The CFHT Adaptive Optics Bonnette : Instrumentation

Instruments available (as of August 1998)

• Infrared Imager

  KIR is a 1024 x 1024 near-infrared imaging camera dedicated to PUEO which has been developed as a collaborative effort between Université de Montréal, CFHT and Observatoire Midi-Pyrenées. KIR is based on the 1K x 1K Rockwell Science Center HAWAII (HgCdTe Astronomical Wide Area Infrared Imaging) focal plane array, sensitive to radiation from 0.7 to 2.5 microns. The camera consists in an LN2 cryostat which harbors the detector, the fixed 0.67:1.0 transfer optics, a F/20 cold stop and a filter wheel (16 positions). The camera plate scale is 0.035"/pixel, yielding a total field-of-view of 36" x 36". The standard I, J, H, K and K' broad-band filters are provided as well as several narrow-band filters.

• Visible Imager

  A visible imager is available with the AO bonnette. It is the existing camera FOCAM, and comes in two flavors: large (!) field of view, coarse sampling, or, when mounted with our focal enlarger, small field of view, fine sampling. The table below summarizes the plate scale and field of view for two CFHT CCDs.

  CCD	Field of view (arcsec)	Pixel size (arcsec)
  STIS2	126	0.061
  Loral3	90	0.044

  With the focal enlarger, the field and the pixel size are divided by two.
  Remember that the actual field of view, where images are substantially improved, will be truly determined by the isoplanetic patch size. This link (FOCAM) provides a description of the basic functionalities of FOCAM. Flexure tests were carried out and are within specifications. We measured flexures of 7 microns per 15 degrees of telescope motion (0.011 arcsec per 1 hour exposure). This level of flexure is characteristics of what has been measured in the AO bonnette (differential between science path and WFS path), and means that FOCAM plus the focal enlarger have a negligible contribution. The focal enlarger optical design insures a good image quality from V to I. No garantee for the B band. Note however, that a marginal image improvement is predicted for the B band. No tests were carried out when FOCAM is mounted directly to PUEO, but flexures are definitely less critical for this setup.
  The overall throughput of PUEO has been measured to be 70% over most of the visible range, excluding the beamsplitter. We have three beamsplitters available : a 50%-50%, 10%-85% and a 85%-10% (percentage of light sent to the wavefront sensor and to the science detector).
  Except for specialized applications, we recommend to use the 50%-50% beamsplitter and STIS2. The choice of the pixel size/field of view is usually set by the program. For fairly bright objects (brighter than R=10) and when the seeing is good to very good, we may get images of FWHM down to 0.06-0.10, for which the coarse sampling may not be adequate. For faint objects or extended objects, we definitely recommend to use the coarse sampling.

• Integral Field Spectroscopy

  The Observatoire de Lyon in France has designed and fabricated OASIS, an Integral Field spectrograph for specific use with the CFHT AO bonnette. The instrument offers two different modes: Imaging and TIGER integral field spectroscopy.