Tuesday, April 10, 2018

Using the tunable filter

One of the most difficult experiments we did in my undergrad physics class involved calibrating a finicky Fabry-Perot interferometer. The MMTF tunable filter on IMACS at Magellan works on the same principles, where you precisely calibrate the alignment and spacing of two parallel plates to allow only a small range of wavelengths to pass through. After talking with fellow Carnegie postdoc Rosalie, we had an idea for a possible project which would involve the tunable filter, and decided to go for it.

We allotted ourselves a big chunk of time in the first afternoon to get everything set up for the first time, and after some skype help from Ben Weiner, got our calibrations all set for the night. We were pretty happy about this, come sunset:

(Decker and Rosalie, after successful calibrations, trying not to think about the clouds in the background)

After some threatening clouds, things cleared up enough to start taking data, and we got on our science target:

(Science data with the MMTF!)

I'm super excited about what we're seeing in the quick-look of the data, and looking forward to seeing what happens after the full reduction!

Unfortunately, the clouds did end up rolling in halfway through the night:

(Clouds seen on the satellite image over the sad red dot which is us)

So, we'll have to try again tomorrow night and hope for clear skies.

Thursday, February 8, 2018

PFS Upgrades Series, Day 15: El Final

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.

So....this happened last night.

As in, the entire night were were closed due to high humidity. Boo. But upon leaving the telescope around 5 am this morning, everything was damp and drippy, so I have no problem with the telescope operator's decision. It was just a bit of a fizzle end to our awesome two+ weeks here at LCO working on PFS. 

Per usual, I started with a focus test, to see if it had changed since the night before. Since the instrument was nearing its ideal temperature, I expected little change in the focus value, and actually found the best focus to be the same as the previous night. We took some images to use in a linearity test -- when does the relationship between incident light and recorded signal become non-linear and thus BAD? -- which Jeff started running through an old IRAF script used with the MIKE instrument. We also figured out that the images we took last night (like in the picture I showed, with the red on the screen) actually were *not* fully saturated, so we did the same test over again, changing the CCD voltages to make sure the saturation limit did not change much between the different voltage settings. It did not change enough to make us want to go back to the voltage setting with the wonky bias. I got a nice explanation from Steve about what A_HIGH and A_LOW mean -- basically they are the top and bottom voltage values of a "bucket" that moves electrons along the detector for readout. Steve drew a diagram almost exactly like the "clocking diagram" here. I learned about this in graduate school, but hadn't really applied it to real life measurements/data until now. Knowledge! 

Then the rest of the night was mostly spent watching for the humidity to drop, which it did a little, to something like 77.5%, but never low enough to open to dome. Sigh. I did take the time to read all about the new TRAPPIST-1 results, though! I also sent all the data to Paul Butler, who replied this morning that he'd received it and would work on a reduction soon. We will eagerly await those results.

After getting a few hours of sleep, I got up this afternoon to tour the Giant Magellan Telescope site, which is one peak over from LCO. Funny enough, that peak is actually Las Campanas peak. The GMT site is leveled off and has chalk designating where the dome and mirror base will go -- GMT will be made of seven 8.4m mirrors, built at my grad school alma mater the University of Arizona -- as well as the auxiliary building where mirror coating will happen and an extra mirror will be stored. We also got a tour of the "casino" (kitchen and dining hall) and recreation facilities for the folks living and working at the site now. It's still hard for me to picture everything coming together, but I still got excited visiting the site. 

Each of those circles represents the footprint of a 8.4m mirror. 
LCO from GMT site. Iiiiiity bitty telescopes.
Above: Mosaic in the recreation area at GMT.

Below: Leon ringing the "las campanas", some of the ground-breaking rocks from the GMT site.

