TIPS-JIM Meeting
13 October 2005, 10am, Auditorium
1.
2.
3.
The Mid-Infrared Instrument (MIRI)
Martyn Wells
Medium Resolution Spectrometer for JWST
Temperature changes for ACS CCDs:
Marco Sirianni
Initial Study on Scientific Performance
Projected STIS performance through
Paul Groudfrooij
2013 with and without the ASCS
Next TIPS Meeting will be held on 17 November 2005.
The Mid-Infrared Instrument (MIRI)
Medium
Resolution Spectrometer for JWST
Martyn Wells
MIRI EC & UKATC
Spectrometer
Main Optics
Netherlands
Spectrometer
Pre Optics
UKATC
Deck (Leicester)
Spectrometer Focal
Plane Module
(USA)
Carbon Fibre Hexapod
(Denmark)
Imager (France)
Input Optics and
Calibration Unit
(Belgium)
Summary description
Spectrometer block diagram
SPO
SMO
Spectrometer fov
Dichroic passbands
Exposure C
Exposure B
Exposure A
Spectrometer – λ ranges, R, sampling
and fov
Ray-trace diagram of the Channel 1 IFU
Diagram of the output slit
Integral Field Unit Optical Layout
Spectrometer Pre-Optics
Here are the flattened envelopes of the
sliced and stacked sky images, heading off
to the spectrometer collimator mirrors in
the Spectrometer Main Optics (SMO)
The position of the Channel 2
collimator mirror
Here, the beam from the Channel 2
collimator is shown, heading back to one of
Channel 2’s three diffraction gratings.
The position of a Channel 2
grating.
The light is dispersed by the grating.
Dispersion
direction
...and heads back to a fold mirror.
...which sends it to the final, camera
mirror, which is a common optical element
for Channels 1 and 2 (as is the fold mirror)
The camera mirror forms the final image...
...on the Focal Plane Module (FPM), shown
here as the green cylinder.
Here comes the beam from the Channel 1
IFU, collimated and sent to one of Channel
1’s 3 gratings...
...where it is dispersed...
...and sent via this fold mirror to share the
last two mirrors on its way to the FPM with
the spectrum from Channel 2.
Channel 2a spectra
Constant
wavelength
positions
Some manufactured components
TIPS-JIM Meeting
13 October 2005, 10am, Auditorium
1.
2.
3.
The Mid-Infrared Instrument (MIRI)
Martyn Wells
Medium Resolution Spectrometer for JWST
Temperature changes for ACS CCDs:
Marco Sirianni
Initial Study on Scientific Performance
Projected STIS performance through
Paul Groudfrooij
2013 with and without the ASCS
Next TIPS Meeting will be held on 17 November 2005.
Temperature change for ACS CCDs:
initial study on scientific performance
M. Sirianni, T. Wheeler,
C.Cox, M. Mutchler,
A. Riess, K. Sembach,
R. Doxsey
TIPS
- Oct 13, 2005
M. Sirianni
Introduction
We have been asked to predict the impact of variations in operating
temperature for WFC and HRC.
The current operating temperature is
-77 C for WFC
-81 C for HRC
On average ~ 80% of the ACS usage is with WFC
The temperature range investigated is -74 to -80 (WFC)
Variation of the CCD temperature
can affect the following aspects:
1.
1.
2.
3.
4.
