SPACE
TELESCOPE
SCIENCE
INSTITUTE
Operated for NASA by AURA
Instrument Science Report STIS 2013-04(v1)
Summary of the Results of STIS
SMOV4 Calibration Activities
Charles R. Proffitt1,2, Alessandra Aloisi1, Ralph Bohlin1, Colin Cox1, Paul
Goudfrooij1, Theodore R. Gull3, Mary Beth Kaiser1,4, Matt Lallo1, Daniel J. Lennon1,
Don J. Lindler5, Russ Makidon1, Sami-Matias Niemi1,6, Beverly Serrano7, Thomas
Wheeler1, Michael A. Wolfe1, Bruce Woodgate3, and Wei Zheng1,4
1
Space Telescope Science Institute, Baltimore, MD
Science Programs, Computer Sciences Corporation, Baltimore, MD
3
NASA/Goddard Space Flight Center, Greenbelt, MD
4
John Hopkins University, Baltimore, MD
5
Sigma Space Corporation, 4600 Forbes Boulevard, Lanham, MD
6
Tuorla Observatory, University of Turku, Väisäläntie 20, Piikkiö, Finland
7
Raytheon/Goddard Space Flight Center, Greenbelt, MD
2
17 January, 2014
ABSTRACT
After HST Servicing Mission 4 (SM4), there was a period of Science Mission
Observatory Verification (SMOV4), to check out the new and repaired instruments.
Here we summarize the execution and results of the Space Telescope Imaging
Spectrograph (STIS) SMOV4 activities undertaken to ensure that the repaired STIS
instrument was ready to carry out its scheduled science program after a nearly five
year hiatus in operation. The results of the initial aliveness and functional tests are
reviewed, anomalies that affected the execution of the STIS SMOV plan are discussed,
and the results of each STIS SMOV activity executed are summarized. In most
respects the performance of STIS after the SM4 repair is very similar to that seen
prior to the 2004 failure. Notable changes include a significant and unexpected
enhancement of the NUV MAMA dark rate that has been declining only very slowly,
and continued degradation of the CCD performance due to radiation damage. Postrepair throughputs of most modes are close to expectations based on extrapolation of
previous trends.
Operated by the Association of Universities for Research in Astronomy, Inc., for the National
Aeronautics and Space Administration
Contents
•
Introduction (page 2)
•
STIS SMOV Activity Plan (page 3)
•
Aliveness and Functional Tests (page 5)
•
SMOV Anomalies Affecting STIS (page 6)
•
Results of Individual Activities and Programs (page 7)
•
Summary (page 63)
•
Change History (page 63)
•
References (page 64)
•
Appendix – STIS SMOV Requirements (page 65)
1. Introduction
The Space Telescope Imaging Spectrograph (STIS) was installed into the Hubble
Space Telescope (HST), in February 1997 during HST Servicing Mission 2 (SM2). It
operated successfully until May 2001, when there was a failure in side-1 of the
instrument’s electronics. Operations were able to resume in July 2001 using the
redundant side-2 electronics. Performance on side-2 was very similar to that on side
one, expect that, on side-2, the temperature of the STIS CCD cannot be directly
measured, and the STIS CCD thermoelectric cooler (TEC) must be run at constant
current rather than in a controlled feedback loop that keeps the detector at a constant
temperature. This means that the actual CCD temperature and dark current now vary
as the thermal environment inside STIS changes. The CCD on side-2 also showed a
slightly increased read noise (Jansen et al. 2010). Following the side switch, STIS
continued to function well until August 2004, when a power converter in the side-2
electronics failed. This disabled the power needed to move the STIS mechanical
mechanisms, as well as the power for the calibration lamps and heaters, rendering
further scientific observations with STIS impossible.
A plan was conceived to restore STIS to operations by replacing the side-2 circuit
board containing the failed component during HST Servicing Mission 4 (SM4).
Details of the repair plan can be found in Rinehart et al. (2008). Accessing the circuit
board required removal of an access panel held in place by 110 small screws, but after
some difficulty removing a rail that blocked access to that panel, astronauts Michael
Good & Michael Massimo successfully made the repair on May 17, 2009.
During the servicing mission, the success of the repair was tested by an Aliveness
Test (AT) that verified the functioning of the replacement board, and by a Functional
Test (FT) that checked the broader functionality of the STIS instrument. Following
the release of HST by Atlantis, there was then a period of Science Mission Orbital
Verification (SMOV) during which HST’s instruments were tested, calibrated, and
prepared for their return to science operations.
The STIS SMOV plan was “success-oriented” in that it assumed that the STIS
instrument would function essentially in the same manner as it had prior to the 2004
Instrument Science Report STIS 2013-04(v0.1) Page 2
failure. Except where the health and safety of the instrument might be an issue, the
sequence of activities was designed to proceed without necessarily waiting to analyze
the results of the preceding activity. The goal was to allow a rapid return to science
operations for STIS, accepting some risk that, if some unexpected problem were to
arise, it might require that a number of activities be repeated at a later time. STIS
SMOV plans only included those tests that are necessary to verify whether STIS
could obtain data of the quality anticipated. Many time consuming calibrations that
could be just as well be applied retroactively were deferred until after the SMOV
period and the resumption of routine science operations. In many cases the analysis of
the SMOV programs was also restricted to the minimum detail needed to meet the
SMOV requirements, even when a more detailed analysis might have been possible.
2. STIS SMOV Activity Plan
The high level requirements that needed to be satisfied by the STIS SMOV program
were finalized in the spring of 2007. A full listing of these requirements are attached
in an appendix to this document. Over these next two years a number of activities
were designed and detailed observational programs were written to satisfy these
requirements. Some requirements did not require an observational program to fulfill,
while other requirements mapped to more than one program. This mapping is given in
Table 1. The planned sequencing of STIS SMOV activities is shown in Figure 1. In
section 5 we will discuss the results for each activity.
Table 1: STIS SMOV Requirements and Mapping to Activities and Proposals
SMOV4
RELEVANT
PROPOSAL ID
TITLE
RQMT
ACTIVITY
Engineering Activities
L.10.4.5.1.1
STIS-01
N/A
Instrument States
L.10.4.5.1.2
STIS-01
Various
Detector States
L.10.4.5.1.3
STIS-01
11347
Data Interface
L.10.4.5.1.4
STIS-02
11347
Memory Dumps
L.10.4.5.1.5
STIS-03
11348
CS Buffer RAM Test
L.10.4.5.1.6
STIS-04
11349
Mechanism Mini-Functional
L.10.4.5.1.7
STIS-08
11383
Calibration Lamps
L.10.4.5.1.8
STIS-05
11399
CCD Annealing
L.10.4.5.1.9
Engineering
N/A
Temperature Monitoring
telemetry
L.10.4.5.1.10 STIS-06
11382
CCD Mini-functional
L.10.4.5.1.11 STIS-17, 18
11350; 11351
MAMA Recovery Procedures
L.10.4.5.1.12 N/A
N/A
Wait 3 Weeks for
Deuterium/Krypton Lamp Use
Acquisition Activities
L.10.4.5.2.1
STIS-09
11384
STIS-to-FGS Alignment
L.10.4.5.2.2
STIS-13,
11388;
ACQ and ACQ/PEAK Tests
15,16, 23
11401,11389,
11393
Alignment Activities
L.10.4.5.3.1
STIS-11,12
11386, 11387
STIS Focus Check
L.10.4.5.3.2
STIS-08
11383
Aperture Wheel Repeatability
Instrument Science Report STIS 2013-04(v0.1) Page 3
L.10.4.5.3.3
STIS-08,10,
21, 22
L.10.4.5.3.4
STIS-13, 23,
24
L.10.4.5.3.5
STIS-16, 26
Calibration Activities
L.10.4.5.4.1
STIS-07, 19,
20
L.10.4.5.4.2
STIS-14
L.10.4.5.4.3
STIS-15, 25
11383; 11385;
11391; 11392
11388; 11393;
11394
11389; 11395
MSM Optical Format
Verification
Spectroscopic Image Quality
11404; 11390;
11402
11400
11401; 11403
Dark Rate Measurements
Pointing Stability Tests
CTI Check
Throughput Check
Figure 1: The planned sequencing and dependencies of the STIS SMOV4 programs are shown
above. White boxes show engineering activities, and yellow boxes show alignment activities.
Activities oriented towards particular detectors are colored in light blue for the CCD, blue for
the FUV MAMA and pink for the NUV MAMA. Activities that used external targets are
enclosed with a double-lined boundary, while activities that were done with only internal
instrument operations are enclosed in a single lined boundary. Activities that had to wait until
after the pointing restrictions of Bright Earth Avoidance (BEA) period were relaxed, are
grouped on the lower right and enclosed within a dotted line.
3. Aliveness and Functional Tests
The STIS SM4 aliveness test (AT) was executed shortly after the astronauts finished
the STIS repair. The AT demonstrated that STIS could be transitioned to hold and
boot mode, and verified the relays and voltages needed to provide power to the lamps,
Instrument Science Report STIS 2013-04(v0.1) Page 4
mechanisms, and heaters supplied by the new LVPS2 circuit board. The calibration
insert mechanism and the slit wheel were also moved. The AT executed without
incident and all tests were fully successful.
The functional test (FT) began a few hours later. The goals of the functional tests
included verification of most STIS mechanisms, including the CCD Shutter, the
Calibration Insert Mechanism, the Mode Select Mechanism, the Aperture Wheel, and
the External Shutter. The MAMA detectors would be tested by turning on their lowvoltage power supplies, doing a minimal HV ramp, and taking dark exposures. The
CCD would be cooled with the TEC to a low enough temperature to operate, and then
dark images and internal tungsten lamp images would be taken using each of the 4
STIS CCD amplifiers to perform the readout. This would verify the ability to get light
to the detector, take images, and transfer those images to the ground.
The FT encountered a number of issues. These were documented by HST
Anomaly Reports (HSTARs). The first delay occurred when one of the bulkhead
thermistors showed a violation of the allowed low temperature limit due to the cold
state of STIS after the initial startup (HSTAR 11834). STIS safed, and could not be
recovered until the thermistor warmed to within the allowed range. Another delay
occurred when the initial set of images could not be dumped to the solid-state
recorder (HSTAR 11836). It turned out that the STIS Science Data Formatter (SDF)
relay was in the incorrect position, being configured for side-A instead of for side-B
as required by the configuration of the HST Science Instrument Control and Data
Handler (SI C&DH). Resetting this relay resulted in clearing the memory of STIS, so
it was then necessary to repeat all of the FT science exposures, which where then
successfully transferred to the ground.
Examination of these images taken during the FT revealed two additional
problems. The first of these was that there was no light visible on the CCD images
that should have been illuminated by the tungsten lamp! Analysis quickly showed that
this was again a configuration problem. The STIS TDF (Take Data Flag) Response
had been mistakenly left enabled rather than disabled as is usual for internal
exposures, and since the TDF was “down” the CCD shutter did not open for the lamp
exposures (HSTAR 11837). There was some discussion of repeating this part of the
FT yet again with the TDF response properly disabled, but it was decided to defer
further CCD operations until another anomaly seen in the image was fully
understood. This meant the ability of light to reach the CCD detector could not be
directly confirmed until later in the SMOV period.
