TIPS/JIM
October 15, 2009
Agenda:
INS News (Jerry Kriss)
JWST Dithering: NIRSpec (Jason Tumlinson)
and a Cross-Instrument View
Persistence: Theory and Observations (Mike Regan)
The Photometric Performance and Calibration of WFC3 (Jason Kalirai)
The Post-Launch Line Spread Function of COS (Parviz Ghavamian)
Next TIPS/JIM: November 19, 2009
Instruments Division News
10/15/2009
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Welcome to our newest staff member: Rachel Anderson joins INS as an RIA working
on JWST.
Farewell, too, to some staff whom we will miss: Robert Upton and Bente Eegholm
will be leaving the institute at the end of the month. We greatly appreciate your
contributions, and wish you well in your new endeavors.
We have merged the NICMOS team with the WFC3 team to conserve resources and
share IR expertise more easily with the WFC3 team.
o Tommy Wiklind and Tomas Dahlen join WFC3.
o Anton Koekemoer moves to the WIT Team, working on JWST data
calibration and pipelines. We thank Anton for his 3 years of service as
NICMOS lead. He has done a superb job revamping the NICMOS
calibration pipeline and leading the effort to reprocess all the pre-SM4
data.
HST news:
o SMOV for all the new and repaired instruments is done! Science
observations are now the bulk of the schedule.
o NICMOS will be completing SMOV in November. We hope to schedule
the remaining NICMOS Cycle 17 science and calibration observations by
March of 2010.
o The STUC will be here November 12 and 13.
o The SMOV closeout review will be here at STScI on November 19.
JWST news:
o The ISIM structure (yes, the real thing!) has been delivered to GSFC and
is currently in the SSDIF.
o The SWG is meeting here yesterday and today.
o The new JWST Advisory Committee, JSTAC, will meet here for the first
time on Nov. 4 & 5.
The Future of the Workplace Committee will visit again on Nov. 2 & 3. Invitations to
the usual focus groups will go out by early next week.
I’d like to have an INS Division Lunch on Thursday, October 29. Please let me know
if you’d like to volunteer to help organize.
TIPS/JIM
October 15, 2009
Agenda:
INS News (Jerry Kriss)
JWST Dithering: NIRSpec (Jason Tumlinson)
and a Cross-Instrument View
Persistence: Theory and Observations (Mike Regan)
The Photometric Performance and Calibration of WFC3 (Jason Kalirai)
The Post-Launch Line Spread Function of COS (Parviz Ghavamian)
Next TIPS/JIM: November 19, 2009
JWST NIRSpec
Dithering Strategies
(and a Cross-SI View)
Jason Tumlinson
JIM / TIPS
Oct 15, 2009
NIRSpec Refresher
JWST SI Dithering Principles
•
Dithering is needed generically for:
1.
2.
3.
•
In keeping with the JWST project “template” approach to ops, we are trying
to “pre-define” the SI dither patterns, which will:
1.
2.
3.
4.
•
mitigating detector flaws and pixel-to-pixel response variations, and for
improving the pixel-space sampling of the point- or line-spread function.
increasing coverage of the sky.
provide the user with a simple set of optimal choices that are still
flexible enough to adapt to a range of science needs.
simplify the on-board scripts that implement dithers
limit the possibilities for user or software errors (patterns are less
handmade than for HST).
simplify things still further by sharing and reusing components (planning
tools, on-board script code) that applies to multiple SIs.
Generally in JWST-land, a visit = one guide star = maximum angular extent
of pointings in a visit limited to ~20” by availability of GS within 2.2’ FGS
field.
Primary vs. Secondary Dithers
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•
•
•
“Primary Pattern” : generally large in scale, >> pixel, designed
to mitigate pixel-to-pixel response variations and/or improve
spatial coverage by moving to different parts of the detector.
Can also apply to large-scale “tiling” of the FOV for large
fields.
“Secondary Pattern” : generally small scale, ~ pixel, designed
to improve pixel-space sampling of the PSF or LSF.
Generally allowed to nest, so execute a secondary pattern at
each of the primary positions.
NIRSpec Fixed Slits
• Primary Pattern: Step down the slit in 1, 2,
3, or 5 positions separated by ~ 0.5”, user
choice.
• Secondary pattern: 0.5 pixel offsets in
spatial, spectral dimensions, or both as a
user choice.
NIRSpec IFU Primary Pattern: “Tiling”
4
2
0
1
3
5
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Primary Pattern: Define a set of “tiles” on the
sky to cover an extended source with the
3”x3” FOV. (Using a NIRSpec-specific tool
resembling the MIRI mosaic tool in APT).
Secondary pattern: slitlets (next page)
NIRSpec IFU: Secondary Patterns
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Simultaneous with these moves, 1.5 pixels
shifts in the spatial, spectral dimensions
can resample the PSF and LSF in pixel
space.
