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The return of the Crow part II:

Edgar Allen Poe—
Once upon a midnight dreary, while I pondered weak and weary,
Over many a quaint and curious volume of forgotten lore…
…Only this, and nothing more:

The excerpt from the poem “The Raven” is brought to you by the Return of the Crow part II.

That is, we put the CRO back on this afternoon, so that we could spend the evening and night making new interaction matrices. We used a new pattern file from Charlie from SciMeasure, and were able to do bins 3, 4, and 5 — the faint modes — as well as testing the chromaticity of the interaction matrices. Tomorrow we will go back on sky to try them out!

We also spent a lot of time making sure we understand our data. We *still* weren’t certain about the orientations of our respective cameras — Jared, Kate, and Laird spent a lot of time disagreeing about which way to rotate the VisAO images to get North up. And T.J., Katie, and Phil spent some time with the Clio FITS headers and with Clio read noise. Our night-lunch sandwiches are wrapped in tinfoil, and T.J. scavenged it to wrap some wires to reduce electrical noise.

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Tyson has left and we miss him — Tyson, when will we see that special blog post of yours?

“I’m not interested in discoveries.  I just want to take data.” – T.J.  (6am after staying up all night)

“It’s a binary. No look, it’s a binary!” – T.J.

Things are always exciting here on the MagAO project. But nothing – not earthquakes, viscacha attacks, not even non-orthogonal basis sets – can keep us from doing what we came here to do. Now that we are on-sky, we are taking advantage of the *amazing* 0.5 arcsecond seeing common at LCO to take some nice pictures. Last night we were looking at the Trapezium cluster to calibrate our plate-scales, and we took a few moments to take this image:

We didn’t cheat – no shift and add or other tricks.

After we solved last night’s communication problems, we did some engineering work, specifically getting Coma-offloading to work. I hate rotation matrices. Later, seeing calmed down, and we took some fantastic images. Here’s a screen grab from VisAO working at 0.982 microns. It’s a log stretch, and captures a single 0.28 second frame on a bright star.

And here’s our M-band PSF from tonight:

We tested turning off the Clio pump to reduce vibrations in the 25-milli-arc-second VisAO PSF.  But since the Clio folks were observing at M-band, a 0.5-degree increase in temperature of Clio’s inner dewar caused a 3% increase in their thermal background.  Therefore, we turned the pump back on again, and the sky background settled back down as the detector cooled.  Here’s a curve showing the effect on Clio of turning off and on the pump:

Runa Briguglio, who is here from Florence helping us take care of the shell, suggests that we operate by this guideline:

Some quotes:
“If I’m doing what I think I’m doing, I’m an idiot. Yes! I’m doing what I think I’m doing!” – Glenn Eychaner, who came up the mountain today just to help us debug our TCS-MagAO communications problem. Thanks Glenn!

Tonight started with a hard to understand communications problem between our AO system and the telescope control system (TCS). It’s been working for days, but tonight we started having some messages get dropped. We have to keep the elevation of the telescope above a certain value to keep our delicate mirror safe, and this communications problem was causing us to stop getting elevation often enough. So our mirror RIP-ed, which means rest-in-peace. We don’t know what’s going on, but we hacked our way out of it by changing some timings. Troubleshooting begins again tomorrow after supper – I can’t wait.

After that, we had a very productive night. We looked at a standard star to calibrate our filters, and also looked at some well known clusters of stars to calibrate the plate-scales of our camera. Both cameras also had their foci checked. Kind of boring scientifically, but it’s important that we characterize our new instruments on real stars.

Katie and I were charged by a Viscacaha on our way down the mountain this morning. They’re turning against us.

And as I’m typing this we just got hit with an earthquake:

We also saw a hare this morning, a MagAO first.

“I’m a fan too, not just your families. I miss viscachas.” – Prof. Dan Marrone, captain of the Steward Observatory softball team and MagAO enthusiast.

“Keep calm and carry on.” – Runa Briguglio.

Our ranks are thinning — Alan Uomoto left today and I didn’t even get to say goodbye.  Bye Alan!  Thanks for all your help in getting us up and running!!

We are still engineering our many modes on sky and debugging telescope and instrument problems.  One of our exciting new modes is Simultaneous Differential Imaging (SDI), which we tried out on-sky tonight!

