Instrument Host Overview
  ========================
    The Keck I telescope began science operations in May, 1993.  It
    was built through the W. M. Keck Foundation and is operated by the
    California Association for Research in Astronomy which includes
    the University of California, the California Institute of
    Technology and the National Aeronautics and Space Administration.
    The Keck I is located at the W. M. Keck Observatory near the
    summit of Mauna Kea, Hawaii. The geodetic coordinates of the
    telescope are:
 
      Longitude    : 155d 28.4' W
      Latitude     : +19d 49.6' N
      Altitude:    : 4124m
      Mean seeing  : about 0.5 arcseconds full-width-half-max in the
                     K-band
 
    The overview and location given here are reproduced from the
    W. M. Keck Observatory web site, http://www2.keck.hawaii.edu/.
 
 
  Telescope Properties
  --------------------
    The primary mirror comprises 36 hexagonal segments.  Each segment
    is 1.8 meters, measured across the corners.  The maximum diameter
    of the primary mirror is 10.5 meters, and its focal length is 17.5
    meters.
 
    The telescope has 2 secondary mirrors.  The f/15 secondary mirror
    forms a Richey Chretien system with the primary mirror.  It can be
    used directly with an instrument mounted at the rear of the
    support structure for the primary mirror or with a flat tertiary
    mirror for a bent Cassegrain or Nasmyth focus.
 
    The f/25 secondary mirror is used with the infrared instruments at
    Keck I. The gold-plated mirror has a central hole to reduce the
    reflection of radiation to the detector from beyond the edge of
    the primary mirror or from the central obstruction for chop angles
    up to +/-150 arcseconds. A chopping mechanism resides behind this
    secondary mirror and does not obstruct the detector.  As the
    chopping mechanism tilts, the image moves on the detector.  This
    provides a way to rapidly center a target on the detector, then
    chop to a nearby part of sky without moving the telescope. The
    Keck Observatory website provides a tutorial for the chopping
    mechanism,
    http://www2.keck.hawaii.edu/inst/tools/chp/Chopping.html.
 
    The optical features of the f/15 and f/25 secondary mirror are:
 
                                   f/15   f/25
                                   -----  ------
      Focal length (m)           : 149.6  249.7
      Scale (mm/arcsec)          : 0.725  1.211
      Field diameter (arcmin)    : 20     10
      Field diameter (mm)        : 870    727
      Radius of curvature* (m)   : 2.14   0.82
 
    The telescope properties given here are reproduced from the Keck
    Telescope and Facility Instrument Guide, available at
    http://www2.keck.hawaii.edu/observing/kecktelgde/ktelinstupdate.pdf.
 
        GROUP                        = OBSERVATORY_PARAMETERS
          OBSERVATORY_ID             = 'OBS378'
          NAME                       = 'W.M. KECK OBSERVATORY'
          COUNTRY                    = 'USA'
          ADDRESS                    = 'California Association for Research in
  Astronomy\n
                                        P.O. Box 220\n
                                        Kamuela, Hawaii'
        END_GROUP                    = OBSERVATORY_PARAMETERS
 
        GROUP                        = TELESCOPE_PARAMETERS
          TELESCOPE_ID               = 'T1'
          NAME                       = '10-M KECK I RITCHEY-CHRETIEN
  ALTAZIMUTH REFLECTOR'
          APERTURE                   = 10 
          LONGITUDE                  = -155.474716 /* -155 28 28.98 */
          LATITUDE                   =   19.825945 /* +19 49 33.4 */
          ALTITUDE                   = 4160 
          COORDINATE_SOURCE          = 'Aerial survey - North American (1983)
  datum'
        END_GROUP                    = TELESCOPE_PARAMETERS