PFS Upgrade Series, Day 8: Spectra Success! But Also Frustrations.

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.

This morning Jeff and I went into battle with the slit mechanism. After taking it apart and putting it back together several times, Jeff asked to see the older version of one of the enclosure side plates. Low-and-behold, an indentation in the old plate, made to allow a screw to travel and not get stuck on the plate, was not as large on the new plate! Ack! We thought this had to be the source of our difficulties in getting the slit mechanism to engage. Luckily, there's a machine shop on the mountain -- where Oscar drilled holes in the same plate a few days ago -- and we got help from another machinist, Gaston.

Old plate -- see that little oval-shaped indentation? The new plate had that, only shorter in length. That's probably because the original drawing, which Jeff went off of to make the new plate, hadn't been updated with some change they made after the first design. 

New plate, with freshly-milled indentation. You can see the shape of the old indentation in black, and where Gaston milled the plate in silver. 

That new indentation did help a little, but it didn't totally solve the problem; the slit mechanism would still not run properly. After another couple of hours fiddling with it, Jeff finally got it to work; the trick seemed to be placing one component in exactly the right position. Also, when we were walking down to lunch, Jeff remembered that we could also change the power going to the moving parts of the slit mechanism, and that that might help it to not get stuck. He tried that after lunch, and it did help, but ultimately we settled on keeping the power the same. 

After lunch we ran into another issue with the slit mechanism that Jeff and I are still incredibly puzzled by. Remember how Steve made that extension cord for the slit mechanism, so we could plug it into the in-instrument connector but then still be working on it outside the instrument? Well, the mechanism works when we use that extension cord, and doesn't work when we don't use it. Really, we verified several times. Our best guess is that one or more of the fifteen pins on the in-instrument connector is mangled in some way, but it's not obvious. We may just end up leaving the extension cord inside the spectrograph. 

Another small issue with the slit mechanism is that the other side plate is a bit too big. We'll have to get Gaston to mill it down for us tomorrow. I don't want to give the impression that Jeff made a bunch of mistakes that we have to correct -- this is *not* the case, it's just that things were not machined with updated plans. Like I said, luckily we have a machine shop on site! 

The rest of the day was mostly playing around with taking images and spectra through the slits. Christoph supervised us using his GUI, which he is continuously updating with our preferences and based on bugs we find. Christoph has also been trying out different settings for the CCD, like how quickly it moves the charge down the rows, and what the low temperature point should be before the dewar heater kicks on. 

So, we ended this frustrating but ultimately satisfying day with our first dispersed light images from the upgraded PFS. Jeff is very adamant about pointing out we have not determined the optimal focus of the instrument, which we'll do tomorrow, but I still think these images look pretty good.

Above: Screen shot of iodine frame, where we illuminate the slit with a quartz lamp and put the iodine cell in the path of the lamp light. You can see lots of absorption lines in the middle of the frame -- those are all of the reference lines we compare to stellar lines to look for shifts in wavelength indicative of planets! In this image red is down and blue is up. Below: Screen shot of old thorium argon exposure (left) and new thorium argon exposure (right), roughly scaled to the real physical difference between the two detectors. Mmmmmm pixels. Red is up in these images.

I have to say, today was frustrating in more ways than one. The new batch of 51 Peg Fellows were announced today. From the Fellowship webpage,

The 51 Pegasi b Fellowship provides exceptional postdoctoral scientists with the opportunity to conduct theoretical, observational, and experimental research in planetary astronomy. Established in 2017, The Heising-Simons Foundation 51 Pegasi b Fellowship is named for the first exoplanet discovered orbiting a Sun-like star. The growing field of planetary astronomy studies celestial objects both within and beyond our solar system, bridging planetary science and astronomy. From accelerating understanding of planetary system formation and evolution, to advancing new technologies for detecting Earth-like worlds, 51 Pegasi b Fellows make unique contributions to the field.