This second problem was an apparently elevated bias level seen in the CCD
images taken using the B Amp (HSTAR 11840). It was eventually concluded this
anomaly resulted from a problem in the transfer of the digital science data from the
CCD Electronics Board (CEB) to the Main Electronics Board (MEB). Only 15 of the
16 bits of each word are being transferred, resulting in the loss of the least significant
bit and misalignment of the remaining bits. A small number of pre-launch images
taken with Amp B had shown the same problem, and it was hoped that the anomaly
would disappear under more normal operating conditions. However, subsequent
operations have since shown that the Amp B serial transfer problem now appears to
be permanent, and Amp B is no longer used for STIS operations. Since another
amplifier, Amp D, is normally used for GO science exposures, the loss of Amp B
affects only a limited number of calibration programs.
Examination of the other FT CCD images showed that the CCD read noise was
slightly enhanced compared to the levels seen in 2004. Measured read noise values in
Instrument Science Report STIS 2013-04(v0.1) Page 5
electrons of the gain=1 exposures taken during the FT for each amplifier were A:8.96,
B:9.42, C:6.97, D:5.79, compared to mean values in 2004 of A:8.73, B: 8.93, C: 6.77,
D:5.49. Even after discarding the B amp value affected by the transfer anomaly, the
remaining amps all show an increase in read noise of between 0.2 to 0.3 electrons.
Subsequent calibration observations have shown that these increases appear to be
permanent.
4. SMOV Anomalies Affecting STIS
In addition to the difficulties during the FT, there were a number of subsequent
instrument and observatory anomalies that delayed the STIS SMOV program.
The event with the greatest impact on the STIS SMOV schedule was the hang up
(HSTAR 1880) of the Science Instrument Control and Data Handler (SI C&DH). This
component had been replaced during SM4, and the replacement unit locked up on
June 15, 2009, preventing most communication with the HST instruments. Resetting
of the SI C&DH cleared the problem and STIS CCD operations were resumed on
June 24. However, during the lockup, the STIS MAMA detectors were in a state that
might have allowed single-event upset events induced by high-energy particles to
damage the detector. As a result, resumption of STIS MAMA activities were delayed
until July 28, 2009 to allow software modifications intended to provide additional
protection to the MAMA detectors in the event of future SI C&DH lockups.
On July 6, 2009, STIS suspended due to a MAMA Interface Electronics (MIE)
communications error (HSTAR 11917). This is believed to have resulted from a
Single Event Upset (SEU) that interrupted the processing in this component. A
similar event had been seen with the ACS MIE in 2006 (HSTAR 9980). Resetting the
STIS MIE appears to have cleared the error. However, subsequent attempts to dump
the MIE memory to provide further diagnostics information failed, (HSTARs 11922
and 11927), resulting in additional STIS suspend events. These were similar to a STIS
suspend event while attempting to dump the MIE RAM that had occurred in 1997
(HSTAR 6235), but the cause of this behavior was never fully understood. Eventually
STIS was recovered without further attempts to dump the MIE memory and normal
operations were resumed on July 24, 2009.
Instrument Science Report STIS 2013-04(v0.1) Page 6
5. Results of Individual Activities and Programs
Activity: STIS-01
Proposal: none, but see also activities STIS-06, 17, and 18.
Title: Verification of Instrument and Detector States
SMOV Requirements: L.10.4.5.1.1, L.10.4.5.1.2, L.10.4.5.1.3
Analysis Lead: Bev Serrano
Other Personnel: Alan Welty, Dennis Garland
Description: This activity demonstrated that STIS could transition to each of the
defined instrument modes, (BOOT, HOLD, OPERATE, and OBSERVER), and
detector states, and verified that the command and engineering data interface via the
RIU. These transitions were verified by monitoring of the usual STIS recovery
sequence and during the course of normal operations and did not require a separate
proposal. While some of the allowed detector states were tested during the course of
the recovery, others required waiting for the first proposals to use the detectors.
Execution: STIS was recovered from SAFE to OPERATE on May 27, 2009. CCD
TEC cooling was then started followed by a CCD transition to the STANDBY state.
The MAMA low voltage (LV) power supplies were also turned on and normal
cycling of the MAMA LV power supplies around SAA passages was initiated.
Verification of the observational detector states was verified by activities STIS-17
(FUV), STIS-18 (NUV), and STIS-06 (CCD).
Results: All executed transitions occurred nominally, and telemetry was nominal.
Instrument Science Report STIS 2013-04(v0.1) Page 7
Activity: STIS-02
Proposal: 11347
Title: Load and Dump STIS Onboard Memory
SMOV Requirements: L.10.4.5.1.3, L.10.4.5.1.4
Analysis lead: Bev Serrano (GSFC)
Other Personnel: Alan Welty, Charles Proffitt
Description: This activity tested and verified the STIS dump of CS memory
capability. Areas dumped include: EEPROM, PROM, EDAC RAM, and Buffer RAM
with the CS in OPERATE mode. With the MAMA Interface Electronics (MIE) and
CS both in OPERATE, a full dump of the Control Section's (CS) EEPROM, PROM,
and EDAC RAM was performed. The MIE data was then copied from MIE RAM and
MIE PROM to CS Buffer RAM. Finally, a portion of the CS Buffer RAM containing
the data was dumped as normal science images.
Execution: Visit 01 of program 11347 successfully executed on May 28, 2009.
Results: The planned memory dumps all executed nominally. The Code 582 flight
software team at GSFC compared the dumped memory with the ground reference
image. No problems were found.
Instrument Science Report STIS 2013-04(v0.1) Page 8
Activity: STIS-03
Proposal: 11348
Title: STIS Science Data Buffer Check with Self-test
SMOV Requirements: L.10.4.5.1.5
Analysis lead: Bev Serrano (GSFC)
Description: Using the set buffer memory macro, zeros were written into CS Buffer
RAM prior to passage into the SAA and then the buffer memory was dumped to the
SSR after exit from the SAA to check for bit flips. Then the CS self-test macro was
used to conduct a pattern test of CS Buffer RAM. The memory fail counter was
checked after the test has completed.
Execution: All three visits of 11348 successfully executed on May 29, 2009
Results: Code 582 flight software team at GSFC examined the zeroed-memory
dumps – no bit flips were found. The formal monitoring of the memory fail counter
was done by the FOT (Flight Ops Team) – the test passed.
Instrument Science Report STIS 2013-04(v0.1) Page 9
Activity: STIS-04
Proposal: 11349
Title: Mechanism Mini-Functional
SMOV Requirements: L.10.4.5.1.6
Analysis lead: Tom Wheeler
Description: All STIS mechanisms, with the exception of the corrector, were
initialized and then commanded to selected positions. Verification of the corrector
alignment mechanisms would have been done only as part of any alignment or focus
adjustments. Each of these mechanisms was exercised over the full range of motion
needed to support operational use of STIS. Telemetry was used to verify whether the
commanded movements have actually occurred.
Execution: Visit 01 of 11349 successfully executed on June 1, 2009.
Results: All mechanism moves were verified successfully by STIS instrument FSW
(no ESB messages) and via telemetry by STScI Engineering. No corrector movement
was needed or performed.
Instrument Science Report STIS 2013-04(v0.1) Page 10
Activity: STIS-05
Proposal: 11399
Title: CCD Anneal
SMOV REQUIREMENTS: L.10.4.5.1.8, L.10.4.5.1.9
Analysis Lead: Michael Wolfe
Other Supporting Personnel: Paul Goudfrooij, Daniel Lennon
Description: The purpose of this activity was to repair hot pixel damage to the STIS
CCD that resulted from cosmic ray induced radiation damage due to cosmic rays.
Radiation damage creates hot pixels in the STIS CCD detector. Many of these hot
pixels can be repaired by warming the CCD from its normal operating temperature
near -83°C to the ambient instrument temperature (~ +5°C) for several hours.
Pre-anneal CCD characteristics were defined by a series of bias, dark and flatfield exposures (duration: 2 orbits). After these exposures executed, the CCD
thermoelectric cooler (TEC) was turned off to allow the CCD detector temperature to
rise (from ~ -80°C to +5°C). The CCD was left in the uncooled state for
approximately 12 hours. The TEC was then turned back on and the CCD cooled to its
normal operating temperature. Since the CCD on Side-2 does not have a thermistor,
the actual temperature fluctuates depending on external conditions. After a 3 hour
wait to allow the CCD to reach normal operational temperatures, the bias, dark and
flat-field images were repeated to assess the post-anneal CCD performance (duration:
2 orbits). Flat field exposures permitted evaluation of any window contamination
acquired during the annealing period. The CCD window is coolest during the
annealing period because the TEC is powered off.
Execution: The first set of anneal visits executed on June 2 and 3, 2009, and a second
set executed on July 2 and 3, 2009.
Results: The anneals were successful, but did not eliminate all hot pixels that
accumulated during the period STIS was inoperative. The number of hot pixels is
somewhat more than would be expected from an extrapolation of pre-failure side-2
data. The number of hot pixels as a function of time for pre- and post-SM4 STIS CCD
data is shown in Figure 05-01, and the number of pixels with count rates of more than
0.1 e-/s before and after the anneal are compared in Figure 05-02. The anneal results
are described in more details in Wolfe et al. (2009), while additional details are given
in Goudfrooij et al., (2009) and Mason (2013).
Reference files: Data taken during this program was combined with data from
program 11404, STIS CCD Bias and Dark Monitor, and used in the production of the
weekly superdark reference files.
Documentation: STIS ISR 2009-01, STIS ISR 2009-02, STIS ISR 2012-02
Instrument Science Report STIS 2013-04(v0.1) Page 11
Figure 05-1: The number of post-anneal hot pixels only at various cut levels. All side-2 images
were scaled to a housing temperature of 18 C. Both this figure and Fig. 05-2 also include data
from the first 3 iterations of the cycle 17 STIS anneal program 11849.
Instrument Science Report STIS 2013-04(v0.1) Page 12
−
Figure 05-2: The number of pixels with a dark current > 0.1 e /s as a function of observation date
for before (red) and after (black) each STIS CCD anneal. For all values after the switch to side-2,
the images are rescaled to a CCD housing temperature of 18 C before analysis.
Instrument Science Report STIS 2013-04(v0.1) Page 13
Activity: STIS-06
Proposal: 11382
Title: STIS SMOV4 CCD Functional
SMOV REQUIREMENTS: L.10.4.5.1.9, 10.4.5.1.10
Analysis Lead: Paul Goudfrooij
Other Personnel: Michael Wolfe
Description: The purpose of this activity was to measure the baseline performance
and commandability of the CCD subsystem. This test assessesed several CCD
functions and performance characteristics, including: bias levels, read noise, dark
current, CTE, and gain. Bias, dark, and flat field exposures were executed to achieve
these goals. Full frame and binned (2 x 1, 1 x 2, and 2 x 2) observations were made.
Biases were taken at GAIN=1 and read-out in subarray mode to support target
acquisition and peakup modes. Only the primary amplifier (Amp D) was used. All
exposures were internals.
