Tuesday, April 28, 2015

More on LBT...

Image by Ken Spencer
It seems as if I'm stuck in a time warp - it has been a week already since we did the trip to Mount Graham and LBT, and yet, there doesn't seem enough hours in the day to post about it. I also had taken so many images (many for time-lapse sets and stereo-pairs) that it takes time to go through and do something with them.

Image by Stan Honda
So I'm going to start tonight's program with a couple images that are not my own! I know, I shouldn't do it, but since our little band of travelers were a tight-knit group, it's ok this time. Particularly filling in the coverage gaps that I didn't get! At left is a nice view of the LBT telescope enclosure taken from near the Vatican Advanced Technology Telescope. Ken took this shot - he is a former photographer from Newsday and runs a great blog - you should go visit! Anyway, it is an interesting structure. The opening (which is closed here) is facing away, and the doors you see here open to promote exchange of air in the dome while observing. The big tubes also help exhaust warm air from the big machinery room where compressors, air conditioners and other heat sources are located.

The image at right was a group shot of our intrepid band of astro-nerds at LBT that night!  Of course, that is the Large Binocular Telescope in back of us - two,  count 'em, two mirrors of 8.4 meters (about 28 feet) diameter working together for some instruments, separately for some.  That is Anne and Kevin at left, the observers for the night.  Then there is Mike and Ken from our group.  Elliot is an LBT engineer who was taking care of our needs, then Stan Honda and myself.  Stan is also a pro photographer, and infamous in our little group for getting an Astronomy Picture of the Day about 5 weeks earlier for his image of the solar eclipse from northern Norway!

Our tour started with the highlight - the telescope itself! I've been working around big scopes at Kitt Peak and big optics at the Mirror Lab most of my working life, but just being next to this gargantuan is breathtaking! And I can lay claim to polishing the pair of mirrors! At left is one of the primary mirrors, the SX or left hand one as viewed from the rear of the scope. You will note that the structure is huge, but they've never engineered a proper mirror cover, so it stays exposed to the telescope enclosure, but always point the telescope to the horizon before opening the shutter to make sure snow, ice, dead birds or whatever else doesn't fall onto the mirror.  While it looks a little dusty, they actually cleaned it a week or two before.  You might notice a swirl pattern in the surface - they use a CO2 cleaning system, much like a carbon dioxide fire extinguisher.  When horizon-pointing, the snow particles stick to the dust, and when it sublimates to a gas, lifts the dust off the mirror.  From the swirl pattern, it looks like the mechanical action of the spray did more to clean off the dust. Elliot informed us that much of it may be sticky pollen that is tough to clean off easily. This mirror is scheduled to be coated this summer shutdown, so will be good as new in a few months. At right is a view of the Gregorian secondary mirror which redirects the light to a focus through the hole in the primary to the instrument located below. In the reflection part of the primary mirror and support structure can be seen. The observers were doing spectroscopy with MODS, the Multi-Object Double Spectrograph. The spectrograph, big as a small house, splits the light into a spectrum allowing the astronomers to measure motions of many star-formation areas at once.
With such a huge structure, it is difficult to get oriented, let alone get it all in a single shot without the distortion of a fisheye. Here at left is a 6-frame mosaic of the telescope in an attempt to take it all in without distorting it too much. The primary and secondary in the SX system is seen. The large cylinder at upper left is the prime focus blue camera, swung out of the beam, as is the tertiary mirror at lower left. You can see the large ports near the center of the mirror where other large instruments are permanently located. The flat tertiary mirror swings into the beam and rotates to feed the instrument of choice. Way over on the far side of the enclosure, the secondary for the DX telescope can be seen. The DX MODS instrument isn't quite commissioned, so the observers were using just the SX side shown here.
The array of instruments is dizzying! Besides the MODS and prime focus cameras, there is PEPSI - the Potsdam Echelle Polarimetric and Spectroscopic Instrument, LUCIFER - the LBT near-infrared spectroscopic Utility with Camera and Integral Field unit for Extragalactic Research, and NIRVANA - the Near-IR/Visible Adaptive iNterferometer for Astronomy.  Astronomers love their acronyms! Starting this week, ARGOS will be in action again - I've posted about it before - ARGOS is the Advanced Rayleigh guided Ground layer adaptive Optics System.  It remains to be seen if I'll have time to track down images of it this run.

The tour ended with the inner workings of the building, including the "bogies". Turns out that this is one of the problem issues of the Observatory. The entire building rotates on a single circular rail on these 4 bogies. The weight is high enough on these 20 wheels that small shards of metal are occasionally peeled off the rail. Talking to one of the mechanical engineers at work who designed much of the telescope and building, he recalls the weight is 50 tons per wheel, so something over 1000 tons of weight supporting the precision motion of the structure... He was also telling me stories of replacing bearings in the drive that failed because of under lubrication. Always something interesting going on in big science!

They opened the telescope right at sunset, when Stan took our group shot above. One of my plans was to borrow Ken's new Canon 6D camera to take some time-lapse images. When I last did it in 2008 with my Canon 20D, I had to use 6 minute exposures in the dark enclosure with ISO 1600 and an F/3.5 lens. Such a long exposure necessitated using in-camera darks to reduce the hot pixels, doubling the exposure again - only 5 frames per hour! With Ken's new camera with its larger, full 35mm format, I used an F/2.8 lens and ISO 6400 for only 60 second exposures, no noise reduction required! The difference was night and day - likely the subject of a subsequent post. At left is one of these 1 minute exposures. The red lights at lower left is Mike or Stan at their camera taking exposures. Thru the open door at left center, the peak of Mount Graham can be spotted and to the left of that door, the crescent moon was casting shadows of the enclosure on the far wall. There were a few thin clouds in the sky, but spectroscopy isn't much affected by them. After my hour or so of 1 minute exposures, before packing up, I took an image or two out the dome enclosure. Shown at right, the lights of Safford, Thatcher and Pima can be seen. Off in the distant left, the bright spot is likely Fort Thomas, the more distant glow over distant mountains is likely Pinetop-Lakeside/Show Low, reflecting off the clouds from over 100 miles away. The North Star, Polaris is the brightish star at upper left center, and the constellation Corona Borealis is in the clear spot at upper right. Also spotted is a greenish layer of airglow low in the sky...

Being a one-time telescope operator myself, it was fun to spend some time with Geno, who was just starting his week-long shift at the scope. Turns out in a former life we worked together - he worked at WYKO here in Tucson and measured some samples for me. Anyway, the work as a telescope operator has certainly changed in 35 years, though technology has too. He demonstrated how he optimized the mirror figure in real time using a star and Schack/Hartman sensor to fine-tune the mirror supports. In a couple minutes the image improved from about 2 arcseconds to sub-arcsecond. At his fingertips he had everything from weather satellite images, all-sky cameras, and readouts from all around the building. They were all needed as he was responsible for the safety and well-being of the telescope. Unfortunately, when I took his photo (an HDR where several exposures are blended), for some reason I had turned off the autofocus and they were out of focus... Oh well, I like it well enough to include.

Well, I've more to show you, but will have to wait for another time...  Stay tuned!

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