MODS Overview

MODS1 and MODS2 are UV to near-IR (0.32-1.1 micron) multi-object double spectrographs mounted at the left and right direct Gregorian focal stations of the LBT.  They were designed and built by The Ohio State University Department of Astronomy in Columbus Ohio. The full field of view of each MODS is 6’ x 6’, and at the focal plane, either a custom multi-object slit mask, one of the 0.3”, 0.6”, 0.8”, 1.0”, 1.2”, 2.4” or 5" long-slits or an empty mask frame for imaging can be inserted. Light can go straight through to the blue channel, be reflected to the red channel, or be split by a dichroic at 565 nm and directed to both blue and red channels. Both blue and red channels contain medium resolution (R~2000) gratings and low resolution (R~500-150) double-pass prisms, as well as flats for imaging at Sloan u and g (blue) and r, i and z (red).


Image of MODS1 & MODS2 while the telescope is pointed at horizon, taken from Level 9.  Photo credit: Rick Pogge.
   
  •  Optical Design: Seeing-limited, dichroic-split double-beam grating spectrometer
  •  Wavelength Coverage: 3200 — 10000Å
  •  Field of View: ~ 6×6-arcminutes 
  •  Pixel Scales:
    •   Blue: 0.120 arcsec/pixel
    •   Red: 0.123 arcsec/pixel

Mode Channel Filter(s) Wavelength Range (nm) CCD Readout Notes
Direct Imaging Dual B:SDSSug
R:SDSSriz
330-1000 3088 x 3088 Simultaneous blue & red filter imaging with pairs of filters
Blue SDSS ug 330-600 extended red coverage
Red SDSS riz 500-1000 extended blue coverage
Grating
Spectroscopy
 (R=~2000 for 0.6" slit)
Dual B: Clear
R: Clear
320-1000 8288 x 3088 Lower s/n at the dichroic crossover wavelength at 5650Å.
GG495 suppresses leaks from very blue targets
Blue B: Clear 320-600 Extended red coverage thru the dichroic cross-over
Red R: GG495 500-1000 Extended blue coverage thru the dichroic cross-over
Prism
Spectroscopy
(R=100-500 for 0.6" slit)
Dual B: Clear
R: GG495
320-1000 4096 x 3088 Lower s/n at the dichroic crossover wavelength at 5650Å.
GG495 suppresses leaks from very blue targets
Blue B: Clear 320-600 Extended red coverage thru the dichroic cross-over
Red R: GG495 500-1000 Extended blue coverage thru the dichroic cross-over