Instrument Science Report WFPC2 98-01
WFPC2 Cycle 6 Calibration Closure
Report
S. Baggett, S. Casertano, and WFPC2 group.
April 21, 1998
ABSTRACT
This report describes in detail the WFPC2 observations used to maintain and improve the
quality of WFPC2 calibrations during Cycle 6, and the status of their analysis as of February 1998. Also included are summaries for three Cycle 5 proposals (Flat Field Check,
UV Throughput, and Polarization and Ramps) which have been completed since the writing of the Cycle 5 Closure Report .
1. Overview
After more than four years in orbit, the most frequently used WFPC2 observing modes
have been calibrated to a level sufficient for the large majority of science programs, and
the performance of the camera has generally proved remarkably stable over the long term.
Cycle 6 saw the successful continuation of the routine monthly decontamination procedures to remove the buildup of contaminants on the CCD windows. The associated routine
monitoring of the basic properties of the camera (flat field, throughput, focus, internal
electronics) revealed no major variations except for those that were expected: the throughput decrease in the UV due to contamination, with the nominal throughput fully restored
after each decontamination; the monthly growth in the number of hot pixels, with the normal number restored at each decontamination; the slow focus drift due to OTA desorption,
with focus restored by movements of the secondary mirror; and the continuing expected
decline (due to usage) in the VISFLAT and UVFLAT lamp throughputs.
The second servicing mission (SM97), which took place roughly halfway through
Cycle 6 in Feb. 1997, entailed additional monitoring and checkouts of the camera which
verified that no performance changes occurred as a consequence of SM97. The details of
the SM97 programs and their results are presented in ISRs 97-03 (SM97 Calibration
Plans, Biretta et al.) and 97-09 (Results of the SM97 Calibration Program, Biretta et al.).
1
In addition to the routine and SM97 calibrations, a few special Cycle 6 programs,
designed to provide data for use in addressing some of the remaining issues such as precision photometry and astrometry, were planned as well. These special proposals had two
general goals: to improve the absolute accuracy (particularly in the popular wide-band filters) and to improve our understanding of the WFPC2 photometric systems compared to
other systems. Acquiring these objectives meant achieving a better understanding of CTE
and other nonlinearities at low light levels, both with and without an underlying background, and effects on the PSF due to focus position, location on chip, and exposure time.
A few of these Cycle 6 programs have not yet been completed due to the shift in scheduling priorities required to maximize the use of NICMOS during its shortened lifetime; once
the data are taken and analyzed, new results will be presented in the usual manner (e.g.,
TIPS meetings, ISRs, Data and Instrument Handbooks) and the results will be summarized in the Cycle 7 Closure report.
We also take this opportunity to close out a few remaining Cycle 5 programs that had
not been completed at the time of the Cycle 5 Closure Report ISR (97-02, Casertano et
al.): the Flat Field Check (proposal 6195), which has yielded some important new results
concerning CTE, the UV Throughput (proposal 6186) program, the results of which have
been incorporated into the SYNPHOT and photometric zeropoint updates, and the Polarization and Ramps (proposal 6194) proposal, which has resulted in an improved
calibration of polarization data as well as new WWW tools to aid in the analysis.
As for all ISRs, an electronic version of this document is available via WWW on the
WFPC2 instrument pages; the individual proposals in their Phase II format are available
on the WWW HST Program Information page maintained by PRESTO (see Bibliography
for addresses of sites).
2. Format of this document
Table 1 presents the calibration plan while Table 2 details the current status as of February 1998, including actual orbits used so far (statistics supplied by the PRESTO DBSA
group), products, and accuracy achieved. The remainder of this document consists of
detailed descriptions of each calibration program in a standard format. For each program,
the first page (“Plan”) contains the original description of the planned observations, their
purpose and expected results; the second page (“Results”) includes any modifications to
the Plan, details on the execution, actual resources used, results achieved, a timeline of
activity, and plans for any future continuation of the program. If the program is not complete, an estimate is given of the resources that will be necessary for completion. All Cycle
6 programs are presented first, followed by the three Cycle 5 proposals that have now been
closed out. Finally, a detailed bibliography is provided for many of the WFPC2 documents
to date, including WWW items.