This is thus a new but lucrative postdoctoral fellowship that has the potential to significantly enhance exoplanet science, and the careers of those who get the fellowship (and their mentors). As someone who also studies exoplanets, I know or am familiar with the work of almost all of these Fellows, and I am sure they deserved this recognition and will go on to do amazing work. But last year 1/4 fellowships were awarded to women, and this year 1/8 fellowships were awarded to women. I don't have the statistics yet (working on it!), but from anecdotal experience, especially among graduate students and postdocs, the subfield of exoplanets has one of the highest percentages of women in all of astronomy/astrophysics. There are probably a lot of reasons for that, but it means that 1/4 or worse, 1/8, does not adequately represent the actual percentage of women working in the subfield. The selection process for these fellows is different than many other US-based fellowships, and could contribute to the disparity in the number of women awarded fellowships. 

I am a scientist, and science is based on evidence, and I don't have all the evidence to fully support that claim. I also don't want to dismiss the quality and potential of the people selected for the fellowship. But it is very troubling that so few are women, especially when the percentage of women who make it through the academic pipeline to senior positions in physics and astronomy is still very low (huh, Heising-Simons seems to know this...). The 51 Peg Fellowship is only two years old, so in theory would be steeped in fewer traditions or assumptions that could disfavor women because we know better now. So what happened? Furthermore, how can the Heising-Simons Foundation espouse increasing of the percentage of women in physics and astronomy and not see how they may be contributing to doing the exact opposite? I hope in the future both the select universities that are allowed to submit two nominations each for the fellowship (yes, that's how it works), as well as the selection committee, will carefully examine their practices and consider the real impact they are having on exoplanet research, and science overall. 

I credit Sarah Hörst for bringing this to my full attention today.

PFS Upgrade Series, Day 7: Reassembly Begins! And Two Problems.

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 started to feel like we were on the downhill part of a hill we had climbed up starting last week. Steve deemed the optical alignment as good as we could get it without more major changes (like, new lenses), and so this morning Jeff and I dismantled the wavefront sensor and replaced the reference mirror with the grating. Next, with Christoph and Steve's help, we replaced the top of the instrument (the roof), and took off the other short side panel so that Jeff could increase the size of the vacuum valve hole that feeds to the dewar from outside of the instrument. Before lunch we mounted the new dewar+CCD in its new mount in the instrument, and then over lunch we used a vacuum pump to decrease the pressure in the CCD dewar down to ~1x10^-6 millibar. After lunch we wanted to try and get images from the CCD, which we were able to do -- just a simple bias, but still exciting! -- but we ran into two problems that turned out to dominate the day.

PFS, slowly looking more like its complete self. Here Jeff is installing our new CCD/dewar. 

We have life! This is Christoph's computer, running the beautiful GUI he designed for PFS. The real data frame is shown on the left. It wasn't totally dark when we took it (just covered the front of the CCD with some cardboard and turned off the lights).

Hello beautiful new 10kx10k, 9 micron pixel CCD! I helped level you a few months ago, remember?

The first problem was a continuation of yesterday -- we still haven't gotten the slit assembly to function properly, so we can't take images through the slits. Big problem, we know! Shec built a connector that would run from inside the instrument (like, sort of behind the dewar), where the pre-slit assembly will plug into the slit assembly inside the instrument, to the slit assembly itself. This will help make it easier to make tweaks to the parts inside the slit assembly (which I showed pictures of yesterday), versus making a tweak, plugging it in and trying it, unplugging it and making a tweak and repeating; we can do everything with this effective extension cord. I helped Shec put it all together (and again, by help I mean mostly watch). Tomorrow we'll keep trying. I'm sure we'll get it  to work eventually...and then we can take real SPECTRA!

Above: One end of completed connector.
Below: Getting ready to solder the other end of the connector. Soldering, yay!

