Transcript NGAO-OSM-ideas.ppt

Object selection ideas for NGAO
NGAO Meeting #6
Anna Moore
April 26, 2007
Key drivers
• Light from TT stars is close to or at same wavelength as
science field
– limited use of beamsplitters to pick-off light
• Shame… as unlike TMT the Keck beam size is
manageable wrt dichroics
– (6-8” diameter ok, ~$20k)
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Beamsplitter-fed TT mode?
•
IF one can do TT sensing close to but out of the science band
–
Have a slide with a user selectable range of beamsplitters ahead of the science instrument
(aka optical switchyard of Indian Wells?)
–
Only feeding 3 TT sensors in any case (!), positionable over max 240” FoR (180mm)
1 of n beamsplitters
Science
H/K band
Have to be VERY careful about
max. simultaneous band coverage
for science arm
TT sensors
J
Plus likely larger non-common
path errors than picking off TT at
science focal plane? (not for super
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high contrast)
Key drivers
• Keck Plate scale is 0.75mm/arcsec
– TMT has larger real estate for fitting in mechanical pick-offs (2.25 mm
per arcsec)
– Should keep in mind AAT/VLT etc like pick-off devices and maybe get
inspiration from those for 30m…
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TMT IRMOS Caltech/LAM
• Richard Ellis (PI) et al
• Prieto/Taylor/Moore based on KMOS2 concept
Steering mirrors lines
DMs
Parabolas
Field mirrors
arrays
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TMT IRMOS Florida/HIA
• Steve Eikenberry PI et al
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IRMOS includes TT pick-off
• Both TMT IRMOS instruments had to provide means of picking off
TT light at instrument focal plane. This has the benefit of sampling
TT light delivered to the instrument.
• NGAO could go this way however:
– Requires full TT field relayed to science instrument
– Possibly will have restricted access to central FoR due to vignetting of
science field
– Requires at least 2 TT pick-off systems, with 3 MEMS per system, one
for d-IFU and one for the on-axis instruments
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Near-future 8m d-IFU concept: KMOS
VLT 2010
Durham/ATC et al
Courtesy of Allington-Smith
24 IFUs, 3
spectrographs
24
field
Arms
NB: KMOS is NOT
combined with AO
To IFU and
spectrograph
Still, quite possible to
have (d-ifu) NGAO
requirement of ~13
pick-offs though at
what cost… should
be a simpler solution
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More radical solutions?
•
•
•
•
Kickbot/Starbug concepts for focal plane pick-off (Moore/McGrath)
In principle low cross sectional area robotic positioners
Cheap, reliable at -40C (piezo driven, like Echidna)
Need vertical path length compensation
Drawing by Andrew McGrath, AAO
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Kickbots for NGAO?
• Maybe…
From telescope
Transparent horizontal glass
window
(must be clean!)
To science instrument/s
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