So at each primary position (“tile”), there
are two positions observed with small
offsets in the dispersion direction, crossdispersion, or both, depending on user
choice.
The 30 “slitlets” are interlaced
such that adjoining slitlets fall on
very different detector regions;
moving over 100 - 500 mas (1 - 5
slitlets) can move the spectrum
vertically by > 1000 pixels. Very
good for avoiding detector
artifacts.
NIRSpec MSA Strategy 1: “Slitlets”
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Place target in each of 3 shutters in a 3x1 slitlet, use the other two for measuring sky background.
Places each target in the “sweet spot” within each microshutter where slit transmission is
maximized (60%) and relatively flat.
This strategy works well if 3x1 shutter slitlets are pre-assigned to each target during the planning
of the MSA configuration.
This strategy (and its close relatives) is the ONLY “dither pattern” for the MSA that can be done
deterministically - because we will fly a non-ideal MSA.
NIRSpec MSA Strategy 1I: “Subshutter”
This strategy does not force every
target into the shutter “sweet spot”.
Rather, it allows them to fall where
they may and averages out
uncertainties in the shutter
transmission curve by observing at,
e.g. 16 positions distributed
symmetrically around the shutter.
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However, this strategy requires multiple configurations that can only be derived at planning time there is no “canned” dither pattern that can accomplish this pattern in the general case of any
astronomical scene and a non-ideal MSA.
This strategy can be implemented in the tool, with the offsets and the corresponding MSA
configurations passed downstream to a script that doesn’t know about the strategy itself.
NIRSpec MSA Strategy III: “Generic”
The great appeal of the MSA, and
therefore of NIRSpec, lies in its ability
to observe an arbitrary pattern of
sources on the sky.
This large degree of complexity,
coupled to a non-ideal MSA, means
that “canned” dithering patterns
cannot exist outside the narrow
range of strategies that can be fully
planned in advance.
Therefore: MSA patterns will be defined generically at planning time in the MSA
planning tool (already well advanced).
We envision that the user will be provided with planning “shortcuts” that help
implement simple patterns like the slitlet or subshutter strategies and iteratively arrive
at optimal coverage of a given target set. Operationally, MSA dithers are just a list of
MSA configurations and center positions on the sky.
JWST Science Instrument Dithering Strategies Summary
Mode
Instrument
Primary
Secondary
Special Purpose
Comments
Downslit
[N = 1,2,3,5 positions]
Subpixel
(1) spectral [yes/no]
AND/OR
(2) spatial [yes/no]
A_200_1 to A_200_2 “λ
-gap-filling”
[yes/no]
(1) no dithers for “large
square”
(2) A_200_2 repeats the
pattern in A_200_1
regular grid for >3” field
[Nx, Ny, Δx, Δy intervals,
rotation, etc.]
(1) Slitlet [N = 0,1,3,5 steps]
AND/OR Subpixel
(2) spatial [yes/no]
(3) spectral [yes/no]
...
“tiling” uses tool like “MIRI
Mosaic” to construct the
pattern
all, defined by MSA planning
tool
...
...
shortcuts in tool will create
simple patterns
deterministically
Extended Source / Mapping
[Nx, Ny, Δx, Δy intervals, etc.]
OR
Point Source/Staring
(2 positions within slit)
...
...
...
regular grid for >3” field
[Nx, Ny, Δx, Δy intervals,
rotation, etc.]
2 pt or 4 pt (details TBD)
[channel, N = 2 or 4 pt]
...
report pending
12-pt Reuleaux [S/M/L]
OR
311-pt Cycling
[S/M/L, N + start]
4 pt box
(subpixel)
...
