KCWI On-Sky Commissioning Plan

KCWI on-sky commissioning plan

1 Background and Overview

The KCWI commissioning plan includes relevant tests from on-sky commissioning plans drafted by Keck Staff and instrument development teams of previous Keck instruments so that the new hardware and software functionality are well tested and characterized. This document is expected to undergo periodic revision up through the commissioning period for KCWI.

To ensure that the necessary tasks are executed and that the relevant information is reported each task will have an assigned task leader. Task leaders are responsible for the test plan, execution, reduction, and analysis of the acquired data, and although they may enlist others to complete the task, they will ensure that the tasks are completed and reported on reasonable timescales.

Observers will be at the telescope acquiring data and running the tests. It is the responsibility of the task leader to ensure that task descriptions clearly identify all the necessary steps to acquire the data. Observers will work with task leaders by reviewing the observing plans for accuracy, completeness, and clarity.

Data Reducers will reduce and analyze the data and will contribute relevant information in test reports. The analysis of some tasks is completed during the observations, but the analysis of other tasks (e.g. zero points) is longer term, and for these tasks, it is important to identify who is responsible for analyzing and reporting these results.

This document is based on a spreadsheet available on the Keck KCWI documentation page. On that spreadsheet, each task is assigned a priority and an order of execution. The individual tasks are identified by task ID.
The same task ID appears here.

2 Tasks

Purpose: Verify the gross pointing of a target after absolute pointing of the telescope

Requirements:

• Reference pointing origin, REF, or similar, defined
• Pointing origin in guider pixel coordinates defined
• Plate scale of guider camera defined
• Orientation and flip of guider camera defined or estimated

Observing plan:

• Set rotator physical angle 0, stationary mode.
• Set exposure time to 1s. A short exposure time makes the rastering faster.
• Set the CA=0, CE=0, previously known goo values, or expected estimated values.
• Slew to a 6th magnitude star near AZ=0, EL=50. This star will produce diffraction spikes. Following the spikes will lead to the star. Because of the brightness, it will be easy to identify.
• If the star does not appears on the guider image, change CA/CE in a spiral pattern with step size equals to one third of the image size. For example, if image size is 3x3 arcmin, then step size should be 1 arcmin.
• Stop the spiral search if CA and CE are greater than 200 arcsec in positive and negative direction.
• Revert to original CA/CE values.
• Set primary mirror focus mode 1000 um and start spiral search again with step size 90 arcsec.
• Stop the spiral search if CA and CE are greater than 600 arcsc in positive and negative direction.
• Slew to an open cluster, the guider image should show some stars. Slowly move forward the center of the cluster where the density of the stars is the highest. Record the CA/CE values and repeat this procedure using these new CA/CE values as initial point.
• If the star still cannot be found at this point, verify the tertiary mirror position and the secondary mirror position and that the dome is not vignetting the view.
• Once the first star is found, if possible adjust pointing and mar collimation to record the CA/CE values. If adjust pointing is not possible because the guider camera orientation is not yet accurate, use hand paddle in CA/CE coordinates to move the star to the REF pixel and then mark collimation.
• Search the star catalog for 5 different near-by stars of magnitude between 8th and 11th and slew to their coordinates to verify pointing.
• Determine guider image orientation and repeat this procedure.

Reduction plan: N/A

Deliverables/Completion verification: The star appears near the center of the field of view of the guider

Purpose: The test determines the angle of the guider image X/Y coordinates relative to the Xim/Yim coordinates.

Requirements:

• Rotator physical angle zero point defined or estimated
• Plate scale of guider image defined
• TV angle defined or estimated

Observing plan:

• Set rotator physical angle 0, and stationary mode.
• Slew to mount coordinates AZ=0, EL=50.
• Start guider camera exposures and set exposure time to 2s. Adjust according on brightness of stars such that star trails can be seen on the guider image, see example below.

• The angle between the star trails and the horizontal axis is the guider image angle, TV angle modulus 180 deg.
• Verify that the star trails agree with the MAGIQ compass roses.
• Slew telescope in mount coordinates to AZ=180 and EL=50 and repeat the exposures.
• The average of the two angles for AZ=0 and AZ=180 is a better estimate of the TV angle.
• The value of TV angle includes the error of the rotator physical angle, which must be corrected with ROTBASE. By determining TV angle at AZ=0 and AZ=180, the rotator zero point error is cancelled out. The half the difference of the two angles at AZ= and AZ=180 is ROTBASE.
• Once the TV angle is determined, update MAGIQ and DCS/TCS configuration files and restart MAGIQ.

