TIPS-JIM Meeting
27 January 2005, 10am, Auditorium
1.
Cycle 14 Statistics
Brett Blacker
2.
NICMOS Grism Flux Calibration and
Non-linearity
Ralph Bohlin
3.
The HST Pointing Drift Anomaly
Stefano Casertano
4.
MultiDrizzle Development Status
and Plans
Anton Koekemoer
Next TIPS Meeting will be held on 17 February 2005.
TIPS-JIM Meeting
27 January 2005, 10am, Auditorium
1.
Cycle 14 Statistics
Brett Blacker
2.
NICMOS Grism Flux Calibration and
Non-linearity
Ralph Bohlin
3.
The HST Pointing Drift Anomaly
Stefano Casertano
4.
MultiDrizzle Development Status
and Plans
Anton Koekemoer
Next TIPS Meeting will be held on 17 February 2005.
The following are checks on the NICMOS grism non-linearity.
•
Curvature in the non-flat fielded background subtraction over
the region between the upper and lower background areas
causes <1% error.
•
The non-linearity is still present for the brighter stars, even
for no background subtraction.
•
The same results are obtained using the independent
NICMOSLOOK spectral extraction package developed at the
ECF by W. Freudling.
•
The differential count rates are constant between the
NICMOS readouts and agree with the cumulative count rates
to <1%.
•
The spectra overlap between dither positions and are
susceptible to persistence; but the first dither positions show
no systematic deviation.
•
Comparisons of NICMOS photometry of galaxies vs. ground
based photometry is inconclusive (Mobasher).
•
Comparisons of NICMOS photometry of stars vs. ground
based photometry on NIC2 has about 5 times less slope than
the NIC3 grism non-linearity (Riess).
•
A proposal to compare photometry for the brightest and
faintest stars has been submitted by the NICMOS group.
•
Grism spectra of 3-4 faint stars in the G191B2B field have
NIC3 photometry for a direct comparison with the
spectrophotometry.
TIPS-JIM Meeting
27 January 2005, 10am, Auditorium
1.
Cycle 14 Statistics
Brett Blacker
2.
NICMOS Grism Flux Calibration and
Non-linearity
Ralph Bohlin
3.
The HST Pointing Drift Anomaly
Stefano Casertano
4.
MultiDrizzle Development Status
and Plans
Anton Koekemoer
Next TIPS Meeting will be held on 17 February 2005.
The HST “Observer Bias
Convergence” Pointing Anomaly
TIPS, 27 January 2005
Stefano Casertano
With input from:
Russ Makidon
Ed Nelan
Ron Gilliland
Bill Zmek (Goodrich)
The Observer Anomaly Working Group
(STScI, GSFC, LMCO, Goodrich, L3)
21
!
!
!
!
!
What is the Observer Bias Convergence Anomaly?
Do we understand how it arises?
Does it affect science observations?
Ongoing work
To find out more:
"
http://edocs1.hst.nasa.gov/ota/Observer/Observer.html
22
What is the anomaly?
!
!
!
!
The gyro drift rate appears to vary rapidly, especially
during the transition from night to day
The variation is seen in the V2 axis, and affects
primarily Gyro 4
The variation was detected starting around June
2004, and is seen consistently since then
The amplitude of the variation appears to be growing
with time
23
An example of the anomaly
nigh
t
da
y
nigh
t
da
y
V2
V3
Nighttime V2/V3 data
(mean-removed) are
strongly correlated;
roughly 2-to-1 ratio
(spikes are
anti-correlated)
V2 is poorly
correlated to V3
during day
Night-Day pattern repeats
24
What is it? (cont.)
!
!
!
!
Total rate variation (interpreted as gyro bias drift) up
to 40 as/hr in extreme cases
Note that there is no change in pointing - the
telescope’s optical axis is held steady by the FGS
No obvious preference for one FGS over another
Some apparent periodicity pattern vs. time - possibly
due to observing program (still under investigation)
25
Gyro bias measured 20 min after fine lock
26
Are there impacts on HST operations?
!
!
!
!
No immediate impact; there could be occasional
losses of lock (none significant to date), but image
quality is unchanged [possibly with some
exceptions]
Concern about HST health (possible thermal effects
due to insulation degradation etc)
If the drift continues to grow, eventually will affect
reacquisitions (at about 70 as/hr)
NOTE: impact may be reduced in 2-gyro mode
27
What is really going on?