2
Table 1: WFPC2 Cycle 6 Calibration Plan
Estimated Time (orbits)
ID
Proposal Title
Frequency
Products
“External”
Accuracy
Notes
“Internal”
Routine Monitoring Programs
6902
Photometric Monitoring
2/4 weeks
6903
Decontamination
1/4 weeks
6904
Darks
26
168
weekly
195
Synphot
1-2%
CDBS
n/a
CDBS
1 e-/hr
Also focus monitor
Used together with darks, internals
Also hot pixel lists on WWW
-
6905
Internal Monitor
weekly
39
CDBS,ISR
0.8 e
6906
Visflat Monitor
2/4 weeks
62
ISR
0.3%
6907
Intflat Monitor
1/4 weeks
18
ISR
0.3%
6908
UV Flat Field Monitor
2/cycle
12
ISR
2-8%
6909
Earth Flats
continuous
155
CDBS
0.3%
Also LRF, Methane quads
6936
UV Throughput and Lyman α
Synphot
3-10%
Include BD+75D325
2/cycle
12
Also monitor lamp health
Special Calibration Programs
6934
Photometric Zeropoint
1
6
Synphot
1-2%
Add 2 new standards
6935
Photometric Transformation
2
12
ISR
2-5%
Also test zeropoint differences between
chips, UV vignetting, astrometry
6937
CTE Calibration
1
3
ISR
1%
6938
PSF Characterization
1
7
CDBS
10%
6939
Linear Ramp Filters
1
6
CDBS
3%
6940
Polarizers
1
4
CDBS
3-5%
6941
Astrometry Verification
1
4
STSDAS
0.01’’
6942
Camera Electronics Verification
1
1
ISR
0.5%
6943
Narrow Band Throughput
1
10
Synphot
3%
TOTAL TIME (including all executions)
91
649
Shift target field by a few arcsec
Accuracy dominated by systematics
SNAP
Table 2: WFPC2 Cycle 6 Calibration Closure Summary
Time Used (orbits)
ID
Proposal Title
Products
Accuracy
Status of analysis, notes
“External” “Internal”
Routine Monitoring Programs
6902 Photometric Monitoring
25
Synphot
1-2%
done
6903 Decontamination
92
CDBS
n/a
6904 Darks
131
CDBS
0.05 e/hr
6905 Internal Monitor
37
CDBS, ISR
0.5 e
6906 Visflat Monitor
36
ISR
~0.5%
in progress
6907 Intflat Monitor
25
ISR
~0.5%
in progress
6908 UV Flat Field Monitor
8
TIPS
2-8%
done
187
CDBS
6909 Earth Flats
6936 UV Throughput and Lyman α
11
Synphot, ISR
done; decontamination date list kept updated on WWW
done; hotpixel lists maintained on WWW; accuracy given is for typical superdark
done; accuracy listed is for typical superbias
updates to flat fields in progress
~2-10%
in progress; see results for 6186
Special Calibration Programs
6934 Photometric Zeropoint
6
Synphot
~1-2%
analysis underway; preliminary results reported at Calib.Workshop
6935 Photometric Transformation
13
ISR
~2-5%
in progress.
6937 CTE Calibration
2
ISR
1%
6938 PSF Characterization
CDBS
6939 Linear Ramp Filters
CDBS,ISR
6940 Polarizers
done; results to be included with Cycle 7 (7630) results
data to be taken in summer 1998
~8%
ISR
see results for 6194
on hold; see section on 6194
6941 Astrometry Verification
4
STSDAS,ISR
analysis in progress
6942 Camera Electronics Verification
1
ISR,TIR
0.5%
6943 Narrow Band Throughput
8
Synphot,ISR
~5-10%
TOTAL CYCLE 6 TIME
86
done
nearly complete
516
Closeout of Remaining Cycle 5 Programs
6186 UV Throughput
6
6194 Polarization and Ramps
24
6195 Flat Field Check
2
Synphot, ISR ~1%, 5%, 10% done; accuracies dependent upon observing mode
76
ISR
1.5%; 8%
ISR
1.5%, 0.6%
done; accuracies for polarizers and ramps, respectively
done; accuracies for single chip & chip-to-chip
Figure 1: Results of the photometric monitoring for WF3 and PC1 from Feb. 1994
through Nov. 1997, illustrating, particularly in the UV, the restoration to “normal”
throughput after each decon (from WWW Memo, Gonzaga et al.). Data for the other cameras show similar trends. Starting with Cycle 5 (July 1995), images were taken in a different camera each month (except for F170W), resulting in the sparser data points - and
halving the required number of orbits. See WWW Memo for a table of all data and a copy
of the most recent figure.
