Tuesday, January 30, 2018

PFS Upgrade Series, Day 6: Slits, Plates, and GUIs

This is part of a series of posts about upgrading an instrument at Las Campanas Observatory. If you want to start at the beginning, it's here.

Today was a slower day for the PFS team. That doesn't mean we didn't get a lot of work done, it just meant that we took a bit of a pause to take stock of our progress thus far. From yesterday, you know that we discovered not only were the lenses very well aligned in our instrument, but that the prism was *not* the source of the aberrations we (used to) see in the images coming out of PFS. Steve took time late last night/early this morning to play round with the PFS optical layout in Zemax, plugging in the zernike coefficients we measured and seeing if he could improve upon them by making small tweaks to the lenses. It turns out that he couldn't make any significant improvements, and he honed in on the fact that much of our aberrations are spherical. We cannot easily fix these aberrations by moving the positions of the lenses, so after much deliberation, we (really Steve) concluded that, save getting new lenses that might cause less spherical aberration, there was nothing we could do. Steve is pondering over it some more tonight, but I expect tomorrow we'll close the optical alignment chapter of this upgrade. 

While Steve was working on the optical alignment, Jeff, Christoph, and I were also addressing more upgrade issues. Jeff and I started out the morning pulling apart the old slit mechanism and putting it back together in a different container that fits better in PFS with the new dewar. And by "Jeff and I", I really mean Jeff did the work and I watched and went and retrieved some screwdrivers. As you can see below, this component is made up of many smaller, finicky components that are easy to lose or misalign.

Jeff's workspace after removing most of the slit mechanism parts so we can put them into a new container. The slit plate is near the top center of the photo, it kind of looks like a lower-case "r". 
We had to pay a visit to the machine shop to ask Oscar to drill a few extra holes in the slit mechanism container pieces. The machine shop is in the basement of the du Pont telescope, so Jeff and I took a quick peek in at APOGEE-2S, where by luck the lovely APOGEE observers have been observing plates for me the last few nights! So even though I've been working on PFS during the day, I've still been getting data at night. Niiiice.

APOGEE-2S cartridge holding a plate with lots of fibers plugged into it, bringing the light from the du Pont telescope to the instrument, which is actually housed in a room a floor below the telescope.

More plates ready to go! Or maybe they were already observed? I'm really not sure.

The mighty du Pont (100'') telescope. It's obviously a lot smaller than the Magellan Telescopes but just as impressive, in my opinion. 
Well lookie here! No, really, look in the upper right corner. "Program = TeskeVanSaders"! 

Christoph started testing the connections between the CCD controller, the computer system that controls the whole instrument, and the GUI he created to allow us to control the instrument from inside the observing room versus sitting out on the instrument platform in the dome. Very handy! Jeff and I took a bit of a break after lunch to catch up on email and other work, and then went to see what Christoph was up to. I felt helpful when I pushed some GUI buttons and Jeff verified the GUI was doing the task I told it to do, and when I pointed out a couple of things to Christoph that would be good to change in the GUI. 

New PFS GUI! Here we've just taken a "snap" frame, to verify that the CCD is reading out, which it is (see the eight stripes)? The upper left window is where we control the slits, focus, exposure times, calibration lamps, etc., and the bottom middle window shows all the instrument readings. Those aren't really ready yet since we haven't buttoned up PFS, or even installed the new CCD. The upper right is a magnified look at a part of the image in the middle window.
We ended the day a little frustrated because the slit mechanism wasn't actually moving the slit plate as it should, so we have to revisit that tomorrow. Jeff already took it apart and put it back together a couple of times, it's just very sensitive to small misalignments of the small parts. That's on our agenda to finish tomorrow, along with removing the optical alignment equipment, replacing the grating, enlarging a hole on one of the side panels, installing the new CCD, maybe testing some temperature sensors...phew! I better go to sleep so I'm ready for another busy day tomorrow. 

Oh, but I would be remiss to not mention that I also got to see a friend and DTM colleague tonight, Jonathan Gagné! He is observing for three nights starting tomorrow, but arrived today and had some time to catch up after dinner. Jonathan also helped me get a pipeline for another instrument installed, and is graciously going to take time to reduce data for me taken on that instrument (the instrument is FIRE, by the way). It's data of...let's just say one of our favorite M dwarfs, and even with a rough reduction Jonathan was impressed by the high signal-to-noise of the data, in only a few exposures! And we have dozens! It's going to be a really exciting result, I'm sure. 

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