Adaptive Optics in the Atacama Desert
Greetings! If you're an astrophysics undergraduate wondering what to do after graduation - like myself only one year ago - this is intended to describe just one option that is not graduate school. After graduating from Lehigh University in May of last year, I was hired to work for the University of Arizona's Steward Observatory. Within Steward there are numerous groups, I belong to the adaptive optics group, the Center for Astronomical Adaptive Optics (CAAO). While I spend time on all the projects in CAAO, including the Large Binocular Telescope Interferometer (LBTI), MMT Adaptive Optics exoPlanet characterization System (MAPS), this post will focus on MagAO.
What is AO?
Adaptive optics was first thought about in science fiction and by astronomer Horace W. Babcock in the 1950's. It wouldn't be until the 1980/1990's when technology would finally catch up to science fiction. Initial development on AO was through the United States military for tracking Soviet satellites during the Cold War. The technology was then realized for astronomical purposes.
AO is essentially the ability to reduce the affect of the atmosphere by deforming a mirror in the optical system that is designed to compensate for atmospheric wavefronts. As a passenger in an airliner we feel atmospheric disturbances as dreaded "turbulence"; in astronomy "turbulence" is described as "seeing". The adaptive optics systems I work with use the secondary mirror of the telescope (optical system) as the deformable mirror, called an Adaptive Secondary Mirror (ASM) and a Wavefront Sensor (WFS) which detects the non-flat wavefront, calculates a correction, and compensates through a complex feedback loop. ASM's are thin mirrors with hundreds of small magnets placed on the non-reflective side of the mirror. Just behind the thin mirror, inside a reference body, there are hundreds of actuators with their placement matched to the magnets. These actuators are computer controlled to deform the mirror in response to the wavefront sensors closed loop feedback calculations of the atmospheric wavefront. The control system is generally a computer that calculates, based on the wavefront-sensor measurements, the commands sent to the actuators to deform the mirror. The calculation must be done very fast (0.5 to 1 ms), otherwise the state of the atmosphere may have changed and thus renders the wavefront correction inaccurate.
Left: Uncorrected and corrected wavefront.
Right: Image of the MAPS ASM. The mirror is usually only millimeters thick in order to be easily deformable, as a result it is extremely fragile. In certain wind conditions we cannot use the telescope for fear of the mirror being ripped away from the reference body.
In 2013, the Clay Telescope was equipped with an ASM called MagAO (Magellan Adaptive Optics) which allowed it to take the sharpest visible-light images to date, capable of resolving objects 0.02 arcseconds (arcseconds = ", for comparison, the moon is 30 arcminutes across)—equivalent to a dime (1.8 cm) seen from 100 miles (160 km) away.
Now that you have a basic AO understanding, let's see how this is implemented on a large telescope.
Where is LCO?
Las Campanas Observatory is located in the southern Atacama Desert Region at an altitude of approximately 2300m (8000ft).
Las Campanas means "The Bells", the observatory was named this due to the many "singing rocks" that are located all over the property, especially on the Giant Magellan Telescope building sight. Hitting these rocks results in a beautiful singing sound.
Since 1969 it has operated through a Cooperative Agreement with the University of Chile and under the auspices of the Ministry of Foreign Affairs of Chile. The twin 6.5-meter Magellan Telescopes were built and continue to be operated by a consortium consisting of the Carnegie Institution of Washington, Harvard University, MIT, University of Michigan, and the University of Arizona. First light for the Baade telescope was September 15, 2000 and the Clay on September 7, 2002.
The journey to the observatory is half the fun! From Tucson we take a flight to Dallas Forth Worth, then an all-night flight from DFW to Chile's capital, Santiago. In our particular case we had to spend all day at the Santiago airport to wait for a flight from Santiago north to a smaller airport in La Serena. Once in La Serena a LCO hired taxi picked us up and drove us 3 hours into the mountainous desert to the summit. After about 26 hours of traveling, we were ready for a real meal and sleep.
During this time Chile was experiencing serious political upheaval. We were safely transported to and from our destinations within the country but did see the devastating aftermath of rioting and looting in the cities. Observatory staff also had to work around a planned government employee strike. This did not affect observatory operation but had transportation schedules to and from the observatory halted for one day for the safety of the LCO employees.
MagAO is used on the Clay telescope, on the right is a setup diagram by Tyson Hare. The top of the telescope houses the ASM in the secondary cage, the mid level (Nasmyth port) is where the WFS is mounted, and just below is the location of the primary mirror cell with diameter 6.5 meters.
And to compare with a real-life image, though it is incredibly difficult to get the entire telescope in the field of an iPhone camera!
The white circular section at the bottom is the primary mirror cell, the silver circle on the left is the altitude bearing (as this is an Alt/Az telescope), and the odd cylindrical/hexapod object attached at the top is the secondary mirror cell (where our ASM would be attached).
