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The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Subaru seminar organizers (Tadayuki Kodama, Kumiko S. Usuda, Naoyuki Tamura, Tomonori Usuda) by email : (please change"_at" to @).

May 19, Thursday, at 11:00 am

" IMAKA: Imaging from MaunA KeA - The finest view from Earth! Challenges and opportunities to develop a GLAO for `IMAKA "

Olivier Lai

(Canada-France-Hawaii Telescope)

In Hawaiian,`IMAKA means scenic point or beautiful view, and indeed Mauna Kea offers a truly unique view into the heavens. The structure of the turbulence of the atmosphere above Mauna Kea may offer yet another window in parameter space to observe the Universe. By including what we know about the atmosphere into our instrument design, we think we can deliver images with a resolution of 0.3" over a 0.8 degree diameter field on the 3.6m CFHT. To achieve such an ambitious goal, we have developed a specific strategy to address the various sources of image degradation. First, we are aware that much of the turbulence is generated within or by our dome. A now independent project has been started at CFHT on dome venting and thermal dissipation mitigation. The next source of turbulence is in the ground or boundary layer. Recent studies have shown that this is very confined in a layer close to the ground (<70m). There is a relationship between the thickness of the turbulence, the size of the corrected field and the order of the correction of a GLAO system and we find that that the measured thickness of the boundary layer would allow for degree size fields to be corrected. Finally, the next major source of image degradation of the dome and GLAO corrected image is the tip-tilt of the free atmosphere. An orthogonal Transfer CCD can shuffle charges across pixels in real time during an exposure and is therefore capable of locally correcting for tip-tilt across sub-arrays. Depending on the density of tip-tilt stars and the trade-off between image quality and homogeneity, simulations have shown it will be possible to achieve a median image quality of 0.3" at 700nm over the required 0.8 degree diameter field. There are many challenges in the `Imaka project, most of them are related to the need to re-image a clean pupil image on a deformable mirror while carrying such a large field: the Lagrange Invariant is as large as MOAO systems on ELTs. But there are also other very interesting issues to be solved in the case of `Imaka. In this talk, I will describe our challenges and opportunities afforded by this original concept.

Seminars are also held at JAC, CFHT, and IfA.

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