Visits 1 and 2 acquired bias frames and flats at the four commandable gain settings, 1,
2, 4, and 8 e/DN. At each of the available but unsupported gain settings (GAIN=2, 8)
31 bias frames were acquired for construction of a superbias. At the supported gain
settings (GAIN=1, 4) only 21 bias frames were acquired since the remaining frames
necessary for construction of a superbias were acquired as part of the normal bias
monitoring program. A pair of flats was acquired in camera mode at two signal levels
(achieved by using the 50CCD and F25ND3 apertures) at each gain setting. The flats
were analyzed to (1) provide a rough confirmation of the nominal gain calibration and
(2) determine if there had been changes in the number or position of cosmetic
artifacts, such as the shadows of particles on the detector window.
Bias and internal lamp exposures were obtained for binned modes, with binning
factors of 2 x 1, 1 x 2, and 2 x 2, for evaluation of read noise, bias level, and gain of
the binned settings.
Biases were acquired using a 100x100 and 1024x32 subarray readout (and gain=4) in
support of target acquisitions and peakups.
Visit 3 acquired dark frames and bias frames for evaluation of the mean dark current
at the operating temperature of the CCD and the identification of hot pixels.
Visit 4 acquired spectral flat field data at three different signal levels, spanning a
factor of 100 in signal intensity, for evaluation of charge transfer efficiency (CTE)
through the edge pixel response method. In addition 29 biases were taken at gain=1 to
enable the construction of superbiases for each of the binned settings used in visit 2.
Execution: All four visits successfully executed on June 3, 2009
Instrument Science Report STIS 2013-04(v0.1) Page 14
Results: The typical readnoise values for Amplifier D between the time of the initial
switch to the side-2 electronics in 2001 and their failure in 2004, were 5.4e- for
GAIN=1 and 7.7e- for GAIN=5. After SM4 these values increased slightly to 5.6 eand 8.0 e- respectively.
An examination of superbiases, shows that at GAIN=1, the level of the “spurious
charge,” which is effectively a position dependent background, was found to be about
60% larger than prior-to SM4.
Estimates of CTE effects from the flat field suggest possible temperature dependence,
but the overall scale of CTE losses appears to be similar to what an extrapolation of
pre-SM4 trends would suggest.
For additional details see Goudfrooij et al. (2009).
Documentation: STIS ISR 2009-02
Reference files delivered: Information from this proposal was used to update values
in the CCDTAB, including readnoise values, and CTE correction coefficients.
Instrument Science Report STIS 2013-04(v0.1) Page 15
Activity: STIS-07
Proposal: 11404
Title: STIS CCD Bias and Dark Monitor
SMOV Requirements: L.10.4.5.4.1
Analysis Lead: Michael Wolfe
Other Supporting Personnel: Paul Goudfrooij, Daniel Lennon
Description: This activity was the first in a series of measurements to characterize
and monitor the CCD biases and darks.
Bias program: This activity took full-frame bias exposures in the 1x1, 1x2, 2x1, and
2x2 bin settings at GAIN=1, and 1x1 at GAIN= 4 to monitor the bias and to build up
high-S/N superbiases and track the evolution of hot columns. At GAIN=1, 14 bias
frames were acquired in each visit with 1x1 binning and 2 bias frames with 1x2, 2x1,
and 2x2 binning. At GAIN=4, 3 bias frames were acquired with 1x1 binning.
Dark program: This activity obtained 1 long (1100s) and 2 short (60s) unbinned darks
per visit at GAIN=1 to monitor CCD behavior and chart growth of hot and bad pixels.
Acquiring dark exposures of different durations provided a test of low-level
instrument noise over a wide range of observing conditions, provided high S/N
calibration frames for subsequent SMOV activities, and permited hot pixel reference
file updates on appropriate time scales.
Execution: Execution of two daily dark visits started on June 3, 2009 and continued
until August 2, 2009, when this program was replaced by the routine Cycle 17
monitoring programs. No visits were executed between June 15 and June 23 due to
the HST SIC&DH lockup (HSTAR 11880). Visits 76 through 84, which were planned
for July 7 to 9, were lost when STIS suspended due to an MIE communications
failure (HSTAR 11917). As discussed in section 4 above, recovery efforts were
delayed due to problems with performing memory dumps of the MIE (HSTARs
11922 and 11927). Routine STIS operations did not resume until July 23, 2009,
resulting in the withdrawal of visits 85 through 93 of this program; the scheduling of
some visits was slipped to extend the duration of this program.
Results: Measured dark rates are similar to or slightly higher than predictions based
on extrapolations of trends seen before STIS failure in August 2004, (see Fig. 07-1
below). Weekly superbias and superdark reference files were created, tested, and
delivered to CDBS. Bias levels were systematically from 0.2e- to 0.3e- higher than in
2004. Additional details are discussed in Goudfrooij et al (2009).
Reference files: Full sets of super-bias and super-dark reference files were delivered
for pipeline use.
Documentation: STIS ISR 2009-02
Instrument Science Report STIS 2013-04(v0.1) Page 16
Figure 07-1: Dark current at center and near the readout for STIS CCD with side-2 electronics.
All results are scaled to a CCD housing temperature of 18 C.
Instrument Science Report STIS 2013-04(v0.1) Page 17
Activity: STIS-08
Proposal: 11383
Title: Aperture Wheel and Lamp Functional Test
SMOV Requirements: L.10.4.5.1.7, 10.4.5.3.2, 10.4.5.3.3
Analysis Lead: Wei Zheng
Other Personnel: Daniel Lennon
Description: This activity verified the ability to accurately position the STIS aperture
wheel, verified the functioning of the tungsten and wavelength calibration lamps, and
demonstrated that the STIS CCD imaging and spectroscopic mode were aligned well
enough to support normal science operations.
The first part of visit 01 took tungsten lamp images, using the CCD imaging mode,
while cycling through various STIS apertures. Frequent returns to the 0.2X0.2
reference aperture were interspersed throughout this sequence. The second part of
this visit took a series of G230MB/2697 LINE lamp images while cycling through the
52X0.1, 52X0.2, and 52X0.5 apertures to verify the repeatability of the slit wheel
mechanism.
Visit 2 performed observations with the HITM1 and HITM2 lamps at both commonly
used current settings (3.8mA and 10mA) using a variety of gratings to check lamp
functionality for routine science operations. The lamp flux and location of the spectra
on the detector was compared to previous side-2 values.
Execution: Visit 01 and 02 executed on June 3, 2009
Results: After subtracting thermal trends, relative aperture positions were found to be
within typical random measurement errors of < 0.2 pixels.
Instrument Science Report STIS 2013-04(v0.1) Page 18
Activity: STIS-09
Proposal: 11384
Title: STIS to FGS Alignment
SMOV requirements: L.10.4.5.2.1
Analysis Lead: Charles Proffitt
Other Personnel: Matt Lallo, Colin Cox, Ed Kimmer
Description: This activity was executed during the BEA period and used to verify
that the alignment of STIS with the FGSs was good enough to allow subsequent
SMOV activities to continue. The target was a 10.6 magnitude A star, and both it and
the two guide stars used were chosen from the Tycho catalog to ensure high
astrometric precision.
A small box pattern exposure of 0.3 s duration using 50CCD with a spacing of a few
pixels was taken first at the center of the detector and then repeated at POS TARG
positions of (+12, 0), (0,+12), (-12, 0), (0,-12). Three tungsten lamp images taken
through the 0.2x0.2 aperture were interspersed with these observations to allow for
measurement of internal instrument alignment changes.
Execution: Visit 05 executed on June 3, 2009. The remaining visits, intended for
other BEA periods appropriate for different possible launch dates, were withdrawn.
Results: The Flight Ops Sensors and Calibrations group at GSFC (Ed Kimmer) took
the guide star raw observations and applied the current FGS distortion and alignment
matrices to obtain V2, V3 locations. They then fit these two points to the
corresponding astrometric RA, Dec values provided by INS to obtain the pointing
solution. Using this, they returned to INS a report giving V2, V3 values associated
with the supplied target RA, Dec values at short time samples throughout the time
period in question. This allows the expected position of the target on the detector to
be calculated as a function of time during the visit. Note that while the GSC2
coordinates were provided by the ground system for the observation itself, the
calculations described here rely only on the astrometric Tycho coordinates and the
measured positions of the FGS’s.
The STIS team at STScI then made detailed measurements of the x, y position of the
target or lamp image in each of the exposures. Comparing the predicted and measured
positions allows the error in the STIS-to-FGS offset to be determined. It was found
that the offset of the detector reference point in V2/V3 coordinates was (+0.231”, 0.062”), while the offset for the lamp image of the reference aperture was (+0.299”,
+0.042”). These should be compared with an estimated error in the positions of the
guide stars and targets of 0.05”. As observations were taken at several dithered
positions, it was also possible to verify the rotation and plate scale of the detector.
The rotation measured within 1.1 arc-min of expected SIAF value, and the plate scale
was differed from the SIAF value by < 0.1%
Instrument Science Report STIS 2013-04(v0.1) Page 19
These results are all well within the SMOV requirements that the location of the
reference STIS camera aperture be determined with respect to the FGS reference
frames to an accuracy of 1 arc second in V2-V3 coordinates and 10 arc minutes in
aperture rotation angle. It was decided that no SIAF update was needed before
continuing with SMOV operations.
Instrument Science Report STIS 2013-04(v0.1) Page 20
Activity: STIS-10
Proposal: 11385
Title: CCD Optical Format Verification
SMOV Requirements: L.10.4.5.3.3
Analysis Lead: Wei Zheng
Other Personnel: Daniel Lennon
Description: For each CCD spectral optical element in the MSM (G230LB,
G230MB, G430L, G430M, G750L, and G750M), a HITM1 lamp spectrum was taken
to match selected observations that were done as part of the cycle 11 STIS/CAL
program 9617. The new observations only needed to be done for one CENWAVE
value of each grating. These observations were intended to verify the optical paths
and MSM positioning used for each of these modes and also allowed a check of the
spectral resolution. The spectral format of CCD imaging modes was verified by
activities STIS-08 and STIS-09. Note that program 9617 had switched to using the
HITM1 in place of the LINE lamp previously used for CCD dispersion solution
checks, because the HITM1 lamp gives much better illumination at the E1 aperture
positions. Program 9617 was also executed after the switch to side-2 operations for
STIS, and as such may provide a better comparison to SMOV4 data than would
earlier programs.
Results: All shifts with respect to the previous data were consistent with the expected
1 - 2 pixel variations due to MSM non-repeatability and thermal flexures. All
positions checked were well within the range needed to support normal operations
and calibrations. Rotations were < 0.3 pixels across the detector width.
Instrument Science Report STIS 2013-04(v0.1) Page 21
Activity: STIS-11
Proposal: 11386
Title: External Focus Check
SMOV Requirements: L.10.4.5.3.1
Analysis Lead: Charles Proffitt
Other Personnel: Russell Makidon, Colin Cox
Description: This program checked STIS image quality using two tests. In the first
test, a dispersed light ACQ/PEAK with the G230LB grating was used to dither the
0.1x0.09 aperture across a point source to sample the PSF. Relative counts at
different wavelengths gave a measure of the PSF shape at different wavelengths. A
comparable ACCUM spectrum with the G230LB and a large aperture was also taken
to provide a baseline flux for estimating the relative throughput of the 0.1x0.09
aperture. In the second test, a point source was imaged onto the CCD through the
F28x50OII filter. The resulting PSF shape was compared with the pre-repair PSF.
