Author Archives: shetrone

The week of December 11

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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.

The week of July 11

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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.

The week of July 4th

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Two weeks ago we had a fairly serious tracker issue. While recovering from a fairly typical tracker failure, the telescope operator requested that the breaks be set but instead the tracker moved in X and generated a hard skew. This hard skew actually caused the bearing to come out of the bearing block. This occurred the day that the blogger and most of the chief engineers were going to their summer conferences. Upon the return the engineers were able to determine that no permanent damage was done to the bearings or the tracker in general. The engineering team was able to move the tracker back into the block using the tracker motors. Unfortunately, the software issues that led to the skew are still present and have not yet been sorted out. This has severely limited our ability to run trajectories for engineering or the start of early science operations.

In the mean time work continues on VIRUS enclosure 2 and with re-coating of the primary mirror segments.

The week of May 23

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In the previous week the HET Board of Directors met and were generally happy with the progress being made on the HET. They are very eager for science operations to begin and have authorized the start of Early Science Operations starting July 1st. This will mean that HET member institutions will be able to submit requests to their local Telescope Allocation Committee in the coming weeks. The amount of time available will grow with time but is likely to start with 1 week per dark period. The instrument that will be available for Early Science Operations will be the new Low Resolution Spectrograph (LRS2).

In this week the HET continued with VIRUS commissioning during bright time with the addition of 7 new VIRUS units. This brings the number of spectrographs units (and IFUs) to 16. We will use these during commissioning in the coming dark run but we can already see that several of them will need some further engineering while others are very good.

The mirror team continues to swap mirrors into the array this week they swapped out 4 mirrors. The array now has an average coating age of 454 days with a swap rate of 1.7 segments/week.

The week of April 18

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We are currently in bright time (near full moon) and the currently active instruments, LRS2 and VIRUS are really designed to operate in dark time (when the moon is below the horizon), thus we spent this week analyzing the data taken in the last dark run, testing and updating the telescope control software and training the night time staff to make sure all of the staff have the same skills and knowledge of the system for the upcoming dark run.

One of the problems we were having in the last dark run was a mysterious end of track due to a hexapod hitting the software limit. Further investigation has revealed that this limit is part of the natural extension of the warming tracker. As the steel structure expands from warmer temperatures we have to move the hexapods down to compensate. We also found that we had set the software limits fairly far from the limit switches so we could give ourselves plenty more room without any changes to the hardware of the telescope. This is an example of the type of tuning that we continue to have to do with the control algorithms.

Both the LRS and the VIRUS are IFU (Integral Field Unit) spectrographs, which means that one could take the spectra for each fiber and reconstruct an image of the field which was observed. Below is the very first reconstruction that we did for a VIRUS field. It was a fairly bright (8th mag) standard star. The image scale is set very wide so that we can see all of the interesting features that come from the unusual design of the HET. The six image spikes comes from the edges of the hexagonal HET segments, and the stronger spikes along the X direction come from the tracker Y superstructure.

First reconstructed IFU image from VIRUS. A very bright 8th mag standard star with the stretch set very wide to show all features.

First reconstructed IFU image from VIRUS. A very bright 8th mag standard star with the stretch set very wide to show all features.

Not long after generating this the software team was able to reconstruct a number of images for each IFU in a pointing of a globular cluster, NGC5272. Below I show a couple of examples of these.

IFU 94 on NGC5272

IFU 94 on NGC5272

IFU 95 for NGC5272

IFU 95 for NGC5272

Here is a schematic of what the current array of IFUs would look like compared to a Digitized Sky Survey Image of the field we pointed at. This is a by-product of our current setup software.

Image made by our setup software to help the astronomer understand where we are pointed.

Image made by our setup software to help the astronomer understand where we are pointed.

The week of April 4

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We have had a very exciting couple of weeks. In the last blog post I had mentioned that we made some repairs and improvements to the top end of the telescope and that the LRS2 team had left the telescope in the hands of the night operations team to gain experience with the system. That is exactly what we did over the bright lunation. We had nights set aside with all of the telescope operators working together at night to make sure that we all know how to operate all of the new software the same way and to work out the kinks in the operations procedures. This was followed by a few nights with the resident astronomers all working at night to do the same. The result was that we had developed a few pieces of code that would allow us to determine the exact position of the LRS2 field of view and could setup any target that the Acquisition camera could see.

