Echelle - Quick Information and Specifications

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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 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