STIS SMOV Science Report, 31 July, 2009
• Visit 3A of NUV MAMA HV recovery
• STIS SMOV Status Summary
• STIS CCD charge transfer inefficiency and time dependent
sensitivity
1
•
11351 Visit 3A, MAMA HV
Recovery
Ramped to -1750 V, 300 V below normal operational voltage
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–
–
–
•
•
•
Time tag image taken during ramp-up - see how dark changes vs voltage
Took dark and then flat with HITM1 lamp at 3.8 mA
Followed with fold test
Don’t have previous fold or flat field data at the -1750 setting
At full voltage of -2050, model of NUV window glow based on observed
temperature history predicts dark current would be ~ 2600 c/s
Friday afternoon visit will ramp to full voltage and repeat same tests
Previous history of HITM1 flats at
full voltage of -2050 V
– Diamonds give measured rate
– +’s are rate after subtracting dark
–
–
At full voltage of -2050, we would now
expect 12,000 to 14,000 c/s from lamp
Expect observed “flat+dark” to dark count
rate ratio of about 6:1.
•
Might hope this is independent of voltage
and MCP tube gain.
2
Results of Visit
• Time-tag taken over rampup
– First see counts at -1750 V as
expected, but at very low level
– Counts increase dramatically as
photocathode ramped up (steps
0, -100, -300, -700 V).
• All voltages and currents as
expected during visit
• Fold test showed distribution
shifted to very small folds
compared with full voltage
– No previous data at -1750 V
– Don’t know how to scale the
-1750 V count rates to -2050 V
3
Relative counts in dark & flat
• Dark and HITM1 flat images
– Strong gradients, upper right up to 8X brighter than center
• Suggests non-uniform field across tube
– Count ratio ~ 1 in vignetted corners
– Flat ≈ uniform 2X brighter elsewhere
– Suggests lamp flux ≈ window glow, not 5X brighter as expected
• If lamp prediction correct, implies dark >> than expected
4
Implications of flat:dark ratio
•
Turning on lamp after ramp-up only doubled counts
– If lamp projection correct, implies larger than expected dark
• If dark ~ 13000 c/s in full HV image this gives ~ 17000 OR counts
• Final stage of ramp up will shut of HV if > 15000 OR counts from dark
• Screening limit increased after rampup and before lamp flat and fold test, so
we will be OK if we get past ramp up
– Could this be an artifact of the very low gain?
• Average HITM1 lamp photon >> redder than window glow
•
•
Large window glow might abort recovery proc, but if dark rate is about
the same size as the lamp flux it shouldn’t hurt detector
Recommend running Ops Request 18505 to clear event flag and allow
final stage of NUV HV recovery to proceed
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–
–
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No evidence for large fold values indicative of tube breakdown
Need to ramp to full voltage to obtain more information
Too late to consider resetting limits in tomorrow’s procedure
If excessive dark rate shuts down HV, will reevaluate
• Proc will set event flag to prevent further HV commanding if limits exceeded
during ramp-up
5
STIS
Activity
PropID
STIS SMOV Program Title
Analysis
Lead
Visits
Done
Total
Visits
STIS02
11347
STIS03
Status
Memory Load and Dump
BS
1
1
Complete
11348
Science Data Buffer Check
BS
3
3
Complete
STIS04
11349
Mechanism Mini-Functional
TW
1
1
Complete
STIS05
11399
CCD Anneal (two anneal iterations)
MW
6
6
Complete
STIS06
11382
CCD Functional
DL
4
4
Complete
STIS07
11404
CCD Dark & Bias Monitor
MW
90
105
Ongoing
STIS08
11383
Aperture Wheel & Lamp Functional
WZ
2
2
Complete
STIS09
11384
STIS-to-FGS Alignment
CP
1
1
Complete
STIS10
11385
CCD Spectral Format Verification
WZ
1
1
Complete
STIS11
11386
External Focus Check
CP
3
3+1
STIS12
11387
Corrector and Focus Alignment
CP
-
8
Contingency
STIS13
11388
CCD External Spectroscopic Quality
TG
1
1
Complete
STIS14
11400
CCD CTI Check
PG
1
1
Complete
STIS15
11401
CCD Spectroscopic Throughputs
DL
3
3
Analysis
STIS16
11389
CCD Image and Pointing Stability
TG
1
1
Complete? LVPS changes?