The second problem was that the CCD dewar did not seem to be holding the vacuum after we filled it with liquid nitrogen to cool it down. The vacuum gauge inside the electronics box was reading a steady 1.9x10^-3 mbars, when it was supposed to be going down to 0.1x10^-3 mbars as the charcoal getting inside the dewar cooled and adsorbed the gas remaining in the camera. Christoph was the one who noticed it really wasn't changing, which was worrisome. Jeff had the great idea of circumventing the software limit on the minimum vacuum needed to get the ion pump working, with the idea that maybe the dewar vacuum gauge needed to be reset, since we installed the new dewar/CCD. And it worked! We were able to get the ion pump to engage, which meant that the vacuum inside the dewar really was at or below 0.1x10^-3 mbars, and the ion pump itself gave us an independent reading of the vacuum inside the dewar, which was something like 1x10^-6 mbar or lower. Problem solved, yay!   We reset the dewar vacuum gauge so that it "knows" now what the real readings are. (Don't worry, Jeff reset the dewar vacuum software limit on the ion pump to where it was before, too.)

Ion pump is on and reading a pressure of below 10^-6 mbar, excellent.

We are happy when we solve problems! From l-r, Me, Christoph, and Steve. You can see the Magellan Telescopes in the background! We've been working in that group of red-brown buildings on the hillside below the telescopes.

What's left to do, at minimum, is get that darn slit assembly working, and figure out how to shim the dewar so the focus in the spectrograph is optimized. Hopefully we can get both of those things done tomorrow...? We'll see, stay tuned!  

Today's animal sightings included a viscacha! They like to hang out up in the rafters, away from prying eyes. 

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. 

PFS Upgrade Series, Day 5: So Good It Can't Be Right...Can It?

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.

Yesterday we aligned the lenses in PFS as best we could, and measured small optical aberrations, small enough that we didn't want to change any of the lens orientations. Today we wanted to isolate and measure any potential optical aberrations in the prism in the instrument, which is rather thick so could have a gradient in its index of refraction that could contribute to the distortions we see in the data (or at least did, prior to these upgrades). 

First Jeff and I installed the "can" that houses the grating and prism for the instrument. We made a time lapse that isn't terribly exciting, but gives a good idea of what instrument work can be like, I think. I stopped recording before we removed the grating, although you can see Jeff take off the grating cover in the video (when we are wearing the face masks to avoid spitting on it). It was hard to find a good position for the camera to record the grating removal, plus I didn't want the added pressure of looking pretty on camera. :) The grating was heavy and in an awkward position, but Jeff took it off without a scratch, like a pro (which he is)!

Above: View of the grating (big rectangle thing) and the prism (mirrored thing) after we took the lid off the can. You can also see the *real* clean room in the background. We're being pretty careful but haven't gone full bunny-suit. Below: View of grating from the other side. Those silver poles help hold the lid of the can, which we took off. The black background is one of the long sides of the instrument. 

After we removed the grating, we put the same reference mirror from yesterday in the place of the grating; you can see it in the first photo below, looking at the mirror from the back towards the wavefront sensor. Jeff build a special holder (metal plate in the second photo below) to support the mirror at the right angle. You can also get a sense in that second photo for how efficiently the design of the instrument is in terms of space -- it's a tight fit but everything is perfectly organized. Steve told me a few days ago that this instrument is a work of art, and Jeff is "an artist" (pronounced "ar-teest").

As you might expect, we had to futz around with the wavefront sensor for a few hours to get a measurement of the prism that we believed. But the result was surprising -- the small aberrations that we found yesterday from the lenses alone changed *very little*. The only really significant change was in one of the astigmatism values, which changed by about 0.1 microns; everything else changed by 0.01-0.02 microns at most! We think (and spent some time convincing ourselves) that this means the prism introduces no optical aberrations, and that the source of the distortions we see in the actual data from PFS is the exact placement of the detector/dewar. Yet again, it seems that Steve and Jeff did an amazing job when first putting together this instrument! Oh, and that the prism is good; Steve suggested we send a holiday card to the company/people that prepared the prism for the instrument. 

Our set-up for the day. Note the mirror on the right side. It's sort of starting to look like a spectrograph again!

After lunch Steve was determined to see if we could get an even better measurement on the whole lay-out. We had been using a reference image that was provided with the wavefront sensor, to get a relative measure of the aberrations that took out whatever "initial" aberrations were present in the wavefront sensor measurement (without going through any lenses or mirrors). It's kind of like if I stood on a step and you measured my height -- first you'd want to know how tall the step was, then you could back out my actual height from (step+Johanna) and (step alone). 

