Category Archives: General

MagAO 2018A Day 14: Not just a phase

It’s the fourteenth sixteenth blog post for this run, but it’s my first ever post for the MagAO blog. I’m Joseph Long, a just-finished-first-year graduate student in astronomy working with Dr. (Astr.?) Jared Males. I’m helping out as an AO operator for part of this run, though it may be more accurate to say everyone else is helping me learn to operate MagAO.

Tonight is a bit of a change from the last few nights: Clio has gone on a vacation to the storage building and a new instrument has been installed. Brian McLeod and the rest of the Giant Magellan Telescope co-phasing prototype instrument team are all here, and we’re quickly running out of chairs. The instrument they bolted on today is designed to demonstrate the ability to phase the Giant Magellan Telescope’s primary mirror segments by treating the 6.5 m Regular Magellan Telescope’s single primary as if it were segmented. (“It had better be in phase!” — Jared) Dedicated readers may recall Derek Kopon’s post from December 2015, which explains some of the motivation and techniques for this project.

Come to the zoo at Las Campanas to see our selection of nocturnal mammals

Standing-room only crowd in the Magellan Clay control room (Photo: Katie Morzinski)

MagAO grew up with VisAO and is good friends with Clio, but is less well-acquainted with the phasing prototype. This means a lot of playing around with stage offsets and rotator angles to get light into the instrument. After fifteen or twenty minutes of manually commanding stage positions in 0.2 mm increments, one’s mind starts wandering to new user-interface paradigms that don’t involve punching in absolute stage positions every few seconds. (Fortunately, Laird and Jared have a workaround: get the graduate student to do it.)

This whole experience brings back memories of KAPAO and Pomona College, but I have to say Las Campanas has the superior facilities. I’m speaking, of course, about the lodging and food.

Un plato de la cena para mi almuerzo nocturno, por favor

Chef Andrés stands next to the outdoor grill at the Las Campanas lodge (Photo: Katie Morzinski)

I’m not sure I ate anything but fistfuls of chocolate-covered espresso beans while on Table Mountain as an undergraduate, so I feel very well taken care of here at Las Campanas.

As someone who grew up in a big city, I can sometimes forget what the night sky is supposed to look like. (Except for the occasional citywide blackout, I remember the night sky as a comforting dark orange.) The view of the Milky Way before moonrise here is spectacular. Of course, I spend most of my night looking at this kind of thing:

Yes, this is a GIF of a cellphone video of a screen. Get off my case.

Short video of the observer’s interface to monitor forces applied to the adaptive secondary mirror. The actuators are shown in their concentric rings, and color coded based on the absolute value of the force applied.

The night sky is hard to photograph (just ask the Clio and VisAO PIs), so instead I’ll leave you with a photo of the Magellan Clay telescope greeting the sunrise.

Close that slit! We didn't order any solar photons.

The Magellan Clay telescope greets the sunrise.

Because blog posts have rules, I have a thematically appropriate song by Spoon: “I Turn My Camera On”…

…and a cover, by Rock Kills Kid…

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The SAO phasing prototype visits MagAO

“Without phasing, there’s no real reason to build the GMT.”
-Andrew Szentgyorgyi

The biggest optical/infrared telescope in world will be the Giant Magellan Telescope, which will be built on a nearby mountain peak within sight of the Clay and Baade telescopes at Las Campanas.  The telescope will have 7 primary mirror segments and 7 adaptive secondary mirrors, similar to the Magellan AO system.

The 25 meter diameter Giant Magellan Telescope

The 25.5 meter diameter Giant Magellan Telescope

Photograph of the GMT site from the Magellan footpath.

Photograph of the GMT site from the Magellan footpath.

If we could build any optic we wanted for the primary of the GMT, we would probably build a monolithic 30 meter diameter (or larger) mirror made of a single piece of glass, with a thin face sheet and a honeycomb lightweight structure on back.  However, at the moment, the largest mirrors in the world are built in the Steward Observatory Mirror lab under the bleachers of the football stadium at the University of Arizona and are limited to a diameter of 8.4 meters.  Depending on who you ask, this 8.4 meter limit comes from either the distance between the columns underneath the stadium bleachers, or the size of an underpass on the highway leading from Tucson.

An 8.4 meter mirror being polished in the Steward Observatory mirror lab underneath the football stadium bleachers.  Making mirrors larger than this will require a larger football stadium.

An 8.4 meter mirror being polished in the Steward Observatory mirror lab underneath the football stadium bleachers. Making mirrors larger than this will require a larger football stadium.

Because of this limit, the GMT is designed to take 7 of the largest mirrors that can be made and combine them to form one giant 25.5 meter primary.  For this to be possible, the seven 8.4 meter segments must be “phased” to a fraction of a wavelength.  That is to say, they must be aligned to each other so that they act as if they are one large continuous mirror.

To achieve the phasing of the GMT segments using off-axis natural guide stars, SAO and our collaborators at GMTO and Flat Wavefronts have designed a sensor that creates dispersed interference fringes using subapertures spanning the 12 segment boundaries.  Phase shifts across the segment boundaries manifest themselves as tilts in the fringes.

Segment boundary subapertures for the dispersed fringe phasing sensor.

Segment boundary subapertures for the dispersed fringe phasing sensor.

Simulated fringes from one subaperture showing 0 piston phase difference (left) and 10 microns (right).

Simulated fringes from one subaperture showing 0 piston phase difference (left) and 10 microns (right).

To test this sensor technology, SAO has built a phasing prototype that simulates 6 of the GMT segment boundaries working in conjunction with the Magellan AO system.  Our three nights at the end of the MagAO run turned out to be a success.

Six sets of fringes as seen by the SAO phasing prototype working in conjunction with the MagAO system.

Six sets of fringes as seen by the SAO phasing prototype working in conjunction with the MagAO system.

The SAO phasing prototype team.  Clockwise from top left: Derek Kopon, Alan Conder, Ken McCracken, Jared Males, Laird Close, Dan Catropa, Brian McLeod, Bill Podgorski.

The SAO phasing prototype team. Clockwise from top left: Derek Kopon, Alan Conder, Ken McCracken, Jared Males, Laird Close, Dan Catropa, Brian McLeod, Bill Podgorski.

We obtained phasing data both on-axis and off-axis, with AO on and off, and at two different wavelength bands (I and J).  This data, and data that we gather during another run possibly in February, will inform the design of the GMT phasing sensor, scheduled for first light in the next decade.

Lastly, a “song of the run:”  Phazing, by Dirty South:

https://www.youtube.com/watch?v=031hzipvnTY

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New Results In The Chamaeleon

Now that the MagAO team has (mostly) recovered from our epic 6 week stay at LCO, we are turning our attention to processing all of the great data we’ve been taking. We’re also happy to announce two new publications based on MagAO data which have been accepted to the Astrophysical Journal, both of which looked at stars in the constellation Chamaeleon.

Ya-Lin Wu has been studying the young star CT Cha with VisAO. You can read about his results here.

Steph Sallum used Clio2, in combination with some other instruments, and used a resolution-boosting technique called non-redundant masking to take a look at T Cha. You can find out about her results here.

We have a bunch of other papers in the works, and we’re already starting to plan for our next run, which starts May 3rd. Stay tuned!

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