FOCAS
(Faint Object Camera and Spectrograph)

FOCAS Photo

Designed for high-sensitivity optical observations of faint celestial objects, this versatile instrument includes all of the fundamental modes of optical astronomy: imaging, spectroscopy, and polarimetry. Its multi-object spectrograph, which enables observations of the spectra of about 50 objects at once, allows astronomers to determine the distance and detailed physical proper-ties (e.g., chemical composition, mass, stellar population) of very faint celestial objects in far-distant galaxies. The data it produces contribute to an under-standing of the origin and evolution of the Universe.



Fast Facts

  • Description:
    • Optical imager
    • Low- to medium-resolution multiple-object spectroscopy
    • Specialied for observing faint objects
  • Operation:
    • Allows broad- and narrow-band imaging, spectroscopy, imaging polarimetry, and spectropolarimetry of a wide range of objects.
    • Several observational modes
      • Direct optical imaging
      • Long-slit spectroscopy
        • Observes a single celestial object through an elongated slit aperture.
        • Refracts light with a prism or diffraction grating.
        • Allows different frequencies of light to fall on different parts of the sensor.
      • Multi-object spectroscopy
        • Uses several slits to observe multiple celestial objects in the field of view.
        • Uses a slit-mask changing system to position a special mask each time, depending on the target area.
        • Obtains simultaneous spectra of up to 50 objects close to each other in the area.
      • Polarimetry
        • Measures polarization of light, i.e., the degree to which light waves vibrate wholly or partially in one direction rather than at random.
        • Gives information about the orientation of the object not obtained by other observational methods.
      • Spectropolarimetry
        • Measures polarization of light from celestial objects
        • Uses spectrograph to isolate the areas for measurement
    • Flexibility of observing modes with quick, efficient exchanges
      • From spectroscopy to polarimetry to imaging
      • Of filters, grisms (a combination of a prism and grating), gratings (fine, parallel, equally spaced grooves)
      • Of the angle of the wave plate, which converts polarized light in different ways
  • Applications:
    • Designed especially for spectroscopy of faint objects, e.g., distant galaxies, quasars, outer asteroids of the Solar System.
    • Confirms actual distances of celestial objects, e.g., supernovae, and measures distances to the most distant, faint galaxies near the edge of the Universe.
  • Specifics:
    • Size and weight
      • Size: 2 x 2 x 2 m
      • Weight: 2 tons
    • Placement: Cassegrain focus
    • Wavelength(s): 0.4-1.0 microns
    • FOV: 6 arcminutes
    • Detectors: CCDs with enhanced sensitivity (Hamamatsu)
      • Two 4,096 x 2,048 pixel 4-side buttable detectors
      • 2 x 1 mosaic pattern
  • Development:
    • 1991-1995 Finalized the detailed design, e.g., optical design, mechanical design, control system, grisms, wave plates for polarimetry, multi-slit exchange mechanism.
    • 1996 Construction began. The collimator lens unit and the camera lens unit were manufactured by Nikon.
    • 1999 Shipped to Hawaii. Action and control tests, adjustments, optimizations on telescope simulators at Mitaka campus in Tokyo and at the Hilo base facility.
    • 2000 (February) First light
    • 2001 Available for common-use observations after commissioning and testing most of the instrument's features
    • 2003 Polarimetry mode available
    • 2010 CCDs replaced with fully-depleted type CCDs manufactured by Hamamatsu Photonics KK
  • Specialized Information about the Instrument and Observing:

 

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