5
Proposal ID 6902: WFPC2 Cycle 6: Photometric Monitor
Plan
Purpose: Monthly external check of instrumental stability.
Description: The standard star grw+70d5829 is observed before and after each decontamination (thus twice in a four-week period) using three different strategies:
(1) F170W in all four chips to monitor contamination in the far UV;
(2) F439W, F555W, F814W on the PC to monitor focus;
(3) F160W, F185W, F218W, F255W, F300W, F336W, F439W, F555W, F675W,
F814W in a different chip each month. Some filters may be cut because of lack of time
(F185W cut first, then F300W, then F675W, then F218W).
Based on Cycle 5 program 6184; added focus monitoring in F439W, F814W at the
expense of some UV filters.
Fraction of GO/GTO Programs Supported: 100%
Resources:
Observation: 26 pointed orbits.
Special Requirements: Needs to be scheduled shortly before and after each decontamination (up to 5 days).
Accuracy: Overall discrepancies between the results of this test need to be measured to
better than 2% and are expected to be less than 1% rms. The point of the test is to measure
this variation.
Products: Instrument Handbook, reports at monthly TIPS meetings, WWW (sensitivity
trends); updates in UV sensitivity variation used in SYNPHOT.
6
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 25 orbits.
Accuracy Achieved: The standard star (grw+70d5824) countrates have remained stable
to better than 1% (see Figure 1), even across the Second Servicing Mission (SM97):
before and after the SM97, the sensitivity was shown to be the same to within 0.7% rms
(Biretta et al., ISR 97-09 and Whitmore, 1997, Calibration Workshop). A slight secular
increase in throughput - at the 1% level - has been observed in some filter/chip combinations (ISR in progress).
Products: The data from this monitoring proposal are used in a variety of studies. The
results have been presented in the Instrument and HST Data Handbooks, reports at TIPS
meeting and 1997 Calibration Workshop, focus monitoring, WWW memo updates, and
SYNPHOT update. Included here are the results from three studies that have this data.
- The photometric monitoring results in WF3 and PC1 are presented in Figure 1
(Gonzaga et al.) and illustrate the improvement in throughput after each monthly decon.
- The drift in focus is also monitored with data from this proposal; Figure 2 shows the
drift in focus since Jan. 1994 (Suchkov & Casertano, ISR 97-01). The magnitude of the
routine focus updates (1-2 per year) are determined from the results of these observations.
Details of the focus monitoring are kept updated on WWW (see Reference section).
- The impact of focus drift, both long and short term, on aperture photometry has been
evaluated (Suchkov & Casertano, ISR 97-01). The effect was found to be small for both
WF and PC when large aperture radii are used (~5 pixels or larger). However, the magnitude corrections for defocusing become important for smaller aperture radii: short-term
variations (orbital timescales) can vary by a few percent and up to 10% for aperture radii
of 1 pixel. On a longer timescale, the PC photometric zeropoint has drifted: the spectrophotometric standard star looks brighter by ~0.05 mag in Jan. 1997 than it did it April
1994 (preliminary results show the same brightening in the WF chips). An example of this
longterm drift is shown in Figure 3; more details are provided in ISR 97-01 (Suchkov &
Casertano).
- The data have also been used in determining the necessary SYNPHOT table update
(summary of proposal 6186 - this ISR - contains details).
Timeline: Observations were taken regularly every month as planned.
