Thursday, February 1, 2018

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.

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