In the mean time, the day staff was prepping the right VIRUS enclosure for the delivery of the first 9 units (18 spectrographs). The spectrographs were brought out in two vans along with the VIRUS commissioning team for the dark run (where the moon is in the new phase). The fibers were strung, the units were vacuum pumped and finally cooled. Everything went ahead of schedule and on Saturday night we were able to make use of some very clear skies to get first light with the VIRUS spectrographs. On Sunday night we were able to get the first LRS2 science spectrum (a supernova for an astronomer at PSU) and a few long exposures for characterization of the VIRUS units.

The telescope is still occasionally fussy but generally performed well and the commissioning work continues on into the next week until quarter moon. At the present time the data reduction software is the thing that is lagging most behind.

The week of March 7

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We have had a great couple of weeks at the HET. Last week we brought out down the focal plane assembly to work on the field calibration unit and replace the acquisition camera. Both went well although some further work on a few specific calibration lamps and changes to the acquisition power supply will still be required. This work took the telescope down for a few days. The telescope control software also went through a large upgrade during this period. With improvements to guiding and offsetting. One of the more complicated aspects that has been commissioned is the ability of offset the telescope and the guide probes so that we can move from one instrument to another while keeping the same guide star.

The LRS2 commissioning team came back out to West Texas from Austin and despite very poor weather they were able to train a few of the resident astronomers in the use of the LRS2 instrument and the calibration scripts. When the skies did finally clear they were able to determine the positions of the LRS2-B and LRS2-R on the acquisition camera. The LRS2 team has departed but the instrument has been left online for the resident astronomers to gain familiarity and perhaps start characterizing on-sky.

The week of February 8

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This week saw the return of the LRS2 but in its full glory, ie. both the B and R components. The instrument cooled down quickly and we were ahead of schedule by the third day. We did have a few problems with calibrations lamps, communications with the TCS, and inexperienced operators but all of that is expected when you get FIRST LIGHT with a science instrument on an effectively brand new telescope.

One of the highlights of the observing was moving back and forth between LRS2-B and LRS2-R, an observing mode we hoped to achieve eventually but were able to take advantage of in this first official commissioning run. The Austin team will be back in the beginning of March. In the mean time the LRS2 instruments remain at the telescope pumped down and cold to test the stability of the cryogenic system.

The week of January 25

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Happy new year. We did conduct some engineering operations over the holidays. Most of this involved small changes to the pointing and collecting data to remove the remaining guider drift we continue to see. We made some changes to the lowest order of the pointing corrections.

We have also been able to move specific stars into the guide probes and wave front sensors. This past week was the first time we actually had stars in two guide probes and in the wavefront sensor at the same time.

At the beginning of January we began commissioning of the calibration wavefront sensor using the deployable wavefront sensor in the central IFU position. This is done with geo-stationary satellites and our procedure is to align the primary mirror and then setup on the deployable wavefront sensor, null out any tip, tilt and focus remaining and then image through the calibration wavefront sensor. Once we have done that a few times back and forth we offset the telescope so that we can image the satellite with the operation wavefront sensor 576″ away. We can now do this repeatably.

The day staff has been getting electronics setup in the 2nd VIRUS enclosure and dealing with small problems that have been popping up with the tracker and other sub-systems. The most critical of these was an uncontrolled warm up of the LRS-r. This was caused by a fault in the liquid nitrogen system and the normal warnings that normally go out were shunted into a dead phone line. The LRS-2 was sent back to Austin for diagnostics and new safeties will be put in place. We hope to have LRS-2 back out here next week.

We have hired a new Telescope Operator and he is being trained. We do have a open position for a computer system admin person currently posted so if you have anyone who wants to get away from the hustle and bustle of city life but still work with cutting edge equipment have them look at the UT job posting.

The week of Dec 7

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Two weeks ago was the HET Board of Director’s meeting in Penn State. The meeting lasted two days and the Board got status reports from HET operations and each of the instrument teams. The main news is that that LRS2 is expecting to reach first science in the first few months of 2016, HRS2 is going to start commissioning before Summer 2016 and VIRUS units are going to be coming in over the next 9 months. The Board was encouraged by the progress being made and hopes that we can continue the pace. They were also pleased to see the progress being made on HPF and were impressed with the clean room facility tour they were given. No major changes or action items were reported by the Board.

Once the commissioning team returned from Happy Valley, we went right back to work and were able to push along the closure of one of our major metrology loops, the guide probes. I am pleased to report that we are able to guide at any telescope Az for full trajectories with the probes at any position within their range.