Feasibility study: done!


Tremendous gains in sensitivity and angular resolution over large fields of view at CFHT are possible. The potential is striking and the scientific impact covers areas from the Solar System to the most distant objects in the universe. Improving the delivered image quality of the telescope to Mauna Kea's exquisite free-atmosphere seeing reduces confusion noise in crowded fields such as star clusters and dense regions in the Milky Way allowing greatly improved photometry and astrometry and increases the sensitivity depths to a level where CFHT will play an important role in z>7 galaxy searches, high redshift supernova cosmology, weak lensing and galaxy and stellar evolution. CFHT is effectively upgraded to an 8-10-meter class telescope.

This report represents the culmination of the IMAKA feasibility study. We conclude that median angular resolutions of 0.3" in the visible across a one-degree field of view are within reach of CFHT. Our main conclusions of the study are as follows:

  • Previous studies on the local turbulence above Mauna Kea and within the CFHT enclosure are confirmed with our new measurements: the local seeing is comparable to the atmosphere. We infer that this local seeing is inside or just outside the CFHT enclosure.
  • We find that an approach using a ground-layer adaptive optics system plus a focal plane detector based on orthogonal-transfer CCDs will deliver superb resolutions under median seeing conditions. The cumulative probability of obtaining a particular level of performance (or better) from the GLAO+OTCCD correction shows significant improvements in the image quality under all seeing conditions. Under median conditions, the telescope will have the sensitivity of an 10-m telescope and deliver angular resolutions unmatched over a onedegree field of view.
  • We have two optical designs (one at prime and one at Cassegrain focus) that meet the basic functional and performance requirements. Both designs use a deformable mirror that is commercially available. Neither design uses an adaptive secondary. We believe that both

  • The cumulative probability distribution of `IMAKA image quality (GLAO+OTCCD) for the input seeing conditions considered within the study. We predict that half of the time `IMAKA can deliver better than 0.37" in g' (0.5um), 0.31 in r' (0.7um), 0.26" in z' (0.9um), and 0.25" in Y band (1um). designs can be realized and that there are no fundamental or technical "show-stoppers" for `IMAKA.

  • The scientific drivers for `IMAKA are the combination of wide field and high angular resolution. There are no current or planned ground-based facilities with similar capabilities. In addition, `IMAKA on CFHT will present a complementary capability to future/planned space-based missions. A timely delivery though is needed to maximize the scientific impact of the system.
  • The breadth of the science cases reflects the broad interest within the community and their desire for wide-fields and high angular resolutions. The cases cover the full spectrum of astronomical objects and studies and the instrument is a natural extension of the expertise and science developed over two decades of wide-field visible imagers at CFHT.
  • To be most effective, 'IMAKA should come online at roughly the same time as JWST (2015) (and presumably when HST is no longer available) and before potential space missions such as JDEM and EUCLID. This will require timely decisions.
  • A Phase A study will provide the needed level of study to make informed cost/schedule decisions on the future of the instrument.
  • A delay now will impact the delivery of the instrument and dilute the full scientific impact from `IMAKA.
  • We believe that the instrument can be built and that it can be built within an overall 5-year development plan. To meet this schedule will require an increased level of resources and a firm commitment from the observatory and the community.


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    Science case

    Instrument ConceptThe whole public feasibility report