MIRI imaging mosaics are
not dithers
(Report #)
Fixed Slits
(1678)
NIRSpec
IFU
(1749)
MSA
(1769)
LRS
(1634)
MIRI
MRS
(TBD)
Imaging
(1657)
Full-field
[3 tight, 3, 6, or 9 tile]
OR
NIRCam
Imaging
(1738)
N-point intra-module
[N = 3 - 16]
OR
N-point intra-SCA
[LW vs. SW, N = 1 - 25, S, M,
L]
Can nest or combine
[user options]
NIRSpec Pre-imaging
N-position subpixel
[N = 1 - 9]
Use [3-tight or 3,6,9-tile]
(4 GS acqs)
OR
OR
“General” 64-pt subpixel
[N = 1 - 64]
“NIRSpec Minimal”
fixed pattern
(2 GS acqs, does not
cover SCA gaps)
NIRSpec Pre-imaging can
also combine with standard
secondary patterns
large-scale tiling in separate
visits has been omitted
report is still under review
Regular, Deterministic (“Canned”) with simple parameters
YES
Executable within a single visit
NIRSpec FS Downslit
NO
NIRSpec FS λ-gap
MIRI LRS Point Source/Staring
YES
MIRI Imaging 12-pt Reuleaux
MIRI Imaging 311-pt Cycling
NIRCam N-point intra-module
ALL SECONDARY
PATTERNS
NIRCam Imaging Full-field
NO
NIRCam N-point intra-SCA
NIRSpec IFU Extended Source
MIRI LRS Extended Source / Mapping
MIRI MRS Extended Source / Mapping (TBD)
NIRSpec MSA generic
TIPS/JIM
October 15, 2009
Agenda:
INS News (Jerry Kriss)
JWST Dithering: NIRSpec (Jason Tumlinson)
and a Cross-Instrument View
Persistence: Theory and Observations (Mike Regan)
The Photometric Performance and Calibration of WFC3 (Jason Kalirai)
The Post-Launch Line Spread Function of COS (Parviz Ghavamian)
Next TIPS/JIM: November 19, 2009
Persistence: Theory and Practice
Mike Regan
Eddie Bergeron
Kevin Lindsay
Doug Long
Experiment Setup
Single Long Exposure
Initial reset
10 Short Exposures
Resets during final
write to disk
Write to disk and Resets at beginning of each exposure
The total persistence in an up-theramp,100 dark (1060 seconds) after the
bright exposure.
The persistence in the single long exposure
is 2.3 time that of the 10 short exposures.
Changing the detector substrate bias yields a
dark image that looks just like persistence.
Photons captured in the depletion region
yield an electron/hole pair.
Roger Smith’s Model
As charge accumulates the depletion
region gets smaller.
After a reset trapped electrons and
holes are left in the depletion region.
During the next exposure the electrons/holes
decay from the traps and are seen as a change in
the voltage.
Each persistence electron/hole generates less voltage than a
photoelectron/hole.
Reset mode does not affect persistence.
The return of persistence after the
reset!?
Conclusions
• The more charge that accumulates the
more the persistence.
• Reset mode does not affect
persistence.
• The Smith model explains most of the
observations [but not all].
TIPS/JIM
October 15, 2009
Agenda:
INS News (Jerry Kriss)
JWST Dithering: NIRSpec (Jason Tumlinson)
and a Cross-Instrument View
Persistence: Theory and Observations (Mike Regan)
The Photometric Performance and Calibration of WFC3 (Jason Kalirai)
The Post-Launch Line Spread Function of COS (Parviz Ghavamian)
Next TIPS/JIM: November 19, 2009
The Photometric Performance and
Calibration of WFC3
Photometry with WFC3
1.) High resolution and sensitivity
2.) UV, optical, and NIR coverage
3.) Wide field of view
4.) 77 filters + 3 grisms
High z Galaxies: Bouwens et al. (2008)
Low Mass Stars:
Dupuy, Liu, & Ireland (2009)
Cosmology: Riess et al. (2007)
Resolved Stellar Pops: Richer et al. (2009)
Oct 15th, 2009
TIPS-JIM Meeting, STScI
The Photometric Performance and
Calibration of WFC3
SMOV4 Calibration: The Photometric Stability and Absolute Throughput of WFC3
UVIS and IR
1.) Observations of HST spectrophotometric standards:
GD153 in 37 UVIS filters; GD153 and P330E in all 15 IR filters
- 1% absolute accuracy in medium and broadband filters.
- 2-3% absolute accuracy in narrow band filters.
2.) Repeat observations: Measure photometry stability, both temporal and spatial.
High S/N subarray imaging, multiple dither positions.
Star
B
V
J
H
G191B2B
11.45
11.77
12.55
12.66
61,193
7.492
GD153
13.06
13.35
14.07
14.19
38,686
7.662
GD71
12.78
13.03
13.74
13.86
32,747
7.683
P330E
13.62
13.00
11.88
11.60
G0V
G0V
Oct 15th, 2009
Temp (K) Log(g)
TIPS-JIM Meeting, STScI
The Photometric Performance and
Calibration of WFC3
SMOV4 Calibration: The Photometric Stability and Absolute Throughput of WFC3
Spatial stability over 4 (small) dither positions; <1%
Temporal stability over 1 month; <0.5%
Oct 15th, 2009
TIPS-JIM Meeting, STScI
The Photometric Performance and
Calibration of WFC3
The WFC3 System Throughput
1.) The HST OTA
2.) Pickoff mirror
3.) CSM
4.) Mirror reflectivity
5.) Filter throughputs
6.) Detector window
7.) Detector QE
Calibration Performed in TV3
ACS/WFC: Sirianni et al. (2002)
Oct 15th, 2009
UVIS: 5-10% boost in efficiency at blue/red λ’s, 15-20% at 400-700 nm
IR: 10-15% boost in efficiency at all λ’s
TIPS-JIM Meeting, STScI
The Photometric Performance and
Calibration of WFC3
Implications
1.) WFC3 is AWESOME!
