Transcript 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.

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 highlyreplicated 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
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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
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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