During the night, the disperser wheel became stuck in a "between" position when changing dispersers. We had to move to zenith and go up to the Cass cage and manually move the disperser wheel to the open position to successfully reinitialize the system. It may be a problem of balance in the disperser wheel. We have 5 grisms installed out of six available slots. We thought that we saw some sign of the grism covers rubbing against a support. When we moved the disperser wheel by hand we didn't see anything obvious. We'll check this out during the day tomorrow. It could be that having five installed grisms and one empty slot lead to the disperser wheel becoming unbalanced during operation not at zenith. We'll test tomorrow in the dome by moving the telescope off zenith and exercising the wheel. The solution may be to remove one of the installed grisms to restore balance.
We also lost communications to the DHS three times during the night. We followed standard practice and shut down the NOCS and removed unnecessary .smc_? files in the tmp directory on the COSMOS DHS computer, followed by a NOCS restart. This problem didn't occur during the July 2017 COSMOS run. It was noted that all COSMOS computers were rebooted at the beginning of the July run. At the end of COSMOS engineering observations we rebooted the COSMOS rack. We'll see if this problem continues tomorrow.
| Total Times | Time Observed | Time Engineering | Time lost technical | Time lost weather | Time lost other | Total Program Time |
|---|---|---|---|---|---|---|
| 2017-08-08 | 0.0 | 10.75 | 0.0 | 0.0 | 0.0 | 10.75 |
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First night of COSMOS observations since the beginning of July. The major change since then was that Points and M. Hernandez and H Tirado installed three of the new VPH grisms in COSMOS. Data were taken to determine the camera focus offset values among the grisms. After analysis, this information will be placed on the COSMOS webpage. We took spectrophotometric standard star observations of two Hamuy standards using the original blue grism. Standard star observations will be continued tomorrow so we can measure the overall system efficiency of the new installed grisms. At 1:30am the telescope was handed over to update the M2 pointing map (last done in Sept-Nov 2016).
During the day we worked on preparing the 22 MOS masks for installation in preparation for the Zezas run of 10-13 Aug.
We also tested a new offset script for COSMOS. The new version of the script prints x,y pixel value offsets from the desired location on the slit. The COSMOS slit is aligned horizontally so the y-offset value is the important number. This modification to the script was made based on a comment by the observer in July, K. Luhman. The script worked as desired and will be added to the COSMOS observing guide. The rule of thumb we are using is that if the y-offset is less than 0.5 pix (~0.15") then it may not be worth the time trying to make additional small offsets.
An overall productive start for COSMOS engineering to be continued tomorrow, weather permitting.