The Path to NGAO Core Science
Requirements
Claire Max and Liz McGrath
NGAO Team Meeting
September 11-12, 2008
Outline of Talk
• What do we mean by "Core Science
Requirements"?
• Suggested approaches
• Next steps
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What do we mean by
"Core Science Requirements"?
• A possible definition:
– A set of science requirements such that NGAO isn't worth building
if these requirements can't be met
– The most minimal "fish or cut bait" set of science goals for NGAO
• Potential problem with this definition:
– As soon as we specify the minimal requirements, they will
probably end up being what the B2C system is designed to meet
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What do we mean by
"Core Science Requirements"? cont'd
•
Another possible definition:
The science that a final build-to-cost design will be able to accomplish
•
We probably don’t want to decide right now, up front, on a very specific
set of science questions that will be answered
– e.g. a "design reference mission" as for a spacecraft
•
Why not?
•
Capability of NGAO at different costs is a continuous variable
– Science capability at different system costs will determine how well you can
do different science cases, but in most cases will not rule out a science
case entirely.
•
The function of the science team is to give continuing input on the
scientific value of design trades as the "build to cost" design is
developed
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What are the distinguishing features
of NGAO science?
• Compared with current Keck AO
• Compared with future planned AO systems elsewhere
• Compared with JWST
• We want NGAO to contribute science capabilities that
are clearly new and that will be unique
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First cut:
Key Aspects of NGAO Science Capability
In priority order:
1. High sensitivity and sky coverage, with NIR encircled energy
< 70 mas
2. Strehl  20% at 850 nm
3. Astrometric accuracy better than 150 as at K band
4. Backup NGS mode (Strehl no worse than K2 NGS)
5. IFU multiplicity (may  larger field of regard)
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Instruments: Key NGAO Capabilities
• Integral field spectroscopy @ high sensitivity and sky coverage.
– Design trades:
• Degree of multiplicity (OSIRIS plus ??? new IFUs)
• Strehl ratio/FWHM for each IFU
• Field of view for each IFU
• Can one of the IFUs be extended down to ~800 nm for the black holes in nearby
galaxies Key Science Driver?
• Imaging at shorter wavelengths, and at higher Strehl (NIR and visible).
– Design trades:
• NIR imager needs excellent astrometry; polarimetry capability
• Should we build both a visible imager and a NIR imager? Or should we extend
the wavelength range of the NIR imager to ~800 nm?
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Recall:
We categorized science cases into 2 classes
1. Key Science Drivers:
– These push the limits of AO system, instrument, and
telescope performance. Determine the most difficult
performance requirements.
2. Science Drivers:
– These are less technically demanding but still place
important requirements on available observing
modes, instruments, and PSF knowledge.
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Key Science Drivers
(in order of distance)
1. High-redshift galaxies
2. Black hole masses in nearby AGNs
3. General Relativity at the Galactic Center
4. Planets around low-mass stars
5. Minor planets as remnants of early Solar System
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Suggested Approach
• Start with existing Key Science Drivers and Science
Drivers
• Work with Keck science community (Science Advisory
Team plus others) to:
– Get broad agreement on the key unique attributes of NGAO,
relative to other AO systems and spacecraft available at the
same epoch
– To the extent possible, prioritize Key Science Drivers and
Science Drivers
• Very hard to get a group of astronomers to agree on this!
• Aim for as clear a statement of priorities as possible
• As B2C design choices become clearer, vet them with
Science Advisory Team plus others to clarify costs /
benefits of design decisions with respect to science
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Next Steps
• CEM
– Take the principal design options emerging from today and
tomorrow, and begin to frame the analysis of science
implications
• Science Advisory Team
– Directors complete roster of Science Advisory Team, and finish
writing its charter
– Convene Team and get their suggestions and buy-in for the B2C
process. [Do I have the ability to convene SAT meetings? The
SAT reports to the Directors, not to me. Needs clarification.]
– Tackle prioritization of Science Drivers, and definition of “core
science requirements” if we can agree on definition
today/tomorrow
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