Continuation Plan: Cycle 7 photometric monitor will be essentially the same as this proposal after each decon; given the instrument’s stability, the pre-decon measurements will
only be taken before every other decon, thereby saving ~12 orbits of observing time.
7
Proposal ID 6903: WFPC2 Cycle 6: Decontamination
Plan
Purpose: UV blocking contaminants are removed by warming the CCDs.
Description: The decontamination itself is implemented via the DECON mode, in which
the TECs (thermo-electric coolers) are turned off and the CCD and heat pipe heaters are
turned on to warm the detectors and window surfaces (cold junctions warmed to ~+22C).
Keeping WFPC2 warm for ~6 hours has been shown in previous cycles to be sufficient to
remove the contaminants and anneal many hot pixels; continuation of 6-hour decons is
anticipated for Cycle 6.
The internal observations taken before and after each decontamination consist of: 4 biases
(2 at each gain setting), 4 INTFLATs (2 at each gain setting), 2 K-spots (both at gain 15,
one short and one long exposure, optimized for PC and WF), and finally, 5 darks (gain 7,
clocks off). To minimize time-dependent effects, each set of internals will be grouped
within 2 days and performed no more than 1 day before the decon and no later that 12
hours after the decon. To protect against residual images in the darks (which results in the
irretrievable loss of the critical pre-decon hot pixel status), the darks will be executed as a
non-interruptible sequence at least 30 minutes after any WFPC2 activity.
Fraction of GO/GTO Programs Supported: 100%
Resources:
Observation: None pointed, 168 internal.
Special Requirements: Requires scheduling at 4 week intervals. Prevents WFPC2 from
being used for several hours, although other instruments can be used most of that time.
Dark frames taken before decontaminations need to be protected from possible residual
images from overexposed sources.
Accuracy: This proposal is mainly designed to maintain the health of the instrument.
Biases, darks, and other internals taken with this proposal are used in generating appropriate reference files (see Proposals 6904 and 6905).
Products: Those obtained from use of darks, biases and other internals (see Proposals
6904 and 6905).
8
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 92 occultation periods.
Accuracy Achieved: N/A; objective is to insure that the contaminants are periodically
removed from the CCD windows.
Products: Data was used in generating dark reference files for the pipeline (Wiggs et al.),
hot pixel lists for the WWW (Wiggs & Casertano), and regular updates to WWW History
File on Web (Baggett & Wiggs). The table below lists all decontamination procedures
done to date; the Photometric Monitoring proposal (6902) section contains a figure illustrating the restoration to nominal throughput after each decon.
Timeline: N/A
Continuation Plan: Decons for Cycle 7 are anticipated to be clones of the Cycle 6
decons.
9
Figure 2: Focus History. Data points are focus measurements (PC, F555W) obtained via
phase retrieval; focus adjustments are marked with a vertical line (from Suchkov & Casertano, ISR 97-01; plot kept updated on WWW, URL is included in Reference section).
Figure 3: Long term magnitude variations in F555W due to focus drift (from Suchkov &
Casertano, ISR 97-01). Aperture radius is given along the right hand side of each data set.
Thick lines are linear regression fits to the magnitudes in each aperture. Vertical lines mark
focus adjustment dates; left and right panels mark PC and WF, respectively.
10
Table 3. WFPC2 Decontamination Dates and Parameters (from the WFPC2 History
Memo on the WWW (http://www.stsci.edu/ftp/instrument_news/WFPC2/
Wfpc2_memos/wfpc2_history.html, maintained by Baggett and Wiggs).
