Date: February 4, 2009

Title: ALMA – The Future of Millimeter Radio Astronomy

Podcaster: Richard B. Drumm

Organization: The Astronomy Bum  http://theastronomybum.blogspot.com/

Description: I’ll interview NRAO (National Radio Astronomy Observatory) personnel to obtain an overview and introduction to the new Atacama Large Millimeter/Submillimeter Array that is being constructed in Chile’s Atacama desert. I’ll ask our guest Dr. Al Wootten, project scientist for ALMA North America about the technology of radio astronomy arrays and the construction progress of the ALMA array.

Bio: Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He’s found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.

Today’s Sponsor: This episode of “365 Days of Astronomy” is sponsored by the National Radio Astronomy Observatory, celebrating Five Decades of Training Young Scientists through summer programs. Explore the hidden universe in radio at http://www.nrao.edu

Transcript:

RBD:
Oh and thanks to George Hrab for that wonderful introduction. Thank you George! If you don’t listen to the Geologic Podcast yet, you should.

Welcome to the 365 Days of Astronomy Podcast series, I’m Richard Drumm, President of the Charlottesville Astronomical Society, here at the headquarters of the National Radio Astronomy Observatory, the NRAO, in Charlottesville, Virginia, and I’m sitting here with Dr. Al Wootten, project scientist for ALMA, North America, the Atacama Large Millimeter/submillimeter array, uh, which is under construction in Chile. Thank you, thank you, thank you Dr. Wootten for agreeing to be uh, here with us, uh, talking with us today!
AW:
Well, thanks for inviting me!

RBD:
Ummm, tell me, the short and sweet, what exactly is ALMA?
AW:
OK, well, ALMA is a project of, 3 executives, financing agencies if you will, in Europe, the European Southern Observatory, the National Science Foundation through NRAO, and the National Institute of Natural Sciences in Japan through the National Astronomical Observatories of Japan to build a telescope of ultimately 80 antennas in Chile. Will be located at the 16,400 foot Chajnantor Plateau right close to where Bolivia, Argentina and Chile come together right at the Tropic of Capricorn, basically, just a little bit North of that.

And it’s to do millimeter and submillimeter imaging of the sky, and the reason for this of course is that because we discovered with the IRAS satellite about 25 years ago that in fact galaxies and the universe emit a large portion of their energy in the far infrared but in order to be able to image that we have to get a big telescope up high it’s just too hard to put a big telescope in space at the moment, and so the biggest we can get, the closest we can get will be ALMA so we hope to be able to image the sources of that radiation.

2:06
RBD:
Ummm… Why the Atacama?
AW:
So the reason we’re there is twofold. One, it’s 16,400 feet, it’ll accommodate 18 kilometer baselines, so it can get very high resolution and secondly it’s only an hour’s drive from San Pedro de Atacama, which is a charming town. There’s a rift in the Andes there, and so, in the valley between the rift the water has flowed down and there’s been a village there for thousands of years. You can go and visit houses from before Christ in this region. So we have everything we need there and we can have the long baselines and the high altitude at the same time.

Already the resolution we’re able to achieve with ALMA is on the order of 4 or 5 milli arcseconds and so, uh, that’s pretty good. The atmosphere of course will be the biggest challenge ’cause the atmosphere at the highest frequencies where we get that high resolution is, uh, problematic. Yeah.

RBD:
And so for the optical astronomers out there, how does that resolution compare with Hubble?
AW:
Oh Hubble’s a tenth of an arcsecond or so, so it’ll be a factor of what, 20 better than Hubble.

3:20
RBD:
What’s unique about these radio antenna dishes that you have down there in Chile?
AW:
Well, first of all they have to operate at very high frequencies, 950 gigahertz. Right now the highest accuracy telescopes in the world, so their surface has to be accurate to 25 microns or better. So the other important thing about the telescope is, in addition to its surface, it tracks very accurately and it moves very fast.