Our ASM is a beautiful piece of advanced technology, keeping our wavefronts flat at 1000 times/second (read Kate’s post for why!).  But occasionally the slopes being sent cause the ASM shell to go into its safe position.  It’s either the switch BCU or the BCU 39.  We have a spare switch BCU (see below), but don’t have a spare BCU 39 with us. Hang in there BCUs.

My mom would like to know what a vizcacha is — They are these little rodents, basically a rabbit, squirrel and kangaroo in one package, that live here at LCO and entertain us sunning themselves on the wall or hopping like kangaroos across the rocks!  The official mascot of VisAO is Vizzy the Vizcacha:

And speaking of mascots, the Clio team have been wearing our UA Wildcat pride here at LCO:

For all of the non-astronomers out there (hi dad!) who have been patiently wading through our blog because they love us, here is a very brief crash course on AO. We thought that this might help you to understand why what we’re doing here at MagAO is so exciting.

The first important concept is that, in an ideal world, the resolution of telescope images is directly proportional to the wavelength of light you’re looking at and inversely proportional to the diameter of your telescope. In other words, the formula for resolution is:

resolution = wavelength / telescope diameter

Small resolutions are the best (we generally call this “high resolution” when we’re talking about cameras or TVs), so you can improve by either (a) going to a bigger telescope (increase diameter = divide by a larger number = smaller resolution) or (b) going to shorter wavelength light.

The first and even second and third generation AO systems all operate on infrared light, which has relatively long wavelengths.  We are the first 8m-class telescope system to push to shorter wavelength visible light (hence the name of our blog, VIS-AO). If there is a resolution advantage to shorter wavelength light  (visible over infrared), why did/does anyone bother with infrared AO?

The reasoning comes down to another formula, this time the formula for the atmospheric coherence length (also known as the Fried parameter). The official definition of this quantity is “the area over which an rms wavefront aberration is less than 1 radian”, which is a little opaque so let’s break it down. RMS is “root-mean-square” and is essentially an average. “Wavefront aberration” is the amount that a wave’s position deviates from perfection (perfectly flat, which is why we’re always talking about “flat wavefronts”). The atmosphere is the culprit here, bending our wavefronts from a perfectly flat shape.

One way to think about the Fried parameter is as the size over which you can expect the atmosphere to “behave” the same. The Fried parameter is proportional to wavelength to the 6/5 power. This means that at infrared (long) wavelengths, the Earth’s atmosphere is coherent over bigger patches. So if you want to correct at visible (short) wavelengths, you have to correct on smaller spatial scales. Adaptive secondary mirrors (ASMs), which are physically large compared to the tertiary mirrors used in other AO systems, can fit enough actuators on the back to correct at the necessary spatial scales for VisAO. In short, VisAO is hard, and we are heroic individuals!

The great irony, no matter what wavelengths you’re using for your AO correction, is that light from astronomical objects spends the vast majority of it’s journey to Earth with perfectly flat wavefronts. It’s only in the last 300 miles, the part where it’s traveling through the Earth’s atmosphere, that it becomes distorted. 300 miles seems like quite a distance on the surface (hah!), but it’s actually only a teeny tiny fraction of the entire journey made by light from an astronomical object.

In fact, let’s quantify that. If we’re looking at the very nearest star, Alpha Centauri, its light will have taken about 4.5 years to reach us. At a speed of 186,000mi/sec, that’s:

4.5yr x 186,000mi/sec x 3600sec/hr x 24hr/day x 365days/yr = 26 trillion (26,000,000,000,000) miles

to get to us. But the Earth’s atmosphere, which does all of the wavefront bending, is only 300 miles thick, so the portion of the light’s journey that is spent in the atmosphere is only 300/26 trillion, or 0.00000000001 (=0.000000001%).

That means that 99.999999999% of the journey was complete before the light found itself in need of our AO services, and that was for the very nearest star. If we’re looking at more distant objects, that fraction only increases!

This, of course, is why people put telescopes in space. If you don’t bother with those last 300 miles, then you don’t have to correct your wavefronts at all.

So why do we put telescopes on the ground? Well, there are lots of reasons. My two favorites are (1) you get a lot more bang for your buck on the ground and (2) you can upgrade the technology on a ground-based telescope whenever you want, so it will never become obsolete.

Hope that helps clarify what we’re up to a bit. Thanks for sticking with us!