My duty here on this run is to give Jared and Katie a bit of a break, which includes taking over some of the blogging.
Tonight we started the night by swapping out the batteries in the wind monitor, which meant that we had to tilt the telescope over so that we could get to it. Jared and Katie have done it many times before, so they’re old pros now, and it was fun for me to climb up on the catwalk and look at the backside of the secondary up close.
Me climbing up the ladder to the catwalk. Katie is leaning over to warn me not to touch the orange stuff, which is insulating some high voltage wires.
We had a brief hiccup at the very start of the night because there was a power outage on the mountain during the day. We just had to restart our software, so it was a pretty minor setback.
Hector Canovas and Adam Hardy started off the night with a continuation of their program from yesterday, then we switched over at midnight to observers Francois Menard and Jos Deboer. Things went so smoothly that we had a little time to analyze our blog stats from the last month. Here are the results for the US, broken down by state:
This triggered an argument regarding whose family loves them best. I’d say it’s pretty well tied between Katie and Jared’s families, but as you can see, I clearly lost. Step it up Brutlags!
Otherwise, not much to report tonight from Las Campanas. Trust us, that’s a good thing!
I’m told that I have to pick a song with deep astrophysical meaning to go with my post. This probably dates me, but here goes…
Greetings everyone! Long time no blog for me, but I’m happy to be back.
In between running the VisAO camera to give Jared a bit of a break, I’ve been working on quick reductions of the data that we’ve been getting for the past few days. It’s useful to reduce the data at the telescope because these “quick looks” can tell you whether you have what you need or, even better, whether there’s something interesting and unexpected in your data to follow up. We’ve had a bit of both over the past few days as TJ, Jared and I have been running our reduction routines.
Without getting too much into specifics of the targets, I’ll tell you that I had the following problem popping up in my reductions last night
See how you see a bright disk but also a shadow with roughly the same shape? I had to think about it for a bit, but eventually I figured out what my problem was. To explain the solution, I think I should first explain how this type of reduction works.
My pipeline does a kind of data reduction called “Angular Differential Imaging”, which is a neat way to get rid of light from the star in your image and see faint things near the star. Here is an official introduction to the technique, but I’ll explain it very briefly for blog purposes.
For most astronomical observations, you use a rotator to keep the orientation of your object exactly the same as the sky rotates so that the rotator essentially cancels out the rotation of the sky. For ADI imaging, you turn the rotator off and allow your object to rotate with the sky. If you then line up the star in all of your images and median combine them, anything real around the star will have moved around it over the observation, and so it won’t show up in the combination because it won’t be in any given location in more than half of them. Anything fake (well, most things) caused by the optics of the telescope and instrument though, will be in the same place in all the images so it will show up in the median. In other words, you intentionally smear out the real circumstellar structure while keeping the fake structure the same and recover the so-called “Point Spread Function” (PSF) of the star in the median image.
You subtract this PSF then from every individual image to remove the starlight and then rotate them all to compensate for the rotation of the sky so that the orientation of the object is the same in each frame (essentially the same thing that the rotator would have been doing if it were on). This trick usually lets you get rid of starlight very nicely and helps you to pull faint objects like planets out from the data.
It’s trickier though for disks, which is mostly what we’ve been observing for the past few days. If you have a disk that’s symmetric about the star, then allowing the field to rotate doesn’t help you much and the disk shows up in your median-combined PSF. When you subtract the PSF, you subtract most of the disk light too. Bummer.
For this reason, people didn’t use ADI for disk observations for a while, but it turns out that you can make it work in two situations. (1) if your disk has any features (blobs, spiral arms, etc) that aren’t circularly symmetric, then they’ll survive and (b) if your disk is inclined enough (so that it’s not a circle but an oval on the sky) and you allow it to rotate enough so that the disk light appears in fewer than half the images at any given location, then you can still get rid of it for a PSF.
I’d never used this method with our SDI mode before because generally we use the opposite (continuum) channel as a PSF, but we recently pioneered a so-called “ASDI” mode (see Close et al. 2014). The idea there is that you can ADI both SDI images and then subtract them and you essentially get the benefits of two forms of differential imaging.
OK so now to the problem with my new ASDI pipeline. As an object reaches it’s highest point in the sky (transits), it starts to spin faster and faster. We generally get on these objects about an hour before transit when it’s still rotating slowly. Since the rotation starts out slow, then gets fast for a while, then slows down again, the images aren’t equally spread in rotational space. You take a lot of images during the long interval when the object is spinning slowly and not as many while it it spinning quickly. In this case, we left the object right after transit, so there were a bunch of images at approximately the same rotational position, then a few where the object was spinning a lot. If I weight all images equally in the median, disk light ends up in some places in more than half of the images, and I get disk in my PSF and therefore a shadow when I subtract it. So I edited the code to combine images according to rotation angle instead of by sheer number of images. It still has a bug though and I’m sleepy, so you’ll have to see the fix in another blog post. 🙂
Here are some pretty pictures to tide you over.
