NGAO System Design Phase
Update
Peter Wizinowich, Rich Dekany, Don Gavel, Claire Max
for NGAO Team
SSC Meeting
April 3, 2007
Presentation Sequence
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Project Report #2
Science Requirements
Performance Budgets
Trade Studies
Summary
2
Project Report #2
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2nd report submitted to Directors on Mar. 31
http://www.oir.caltech.edu/twiki_oir/bin/view.cgi/Keck/NGAO/SystemDesignPhasePlanning
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Emphasis to date continues to be understanding the major
design drivers through a process of iteratively developing
the science case requirements & the performance budgets
Work also continues on a number of trade studies in
support of the performance budgets & the future design
choices
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Project Report #2
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MILESTONE
DATE
DESCRIPTION
1
SD SEMP Approved
10/9/06
2
SD phase contracts in place
10/27/06
Contracts issued to Caltech & UCSC
for the system design phase.
$50k initial contracts
issued on 12/20
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Science Case Requirements
Summary v1.0 Release
10/27/06
Initial Release as input to trade
studies & performance
budgeting
Complete
4
System Requirements
Document v1.0 Release
12/8/06
Initial release of System
Requirements with emphasis on
science requirements
5
Performance Budgets
Summary v1.0 Release
2/27/07
1st round of all performance budgets
complete & documented
Good progress
6
System Requirements Doc
v2.0 Release
3/22/07
2nd release of System Requirements
Document
Recently started
7
Trade Studies Complete
5/25/07
All trade studies complete (Keck
Adaptive Optics Notes)
Good progress
Approval of this plan by the
Directors. SEMP released to
Directors on 9/29/06.
STATUS
Verbal approval received.
Written approval
requested
Complete
4
Project Report #2
5
Project Report #2
Schedule
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Still behind schedule, but catching up some (need to catch up more)
21% of System Design Phase activities complete through Mar.
Budget
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$772k initially budgeted for FY07. $46k recently added to achieve
SEMP request.
$234k spent through Feb.
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29% of the FY07 budget (versus plan of ~ 40%)
20% of the System Design Phase budget
Replan
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Scheduled mid-year replan in process
Will use this to help address schedule slip
Still intend to hold to overall schedule & budget
6
Science Case Requirements
& Science Instruments
Science Case Requirements Document
• Release 1 contains the following:
– JWST and ALMA capabilities
– Future AO capabilities of other observatories
– Key science cases that stress various aspects of AO:
• Multiplicity, size, and shape of minor planets
• Planetary & brown dwarf companions to low mass stars
• General relativistic effects in the Galactic Center
• Assembly and star formation history of high z galaxies
• Release 2 (in progress) will also include
– Solar System: Titan, Io, Jovian planet icy moons
– Galactic astronomy: Protostellar objects, Debris disks
– Extragalactic astronomy: Strong lensing, AGNs, QSO host gals
• Still to come: resolved stellar populations
9
Developments since Release 1:
Complementarity of JWST and NGAO
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C. Max trip to GSFC to meet with JWST folks
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Broad-band imaging: limiting mag of JWST ~ 4-5 mags fainter than NGAO
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JWST not diffraction limited below K band
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PSF FWHM same for 0.6 m < l < 2 m as it is at 2 m: FWHM ~ 0.07 arc sec
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Spectroscopy:
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NIRSpec px scale 0.1”
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Enclosed energy at 1 m = 60-64% within 0.15”
Areas where Keck NGAO would nicely complement JWST
1.
Spectra @ spatial resolution better than 0.1”, l = 0.6 - 2 μm
2.
Imaging @ spatial resolution better than 0.07”, l = 0.6 - 2 μm
3.
Spectral resolution R > 2700
4.
Multi-IFU spectroscopy
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JWST: Implications for high-z galaxy science case
• One of our key science cases: IFU
spectroscopy of high-z galaxies
• H is redshifted into K band for z =
2 - 2.6
• Yet forl > 2.1 m, NGAO sky
background starts to hurt a lot
• Cooling the AO system can help
– Much more feasible if we use
MEMS (small volume to be cooled)
OAP relay
l/l = 2000
TAO = 277.5 K
11
How cool is cool enough?
• Target goal: AO to contribute
at most 30% of background
• This opens “typical” z~2.6
galaxies within reasonable
observing times ~ 3 hours
• How to achieve this?