Sufficient S/N in the O II image was obtained to allow the use of phase retrieval
techniques to estimate the focus position.
Execution: Visit 01 executed on June 04-05, 2009. The sequence of G230LB
ACQ/PEAK and ACCUM exposures described above was repeated a second time
after the O II imaging exposures. Visit 11 was a shortened repeat of visit 01, that
omitted this 2nd iteration of the G230LB exposures, and was executed on August 3,
2009 to recheck the STIS focus after a move of the HST secondary. Other visits were
contingencies with alternate targets to allow this program to execute within the BEA
period for a variety of launch dates.
Results: The net count rate for the source was measured in the 0.1X0.09 G230LB
peakup confirmation images and divided by the synphot predictions for that source,
including time dependent sensitivity (TDS) corrections appropriate for the
observation date. The measured count rates for the SMOV4 observations are between
94% and 97% of the predicted values (see Fig. 11-1). In addition, the ratio of these
count rates to contemporaneous G230LB observations taken using a large aperture are
consistent with measurements done in 1997 (see Fig. 11-2). The second iteration of
the G230LB ACQ/PEAK and ACCUM exposures in visit 01 showed significantly
higher throughput than did the first set that had been taken about 2 hours earlier,
suggesting that the pointing of HST was more stable later in the visit. This variability
in the throughput is consistent with level of pre-SMOV4 scatter in the integrated flux
that is illustrated in Fig 11-1.
Phase retrieval focus results for observations with the narrow band F28X50OII filter
are also consistent with the expected historical range. We conclude that the NUV
small aperture throughput of STIS is within 7% of nominal values as specified in the
SMOV requirements. Therefore no adjustment of the corrector mechanism was
necessary.
Instrument Science Report STIS 2013-04(v0.1) Page 22
Figure 11-1: Fraction of predicted count rate observed with STIS G230LB & 0.1X0.09 aperture
in ACQ/PEAK exposures (before ~ MJD 51500 corresponding to November 1999 ACQ/PEAK
exposures clipped the bias at too high a level causing underestimates of the throughput). In
addition to the SMOV4 observations of BD+75 325 (diamond symbols) taken as part of 11386,
this plot also includes an observation of the standard GD 153 (triangle) taken as part of the
SMOV4 program 11403. Values calculated from the regular focus monitor over the years (+
symbols), are also shown.
Instrument Science Report STIS 2013-04(v0.1) Page 23
Figure 11-2: The ratios of 0.1x0.09 to large aperture net count rates as measured with deep
G230LB ACCUM spectra are compared for data from 1997 (black) and 2009 SMOV4 (color).
The 2009 observations bracket the 1997 measurement.
Instrument Science Report STIS 2013-04(v0.1) Page 24
Activity: STIS-12
Proposal: 11387
Title: Corrector and Focus Alignment
SMOV Requirements: L.10.4.5.3.1
Analysis Lead: Charles Proffitt
Other Personnel: Colin Cox, Russell Makidon
Description: This was a contingency activity only needed if STIS-11 would have
found a significant problem with the STIS focus or optical alignment. SMOV4 visits
were prepared to repeat the coarse alignment sweeps that were done during SMOV2
(program 7075), and the fine alignment sweeps that were prepared for SMOV3a/b
(programs 8512/8966), and to repeat the checks done by STIS-11. Only those visits
judged necessary during SMOV4 were to have been executed. Coarse sweeps would
have been done by taking images of a bright star using the F28X50OII filter; phase
retrieval techniques would then have been used to analyze the focus and alignment.
Fine sweeps would have used the G230LB grating together with the 0.1x0.09
aperture, and the optimal focus and alignment would be defined as the settings that
maximize the throughput for this combination. After the optimal corrector positions
were determined and set, a version of the observations done by STIS-11 would have
been repeated to confirm the success of these procedures.
Since the STIS corrector mechanism has not been moved since 1997, two brief visits
were also included to perform a functional test of the focus and tip-tilt movements
respectively.
The corrector system adjustments would have to be up-linked in real-time per design.
The data would have been rapidly down-linked and analyzed to produce the corrector
positions for each iteration in order to efficiently proceed through this serial activity.
Execution: This contingency was unnecessary, so no visits were executed.
Instrument Science Report STIS 2013-04(v0.1) Page 25
Activity: STIS-13
Proposal: 11388
Title: CCD Spectroscopic Image Quality and ACQ Tests
SMOV Requirements: L.10.4.5.2.2, 10.4.5.3.4
Analysis Lead: Ted Gull
Other Personnel: Don Lindler, Bruce Woodgate, Charles Proffitt
Description: This program checked image quality along the 52x0.1 aperture in
combination with the STIS G230LB grating. The target star was positioned at several
positions along the aperture including 52X0.1 (nominal center position), 52X0.1E1
(CTE position) and 51X0.1D1 (MAMA acquisitions near low background for FUV
MAMA). Positioning of the target was done utilizing PATTERN and offsets of 0.1”
between seven positions perpendicular to the aperture. Additional image quality
checks were done with PATTERN and SUBPATTERN for five positions along the
aperture, centered on the nominal center position with 2” offsets.
Execution: Visit 03 successfully observed the hot standard BD+75 325 on June 5,
2009. The other five visits in this program were contingencies with different targets to
allow observations during the post-SMOV Bright Earth Avoidance (BEA) period for
variety of possible SM4 launch dates. These extra visits were withdrawn after the
execution of visit 03.
Results: Comparison of the 2009 spectrum of BD+75 325 taken at the default
detector location was compared with a similar 2002 spectrum. The 2009 spectrum
was shifted by < 1 pixel in the dispersion direction and by about 5 pixels in the crossdispersion direction. Net count rates were approximately 4% less, but once the
estimated TDS corrections were applied, the 2009 spectrum was only about 1%
fainter than expectations based on extrapolated pre-SM4 trends. In the high S/N core
of the observation, the collapsed cross-dispersion profile is essentially identical (Fig.
13-1) but the wings show evidence for changes in CTI, increasing the sag of the
spectrum towards lower row numbers. Similar results were found for observations
taken at other positions along the slit; results at the 52X0.1E1 position are shown in
Fig. 13-2. Exposures that dithered the target out of the narrower 52X0.1 aperture
along the dispersion direction, showed no evidence for unexpected levels of scattered
light.
Instrument Science Report STIS 2013-04(v0.1) Page 26
Figure 13-1: This plot compares the cross dispersion profile of two G230LB 52X2 observations of
BD+75 325 taken at the center of the detector, one done in 2002 and the second in 2009. The core
of the PSF is essentially identical, but the wings of the later image show the effects of the
decreased CTI, which causes the profile to sag towards lower row numbers.
All target acquisition and peakup exposures in this program performed as expected.
Instrument Science Report STIS 2013-04(v0.1) Page 27
Figure 13-2: the same as the preceding figure, except that results are shown for observations
done at the 52X0.1E1 aperture position. Again, the cores of the profiles are similar, but the postSM4 exposure shows a significant increase in CTI effects.
Instrument Science Report STIS 2013-04(v0.1) Page 28
Activity: STIS-14
Proposal: 11400
Title: STIS CCD CTI Check
SMOV Requirements: L.10.4.5.4.2
Analysis Lead: Paul Goudfrooij
Other Supporting Personnel: Michael Wolfe, Paul Goudfrooij, Daniel Lennon
Description: This activity was the first in a series of measurements that were made to
characterize the dependence of the CCD Charge Transfer Inefficiency (CTI) as a
function of signal level, source position, and time. This activity executed during the
SMOV period and enabled measurement of the magnitude of the CTI for a limited
parameter set and provided a comparison of the current CTI performance with the
CTI performance prior to the Side-2 failure.
These CTI measurements were made using an "internal sparse field test", which
illuminated the detector with a stripe of light along the parallel axis. This test utilized
the ability of the STIS CCD and its associated electronics to read out the image with
any amplifier, i.e., by clocking the accumulated charge in either direction along both
parallel and serial registers. A sequence of nominally identical exposures was taken
alternating the readout between amplifiers on opposite sides of the CCD. Amplifier D
(the default) and amplifier B were used to check the parallel CTI at the default gain=1
setting. Comparison of the charge readout using the D and B amplifiers yielded a
measure of the CTI. If there were no CTI, then the ratio of the signals read out using
the two different amplifiers for a source at the same position would have been
identically 1.
First a series of bias images were taken with amplifier D and amplifier B. These
were followed by a series of 5 tungsten lamp exposures with the 0.05X31NDA slit in
mode G430M at the 5471Å central wavelength setting. The image of the long-slit,
0.05X31NDA, lies along the dispersion direction and has a narrow (2 pixel FWHM)
profile. Measurement of the CTI using a slit oriented in the dispersion direction
presents a “worst case” since there is no background source (“sky”) to fill the charge
traps on the CCD. This test was executed for a single signal level and a single slit
image position on the detector. Subsequent executions of the internal sparse field CTI
test moved the mode select mechanism (MSM) over a range of MSM positions to
vary the location of the slit image (and hence the number of parallel shifts) on the
detector.
Execution: Visit 01 executed on June 3, 2009, but the data was unusable due to the
fault with the B amp. The first iterations of the Cycle 17 program 11400 were revised
to use the A & C amps and were executed in July 2009 to allow an early CTI
measurement.
Results: The results from the substitute program 11400 are consistent with
predictions based on extrapolations of trends seen before STIS failure in August
Instrument Science Report STIS 2013-04(v0.1) Page 29
2004. The time constant coefficient of the CTI correction formula changed only
slightly, from 0.218 to 0.216 %/yr.
Documentation: STIS ISR 2009-002
Reference Files: The updated CTI time coefficient was incorporated into an updated
CCDTAB reference file.
Instrument Science Report STIS 2013-04(v0.1) Page 30
Activity: STIS-15
Proposal: 11401
Title: CCD Spectroscopic Throughputs
SMOV Requirements: L.10.4.5.4.3, L.10.4.5.2.2
Analysis Lead: Michael Wolfe
Other Personnel: Ralph Bohlin, Charles Proffitt, Daniel Lennon
Description: This activity had two functions: determination of the STIS sensitivity
for the CCD spectroscopic modes and verification of the CTE correction at high
signal levels. It also provided a measure of the resolution in the spatial direction at
two positions along the slit for each CCD spectroscopic mode.
The program obtained exposures in each of the 3 low-resolution CCD
spectroscopic modes (G230LB, G430L, and G750L) to establish the post-SM4 STIS
baseline sensitivity at both the nominal (central) target position along the 52X2 slit
and at the E1 position, which is closer to the default CCD amplifier, minimizing the
number of parallel transfers and the resulting CTI effects. The sensitivity of the
medium resolution CCD modes (G230MB, G430M, G750M) is also checked at the
nominal and E1 slit positions for two grating settings for each mode.
To verify the applicability of the pipeline CTE correction at high signal levels, the
target was also observed with the G430L at 7 positions along the 52X2 slit.
