LBTI October Run: Night 6 (and 7)

Night 6 of the October run was dedicated to commissioning the LBTI phase loop and acquiring HOSTS nulling data for testing. We had clouds move in during the afternoon. We waited for them to thin and opened a couple hours late. Seeing was good (0.7-0.9 arcsec) but the transparency at 10 microns was unusable.

We further tested the phase loop. Several bugs were found in the new implementation which improved our stability compared to the previous nights. Seeing degraded during the night (1.2 arcsec) and we demonstrated continued good performance of the loop under these conditions.

During a rare clear patch Denis started to test his automated nulling setpoint script. While it appeared to work, testing was interrupted by clouds. It did allow enough testing for us to refine the logic behind the script from our pre-run plans.

We tested and had success with the fringe envelope outer tracker. We were able to demonstrate the ability of the loop to stay on the "white light" fringe at ~1 Hz, while the pathlength loop stabilized the phase at 1000 Hz.

Finally, we again tested the accelerometer feed-forward. This night the dominant frequency on the secondary was at 13.5 Hz. We set our filter and were able to reduce the amplitude by 2-3x.

We ended the night by taking some Fizeau images using LMIRcam to demonstrate our phase stability.

Night 7

Night 7 was the beginning of tropical storm Simon moving into Arizona. We did not open.

We did, however, align our artificial source and start to use it for control loop refinement and internal system checks. The sources have some noise at 35-40 Hz, but we can also see the beamcombiner mirrors contribute some noise at 90-200 Hz. The total contribution from the beamcombiner appears to be approximately 150 nm RMS.

The interesting point came when we tested which components are creating the peaks in the power spectrum. By perturbing each mirror we were able to determine that the ellipse mirrors are the culprit for the noise at ~90 Hz and maybe the higher peaks. All the other mirrors looked solid.

While this noise does not dominate our current performance, we will want to improve the ellipse mounts in order to reduce this source of noise eventually.


LBTI October Run: Night 5

Night 5 was half LEECH and half HOSTS commissioning. The LEECH part was clear with 0.7-0.8 arcsec seeing.

The nulling commissioning made significant progress in several areas. We
  • Optimized our gain parameters for pathlength control
  • Measured throughput of each of our beams
  • Tested feed-forward of the accelerometer signals
  • Tested "fringe hopping" on sky.
  • Tested vibration filtering within the loop.

Gain Optimization

The loop performed under conditions from 0.6-0.9" with integral gains of 400-700 and proportional gains of 2 (these will need to be rescaled once our corrector values are calibrated). The RMS values recorded with phasecam were 50-70 degrees RMS (300-400 nm at 2.2 um wavelength). With an I gain of 10 we see 200 degrees RMS. With a gain of zero we see ~500 degrees RMS.

The closed, vs. open loop amplitude spectra indicate we are providing correction at frequencies up to 50 Hz. This is consistent with our model of the system, if we assume a lag of approximately 2 ms between sensing and correction.


We confirmed that there is no vignetting on the right or left side with our nominal nulling alignment. The measured intensity ratio between the left and right beams was right/left=80%. This is lower than the February measurement of ~88%. The former would leave a residual of 0.3% and the latter would leave a residual of 0.1% in the null beam. This effect can be calibrated out, so either level is acceptable. We suspect this measurement may have been contaminated by clouds.

Accelerometer Feed Forward

The accelerometers were used to measure a prominent vibration at 11.5 Hz on the secondary mirrors. This signal was fed into the FPC and we successfully demonstrated reduction of the 11.5 Hz peak by roughly a factor of three (needs confirmation with the telemetry data). However, there were other prominent vibration peaks in the 9-15 Hz range, which meant that the total RMS was not significantly improved in our initial test. These vibrations appeared to be coming from the left tertiary (but not the right one). Prominent peaks were seen in both phase and accelerometers at 14 Hz in particular.

Fringe Hopping

The ability for the phases sensor to move be n-lambda steps is important for setting the 2 um to 10 um setpoint. Denis tested a script during the afternoon to carry out this procedure automatically. The script adjusts the 2 um setpoint to one side and then the other of the setpoint which corresponds to the best null at 10 um. It then measures the 10 um flux imbalance for each dither and refines the setpoint.

We could not test this script on sky due to variable clouds, which prevented reliable 10 um flux measurements. However, we did confirm that the ability to hop from one fringe to another and change the 2 um setpoint both worked on sky.