But for now, I'm perfectly delighted to work at LCO and use the telescopes here. Part of me is ready to go home, but part of me could stay here forever. Tomorrow Jeff and I go back to the US, while Christoph and Steve are staying a few more nights to observe with MIKE, another high resolution spectrograph that Steve built. Jeff and Steve will be back here in March to install a new dewar in PFS and hopefully something to control the icicle formation and melting that has been happening in the tube were we fill the dewar with nitrogen. At some point we'll install fibers and a pupil slicer, I hope by the 2018B semester. I won't be back until May for more PFS observing, when, I realized, it will be my 10 year anniversary of coming to Magellan! My first visit was right after I graduated college in 2008, when I was finishing up an internship at Carnegie DTM with Alycia Weinberger, who continues to be a great mentor and friend. So many good memories here! 

I'll sign off with some pretty pictures. :)

Hawk friends saying goodnight last night. 
I always think of the Stairs of Cirith Ungol when I go up and down these. I don't know why, they are happy stairs, not scary stairs!
The previous photo was look down the stairs after climbing them, this photo is what you see when you reach the top. See, happy stairs! From left to right, Clay Telescope (Magellan II), auxiliary building, Baade Telescope (Magellan I).
Looks like a good night tonight! I will be spending it sleeping, but hopefully the humidity stays low for the observers.

Wednesday, February 7, 2018

PFS Upgrade Series, Day 14: Getting Into the Groove

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.

Last night was our third night on sky, and it really started to feel like observing with the "old" PFS. The last two weeks, I/we have been super focused installing new components and getting them to work, and then getting the instrument as a whole working the way we want and expect it to. That has been tiring but also extremely satisfying in its own right -- for instance, when we finally figured out how to do the optical alignment with the HASO, or when we (Jeff really) got the slit mechanism working. But it wasn't until last night that it seemed to all come together, and come back to the scientific goal of the whole project, finding and characterizing planets orbiting other stars. The data we are taking on this run may or may not actually be used to do this planet-finding work directly, but it most certainly will help us figure out how to take and reduce data in the near future to do just that. I think it's rare for astronomers to be so fully connected to a project as I feel I am with this one, and I'm not even dealing closely with the software side of things, which is a *huge* part! I feel very, very lucky to have this opportunity to work with this team of folks on this instrument. 

Before diving into 1x1 binning observations of some stable stars, we did another quick focus test of the instrument, as well as played around with the voltages on the CCD to mitigate the weird bias pattern I mentioned yesterday. In the photo below, Steve is keeping track of what voltages Christoph inputs into the CCD controller and what the images look like; we wanted to see if saturating the detector had different effects with the different voltages. Turns out it didn't, so we settled on a setting of A_HIGH=7 and A_LOW=-6, although we (or at least Christoph and me) don't know exactly what those values mean. But it evens out the bias structure the best! We still have those residual bright columns on the right side, but we hope those can be masked out in the reduction. Our contact at STA,  Kasey, said, "Based on the shape I think we are seeing residual P+ from the thinning process. I don't think we will be able to reduce this more without jeopardizing other aspects of the device.  The column defect is now generating more charge so it is near the surface." 

We still like to take paper logs. Call us old-fashioned. 

The weather last night was pretty good, but the seeing deteriorated during the middle of the night to >1''! Yick. It settled down towards the end of the night, but we were almost through by then. 

Clay seeing is in red, Baade (the other Magellan telescope) in blue. See that big spike around 5:00 UT? 

We also got a few errors from the GUI last night, after trying to do loops of exposures, so I'll have to ask Christoph about that. He added a nice feature in the GUI where we can reconnect to the CCD controller, rather than having to go manually reboot it, but it still takes a minute or two, which we'd like to avoid wasting on non-engineering nights. Tonight the plan is to observe the same stars we've been observing every night (ha, does anyone remember Pinky and the Brain?), and transfer the data to Paul Butler at Carnegie DTM in Washington, DC for more in-depth analysis. We sent him the first two nights of data already, although I don't know that he knows it...I shall email him now! 

Tuesday, February 6, 2018

PFS Upgrade Series, Day 13: Windowing, Bias, Binning, Oh My! And some modern art.

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.