So what we want to do with the telescope is be able to map a large area source by rastering the telescope very quickly in under a second. And so we can basically do, you know, a point every millisecond, and if the source is bright enough, we could cover an area, you know, the size, almost the size of the Moon, a good fraction of a degree, in uh, in a second, and just be able to map it.

4:16
Secondly you want to be able to calibrate out these blobs of water that are moving in front, so we want to be able to move from our target object, which may not be very bright, to a nearby calibrator very rapidly, and so we estimate that on average there’s a calibrator that’s bright enough within 2 degrees in the sky. So we have to be able to move the antenna fast enough to get over there in a minimum amount of time and calibrate and then get back. And so the specification on that is to be able to get to that spot in the sky and back again within a few seconds. So we have all-sky pointing accuracy of 2 arcseconds.

4:54
And then for offset pointing, if you want to be able to image a large source, our beam size at the highest frequencies is only 7 or 8 arcseconds. So you’ll have to have to have many, many beams to cover a source of any appreciable size. And so you want all those pointing to register perfectly and we’ve determined that you need to have offset pointing that’s good to 6 tenths of an arcsecond in order to be able to achieve the imaging quality that we want to achieve.

So the antenna has to be able to point accurately, has to have a perfect surface, has to be able to move quickly. They’re pretty strong demands on it.

5:32
RBD:
How far along is the construction and when will there be, uh, first science, and when will (it) be complete?
AW:
Well, there are 12 antennas on the site now. There are 4 Japanese and 8 North American antennas made by Vertex, and there is parts of the first European antenna. And so these are coming along, we’ll have 50 antennas up and operating by September of 2012 when the, the original scope of the array will be achieved, but then we’ll bring all the rest of the antennas on within a year or so after that. So by about a year from now we should have 3 antennas fully equipped with all the instrumentation available at 16,000 feet. So then we can start debugging all the modes, especially the high frequency modes, that we can’t, uh, we can’t even see out of the atmosphere at 10,000 feet at the intermediate level facility.

6:35
RBD:
When do you expect to move the first antennas from the, up to the high site?
AW:
Well, we’ve moved a couple of them around on the intermediate site now. And we’ve moved a dummy antenna, a big concrete load up to the high site, ’cause the first thing we wanted to determine was are the engines up to it at 16,000 feet, and we did discover a few tune-ups that were needed.

So the first antennas should go to the high site sometime in the course of the next year, and we should have them all hooked up and operating by the end of the year at the high site.

7:11
RBD:
What percentage of the correlator is up at the high site, only one quadrant, right?
AW:
Yeah, so it’s a quarter of the correlator and that can service 16 antennas. An additional unit, the one for the 16 Japanese antennas is also on the site. So we have the capability of correlating two 16 antenna sets at the moment at the high site. The second unit of the correlator is actually constructed and undergoing tests here in Charlottesville, that’ll be shipped over the course of the coming year down to join the first quadrant.

The correlator is pretty big and so they don’t really have room for all 4 quadrants here in Charlottesville, so we need to get them down there and so far the first quadrant moved fantastically. There are an incredible number of wires connecting the correlator up and when they connected them up there was only 1 connector that was in the wrong place. So it all worked very well.

8:13
RBD:
All right, well, anything else you’d like to add that you can think of?
AW:
No, I think it’s just an exciting project. We will have a visitor’s center in Chile so if anybody comes down there’ll be a gallery, We’ll have a, there’s a wonderful museum in San Pedro on the Atacamanian culture, and there are plans for having a mechanism whereby people can be notified in San Pedro when an antenna is coming down from the mountain on the transporter or something exciting is going to happen on the site and you can go up and watch from a visitor’s gallery there as well as having an introduction to the sorts of science that ALMA will be producing very shortly now.

RBD:
Thank you very much, Dr. Wootten.
AW:
Sure, thank you, I appreciate the opportunity. Any time.
RBD:
Ah, well, we’ll look forward to first science in a few years.
9:06

End of podcast:

365 Days of Astronomy
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The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.