Field Aberration measurements with AGw and IRTC


Two separate tests for field aberration measurement described below


*Prerequisites: stable telescope, good seeing, with active optics routinely converging to ~ 200 nm.

Test 1

In the PSF Left GUI open the "arbitrator" and select "send corrections to primary" (default is "split")

Copy field data table format from previous field measurement run into current nights wiki, see for example 090406-07 commissioning notes.

Set up IDL for active optics following instructions in

In particular, set up directory /Repository/AGW_Data/yymmddw, and set R/W permissons (chmod ugo+rwx 090428w say)

In this directory open IDL, enter "@wfsc_init", and at the prompt enter "agw_wfsc_collimate, EXP=1"

This will return an error as it writes the first file to the directory, subsequent commands should then work

Select suitable field and preset in guide mode to GS0 (BS9152 or later in the night BS 9157)

With stable guiding on GS 0 (and make sure GCS is in "GUIDE" mode) , type "agw_wfsc_collimate", and at the prompt select "yes" to send Zernikes to primary.

Repeat until reported Z4-Z11 aberration is at or around 200 nm.

Once a measurement returns with acceptable wavefront immediately preset to first off-axis guide star, with TelMode = "Guide" and PA set to "indef".

Time is off the essence here, we want to minimize the gap between collimation on-axis and measurement off-axis.

While preset is acquiring the off-axis guide star type "agw_wfsc_measure, 3" in IDL terminal and as soon as guiding has locked, enter the command.

In an "agw-control" terminal type "getdat" and record AGw stage (x,y) coordinates of guidestar.

Also record GS number, wfsc file numbers, "Doug's angle" and position angle for guide star. Dougs angle can be seen on lower right IDL wavefront display window.

As soon as the first IDL wavefront measurement has received the first image and starts processing press the "collimate" button on the lower right of the Primary Mirror PSF GUI

Repeat this step after the second measurement is processing.

Have a preset ready in IRAF so that as soon as the third measurement is made and IDL starts processing the image, preset to GS 0 with the PA set to that of the off-axis star just measured.

Again, this preset is sent in "GUIDE" mode.

In the data table record the AGw stage values for the on-axis star and record wfsc file numbers , Mean "Doug's angle and PA in data table while collimating.

If at any point between the last iteration of initial collimation on-axis, taking the three measurements off-axis, and getting the first collimation back on axis, there is any delay lasting more than a minute or so, discard that measurement and start again.

Repeat for a number of stars at different field angles, a good data set is 15+ measurements (20 is plenty).

If measuring in the BS9152 then please mesure guides stars in the following order: 17,18,7,4,1,9, and then back to 17, repeat 3 times.

If a set of data is thus acquired, email Doug Miller and ask him to process the data into an ASCII file for me (Andrew).

Test 2

Another test of collimation that will be useful to do while the IRTC is mounted is as follows:

In a suitable field, as above, or M67 say, send "ACTIVE" presets in to a variety of stars, sampling many different field angles and aiming for stars >4' off-axis.

Note that GCS is collimating here, not IDL.

For each preset, when GCS is reporting stable collimation, take a cube of data on IRTC, arranging exposure time and sequence number such that we get ~ 30s or more of images to integrate.

Record Guide star number, AGw stage coordinates associated with each IRTC cube.

Arrange presets such that for each guide star the first preset is sent with PA="INDEF" and an IRTC cube taken once collimation is stable.

For an immediately subsequent preset on the same off-axis GS, send PA = the PA of the previous measurement + 20 degrees, and re-collimate, take another measurement.

For the next preset repeat but this time subtract 20 degrees from the original PA.

In this way, for each off-axis guide star we get three IRTC cubes, one taken when collimation has converged with the x axis of the AGw stage near zero, the second with a large x value of one sign, and the last with a large x value of the opposite sign.

Repeat for approximately 30 measurements (10 guide stars 3 measuremetns on each one). Try to get a good sampling around the field. If running on BS9152 follow the order suggested above, by the time the cylcle repeats on GS17 the rotator angle will have changed by >30 degrees).

-- AndrewRakich - 29 Apr 2009
Topic revision: r1 - 29 Apr 2009, AndrewRakich
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