Science News
Instrument Status Post SSD2023
Posted Sep 09, 2023
LBC
During SSD, the filters and accessible lenses were cleaned, and the TMS collimators were reinstalled and realigned. A software service was put in place to simplify operation of the LBCs with TMS.
During restart, the LBCs were run through tests, checking for gross focal-plane tilt, running science-like scripts that dithered and guided, and executing non-sidereal observations. Photometric standard star fields were also observed, results of which will be made available soon.
The LBCs are fully checked out and ready for science.
MODS
During SSD, all of the mask frames were replaced by new ones with steel stow sensor targets that enable a larger sensor gap which will reduce the risk of collisions like those which occurred during the 2021B and 2022A semesters. Rick Pogge & Mark Derwent (OSU) inspected the slitmask cassettes and optics as well.
During restart, tests were made to ensure that the instruments were aligned at the focal station, and science-like and spectrophotometric and photometric standard star scripts were run which used all modes. Standard star data are being reduced and the results will be made available soon. The instruments are ready for science with the following caveats: 1) a problem which emerged with the MODS1 Blue IMCS, where one or more quad cell readings would be 0 causing lock to fail, is still being worked on. This problem appeared only once during on-sky checkouts. And 2), another issue which was first seen in early 2022 has reappeared: a variable bias level in one of the readout channels in the lower right quadrant of MODS1B. The prescan can be used to correct for this in the full frame (8K x 3K) 2D spectra, but the smaller readout regions used by imaging and prism modes do not have a prescan. It is recommended to avoid placing targets or spectra in the lower right quadrant when possible. The chronic problems of long, ~100-sec, readout delays, which affect a fraction (10-20%; to be confirmed) of MODS1R and MODS2B images, remain.
LUCI
Please see LUCI1 and LUC2 2023B restart delays for details
The work on LUCI1 is wrapping up and it will start cooling in the lab next week. Immediately following its installation on the telescope, LUCI2 will be moved in to the lab for repairs to address the leak discovered at the end of SSD 2023B.
LUCI1 and LUCI2 are unavailable for science at this time.
PEPSI
See PEPSI upgrades And Work Status SSD23 for details about the recent PEPSI overhaul. PEPSI Camera focus has been determined. A full CCD report is being generated. The CCD gain is 2.3 e/ADU on average. We aligned on sky and took several spectrophotometric standards. Ilya reviewed and found the results are good. He is actively updating the ETC with the results. PEPSI is released for science.
PEPSI upgrades and work status SSD23
Posted Sep 01, 2023
All is back to normal and PEPSI is ready for observing in 23B after extensive work during the summer of 2023.
The two new STA1600 CCDs were integrated into the existing dewars at STA premises in California over the August time period. The new package has now much better bonding protection with the preamps closer to the amplifiers than before (and
much more), which reduces noise. All went smoothly at STA. AIP folks were participating in the final lab tests and did the focus alignment of the dewars’ windows (which are the last lens groups in both optical cameras of PEPSI), and then drove down both units by car from California straight to the mountain bypassing the obligatory x-raying at the airport. Thanks to their heroic road efforts both units arrived back safely and without any damage. Reintegration on the mountain succeeded on the weekend Aug. 26/27 and both dewars were cold on the 29th. After all, the first calibration images were taken and looked as expected from the CCD acceptance protocols earlier this year.
The normalized image of the de-focused flat field in CD35 in ADUs after amplifiers equalization in TAPLINEx of the Archon config file. September 6, 2023
Above is an example de-focused flat field image (taken with CD3&5, i.e., blue and red CCD) with bias subtracted and normalized to a spline fit to remove the blaze function and the spectral orders. You can see all defects immediately then. Due to the enormous real estate (12k x 10k; incl. the overscan regions), there are several hot rows on the chips plus the usual coating defects. Residual fringing is still visible on the red image (because not been corrected yet). The bias level is at 1000 ADUs on both, full well at 65k. ROT remained at 80s. Ilya is in the midst of the final characterization and a document will be made available soon. Gain and RON tables were calibrated and implemented into SDS4PEPSI as part of the automatic data reduction. Gain is on average 2.2, RON on average 3 e-/amp. There is no visible fixed-pattern noise structure seen so far, the red-device hot spot is gone.
Pending tasks include observing our usual flux standard stars in photometric conditions in order to revise the ETC. This is work in progress and planned during our restart period.
Besides the CCD exchange, the Red cross-disperser (CD) lift was replaced after the Blue one had already been exchanged in June. All allowed CD combinations are available again.