Vibration Filtering

We also tested the capability to measure the 12 Hz vibration from Phasecam and separately add a correction to the phase loop. This test did not show any improvement over the correction already being provided by the PID controller. We expected this may be the case, if the PID were properly tuned.


LBTI October Run: Night 4

Night 4 was a relatively routine LEECH observing night. We started out with 0.8 arcsec seeing. In the middle of the night it blew up to 3 arcsec. We spent the time taking emissivity measurements and sky brightness variation measurements for the nulling mode.

Sometime after midnight the seeing came back to reasonable values and we continued with observing.

I spent some time wondering around the LBT chamber taking thermal IR pictures, looking for hot spots. Here's one looking out the chamber.

IR view of the LBT

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LBTI October Run: Night 3

Tonight was a LEECH night. The seeing was 0.5-0.9 arcseconds most of the night. Light clouds at the beginning. We had an intermittent heating problem with the right side AO system. Other than that, it was a routine night.

Light clouds at sunset


LBTI October Run: Night 2

Night 2 of our run was clear and calm. We continued Kepler followup in the first half of the night. Justin Crepp and his team were here to observe as well as work on plans for iLOCATER.

Kepler Observing

At midnight we switched over to aligning the system for LBTI.

Interferometry Testing

This was LBTI's first night trying out interferometry this observing season. We acquired fringes after 10 minutes of scanning for the "zero pathlength" setpoint, a new record. We then setup the Phasecam sensor to measure phase and tip-tilt offset. Elwood had rewritten our phase control system over the summer. Among the improvements were better timing stability, an improved, proper PID implementation, vibration filtering to increase correction at specific frequencies, and accelerometer feed-forward input.

After playing around with the correct gain values for awhile, we successfully closed the loop on the phase error measurement. All previous phase stabilization has used the fringe envelope, a less precise technique, and one which was more difficult to use for nulling suppression.

By tuning the gain we were able to reduce the phase RMS to 400 nm. Our previous best performance (March 2014) was 1-1.2 um RMS. With low gains we saw the error was dominated by a 12 Hz vibration. As we raised the gain we noticed that we were able to (our eyes at least) nearly eliminate the 12 Hz sine wave.
Time Series
Power Spectrum of the Phase ErrorsLooking at the PSD of our errors, we still have residuals at 10-20 Hz which contribute to the phase error. However, we seem to have a closed loop bandwidth of around 50 Hz, similar to our model for our system.

We were happy.

Phasing Success

This was all a half night's work on the interferometry. Work remains to fine tune this and integrate the stabilization with nulling observations. We will resume the phase testing Oct. 5-7.

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LBTI October Run: Night 1

LBTI had a productive first operational first night.

In the afternoon, Vanessa fixed a problem with the lefts side WFS modulator. A zero point adjustment appeared to fix the malfunction we were seeing on Monday.

Phil and Andy looked into the noise problem on LMIRcam. Adjusting the bias boards appeared to fix the problem.

The night was used for Kepler followup (ND program, PI: Crepp) and walleyed pointing checkout.

AO Checkout

AO systems performed well throughout the night. The right side showed no "RIP's". The left side had five total. Vanessa worked with Marco to put the same adjustments on the left side which should minimize these in the future.

Walleyed Pointing

Andy and Eckhart (new LBTI grad student) tested out walleyed pointing of the telescope on stars separated by 40 arcsec. This will enable precision photometry with the system. Careful pointing is needed. Tests were done of pointing repeatability. We may be limited by WFS translation stage precision and/or LBTI internal flexure. Good data acquired to allow photometry precision to be estimated.

Nulling Alignment

Denis confirmed that the LBTI mirrors could be reconfigured remotely between LMIRcam imaging and nulling modes. The pupils appear at larger separations when they are aligned for nulling, as seen by LMIRcam. This confirms the fix of a problem from spring 2014 where the roof mirrors did not work properly.

Daytime Work

Phil installed the beamcombiner sources. Elwood finished software to allow remote insertion of the sources. Testing confirmed the stages worked as needed. Denis and Phil acquired the sources. We scanned for fringes over the full SPC range but were unsuccessful in finding the zero OPD setpoint. More alignment check will be carried out on Friday afternoon.

The SPC was rotated to fix a coordinate problem introduced in Spring 2014.