– 65% thruput, cool to -18C
– 75% thruput, cool to -12 C
–
We have to assess how much it’s
worth investing to cool NGAO at
K band, in view of JWST’s great
advantage in sensitivity
12
Astrometry: goal 0.1 mas for Galactic Center
• Ghez et al. are studying what is
limiting astrometric accuracy for
current LGS AO system
• Can achieve average positional
uncertainty close to 0.1 mas for
bright stars (K < 14).
• But what is causing the broad
spread?
• Under active investigation: PSF
changes due to
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Anisoplanatism
Differential atmospheric refraction
Wind shake
.....
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NGAO Instruments Working Group
• Focused on interactions with Science team
• Developing more complete instrument requirements
– Requirements for deployable IFU are converging
– Further work needed to refine imager requirements
– Further work needed to refine visible wavelength instrumentation
• Membership:
Sean Adkins (chair), Steve Eikenberry, Claire Max,
David Le Mignant, Anna Moore
(and later, James Larkin)
• Regular telecons & planning future in person workshop sessions
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Current Instrumentation Thoughts
• Visible and near-IR
– Natural configuration breakpoints based on wavelength coverage
– Trying to balance performance, features, cost and risk
• Imagers
– Simple, Nyquist or Nyquist/2 spatial sampling
– Coronagraph
– Deployable imagers?
• Spectrographs
– Single object IFU
– Deployable IFU
• Specialized instruments?
– R ~100 IFU
– High contrast imaging
15
NGAO Performance Budget Development
Developing Science-based Performance Budgets
• Systems engineering considers all of the following:
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Model assumptions
Model/tool validation
Wavefront error vs. sky coverage
for 5-7 science cases
Photometric precision in crowded and sparse stellar fields
Astrometric accuracy
at the GC and in sparse fields
High-contrast for diffuse debris disks and compact companions
Polarimetric precision
for high-contrast observations
Transmission/background/SNR
for several science cases
Observing efficiency
Observing uptime
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Photometric Precision with NGAO
• Technical report completed
(see Britton, et al., at http://eraserhead.caltech.edu/keck/ngao/photometry/drafts/)
– Considered r0 variations, stellar crowding (K. Olsen), scintillation, & techniques of PSF estimation
• Conclusions
– Photometric precision intimately tied to knowledge of the PSF
• On-axis PSF can sometimes be estimated from direct imaging
• In principle, on-axis PSF can be estimated from AO telemetry (but this has not
been tackled for Shack-Hartmann WFS)
• Off-axis PSF can be estimated using Cn2(h) information
– Single conjugate AO & MOAO relative photometric precision better than 1% should
be achievable with NGAO over 30” FoV, assuming appropriate auxiliary systems
• This meets all of the NGAO science case goals developed so far
– The photometric precision performance of MCAO cannot be easily estimated (due to
both space & time variability)
• No obvious precision advantage over MOAO
• We will have to await ESO’s MAD & Gemini S MCAO to evaluate the performance w.r.t.
single conjugate AO & MOAO
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Photometric Precision IPT Recommendations
•
Active, concurrent Cn2(h) measurements on minute time scales are essential to
precision photometry with NGAO
– Provides significant benefit for estimation of off-axis PSF’s
– Allows additional optimization of NGAO performance (e.g. tomography algorithms)
•
NGAO should provide an auxiliary PSF imaging capability for all instruments &
observing modes
– This camera should be Nyquist sampled and deployable over sufficient field of regard to
ensure acquisition of an appropriate PSF stars (for narrow field science instruments.)
