Optical interferometry in astronomy
3 Dec 2009 2:23:37 UTC
Topic 194652
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For those of you who are scientifically attracted to fringes, vacuum systems and high precision optics, here's another revolutionary instrument: CHARA, the Center for High Angular Resolution Astronomy, operates a network of 6 optical telescopes, linked together as an interferometer of impressive baseline length, on Mt. Wilson, USA.
http://www.chara.gsu.edu/CHARA/array.php
A similar installation is SUSI in Australia:
http://www.physics.usyd.edu.au/sifa/Main/SUSI
Remarkable stuff. Completely unrelated to GW search of course, and not in the billion $ budget league, but still impressive IMHO.
Bikeman
Optical interferometry in astronomy
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Don't you need to know the distance between each of the telescopes to within half the wavelength of the light you're looking at, or something like that, to use them as an interferometer? Very impressive stuff. To be honest, I can't wait until we get formation flying in space down - that seems like it would open up so many new opportunities.
I understand they use kind of
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I understand they use kind of an adjustable delay element (although calling it that must be a gross understatement of its complexity) so that you can combine the rays. Apart from compensating for any differences in distance of the telescopes to the fringe point, you also have to compensate for the fact that the observation will be made at a changing(!!) angle, I think the slide on page 10 of this presentation from CHARA demonstrates this pretty intuitively. Amazing.
CU
Bikeman
I think it was the Keck group
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I think it was the Keck group that started the hi-res stuff between separated optics. You see 'within half a wavelength' or better is what's been happening with telescopes all along. It's just generally not stated as such. With a single optical system as by definition all detected photon's are going to experience the same optics ( if correctly done ). It all goes back to Fermat's Principle of Least Time ( analogised in QED to the path integral summation, or the classical Principle of Least Action also ). Thus for 'focus' to occur in some region of the optics where image capture occurs to some alternate/permanent form, the arrival times from separated sources in the view field must be as close as possible. You can phrase that in wavelength terms if you like.
For that matter, radio astronomers have been applying that for years, but as a much easier task due to the longer wavelengths. The US military developed phased array radar systems with a static frame of receptors in a grid. By introducing ( electronically or by switching of wave guides ) phase delays to suit equal times of arrival for a chosen direction in the field of view. It's those big flat plates on the superstructures of the more recent ships. I saw one on the side of a US sigint plane at a recent airshow. The guy said it was 'communications backup equipment'. Yeah, right. :-)
So if you look at the original HST stuff up : the geometry as manufactured introduced relative phase offsets leading to a the blurred image. The applied corrections to that problem added elements that differentially handicapped certain paths over others to bring the phases into line.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
RE: Remarkable stuff.
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I took a look at their Pictorial Overview and it's incredible, from the maths to the images! If you look at the picture of Beta Lyrae (Prototype Mass Transfer Eclipsing/Spectroscopic Binary [on P. 53]), the huge bulge on one of the stars looks like might it alter the standard inspiral 'chirp' waveform. In some of the other images of rapidly rotating stars, the stars appear to have slightly asymmetrical shapes, but maybe that's wishful thinking ... It's a phenomenal set of instruments and engineering, that's for sure!
There is an article in
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There is an article in "Nature" magazine of April 8 that says that a network of small telescopes on the venerable Mount Wilson Observatory in Los Angeles has the resolving power of a 330 meters mirror and 50 times the resolving power of the Hubble Space Telescope. All this via optical interferometry. The telescopes are linked by tunnels. All this risked to be burned by the last California big fire.
Tullio
RE: There is an article in
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Yup, this is the CHARA telescope network , see links in my original post. The article is about a system, epsilon Aurigae, that is also at the center of the Citizen Sky citizen science astronomy project. Very interesting indeed.
CU
HB