Object selection ideas for NGAOObject selection ideas for NGAO

NGAO Meeting #6NGAO Meeting #6Anna MooreAnna Moore

April 26, 2007April 26, 2007

2

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)

3

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)

ScienceH/K band

TT sensorsJ

1 of n beamsplitters

Have to be VERY careful about max. simultaneous band coverage for science arm

Plus likely larger non-common path errors than picking off TT at science focal plane? (not for super high contrast)

4

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…

5

TMT IRMOS Caltech/LAM

• Richard Ellis (PI) et al• Prieto/Taylor/Moore based on KMOS2 concept

Field mirrors arrays

Steering mirrors lines

Parabolas

DMs

6

TMT IRMOS Florida/HIA

• Steve Eikenberry PI et al

7

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

8

Near-future 8m d-IFU concept: KMOSVLT 2010

Durham/ATC et al

Courtesy of Allington-Smith

To IFU and spectrograph

field2424

ArmsArms

24 IFUs, 324 IFUs, 3spectrographsspectrographs

NB: KMOS is NOT combined with AO

Still, quite possible to have (d-ifu) NGAO requirement of ~13 pick-offs though at what cost… should be a simpler solution

9

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

10

Kickbots for NGAO?

• Maybe…

Transparent horizontal glass window(must be clean!)

From telescope

To science instrument/s