After lots of iterating on this intrinsic measurement reference image, and applying it instead of the provided reference image, we *were* able to decrease the aberration values! Not by a huge amount, but at this point even 0.1 microns was significant. I don't have a picture of that pupil image or those zernike values, but the largest one was about 0.25, and the final wavefront RMS was 0.14 microns! (Okay, that's not counting the spherical aberrations, but we can't do anything about those.) We are happy. 

Before dinner, Jeff started pumping down our shiny new CCD to get it ready for testing by our colleague Christoph, who arrived today from California. Below you can see the difference between the old CCD/dewar (right, standing upright) and the new one (left) -- the new one is larger because it holds a 10k x 10k CCD with 9 micron pixels, versus our old 4kx4k CCD with 15 micron pixels. The new CCD was necessary to increase the sampling to match our new fiber feed (that will replace the traditional slit where light enters the instrument). The fiber feed isn't ready yet (whomp whomp), but hopefully that will get installed in the next trip. 

The theme of today seemed to be birds that hunt/eat meat. On my walk this morning I saw a beautiful owl -- the photo below doesn't do it justice -- who followed me with its eyes as I walked by. It's a little disturbing how their heads turn all the way around. Then later during the day, we all had encounters with a hawk (or maybe hawks, there are two) that flew close to us and in Jeff's case was curious enough to approach him while walking on the pavement. Are birds of prey our good luck charm? We'll see. I'm a little worried they are driving away the viscachas! 

PFS Upgrade Series, Day 4: Rollercoaster!

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.

As you may recall, on the first day of PFS upgrades, we had to move the instrument from a building at the top of a hill down the hill to another building, where we are working now. This was a literal down-hill move, and we'll have to go back up again in a week or so to (hopefully) use the instrument on the telescope. But today, we started at the top of a figurative hill, fell off and mulled around for a few hours, and slowly climbed our way back up. 

Caveat: This is my impression of the day. I'm not as experienced in this work as Jeff and Steve, so I'm certainly simplifying things, but hopefully not getting things really wrong. 

We started the morning thinking that we had defined the optical axis of the instrument, and were thus ready to start measuring the alignment of the collimator/camera optics of the instrument, pictured below. Jeff and I bolted this piece to the optical bench inside the instrument this morning, using the hoist to help lift and position it. Steve arrived and we thought we were all ready to go, but we soon discovered that (1) the pupil image was offset from center on the wavefront sensor when using the objective lenses that came with the sensor [and our optical set-up], and, relatedly, (2) when we changed the focus of the set-up by moving the wavefront sensor, it introduced significant aberrations (astigmatism and coma). The expectation was that this shouldn't happen.

Above and below, our set-up this morning. The paper on the flat mirror (seen below) is to restrict the area we are analyzing to match that of the real instrument on the telescope. I think this is before we put the objective lenses on the wavefront sensor; I can sort of make out our metal pinhole attached to the wavefront sensor on the left.

Observing something one doesn't expect is sometimes exciting, but in this case was very puzzling, such that we had to ponder it over lunch. After we had fun talking about a possible new speckle camera for Magellan, we decided to put a metal pinhole in front of the wavefront sensor and try to get the light to come out of and go back into the pinhole, after going through the lenses, off the mirror, and back through the lenses again. We planned to do this by adjusting the wavefront sensor and *not* the flat mirror on the other end of the optical bench; we wanted to preserve that well-defined optical axis. For the same reason, we were reluctant to tilt the wavefront sensor stage -- moving it in x, y, and z was easy to "undo", because the knobs have gauges, but the two tilt knobs do not, and are very sensitive. 

We tried this set-up, with no tilting, but were still having the same focus problem, and (I think?) the pupil image was still not centered on the wavefront sensor. At this point I stepped out to get some sun and then call my mom. When I came back into the clean room, the plan had changed. Steve and Jeff thought they had worked out how to interpret the alignment procedure in the wavefront sensor manual, and were executing it. We thought we had done it correctly before, but really had not. Go figure! The true alignment procedure consisted of installing the pin hole provided with the wavefront sensor in front of the sensor, and moving the wavefront sensor stage in the (x,y) directions until we could align the point of light coming back to the sensor with its center. It was kind of like trying to play skee-ball and get the ball right in the center of a hole to get the most points. 