Execution: Visits 01 and 02 executed on July 1, 2009
Results: For the CCD gratings, throughputs measured immediately after SM4 were
very close to an extrapolation of pre-SM4 trends. Results for the low dispersion
gratings are shown below in Figures 15-1 through 15-3 below. A comparison of the
CTI effects on the dithered G430L data taken as part of this program are discussed in
Goudfrooij et al. (2009); they found that the existing correction works well for these
data.
Documentation: ISR STIS 2009-01. A more detailed analysis of the sensitivity of
STIS dispersed light modes over the whole history of the instrument is in preparation
by Holland et al. (2013), and will be published shortly as a STIS ISR.
Reference files: Reference files for the time dependent sensitivity of STIS modes
were updated to reflect the new results.
Instrument Science Report STIS 2013-04(v0.1) Page 31
Figure 15-1: The relative sensitivity of the STIS G230LB grating over time is shown. The post
SM-4 points shown include results from SMOV program 11401 as well as the first several visits
of the follow-on Cycle 17 calibration program 11855.
Figure 15-2: Relative sensitivity over time for the STIS G430L grating.
Instrument Science Report STIS 2013-04(v0.1) Page 32
Figure 15-3: Relative sensitivity over time for the STIS G750L grating.
Instrument Science Report STIS 2013-04(v0.1) Page 33
Activity: STIS-16
Proposal: 11389
Title: CCD Image and Pointing Stability
SMOV Requirements: L.10.4.5.2.2, 10.4.5.3.5
Analysis Lead: Ted Gull
Other Personnel: Don Lindler, Bruce Woodgate, Charles Proffitt
Description: The goal of this proposal was to measure image motion on the CCD
detector over two orbits using both an external star field and internal apertures
illuminated by a lamp. This activity was executed after a large angle maneuver was
predicted to induce significant thermal change that might affect focal plane-to-STIS
and internal STIS optical stabilities. Advice was sought from the scheduling team to
produce a maneuver expected to produce a significant thermal change. The chosen
target had been previously observed with the STIS CCD and used to verify the STISto-FGS alignment, which would have allowed this program to serve as backup to
program 11836 in support of activity STIS-11, STIS-to-FGS alignment, had that been
necessary.
Execution: Visit 01 executed on June 30, 2009, observing a field in NGC 188. The
contingency visit 02 targeting an M35 field was withdrawn. For approximately 12
hours prior to this visit, HST had been pointing near RA=17 44 00 -61 30 00, and was
then maneuvered to RA=00 47 04.4 +85 16 32.6 immediately before this program.
Results: Proposal 11389 consisted of a series of 47 individual 10 s external exposures
centered on the V=14.5 magnitude cluster star NGC 188 UMK 183, taken with the
MIRVIS optical element and the 50CCD aperture over the course of 2 orbits.
Interspersed with these external observations there were also a number of HITM2
lamp images taken with the 0.1X0.09 and the 52X0.1slits. The lamp observations
allow distinguishing between image motion internal to STIS and image motion
caused by changes in the telescope pointing or the STIS-to-FGS alignment. A typical
image is shown in Figure 16-1 and shows the five stars that were used for the stability
analysis.
The measured axis-1 or X direction displacements of each star from its mean
position as a function of time are shown in Figure 16-1. Also shown are the shifts for
the 0.1X0.09 aperture, and for two positions along the 52X0.05 aperture. During both
orbits the image positions shifted slightly. For the external targets, the rate of change
in the axis-1 direction was as large as 0.5 pixels/hour or 0.025”/hour with a total
amplitude of about 0.25 to 0.3 pixels or about 0.015”. As would be expected for
changes induced by telescope breathing, the pattern of shifts is similar from orbit-toorbit. The shifts in the axis-1 positions for the internal lamp images, show a similar
pattern, but with about half the amplitude. This suggests that optical bench flexures
within STIS and changes in the STIS-to-FGS alignment each make comparable
contributions to the image shifts, and that the actual shifts of the stellar image in the
Instrument Science Report STIS 2013-04(v0.1) Page 34
STIS aperture plane are of order 0.1” or about 1/5 of a pixel over the course of an
orbit.
Figure 16-2 shows the results for the measured axis-2 or Y direction
displacements. The amplitudes in the axis-2 direction are considerably smaller, with
an approximately 0.05” mean offset between the positions of the external images
measured between the two orbits of observations.
Program 11389 executed during a period when the STIS MAMA LVPSs were
powered off due to concerns about the response of STIS during an SI C&DH
anomaly. As the daily cycling of the MAMA LVPSs are the primary driver of
temperature variations in the STIS optical bench, this may have resulted in STIS
remaining more thermally stable than it would otherwise have been during this test.
Empirical models of the focus variation also showed rather small amplitude for the
predicted breathing changes during this visit (see the description of the MAMA
stability tests and Fig. 26-5 later in this document). Some thought was given to the
possibility of repeating this visit after the MAMAs were restored to normal operation,
but after consideration of the results of the purely internal MAMA stability tests done
in activity STIS-26 (program 11395), it was decided that STIS appeared to be
sufficiently stable that a repeat visit of this program was not necessary.
The most comparable program done during the original 1997 SMOV period was
program 7087 which observed a stellar target over the course of 8 orbits with the
G230MB grating and the 6X0.1 aperture. Shifts observed during that program were
substantially larger than seen in 11389. The position of the 7087 target changed by
nearly 0.9 pixels in the axis 1 and 0.5 pixels in axis 2 over the course of the 1st two
orbits. The differential shifts between the external target and internal lamp image
were up to 0.5 pixels. The measured flux began to drop substantially after the 7th orbit
indicating that the target had moved in the dispersion direction to near the edge of the
0.1” wide aperture.
Instrument Science Report STIS 2013-04(v0.1) Page 35
Figure 16-1: An image from program 11389 centered on the cluster star NGC 188 UMK 183
(=FTS 56). The five stars used to monitor the image stability are marked; their primary
identifications and V magnitudes given in SIMBAD are Star 1 = Cl* NGC 188 WV9 V=19.06,
Star 2 = Cl* NGC 188 FTS165 V=15.29, Star 3 = Cl* NGC 188 FTS 68 V=14.74, star 4 = Cl*
NGC 188 FTS 56 V=14.51, and star 5 = Cl* NGC 188 FTS 204 V=15.69.
Instrument Science Report STIS 2013-04(v0.1) Page 36
Figure 16-2: The motion in the axis 1 (X) direction of the stellar image centroids versus the time
elapsed since the first lamp observation in the visit is plotted. Also shown is the motion of the
0.1X0.09 aperture illuminated by the HITM2 lamp and the 52X0.1 slit at Y-positions of 150 and
850 pixels. Much, but not all, of the stellar motion tracks with the internal lamp observations
indicating that the motion is a result of changes internal to the STIS optics. The total range of Xmotion is approximately ¼ of a pixel or 0.0125 arc-seconds.
Instrument Science Report STIS 2013-04(v0.1) Page 37
Figure 16-3: Results are shown here for the axis 2 (Y) direction in a format similar to that of Fig.
16-2. The Y motion of the 52X0.1 slit was computed using the occulting bars at approximate Ylocations of 300 and 750 pixels. The total range of Y-motion was approximately 0.1 pixels or
0.005 arc-seconds.
Instrument Science Report STIS 2013-04(v0.1) Page 38
Activity: STIS-17
Proposal: 11350
Title: FUV MAMA HV Recovery
SMOV Requirements: L.10.4.5.1.11
Analysis lead: Tom Wheeler
Other Personnel: Charles Proffitt
Description: This activity addressed the concerns over Cesium migration from the
FUV-MAMA photocathode into the pores of the microchannel plate and laid out the
procedures necessary to permit a safe and controlled recovery of the FUV-MAMA
detector to science after 5 years of hiatus.
The recovery consisted of four separate and unique procedures (visits) that were
completed successfully and in order. They are: (1) a signal processing electronics
check, (2) a 1st high voltage ramp-up to an intermediate MCP voltage of -1500V with
limits modifications and voltage plateaus, (3) a 2nd high voltage ramp-up to an
intermediate MCP voltage of -1950V (300V below the nominal MCP voltage) with
limits modifications and voltage plateaus followed by a fold distribution test, and (4)
a final high voltage ramp-up to the full operating voltage, again with limits
modifications and voltage plateaus, followed by a fold distribution test.
During the 1st high voltage ramp-up, a time-tag exposure and diagnostics were
performed followed by a dark exposure. During the 2nd and 3rd high voltage rampups, time-tag exposures were taken, diagnostics were performed, followed by darks,
flat field ACCUMs, and fold analysis tests.
Execution: Visits executed successfully on June 2, 3, 5, and 7 of 2009.
Results: The FUV detector successfully passed each test. The final fold distribution
was within family, showing a slight shift in the folds towards higher fold numbers.
This is consistent with aging expected for MAMA detectors. The diagnostic
exposures showed no unusual or unexpected features.
Instrument Science Report STIS 2013-04(v0.1) Page 39
Activity: STIS-18
Proposal: 11351
Title: NUV MAMA HV Recovery
SMOV Requirements: L.10.4.5.1.11
Analysis Lead: Tom Wheeler
Other Personnel: Charles Proffitt
Description: This activity addressed the concerns over Cesium migration from the
NUV-MAMA photocathode into the pores of the micro-channel plate and laid out the
procedures necessary to permit a safe and controlled recovery of the NUV-MAMA
detector to science.
The recovery consisted of four separate and unique procedures (visits) that were
completed successfully and in order. They are: (1) a signal processing electronics
check, (2) a 1st high voltage ramp-up to an intermediate MCP voltage of -1500V with
limits modifications and voltage plateaus, (3) a 2nd high voltage ramp-up to an
intermediate MCP voltage of -1750V (300V below the nominal MCP voltage) with
limits modifications and voltage plateaus followed by a fold distribution test, and (4)
a final high voltage ramp-up to the full operating voltage, again with limits
modifications and voltage plateaus, followed by a fold distribution test .
During the 1st high voltage ramp-up, a time-tag exposure and diagnostics were
performed followed by a dark exposure. During the 2nd and 3rd high voltage rampups, time-tag exposures were taken, diagnostics were performed, followed by darks,
flat field ACCUMs, and fold analysis tests.
Execution: Visits 01 and 02 executed successfully on June 8, and 9, 2011. Visit 03 on
June 11 resulted in a detector shutdown (HSTAR 11875). The cause was an
unexpectedly large NUV detector dark rate, which caused the count rate to exceed the
conservative levels set during that stage of the HV rampup. Because of this anomaly,
the event flag was not cleared for visit 04 and the visit executed with NUV MAMA
commanding inhibited resulting in no useful data. Repeats of the failed visits were
delayed due to the HST SI C&DH anomaly, and visits 3A and 4A finally executed
successfully on July 29 and 31, 2009.
Results: The NUV detector exhibited an initial dark count rate 4-5 X higher than
predicted. This was attributed to increased window glow that had not been previously
modeled. This led to a modification of the NUV monitored voltage ramp yellow an
red counter limits increasing them from 15,000 to 25,000 counts/sec to allow visit 3A
and 4A as well as subsequent observations to execute. No modification was required
to the normal 770,000 counts/sec observing limit.