AO Engineering Tests

The second half of Sep. 29 was scheduled for tests of the LBT AO system prior to the LBTI run. Vanessa put the system through their paces, and we had both loops locked by 12:30. However, a problem was noticed with the left side AO system performance. The symptom was a large tip-tilt variation (0.2-0.4") in the image. This issue has been tracked to a malfunctioning modulator mirror in the LBTI WFS. Troubleshooting will continue during the daytime.

Pupil alignment of the UBC was completed. Both stars were acquired on LMIRcam. This confirms the system is ready to go for observing, barring problems fixing the modulator mirror.

Vanessa and Marco tested out a refinement to the AO system which will make the triggering of the mirror's safe mode much less likely. This will improve efficiency of the AO system. The system was demonstrated to work with a manual reconfiguration on both sides. The night ended with tests which integrated this fix into the core software.


LBT AO Returns

The LBT AO system was being repaired over the summer of 2014. Yesterday, we received a welcome email from our colleagues at LBTO:

"Juan Carlos and Guido just Set the DX AdSec while the telescope was at Zenith and everything worked properly.
The shell is now rested and ready for the telescope to move back to Horizon.
Thus, the DX AdSec is ready for Seeing Limited operation.
Vanessa and the LBTI group has made arrangements with ARGOS to run some Diffraction Limited test with
DX LBTI and the DX AdSec Wednesday daytime. LBTI does not require a quite telescope nor do they need lights off.They will be coordinating directly with ARGOS during the day on Wednesday.
On Monday and possibly Tuesday nights, Sept. 29 and 30, LBTI will close their DX (and SX) AO loop to
make sure the DX AdSec works properly in Diffraction Limited mode.
Thanks to the IQ AdSec team for getting the DX AdSec repaired and the mountain crew for mounting and hooking up
the AdSec.
Its great to have both ours eye open again with the Adaptive Secondaries.


Fall 2014 Observing Preparation: Day 2

Saturday was alignment and checkout day. We verified that the pupil of NIC could be aligned to the beamcombiner. NOMIC, LMIRcam and phasecam were all turned on and verified to operate. Vanessa remotely checked out both WFS artificial light sources. The beamcombiner sources were aligned and tested.

We had a few issues with the system:
The Nimble disk array has some faulty components that need to be replaced.
The beamcombiner source needs mechanical rework to improve its stability.
The new phasecam electronics was not operational and needs to be checked out in Tucson.

Overall, it was a productive preparation block. None of the above issues are critical for beginning the fall observing season. At the end of the (very long) day we were happy to conclude that LBTI is on-sky ready.


Fall2014 Observing Preparation: Day 1

We (Manny, Paul A., Elwood, Denis, Eckhart and Phil) are finally up on Mt. Graham to install NIC (the camera portion of LBTI). The plan was to leave on Wednesday. Hurricane Odile delayed us. It didn't rain much in Tucson, but poured on Mt. Graham.

Friday was spent unpacking and installing all the hardware. NIC was brought up cold. We had problems keeping the compressor running due to coolant flow. Manny babied it until it was stable.

We installed and tested the beamcombiner source (sometimes referred to as the Arizona source). Saturday work will attempt to align it to NIC and phase the beams for system level testing of Phasecam.

Cabling and motor control boxes were also installed but not fully tested. It was a productive first day.


Imaging, Single and Dual Aperture

The evenings of Feb. 12 and 13 were spent executing several different observing programs with LMIRCam (and some supporting NOMIC data). Winds were high and seeing mediocre on Feb. 12. It was much more reasonable on Feb. 13. We are now preparing for our last night of Nulling. We have a new algorithm to try and plenty of sources lined up to observe for the night.

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Second February Nulling Night: First Nulling Disk Detection

We saw our first dust disk last night with the LBTI nulling interferometer! First, the night details:

We carried out further nulling engineering last night, along with some test science to determine the state of the system. We began the night by optimizing our group delay tracker (also called the contrast gradient approach). This has allowed us to stabilize the phase, but has higher RMS variation than we need to hit our specs. We tried adding an integral term to this, and saw no improvement. Based on simulatons from Amali and Bertrand, we also tried merging the group delay and phase delay, to fine tune the performance. Also no improvement there. Its good to have ruled these out as the cause of the large RMS, but was disappointing.

