The Double Spectrograph

The Double Spectrograph is a multi-purpose dual channel grating spectrograph. It can operating in single output mode, or a dichroic can be inserted which splits the incoming beam into two bands, blue and red, which are then dispersed with separate gratings. The single slit is 128 arcseconds in length; the width can be set to 1/2, 1, 2, 4, 6, 8, or 10 arcsecs. Click here to see a schematic drawing of the upper portion of the Double Spectrograph (after Oke and Gunn 1982).

  • The red camera uses a 1024 by 1024 CCD with 24 micron pixels and is sensitive over the range 4700 to 10000 Angstroms. The blue camera uses an 800 by 800 CCD with 15 micron pixels over the range 3100 to 7000 Angstroms.

    Gratings:

    1st Order Dispersion (Å/mm) 1
    lines/mm Blaze (Å) Red Cam Blue Cam
    158
    300
    316
    600
    600
    1200
    1200
    1200
    7500
    3990
    7500
    4000
    10000
    5000
    7100
    9400
    404
    -
    204
    -
    108
    53
    53
    53
    134 (2nd order)
    140
    -
    72
    -
    36
    36
    36

  • The angle of the grating must be set to give you proper wavelength coverage. Tables are provided that predict the center wavelength for a given angle tilt for each grating.

  • Four dichroic filters are available. They provide for splitting the incoming light beam at wavelengths of 4800, 5200, 5500, and 6800 Angstroms respectively.

    More details on Double Spectrograph can be found at the Palomar Observatory Double Spectrograph setup page. It is also described well in the paper by Oke and Gunn, 1982, PASP 94, 586.


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