!
!
!
We know that the telescope optical axis axis is steady on
these scales (no significant increase in PSF size)
but Gyro 4 reports that the telescope is moving
Three basic possibilities:
"
"
"
The optical axis is moving, and the inertial axis is not; the gyro
reading is correct, and the FGS compensate for the true motion of
the spacecraft
The gyro is malfunctioning, and registers a motion where there is
none
The gyro mount (the equipment shelf) is moving with respect to the
telescope; the gyro reading is correct, but it registers a local motion
in the telescope that does not affect its functioning
28
Can we detect an optical tilt?
!
If the optical axis is moving with respect to the
telescope, the most likely reason is a tilt of the
secondary
"
"
"
Tilting the secondary produces coma
Coma can be detected by phase retrieval (ACS/HRC
focus data) and in the FGS s-curves
The expected effect is ~ 12-25 nm rms
29
ZEMAX Analysis: SM Drift Due to Pure Tilt
Detachment of bipod* removes
constraint on tilt, allowing drift;
no decenter
S
M
SM tilt necessary to reach 3
arc-seconds in object space
was calculated
SM tilt ! = 0.00377
degree
Aberration: all coma, 0.012
um RMS
Strehl loss ~ 2.3% @
0.5um wavelength
4907.1
mm
S = 6407.13 mm
!
P
M
Focal Plane
"
" ~ 2 ! S = (3 arc-seconds) / (plate scale, arc-sec/mm)
* Speculative
30
Zemax analysis - SM Drift Due to Metering
Truss Strain
Metering truss assumed to strain in
‘banana’ form* (thermal cause?)
Quadratic bend assumed
SM optical axis assumed to
remain tangent to centerline of
truss (see sketch)
SM deflections necessary to
reach 3 arc-seconds in object
space were calculated
Decenter result: $ ~ 60
um
Tilt result: # ~ 0.0014
degree
Aberration: all coma, ~0.025
um RMS
Strehl loss ~ 10% @
0.5um wavelength
$
S
M
#
s = 4907.1 mm
!
S = 6407.13 mm
$
P
M
Focal Plane
# ~ 2 $/
s ~ 2 {# + $/ROC
!
"
SM }
ROCSM = 1358.065 mm
" ~ ! S – $ = (3 arc-seconds) / (plate scale, arc-sec/mm)
* Speculative
31
Coma traced from focus data
•Coma has varied
systematically over time
•Typical variation within
an orbit much less than
predicted
•Y coma correlates with
focus within a single
observation – suggests
deformation associated
with breathing
32
Predicted change in S-curve with coma
33
34
Comparison of day and night fringes
with FGS1R - no change
Xaxis
Yaxis
35
However...
!
!
!
!
It is possible for tilt and decenter to compensate and
produce a smaller coma variation
Resulting optical effect undetectable at field center
Astigmatism produced away from field center (at
HRC, FGS)
Some astigmatism change seen in focus data
36
Focus observations - anomaly (June 2004)
37
Phase retrieval (June 2004)
•Focus changes smoothly
through observation
•No jump at day-night
transition
•Change consistent with
breathing model
•Y coma changes at transition,
much less than predicted
•X,Y astigmatism also change
at transition
38
Further analysis needed
!
!
!
!
Astigmatism measurement has
large measuring error
Astigmatism changes occurred
before the anomaly
In principle, can determine exact
3D position of secondary from
focus data
Optical modeling by Makidon and
Zmek continuing
39
Focus adjustment
•Concerns about secondary have delayed focus adjustment
•Move executed December 22, 2004 (+4.16 mm)
•Current focus nominal
December 18, 2004 (-4 µm)
January 14, 2005 (~ 0 µm)
40
How about gyros?
!
The bias drift around V2 is almost entirely on Gyro 4
"
"
!
Analysis of the output from Gyro 4 shows no anomalies
"
"
"
!
!
Expected effect on 1, 2 is small
Could be due to Gyro 4 itself
Digital output remains normal during supposed bias variation; behavior similar
to 2002 data
No changes in data available through telemetry (temperature, input voltages)
Other forcing functions (e.g., magnetic) do not have correct time scales
Manufacturer concludes that gyro anomaly is unlikely
More detailed analysis could separate V2 and Gyro 4 errors (some
sensitivity to V2 in the other gyros)
41
Tilt in equipment shelf?
!
!
!
