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Astrophysical Research Consortium - Apache Point Observatory

Astrophysical Research Consortium
Apache Point Observatory
3.5m Telescope

 

Echelle - Quick Information and Specifications

Contact Webmaster for web page errors, corrections, ommisions, and/or additions.

This page last updated: Sept 27, 2007 - GS
This page last checked: September 28, 2004 - JMD

Basic User's Guide: Echelle - 2007

Information in Yellow may not be correct or is missing for this instrument!!!

Brief Instrument Description

The ARC echelle spectrograph records the entire visible and near-IR spectrum in one exposure on a 2048 x 2048 SITe CCD chip with 24 micron pixels, with a resolution of 30,000. (2.5 pixels)

The spectrograph records the spectrum in about 105 echelle orders. The separation between orders ranges from about 9" (9 arc-sec) in the blue, to 5" in the near IR.

The design goal calls for total spectrograph throughput of 9% for wavelengths > 4100 Ang.

Camera

  • CCD is a SITe TK2048E back illuminated CCD
  • CCD is a 2048 x 2048 pixel array
  • CCD pixel size = 24 µm
  • CCD gain = 3.8 e-/ADU
  • CCD read noise = 7e-
  • Quantum Efficiency ~70%
  • Dark Current: 0.002 e-/sec/pix (7.25 e- per hour) (Needs checking!)
  • Pixel scale: see Field of View
  • Full well depth: 150k e-
  • Linear up to35k, Saturation at 48K
  • Installed filters (User selectable): (QTH) Filters: Open, Blue
  • Available gratings (Observing Specialist installable):
  • Grating resolution 31.6 grooves/mm, blaze angle b = 63.5°
  • Spectral coverage: about 3,500 Å to 9,800 Å
  • Schmidt camera f/2.7, focal length = 540 mm
  • Field of View: Available slits (Observing Specialist installable): 1.6" x 1.6" , 1.6" x 3.2" (default), 1.6" x 4.7", 0.9" x 0.9" (pinhole)
  • Minimum Exposure:
  • Chip Temperature: -120C

ECHELLE CHARACTERISTICS

SPECTRAL COVERAGE:

  • about 3,500 A to 9,800 A (in one exposure)
  • UV cutoff is set primarily by UBK7 prisms

RESOLVING POWER:

  • entrance slit width = 272 microns (or 1.6 arcsec)
  • projects to 48 microns on CCD, with resolving power = 37,500, or a velocity resolution = 8 km/s

SENSITIVITY:

  • m(v) = 16 yields 1 count/sec/pix/A

DETECTOR:

  • SITe TK2048E back illuminated 2048x2048 CCD with 24 micron pixels
  • gain 3.8e-/DN, read noise 7e-
  • Dark Current: 0.002 e-/sec/pix (7.25 e- per hour) (Needs checking!)

COLLIMATOR:

  • off-axis parabola
  • diameter = 225 mm, of which 200 mm (beam size) is actually used
  • focal length = 2000 mm
  • focal ratio = f/10

GRATING:

  • 31.6 grooves/mm, blaze angle b = 63.5 deg (nominal), or tan b = 2
  • incident angle = 69.5 deg

CROSS DISPERSION:

  • two 45 deg prisms of UBK7, used at minimum deviation
  • total deviation through both = 52.7 deg

SCHMIDT CAMERA:

  • f/2.7, focal length = 540 mm
  • corrector has LLF2 (flint) and UBK7 (crown) elements
  • effectively achromatic over entire spectral range (below)
  • spherical mirror with diameter = 381 mm
  • (reciprocal) dispersion at CCD = 3.3 A/mm at 6000 A
  • perpendicular to dispersion at CCD, scale = 22 arcsec/mm