Last night started off a bit faster than our first night, namely because we didn't spend a few hours opening up the instrument to make adjustments. While Steve gave Leon a tour of the Magellan Telescopes, and Jeff worked on getting the dewar heater working, I started another focus run with the instrument, since it had started warming up a bit more. The ideal temperature is 24.7C, and by the end of the night we were almost there! Then of course we had to fill the dewar with liquid nitrogen to keep the CCD cool, but we are definitely closer reaching our desired optimal temperature. Usually this is achieved before or shortly after observing begins, but because we had the instrument open and moved it and started observing right away, we have to wait a few days. 

During the rest of the night, I would say there were two significant points/items to deal with. One was the windowing and binning of the image, and the other was the structure in the CCD bias. We knew all along that we wanted to window the array -- cut off some of the bottom since there is not much light there, and because it is shadowed by the slit assembly -- and we got that working last night! I forgot to take a without-window image, but you can see the dark region in a calibration image from Sunday. 

Then, you can see in the photo below two images displayed in DS9,  the one on the left with windowing and no binning, and the one on the right with windowing and binning 1x2, in the spatial direction. Both of these things -- windowing and binning -- cut down on the file size, and the binning cuts down on the readout time from the CCD to a saved file.

However, after more discussion and pondering last night, we (Steve especially) is not sure 1x2 binning is really the way to go because it could make flat fielding harder if the flat field is not uniform. Tonight we're going to take all our science observations in 1x1 binning and then check for sure which way is best, or rather, ask Paul Butler to reduce the data and tell us the answer. :) We're definitely going to stick with the windowing, though. 

The other issue was/is the structure in the CCD bias. Christoph spent some time today emailing with STA, the company that made the detector, to try and work out how to fix the problem. It seems to be caused by spurious charge in the CCD, but we have to decide on the exact voltage values to use to balance between reducing the gradient in counts across the detector versus increasing the counts in a few columns, which might complicate the reduction.

Bias we were working with, no change in voltage. 
Bias after Christoph changed the voltage. You can see the super bright/bad columns on the right side.
Other than these things, most of last night was spent taking ~science~ data! More standard (low variability) stars, more templates. We did run into a few issues with errors popping up in the GUI, but we think that was due to modifying the PLC code while also trying to take data. I got a fright when I saw all these error messages, though, they just kept coming! 

Also, I think we might make some extra money on the side for PFS by selling our "snap" images (flushing out the detector after a restart) to modern art museums.

Night 3 commences shortly! I've now been away from home for two weeks, and it will be another week until I return. We leave LCO on Friday but before going home I'm stopping over in NYC for a meeting about a new observational survey in SDSS-V, the Milky Way Mapper. It should be a productive, informative meeting, but I think I might need a day off when I get back to Pasadena...

PFS Upgrade Series, Day 12: First Night of Observing on Sky

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.

Last night was our first night on sky with PFSv1.5, and it went...okay. The weather did not cooperate with us, so we had clouds intermittently throughout the night, getting worse as time went by. At one point I couldn't even see a fifth magnitude star (which is really bright!), so that was a bit frustrating. We spent the time trying to take new template (iodine-free) exposures of a few bright, stable stars, for which we have some "old" PFS data to compare to. We need the iodine free exposures to analyze the iodine exposures and measure if there are very small changes in the stellar absorption lines indicative of planets. Actually, for these stable stars, if there are planets they must be very small, since we already know they do not have large radial velocity signals. The idea is to monitor these stars every night if possible, to compare the resulting precision to that of the "old" instrument. We got through three and a half stars (with the half being a template but not an iodine exposure), so hopefully we can get those again tonight plus a few more; the weather looks clearer, although the humidity is still a bit high. 

Oh, I forgot, we also redid the focus sequence with the install instrument, and found it changed a bit after the move, and with temperature. We'll have to do it again tonight as the instrument has changed temperature again, equilibrating to around 23C. 

Today our friends Charlie, Leon, and Nick from Carnegie showed up. It's good to see friends here! I'll try to get a photo of all the Carnegie folks at some point. 