STIS17
11350
FUV MAMA HV Recovery
TW
4
4
Complete
STIS18
11351
NUV MAMA HV Recovery
TW
2 (+2F)
4 (+2F)
STIS19
11390
FUV MAMA Dark Measure
CP
5
10
SMS 215 (Aug 7-8)
STIS20
11402
NUV Dark Monitor
CP
20
SMS 208 +
STIS21
11391
FUV Optical Format Verification
WZ
2
Analysis
STIS22
11392
NUV Optical Format Verification
WZ
2
SMS 208 (Aug 2)
STIS23
11393
FUV MAMA Spectroscopic Quality
TG
1
SMS 215 (Aug 4-5)
STIS24
11394
NUV MAMA Spectroscopic Quality
TG
1
SMS 215 (Aug 5)
STIS25
11403
MAMA Spectroscopic Throughputs
DL
3
SMS 215 (Aug 5-6)
STIS26
11395
MAMA Image Stability
TG
2
SMS 215 (Aug 3)
SMS 208 (Jul 29, 31)
6
Near term activities
•
208 SMS
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NUV MAMA recovery
•
–
NUV Darks
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NUV Spectra Format (Internal wavecals)
•
•
•
•
113514A 212:18:15:00 - 212:20:45:22
1140201 214:18:18:39 - 214:18:48:09
1139201 214:18:48:09 - 214:19:11:43
1139202 214:19:11:43 - 214:19:46:23
215 SMS
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NUV Darks - 5 visits
•
–
Focus check (repeat after secondary move; uses CCD only)
•
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1139402 217:14:15.34 - 217:17:34.41 - external
MAMA Sensitivity (both detectors)
•
•
•
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1139302 216:22:01:40 - 217:00:37:57 - external
NUV External Image Quality
•
–
1138611 215:05:59:04 - 215:06:56:28
FUV External Image Quality
•
–
215, 218, 221
1140302 217:17:57:39 - 217:19:29:39
1140303 217:20:51:48 - 217:23:17:24
1140305 218:14:38:05 - 218:16:20:25
FUV Dark measure
•
1139011,12,13,14,15
219:14:17:43 - 220:00:25:00
7
CCD Charge Transfer Efficiency and Time
Dependent Sensitivity Changes
Slides from Paul Goudfrooij with assistance from Ralph
Bohlin, Michael Wolfe and Danny Lennon
8
Update on CCD Calibrations after SM4:
CTE Correction and TDS
•
Main contributor of effective throughput loss is increase of Charge Transfer Inefficiency
(CTI = 1–CTE) with time (due to accumulated radiation damage)
–
–
–
–
Strong dependence on background level (which includes signal in bias file)
Level and slope of “spurious charge” in superbiases increased significantly
Affects CTE correction at low background levels (and actual analysis of CTE calibration
program)
To implement by adding new columns in CCDTAB ref. files + update to calstis
Average column in superbias
(July 2000)
Average column in superbias
(July 2009)
9
Update on CCD Calibrations after SM4:
CTE Correction and TDS
•
Analysis of SMOV4 CCD Spectroscopic Sensitivity data
–
–
No evidence of systematic errors related to application of current CTE correction formula (to
within < 1%!)
SMOV data included several data points at low and high CCD (housing) temp → Led to
improved temp dependence of sensitivity on side-2
•
–
Temp dependence of CTI (rather than sensitivity) does not fit data (to date) as well
Redetermined time constants for time dependence of sensitivity (TDS)
•
New TDS reference files to be created & delivered to CDBS
G230LB Grating
1700-1800 Å
1900-2000 Å
2100-2200 Å
2900-3000 Å
10
Update on CCD Calibrations after SM4:
CTE Correction and TDS
•
Analysis of SMOV4 CCD Spectroscopic Sensitivity data
–
–
No evidence of systematic errors related to application of current CTE correction formula (to
within < 1%!)
SMOV data included several data points at low and high CCD (housing) temp → Led to
improved temp dependence of sensitivity on side-2
•
–
Temp dependence of CTI (rather than sensitivity) does not fit data (to date) as well
Redetermined time constants for time dependence of sensitivity (TDS)
•
New TDS reference files to be created & delivered to CDBS
G430L Grating
3000-3400 Å
3400-3800 Å
3800-4200 Å
4800-5200 Å
11
Update of Gain Value for
CCDGAIN=4
•
Analysis of TDS and CTE corrections
revealed that sensitivities derived from
CCDGAIN=4
spectra
were
systematically high
– Recalibration of gain value done by means of
ratios of standard star spectra done in
CCDGAIN=1 and CCDGAIN=4 in same visit
– Result: Gain = 4.015 (as opposed to 4.034
currently in pipeline)
– Will be updated together with Spurious
Charge values in CCDTABs
(Figure courtesy of Ralph Bohlin)
12