This week we had a number of break through moments. Perhaps the most prominent is that after weeks of rewiring and adding new shielding we may finally be at a point where the VIRUS array is fairly stable. We have 36 VIRUS units installed (each unit is 2 spectrographs) so a total of 72 spectrographs up for the last 5 days.
Another big breakthrough is in observing automation. We have a piece of software called OCD (Observatory Conditions Decision tool) which monitors the metrology (seeing, transmission and sky brightness) from the telescope and decides if HETDEX observations can be made. If allowed it will also take over the control of the TCS and VIRUS instrument and start observing HETDEX targets with only brief pauses to get confirmation from the telescope operator that we are on the right setup star. Using this new tool we were able to observe a full night of HETDEX targets with a minimum of overhead (even a few targets with just 3 minute setup times). This is faster than the fastest resident astronomer and telescope operator pair working together. Congratulations to the HETDEX software team who traveled out from Germany to help us get it all working efficiently.
Congratulations to Resident Astronomer John Caldwell on his retirement! It is bittersweet to see Anneke and you leave, but we know you are heading on a new and exciting adventure. Thank you for your many years of dedicated service. Safe travels and keep us posted!
HET Staff Picture taken Feb. 8th, 2018
This week we continued with HPF and Laser Frequency Comb (LFC) commissioning. We made a lot forward progress in getting spectra with the comb and had our official “first light”. Below are a few pictures that might help visualize some of what transpired.
A slide that shows the basement of the HET where the HPF and LFC live.
A part of the spectrum from HPF which shows the very regular picket fense of emission lines generated from the LFC just below a stellar spectrum. The spectra are stacked up in an echellogram.
A very happy HPF team, NIST team and HET Night Operations team celebrate first spectrum on the sky. It took a large number of people to get this entire effort going but here are the lucky ones to see it live!
In the last week we have had a few updates for two of our instruments. For VIRUS we are up to 29 working spectrographs. We actually have several more units but some of the oldest and slightly mis-behaving units have been sent back to Austin for realignment and recommissioning. For HPF we are thrilled to announce that a NIST laser comb has been installed in the calibration room in the HET basement. This allows us to send a picket fence of spectral features through a separate fiber next to the science fibers. During the data reduction and analysis of the HPF spectra they can look at the position of these pickets and determine how the instrument might be subtly moving and correct for it. So far it seems like it is working great.
A brief advertisement before we get into this week’s news: One of our Resident Astronomers is retiring. If you are a PhD astronomer and interested in working on one of the largest optical telescopes in the world doing cutting edge research please consider applying: https://utdirect.utexas.edu/apps/hr/jobs/nlogon/171020014209
This week the big changes to the telescope have been the removal of the Prime Focus Instrument Platform (PFIP) work platform and the arrival of 3 more VIRUS units. The PFIP work platform, as the name suggests, allowed us to drop people off to work on the PFIP. We will still be able to work on the PFIP but now we have to do it from the JLG worker-lift. The work platform covered up a number of mirrors (about 10% of the light collecting area) as can be seen in the images below taken with our pupil viewing camera.
Two images of the HET pupil taken with our pupil viewing camera before (left) and after (right) the PFIP work platform was removed.
With the delivery of 3 more VIRUS units we now have 28 working VIRUS units or 56 spectrographs or more than 12,000 fibers on the sky!
We are in another 3 week science period but our big news this week is that we have been able to bring a few more VIRUS Units on-line which brings our total number of active units up to 21 units. Recall that a VIRUS unit is made up of 2 spectrographs so we now have 42 spectrographs on-line. These newest units are located in VIRUS enclosure 2 which means that we are now making use of both of the “saddle bags” which were installed at the HET as part of the Wide Field Upgrade. This makes the VIRUS closer to being ready for the main part of the HETDEX survey. As we add more Spectrograph units the system continues to get more complex with multiplexers and timing systems.
In some recent very clear nights we were able to observe 10 HETDEX shots (what we call a pointing for the survey) in a single night. This is a new record and our setup times are now typically below 5 minutes when moving from one shot to another. Further small milestones….
We have now observed one month out of four in the 2017-3 period. The month started off pretty slow with lots of bad weather in August but we have had some good clear nights. We are still conducting 7 days of engineering around full moon, at least until we get our first bright time instrument. So far we have collected 52.9 hours of charged time and completed 21.8% of the TAC allocated time. We have started collecting the first LRS2 Guaranteed Time Observations (GTO) allocated by the HET board for the instrument team as well as the first time allocated by the HET board for the HETDEX experiment. The latter includes time on well studied fields to make sure that our Lyman alpha emitters detected not really other types of emission sources and to better quantify our sensitivity/throughput.
We have completed the 2017-2 trimester (April – July). It was a very successful. The HET Board allowed us to transition from 2 weeks of science operations per lunation to 3 weeks of science operations. We also completed a large commissioning effort of 27 hours of VIRUS exposures on well studied EGS fields. Below are some statistics from the trimester: 138.5 hours of acceptable high priority exposures and 40.5 hours of low priority filler exposures. The average overhead for LRS2 per requested visit was 7.9 minutes which is nearly a factor of two better than the overheads with LRS before the Wide Field Upgrade. The average visit length was 18 minutes long and the longest completed visit was 120 minutes. The completion rate for priority 0 targets was 97.2%, for priority 1 targets was 98.1%, for priority 2 targets was 90.1% and for priority 3 targets was 96.4%.
For the new 2017-3 trimester (August – November) we will continue with the 3 weeks of science per lunation. The HET board has approved the first HETDEX time as well as Guaranteed Time Observing (GTO) for the commissioning team of LRS2. In addition, we are expecting to see the arrival of the Habitable-zone Planet Finder (HPF) spectrograph.
The next few days are going to be very busy at the HET. The HET team along with help from Austin will be installing IFU’s for the second virus enclosure in preparation for more virus units to be installed. This involves stringing fiber cables from the enclosure up to the top of the tracker to be attached to the IHMP (Input Head Mounting Plate). The team will also be investigating and trying to remedy problems with the IHMP dither mechanism. During this time there will be no science or engineering related night work due to immobility of tracker, structure or dome for the IFU deployment.
This week marked the end of another dark run and thus the end of another science period. We are now also three quarters of the way through the current science period labeled 17-1. As such we are starting to see a larger number of filler Priority 4 targets being observed. In this last dark run we observed 374 acceptable observations for a total of 38 hours and 122 Priority 4 targets for a total of 22 hours. We saw 6% of the time lost due to problems. This is a fairly respectable number and fairly typical of the mature HET before the takedown.
We are now three quarters of the way through the current 17-1 period. The Telescope Allocation Committees have begun meeting and the new allocations are being submitted for the 17-2 period which begins April 1. For this period the same suite of instruments will be available for the PIs: LRS2-B and LRS2-R and the two weeks around dark time will also be fully committed to science observing.