We made more progress on scripting last night. Denis now has an automated routine for setting the group delay setpoint and routine. Dual position nodding was also further refined.

We took test data on fainter stars last night (1.7 Jy) with good results. This will be important for carrying out observations on the full HOSTS sample.

Finally, we looked at a star with a bright dust disk to test our performance. Denis carried out on-the-fly data reduction which confirmed we were seeing the disk. It made for a good end of the night.

Denis shows off the first LBTI disk detection
Denis shows off the disk detection.

Bill and Rafael run the AO systems
Bill and Rafael run the AO systems.

Our first detection. (rough reduction only).


First February Nulling Night

Last night was our first night testing out the nulling and phasing system since December. Our first three nights, used for general commissioning and science, were rocky and plagued by poor seeing. We had several failures which has made working with the system more challenging. Our right fine alignment mirror stopped working, presumably due to a problem with cooling it down. Similarly, our right pupil alignment motor was found to have failed. These problems required us to warm and open the beamcombiner in order to fix the problems. On the AO side we are seeing an unusually high occurence of loop failures, which were affecting our productivity.

Sunday night started out similarly. However, by 11 pm or so the seeing had calmed down and the AO systems stopped misbehaving. In brief, we achieved several milestones:
  • Automated measurement of the null depth for use in scripts.
  • First testing of measuring the K band to N band setpoint automatically via a script
  • Measured and reduced the intensity mismatch to reduce the effect by 5x (~1% to 0.2%)
  • First testing of automated nodding via a script to allow nulling measurements in both beams (doubles our efficiency).
  • Acquired lengthy dataset to measure setpoint variations over time and elevation.
We are now on the sky for a second night and have more commissioning planned.


February '14 Observing Run Weather Predictions

Observing Dates: February 7 - February 14.


December 2013 Run Completed

Last night was the final observing night of the December 2013 observing block. In a nutshell, here's how it went. More details soon.


December 2013 Run: First Stabilized Fringes

We have been doing a lot of testing. The last time I wrote we had confirmed that the phase sensing was working. However, control of it was not.

Last night we were able to stabilize fringes for the first time. The key to it was tracking the group delay. For the implementation we have this corresponds to a left-right gradient in the visibility. The movie below shows the loop grabbing the fringes and centering the fringe packet.

This allowed us to reduce the variations in the pathlength and set the 10 micron interference to be approximately at null (destructive interference). It also made people in the control room very happy.

We are about to go back on sky for our last night, so the details will need to wait for a later post. We are excited to start using our new 23 m telescope.


December 2013 Run: Christmas day

Christmas day 2013, 20:00 pm -- the day and night crews having Christmas dinner at the LBT. Thanks to the participation of everyone, we had a delicious (and copious) meal including ham, asparagus, mashed potatoes, mac & cheese, "french" oignon beans, and various desserts.

Meanwhile in the control room, science observations are being carried out for LEECH. The telescope is nodding back and forth while LMIRcam is taking data. One might almost think that this is going on without any supervision....

But of course not. Andy has ingeniously put his laptop in front of the LMIRcam quick-look display and called Denis on skype.

Vanessa and Andy can now keep an eye on the observations from the dining room while we all share a good meal together on this special day.

We wish you a Merry Christmas from the LBT.


December 2013 Run: Photo Blog

Hi LBTI Blog followers!

My name is Kim, and I'm a 3rd year graduate student who has been helping with the LBTI run over the past few days (along with post-doc Rob De Rosa and soon fellow grad student Abhi Rajan -- we all work in Jenny Patience's group at ASU). I've taken some photos while I've been here, and Phil and Vanessa suggested I write a guest post and add these to the blog. Hope you enjoy!

After this run started with a wintry blast, the skies finally cleared yesterday and began to melt the snow -- a good chance to snap a panorama from the balcony.

Cold and clear!

The snow survived long enough during the day for a snowy nighttime panorama too, with the city of Willcox visible on the left, along with the light domes of Tucson (middle) and Phoenix (rightmost). The starry skies belie an extraordinarily turbulent atmosphere -- at some points, we had seeing near 4 arcseconds!

4" seeing - not great for observing, but okay for panoramas. The Vatican Advanced Technology Telescope and the Sub-Millimeter Telescope can be seen on the right.
Much of the snow melted this morning and afternoon. By sunset, the forecast boded well for clear skies and improved seeing.

No inversion layer today. Clear as far as the eye can see.

