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.
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.
Despite some pretty poor weather this past week we are finished with the bright time engineering run and ready to start science over the 14 days around new moon. In this past engineering run we found some problems with the wave-front sensor software and implemented a new forward model of the hexapod motion. This new model allows for us to compensate for an unintended very small rotation that is induced by hexapod motion over the course of a trajectory. The impact of this rotation was to cause the field to rotate by several arcseconds over a trajectory. Our new forward model eliminates all of the hexapod induced rotation but allowed us to see a much smaller Azimuth dependent rotation term. This much smaller term will be addressed after this next science run, during the next full moon. Overall, a good improvement to the telescope’s operation.
The end of this week marks us as half way through the current 4 month period (December – March). We have completed 70% of the highest priority band P1, 52% of the P2 band and 41% of the P3 band time. The bad weather we had at the beginning of the period, back in December, really kept us from completing many of the high priority targets in the Sheila field which is now unreachable until the late summer.
There are 10 programs that have been completed out of 27 programs. Some of our users have never been granted HET time before so there is a bit of a learning curve in how to optimize the HET time. Hopefully our Synoptic Supernova teams can make excellent use of the remaining 2 months of the period.
For the next 2 weeks (during the bright time) we will be concentrating on making further improvements to our telescope control systems, wavefront sensor systems and instrument control systems. It is going to be a very busy 2 weeks!
We have finished another dark period from the first trimester back observing with the HET. Recall that we are only observing during the two weeks around the new moon. Thus, we finished up last week with our targets that can be observed with some moon. We have completed 63.4 hours of charged time with typical setup times of 10 minutes for LRS2 targets. Some programs, particularly those from our smaller partners, have been completed finished while a few of the larger programs have only had a small dent made in their total Telescope Allocation Committee (TAC) allocations.
There are a few fields that seem to be very popular. The Shelia and Cosmos fields are among the most heavily over-subscribed. We will not be able to complete the requested visits to the Shelia fields but if the weather permits and the engineering efforts during the 1st quarter are not to heavy we might try to sneak in a few more targets.
We are developing a hole at the start of the night after the Shelia field sets and will likely have to deal with that in the next few weeks unless some new targets arrive.
This week we are firmly back in our 2 weeks of engineering time. The big news is that we were able to get the wave-front sensors to properly operate in closed loop mode. This means that we are able to optimize our image quality during a trajectory small tweaks to the overall tip and tilt of the corrector above the primary mirror.
The mirror teams has kept up their rapid pace of pulling mirrors out of the array and putting in recoated mirrors. The current swap rate is 1.67 segments per week with 69 segments having been swapped since 29 February.
This week marks the first full week of the new trimester (December – March). During this period we will be observing for 2 weeks around the new moon with LRS2-B and LRS2-R and to a very limited extent the first 16 units of VIRUS for science projects from our partners. We have 27 separate projects from our 4 partners. During this first week of the new trimester we took data for 10 programs.
During the 2 weeks around the full moon we will be concentrating on engineering but we may if it does not impose any constraint on the engineering obtain a few science targets during grey and bright time.
It is good to be back online taking science data.
Last week we reported on a incident with the HET tracker that put us in a hard skew condition and shut us down. We had recovered from that skew condition but the software issues that led to the skew had continued. This week I am happy to report that we have not only installed additional skew sensors but we have found the source of the software issues. The software teams in Austin and West Texas were able to perform a series of experiments which allowed them to isolate the problem as coming from the ethernet card inside the dSpace box. This is a very specialized ethernet card but thankfully we were able to swap out a different card for it and found that all of our TCS communications problems, hexapod faults, and loading trajectory errors have gone away. We will look into getting a spare card and send the card in to see what kind of fault occurred in the card.
With the improved tracker performance we were able to start our early science operations. We took our first science targets on the night of the 16th. Unfortunately, we are now headed towards full moon which is not the ideal time to do science targets with LRS2. However, it does give us a chance to work out any inefficiencies in our PI interface, night operations interfaces and queue tools so that we can be fully ready once we get some dark time a few days after full moon.