• Details of wavelength coverage & other requirements will depend on NGAO architecture
•
As a step toward understand the requirements of the PSF imager, near-term
experiments with OSIRIS &/or NIRC2 & the T6 MASS/DIMM should be undertaken
– Open issues of access to Keck engineering time & funding for this investigation
•
NGAO should consider incorporating a facility deconvolution pipeline as a program
deliverable
– This would likely improve consistency & uniformity of photometric & astrometric results
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Companion Sensitivity
NGAO high-contrast science goals and drivers:
• Direct imaging & spectroscopy of 1) Planets around low-mass stars &
brown dwarfs, 2) Resolved debris disks and proto-stellar envelopes
• LGS tomography
– Fainter host stars: larger sky coverage & relaxed contrast requirements
– Multi-band studies: optical & near-IR
Status (1st draft of report posted)
• Contrast budget spreadsheet tool (1st order approximation)
– No coronagraph model; no dynamic telescope aberrations
• Numerical AO simulations partly done (more accurate modeling)
– Band-limited Lyot coronagraph; static & dynamic telescope errors
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NGAO Trade Studies
Trade Studies
• The following studies have been completed since the last meeting:
– Keck AO upgrade
– GLAO for non-NGAO instruments
– Low order wavefront sensor type & number
• Additional design studies nearing completion include:
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MOAO vs MCAO
Keck Interferometer support
Science instrument re-use
Telescope wavefront errors
Observing model
Rayleigh rejection
LGS wavefront sensor number and type
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Keck AO Upgrade
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Anchored NGAO tool to
measured Keck AO
performance
Upgrades part 1 (NGWFC, K1
LGS, CCID-56, 2x DM, new
science instrument, simplified
tomography, vibration
reduction, 50W laser)
Upgrades 2 would need
multiple LGS & multiple IR
tip/tilt sensors
Companion Sensitivity
•
Performance improvement
with Strehl
Case
NGS
LGS
LGS
Rmag
8
10
18
Current Upgrade 1
258
149
378
229
557
419
NGAO
148
155
158
Contrast versus Radius
K1 LGS (1.0um)
K1 LGS (1.25um)
-2.00
K1 LGS (1.65um)
-3.00
K1 LGS (2.2 um)
-4.00
Contrast (magnitudes)
Wavefront error budget
Upgrade (1.0um)
-5.00
Upgrade (1.25um)
-6.00
Upgrade(1.65um)
Upgrade 2.2um)
-7.00
NGAO (1.0um)
-8.00
NGAO (1.25um)
-9.00
NGAO (1.65um)
NGAO (2.2um)
-10.00
-11.00
-12.00
-13.00
0
0.1
0.2
0.3
0.4
0.5
Radius (arcsec)
0.6
0.7
0.8
0.9
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Keck AO Upgrade
• Pros & cons
– Potentially lower cost, but likely lower performance
– Interferometer needs addressed
• Would allow for an incremental approach
• Conclusion:
– Keck AO upgrade worth further consideration, especially as a reduced
funding/scope option.
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GLAO for non-NGAO Instruments
GLAO = ground-layer adaptive optics
• NGAO provides multiple LGS; adaptive secondary mirror assumed
• GLAO then “only” requires additional WFS, RTC & software to be
employed with non-NGAO Keck instruments
• GLAO produces a modest, but dependable improvement in FWHM & EE
over wide fields of view (several arc minutes)
– Increase angular resolution, sensitivity &
observing efficiency
– Recover bad seeing nights to science
grade observing
– Large sky coverage (>50% at b=30°)
From GLAO TS report (KAON 472 - see document for explanation of figures)
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Low Order Wavefront Sensor
• IR WFS (J+H bands) preferable to visible WFS
• Multiple NGS WFS significantly improve tip/tilt estimate over science field
• Measuring focus with one tilt sensors also helps tip/tilt estimate
J=17.1
J=16.4
J=17.4
Field Galaxies
science case:
Latitude=30 deg
J=16.6
J=19.0
J=18.7
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Keck Interferometer Trade Study
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•
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Consider the relative performance, cost, risk, & schedule of feeding
KI with NGAO or a repackaged version of the current AO system
Decoupling of NGAO from interferometer support may simplify &
improve performance of NGAO
The feasibility of maintaining a version of the two current AO
systems for KI use should be evaluated
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Keck Interferometer Preliminary Options
• Swapping Keck I/II AO with NGAO
• Matching NGAO to Keck I/II AO
• Two AO systems + NGAO
– AO secondary on each telescope
• GLAO trade study
Move Large
Instruments
– MEMs AO for each IF arm
LAO/UCSC
Challenging with current IF
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Telescope Dynamic & Static Wavefront Errors
Goal: Improve/document understanding of telescope wavefront errors
• Telescope tip/tilt errors could dominate tip/tilt error budget
– “Encircled Energy Science” might be impacted less
– Consider correction or mitigation on current system
• Segment motion
– Acceptable error, comparable to NGAO proposal
• Segment figures
– Acceptable error, already included in NGAO proposal
• Segment phasing
– Small, interaction with figure errors needs testing
Correcting for segment figure errors
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Summary
• Management:
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System design phase efforts continue to be behind schedule
Now at reasonable staffing levels versus plan
Scheduled mid-year replan in process
Intention continues to be to deliver the system design within
budget & schedule
• Technical:
– Good progress being made on requirements, performance
budgets & trade studies
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