Then we took out the pin-hole and used the tilt screws on the wavefront sensor stage -- yes, we changed the tilts! -- to fully center the pupil image. We iterated this procedure a few times, also trying to minimize the tilt and curvature values (by adjusting in the z-direction of the wavefront sensor mount). In the end, we got a very nicely centered pupil image, a small focus offset, and small optical aberrations. 

Centered image (large gray/black graphic and pink intensity map), yay! Also, it maybe hard to see, but the middle lower window lists the Zernike coefficients, which correspond to different deviations in the wavefront (light path).

We think this is the correct alignment procedure to use, such that any aberrations we measure are now due to the instrument optics and not the wavefront sensor itself. But -- second unexpected thing of the day -- the aberrations were very small, tenths of a micron! This means that the original optical alignment of PFS that Steve and Jeff did almost ten years ago, without the fancy-shmancy wavefront sensor, was very good, good enough to not change any of the lenses now to try and improve it. It took about an hour for Steve and Jeff to convince themselves that they really did do such a good job aligning the instrument originally, given that we do see some aberrations in the images PFS produces when in use. That is, something must be causing those aberrations, but it appears not to be the lenses. 

I was honestly very excited (and impressed!) by this news, but it was also kind of a "whomp-whomp" moment, since this source of aberrations would have been the easiest to fix. Tomorrow we will examine one of the other potential sources, inhomogeneities in the prism, but this isn't really fixable; we can't change anything about the prism other than getting a new one. If the prism is obviously the cause of the aberrations, we could try tweaking slightly the lenses to correct for the prism, but that's dicey. A third source of aberrations could be in the exact position of the dewar (holds the CCD detector), but to test that we have to get the new CCD ready to mount. 

So, all in all, a roller-coaster day! 

PFS Upgrade Series, Day 3: Optical Alignment

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.

One of the best parts of my job is learning new things. I like puzzles and intellectual challenges (as well as some physical ones), and very often that's what my work comes down to -- solving challenging puzzles. This process often consists of a lot of trial and error, and can sometimes be frustrating, but it makes solving the puzzles even more rewarding. Today was a day of puzzles. 

We want to make sure that the light inside our instrument will go where we want it to, namely straight through the lenses, off the grating and through the prism and back to the right spot on our detector, so it can record the light and we can detect planets. To make the light go where we want it to, we have to change the positions of the different components in our instrument so they guide the light path correctly. This is one of the three "upgrades" to PFS we have planned -- a precise (as possible) optical alignment of the lenses inside the instrument. 

To accomplish this optical alignment, we want to use our fancy-shmancy Shack-Hartmann wavefront sensor. It produces a beam of light that we can (eventually) use to shine down all of the lenses in the instrument and make sure the light is reflected off the grating and comes right back to the sensor in the same spot. Then we know the same thing will happen when we replace the sensor with our CCD.

We ended yesterday and started today somewhat confused about how to use it; the manual was originally written in French and translated to English, but unfortunately not very well, so it was a challenge to even know where to start. After several hours of just playing around -- turning knobs, watching how the wavefront changed (using the computer software that came with the sensor), turning knobs again, putting in a pinhole, taking it out, etc. We first wanted to make sure that the wavefront sensor itself was producing a beam perfectly perpendicular to our optical bench, parallel with the desire optical axis inside the instrument. Steve developed his own method for doing this wavefront sensor calibration, but we determined this morning that the method recommended by the sensor manual (as best we could tell) worked just as well, and was easier to replicate. Check.

Next, we needed to make sure the light beam from the sensor would hit the grating in the right spot and come back towards the sensor. Instead of using the grating from the start, we are using a large mirror in its place for now. We kind of got stuck at this part -- how could we make sure the light was leaving the sensor and coming back to the same place, and hitting the mirror on the other side of the instrument? It sounds trivial but it was not. Steve had a great breakthrough after lunch, though, when he rigged up a small aperture in front of the sensor, got the light beam adjusted to go through that aperture, and then we adjusted the sensor so that the light beam that fell on the mirror's surface reflected back nearly perfectly through the same aperture. 