I don't have any pictures from the rest of last night, so I will leave you with some more viscacha photos, and a few of telescopes. I have to say, being and observing at LCO never gets old for me. Every time I walk up the road to the Magellan telescopes, or out to du Pont, I feel deeply grateful and lucky that I get to come to this mountain, work with wonderful people, and study the universe. And yay, we just opened the dome for Night 2! 

Hello telescopes! Yes, I have about fifty pictures that look just like this, but the view never gets old!

Look at that sky! Stay away, clouds. 

Sleeping giants.
From yesterday, I see you, friend! 
Yesterday, later, sneak check.

Sitting upright, this afternoon after lunch. 

Sunday, February 4, 2018

PFS Upgrade Series, Day 11: Moving The Instrument (and things inside of it), Again

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 started off the day as I usually do, with a walk out to the du Pont Telescope, but since I slept in a bit I was taking this walk later than I normally do. I was lucky enough to see some guanacos! 

Okay, but to the business of the day -- moving PFS from the clean room. 
PFS, ready to get buttoned up and moved!

First we had to put the side panel back on. Here is Emilio helping to take off the straps after we aligned the side panel and put all the screws in around the outside of the panel.

This time I took a time lapse of the process of loading the instrument onto the truck. I mostly stayed out of the way but you can see me come in towards the end to help raise the instrument to turn the wheels, then lower it again. 

And after another harrowing walk, this time up the hill, we made it safe and sound. Again, super big props to the LCO staff. They are making our science possible! 

Putting the instrument on the telescope is in itself not trivial, let alone moving it up the hill first! We lift the instrument up to the dome platform from the ground level using an elevator, on which we have to take off most of the side railings to accommodate the instrument. Once the elevator is aligned with the nasmyth platform, it is rolled off onto the platform, where we plug in the electronics, glycol feed, and ethernet cables. We also install our custom telescope guider cover plate that narrows the light beam right into our instrument, and in that path we put a baffle and a filter that cuts off some  of the red light that, for our purposes, we aren't that interested in. Then we gently maneuver the instrument so it is lined up exactly with three spherolinder mount plates, in which we place spherolinder blocks. The blocks align with holes in the bottom of the instrument cart, and we lower the instrument so that its weight is mostly supported by these blocks, rather than the wheels of the cart. That is a slightly simplified version of the procedure, which is detailed here, and the whole thing takes about an hour if all goes well. 

Above: You can see the three spherolinder blocks in their mounts, two in the foreground and one in the background. Below: Close-up of pre-slit assembly, with guider camera and glycol feed plugged in at the top. Here to the right is our guider cover plate (big round thing with handles), and the baffle and filter in between the two (little round connectors).

After we got the instrument installed, we spent the rest of the afternoon making sure the GUI was working, calibrating the slit positions, and examining images to convince ourselves we were good with all the settings/positions of the CCD and grating. 

Our first frame of real data at the telescope! See, it says "GUANACO WORKSTATION".

However, upon this examination, Steve decided he did not like how we had positioned the blaze on the detector, and he wanted to move the grating by a little bit. So, after dinner, with the instrument on the platform, we took off the side panel closest to the grating -- eeps! -- and took off the back end of the grating can to tilt it a bit more in one direction. This also meant we had to break the vacuum inside the grating can, so we'll have to pump that down later, meaning we'll have to move the instrument a bit on the platform to be able to fit the vacuum pump close to the grating valve. Phew! But we made Steve happy, that's what counts. 

Above: Side panel of instrument floating in the air in the dome. Don't worry, we put it on the ground, we did not leave it hanging in mid-air. Below: Grating adjusted to get the blaze in the Steve-approved position, see right monitor, plot with a bell-shaped curve. 

Before we replace the side panel (we've been using a black piece of cardboard to keep it relatively dark), we want to take a stellar spectrum to verify the positioning of the light in the spectral direction. That is, do we get our coveted Ca II H&K lines in the blue and the Halpha line in the red? If so, which I suspect is the case, then we are good to go!

I'll report back tomorrow, but for now I'll leave you with some glamour shots...by which I mean in black and white. 