With the moon approaching 3rd quarter, we've had the nice privilege of dark time for our first half nights. Below, the Milky Way provides a great backdrop for the open LBT dome. (Not pictured: IR starlight from a LEECH target makes its way into LMIRCam.)

Not sure what's happening with that little red light, sorry Andy!
Viewed from another angle, the Andromeda Galaxy (seen at the top left) and the Pleiades (top right) grace the LBT dome, while more stars within the galactic plane peek through the ventilation doors.

M31 as a small fuzzy - LBT - M45 (Pleiades)

(Also, a huge thanks to Chick Woodward for his kind donation of handwarmers, without which these nighttime shots would've been a lot less pleasant!)

Toward the northwest, the Milky Way sets over the treeline and surrounding forest.

A bit of light glow from Phoenix.
On the opposite horizon, the eastern sky rose bearing Jupiter (reflecting brightly on the left), Orion, and a bit more of the galactic plane in between. We'd soon be pointing the telescope in that direction to get a glimpse of the Galilean moons. The excellent dark sky at Mount Graham provides a nice view of M42, the Orion Nebula, to boot.

Spectacular dark skies - Jupiter looks brilliant.
Meanwhile, indoors we were getting some great results with excellent seeing (~0".5) and (mostly) nicely-behaved AO systems. The black plot on the middle monitor shows AO-corrected rms wavefront error of less than 1 nanometer on the highest orders, with overall correction (white curve) at a factor of 5-10 improvement over the input wavefronts (red curve) -- the first time we've reached these levels of correction. Vanessa approves!

Stamp of approval!

On the LMIRCam side, Andy and Phil pored over interferometric imaging at M' band of Jupiter's extremely volcanically-active moon, Io. Warm bright spots corresponding to volcanic activity could be seen on the moon's resolved disk.

Imaging Io with LMIRCAM.
The telescope phased well over the separation, providing great fringes of the bright spots!

Zooming in on the volcano spot.
Meanwhile on NOMIC, Denis was also spotting fringes of the Io volcano spots, this time at N-prime and 8.7 ┬Ám.

Volcano spots look great at longer wavelengths too!
Back outside, the cold clear night continued with reasonably good seeing, and a nice chance to get some parting star trails. A great end to a fantastic opportunity to work at the LBT and see the awesome progress being made with LBTI -- we've learned so much this run!

~20 minutes of exposure provides some small trails.


December 2013 Run: Day 4

We finally got sky time tonight! We were able to open at sunset and begin observing soon after. The cold weather and difference in temperature causes some early night problems with AO stability (we were seeing large tip-tilt variations). The left AO system seems to operate fine on sky.

We scanned for fringes and had a system ready for phase testing by 9 pm. Seeing was okay early on, but degraded throughout the night.

We were again able to show regular control of the tip-tilt loop, but no significant improvement in stability with the phase loop. We did show, however, that for the first time we could adjust the phase setpoint of the system and have the corrector react as expected.

We identified several areas to test further:
  • Phase unwrapping was done only for a single wavelength jump. Multiple lambda jumps are now implemented.
  • Variations in tip-tilt may have been affecting phase stability, a work around was implemented.
  • poor SNR data may have been causing wavelength jumps. Revised software was implemented to remove these.
Attempts to test these variations later in the night were hampered by 1.5-4" seeing. We plan to continue testing of the phase loop after Christmas.


December 2013 Run: Day 3

Another snow day on Saturday. We spent the time playing around with the test source. In particular, we explored vibration contributions. What we found:
  • Our pulse tube cooler does not contribute to vibrations seen with the artificial source
  • LUCI's coolers do not contribute to vibration.
  • Walking around on the back of the platform creates lots of vibrations.
  • Taping down the fold mirrors to dampen their motion doesn't reduce vibrations.
  • The cap. sensors on the FPC were creating very slow (3-10 Hz) responsiveness. We turned them off
Denis, Elwood, and Andy also refined the tip-tilt loop to use subpixel centroiding. This improved the performance. They are exploring an alternative phase calculation (parametric fitting, rather than angle of the Fourier Transform).

Sunday afternoon Vanessa and Phil realigned the SX wavefront sensor to allow removal of shims on the left dichroic. This should fix the vacuum leak we had earlier.

This afternoon it's been sunny but cold, so we are waiting to hear whether we can open tonight.