TMT Instrument Working Group MCAOMOAO, Deployable Integral Field Spectrograph

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TMT Instrument Working GroupMCAO/MOAO,
Deployable Integral Field Spectrograph

• TMT Instrument Working Group
• James Larkin
• March 19, 2004

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Scientific Justifications

• Spatially resolved kinematics and chemistry
  within high z galaxies.
• Core sizes 0.2, scale 19 kpc
• R5000
• 40-100 objects per 2 field (K22-23mag)
• Star and planet formation (YSOs)
• Probably only one per field.
• Stellar Clusters (population studies)
• Single Field many objects.
• Galactic Center
• Single Field many objects.
• Planets Moons
• One per field
• AGN Quasars Radio Galaxies
• One per field
• 1 priority from TMT science committee.

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Basic Operational Requirements

• 0.8-2.5 mm
• 5 mm especially for YSOs
• R5000 (OH lines, kinematics)
• Rgt10,000 for UV lines from z6-10
• Broad band coverage in each spectrum (2000-4000
  spectral elements)
• Spatial sampling
• 0.02-0.05 for galaxies
• 0.005 for Nyquist at J
• Spectroscopy over 2x2 arcmin in gt10 movable
  groups (high fill factor).
• Driven by high redshift objects (10x10 elements
  each group).
• Number of resolution elements gt 10x(10x10) x
  20002,000,000
• Monolithic imaging spectroscopy over gt1 arcsecond
  at 0.005 sampling (200x200 elements).
• Dissect individual objects, precision astrometry
• Number of independent resolution elements gt
  80,000,000

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Traditional Integral Field Techniques
Focal Plane Feed to Spectrograph Detector
Lenslet Array Fiber Bundle Image Slicer
1 2 3 4
1 2 3 4
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Many Strawmen Designs

• ELT, CELT and other working groups have already
  fleshed out several possible solutions.
• Many overlapping concepts.
• Movable pickoff mirrors to direct light to image
  slicers.
• Lenslet arrays attached to fiber bundles.
• Usually break spectroscopy into multiple
  spectrograph modules (2k x 2k or 4k x 4k
  detectors each).
• Often break focal plane into multiple feeds (4)
• There are additional proprietary concepts being
  pursued.

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Spectral Format

• Need Rgt4000, and full broad band
• If 4kx4k detectors are available then a column
  can contain a full broad band spectrum with
  R8000
• Cross disperse for entire J,H K?

JHK JHK JHK JHK
JJJJ HHHH KKKK
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Current AO IFSs

• Several groups are developing or have recently
  completed near-IR IFSs.
• SINFONI (ESO/MPE)
• CIRPASS (Gemini visitor)
• GNIRS (Gemini South)
• NIFS (Gemini North)
• Atlantis (GranTeCan)
• OSIRIS (Keck)

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OSIRIS Point Source Sensitivities

• AO-fed IFUs can achieve extremely high
  sensitivity.
• Small background per spatial element.
• Low background between OH lines.
• Excellent infrared detectors.
• On Keck with 30 Strehl, comparable to NIRSPEC on
  JWST even at H band.
• Detector limited same detector.
• These are the limiting magnitudes per resolution
  element for a 5-s detection in 1 hour (4 x 15
  minute frames)

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Fundamental Concerns

• Detector Limited
• Background in 0.005, dispersed to R5000 is two
  orders of magnitude below existing detector dark
  currents between OH lines.
• 1-5 micron devices may have significantly higher
  dark current and read noise.
• Lose significant sensitivity in 1-2.5 microns
  region.
• Latest Rockwell 1-5 micron detectors claim good
  performance.
• Probably NOT a problem for coarse sampling
  (gt0.05).

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Fundamental Concerns

• Wavefront error more this afternoon
• If 0.005 is desired, the instrument wfe budget
  will probably be around 10 nm (rms).
• This may require very early sampling of the focal
  plane Lenslets, lenslets with fibers.
• If 0.05 is sufficient, then all solutions may
  work.
• In general, there is a factor of 10 in possible
  plate scales discussed by Science team!

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Fundamental Concerns

• PSF knowledge Quantitative science will require
  a high quality estimate of the PSF.
• Will the AO system provide sufficient telemetry
  to model the PSF?
• Simultaneous imaging of psf stars within the
  field.
• Parallel imager? OSIRIS has one.
• Can you measure a few stars at one field location
  and extrapolate to MCAO/MOAO field of view?

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Fundamental Concerns

• Instrument and Focal plane stability
• 0.005 10 microns in the F/15 focal plane.
• Active stabilization of the instrument alignment.
• On board wavefront sensor (at least focus?)
• Atmospheric dispersion. J band at 45o is 0.02
  across the band.
• Positioning could be very difficult. If deployed
  unit has small scale (0.005), then its field
  will be VERY small (0.05).
• Number of pixels. If 1x1 is to tiled with
  0.005x0.005 samples and R5000, this is
  80,000,000 resolution elements (perhaps
  160,000,000 pixels).
• Reducibility of the Data
• Thousands of spectra with complex geometry.

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Fundamental Concerns

• MCAO Field is quite large. Two arcminutes is
  24,000x24,000 resolution elements.
• If sampling elements are 100 microns, then they
  must have reimaging optics in front of each
  bundle. This will set the closest spacing of
  neighboring bundles.
• MOAO Same packaging problem. Plus each bundle
  has to have the AO mirror, and probably the
  filter and cold pupil stop.
• Plate scale changes? Filter wheels?
• Maybe some bundles are dedicated J, H or K?
• Maybe some bundles have different scales?

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Two Instruments?

• 1. Deployable 1-5 micron instrument.
• Coarse sampling (0.05).
• 20 deployable units of 10x10 elements.
• Up to 2 arcmin diameter field.
• R5000.
• Telemetry may be sufficient for PSF.

Common Window
Reimagers with Filters
Fiber bundles
Spectrograph Modules
Cryostat
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• 2. Monolithic 1-5 or 1-2.5 micron wavelength.
• Fine Sampling 0.005
• Small single field of view 1-2
• High stability precision relative astrometry
• Few moving parts.
• On-board active alignment and focus.
• Very early sampling of the focal plane (high
  Strehl).
• Might also serve as extreme-AO instrument
• Parallel imaging capability for PSF.
• Will be detector limited in sensitivity.

Spectrograph
Collimator Optics
Lenslet Array
Cold Lyot Stop
AO Focus
Grating
Filters
R. I. Collimating Singlet
R.I. Camera Singlet
Pupil Plane
Camera Optics
Focal Plane
Other scales
Lenslet
Detector
Reimaging Optics
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Hybrid?
Common Window
Reimagers with Filters
Fiber bundles
Spectrograph Modules
Cryostat