TIPS-JIM Meeting
15 July 2004, 10am, Auditorium
1.
Radiation damage in ACS CCDs:
comparison with STIS and WFPC2
Marco Sirianni
2.
ACS/HRC astrometry of polarized
filters: Why should we care?
Vera Platais
3.
The STScI near-IR detector simulation
package and its application to JWST
wavefront sensing
Anand Sivaramakrishnan
4.
NIRSpec Update
Mike Regan
Next TIPS Meeting will be held on 19 August 2004.
Marco Sirianni
TIPS 07.15..2004
Radiation damage in ACS CCDs:
And comparison with STIS and WFPC2
M. Sirianni
M. Mutchler, T.Wheeler, D. Van Orsow
ACS – Detectors
Marco Sirianni
TIPS 07.15..2004
WFC FPA:
A
HRC FPA:
1x SiTe 1024x1024 Thinned Backside CCDs
21 mm pixel size - MPP - Site NUV AR Coating
1 amp readout
T = - 81 °C
3 mm minichannel
STIS FPA:
Same as HRC, different AR coating
T = - 83 °C
WFPC2 FPA:
4x Loral 800x800 Thick Frontside CCDs
15 mm pixel size - MPP
1 amp readout
T = - 88 °C
D
WFC-2
B
WFC-1
2x SiTe 2048x4096 Thinned Backside CCDs
15mm pixel size - MPP (integration only)
Site VIS-AR Coating - 4 amps readout
T = -77 °C
3 mm minichannel
C
CCD Degradation
Marco Sirianni
TIPS 07.15..2004
HST is in a low earth Orbit with periodic transits through the SAA.
CCDs degrade due to Ionizing and displacement damage
CCD parameters that degrades on orbit:
Parameter
Dark Current
Ionizing
Damage
Displacement
Damage
(Surface)
(Bulk)
Hot Pixels
Full Well
Capacity
Voltage Shift
CTE degradation
MPP mode greatly reduces the impact of Ionizing Damage
Marco Sirianni
TIPS 07.15..2004
Radiaton damage: effects on ACS
Do we see signs of degradation for ACS ?
• YES (first signs already during SMOV)
• BIAS ( hot columns)
• Read Noise
• Dark Rate
• Hot Pixels
• CTE
WFC Bias Frame
Marco Sirianni
TIPS 07.15..2004
March 2002
May 2004
Marco Sirianni
TIPS 07.15..2004
Read Noise WFC
Marco Sirianni
TIPS 07.15..2004
Read noise Jump WFC- A
• Only WFC-Amp A
• Same amplitude at
Gain=1 and Gain=2
• Occurred on June 2003
• No apparent anomaly in
Telemetry data
• SAA transit just before
RN Jump
• Initial sensitivity to anneal
process
• Possible cause: radiation
damage
• Stabilized to ~ +0.5 e-
Read Noise HRC
Marco Sirianni
TIPS 07.15..2004
No anomaly in HRC read noise.
Marco Sirianni
TIPS 07.15..2004
Read Noise : comparison
STIS:
RN jump Dec 1999 (~ 0.5e-)
Some instability after it
Only at Gain=1
Side-1 failed in May 2001
No anomaly
reported for
WFPC2
Marco Sirianni
TIPS 07.15..2004
Dark Current Variation
Dark Current is expected to increase:
Anneals have no impact on dark current rate
Dark Current : comparison
Marco Sirianni
TIPS 07.15..2004
STIS
21.6
May 2001
Dec 1999
14.4
e-/pix/hr
Side-2
7.2
Dark current growth: e-/pix/hr per year
Predicted
(rad. Test)
Observed
Temp.
Current rate
(e/pix/hr)
WFC
HRC
STIS
WFPC2
WF3
1.5 (-81 C)
n.a
n.a
n.a
1.4 (-83 C)
1.4-2.0
1.8
3.3 (side 1)
2.2 (side 2)
2.0 (0-5 yr)
~ 0 after
-77 C
-81 C
-83 C / (?)
-88 C
12.5/11.0
13
21.5
27.3
0.2
Hot Pixels
Marco Sirianni
TIPS 07.15..2004
• Population evolves with time
• Mitigation: annealing the CCD (at ambient temperature - monthly).