2.) WFC3 represents 50% of cycle 17 HST orbits.
3.) vs ACS: - 20% smaller pixels
- 50% lower read noise
- negligible CTE correction
- much lower dark current
Early Science Highlights
1.) Ten WFC3 publications submitted to journals.
2.) Highest redshift galaxies in the Universe discovered.
Stellar evolution models/isochrones already available
A Look Forward to Cycle 17
1.) Observations of additional flux standards.
2.) Observations in all filters.
3.) Absolute flux calibration of WDs.
4.) Photometric transformations.
5.) Color corrections and tests of filter bandpasses.
For details: Kalirai et al. (2009, WFC3 ISR ---), CAL11450)
Kalirai et al. (2009, WFC3 ISR ---), CAL11451)
Oct 15th, 2009
TIPS-JIM Meeting, STScI
TIPS/JIM
October 15, 2009
Agenda:
INS News (Jerry Kriss)
JWST Dithering: NIRSpec (Jason Tumlinson)
and a Cross-Instrument View
Persistence: Theory and Observations (Mike Regan)
The Photometric Performance and Calibration of WFC3 (Jason Kalirai)
The Post-Launch Line Spread Function of COS (Parviz Ghavamian)
Next TIPS/JIM: November 19, 2009
Characterization of the Post-Launch
Line Spread Function of COS
Parviz Ghavamian
A. Aloisi, C. Proffitt, D. Lennon, G. Hartig, G. Kriss, C.
Oliveira, D. Massa, T. Keyes
(STScI)
T. Delker (Ball Aerospace)
S. Osterman (Colorado)
The COS LSF: Ground Tests
• During TV03/TV06, light from PtNe lamp
was passed into COS after passing through
RAS/Cal stimulus, which mimicked lowfrequency errors from HST OTA (spherical
aberration, astigmatism, coma...)
• COS gratings correct for these LFEs,
designed to produce R ~ 20,000 across
80% of bandpass in the resulting M-mode
spectra (FUV and NUV)
• The LSF profile in the FUV was well
described by Gaussian shape during
TV03/TV06
• In NUV, LSF profile has non-Gaussian wings
due to MAMA detector response; optical
models give FWHM ~ 2.5 pixels
Gaussian
6.5 pixels FWHM
COS LSF: Effect of Mid-Frequency Errors
3
• During SMOV, the shape of the on-orbit
COS LSF was found to differ from the
profile in ground testing, due to the
presence of zonal (polishing) errors on
primary and secondary HST mirrors
• Zonal errors introduce mid-frequency
errors (~18 nm) into beam entering
COS; not included in RAS/Cal testing
Fraction of flux falling outside of FWHM
LSF model G130M
no WFEs
24%
G160M G185M G225M
24%
36%
37%
G285M
39%
COS/NUV Model LSF: Mid-Frequency WFEs included
• Result is a lowered, broadened core
and broad non-Gaussian wings on LSF
• Mid-freq. WFEs are strongest at shortest
wavelengths of COS (~1150 Å), diminishing with increasing wavelength, and
becoming negligible beyond ~ 2500 Å
with WFEs
(wav-avg)
41%
37%
51%
49%
Krist & Burrows (1995)
47%
Example: Impact of Mid-Frequency Errors on Spectra
• FUV: Sk 155 in the SMC (O9 Ib, V=12.4),
observed during SMOV with G130M,
G160M gratings
• E140H STIS echelle spectra exist (R ~
114,000; E0.2x0.09) on archive and as
part of Cycle 17 calibration data
• Wings on LSF cause:
1. Significant filling-in of saturated absorption
features
2. Merging of narrow absorption lines into
wings of nearby saturated absorption
features
• Model the COS spectrum by convolving
STIS E140H spectrum with model LSFs
Application of COS LSF models
Impact on COS Science
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Programs using full resolution of FUV
G130M, G160M and NUV G185M:
3σ Limiting Equivalent Widths
(assumes S/N=10 pixel
pixel-1 in continuum)
1. Close together lines harder to isolate
2. Weak, narrow absorption features (b < 35
km s-1) more difficult to detect at a given
S/N; lower contrast between core and wings
dotted: with WFEs
solid: no WFEs
3. Analysis of saturated absorption lines will
require full consideration of LSF
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Programs minimally affected are:
4. Those observing broad lines (b > 35 km s-1)
5. SED and continuum flux measurements
6. G140L observations, since they typically are
done for SED measurements, or to observe
sources with line widths larger than
instrumental resolution
Rough calculation; result may be improved with
flux-weighted extraction, etc.
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http://www.stsci.edu/hst/cos/performance/spectral_resolution