-77 to -84 (HRC)
Read noise
Dark Current
Hot pixel population
Quantum Efficiency (and Flat Field)
Charge Transfer Efficiency
TIPS
- Oct 13, 2005
M. Sirianni
Dark Current Variation
• Dark Current changes with Temperature:
D(T) = C T1.5 exp(-Eg/2kT)
Ground Test: Flight build (and similar devices) tested
from -100 C to -55 C
On-orbit test: Tests at warmer temperature (-71.5 and -66.7C) were
executed on March 2003 (Proposal 9097
Cox et al - ISR 2003-04)
• On-orbit, dark current increases with time due to
radiation damage :
~ 2.0 e-/pix/hr/yr for WFC1
~ 1.6 e-/pix/hr/yr for WFC2
~ 2.1 e-/pix/hr/yr for HRC
TIPS
- Oct 13, 2005
M. Sirianni
Dark variation with temperature
85
75
65
variation (%) of dark current
55
45
35
25
15
5
-5
-15
-25
-35
-45
-55
-65
-75
-85
-85
-83
-81
-79
-77
Temperature (C)
Using -77 C as a reference:
At -74 C the dark rate increases by 71%
At -81 C the dark rate decreases by 55 %
TIPS
- Oct 13, 2005
M. Sirianni
-75
-73
On-orbit dark variation due to radiation damage
Dark Rate WFC (-77 C)
30
e-/pix/hr
25
20
WFC1_trend
WFC2_trend
WFC1
WFC2
15
10
5
0
0
2
4
6
8
Years from launch
Mean dark current doubles every ~ 4 years
TIPS
- Oct 13, 2005
M. Sirianni
10
Dark variation: prediction
1000
10-02_first
10-01_second
e-/pix/hr
100
Flight data at 1 year
10-02_second
fit
10-01_1yr
Ground Test data
10-02_yr
fit_1yr
10
1
-95
re
u
at
r
pe
m
e
T
-90
-85
-80
-75
-70
-65
-60
-55
Radiation Damage
Lot 7b 13-02
-50
Temperature (C)
WFC -74 C
-77 C
-81 C
2008 31.9
18.6
8.4
2013 47.6
27.7
12.5
HRC -77 C
-80 C
-84 C
2008 37.7
21.3
9.8
2013 55.8
31.8
14.6
TIPS
• A change to -81 C in 2008 would bring
(e-/pix/hr)
back the dark current at the same level
after 1 year on orbit.
• A change to -74 C in 2008 would bring
the dark current at the level we
would reach after 18 years on orbit at -77
C.
(e-/pix/hr)
- Oct 13, 2005
M. Sirianni
Dark variation: scientific impact
• In order to assess the impact of the predicted dark current variation
on the science with ACS/WFC, we estimated the noise budget for a
typical observation:
– Most used filter : F814W
– Default gain (2e-/DN) : Read Noise: 5.36 e– Average Sky: 0.1 e-/pix/sec
– Star A0V magnitude F814W = 26
– One single exposure
– Aperture 3 pixels (76% of light)
– exposure time:
•
•
628 sec average exposure time for WFC observations
339 sec min exposure time for efficient use of WFC
Note: potential variations of QE and CTE are not included
TIPS
- Oct 13, 2005
M. Sirianni
Dark variation : scientific impact
2008
T exp=
628s
Noise ∫
Signal + Dark + Sky + RN
2013
Temp (C)
- 74
- 77
- 81
- 74
- 77
- 81
Signal
303
303
303
303
303
303
Dark
157
91.7
41.3
234
136
61.6
Sky
1775
1775
1775
1775
1775
1775
RN
812
812
812
812
812
812
Noise
55.2
54.6
54.1
55.9
55.0
54.3
S/N
5.49
5.55
5.59
5.42
5.51
5.57
CONCLUSION:
An increase in Dark Rate does not impact the S/N
When the noise due to dark current D [e-/pix/hr] competes with read noise?
For a given aperture and an exposure time EXPTIME (sec)
D =3600*Read_Noise^2/Exptime ~ 90000/EXPTIME
1000 sec => D=90e-/pix/hr
TIPS
- Oct 13, 2005
M. Sirianni
Hot pixel variation
• Dark non uniformity is more serious than the
increase in the dark current.
• Hot pixel threshold: 0.08 e-/pix/sec
• The number of hot pixels increases with time due
to radiation damage.
• The average signal level of the hot pixels shows
the same temperature dependence as normal dark
pixels.
TIPS
- Oct 13, 2005
M. Sirianni
Number of hot pixels vs Temp
TIPS
- Oct 13, 2005
M. Sirianni
Hot pixel growth
•
The number of hot pixels changes with time due to radiation damage. In 2008 the
number of hot pixels (dark current > 0.08e-/pix/sec) will reach the same level of
contamination of cosmic rays in a 1000 sec exposure
Hot pixel
threshold
TIPS
- Oct 13, 2005
M. Sirianni
Hot pixel growth
Percentage of pixels that are hot:
2008
4.8 %
1.8 %
1.3 %
-74 C
-77C
-81C
2013
8.7 %
3.3 %
2.5 %
• Hot pixels are removed by taking multiple images at
offset positions (“dithers”). More hot pixels require more
readouts for effective removal.