This band of clouds to the West was just the beginning of our weather problems last night, but it made for a pretty sunset.But no green flash this time
I feel like the pictures we post here can’t really capture how beautiful the 360 degree view of the Andes is, so I’ve been playing with the panorama function on my iphone. It only gives you a 180 degree view, but I think it’s an improvement. Here are a few of my favorites.
We are officially halfway through our run. Although we are super happy to be here and getting great data, we all miss our families and want to thank them for putting up with our long trips here every semester (and for being our most devoted blog followers). Also, thank goodness for Skype/FaceTime. I don’t know how astronomers managed these long runs before video chat!
As I worked on improving my ADI reduction scripts tonight, I kept an ear out for some of Laird and TJ’s usual gems. Here’s a smattering of my favorite quotes from tonight. Everyone gets a little punchy and weird this far into a run, so there are quite a few.
“Technically plants are animals too” -TJ
“I am a marshmallow, your advisor.” -Laird
“I’m just very lucky I have good students” – Laird (yay!)
“I’m the new Alfio” – Laird
“There’s a Clio manual?” – TJ, the Clio operator
“Signal to noise is always lower at home than you think it was at the telescope” – Alycia
“Aww. TJ’s so cute” – Laird, in response to TJ’s optimism about a target
“don’t use your finger to point to the screen” -Laird
“oh sorry you don’t want me touching your screen” -TJ
“no it’s just that your finger is fat” -Laird
“guys, what was your first CD?” – TJ
“my first TAPE was the soundtrack to Miami Vice” -Jared
“Laird probably owned LPs” – Alycia
We also spent a while tonight debating whether the They Might be Giants version of “The Sun is a Mass of Incandescent Gas” was better than the original, but I’m writing the blog post so my opinion is what counts for today.
We started off the night trying to track down the mysterious source of a perfectly symmetrical spider (literally a spider!) that kept popping up in the Clio viewer (see Jared’s post from earlier today for more details). Luckily, Povilas was working on the pointing model at the time, so we were able to indulge in tracking down the source of the April Fool’s joke. It turned out to be none other than Clio PI and advisor for half of the observing team, Phil Hinz. Nice one, Phil!
The new Clio “spider”
Shortly thereafter, I spotted this guy in the bathroom downstairs. Some squabbling ensued about what to do with him. He was eventually removed from the bathroom, and was not harmed in the process.
Tarantula-esque spider that at first was thought to be part of the April fool’s joke. Turned out it was real.
It took the first half of the night to finish the pointing model tests, and then we spent some time doing engineering calibrations. Clio did more focusing and tested the prism, nodding and image quality. By the way, Clio has real “spiders” all the time, not just on April Fool’s. See image below.
The four telescope spiders and two cold stop spiders make some gorgeous diffraction spikes (the long lines extending out from the stars) on Clio. (The bright star is saturated pretty far out, but you can see some beautiful Airy rings on the faint 4” companion.)
Meanwhile, VisAO did some spectrophotometric standards and tested the symmetry of the coronagraph.
Towards the end of the night, we were also able to do a little bit of engineering/science by looking at a nice bright disk with both cameras. We’re particularly eager to characterize how well we can image extended objects with VisAO, so we’ll report back on this.
We said goodbye to Marco and Povilas tonight. Thank you both for all of your hard work! Before Marco left, we managed to take one picture of the full commissioning team.
From left: Marco, Alfio, TJ, Laird, Jared, Katie, Vanessa and Kate
“Believe me, we aren’t hiring friendly people.” — Laird
“Guys, I have bad news. We are out of cheese.” — Marco
“I do not like spiders. I don’t like them.” — Vanessa
“It’s so rare that I can teach a student something that has to do with computers.”– Laird
Tonight is the last on-sky night for MagAO in 2012. Don’t panic. We’ll be back with a vengeance in Spring, 2013!
And just in time too! Jared and KT's coffee supply ran out tonight!
We began the night tonight by looking at a bright star that Runa chose for calibration. Upon further inspection, and much to our surprise, it turned out to be a heretofore unknown binary! We’re calling it “Runa’s star” and will have to follow up on our next run.
These images were taken in greater than 0.8" V band seeing. That's roughly 75%-ile here. VisAO has performed very well.
We also commissioned a few of the more exotic Clio modes today, including the Apodizing Phase Plate (technical link, non-technical link) and Non-Redundant Masks (technical link, non-technical link). Both of these techniques are designed to probe the regions close to a star. One (APP) allows you to achieve extra high contrast close to your star (distinguishing faint planets from bright stars) and the other (NRM) allows you to image the inner regions of a system at extra high spatial resolution.
