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The Faint-object Nasmyth Spectrograph of the Tautenburg 2m-Telescope


The Nasmyth spectrograph is a single object spectrograph in combination with a focal reducer camera. It was developed and built at TLS for the spectroscopy of faint objects at low dispersion. First light was in 2001.

The imaging optics of the focal reducer consists of the collimator (f = 482.2mm) which re-images the entrance pupil of the telescope and the camera optics (f = 135 mm) which focusses the beam onto the CCD detector. Direct imaging mode is useful only for aquisition in order to position the object on the slit. (There is no field flattening lens used and there is not enough space to insert a filter wheel.)

For spectroscopy a longslit of tunable width is used in combination with a grism wheel. The grism wheel allows to select one out of five grims or, alternatively, a grism-free position ("white") for aquisition.

The detector is a nitrogen-cooled SITe CCD with 1024x800 pixels. The pixel size is 15 µm, corresponding to 0.53 arcsec.

A graphical user interface allows simple and quick handling of the spectrograph. 

Gerneral data

  • General datafield of view: ~5 arcmin (no field flattening!) 
  • longslit of 20 mm (~3 arcmin) length and tunable width 
  • five grisms with dispersions between 100 and 230 Å per mm 
  • wavelength coverage: 3500 Å to 10000 Å (depending on grism) 
  • wavelength calibration: night sky lines

Available grism

grismlines per mmwavelength range ÅÅ per pix    Å per mmresolution (2 px) in Å
B2003001210 - 7490     3.56231580 (at 4000 Å)
V2003002310 - 93503.38     225960 (at 6500 Å)
R2003005480 - 115603.062041310 (at 8000 Å)
B1006002160 - 57301.64     1091220 (at 4000 Å)
V1006004670 - 76901.52     1012140 (at 6500 Å)