Club Address: An electronic publication of The West Hawaii Astronomy Club - Club Officers: Vice President: Secretary: Treasurer: With Support From:
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March 2007 Club Meeting Report
A light-hearted Messier Marathon debate was next on the agenda. New member and self-proclaimed Messier Marathon advocate, Andrew Cooper, began the discussion with his experiences in Arizona. Last year, they had 25 people all get the whole 110 objects during their marathon. Andrew's reasons why people should participate in the marathon are:
The "debate" ended with both sides agreeing that it's great fun to do a Messier Marathon! So, come join the club this weekend at the dark site. It will be the for the most favorable weekend at almost the optimal latitude.
We had a short break before the featured talk of the evening, Olivier Lai of CFHT presented details about the 'OHANA project.
'OHANA is an acronym for Optical Hawaiian Array for Nanoradian Astronomy. Olivier described how astronomers are always anxious for bigger telescopes for fainter and fainter objects. However, there are diminishing returns for resolving power in attempting to build ever-larger
telescopes. To solve some astrophysical problems requires much more resolution, not necessarily more light gathering. To get this resolution, you need different techniques.
'OHANA uses interferometry between multiple, widely-separated telescopes to get better resolution.
Olivier spent some time introducing adaptive optics (AO) as a coupled technology to interferometry. Atmosphere distorts the photons coming to Earth, so we need to use space telescopes, or correct in real-time. Space telescopes are expensive and have small apetures. Correcting in real-time is limited by having bright natural guide stars close to our objects of study. 'OHANA will correct in real-time, using
adaptive optics techniques. Olivier went through a very good overview of how adaptive optics works.
Olivier discussed the concept of diffraction. Diffraction was discussed as a wave phenomena. A variety of diffraction effects were illustrated, and their application and utility in interferometry were discussed. A variety of different telescope pupils and rotation angles were used to show the concept of a Point Spread Function (PSF). Different telescopes and pupil sizes can be used together; just the PSF changes.
The different pupil sizes of the various telescopes on Mauna Kea actually works relatively well as far as the combined PSF is concerned.
Several interesting interferometric baselines can be used for valid scientific studies.
Mauna Kea is the largest site of optical telescopes with AO systems. 'OHANA is a multinational collaboration to combine the light from several of the observatories on Mauna Kea interferometrically, using 85m to 800m baselines. The master plan on Mauna Kea does not allow for any more development, so 'OHANA is using fibers to move the light between the telescopes on Mauna Kea.
The first proof-of-concept was coupling the light of the two Keck telescopes via single-mode fibers, reported in Science magazine. Currently, Olivier and his team are building delay lines at CFHT for combining light from CFHT and Gemini telescopes in the next phase.
There is a long way to go, with more and longer baselines (using other telescopes on Mauna Kea), better fibers for more wavelength coverage, and even harder problems like how to schedule time on such an instrument. This project is full of interesting challenges! If successful, 'OHANA will be the largest optical interferometer with no competition for the forseeable future.
Previous meeting minutes
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