• Most of the pixels anneal with the first cycle, few more in following cycles
• Hot pixels not annealed in 6-7 cycles became permanent
Mar 02
HRC : (section 255 x 256)
permanent hot pixels growth:
(Sequence of CR-free dark
Frames after each anneal cycle)
Nov 02
May 03
Nov 03
Mar 04
Hot Pixel Annealing
Marco Sirianni
TIPS 07.15..2004
A
Anneal day
Daily
Hot Pixel
growth
B
C
Permanent
Hot pixels
growth
Annealing
rate
(A - B) / ( A - C)
Annealing Rate :
constant with time
depends on the threshold
Annealing rate
Marco Sirianni
TIPS 07.15..2004
Anneal Rate
100
WFC (-77/+20)
Anneal Rate (%)
90
Hot pixels anneal
better than warm
pixels
HRC (-81/+20)
80
70
60
50
Rate comparison:
Should take into account:
-threshold, Top and Tann
Shielding, pixel size
c
40
30
20
10
0
> 0.02
> 0.04
> 0.06
> 0.08
> 0.1
Hot pixel Threshold (e-/pix/sec)
HRC vs STIS
Instrument
Temp
(CCD/ann.)
Threshold
(e-/pix/sec)
Anneal rate
Source
STIS
orbit
-83 / +5
> 0.1
~ 80 %
~ 75 %
Hayes et al.1998
Kim Quijano et al. 2003
WFPC2
orbit
-88 / +22
> 0.02
variable
~ 80 %
Koekemoer et al. 2003
WFC3
ground
-83 / +30
>0.01
>0.02
>0.044
67 - 80 %
~ 80 %
93 - 97%
Polidan et al. 2004/2005
Marco Sirianni
TIPS 07.15..2004
Permanent Hot Pixel Growth
HRC
WFC
# of permanent hot pixels increase linearly with time
Hot pixel growth - comparison
Marco Sirianni
TIPS 07.15..2004
STIS
SIDE2
> 0.1
> 1.0
> 0.02 e-pix/sec
Hot Pixel Growth:science impact
Marco Sirianni
TIPS 07.15..2004
Permanent hot pixel growth
(% of total number of pixels / year)
Threshold
e-/pix/sec
WFC
HRC
STIS
WFPC2
temp
- 77 C
- 80 C
- 83 C
- 88 C
Dark curr.
0.003
0.004
0.006
0.008
> 0.02
1.60
1.54
2.99
(0.30--0.11)
>0.04
0.78
0.52
>0.06
0.46
0.29
>0.08
0.30
0.21
>0.10
0.23
0.17
0.36
>1
0.03
0.02
0.08
Hot Pixels have greater impact in STIS than WFC and HRC
Hot pixels are not fully stable, noise > shot noise
Best Solution: dither the observations
CTE monitoring
Marco Sirianni
TIPS 07.15..2004
ACS WFC1 parallel EPER amp A
“INTERNAL’ TESTs:
HRC EPER (S/P)
FPR (S/P)
TV3
0.99999
SMOV
Oct-02
0.99998
Mar-03
0.99997
CTE per pixel
WFC EPER (S/P)
FPR (S)
1.00000
Apr-03
0.99996
May-03
0.99995
Oct-03
0.99994
Apr-04
0.99993
0.99992
0.99991
First signs of degradation after
one month in orbit (SMOV)
0.99990
100
1000
10000
Signal (e-)
ACS HRC parallel FPR amp C
1.00000
Lost signal = f(signal,background,
Position, time) (Riess et al. 2004)
First signs of degradation but
still not a serious problem for
science.
CTE per pixel
“EXTERNAL” Test
0.99990
TV3
SMOV
Oct-02
May-03
Oct-03
"Apr 04"
0.99980
0.99970
0.99960
0.99950
0.99940
10
100
1000
log (signal)
10000
CTE degradation: trend
Marco Sirianni
TIPS 07.15..2004
EPER PAR (1620 e-)
1
0.99999
0.99998
0.99997
At each signal level CTE
degrades linearly
CTE
0.99996
WFC-2 AMP D
0.99995
WFC-1 AMP A
0.99994
Linear (WFC-2 AMP D)
0.99993
0
10
20
30
Months Since Launch
40
Comparison of results is problematic
- different tests measure different aspects of CTE (deferred vs trapped charges)
- strong dependence on Temp and clocking rates
We compare not the absolute value (0.9999??) but the monthly CTE
degradation rate.
Dmag from external test converted to CTE figure for s=1620e- b=1e-.
