Transcript (Instrument-Reuse-Questions-012407_2.ppt)

NGAO Science Instrument Reuse
Part 2: Update and required feedback
NGAO IWG
Anna Moore, Sean Adkins
NGAO Team Meeting
January 22, 2007
Status: NIRC2
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NIRC2 suitability for thermal L/M imager presented at last meeting
– In summary, yes, NIRC2 would (over) satisfy imager requirements
– Some upgrades would be required for this, but likely would not cost anything like
a new instrument
– Science flow down for thermal L/M imager needs developing, especially
acceptable range of WFE
– Telescope background in the M band is currently very high according to NIRC2
PI. This science is optimally done using a deformable secondary and Cassegrain
mounted imager, there will be other 8 m telescopes that have deformable
secondaries in the future, can Keck-NGAO compete?
NGAO IWG 1/22/07
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Status: OSIRIS
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OSIRIS documentation has been reviewed and list of clarification questions sent to
James Larkin, we expect a reply shortly
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We plan to summarize the results of the OSIRIS re-use trade study at the next NGAO
team meeting, but at this point we have some questions that we need the science
team to answer.
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The top question is regarding field of view
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OSIRIS FOVs range from 1.28″ x 0.32″ to 6.4″ x 4.8″
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In the development last June of the NGAO science requirements we carried forward a
concept for a “wide field OSIRIS” which led to these notional requirements for the NGAO
near-IR IFU:
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64 x 48 NB mode
64 x 16 BB mode
4 spaxel scales (20/35/50/100 mas) at R~3800 for 3 smallest plate scales and R~3000 at the
100 mas scale
160 x 50 spaxels in NB mode (largest FOV 16″ x 5″)
80 x 50 spaxels in BB mode (largest FOV 8″ x 5″)
3 plate scales (20/50/100mas) at R~4000
The current NGAO SRD (version 3) so far indicates only a 1″ x 1″ near-IR IFU FOV
NGAO IWG 1/22/07
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Required feedback:
NIRC2 as NGAO “Thermal Near-IR Imager”
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We ask your concurrence to change the name of the instrument from
“Thermal Near-IR Imager” to “L and M band Imager” to avoid confusion.
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The requirements for this instrument are sketchy, very limited treatment so
far in the current SRD
– The notional 25″ x 25″ FOV is based on simply scaling from the nominal plate
scale with a 1K x 1K detector, what are the real science driven FOV
requirements?
– Further work is required to define the acceptable range of residual wavefront
error for this instrument (this is critical for NIRC2 as it is known to have a
reasonable amount of WFE and field dependent WFE)
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Should NIRC2 be seriously considered for reuse as the NIR imager?
NGAO IWG 1/22/07
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Required feedback:
OSIRIS as the NGAO near-IR IFU
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In the current SRD we find only one specific reference to a requirement for a near-IR
IFU (radial velocities at the GC):
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It would be helpful to have information to:
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20 or 35 mas spaxels
1″ x 1″ FOV
goal of 10 km/s RV precision
Prioritize the importance of higher spectral resolution (up to R ~15,000) that may be needed
to better resolve Brγ and He lines in K-band
Clarify if OSIRIS R ~3800 is close enough to R ~4000 given in the observing plan discussion
(SRD §2.3.6)
What about the need for different plate scales? OSIRIS offers 20/35/50/100 mas
Other possible single near-IR IFU science?
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Extragalactic science makes a clear case for the deployable near-IR IFU
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Would a single object near-IR IFU have any applications in extragalactic science that should drive
requirements, for example:
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Gravitationally lensed galaxies
2D spectroscopy of galaxies
Extrasolar planet characterization
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High contrast imaging mentions low resolution IFU
For low resolution spectroscopy: answer question in text, “Can it just use narrow-band filters?”
Does not seem a definitive request for an IFU, and only R ~100 needed so using NGAO NIR IFU
possibly overkill?
Since a coronagraph is needed, and high contrast is emphasized should this a special instrument?
NGAO IWG 1/22/07
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Required feedback:
OSIRIS as NGAO near-IR IFU
• Are there science cases that demand near-IR IFU FOVs greater
than what OSIRIS provides?
• The NGAO system is expected to have very low K band thermal
background. OSIRIS also has low internal backgrounds, but the
pupil stop sizes (and shape) still dominate the background levels.
How much lower do the backgrounds need to go for the 50/35/20
mas spaxel scales to be acceptable for NGAO science?
• How critical is the 100 mas spaxel scale for science? This mode in
OSIRIS was not designed for science initially and as a result it was
allowed to have an oversized pupil stop, and therefore a
correspondingly large thermal background. It also has a reduced
resolution (R ~3000) compared to the other plate scales.
NGAO IWG 1/22/07
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