TIPS
- Oct 13, 2005
M. Sirianni
Hot pixel Mitigation
8.0
Max number of WFC readouts in 1 orbit
6.0
5.0
4.0
0
2013
-74 C
-74 C
2008
2013
2013
-81 C
2
-77 C
2008
0.0
-77 C
1.0
2008
2.0
-81 C
3.0
CRs in 628 sec
number of frames needed
7.0
4
6
8
10
pixel contamination (%)
For average exposure times, obtaining 3-4 dithered frames is the optimal strategy.
The number of readouts needs to be increased only if the temperature changes
to -74C.
CONCLUSIONS: No
TIPSimpact if -increase
Oct 13, 2005 in temperature
M. Sirianni can be avoided
QE/Flat Field Variation
• We do see small variations (< 0.5%) in the flat field at F435W
(WFC) when CCDs are warmer
• We need to investigate variations in the near-IR.
• Variations in the flat field may require new calibration.
• QE variations need to be investigated: some impact is
expected in the near-IR where WFC is most used.
• After ~ 3.5 years on orbit we do not observe a significant
variation of QE.
TENTATIVE CONCLUSION: We do not expect QE or Flat Field
variations with temperature to have a serious scientific
impact. Better on orbit data can be obtained
TIPS
- Oct 13, 2005
M. Sirianni
CTE variations with Temp
•
difficult to predict without a direct test
– Temperature and clocking rate are major player
• Broadly speaking, there are two sort of traps responsible
for CTE problems:
Shallow Traps
Deep Traps
Short emission time constant
Long emission time constant
CTE improves if the emission time
is decreased (allowing more time
for e- to escape from trap)
CTE improves if the emission time is
increased (keeping the traps filled)
CTE
 if T 
CTE
 if T 
Given the different clocking rate the effect on Parallel/Serial
directions and WFC/HRC can be different.
TIPS
- Oct 13, 2005
M. Sirianni
Summary
Lower
Temp
Read Noise
=
Dark Current
-
Hot Pixels
QE
Higher
Temp
=
+
+
+/- ? +/- ?
Flat Field
=?
CTE
+/- ? +/- ?
TIPS
=?
- Oct 13, 2005
Scientific
impact
Notes
none
none
low
Only if temperature
increases to -74C
few %
~ few %
Unknown
M. Sirianni
Flight test
can
measure
this
WFC Cooling Margin
• Data from cool down period after anneals
indicate that there is additional cooling
margin:
– TEC current is well away from maximum
– TEC hot side temperatures are well below CARD
limits (21 C vs 35 C)
• Margin should allow:
– “cold test” now
– some mitigation of aft shroud temperature
increase in the future.
TIPS
- Oct 13, 2005
M. Sirianni
WFC cool down profile
WFC housing temp.
WFC TEC current
WFC CCD temp.
TIPS
- Oct 13, 2005
M. Sirianni
Tests on orbit
• Previous on-orbit test provided temperature dependence of
– Read Noise
- Dark Current
-Hot pixels
• PROGRAM 10771 (Nov-Dec 05)
• study temperature dependence of
–
–
–
QE
Flat Field
CTE
• HRC and WFC at three different temperatures
• WFC [-74,-77,-80] HRC [-77,-80,-84]
Mix of internal and external orbits: total 12 internal + 12 external
– for CTE and QE : observation of 47 Tuc (or M3)
– for Flat Field and CTE : internal EPER tests
– for impact of CTE tails on detection threshold: z band HDFN
TIPS
- Oct 13, 2005
M. Sirianni
TIPS-JIM Meeting
13 October 2005, 10am, Auditorium
1.
2.
3.
The Mid-Infrared Instrument (MIRI)
Martyn Wells
Medium Resolution Spectrometer for JWST
Temperature changes for ACS CCDs:
Marco Sirianni
Initial Study on Scientific Performance
Projected STIS performance through
Paul Groudfrooij
2013 with and without the ASCS
Next TIPS Meeting will be held on 17 November 2005.
