort of sign discrepancy.

03:14 0021 makes a set_local error (John was in a forbidden IDL directory) stop and restart IDL in proper /home/lbto/.

0022 -314 -455 (spots at edge of boxes)

send -1000 Z8 (making less coma by eye)

0023 -922 -994

send -1000 Z8

0024 -910 -85 (The Z8 correction worked well!)

send -1000 Z7

03:25 0025 -131 -147 (The Z7 correction worked well!)

send -386 Z4, -131 Z7, -147 Z8

0026 -65 -57

03:33 UT 0,612.5 is with a couple arcsec of Ilya's fiber on SX when I retract the probe. Switching to DX.

Closed-dome work DX PEPSIPOL with AGW4

starting with rot_offset +124 deg for RPOL

DX Total Collimation M2 to put ARGOS spot on AGW: X=-2.530 Y=-2.367 Z=+0.484 RX=-187 RY=-264

03:57 0001

send -260 Z4


send -1500 Z4


send -1500 Z4


send -200 Z4

0005 -659 +394 (the measured Z7, Z8 correction)

send -700 Z7

0006 -196 +349

send +400 Z8

0007 -250 +29

send -260 Z7

0008 -51 22

send -360 Z4

0009 -87 -27 (conclude the rot_offset +124 is correct for DX coma also)

04:07 UT retract guide probe, but don't see source on DX PEPSI. Defocused to find where it was.

DX Total Collimation M2 for AGW4@0,612.5 X=-3.016 Y=-1.514 Z=+0.484 RX=-282 RY=-310
DX Total Collimation M2 for PEPSI fiber X=-3.016 Y=-1.514 Z=+0.484 RX=-268 RY=-238

Probe has to move to +10.5, 611.2 to match the PEPSI DX fiber position. Why so far off?

04:26 turning DX rotator by 360 degrees while watching the ARGOS star image.

with probe at 0,612.5 star makes a circle which started at center and has a diameter 1/3 of the guider FOV.

move probe to 14,611.2 so star is at center of above circle. Now the circle seems larger.... why?

move probe to 0,611.2 and circle is even bigger ??

retract probe

PEPSIPOL DX fiber is closer to the rotator axis, but neither is exactly on-axis.

PEPSIPOL SX fiber circle is about the same diameter as the pickoff mirror.

05:04 UT Reconfigure telescope for DX ARGOS observing as I am out of things to do, and the humidity shows signs of dropping.

Applied 124 deg WFS_rotAngleOffs on both sides in GCS. Stop and restart GCS.

-- JohnHill - 19 Jan 2019
Topic revision: r1 - 19 Jan 2019, JohnHill
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