| The Ohio State University
College of Mathematical & Physical Sciences
Department of Astronomy
Baseline Operating Modes
Spectroscopic modes include long-slit and multi-slit modes. The details of these modes are still under development. Potential OSMOS users interested in particular spectroscopic capabilities are strongly encouraged to contact Paul Martini as soon as possible.
Mode Scale Resolution Total Range
Coverage Order Notes Low-Res Grism 3.6 pixel/arcsec 1000-2000 TBD TBD 1st 1 Triple Prism var. 550-40 350-1000 all N/A ... Imaging Filters 350-1000 Filter N/A ... Medium-Res Grism TBD 3000-5000 TBD TBD 1st 2
- Currently being designed
- A grism with these parameters is planned for the future (post deployment)
Design All refractive, spherical optics Focal Station f/7.8 RC at MDM 2.4m telescope Focal Surface Scale 11.528 arcsec/mm Approx Dimensions 1.5x0.5 meters Approx Mass 160kg Construction Optical bench supported by welded steel frame Flexure goal 4um P-V (~1/4 pixel) over a 1hr integration Slit Masks 6 position mask weel, spherical surface to match focal-plane curvature, slits laser-machined in electroformed NiColloy masks approximately 105mm in diameter Long Slits Fixed long slits (0.6, 0.9, and 1.2-arcsec width corresponding to 2, 3, and 4 pixels or 52, 78, 104 microns physical size) that are curved to match the focal surface Slitlets Arbitrary size, shape, and orientation Dispersers 6 position disperser wheel with one 100x85mm direct vision prism and up to 4 VPH grisms (TBD) Imaging Open aperture in slit and disperser wheel Filters Two 6 position filter wheels tilted by 8 degrees, 100x100mm cells (compatible with MDM 'Buckeye' filter wheels). Collimator Design f/7.8, 14 degree FOV Double Gauss optimized for telescope input Collimator Pupil Relief1 70mm Collimator Focal Length 430mm Collimated Beam Diameter 55mm Camera Design f/4.9, 18 degree FOV Petzval with pupil relief and focal plane relief Camera Focal Length 270mm Camera Pupil Relief1 100mm Detector Focal Plane Relief1 50mm Detector Focal Plane Scale 18 arcsec/mm, 55microns/arcsec Imaging Pixel Scale 0.273 arcsec/pixel (15 micron pixels) (De)magnification 1.6x reimaging of telescope focal surface CCD 4096x4096 (15 micron pixels) STA0500A thinned Silicon Guider/Acqusition MDM guider, acquisition via imaging through slit Calibration System Existing MIS (Multi Instrument System) calibration lamps User Access Filter wheels, Slit Mask cassette
Expected Imaging Performance
Wavelength Range 350-1000nm Field of View 20 arcminute diameter circle CCD Pixel Scale 0.273 arcsec/pixel (15um pixels) Standard Filters MDM filter set Throughput1 52% at 350nm, 62% from 400-1000nm Designed Image Quality (80%EE)
- U band: 0.6 arcsec (zenith3), 0.9 arcsec (40 deg zenith angle3)
- B band: 0.3 arcsec
- V band: 0.3 arcsec
- R band: 0.3 arcsec
- I band: 0.4 arcsec
- 350-1000nm (polychromatic): 0.5 arcsec
Expected Count Rates2 Blue: TBD e-/sec for B=21mag
Red: TBD e-/sec for R=21mag
- Transmission through OSMOS collimator and camera only, excluding atmospheric transmission, telescope coating, and CCD quantum efficiency. 2% AR coatings on all air-glass surfaces are assumed (although the goal is 1.5% coatings).
- Magnitudes are at the top of the telescope, rates are for standard Kron-Cousins B and R filters.
- Includes atmospheric dispersion
Expected Spectroscopic Performance
Max Slit Length 20 arcminutes Total Slitlets 50-100 slits/mask CCD Pixel Scale 0.273 arcsec/pixel Wavelength range 350-1000nm Fixed Long-Slits 0.6, 0.9, 1.2-arcsec (2, 3, and 4-pixel width) Gratings up to 4 Planned Gratings R=1000 (params TBD)
R=5000 (params TBD)
Expected Counts/resolution element TBD S/N on point source in 1 hour TBD
Multi-Object Slit Masks
Mask Surface Shape Spherical, matching f/7.8 focal plane Slitlet Shape Arbitrary shape & size Slitlet Orientation Tilted up to +/-30° from vertical Slitlet Length >0.6arcsec (>52um), typically <20" (1.73mm) Slit Widths >0.6-arcsec (>52um), typically 1.2-arcsec (104um) Edge Smoothness ~1.8um rms (2% of 1.2-arcsec wide slit) Parallelism TBD Slit-to-Slit Position Tolerance 5um rms perpendicular (5% of 1.2-arcsec width)
150um rms parallel (10% of 20-arcsec length)
End Shapes Square or Round Cost per mask Estimated to be $100-$200 Mask Generation Laser machine at the University of Arizona (primarily used for LBT instruments)
- Masks will be laser-machined and mounted in metal frames for loading into the slit mask wheel. The substrate will be electroformed NiColloy metal (Nickel-Cobalt alloy) coated with copper black.
- During manufacturing, a barcode could be applied for tracking purposes. This barcode would be read with a hand scanner when the mask is stored off-instrument.