Life of an AO Operator
At LCO all accommodations are taken care of for observers. Imagine a hotel with regular meal service or an awesome astronomy sleep-away camp. With basic needs taken care of we can get right to work. The MagAO system is one of many instruments that are used on the Clay, which means there is time allotted for removal of the previous instrument and installation of the ASM and the WFS assembly during the day. Before the install, we begin prepping the science camera, named Clio, and the NAS (Nasmyth Wavefront sensor assembly, named because it will be placed at the Nasmyth port). Clio takes approximately 3 days to cool and stabilize at 56K. Checking Clio's computer was also necessary, and interesting to find that in the year and a half that it had been sitting waiting for us it pinged and wrote to the network every ten minutes, filling nearly all its disk space! Clio missed its operators. Below are images: Left is the side that is mounted into the telescope on the NAS, the ring attaches it to the NAS. Middle is the side that faces out of the telescope, allowing us access to the liquid nitrogen dewar (bucket looking top) for daily refills. Right shows the instrument getting pumped down and periodically filled, its computer stack is tucked on the right.
This afternoon we also moved the ASM from the astronomy support building (which includes a clean room) to the Auxiliary Building between the two Magellan Domes. The rest of this day was fairly relaxed, developing the technical documents required for cooling and setup and continuing to cool Clio.
Always wear protective gear when working with liquid nitrogen!
Photo by Katie Morzinski.
Driving the mirror up to the dome. A very tense drive from the astronomy support building to the dome.
The following day was prepping the Nasmyth platform for the MagAO instruments, turning pumps on, locating cables, and moving Clio, the NAS, and the ASM to the dome floor. During this afternoon we also had an in depth meeting with the observatory crew detailing the next days plans, the big install day. Most of the mechanics do not speak English, thus Juan - the head mechanic - gave the details in Spanish with an English PDF document on screen for non-Spanish speakers to follow.
The following day was all for installing the NAS, Clio, and the ASM, for which we spent an entire day! The observatory mechanics began with removing the previous nights instrument. While they worked, we began prepping the ASM by taking off the protective green wrap, taping over some possible dust intrusion areas, and wiping the metal free of dust.
Once the NAS was ready to be taken up the elevator and installed, the dome crane picked it up from its top and carefully positioned and bolted it to the Nasmyth focus of the telescope. Clio was then raised to the platform and attached to the NAS, since this a delicate instrument containing the camera, it required very skilled personnel to operate the crane.
Riding the elevator up to the telescope floor. Photo by Katie Morzinski.
Now the ASM was ready to be attached to crane and raise to the secondary cage. Laird and I had to climb to secondary cage in order to cable the glycol cooling lines and electronics to the back of the ASM.
Standing at the focal point of the ASM before it was lifted to the telescope. Alex is the foreground for height comparison. The diameter of this mirror is 84cm.
The rest of the afternoon was spent fine tuning the ASM and NAS cooling pressures, ensuring rotator angles were correct for the telescope, and balancing the telescope with its new equipment.
We did break for dinner but had to be right back up at the telescope for our one and only engineering night. This night would allow us to ensure that everything we had installed during the day was working properly for the following weeks observers.
Sunset was around 2000 local time and it wasn't until 2250 the was finally got our first Closed Loop!
While we had a few communication issues, they were easily solved and not anything run-cancelling.
Observers really do stay up all night. Although we all began on the day schedule during the prep stages, we forced ourselves onto the night schedule through that long 24 hour working awake period - and a lot of caffeine and sugar.
Once we are on the night schedule, wake up was typically a few hours before sunset, just in time for the scheduled dinner. We would fill in "Night Lunch forms" right before sunrise (bedtime). These forms had sandwich options or "la plata de cena" for a plate of dinner. The telescope operator would pick up the night lunches for all the observers and operators at dinner each evening and bring them to the telescope. Each dome has its own kitchen as well, stocked with cookies, cheese, crackers, and plenty of caffeinated beverages.
From sunset to sunrise the below image was my view, many, many screens detailing the conditions of the mirror. The bright magenta shades are the life of each and every actuator on the mirror, 465 in all, telling us their health and thus the quality of correction. The seeing (the exact blurring and twinkling we are correcting for) at this location is typically excellent, and our observing run was no exception. Lowest seeing during our run was 0.43”, the highest 1.07” (the lower the better) compare that to the Large Binocular Telescopes location, Mt. Graham, where we routinely battle 2" seeing! I would spend the next few nights operating the secondary mirror for various observers visiting to take data with the telescope.
In all the work of each evening, I never got a good photograph of the Clio science camera images. And the images I see are the "pupil' images for ensuring good correction through the wavefront sensor, not the true science images. There is a dichroic sending light to different detectors. Instead, to show the incredibly powerful results of adaptive optics, below is the result of the MagAO system on the Clay telescope, from Laird Close, when it was first installed. AO takes an atmosphere ridden image of a star and real-time corrects to a beautiful airy ring. This allows for observations of exoplanets and planetary disks.
Yes, we do have to reverse the entire process before we head back to the U.S. Which for some of us meant another long 24 hour day! The observatory crew must also being prepping the telescope for its next scheduled instruments.
Below are images of the ASM coming off the telescope with great care by the telescope operator.
Somehow the uninstall day was easier than the install day maybe because we had the intense stares of the "locals". During our observing run I took just as many photographs of the wildlife as I did the telescope. Here is a video of wild horses and guanacos near the observers quarters: https://www.youtube.com/watch?v=zT54F91SJu0
It had now been 15 days since we had last been home and some were getting anxious to return to their cats (and families!). With the instruments all tucked away until our next observing run we reversed the long journey back to Tucson for some much needed rest. LCO certainly was a magical place!
If you want to read more about this observing run visit the MagAO and MagAO-X blog! https://xwcl.science/magao-c-2019b/