CTE degradation rate
Marco Sirianni
TIPS 07.15..2004
Monthly CTE degradation rate at 1620 e-:
Camera
Test
Temp
Direction CTE deg.
HRC
Eper
FPR
-81 C
Parallel
-8 x 10-7
-2 x 10-6
WFC
Eper
External
-77 C
Parallel
- 7 x 10-7
- 6 x 10-7
WFC
Ground
EPER
Fe55
-81 C
Parallel
-4 x 10-6
-6 x 10-6
WFC
EPER
-77 C
Serial
-6 x 10-8
WFC
Ground
FPR
Fe55
-81 C
Serial
-5 x 10-7
Note
s=1620 b=1eDifferent clocking
Same clocking
WFC : agreement between internal and external tests.
P and S DCTE on-orbit better than ground prediction.
ground predictions too negative or just not a fair comp?
is it the effect of the minichannel?
What is the role of the non-MPP readout?
Marco Sirianni
TIPS 07.15..2004
Conclusions
ACS CCDs have been exposed to radiation for two years
The damage is visible in terms of
- increased dark current
as expected
- hot pixel growth
comparable (≤) to other HST CCDs
- CTE degradation
≤ than predicted
- (Read noise jump - WFC1 A)
So far the damage has minimum impact on science
What next: keep monitoring and possibly discover WFPC2
longevity secrets
We are building a unique database of information:
it that can be used to predict future scientific capabilities
of HST SI and for other missions.
External 2 CTE
Marco Sirianni
TIPS 07.15..2004
magn = -2.5Log(countsn )
countsn = counts0 ⋅CTE
Dmag = mag0 - magn
n
Dmag = n ⋅ 2.5Log(CTE)
CTE = 10
Ê Dmagˆ
Á
˜
Ë 2.5⋅n ¯
Marco Sirianni
TIPS 07.15..2004
ACS/HRC astrometry of polarized filters:
Why should we care?
Vera Platais
&
John Biretta
Anderson & King Geometric distortion for ACS/HRC
X, Y – observed positions
X 0=(X-512)/512
Y 0=(Y-512)/512
X' = X + X (X0,Y0) + Fx(X0,Y0)
Y' = Y + Y (X0,Y0) + Fy(X0,Y0)
X(X0,Y0), Y(X0,Y0) - 4th order polynomials, low-frequency
component
Fx(X0,Y0), Fy(X0,Y0) – look-up table, high frequency component
filter dependent
X
X=128
Y=128
Y
Y=512
Y=896
X=512
X=896
¸Why do we see complicated anisotropic structure and high RMS of
residuals?
¸Is there a third component of distortion?
¸ What are the properties of this new component?
The observation of 47 Tuc
(~4000 stars per HRC)
¸
non-polarized, F220W – F775W
¸
polarized , FILTER+POLnUV, where n=0,60,120 deg
¸
polarized, FILTER+POLnV, where n=0,60,120 deg
The measurement:
¸ ePSF library by Anderson and King.
If ePSF vary as a function of wavelength,
does it vary if polarizer is introduced?
Non-polarized images:
1) Measured with e_PSF ;
2) Corrected for geometry distortion,applying Anderson model;
X' =X + X (X0,Y0) + Fx(X0,Y0)
Y' =Y + Y(X0,Y0) + Fy(X0,Y0)
3) served as a standard astrometric
catalog for each spectral filter.
Polarized images:
1) Measured with e_PSF;
2) Corrected for distortion + filter dependency ;
3) Linearly transformed into distortion free master catalog.
The residuals of positions between polarized image
through F606W+POL0V and non-polarized through
F606W
The residuals of positions between polarized image
through F606W+POL60V and non-polarized through
F606W
The residuals of positions between polarized image
through F606W+POL120V and non-polarized through
F606W
Angle from+V3 to polarizer E-vector
POL0V POL60V POL120V
-69.7
-7.9
50.5
-69.4
-9.4
50.6
(See ACS-ISR-0410,
by Biretta & Kozhurina-Platais)
What polynomial should be fitted
to remove this anisotropic structure?
q2D corrections on a 65x65 grid
over 1024x1024 pixels
q5x5 quadratic smoothing kernel
(Anderson & King, 2000)
Distortion Model of polarized Filters
X' = X + X (X0,Y0) + Fx(X0,Y0) + Px (X0,Y0)
Y' = Y + Y (X0,Y0) + Fy(X0,Y0) + Py (X0,Y0)
X (X0,Y0), Y(X0,Y0) - 4th order polynomials, low-frequency
distortion component
Fx(X0,Y0), Fy(X0,Y0) – look-up table, high frequency component
(filter dependent)
Px(X0,Y0), Py(X0,Y0) – look-up table, anisotropic component
(polarizer dependent)
Why should we concern about the astrometry for polarizer filter?
vobtained polarizer E vector
v corrected the geometry distortion induced by polarizer
vpreserve photometric accuracy for extended and point sources
Acknowledgments.