Katie with an NRM image... and soup.
On the VisAO side, we managed to achieve, as our PI describes it, “the highest resolution image ever taken in the universe”. This means that we had great seeing and great AO correction and looked through our shortest wavelength (“bluest”) filter – [OI] at 6300Angstroms. We were able to achieve resolutions of <25milliarcseconds. An arcsecond is 1/3600th of a degree, so 25 milliarcsecond resolution means we can distinguish objects that are separated by only 0.0000007 degrees on the sky! By contrast, the resolution of the human eye is a paltry 16 arcseconds or so. Stay tuned for Laird to write a paper with a title something like his quote above.
Me operating VisAO. Jared wanted me to post this to demonstrate that he's not the only one who can operate it. In fact, his GUI is excellent. I'm pretty sure he'll be obsolete soon.
Don’t stop reading the blog because we’re pulling MagAO off the telscope tomorrow either! We’re taking lots and lots of data home that we will have to analyze “for real” instead of on the fly at 3am. We expect to do much better when we return to Arizona, triumphant and well rested! We’ll be keeping you updated as we begin to quantify our on-sky performance for future observers, establish bragging rights, prepare for conferences and make new scientific discoveries.
Quotes of the Day:
“Clio sucks!” -nameless Clio operator
[sadly] “What? Your TO sucks?” – Jorge, the TO (Telescope Operator)
“Time to leave this valley of tears” -Runa. Apparently having a new star named after him wasn’t enough to counter the valley of tears effect.
“If my plane crashed, I would still want you to graduate” -Kate to Jared, after he showed her the data drive she would be taking back on the plane with her. We’re sending several copies on several planes just in case. I swear this was going to be a quote even before I agreed to write the blog post!
In honor of our last night on sky, I’ll leave you with some of the nighttime shots that I’ve taken this week.
Before I learned to focus my camera properly for star shots, I took this slightly blurry picture of the southern Milky Way. You'll see the southern cross near the lefthand edge of the frame and the LMC (more on this in the next caption) on the right.The Large and Small Magellenic Clouds, two satellite galaxies of the Milky Way that are visible to the naked eye in the southern hemisphere. Although he certainly wasn't the first to see them, Magellan noticed them on one of his voyages and so they are named after him. The red dashed line on the left is a plane with it's lights flashing, and not a UFO.More like a sunset shot than a nighttime shot, but I thought that I should point out that the moon has gone through almost a full cycle since we arrived!A 2hr star trail that I took last night. I set my camera up outside at sunset to take three of these during the evening. You can see that the telescope was pointed at several places during this interval, as several dome orientations are superimposed. After the first shot, my camera blew over. TJ thought this shot was cooler than the first one. I was confused at first because I thought one of the other telescopes on the mountain had a laser guide star system... and was pointing it at the ground (dummies!). It's actually a highway, which makes much more sense!The skies of LCOMy favorite. A 2hr star trail shot that I set up before I hiked up to the telescope one night. The psychedelic red lights are the taillights of cars driving up and down to the telescopes. No headlights though!
Here at LCO, we spend a lot of time staring at the sky, and not just with our instruments! I’ve noticed, for example, that the Belt of Venus is quite prominent and beautiful at sunrise and sunset. For those of you who’ve never noticed it, the Belt of Venus is the pink band of light that stretches all along the horizon at sunrise and sunset. It’s most interesting if you look opposite the setting or rising sun. There, you’ll see a dark band spread up from the horizon at sunset or recede into the horizon at sunrise. This is the Earth’s shadow! You’re seeing a place on earth where the sun has already set (or not yet risen).
Opposite the setting sun, you see a place on earth where sunset has already happened, represented by the dark band on the horizon.But the pink Belt of Venus extends all the way around the sky. Here it is with Magellan at sunset.Belt of Venus at Sunrise, with a waning gibbous moon.
I also took a video panning around the horizon at both sunrise and sunset so that you could see the full effect.
[Video coming soon]
We also have a tradition of looking for the green flash at sunset from the Clay balcony. A few days ago, we finally saw it, and I managed to capture a picture!
Here’s a zoomed-in version:
There are lots of misconceptions about the green flash, and I’ve looked for it many times before, but this is only my second time seeing it. It should happen just AFTER the red setting sun drops below the horizon. What you are seeing is earth’s atmosphere acting like a prism and refracting (bending) different colors of light by different amounts. The blue/green limb of the sun sets last.
You can actually see this effect even during the day if you (carefully!) create a large image of the sun. Here, for example, is a picture of the red limb of the sun taken at a teen Astronomy Camp:
See how the leading edge of the sun appears red?
That’s all for today, but I’ve been practicing my astrophotography too, so stay tuned for some nighttime shots!
I’m told that I have to pick a song with deep astrophysical meaning to go with my post. This probably dates me, but here goes…