The detector otherwise successfully passed each test once the problems discussed
above were resolved. The final fold distribution was within family, showing a slight
shift in the folds towards higher fold numbers. This is consistent with aging expected
for MAMA detectors. The diagnostic exposures showed no unusual or unexpected
features.
Instrument Science Report STIS 2013-04(v0.1) Page 40
Activity: STIS-19
Proposal: 11390
Title: FUV-MAMA Dark Measure
SMOV Requirements: L.10.4.5.4.1
Analysis Lead: Charles Proffitt
Other Personnel: Tom Wheeler, Wei Zheng
Description: The STIS MAMA HV power supplies are turned on only during each
day’s block of SAA-free orbits. The FUV MAMA dark current glow has been
observed to increase with the length of time the FUV HV power supply has been on.
The rate of this daily increase has changed over the years and also appears to be
sensitive to temperature. To measure the rate at which the dark current increases, a
series of five 1380s FUV MAMA dark exposures spread over 5 or more orbits of a
single SAA period was taken as soon as possible after the completion of activity
STIS-17 which recovered the FUV detector to operation. All exposures were internals
that fit into short occultation orbits. A second similar block of five exposures was
done near the end of the SMOV period when the temperature of the aft-shroud and
STIS were in the range expected for normal Cycle 17 operations.
Execution: The first block of 5 visits executed on June 9 and 10, 2009, while the 2nd
block of 5 visits executed on August 7, 2009.
Results: While the initial dark rate seen in the first FUV MAMA dark exposures
taken were surprisingly low, by the time the 2nd block of exposures were taken, the
dark rate had returned to levels comparable to those seen from 2002 – 2004, (see Fig.
19-1 below). In both cases, however, the dark rate increased rapidly with time after
the detector had been turned on. Since the behavior was very similar to that seen in
2004, there was no need to reconsider planned science or calibration exposures.
Documentation: ISR 2011-03
Instrument Science Report STIS 2013-04(v0.1) Page 41
Figure 19-1: The FUV MAMA dark current is lowest immediately after HV turn-on and
increases as a function of turn-on time. The symbol size scales with the estimated time from the
most recent ramp up of the FUV MAMA voltage. The initial dark rate after SM4, as shown by
the points just before MJD=55000, was substantially lower than during 2004, but within a few
weeks this had increased to a level comparable to that seen prior to the 2004 STIS failure.
Instrument Science Report STIS 2013-04(v0.1) Page 42
Activity: STIS-20
Proposal: 11402
Title: NUV-MAMA Dark Monitor
SMOV Requirements: L.10.4.5.4.1
Analysis Lead: Charles Proffitt
Other Personnel: Thomas Wheeler, Wei Zheng
Description: The STIS NUV-MAMA dark current is dominated by a phosphorescent
glow from the detector window. Meta-stable states in this window are populated by
cosmic ray impacts, which, days later, can be thermally excited to an unstable state
from which they decay, emitting a UV photon. The equilibrium population of these
meta-stable states is larger at lower temperatures; so warming up the detector from its
cold safing will lead to a large, but temporary, increase in the dark current.
To monitor the decay of this glow, and to determine the equilibrium dark current for
Cycle 17, four 1380s NUV-MAMA ACCUM mode darks were taken each week
during the SMOV period. The observations were done in pairs, with the two
observations of each pair separated by 4 to 7 orbits to ensure that they were taken at
different parts of the same SAA-free block. Each pair was taken 3 to 4 days after the
preceding pair. Once the observed dark current has reached an approximate
equilibrium with the mean detector temperature, the frequency of this monitor was
reduced to one pair of darks per week.
Execution: The first visits of this program executed on August 2 and 3, 2009. The
first visit resulted in a detector shutdown during the initial HV ramp up (HSTARs
11959 and 11961). The cause was shown to be incorrect values of the red and yellow
limits in the real-time commanding that executed the HV ramp. The high voltage
remained off for visit 02, and normal execution commenced with visit 03 on August
06, 2009. Due to the extended SMOV period and the much higher than expected
NUV dark current, this program was expanded from the originally allocated 20 orbits
to a total of 45 orbits. An additional 11 orbits were withdrawn as unnecessary. The
program continued until Sep 6, 2009. Monitoring was continued by the follow-on
cycle 17 calibration program 11857.
Results: Initial measurements showed the NUV detector dark rate to be about 10X
larger than expected. Initially this extra dark rate was declining with ~ 100 day efolding time, (see Fig. 20-1), but this time scale has lengthened as the dark current
declined, and by mid-2013 the NUV MAMA dark rate was still about 50% higher
than typical pre-SM4 levels. Observers with programs that might be sensitive to this
substantial increase of dark rate were advised of the change in performance so they
could reconsider their observational strategy.
Documentation: ISR 2011-03
Instrument Science Report STIS 2013-04(v0.1) Page 43
Figure 20-1: The orange curve shows prediction of the pre-SM4 dark current model. The shortterm fluctuations are due to daily temperature cycling. The circles show results from actual dark
exposures, while the X’s are estimated from telemetry. The black symbols show the actual postSM4 STIS NUV MAMA dark current measurements, which were far higher than expected. Also
shown are curves that add a term proportional to exp(-ΔE/kT)exp(-t/τ) to the pre-SM4
prediction, with τ =100 days (red curve) and τ = ∞ (blue curve).
Instrument Science Report STIS 2013-04(v0.1) Page 44
Activity: STIS-21
Proposal: 11391
Title: FUV-MAMA Optical Format Verification
SMOV Requirements: L.10.4.5.3.3
Analysis Lead: Wei Zheng
Other Personnel: Don Lindler and Charles Proffitt
Description: For each FUV-MAMA spectral optical element in the MSM (G140L,
G140M, E140M, E140H), a LINE lamp spectrum was taken to match selected
observations that were done as part of the cycle 11 STIS/CAL program 9618. The
new observations needed only be done for one CENWAVE value of each grating.
These observations verified the optical paths and MSM positioning used for each of
these modes, and also allowed for a check of the spectral resolution. The normal
monthly MSM offsetting was turned off and the zero-offset MSM positions were used
for these observations. CENWAVE settings matched those used for the initial
alignment checks done during SMOV2 by program 7078.
Execution: Visits 01 and 02 executed on July 28, 2009
Results: The positions of the FUV spectra were compared with the templates from
previous cycles. The shifts were all found to be consistent with the expected 1 to 2
pixel variations expected from MSM non-repeatability and thermal flexures of the
STIS bench. Any rotations were < 0.3 pixels across the width of the detector. This
easily meets the requirement that spectral images remain close enough to their old
positions that no modification to planned observations are necessary.
Instrument Science Report STIS 2013-04(v0.1) Page 45
Activity: STIS-22
Proposal: 11392
Title: NUV-MAMA Optical Format Verification
SMOV Requirements: L.10.4.5.3.3
Analysis Lead: Wei Zheng
Other Personnel: Daniel Lennon
Description: For each NUV-MAMA spectral optical element in the MSM (G230L,
G230M, E230M, E230H, and PRISM), a LINE or HITM1 lamp spectrum was taken
to match selected observations that were done as part of the cycle 11 STIS/CAL
program 9618. The new observations needed only be done for one CENWAVE value
of each grating. These observations verified the optical paths and MSM positioning
used for each of these modes, and also allowed for a check of the spectral resolution.
The normal monthly MSM offsetting was turned off and the zero-offset MSM
positions used for these observations. A subset of CENWAVE settings was taken to
match those used for the initial alignment checks done during SMOV2 by program
7078. Settings used are: G230L 52X0.05 100s LINE lamp at 3.8mA; G230M 2338
52X0.05 100s; E230M 2561 0.2X0.06 120s; E230H 2513 0.1X0.09 872s; PRISM
2125 52X0.05 HITM1.
Execution: Visits 01 and 2 executed on August 2, 2009, but due to the anomaly
described in HSTAR 11959, (see also the description of activity STIS20 above), the
HV was off and no useful data were obtained. These failed visits were successfully
repeated as visit 03 and 04 on August 13, 2009.
Results: The positions of the NUV spectra were compared with the templates from
previous cycles. The shifts found were all consistent with the expected 1 to 2 pixel
variations expected from MSM non-repeatability and thermal flexures of the STIS
bench. Any rotations were < 0.3 pixels across the width of the detector. These results
easily meet the requirement that spectral images remain close enough to their old
positions that no modification to planned observations are necessary.
Instrument Science Report STIS 2013-04(v0.1) Page 46
Activity: STIS-23
Proposal: 11393
Title: FUV MAMA Image Quality
SMOV Requirements: L.10.4.5.2.2, 10.4.5.3.4
Analysis Lead: Ted Gull
Other Personnel: Don Lindler, Bruce Woodgate, Charles Proffitt
Description: A reference exposure of a bright standard star was first taken at the
default 52X2 aperture position using the G140L grating. This source was then placed
at five locations along the 52X0.1 aperture. Then at the nominal center of the 52X0.1
aperture, a pattern of five exposures were taken spaced at 0.1 arcsec intervals using a
centered pattern to step the target perpendicular to the slit. This pattern was done at
five locations, on the nominal aperture center and offset at 2 arcsecs intervals above
the nominal aperture center (including the 52X0.1D1 position) and 2 arc seconds
below aperture center.
Execution: Visit 02 was executed on August 4, 2009.
Results: The 52X2 observation of GD153 was compared to a similar observation of
the star taken on July 16, 2002. The position of spectrum differed by only 2.3 pixels
in the Y-direction and less than a quarter of a pixel in the X-direction. For the G140L
spectra taken at the center of the 52X2, the cross dispersion profiles observed for this
program are virtually identical to those seen in 2002 (see Figs. 23-1 and 23-2).
Observations taken through the small 52X0.1 aperture appear as expected, and the
FUV throughput of this narrow aperture relative to wider ones appears consistent with
previous observations (see Fig. 23-3).
It is concluded that the post-SM4 image quality of spectra taken using the G140L
grating with the STIS FUV-MAMA is very similar to that obtained before the STIS
failure in 2004 and subsequent repair in 2009.
Instrument Science Report STIS 2013-04(v0.1) Page 47
Figure 23-1: Comparison of the cross dispersion profile for G140L seen in 2002 with that of 2009.
Figure 23-2: Central core of the cross-dispersion profiles shown in Figure 23-1.
Instrument Science Report STIS 2013-04(v0.1) Page 48
Figure 23-3: The throughput ratio of G140L observations taken in the 52X0.1 aperture to that of
the 52X2 aperture is compared for data taken in both 1998 and 2009.
Instrument Science Report STIS 2013-04(v0.1) Page 49
Activity: STIS-24
Proposal: 11394
Title: NUV MAMA Spectroscopic Image Quality
SMOV Requirements: L.10.4.5.3.4
Analysis Lead: Ted Gull
Other Personnel: Don Lindler, Bruce Woodgate, Charles Proffitt
Description: A reference exposure of a bright standard star was first taken at the
default 52X2 aperture position using the G230L grating. This source was then placed
at five locations along the 52X0.1 aperture. Then at the nominal center of the 52X0.1
aperture, a pattern of five exposures will be taken spaced at 0.1 arcsec intervals using
a centered pattern to step the target perpendicular to the slit. This pattern was done at
five locations, on the nominal aperture center and offset at 2 arcsecs intervals above
the nominal aperture center (including the 52X0.1D1 position) and 2 arc seconds
below aperture center.
