Keck NGAO Science Requirements

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Keck NGAO Science Requirements

• Claire Max
• UC Santa Cruz
• Caltech NGAO Meeting
• November 14, 2006

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Outline

• Background
• JWST and ALMA
• Science requirements for selected key areas
• Multiplicity and size of minor planets
• Imaging extrasolar planets around brown dwarfs
  and low mass stars
• General relativistic effects in the Galactic
  Center
• Galaxy assembly and star formation history
• Other science cases are in progress
• Roll-up of requirements to date
• Some key issues that have emerged

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Background

• Science Requirements Document (SRD) is a living
  document and will be updated as the science case
  is developed with increasing fidelity.
• Initially, SRD will heavily reference the science
  cases developed for Proposal to Keck SSC in June
  2006.
• Key issues
• Importance of science enabled by NGAO system and
  accompanying instruments
• Advances offered by NGAO relative to existing
  systems and new AO systems being developed on
  other telescopes
• Complementarity to JWST and ALMA, which will be
  commissioned on the same timescale as Keck NGAO
  will be commissioned.

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JWST Capabilities

• Cryogenic 6.5m space telescope to be launched in
  2013
• Higher faint-source sensitivity than Keck NGAO
  (very low backgrounds)
• NIRCAM will image from 0.6-5 µm
• 2.2 x 2.2 arc-minute field of view, pixel scale
  of 0.035 arc sec for 0.6-2.3 µm, and
  coronagraphic capability
• NIRSpec multi-object spectrograph with an IFU
• In R100 and R1000 modes will obtain
  simultaneous spectra of gt100 objects in 3.4 x 3.4
  arcmin field of view
• Has an IFU with field of view 3 x 3 (R1000 or
  3000 not clear which)
• Spatial pixel size will be 0.1 arc sec in all
  cases
• Conclusions for NGAO? We can compete at higher
  spatial resolution (lt0.1 arc sec) and shorter
  wavelengths (lt2 µm) where JWST will not be
  diffraction limited or Nyquist sampled.

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ALMA Capabilities

• Very powerful new facility for mm and sub-mm
  astrophysics
• Currently scheduled to begin science operations
  in 2012
• Consists of 54 12-m and 12 7-m antennas located
  at 5000m (16,500 feet) in the Atacama desert
• Typical spatial resolution 0.1 arc-second (down
  to 0.01 arc-seconds at high frequencies)
• Chemical evolution in star-forming regions at
  z3, dust-gas interactions, molecules surrounding
  stars, molecular clouds, dust emission out to
  z20, kinematics of obscured galactic nuclei and
  quasi-stellar objects on spatial scales smaller
  than 100 pc
• Conclusions for NGAO? A renaissance in star
  formation studies near and far new insights into
  highly obscured distant galaxies

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Science case Size and shape of minor planets
Ceres, K band, Keck NGS AO

• Shape and size
• Some are round, many are not
• IAU planet definition debate!
• Surface features
• Ceres is one example low contrast will be helped
  by high NGAO Strehl ratio
• Observations of the 15 - 20 largest asteroids
  will provide strong constraints on frequency of
  large collisions
• NGAO should be able to resolve 800 main-belt
  asteroids

Eros
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Science case Multiplicity of minor planets
Simulation of fake moonlet around 87 Sylvia

• Recent data suggest that primary asteroid of most
  binary asteroid systems has rubble-pile
  structure, weak shear strength
• Hence shape is directly related to angular
  momentum at formation
• Moonlet orbit plus shape of primary gives mass of
  primary
• NGAO, particularly at R band, increases detection
  rate of moonlets dramatically

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Minor planets science requirements

• Driver for visible wavelengths 0.7 lt ? lt 2.4
  microns
• Reflected sunlight, important spectral bands
• Preferred instrument visible imager
• Other instruments visible IFU
• Instantaneous FOV 2 arc sec, Nyquist-sampled
• Image quality 170 nm OK, still doing simulations
• Photometric accuracy 5 for satellite relative
  to primary
• Astrometric accuracy Nyquist/4
• Contrast ratio ?m gt 5.5 at 5 arc sec from
  primary
• Other important considerations
• Need non-sidereal tracking need rapid
  retargeting in LGS mode (10 min compared with 25
  min today) request service observing

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Science case Extrasolar planets around nearby
stars

• Gemini ESO extreme AO systems very powerful,
  but cant look around low-mass stars or brown
  dwarfs
• Too faint for wavefront sensing
• Low-mass stars are much more abundant than higher
  mass stars they might be most common hosts of
  planetary systems
• Survey of young T Tauri stars will constrain
  planet formation timescales

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Extrasolar planets Science Requirements

