A Back-up Method for Coarse Phasing
JWST - Operational Considerations
possible with any/all of NIRCam LW, NIRCam SW, NIRISS, MIRI
Anand Sivaramakrishnan
Space Telescope Science Institute
Peter Tuthill, Anthony Cheetham
University of Sydney
Scott Acton
Ball Aerospace
Alexandra Greenbaum
Johns Hopkins University
Ed Nelan
Space Telescope Science Institute
1
A long time ago in a galaxy far,
far away.…
…the big one near the Andromeda, you know
the one, they’re almost twins
Milky Way, Sun, Earth, Hawaii, Keck telescope, 2007…
2
Mid-Infrared Segment-Tilt `Masking’:
9-segment pattern
Peter Tuthill
Mid-Infrared Segment-Tilting: Raw Data
CCD Chip
Peter Tuthill
1st Mid-IR Sparse-Aperture results:
Rebirth from the Ashes
23% of 1-1.5 Msun
have companion
with log(P)=4 – 6.5
Total accretion one
to a few Mjup
(3Mjup)
Ireland, Monnier & Tuthill
ApJ 2007
Birth rate = 0.25 x
death rate.
Therefore MiraAB
type systems about
as common as
YSOs
Fizeau Interferometric Cophasing of
Segmented Mirrors
precomputed look-up tables from detector data
Perfect
Piston errors
Piston and tilt errors
Cheetham, Tuthill, Sivaramakrishnan & Lloyd
Optics Express 2012
Three NRT’ed segments
FICSM
Fizeau 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
DHS – coarse phasing baseline
FICSM – coarse phasing backup
Exit gate: no segment deviates in piston from
8
PM segments’ mean by > 150nm
PSFS during commissioning?
a
b
c
d
e
f
9
Contos et al. 2006 SPIE
Image Stacking process
Ball Testbed Telescope data
Baseline: move all segments to a single STACK CENTER
Large moves inaccurate small moves accurate
Must guide during this process
10
Acton et al. 2006 SPIE
Image Stacking before Coarse
Phasing
segment images moved to fall at a common location on
one detector - “Stack Center”
Large moves inaccurate, small moves accurate
Not ITAR-restricted information
11
Optics Express
FICSM
Coarse Phasing with NonRedundant Tilts and FICSM
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
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If you want details…
Keck – 36 segments, atmospheric blur
determines separation of NRT sets on detector
(few to several arcsec)
JWST – 18 segments, l/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,
14
Tuthill)