Space Telescope Imaging Spectrograph:
Projected Performance through 2013
Paul Goudfrooij
STScI
• Part of procedure to address necessity of ASCS installation
• CCD and MAMA Performance Estimates with/without ASCS
–
Science Impact example
TIPS meeting
October 13, 2005
Paul Goudfrooij
47
CCD Performance after SM4
•
•
•
•
•
•
Main contributor of effective throughput loss is increase of Charge
Transfer Inefficiency (CTI = 1–CTE) with time (due to accumulated
radiation damage)
–
Performance degradation continues in current Safe mode
Functional dependence of CTI on source counts, background level,
and elapsed on-orbit time determined in 2003 (Goudfrooij & Bohlin)
–
CCD spectroscopy mode unique to STIS and hence deemed
most relevant for current exercise
Issues related to growth of number of hot pixels similar to those for
ACS CCDs (cf. Marco’s talk), but can be mitigated by dithering
On-orbit increase of dark current typically has less impact than that of
CTI for faint sources
No positive impact of ASCS/STIK expected on CCD performance
Effect of higher temp’s on CTI would need to be calibrated in flight
TIPS meeting
October 13, 2005
Paul Goudfrooij
48
Science Impact of CTI Increase
•
Example of popular use of STIS CCD: Measurement of Black Hole
Mass in center of typical bulge in low-mass galaxy (plenty of mediumand high-mass galaxies already done).
SETUP:
• G750M/8561 Å
• 52x0.2 slit
• CCD binning 2x1
• galaxy with μV =
16 mag/arcsec2
TIPS meeting
October 13, 2005
Paul Goudfrooij
49
FUV-MAMA Performance after SM4
• Dark Current Limited: Exp time needed ∝ Dark Counts
–
–
–
Echelle data
FUV-MAMA dark in “glow” region generally increasing with tube
temp, but no clear relation between the two.
relation between dark in glow region and time since HV turn-on
If tube temp will rise significantly after SM4, might consider
constraining use to only few hours after every HV turn-on
F1 apertures
ѽ NUV-MAMA on
♦ NUV-MAMA off
TIPS meeting
October 13, 2005
Paul Goudfrooij
50
FUV-MAMA Performance after SM4
• Past Long-term Evolution of FUV-MAMA Temperature
–
–
Overall increase with time, but rate of increase declining
Temp stayed ~ constant with time since 2002
SM3B
SM3A
TIPS meeting
Solar Max
October 13, 2005
Note: Tube Temp is ~
4 ºC lower than
Charge Amp Temp
(latter shown on left)
Paul Goudfrooij
51
NUV-MAMA Performance after SM4
• NUV-MAMA Dark Current
–
–
–
Due to phosphorescence in impurity sites in MgF2 window, where
e– can be in metastable level just below level decaying to emit γ
Dark level strongly dependent on thermal environment
Long-term history of dark current (and temp) shows leveling off
Plot by James Davies
SM3A
TIPS meeting
October 13, 2005
SM3B
Solar Max
Paul Goudfrooij
52
NUV-MAMA Performance after SM4
•
•
•
•
Dark can be substantially
reduced with ASCS/STIK
Temp’s (and hence dark
Approx.
current
and exp time for darklimited obs.) down by nearlydark level
factor of 2
Dark down extra factor ~2 if
cooling campaigns
established
Would open up whole new
field of applications
–
–
Model of dark
during cooling
campaign
Echelle spectroscopy of
absorption lines in faint,
distant QSOs
NUV imaging of distant, low
surface brightness galaxies
TIPS meeting
October 13, 2005
Paul Goudfrooij
53
Summary of potential impact of ASCS
on STIS performance
Detector
FUV-MAMA
NUV-MAMA
CCD
Impacted by
ASCS?
How?
Science
Impact
What if NO
ASCS?
YES
Positive: Able to
run colder than
lately
Somewhat
lower dark and
better
performance
If temps higher
than now, may find
operational
workaround
YES
Positive: Able to
run colder than
lately
Significantly
lower dark and
better
performance
If temps higher
than now,
somewhat lower
performance
• Performance dependent on postSM4 thermal environment
• impact of CTE degradation at
current temp not substantial
NO
• Need recalibration if temp ≠
TIPS meeting
October 13, 2005
Paul Goudfrooij
54
TIPS-JIM Meeting
13 October 2005, 10am, Auditorium
1.
2.
3.
The Mid-Infrared Instrument (MIRI)
Martyn Wells
Medium Resolution Spectrometer for JWST
Temperature changes for ACS CCDs:
Marco Sirianni
Initial Study on Scientific Performance
Projected STIS performance through
Paul Groudfrooij
2013 with and without the ASCS
Next TIPS Meeting will be held on 17 November 2005.