Purpose: Guider camera flip determines the handiness of the guider camera coordinate system

Requirements:

Guider camera orientation, TV angle, defined

Rotator zero point defined or estimated

Observing plan:

• Slew to a start at A=0 and EL=0, 10th magnitude.
• Set rotator angle to 0 deg and stationary mode.
• Start guider exposures.
• MAGIQ compass roses, East/North and AZ/EL, are approximately aligned depending on how well TV angle and rotator zero point are defined.
• For each of the following coordinates systems
• RA/DEC coordinates,
• AZ/EL coordinates, and
• TV X/Y pixel coordinates

perform offsets on each axis in positive and negative direction and verify that the motion and the direction match the direction of the compass roses.

• Adjust TV angle and TV flip accordingly in configuration files and restart MAGIQ.
• There is also an additional image flip flag that is only in the MAGIQ configuration. This flag depends on the focal station, on the number of reflections and how the image is read out.

Reduction plan:

Deliverables/Completion verification: TVFLIP and TVANGL are correctly set, and saved on the corresponding configuration files. The star moves in the correct way on the guider when telescope moves are issued.

Purpose: Establish the fundamental pointing origin REF, which is usually the center of the guider

Observing plan:

1- Slew to a bright star at high elevation, get a handpaddel in Xim,Yim coords, PA = 0, Rotator in stationary mode

2- Center the star on the guider, measure the centroid (x1, y1)

3- Rotate 180 degrees

4- Measure centroid (x2, y2)

5- calculate the mid point between (x1,y1) and (x2,y2), move the star to the new center with handpaddle

6- repeat if necessary. Set as REF

Reduction plan:

Deliverables/Completion verification: REF pointing origin is determined and saved to the configuration database for TCSU. A star on the guider ends on the center of the guider if it is “sent to REF”.

Purpose: Make sure that all the necessary KCWI pointing origins are defined. The list of pointing origins is:

REF: Center of the guider

FPC: Center of the focal plane camera

SLS: Center of the middle slice of the small slicer (Optional)

SLM: Center of the middle slice of the medium slicer (Optional)

SLL: Center of the middle slice of the large slicer (Optional)

Observing plan:

Questions to be solved before we can come up with an observing plan:

1- Do we need separate pointing origins for each of the IFU or are they aligned with sufficient precision?

We need separate PO for each slicer. The precision is sufficient but they are aligned at the edge between two slices, not at their center

2- Do we need separate pointing origins for each slice of a given IFU?

No. We can use scripts

If possible, it would probably make sense to have just one PO and then have scripts that automatically offset the telescope to each slice if the observer requires the object to be on a particular position.

Reduction plan:

Deliverables/Completion verification: The necessary pointing origins from the list above are defined. A star sent to those origins ends up at the right coordinates

Purpose: Main guiding mode. We want to verify that we can guide at different values of the PA

Observing plan:

1- Slew to bright high elevation star

2- Set PA=0, start guiding

3- Save focal plane camera image

4- Guide for 5 minutes

5- Save focal plane camera image for comparison

6- Repeat for other PAs as desired

Reduction plan:

Compare initial and final focal plane images, verify that the star motion is within acceptable tolerance

Deliverables/Completion verification:

The guider can guide at all PA values. The motion is within the acceptable tolerance (what is the tolerance?)

Purpose: Verify that we can guide in non-sidereal mode

Observing plan:

1- Slew to non-sidereal target

2- Set PA=0, start guiding

3- Verify that the target maintains the position

Reduction plan:

Deliverables/Completion verification:

The guider can guide in non-sidereal mode

Purpose: Verify the plate scale of the guider and compare with the expected values

Observing plan:

1- Slew to dense field

2- Acquire image

3- Analyze offline

Reduction plan: Shui has a program to do this, almost in real time.

Deliverables/Completion verification:

Purpose: If the high order distortion terms are correct, large offsets are accurate

Observing plan: TBD

Reduction plan:

Deliverables/Completion verification:

Purpose: Test the guider focus procedure

Observing plan:

1. slew to bright star, center at REF
2. start the guider focus procedure

Reduction plan:

Deliverables/Completion verification: The guider can be focused. Estimate of the required time to complete the procedure.