Execution: Visit 02 was executed on August 5, 2009.
Results: The 52X2 observation of GD153 taken during this program was compared to
a similar observation of the star taken on July 17, 2002. The position of spectrum
differed by less than one pixel in the Y-direction and approximately 3 pixels in the Xdirection. For the G230L spectra taken at the center of the 52X2, the cross-dispersion
profiles observed for this program are virtually identical to those seen in 2002 (see
Figs. 24-1 and 24-2). Observations taken through the small 52X0.1 aperture appear as
expected, and the relative NUV throughput of this narrow aperture appear to be only a
few percent below results measured from the ratio of previous narrow-to-wide slit
observations (see Fig. 23-3). We conclude that post-SM4 NUV spectroscopic image
quality remains similar to that seen prior to the 2004 STIS failure.
Instrument Science Report STIS 2013-04(v0.1) Page 50
Figure 24-1: Comparison of the cross dispersion profile for G230L between 2002 and 2009.
Figure 24-2: Central core of the cross-dispersion profile shown in Figure 24-1.
Instrument Science Report STIS 2013-04(v0.1) Page 51
Figure 24-3: The throughput ratio of G230L observations taken in the 52X0.1 aperture to that of
the 52X2 aperture is compared for data taken in 1997 and 2009.
Instrument Science Report STIS 2013-04(v0.1) Page 52
Activity: STIS-25
Proposal: 11403
Title: MAMA Spectroscopic Throughputs
SMOV Requirements: L.10.4.5.4.3
Analysis Lead: Michael Wolfe
Other Personnel: Rachel Osten, Ralph Bohlin, Charles Proffitt, Azalee Bostroem,
Daniel Lennon
Description: This activity has two functions: Determination of the STIS sensitivity
for the MAMA spectroscopic modes and checked the small aperture throughput at
NUV wavelengths to verify the instrument focus.
This activity comprises the three visits of the nominal Cycle 17 MAMA
Spectroscopic Sensitivity Monitoring program: one visit each for the low-resolution
(G140L, G230L), medium-resolution (G140M, G230M), and echelle (E140M,
E140H, E230M, E230H) modes. As part of the low dispersion visit, a fine peakup in
the 0.1X0.09 aperture is done with the G230LB grating to allow the throughput to be
compared to previous measurements. The first-order medium-resolution spectral
sensitivity visit includes an image taken using the F28X50OII aperture with the CCD
as an additional verification of the focus.
Execution: Visits 02, 03, and 05 executed on August 5 and 6, 2009. Visit 03 and 04
were contingency visits using alternate targets and were withdrawn after the
successful execution of the primary visits.
Results: As was the case with the CCD gratings, the post-SM4 throughputs of most
STIS MAMA gratings were close to the extrapolation of the pre-failure trends.
Results for the low-dispersion first-order modes are shown in Figures 25-01 through
25-03 below. The time dependent trends for the medium resolution first order modes
appear to be consistent with the L mode trends to within 1%. Most echelle settings
also appear to be consistent, but one significant exception was the E140H grating,
where initial measurements of the throughput appeared to be 10% to 15% below
expectations, and the image quality in the cross-dispersion direction was noticeably
degraded (see Fig. 25-3 and Bostroem et al. 2009). Some of the other echelle gratings
showed a similar, but milder, anomaly. However, this discrepancy faded over time,
and by early 2010, throughputs and image quality had returned to the expected trends.
Documentation: ISR STIS 2012-01, Holland et al. (ISR in preparation).
Reference File Updates: Results of this program were used to provide preliminary
updates to the time-dependent senility correction files used in the flux calibration of
STIS MAMA spectroscopic and imaging data.
Instrument Science Report STIS 2013-04(v0.1) Page 53
Figure 25-1: Relative net count rates for G140L observations of the standard star GRW+70 324
obtained between 1997 and early 2010 are shown. The times of significant changes in the slope of
the sensitivity as a function of time are marked by vertical dotted lines.
Figure 25-2: Relative net count rates for G230L observations of the standard star GRW+70 324
obtained between 1997 and early 2010 are shown.
Instrument Science Report STIS 2013-04(v0.1) Page 54
Figure 25-3: Count rates for SMOV observations of some echelle gratings, especially the E140H,
initially showed larger than expected sensitivity declines, but the throughput recovered over the
next few months.
Instrument Science Report STIS 2013-04(v0.1) Page 55
Activity: STIS-26
Proposal: 11395
Title: MAMA Image Stability
SMOV Requirements: L.10.4.5.3.5
Analysis Lead: Ted Gull
Other Personnel: Don Lindler, Bruce Woodgate, Charles Proffitt
Description: The maximum thermal motion of the MAMA detectors occurs in the
first portion of the orbit immediately following a large angle maneuver leading to
maximum external changes on the portion of axial bay closest to the STIS instrument.
By the second orbit on the same target, the thermal motions settle down to a
significant displacement right after target rise, a possible change later in the orbit due
to sun/bright earth/dark earth/ deep space. This program followed these changes for
two orbits with each MAMA using an internal wavelength calibration lamp and the
medium dispersion echelle formats in order to obtain a two-dimension series of
reference points on the 2-dimensional detector format. Exposures were done using the
0.1X0.03 aperture and medium resolution echelle gratings with exposure times of 120
seconds for deep, sharp spectral line images.
In each orbit, six spectral line images followed each other, with interspersed dark
frames of 300 seconds to 600 seconds duration. This sequence of exposures were
designed to have good resolution near the portion of the orbit where thermal flexure is
largest, while avoiding excessive lamp use when shifts are expected to be slower.
Execution: Visit 01, using the FUV MAMA, executed on August 23, 2009 while the
NUV MAMA visit 02 executed on August 24.
Results: Each series of line lamp images was cross-correlated to find relative shifts.
This was done for the entire image and for each half of the image, (left vs. right and
top vs. bottom), to look for evidences of rotation or shearing during the sequence of
observations. Results are shown in Figures 26-1 through 26-4. The E140M images
showed a slow drift of the X position during the three hours of observations with a
total shift of about 0.5 MAMA pixels. The E140M Y shift and both the X an Y shifts
for the E230M observations changed by less than 0.5 pixels during each visit. There is
no evidence for rotation or stretching of the images during the course of these
observations.
Instrument Science Report STIS 2013-04(v0.1) Page 56
Figure 26-1: Relative shifts in the axis 1, (X or dispersion direction), for the E140M 0.1X0.03
wavelength calibration images taken during visit 01 of proposal 11395.
Figure 26-2: Relative shifts in the axis 2, (Y or cross-dispersion direction), for the E140M
0.1X0.03 wavelength calibration images taken during visit 01 of proposal 11395.
Instrument Science Report STIS 2013-04(v0.1) Page 57
Figure 26-3: Relative shifts in the axis 1, (X or dispersion direction), for the E230M 0.1X0.03
wavelength calibration images taken during visit 02 of proposal 11395.
Figure 26-4: Relative shifts in the axis 2, (Y or cross-dispersion direction), for the E230M
0.1X0.03 wavelength calibration images taken during visit 02 of proposal 11395.
Instrument Science Report STIS 2013-04(v0.1) Page 58
Figure 26-5: Predictions for the HST defocus in microns of secondary offset during the two visits
of the MAMA stability test 11395 (solid line for the FUV E140M test and dashed line for the
NUV E230M test) and the CCD stability test 11389 (dotted line). The focus model is based on an
empirical fit to a variety of HST thermal and attitude parameters (see Di Nino et al. 2008 and
also Cox & Niemi 2011).
Instrument Science Report STIS 2013-04(v0.1) Page 59
Activity: N/A
Proposal: N/A
Title: Temperature Monitoring
SMOV Requirements: L.10.4.5.1.9
Description: While not formally identified as a separate activity, there was a STIS
SMOV requirement that detector temperatures be monitored and compared to prefailure values. Due to ongoing deterioration of HST’s multi-layer installation,
temperatures in the aft-shroud have been increasing over time, but it is not possible to
predict how this degradation affects instrument and detector temperatures. This is
important not only because higher temperatures tend to increase detector background
rates, but also because the ability to cool the STIS CCD is essential for its use.
Results: Since switching to its side-2 electronics, the temperature of the STIS CCD
cannot be directly measured, and the STIS CCD thermoelectric cooler (TEC) is run at
constant current rather than in a controlled feedback loop that keeps the detector at a
constant temperature. This means that the actual CCD temperature and dark current
now vary as the thermal environment inside STIS changes. The temperature of the
STIS CCD housing, as given by the keyword OCCDHTAV, can be measured and has
been shown to provide a useful surrogate to track the temperature fluctuations of the
detector during normal operations (Brown 2001). In Figure 27-1, OCCDHTAV
measurements for the first several months of SMOV operations are compared to data
taken at the same time of year for each pre-SM4 year of operation on the side-2
electronics, (modest seasonal temperature variations are expected due to the
eccentricity of the Earth’s orbit). When the STIS MAMA detectors were off,
OCCHTAV would drop to as low as 16 C, but if we only consider periods when both
MAMA detectors were on, CCD housing temperatures averaged about 3 C higher
than they had prior to the 2004 failure.
OCCDHTAV averages (excluding anneals)
• 22.1 C, 2009.65 - 2009.80
• 19.6 C, 2003.65 - 2003.80
• 19.5 C, 2002.65 - 2002.80
• 17.5 C, 2001.65 - 2001.80
While this higher operating temperature causes an ~20% increase in the detector dark
current, the increase is not enough to significantly affect science operations.
The STIS MAMA Tube temperatures also ran slightly warmer, showing increases
of 1.1 to 1.3 C above 2003 levels (see Figs. 27-2 and 27-3). While this is expected to
also result in slight enhancements of the dark rates, these are small compared to the
dark rate changes from other causes, (see the results of activities STIS-19 and STIS20).
Instrument Science Report STIS 2013-04(v0.1) Page 60
Figure 27-1: The CCD housing temperature between May and September 2009 (blue curve) is
compared with the values from 2001 through 2004 taken at the same time of year (red curves).
Figure 27-2: The FUV MAMA tube temperature, OM1TUBET, is plotted as a function of time over
the history of STIS. Each telemetry point is marked by a small dot, but because of the quantization of
the telemetry values, these blend together in horizontal bands. For each year the mean value of the data
taken between August 25 and September 16 is also shown (large diamond symbols). This allows
comparison of data taken at the same time of year as the SMOV period where there were no major
interruptions to STIS MAMA operations.
Instrument Science Report STIS 2013-04(v0.1) Page 61
Figure 27-3: The NUV MAMA tube temperature, OM2TUBET, is plotted as a function of time over
the history of STIS. Symbols have the same meanings as in Fig. 27-2.