Steve examining the electronics box as we wait for the transport truck.

Jeff and his instrument, waiting on the truck for some straps to hold it down.

Christoph, me, Steve, and Jeff, after PFS was closed up and we were waiting to move it up to the telescope.

UPDATE: 20:37 local time WE JUST GOT OUR FIRST STELLAR SPECTRUM with the new instrument! You can see vignetting at the bottom because we took out the filter as an experiment, but those photons are from a star.

Saturday, February 3, 2018

PFS Upgrade Series, Day 10: Focus, Focus, Focus

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.

-Get newly trimmed slit mechanism side panel from Gaston and install
     Did this morning
-Heat tape for dewar to keep the temperature stable when we fill it with liquid nitrogen
     Jeff is working on as I type
-Figure out what is wrong with two thermistors that are giving wonky or no reading
     Probably saving for next time
-Figure out what's wrong with the connector for the slit mechanism
     Saving for next time, we have Steve's cable as a fix for now
-Stuff insulation in every little corner and around any opening to the outside
     Did a bit after dinner, Jeff will finish up
-Close up instrument and move up to the telescope
      Tonight and tomorrow after lunch! Eeee!

Missing from the to-do list is, of course, finishing the focus test. As a reminder, we tried five to six different focus values with four different shims and measured twelve lines in each image we took, resulting in 360 lines for which we measured the full-width-half-max (FWHM) in both the spectral and spatial dispersion directions. Jeff stayed up way late last night to get his code working and the measurements read in, to produce the plots shown below. Each page represents a line, with a spectral dispersion FWHM plot (top) and a spatial dispersion FWHM plot (bottom), with four parabolic fits each for each shim. Phew! The idea was to see which shim gave the best (lowest) FWHM values, and how this changed across the face of the CCD (represented by the twelve lines, three in the vertical direction and four in the horizontal direction, since there is more change from left to right on the face of the CCD). This would tell us which shim to use, or some intermediate value between the actual shim thicknesses we tested, as well as how tilted the CCD is in the right-left dimension. 

Focus plots that Jeff made. SUPER useful!

From these plots, we saw that the focus value shifted by about one "unit" from left to right, so that told us how much tilt to introduce into the CCD mount so that the focus would be as uniform as possible. Then, we saw that the third shim (the third from the left in the parabolas below) gave consistently the best focus values, as well as the lowest differences between the spectral and spatial FWHM values, suggesting the most circular shape.

Steve wanted to verify things by looking at the images themselves, which he worked on which Jeff was making more plots and I was on a telecon with colleagues Steve Howell and David Ciardi. I wanted to talk to them about a paper I'm writing, on which they'll be co-authors, about the effect of binary or multiple stars on our measurements of exoplanet radii. Rachel Johnson, a post-baccalaureate student I've been working with, is also a co-author. Hopefully we can get that paper written and submitted by the end of February, only a month later than I originally expected. 

From Steve's by-eye examination, we settled on using the second shim with some washers also attached on one side to help fix the tilt. Jeff and I got to installing those, and then Christoph helped us run another set of focus images to make sure we were happy with the configuration we chose. Actually, we didn't know a priori which side to put the washers on, but guessed the side closest to the opening of the instrument and were right. Phew! It was already hard to get the washers in between the shim and the CCD mount on the closest side; I think we might have had to remove things to get to the far side. 

So, I left Jeff and Steve puzzling over a bit of dripping inside the instrument that we hadn't see with the old detector, to come write and get some rest. Tomorrow is going to be a really long day -- moving the instrument after lunch, installing it on Magellan II, making sure all the electronics are working, and doing another focus test. We found the optimal focus from our test this afternoon, but things might shift a little during the moving tomorrow so Steve wants to do another, more quantitative and comprehensive test. And then we are supposed to be observing tomorrow night! 

The four largest telescopes at Las Campanas Observatory, including Magellan II (left-most of top two telescopes), where we'll be working and observing from starting tomorrow. Home away from home. :)