Purpose: Acquire image of near-overhead star on the focal plane camera to verify functionality and image display. Get an on-sky handle of the camera response with and without the CAL ND filter in the beam.

*Note: This task, along with task 25 might be useful to perform before determining the pointing origin for the slicers (Task 4) or general pointing acquisition (Task 10). A live feedback of telescope moves should be more efficient than waiting on science CCD readout. We will have a fairly good idea of the relative location of the center of the FPC and the slicers from calibration activities (Task 27)

Observing plan:

1. Telescope in PA mode, Image de-rotator at PA=0°
2. Slew to a high elevation star (B=TBD) near the slicer PO, use this star for guiding
   (If doing this before KCWI POs are established, may need to manually command offsets to land the star on the focal plane camera. Record this offset, once done)
3. Make sure CAL ND filter is retracted
4. Take a short exposures (t = TBD)
5. Verify that the images are being displayed properly on the ds9 window
6. Make sure images are not saturated, slew to a dimmer nearby star if so, repeat
7. Take a series of images and a stack of images
8. Insert CAL ND filter, verify telescope does not lose tracking
9. Take a longer exposure (t=TBD)
10. Take a series of images and a stack of images
11. Verify image display in ds9 and approximate reduction in flux
12. Retract CAL ND filter

Reduction plan: Inspect saved images offline, verify ND filter acts as expected. Compute rough sensitivity.

Deliverables/Completion verification: A first pass estimate of the camera throughput and refined (but still not final) B-mag to exposure time calculator for FPC with and without the ND filter.

Purpose: Measure the plate scale and handedness of the focal plane camera

Requirements:

• Guider angle and flip defined
• Rotation zero point defined
• Instrument angle defined or estimated
• A pointing origin within the field of view of the instrument

Observing plan:

• Slew to a star, 10th to 11th magnitude and center on REF.
• Change to the instrument pointing origin.
• Put PMFM = 300um or greater depending on the plate scale of the instrument detector.
• Take an image.
• Find the segments #22, #9, #2, #5, #15 and #31. They are aligned with the vertical axis.
• Segment #22 points to lower elevation and #31 points to higher elevation.
• Calculate the centroids of the said segments.
• The centroids must lie on a line.
• The angle between this line and the columns of the detector is the instrument angle. Depending on the flip of the image, the angle can be the 180 deg complement.

Reduction plan: Analyze the images offline (S. Kwok’s software) Centroid the star in each image compute plate scale and refine tkrose.

Deliverables/Completion verification:

Refined tkrose and FPC plate scale

Purpose: Determine the limiting B magnitude of the Focal Plane Camera for a SNR of 5 in 30 seconds. The FPC field of view is small 18 x 16 arc seconds unvignetted.

Observing plan:

Option 1:

1. Telescope in PA mode with suitable PA angle
2. Slew to a dense star field (TBD)
3. Take a short (1 s) exposure to estimate time T to saturation
4. Take a series of T length exposures to add up to 30 s, repeat. Save all images

Option 2:

1. Telescope in PA mode with PA=0°
2. Slew to a series of high elevation stars from B=18 in dB ~ 1 increments, preferably of the same or very similar spectral type
3. Take a series of t = 1 s images for each star, save images
4. With a single star in view, use a script to quickly determine the acquired SNR. Script could (should?) generate exposure times for dimmer stars
5. Be flexible in magnitude increments, skip steps if SNR high to converge on limiting magnitude as quickly as possible
6. Once limiting magnitude found, confirm with object of similar brightness

Reduction plan:

Option 1:

Reduce offline using standard astronomical tools (SExtractor) and a deep star catalog (e.g., USNO B 2.0).

Option 2:

Use script to compute magnitudes (verify later offline). Need to write script.

Deliverables/Completion verification:

Limiting magnitude of the FPC for a point source in a 30 s exposure. Exposure T calculator?

Purpose: Find the astrometric solution for the focal plane camera. Note, that the focal plane camera has a very small field of view (comparable to the medium KCWI slicer, or 15 x 20 arc seconds). As such, the expected distortions are not anticipated to be particularly large.