Instrument Science Report STIS 2013-04(v0.1) Page 62
6. Summary
For the most part, the performance and capabilities of STIS after SM4 have proved to
be very similar to that exhibited prior to the 2004 side-2 failure. The most notable
differences are the unexpectedly large NUV MAMA dark current discussed in the
section on activity STIS-20, and the continued degradation of the STIS CCD due to
radiation damage which was discussed in the sections on activities STIS-05 and STIS07.
The increased NUV MAMA dark current primarily affects background-limited
observations, which are a relatively minor part of STIS science. One example of the
kind of science that was impacted by this change is studies of heavy elements in the
spectra of cool metal poor stars. Such programs often require several orbits of echelle
data at each setting to build up enough S/N to measure the weak lines seen against the
faint NUV continuum flux.
The CCD changes, while not unexpected, do affect a significantly larger
fraction of the potential science done with STIS. The increased dark current,
decreased charge transfer inefficiency (CTI), and increasing number of hot pixels
especially impact observations of faint objects. Some examples of the impact these
effects have on STIS data have been discussed by Dixon (2011). While moving the
target as close as possible to the CCD readout can mitigate much of this impact, for
some science programs this is not possible. Work is underway at STScI to both better
understand the behavior of the CCD CTI and dark current, and to develop a pixel
based correction algorithm similar to that described by Anderson and Bedin (2010) to
mitigate the CTI effects, (see Lockwood et al. 2013).
7. Acknowledgements
The success of SM4 and the STIS repair was the result of the hard work of a very
large number of people including many at STScI and at several NASA centers. We
would like to thank them all for their time, skill, hard work, and dedication that have
made the continuation of STIS science possible.
8. Change History for STIS ISR 2013-­‐04 Version 0.1: 17 January 2014 – Original Document
Instrument Science Report STIS 2013-04(v0.1) Page 63
References
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Bostroem, K.A., Aloisi, A., Bohlin, R., Hodge, P., & Proffitt, C. 2012 ISR STIS
2012-01: Post-SM4 Sensitivity Calibration of the STIS Echelle Modes
Bostroem, A., Aloisi, A., Bohlin, R.C., Proffitt, C.R., Osten, R.A., & Lennon, D.
2010, in “The 2010 STScI Calibration Workshop”, Space Telescope Science
Institute, 2010 Susana Deustua and Cristina Oliveira, eds., p 62
Brown, T. 2001, ISR STIS 2001-03: Temperature Dependence of the STIS CCD Dark
Rate During Side-2 Operations
Cox, C. 2013, ISR STIS in preparation, Dark Count Rates in the STIS MAMA
Cox, C. & Niemi, S.-M. 2011, ISR TEL 2011-01: Evaluation of a Temperature-based
HST Focus Model
Di Nino, D., Makidon, R.B., Lallo, M., Sahu, K.C., Sirianni, M, & Casertano, S.
2008, ISR ACS 2008-03: HST Focus Variations with Temperature,
Dixon, W.V. 2011, ISR STIS 2011-02: Effects of CTE Degradation on Cycle 18
Observations with the STIS CCD
Goudfrooij, P., Wolfe, M.A., Bohlin, R.C., Proffitt, C.R., & Lennon, D.J. 2009, ISR
STIS 2009-02: STIS CCD Performance after SM4: Read Noise, Dark Current,
Hot Pixel Annealing, CTE, Gain, and Spectroscopic Sensitivity
Holland, S. et al. 2013 ISR STIS in prep, Time Dependence of STIS Spectroscopic
Sensitivity
Jansen, R.~A., Windhorst, R., Kim, H., Hati, N., Goudfrooij, P., Collins, N.\ 2010, in
Hubble after SM4. Preparing JWST, Space Telescope Science Institute, 2010
Susana Deustua and Cristina Oliveira, eds., p 50
Lockwood, S. A., Debes, J. H., Anderson, J., Aloisi, A., & Proffitt, C. R. 2013,
American Astronomical Society Meeting Abstracts, 221, #344.10
Mason, E. 2012, ISR STIS 2012-02: Post SM4 Behavior of STIS CCD darks
Pascucci, I. , Hodge, P. Proffitt, C.R., & Ayres, T. 2011, ISR STIS 2011-01:
Wavelength Calibration Accuracy for the STIS CCD and MAMA Modes
Proffitt, C.R., Goudfrooij, P., Gull, T.R., Lennon, D.J., Wheeler, T., Wolfe, M.A., &
Zheng, W., TIR STIS 2009-02, STIS SMOV4 Analysis Plan
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Lamps for the Hubble Space Telescope, Proceedings of the SPIE, 7731, 105
Rinehart, S. A.; Domber, J.; Faulkner, T.; Gull, T.; Kimble, R.; Klappenberger, M.;
Leckrone, D.; Niedner, M.; Proffitt, C.; Smith, H.; Woodgate, B. 2008,
Proceedings of the SPIE, 7010, 138
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STIS CCD Anneal Results
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STIS NUV Detector
Instrument Science Report STIS 2013-04(v0.1) Page 64
Appendix: STIS SMOV Requirements
L.10.4.5 STIS Verification Requirements
L.10.4.5.1 Engineering Requirements
L.10.4.5.1.1 - STIS entry into each of four instrument states (Boot, Hold, Operate,
Observe) shall be demonstrated.
L.10.4.5.1.2 - STIS entry into each of the defined detector states needed to support
normal operations shall be demonstrated.
L.10.4.5.1.3 - STIS command and engineering data interface via the RIU and science
data transmission via the Science Data Formatter (SDF) shall be verified by
monitoring of normal configuration and science activities.
L.10.4.5.1.4 - Onboard memory will be checked by performing dumps of EEPROM,
PROM, EDAC RAM and Buffer RAM. (Special Commanding)
L.10.4.5.1.5 - Conduct a test of the ability to write to and read from the CS (control
section) Buffer RAM. (Special Commanding)
L.10.4.5.1.6 - Verify the proper functioning of all STIS mechanisms needed for
routine operations (the three MSM wheels, the aperture wheel, CIM, echelle blockers,
CCD shutter, aperture door, & mode isolation shutter) over the full ranges of motion
needed for normal operations. Contingency: verification of the corrector alignment
mechanisms will be done only as part of any alignment or focus adjustments.
Movement of the corrector mechanisms should otherwise be avoided.
L.10.4.5.1.7 - Check the functioning of the calibrations lamps used for routine science
and SMOV operations (LINE, Tungsten, HITM1, & HITM2), at each of the current
levels used for normal operations.
Contingency: if one or more of these lamps either shows significantly degraded
behavior or fails to function, then make those changes which are necessary to support
science operations; this contingency may include changes to the ground system and/or
on-board tables to allow substitution of one of the operable lamps for the critical
functions of a failed one. Verification of the Krypton and Deuterium lamps may be
deferred until after SMOV.
L.10.4.5.1.8 - The CCD shall be annealed as necessary to ameliorate accumulated hot
pixels.
L.10.4.5.1.9 - During the course of routine operations throughout SMOV, the
temperature variations of each detector will be monitored and compared to previous
side-2 values. The ability of the CCD TEC to cool that detector to the required
operating temperature range will be evaluated.
L.10.4.5.1.10 - Perform a mini-functional test of the STIS CCD.
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L.10.4.5.1.11 - Verify the proper functioning of the MAMA detectors by following
procedures similar to those defined for MAMA anomalous recovery (ISR STIS 9803). A MAMA detector should not be otherwise used prior to completing this
functional test. The high voltage for the STIS MAMA detectors will not be activated
until at least four days after release and not until the pressure in the aft shroud has
been below 5x10-6 torr for at least 24 hours.
(Special Commanding. Four days wait to be confirmed based on contamination
models).
L.10.4.5.1.12 - The STIS Deuterium and Krypton lamps will not be operated until 3
weeks after release.
L.10.4.5.2 Target Acquisition Requirements
L.10.4.5.2.1 - The location of a reference STIS camera aperture shall be determined
with respect to the FGS reference frames to an accuracy of 1 arc second in V2-V3
coordinates and 10 arc minutes in aperture rotation angle.
L.10.4.5.2.2 - The ability to acquire and properly center targets with standard ACQs
and the ability to center targets in small apertures with ACQ/PEAK exposures will be
demonstrated for both standard and E1 aperture positions.
(E1 aperture positions are defined near CCD readout; ~ 20” away from standard
acquisition aperture. This requires a much larger pointing change after a standard
ACQ than do other apertures).
L.10.4.5.3 Optical Alignment Requirements
L.10.4.5.3.1 - An aperture throughput test using a previously observed external point
source calibration target shall be used to assess STIS focus. The slit plane encircled
energy vs. wavelength shall also be measured using this external target.
Contingency: if throughput is down by more than 3 sigma (7%), relative to the
expected mean after correction for expected secular sensitivity changes, additional
tests and perhaps a STIS corrector alignment and/or focus adjustment shall be done.
This test is dependent on the setting of the HST secondary mirror position, which
must have been first set to its expected nominal focus.
(Contingencies to adjust alignment require special commanding. For STIS, best focus
is set at the plane of the aperture wheel, not at the detectors).
L.10.4.5.3.2 - The positioning of the STIS aperture wheel should be checked for a
representative subset of STIS apertures, and compared to previous side-2
measurements.
Contingency: if operationally significant discrepancies are found in relative aperture
positions, all aperture locations will be remeasured, and appropriate updates made to
ground and on-board calibration tables.
L.10.4.5.3.3 - For each optical element in the MSM, (except for MAMA imaging
modes), the location of a lamp spectrum or slit image on the detector appropriate for
that optical element shall be compared to previous side-2 values.
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Contingency: operationally significant shifts shall be corrected by updating on-board
mechanism calibration tables. Only one MSM position of each optical element need
be tested. Checks of MAMA imaging mode alignments may be deferred until after
SMOV.
L10.4.5.3.4. - The spectroscopic image quality and cross dispersion PSF at each
detector will be measured as a function of position and wavelength using an external
point source calibration target. This test is dependent on the settings of the HST
secondary mirror position and of the STIS corrector mechanism, which must have
been first set to their nominal values.
L.10.4.5.3.5 - The pointing stability of external targets on the STIS CCD detector, and
the relative stability of the CCD detector with respect to the aperture plane, will be
monitored over the course of the two orbits immediately following an attitude change
that is expected to produce a significant thermal change in STIS. Separate test(s) will
be done to measure the stability of at least one of the two MAMA detectors with
respect to either the aperture plane or an external target, over two orbits following a
similar large maneuver.
L.10.4.5.4 Calibration Requirements
L.10.4.5.4.1 - The dark rate for each detector shall be measured for normal operating
temperatures and conditions. For the CCD, bias and read-noise measurements will
also be made. Sufficient CCD dark and bias measurements will be done to allow
proper calibration of other STIS SMOV and ERO data. Sufficient NUV MAMA dark
measurements will be taken to determine whether the phosphorescent window glow
has declined to a level that will support expected GO observations. The FUV MAMA
dark rate will be monitored over at least one 5 orbit interval to measure how the dark
rate increases as a function of time after detector high voltage turn-on.
L.10.4.5.4.2 - A test will be done to check predictions for CTI losses on the STIS
CCD detector. Results will be evaluated for any impact on planned GO observations.
L.10.4.5.4.3 - For one wavelength setting of each STIS grating, the throughput will be
checked using an external calibration target.
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