The fiber-to-Image Slicer coupling was cleaned and realigned and a refractive-index-matching oil inserted. Alignment is somewhat better than before (one missed slice in one of the 7-slice R=250,000 configurations was recovered) but is still PEPSI’s largest light-loss location. We are working on a replacement of that unit that then will make each individual fiber adjustable wrt its Image Slicer entrance (recall that every science fiber has its own Image Slicer grouped in two blocks SX-DX on a joint optical carrier). All modes are operable at this time.
SDI-POL: We discovered that the polarimeter’s main retarder plate, a multi-layer quarter-wave plate from Astropribor, got loose in its mount so that it experienced an extra tilt whenever rotated. This produced very subtle effects in the spectrum in Stokes V (Stokes QU were unaffected) and prevented us from routine SDI operation in the past. The problem is now fixed but we had no time yet to resume SDI-POL operation because the entire POL calibration must be redone and implemented in SDS4PEPSI (planned for late September, early October).
Amazing work by the PEPSI team and LBTO support to make this PEPSI overhaul possilbe.
Public Data Policy Expanded
Posted Aug 10, 2023
Beginning February 1st 2024, all science data in the archive will be publicly available after the proprietary period for that data has ended. Therefore, all partner data acquired after February 1st 2024 with the 12 month default proprietary period will start becoming publicly available on February 1st 2025. Although this policy has been in place for INAF data since 2010, the policy is now expanded to include all partner science data. Data acquired before February 1st 2024 are unaffected for now. Public data policy for that, older data will be revisited at a later date.
Resolved: LUCI2 Detector Stage Failure – LUCI2 Unavailable
Posted Jun 16, 2023
Resolved during SSD23: LUCI2 had a failure of its detector focus stage on June 14, 2023. Repeated attempts at restoring function have been unsuccessful. The instrument is currently offline for N1.8 & N3.75 (seeing limited and ESM) use as they are too far out of foucs. This will be repaired during the summer shutdown.
However, the focus stage failed at the end of travel closest to the nominal N30 focus. With a small offset in the external focus set by the AO system, full AO N30 imaging remains available. There are a couple small operational changes, but any scripts should still be prepared as normal.
SX M2 swap
Posted Jun 03, 2023
During the afternoon of May 25th, the SX M2 adaptive secondary (ASM) was removed and the rigid secondary installed in its place. The coating on the SX ASM had been degrading, and it is being sent to Italy for recoating. Lab measurements indicated relative reflectivities of the SX ASM to the rigid secondary of 0.54, 0.66 and 0.72, at 4200, 5220 and 6500 angstroms, respectively.
After the secondary swap, spectrophotometric standard stars and a photometric imaging field were observed with MODS, and the zeropoints and signal-to-noise tracks are being updated.
The sensitivity of MODS1 shows an improvement consistent with the reflectivity measurements. In the blue channel, it was most dramatic and brings MODS1 almost up to its level at commissioning and to the level of MODS2. However, in the red channel there was less improvement and the sensitivity of MODS1 Red remains below its level at commissioning and that of MODS2 Red. The relative flux ratios of MODS1/MODS2 are now ~0.9-1 in the blue and ~0.5-0.6 in the red.
Restricted LUCI1-AGw1 Guider Patrol Field (resolved)
Posted Mar 04, 2023
Update Jan 10 2024: The issue was resolved during SSD23 and the AGw patrol field is back to the nominal area described in the LUCI pages (here). The problem was traced to the camera cable, where a couple of wires were broken but the disconnection only manifested at certain positions in the patrol field.
Update June 30: Despite yesterday’s additional inspection, testing, and re-seating an accessible cable for the guide camera, last night we had another dropout of the guide camera right at the limit established in March. For normal observing I would still recommend avoiding guide stars at all dither positions landing in the red shaded area in the plot. When planning your observations in the OT, use the inflection point at left (marked in the diagram below) where the theta stage limit and the 5.5 arcminute Gregorian focal plane radius intersect as a reference.
When observing, the symptom of encountering this problem is a “no guide star found” error when otherwise it should be there. The only remedy is to select a better-positioned guide star and start the observations over.
March 2023: We have identified a position-dependent electrical problem in the AGw1 (LUCI1) off-axis guider camera. It is most likely in the cable between the guider CCD and the controller box. This cable is inaccessible on the telescope, so until we can schedule a repair it will be necessary to ensure that any off-axis guide stars (and all the dither positions used!) avoid moving into the upper third of the AGw patrol field (see below).
When planning your observations in the OT, use the inflection point at left (marked in the diagram below) where the theta stage limit and the 5.5 arcminute Gregorian focal plane radius intersect. If you have any questions please send them to us at scienceops@lbto.org.