• Wavelength range 0.9 lt ? lt 2.4 microns
• Preferred instrument NIR imager
• Other instruments Low-resolution (R100) near-IR
  spectroscopy (could this be done with narrow-band
  filters?), L-band imager
• Instantaneous FOV 5 - 10 arc sec, 5 - 10 mas
  sampling
• Image quality 140 nm OK, still doing simulations
  of 170 nm
• Photometric accuracy 5 for planet relative to
  primary
• Astrometric accuracy lt 5 mas
• Contrast ratio ?H10 at 0.5 separation
• Other important considerations
• Need coronagraph Need low residual static WFE
  (how low?) Need rapid retargeting in LGS mode
  (10 min compared with 25 min today) Need IR
  tip-tilt (both on and off axis)

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Science Case General Relativistic Effects at
Galactic Center

• Detect deviations from Keplerian orbits around
  black hole
• Highest priority strong-field GR precession
• Can be measured even for single orbits of known
  stars (S0-2) if astrometric precision is 100
  µas coupled with radial velocity precision of 10
  km/s
• If NGAO allows discovery of other (fainter)
  close-in stars, may be able to measure other
  effects too

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Galactic Center science requirements

• Wavelength range K band
• Preferred instruments NIR imager and NIR IFU
• Imager instantaneous FOV 10 arc sec (now 20
  km/s), Nyquist samp
• IFU instantaneous FOV 1 arc sec, 20 or 35 mas
  sampling
• Other instruments R15,000 IR spectrograph would
  be good
• Spectral resolution 3000 - 4000
• Image quality 170 nm OK, doing simulations of
  other WFEs
• Astrometric accuracy 0.1 mas
• Radial velocity accuracy 10 km/s
• Contrast ratio ?K4 at 0.05 separation
• Other important considerations
• Need IR tip-tilt (consider H or K band, because
  of very high extinction at J band)

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We need to understand what is limiting
astrometric accuracy today

• Uncertainty decreases as expected for brighter
  stars, then hits a floor.
• Why the floor? Tip-tilt anisoplanatism? Work is
  underway.

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Comment on astrometric accuracy and AO design

• MCAO systems are known to suffer from focal plane
  distortions.
• In addition to tip and tilt, differential
  astigmatism and defocus between the DMs is
  unconstrained. These three unconstrained modes do
  not influence on-axis image quality, but produce
  differential tilt between the different parts of
  the field of view.
• Our Point Design has a large DM for high stroke
  correction, and a smaller DM (MEMS or other) for
  high-order correction. Need to analyze
  interaction of the two DMs to avoid or minimize
  focal plane distortions.

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Science Case Galaxy assembly and star formation
history

• Overview
• Study galaxies at z gt 1 via their emission lines
• Star formation H?
• Metallicity NII / H?
• Excitation OII, OIII (star formation, AGN
  activity)

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Space densities of types of galaxies

• Tens of galaxies per square arc min
• Clear benefit to deployable IFUs
• How many? Decide based on total cost and design
  issues (e.g. all fit into one dewar)
• Reasonable number? 6 - 12 IFU heads

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Low backgrounds are key

• Backgrounds are current limit for OSIRIS science
  in this field
• Requirement background AO system less than 10 to
  20 of that from sky and telescope
• We need to address cooling issues vigorously
• What is practical, what are costs?

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High z Galaxies science requirements

• Wavelength range JHK bands
• Preferred instruments deployable NIR IFUs (6 -
  12)
• IFU instantaneous FOV 3 x1 arc sec requirement,
  3 x 3 arc sec goal
• Spectral resolution 3000 - 4000
• Spatial sampling 50 mas
• Image quality 50 mas enclosed energy (what
  fraction?) for optimal tip-tilt star
  configuration
• Sky coverage fraction gt 30 on average, if
  consistent with above image quality spec. If
  not, iterate.
• Sky background less than 10-20 above sky
  telescope
• Other important considerations
• No. of IFUs should be determined by total cost,
  and by design issues

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Spreadsheet summary
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Key issues that have emerged

• Keep asking how does this science complement
  JWST capabilities? or where is NGAOs sweet
  spot relative to JWST?
• Need non-sidereal tracking (asteroids)
• Need rapid retargeting in LGS mode (10 min
  compared with 25 min today)
• Need coronagraph and low residual static WFE (how
  low?) (planet detection)
• Need IR tip-tilt (think about H or K for Galactic
  Ctr)
• Need to understand what is limiting astrometric
  accuracy for Galactic Center today (need 0.1 mas)
• Need to understand astrometric implications of
  having gt 1 DM
• Need sky background less than 10-20 above sky
  telescope
• Determine of IFUs from total cost and from
  design issues (below what is it possible to fit
  all into one dewar?)