DESpec spectrographs Jennifer Marshall Darren DePoy Texas A&M University.
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Transcript of DESpec spectrographs Jennifer Marshall Darren DePoy Texas A&M University.
DESpec spectrographs
Jennifer Marshall
Darren DePoy
Texas A&M University
Prototype design: VIRUS clone
• 10 fiber-fed unit spectrographs, 400 fibers each
• Wavelength range 550-950 nm in one arm
• Resolution at 950 nm = 3167• Uses 2 DECam CCDs in each arm• Based on VIRUS design
VIRUS
• The first highly-replicated instrument in optical astronomy
• 150+ channel fiber-fed Integral Field Spectrograph placing >33,000 1.5” dia fibers on sky
• 350-550 nm coverage and R~700
VIRUS spectrographs
• Simple design– Single reflection spherical collimator– Schmidt camera
• Two lenses + one spherical mirror– VPH grating
• High throughput
Unit spectrographs packaged in pairs
Texas A&M’s role in HETDEX
• Participate in optical and mechanical design of VIRUS
• Fabrication and procurement of VIRUS components
• Assemble VIRUS unit spectrographs• Optically align instruments in lab• Ship to McDonald
HETDEX+VIRUS specs
• Wavelength: 350 – 550 nm• Resolution: R~700• Integration time: t=20 minute• Fiber diameter: 1.5” on sky• Sensitivity
– Line flux limit 3.5e-17 – Continuum detection gAB~22 mag
Flexibility of VIRUS design
• VIRUS design is readily adaptable to other fiber-fed spectrograph systems– Easy to change resolution, wavelength
range, etc. with simple redesigns• Has already been used as basis of new
spectrograph design– LRS2, a moderate resolution red-optimized
spectrograph for HET
DESpec as VIRUS clone
• Relatively straightforward redesign of VIRUS can produce DESpec– Change grating– Reoptimize coatings– Refractive camera?
Alternate design: two arms
• 10 fiber-fed unit spectrographs, 400 fibers each• Increased wavelength range• Two arms, blue (500-760) and red (760-1050)• Different resolution in each arm
– 625 nm, R~1923– 950 nm, R~3276
• Uses 2 DECam CCDs in each arm• Significant design modification from VIRUS
– Similar optical layout to GMACS
GMACS
• Wide-field, multi-object optical spectrograph for GMT
• Four quadrants with two arms (red and blue) each– One quadrant could be
modified to become DESpec unit spectrographs
How to decide
• Need science input to provide instrument requirements:– Wavelength range– Resolution– Density of targets/number of fibers– Fiber size on sky
Work required to design DESpec as VIRUS clone
• Science input for instrument requirements
• New optical design for camera• Mechanical redesign of camera• Mechanical design of instrument
mounting scheme on telescope• Cooling system redesign
Work required to design DESpec as VIRUS clone
• We would need about 2 years of engineering effort for redesign
• A&M could assemble and test spectrographs in ~2 years– Lots of experience from VIRUS!
• These are estimates; will require more careful schedule/planning
Work required to design DESpec two-arm design
• More optical and mechanical design work required– Increases cost
• May need non-DECam CCDs for blue channel– Increases cost
Summary
• VIRUS design could be easily and relatively cheaply adapted to DESpec spectrographs– Two-arm re-design is more involved but
possible• Would need ~10 spectrographs• 3-4 years of effort in redesign and
assembly
Sky lines
Resolution Percent Free Resolution Percent Free
6833 75 10000 72
5198 70 8846 70
3089 60 5610 60
1984 50 3538 50
1347 40 2383 40
905 30 1565 30
799 25 1288 25
312 10 603 10