2100‐AD‐015‐0007
Mayall4mPost‐ShutdownTelescope
Checkout
July15,2014
Dick Joyce, David Sprayberry, Ron Probst, and Lori Allen This document describes the plans for bringing the 4m telescope back into operation following the 4 meter mirror coating and reinstallation. 2100‐AD‐015‐0007 Mayall 4 Meter Post‐Shutdown Telescope Checkout Revision: ‐ Contents K&E alignment test: ...................................................................................................................................... 3 Prime Focus Image Tests:.............................................................................................................................. 3 Proposed Schedule: .................................................................................................................................. 3 Day 1: .................................................................................................................................................... 3 Day 2: .................................................................................................................................................... 3 Day 3: .................................................................................................................................................... 4 Day 4‐8: ................................................................................................................................................. 4 Wavefront tests at f/8: ................................................................................................................................. 4 Proposed Schedule: .................................................................................................................................. 4 Day 8‐12 ................................................................................................................................................ 4 Potential Issue: .......................................................................................................................................... 4 Pointing Verification f/8: ............................................................................................................................... 4 Other Testing: ............................................................................................................................................... 5 2100‐AD‐015‐0007 Mayall 4 Meter Post‐Shutdown Telescope Checkout Revision: ‐ K&Ealignmenttest:
The K&E alignment test is a simple confirmation that the mirror cell was reinstalled correctly. Note: There is very little which can be done if there is a misalignment without removing the mirror cell PrimeFocusImageTests:
The purpose of these tests is to use the Mosaic imager to obtain defocused images on both sides to permit curvature sensing analysis of the wavefront errors. This will, unfortunately, be a rather inefficient procedure, since the only way to obtain the images is by using the pedestal to move Mosaic to the two defocused positions. Since Mosaic is installed at Prime Focus, it will be necessary to pump and cool Mosaic for these tests. This will actually provide Heidi the chance to ensure that the system is working well prior to the scheduled T&E on 15 August. In May 2013, Charles Corson and Ron Probst carried out an extensive wavefront campaign to determine the parameters for the 4mAPS lookup table. This involved using an on‐axis CCD installed on a jig at the PF position and a grid of 33 points around the sky. Such an exhaustive test may be difficult with Mosaic, particularly given the limited availability of clear weather. The extensive tests in May 2013 showed that 4mAPS was working quite well, and Charles made only small adjustments to the Z5 astigmatism term. The purpose of carrying out these tests here is to ensure that the primary is not significantly tipped in its cell and that 4mAPS is working properly. The procedure would be to obtain images of a bright star in the R filter on either side of focus which are approximately 150 ‐ 200 pixels in diameter. The star will have to be offset from the axial location so that the defocused image falls entirely within one of the Mosaic arrays. One can empirically determine the focus positions to give an image of that size and then take the images at those two positions. It will probably be necessary to adjust the exposure time depending on the brightness of the star. However, one should try to pick stars sufficiently bright to give good signal in a short exposure, since it will not be possible to use the Mosaic guider with the stars defocused. Charles Corson mentioned a signal of ~ 10000 ADU as desirable (this is of course the per pixel signal, not that of the focused star). A minimum set of images would probably be taken at the zenith, and then at the cardinal points about 45 degrees zenith distance, and if possible, around 55 – 60 degrees zenith distance. ProposedSchedule:
Day1: Shutdown activities completed. Day2: Flip top end for Mosaic operation and hook up cables. Pump on Mosaic vacuum. I have asked Brent to do this. 2100‐AD‐015‐0007 Revision: ‐ Mayall 4 Meter Post‐Shutdown Telescope Checkout Day3: Cool down Mosaic in the morning. Again, I have asked Brent to do this. The instrument should be cold enough to operate by 2100 in the evening. I have asked Heidi to log in remotely and obtain the images. Dave Summers would be the OA. Both Charles Corson and Chuck Claver have offered to assist in evaluating the images. Chuck and Bo Xim have written a curvature sensing analysis program which they have ported to Python, and they would like to compare the results with those calculated by Charles’ program. Day4‐8: Contingency for obtaining the Mosaic wavefront images. Wavefronttestsatf/8:
After carrying out the PF tests, the top end is flipped to put the f/8 secondary in place for wavefront testing using the wavefront camera (The 4m‐wfc computer should be checked out as part of the Telescope Checkout, item 78). These can be carried out using a similar grid as for the PF wavefront measurements, using the manual in the 4m Operations Guide. Since these will be used to verify the f/8 tip/tilt, one should take a few darks at the same integration time as used for the wavefront exposures (typically 30 sec). Refer to the online manual. ProposedSchedule:
Day8‐12: Flip from PF to f/8 and carry out the f/8 wavefront tests as described in the online manual. Charles Corson should be able to evaluate the wavefront images. Charles has suggested taking measurements at zenith, and 45 degrees zenith distance on the four cardinal directions, and repeating the process three times to see how well the coma residuals repeat. PotentialIssue:
The designated OA for the beginning of this week is Christian Soto, who has not used the wavefront camera previously. I am looking into alternative approaches. If the PF wavefronts are completed successfully early in the week of 28 July, one could switch immediately to f/8 and carry out wavefront measurements at this focus. Both Dave Summers and Karen Butler have used the f/8 wavefront camera. PointingVerificationf/8:
Run a simple pointing verification to compare to the current pointing performance (roughly 17 arcsec rms in HA, 10 arcsec rms in DEC). This can be done on any night at f/8 where it is likely to be clear around the sky for ~ 1 hour or so. 2100‐AD‐015‐0007 Mayall 4 Meter Post‐Shutdown Telescope Checkout Revision: ‐ OtherTesting:
The PF wavefront observations should be a good checkout of the Mosaic operation, but Heidi will still want to check things out prior to the first science run on 16 August. A T&E night is currently scheduled for 15 August, but this could be started earlier if weather may be a concern. Di and Daryl have requested sufficient time to do a full checkout of RCSP and its ancillary systems prior to 15 August.