Gyros and FHST are mounted on equipment shelf
Shifts in shelf are believed to be the cause of V2
disturbances (impulsive tilts that affect telescope pointing)
However:
"
"
"
"
Shelf is located on -V3 side of Aft Shroud
Not expected to respond to day-night temperature cycles
Time behavior of anomaly inconsistent with predicted temperature
profile
No long-term drifts in temperature data
42
Location of equipment shelf
FGS 2
STIS
COSTAR
FGS 3
FGS 1
NICMOS
ACS
RSU 2
FHST 3
RSU 3
FHST 1
FHST 2
43
Location of shelf (cont.)
44
Equipment shelf temperature
trends
20
18
16
14
12
10
8
6
+V2 ESHLF1T E339 Mean
+V2 ESHLF7T E520 Mean
-V2 ESHLF3T E324 Mean
-V2 ESHLF6T E519 Mean
-V1/+V3 ESHLF2T E323 Mean
-V1/+V3 ESHLF4T E425 Mean
-V1/+V3 ESHLF5T E426 Mean
4
2
0
37257
37288
37316
37347
37377
37408
37438
37469
37500
37530
37561
37591
37622
37653
37681
37712
37742
37773
37803
37834
37865
37895
37926
37956
37987
38018
38047
38078
38108
38139
38169
38200
38231
38261
45
Other temperature trends
!
!
Thermal analysis of sensors at light shield, forward
shell, and metering truss assembly shows no obvious
long-term changes
More detailed analysis in correlation with anomaly
needed
46
Also of interest…
!
!
!
!
!
A small variation in PSF width
has been detected in GO data
(Gilliland, GO 10441)
Variation appears to correlate
with day/night cycle
Possible jump in detected jitter
when variation occurs
Telemetry and pointing data are
being analyzed
Relation with Observer Bias
Correction Anomaly unclear
47
Fault Tree Analysis
!
The anomaly could be due to many causes:
#
#
#
#
#
#
#
#
!
!
OTA outer shell or metering truss
Secondary Mirror
Primary Mirror
SA3
Gyros
Gyro Equipment Shelf
FGS
Flight Software
At this point, Primary Mirror, SA3, FGS, Flight Software appear
unlikely
Further analysis required for OTA, Secondary, Gyros, Equipment Shelf
48
Summary
!
!
!
!
No credible cause established for the Anomaly
Effect is growing over time; may become a concern
in ~ 6 months
No current science impact
Possible investigations:
"
"
"
"
Optics: measure position of Secondary over time
Thermal: correlate temperature data with variations
Equipment shelf: study V2 anomalies, FHST data
Gyros: study response of Gyros 1 and 2
49
50
Serendipitous monitoring from GO data
•Ellipticity pattern of PSF
depends on focus position
•Pattern measured from GO
observation of stellar field
•Before focus adjustment:
pattern consistent with
model at -5 mm
•After focus adjustment:
pattern consistent with
nominal focus
•Note: deviant points are not
significant (cosmic rays or
other artifacts)
51
Support of Observer Bias Anomaly analysis
!
Observer Anomaly: increased values of gyro drift rate are
seen at night-day transition while on FGS lock
"
"
"
"
!
Drift rate corrections (V2) up to 40 as/hr observed since June 2004
RMS correction up to 12 as/hr (<5 a year ago); some temporal
structure over time scale of 1-2 months, possibly due to frequency
of day-night transitions
Worst-case disturbances correspond to an apparent integrated
displacement of gyro to optical axis of about 3” in a few minutes
No significant impact yet on science, efficiency, image quality
Possible sources include:
"
"
"
Motion in the OTA metering truss and/or secondary mirror
Gyro anomaly
Motion in support structure (e.g., equipment shelf)
52
Observer’s Anomaly (cont.)
!
Image data useful to assess possibility of optical
displacement
"
A 3” displacement of the optical axis due to secondary
tilt induces coma (~ 12 nm rms) and astigmatism
#
#
#
#
Phase retrieval on focus data and FGS S-curves place upper
limits of ~ 4 nm rms on coma variations during the anomaly
A concurrent decenter of the secondary, due to a “banana”
distortion of the metering truss, can reduce the coma impact
Astigmatism measurements noisy; analysis not yet final
Eventually, coma and astigmatism could help trace the position
and tilt of the secondary vs. time
53
TIPS-JIM Meeting
27 January 2005, 10am, Auditorium
1.
