The CFHT Adaptive Optics Bonnette : Instrumentation

Introduction

A basic Instrumentation plan for the AO Bonnette has been defined although it keeps evolving with time. The following two sections describe what is available, being fabricated, and planned for the near future.

Instruments available (March 1997)

• 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.

• Infrared Imager The Universite of Montreal infrared Camera, MONICA, is available for visiting observers on the AO bonnette. The detector is a NICMOS device of 256x256 pixels. The transfer optics has been modified to provide a 0.035 arcsec/pixel sampling. The overall field of view is 9x9 arcsec. MONICA has been used for the commissioning of the AOB during the first semester 1996 and during science run since then. The infrared group of the Universite de Montreal has kindly agreed to put MONICA at CFHT's disposal until a larger format detector becomes available (see below).

Instruments being fabricated

• Dedicated Infrared Imager, KIR@. The Universite de Montreal is building a 1Kx1K infrared detector, based on a Rockwell chip. This camera is dedicated to PUEO. The optical quality has been specified to match the diffraction limited images delivered by PUEO. We expect to receive KIR by June 1997. It should be available for scientific observations for 1997 II.

• Integral Field Spectroscopy The Observatoire de Lyon in France is fabricating OASIS , an Integral Field spectrograph for specific use with the CFHT AO bonnette. The instrument offers a variety of modes: Imaging, slit spectroscopy, TIGER integral field spectroscopy, ARGUS integral field spectroscopy, Fabry-Perot scanning interferometer, and PYTHEAS scanning Fabry-Perot mode.

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