J. Anderson for sharing the ACS/HRC ePSF library,
centering code and distortion code.
ACS+WFPC2 branch for useful comments.
STScI/IDTL Near-IR
Detector Simulations
Anand Sivaramakrishnan Ernie Morse,
Russ Makidon, Eddie Bergeron,
Stefano Casertano, Don Figer
Space Telescope Science Institute
with
Scott Acton, Paul Atcheson
Ball Aerospace
Marcia Rieke
Steward Observatory
Sivaramakrishnan
STScI July 2004
JIM
Why?
Sivaramakrishnan
•
Wavefront sensing relies on nIR detectors in NIRCam
•
nIR detectors worse than CCDs
•
HST NICMOS photometry good to 3-5%
•
Wavelength-dependent flat fields
•
Intra-pixel sensitivity, crosstalk between output channels
•
Persistent after-images
•
Electronics settling time of cabling to ADC
•
CRs worse for JWST cf HST
•
Flat errors, 1/f component of read noise
•
•
Amp glow
Science data simulations
STScI July 2004
JIM
Modelling science data – First cut
Python prototype code
IDTL darks, flats, settling time: real read noise, dark currents
Poisson photon noise in 1000s
Simulated CR’s up the ramp 10 read
NICMOS CALNIC A pipeline software
CR Images
Background
“Sky” Image
Background
Image with
Stellar PSFs
Input PSFs at
GSC2 Positions
Exposure Time
Image with
Poisson Noise
(IPS + QE),
Telescope Area,
Exposure Time,
Poisson Noise
Data
Apply Darks (w/bias)
Image with
Poisson Noise
and
Cosmic Rays
Data
MuxIR Read
“IR Detector”
Image
CALNIC A
Final “Science”
Image
Sivaramakrishnan, Makidon, Figer, Bergeron, Rauscher, Bushouse, Jedzrejewski, Stockman, Im, …
SPIE Kona 2002
Sivaramakrishnan
STScI July 2004
JIM
Cosmic Ray Model
Offenberg C++
•
•
•
•
•
•
•
18 x 18 x 7 um pixels
100 e per 0.1 um liberated (+/- 10)
NGST sun shield blocks all CR’s
10% of CR’s are He nuclei (4x effect)
Neighbouring pixels affected
No pixel crosstalk
No persistence
Uncertainties
• CR spectrum at L2
• CR effects through titanium shielding (of detectors)
Sivaramakrishnan
STScI July 2004
JIM
Galaxy Background
(recycled Im & Stockman fortran)
1hour exp
E S0
Pec Sp
Hi z
Sivaramakrishnan
STScI July 2004
JIM
Stars + Galaxies: no shot noise
(same image, different stretches)
Sivaramakrishnan, Makidon, Figer, Bergeron,
Rauscher, Stockman,… SPIE Kona 2002
Sivaramakrishnan
Star on postage stamp
brighter than galaxies
STScI July 2004
JIM
1 hour exposure w/CR’s: raw ‘data’
Sivaramakrishnan
STScI July 2004
JIM
Modelling WFSC data – second cut
IDL O-O code based on python Detector & Amp objects (Morse)
Read patterns & timing for HAWAII-2RG (4 on-chip outputs used)
IDTL darks, flats, settling time: real read noise, dark currents
60s exposure
Simulated CR’s
Double-correlated sample (two reads)
Out-of-focus images as per Ball WFSC algorithms (Acton, Atcheson)
No intra-pixel sensitivity modelled (image structures >> pixel on nIRCam)
Offenberg CR model improved
After-market Poisson photon (ARTDATA in IRAF)
Simple IRAF cl script data reduction
Three undithered exposures, median-filtered for CRs
Sivaramakrishnan, Morse, Makidon, Bergeron, Casertano, Figer, Acton, Atcheson, Rieke
SPIE Glasgow 2004
Sivaramakrishnan
STScI July 2004
JIM
JWST PM figure and PSF
below spec of 80%
JWST OPD
160 nm rms
JWST 2micron PSF
Strehl 78%, log stretch
Highly oversampled cf NIRCam
Sivaramakrishnan, Morse, Makidon, Bergeron, Casertano, Figer,