Cycle 14 Statistics
Brett Blacker
2.
NICMOS Grism Flux Calibration and
Non-linearity
Ralph Bohlin
3.
The HST Pointing Drift Anomaly
Stefano Casertano
4.
MultiDrizzle Development Status
and Plans
Anton Koekemoer
Next TIPS Meeting will be held on 17 February 2005.
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
55
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
Current Status
$
STSDAS / Pipeline
Near-Term Priorities
$
$
$
Continue MultiDrizzle maintenance & testing
Develop/test Tweakshifts (for off-line & pipeline use)
Expand definition of ACS associations
Longer-Term Strategy
$
$
Science Working Group – prioritization / planning
MultiDrizzle enhancements:
– Refine CR rejection algorithms (CTE, single-image, etc)
– STIS spectroscopy
– NICMOS iterative background correction
$
Archive/VO-related improvements:
– Further expand associations to include multiple visits
– Allow MultiDrizzle parameter changes in archive interface
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
56
Current Status
STSDAS MultiDrizzle - current v2.4.2 (can be used off-line):
$
$
$
$
ACS: all observation modes WFC, HRC, SBC, fully tested
WFPC2: all observation modes, partially tested
STIS: all imaging modes (CCD, MAMAs), fully tested
NICMOS: all observation modes, testing in progress
Pipeline MultiDrizzle - current v2.3.6 (runs in OTFR):
$
$
$
$
Same code base as STSDAS version, frozen every ~3-6 months
Runs on all ACS associations in pipeline
Very few problems since OPUS15.4 installation in September 2004, all
have been addressed or are currently being resolved
MultiDrizzle pipeline products include:
– CR information in FLT file DQ arrays
– Improved astrometric header keywords in FLT files
– Header values in drizzled image containing history of drizzle parameters
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
57
Near-Term Priorities - MultiDrizzle
MultiDrizzle Maintenance:
$
$
Improvements in response to user problems (often installation-related)
Direct and efficient interaction between OPUS and SSB groups to resolve
pipeline-related problems:
– Occur rarely
– Typically due to problems with data, eg science exposures with EXPTIME=0
MultiDrizzle Testing:
$
Functional / regression testing (SSB: Hack/Hanley/Jedrzejweski):
– Run a subset of datasets nightly, the full set is run once/week
– Ensure that the code still successfully executes after modifications
– Augment with new datasets that have revealed problems in the code
$
Scientific testing (INS):
– ACS (Gonzaga), WFPC2 (Platais), STIS (Dressel/Davies), NIC (Bergeron)
– Explore optimum parameters to ensure good default/pipeline behaviour for the
widest possible range of datasets
– Quantify accuracy of astrometry, photometry, CR rejection
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
58
Near-Term Priorities - Tweakshifts
Shift measurement method:
$
$
$
catalog-based (currently DAOfind, expect later to also use SExtractor)
cross-correlation
wavelet transforms
Two basic uses for Tweakshifts:
$
$
Refine relative shifts between exposures in an association
Refine absolute astrometry, by comparing with external catalog (eg GSC2)
Initial pipeline implementation – improve relative shifts:
$
$
Initially for data with guidestar problems, where header shifts can be bad
If robust after extensive experience, may extend to all ACS data
Absolute astrometric improvement:
$
$
Most ACS images have several GSC2 objects % can improve to <0.3-0.5”
absolute astrometry by using Tweakshifts in catalog-based mode
Currently exploring pipeline implementation (Koekemoer/McLean/Jenkner)
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
59
Near-Term Priorities- ACS Associations
Current definition of ACS associations:
$
$
$
Observations obtained using dither pattern or CR-SPLIT
Exposures are not associated if obtained using POS TARGs
Often, observers use POS TARGS either because:
– they are confused by the dither patterns
– they have a specific need not covered by the dither patterns
– BUT they still expect the data to be associated and combined
Proposal to expand ACS associations:
$
Build association from all exposures that satisfy the following:
– same filter
– within the same visit
$
Benefits of initially restricting this to exposures in the same visit:
– same guidestars, therefore header shifts can be used
– provides limitation on the size of the largest offset (less than ~1’)
$
$
TRANS implementation for future observations (tbd with Tony Krueger)
Archive implementation for previous obs’s (talks with ASB, CADC, ECF)
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
60
Longer-Term Strategy
Science Working Group – prioritization / planning
$
$
$
$
