A Back-up Method for Coarse Phasing JWST - Operational Considerations

possible with any/all of NIRCam LW, NIRCam SW, NIRISS, MIRI

Anand SivaramakrishnanSpace Telescope Science Institute

Peter Tuthill, Anthony CheethamUniversity of Sydney

Scott ActonBall Aerospace

Alexandra GreenbaumJohns Hopkins University

Ed NelanSpace Telescope Science Institute

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A long time ago in a galaxy far, far away.…

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…the big one near the Andromeda, you know the one, they’re almost

twins

Milky Way, Sun, Earth, Hawaii, Keck telescope, 2007…

Mid-Infrared Segment-Tilt `Masking’: 9-segment pattern

Peter Tuthill

Mid-Infrared Segment-Tilting: Raw Data

CCD Chip

Peter Tuthill

Ireland, Monnier & Tuthill ApJ 2007

23% of 1-1.5 Msun have companion with log(P)=4 – 6.5

Total accretion one to a few Mjup (3Mjup)

Birth rate = 0.25 x death rate. Therefore MiraAB type systems about as common as YSOs

1st Mid-IR Sparse-Aperture results:Rebirth from the Ashes

Fizeau Interferometric Cophasing of Segmented Mirrors

precomputed look-up tables from detector data

Three NRT’ed segments

Perfect

Piston errors

Piston and tilt errors

Cheetham, Tuthill, Sivaramakrishnan & Lloyd Optics Express 2012

FICSMFizeau Interferometric Cophasing of Segmented Mirrors

Segment tilting – choose non-redundant patterns NRT

Recover segment piston (few nm) & tip-tilt (10mas)

Capture range >150 micron pistons, 0.5 arcsec tilts (NIRCam LW)

Should work on NIRISS/NIRCamLW/NIRCamSW/MIRI

Cheetham, Tuthill, Sivaramakrishnan & Lloyd Optics Express 2012

JWST Commissioning

8Exit gate: no segment deviates in piston from PM segments’ mean by > 150nm

DHS – coarse phasing baselineFICSM – coarse phasing backup

PSFS during commissioning?

9Contos et al. 2006 SPIE

d e f

a b c

Image Stacking process

10Acton et al. 2006 SPIE

Baseline: move all segments to a single STACK CENTERLarge moves inaccurate small moves accurateMust guide during this process

Ball Testbed Telescope data

Image Stacking before Coarse Phasing

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segment images moved to fall at a common location on one detector - “Stack Center”

Large moves inaccurate, small moves accurate

Not ITAR-restricted information

FICSMOptics Express 2012

Coarse Phasing with Non-Redundant Tilts and FICSM

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Instead of stacking all segments at same location, separate them into NRT’ed sets, use FICSM on them to phase them (images in 3 filters yield pistons + tilts)

3 applications of FICSM to sets of NRT’ed segments

If you want details…

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Keck – 36 segments, atmospheric blur determines separation of NRT sets on detector (few to several arcsec)

JWST – 18 segments, /segmentDia determines separation of NRT sets on detector (½ - 1 arcsec)

A scaled down Keck-type segment tilting approach works well for JWST

Shorter baselines mitigate against higher vibration during JWST commissioning

Seed segments and first guiding segments on backplane (not wings)

JWST-STScI-002527 on NRT (Sivaramakrishnan & Acton)

Tests at Ball Testbed Telescope planned (Acton, Greenbaum, Sivaramakrshnan, Cheetham, Tuthill)