Acton, Atcheson, Rieke SPIE Glasgow 2004
Sivaramakrishnan
STScI July 2004
JIM
Three exposures
NOISELESS
RAW DATA 1
3 waves defocus
6 waves defocus
RAW DATA 2
RAW DATA 3
Sivaramakrishnan, Morse, Makidon, Bergeron, Casertano, Figer,
Acton, Atcheson, Rieke SPIE Glasgow 2004
Sivaramakrishnan
STScI July 2004
JIM
Simple data reduction
Sivaramakrishnan,
Morse, Makidon,
Bergeron,
Casertano, Figer,
Acton, Atcheson,
Rieke SPIE
Glasgow 2004
Sivaramakrishnan
A. Median filtered
B.Dark-subtracted
C.Double-correlated
(zero-read subtraction)
D. Flattened
(bad pixels high)
STScI July 2004
JIM
‘Algorithm’ for routine JWST WFS
Misell-Gerchberg-Saxton (MGS)
phase retrieval from focus-diverse,
known pupil support, data
(Acton, Atcheson (Ball))
Local expert: John Krist
Sivaramakrishnan, Morse, Makidon, Bergeron, Casertano, Figer,
Acton, Atcheson, Rieke SPIE Glasgow 2004
Sivaramakrishnan
STScI July 2004
JIM
End product after processing by
Scott Acton’s MGS implementation
JWST 2micron PSF
Applying the tip-tilt-piston and
radius of curvature segment
corrections determined by this data
reduction and analysis perfectly to
each segment will result in a 99%
Strehl ratio image as shown here
Strehl >99%
Sivaramakrishnan, Morse, Makidon, Bergeron, Casertano, Figer,
Acton, Atcheson, Rieke SPIE Glasgow 2004
Sivaramakrishnan
STScI July 2004
JIM
Is this good enough?
JWST 2micron PSF
Strehl >99%
•11.3 nm rms on wavefront
•Detector noise added 10nm rms
•Need to halve this noise
•More/deeper observations
•Dither for better flat
•Look at CR noise more carefully
•Use reference pixels well
•Develop good cal pipeline (IDT?)
Sivaramakrishnan, Morse, Makidon, Bergeron, Casertano, Figer,
Acton, Atcheson, Rieke SPIE Glasgow 2004
Sivaramakrishnan
STScI July 2004
JIM
NIRSpec Status
Mike Regan
Primary Science Goals for NIRSpec
Confirm high redshift NIRCAM proto-galaxies [R=100
mode]
Faint
Small
Relatively Rare
Measure clustering properties of these proto-galaxies
[multi-object R=1000]
Measure properties of galaxies as a function of redshift
[R=1000 mode]
Measure galaxy kinematics to constrain masses (IFU,
R=3000)
Be a general purpose multi-object spectrograph
Why Astrium Won.
Astrium
better.
s optical design was
Aligning the field makes the optics
simpler
Field Rotation has many
advantages
Mirrors are easier to make
More room for microshutters
More compact fore-optics
Better optical performance
No
Rotation
Rotated
FOV
An overview of NIRSpec
The grating wheel has a mirror
that is used for target acquisition.
Shifts in the location of
the grating wheel cause
the apparent FOV to
shift.
Only by directly imaging
the MSA can we
determine the mirror
location.
This adds time, flight
software complexity,
and uncertainty.
Solution is to image a fixed mirror
through a cut out in the grating wheel.
Demonstration of how the MicroShutter Array (MSA) works.
The Integral Field Unit (IFU) is now
in the baseline.
Field of view is 3 x3
Pixel scale is 0.075
Spectral Resolution is ~3000
Mass = 1.2 Kg
How the Integral Field Unit (IFU)
works
IFU and MOS modes are mutually
exclusive.
MOS Mode
IFU Mode
Summary
Astrium is the prime contractor
The integral field unit is part of the baseline.
Significant progress has been made on the
fabrication of the micro-shutter arrays.