Cross-section between Dither Group, SAR initiatives, and discussions with
HST MO - current discussions on-going with SD mgmt
Develop “wishlist” of ideas
Propagate to ESS for resource estimates
Carry out subsequent prioritization, interacting with HST MO
MultiDrizzle enhancements:
$
Refine CR rejection algorithms:
– CTE
– single-image (useful for datasets with only 2-3 exposures)
$
$
STIS spectroscopy
NICMOS iterative background correction
Archive/VO-related improvements:
$
$
Further expand associations to multiple visits (incl more Tweakshift work)
Allow MultiDrizzle parameter changes in archive interface
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
61
MultiDrizzle Enhancements – CR rejection
Current CR rejection scheme:
$
Uses driz_cr, which has the following features:
– essentially based on sigma-clipping, combined with a slight “softening” from flux
gradients in the image to avoid clipping bright concentrated source
– works best for large numbers of images, although with sufficient testing &
exploration of parameter space, also gives acceptable results for 3-4 images
$
Main limitations:
– in 2-3 image datasets, doesn’t always succeed when there is just 1 good pixel
– doesn’t reject CTE tails on CRs
– to work well, need to create sub-sampled image % resource-intensive
Two possible improvements:
$
CTE tails can be rejected in a second more stringent pass, examining only
pixels along the read-out direction from CRs identified in the first pass:
– relatively easy to implement
– some preliminary experiments have been done by Koekemoer/Busko
$
Consider rejecting CRs on single images, eg by Laplacian edge detection,
prior to running MultiDrizzle
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
62
MultiDrizzle Enhancements - STIS
Current situation:
$
$
MultiDrizzle works for all STIS imaging modes
All 3 STIS cameras: CCD, NUV-MAMA, FUV-MAMA
Eventual goal – spectroscopy:
$
$
$
Many observers dither along the slit to mitigate hot pixels; CTE from hot
pixels is along slit direction, thus dithering is important in obtaining good
spectra
Some observers also dither along wavelength direction to better sample the
spectral line spread function
Some studies currently underway within STIS group (Dressel/Davies):
– examine changes required (e.g., new keywords) as well as the extent of code
modifications
– examine scientific usefulness of incorporating this capability: would the resulting
products be usable as-is for the majority of science data?
$
The STIS studies will determine whether or not to proceed with this
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
63
MultiDrizzle Enhancements - NICMOS
Current capabilities:
$
$
MultiDrizzle can now read all types of NICMOS data, and can perform the
basic tasks of CR rejection and image combination
Main limitation is that background correction is treated the same way as for
optical CCDs, which is incorrect for NISMOS
Improved background correction:
$
$
$
$
$
$
Create a first-pass image, assuming static background correction
Run object detection / identification on the resulting combined image
Use the objects to create a “mask” excluding any regions with flux
For each exposure, fit the remaining unmasked background and subtract
Re-do the drizzle combination
Iterate the above if necessary
Status:
$
Tests underway to investigate required software changes (Bergeron/Hanley)
STScI TIPS/JIM
27 January 2005
MultiDrizzle Development Status & Plans
Anton Koekemoer (INS)
64
Archive/VO-Related Enhancements
Absolute Astrometry improvements:
$
Experiments to date (Koekemoer/McMaster/McClean) find improvement in
absolute astrometry accuracy to ~0.3”, ie about 10x improvement
Further expand associations – include adjacent visits
$
Benefits:
– Move HST data products from large mosaic programs into the “VO era”
$
Two potential concerns:
– different guidestars, and the need to very accurately align to < 0.1 pixel; can be
solved in principle by running Tweakshifts in a specialized fashion
– Processing resource issues (much larger images than currently); can be solved by
letting the user specify a central RA,Dec and a limiting radius around this
Parameter control in archive interface:
$
$
Can further increase scientific value of products (observers can select
exactly the parameters they want, eg North=up, pixel scale, etc)
Concerns about processing load – can be addressed by limiting the options
TIPS-JIM Meeting
27 January 2005, 10am, Auditorium
1.
Cycle 14 Statistics
Brett Blacker
2.
NICMOS Grism Flux Calibration and
Non-linearity
Ralph Bohlin
3.
The HST Pointing Drift Anomaly
Stefano Casertano
4.
MultiDrizzle Development Status
and Plans
Anton Koekemoer
Next TIPS Meeting will be held on 17 February 2005.