The photos above show Steve's set-up for verifying that the light beam from the sensor was properly aligned with the optical axis of the instrument. The yellow arrows in the top photo represent the (ideal) path of light, except really it's all in one line, not two lines on top of each other  The bottom left photo shows the metal beam that Jeff made, originally to hold a lens or mirror, but here without anything in the holder. The blue thing you see through the holder is Steve's homemade "work of art" aperture (paper, blue tape, and a metal washer), which is in front of the wavefront sensor. The wires going across the holder mark the center of the aperture (my photo wasn't perfectly aligned). In the bottom right photo, the reflective mirror at the other end of the instrument is shown (reflecting some tubing!). There is blue tape on each side of the mirror, holding thin wires to mark the exact same spot in space as the wires in front of Steve's aperture (except translated down the length of the instrument) on the surface of the mirror. 

And it worked! Below is a not-great photo of the screen of the computer, showing what the wavefront sensor was detecting when we had Steve's set-up aligned. The green cross in the center marks the true  center of the image, and we were trying to line up our circular image so its center matched that green cross. Actually, first we just had to get the circular image, then make fine adjustments to center it. We did pretty good! (I think there might have been one more iteration of the adjustments after this photo was taken.)

So, step 2 of the puzzle is solved, at least we think so. :) Tomorrow we will start on step 3, which is adding in the lenses that actually go in the instrument and trying to recreate that light beam path that goes out through a pin hole, through the lenses, off the mirror, back through the lenses, and back through the pinhole. This is probably the hardest task we have to do during this trip, or at least the one with the most uncertainty. But that's what makes puzzles fun, right? If you went in knowing the answer it would be boring. Onward towards discovery! 

Sunrise at LCO this morning. How many telescopes can you spot?

PFS Upgrade Series: Day 2, Taking Apart the Puzzle and Putting (Some of) It Back Together

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.

I wanted to focus my post yesterday about moving PFS, but that was really only the first half of the day. During the rest of the day, Jeff, Steve, and I worked to disassemble the instrument into its component parts, beginning with taking off two of the sides and the top. I didn't get many pictures of that work because we were pretty focused, but today I snapped some photos of the parts we took out, as well as the new things we installed (mostly today). 

Above: PFS stopped of almost all component parts! Eeeps! Below: Old dewar, holding old CCD. 

Above: New dewar holding new CCD. So shiny and big (10kx10k!) Below: Pre-slit assembly, which holds the calibration units and our precious iodine cell (here we're looking at it face on, it's on the right inside the enclosure). The pre-slit assembly actually hangs outside the temperature-controlled enclosure (the big white box) of the instrument.

Above: Prism/grating mount, and hoist (see top of photo) we used to move it out of the instrument. That was also really nerve-wracking. Below: White side panel of instrument (insulation), and collimater/camera assembly (lenses and rods).

Above: New pre-slit assembly anchor, which goes inside the instrument/insulation. You can't tell from this photo but the left-most hole (three holes make a triangle) changed its shape in the new design to accommodate a new cable from the new detector. Below: New CCD camera mount, installed on optical table. In this photo, you can better see that left-most hole I mentioned. We don't have the CCD installed here, but a stand for a fancy-shmancy wavefront sensor instead. 

Above: Fancy-shmancy HASO wavefront sensor, now on its mount. We will be using this to optically align the camera assembly. Below: Pre-slit assembly re-installed on side of instrument (top black box). We also installed a new power supply unit (bottom, smaller black box). I tried to rivet one of the holes on the side of the enclosure to mount the new power supply, but my hand strength wasn't up to snuff. Instead I held things and handed them to Jeff.

Steve (left) and Jeff (right), working on setting up our optical alignment software and hardware. More on that tomorrow...

I am really starting to feel the physical effects of instrumentation work, at least this type. I'm not used to being on my feet all day! Good thing I like the people I'm working with (and they are so patient with me), and the food the chefs here cook for us is so yummy. :)