date
MJD
ta
1994
date
MJD
ta
date
MJD
ta
22 Sep 03:40
49982.1528
6
27 Feb 06:31
50506.2721
6b
Feb 22 11:37
49405.4840
6
17 Oct 09:43
50007.4053
6
04 Mar 10:16
50511.4278
6c
Mar 24 11:08
49435.4639
6
15 Nov 08:53
50036.3706
6
21 Mar 03:35
50528.1494
6
Apr 24 00:49
49466.0340
6d
14 Dec 07:03
50065.2929
6
05 Apr 08:50
50543.3681
6
May 23 15:00
49495.6250
5.5e
25 Apr 23:00
50563.9583
6
Jun 13 11:02
49516.4597
12
11 Jan 23:24
50093.9750
6
15 May 20:18
50583.8460
6
Jul 10 11:40
49543.4861
12
11 Feb 00:30
50124.0208
6
07 Jun 13:06
50606.5461
6
Jul 28 07:12
49561.3000
12
10 Mar 00:21
50152.0147
6
24 Jun 11:04
50623.4612
6
Aug 27 09:46
49591.4069
12
02 Apr 00:16
50175.0111
6
24 Jul 18:42
50653.7795
6
Sep 25 00:46
49620.0319
12
04 May 17:09
50207.7146
6
20 Aug 02:17
50680.0952
6
Oct 21 00:41
49646.0285
12
28 May 06:16
50231.2614
6
17 Sep 17:24
50708.7256
6
Nov 19 17:29
49675.7285
6
22 Jun 22:15
50256.9277
6
13 Oct 18:00
50734.7506
6
Dec 18 06:00
49704.2500
6
28 Jul 13:34
50292.5653
6
14 Nov 05:19
50766.2217
6
23 Aug 10:10
50318.4242
6
10 Dec 09:40
50792.4027
6
1995
1996
13 Jan 16:14
49730.6764
6
18 Sep 16:25
50344.6840
6
12 Feb 01:54
49760.0792
6
18 Oct 07:46
50374.3236
6
Jan 08 00:03
50821.0025
6
11 Mar 14:30
49787.6042
6
12 Nov 09:40
50399.4031
6
Feb 01 19:15
50821.0025
6
8 Apr 10:29
49815.4368
6
15 Dec 00:00
50432.0417
8
Mar 06 09:18
50878.3877
6
7 May 01:13
49844.0507
6
19 Dec 12:33
50436.5229
6
2 Jun 18:30
49870.7708
6
27 Jun 20:00
49895.8333
6
07 Jan 23:41
50455.9875
6
30 Jul 08:50
49928.3681
6
09 Feb 00:00
50488.0006
6
27 Aug 05:43
49956.2382
6
23 Feb 19:08
50502.7978
6f
a.
b.
c.
d.
e.
f.
1998
1997
t is length of time chips are kept warm.
Post-SM97 decontamination procedure: CCD’s to -88˚ C, TEC on 07:10:48.
Post-SM97 decontamination procedure: CCD’s to -88˚ C, TEC on 10:55:46
Operating temperature set colder (-88˚C).
Realtime contingency decon used.
Post-SM97 decontamination procedure: CCD’s to -43˚ C, TEC on 19:40:46.
11
Proposal ID 6904: WFPC2 Cycle 6: Darks
Plan
Purpose: Measure dark current on individual pixels and identify hot pixels at frequent
intervals.
Description: Every week, five 1800s exposures are taken with the shutter closed. The
length of the exposures is chosen to fit nicely within an occultation period. The weekly
frequency is required because of the high formation rate of new hot pixels (several tens per
CCD per day). Five darks a week are required for cosmic ray rejection, to counterbalance
losses due to residual images, and to improve the noise of individual measurements. Even
with these measures, some weeks no usable darks will be available because of residual
images. Normally this results only in a longer-than-usual gap in the hot pixel lists, but in a
decontamination week, information on pixels that became hot and then annealed would be
lost irretrievably. For this reason, pre-decon darks are to be executed NON-INT and at
least 30 minutes after any WFPC2 activity (see Proposal 6903). Normal darks do not need
to be protected in this fashion.
Fraction of GO/GTO Programs Supported: 90%
Resources:
Observation: 195 internal orbits (occultation periods).
Special Requirements: None. (Darks associated with decontaminations (proposal 6903)
are protected from residual images due to saturated sources).
Accuracy: The required accuracy for darks is about 1 e-/hour (single-pixel rms) for the
vast majority of science applications. The expected accuracy in a typical superdark is 0.05
e-/hour for normal pixels. The need for regular dark frames is driven by systematic effects,
such as dark glow (a spatially and temporally variable component of dark signal) and hot
pixels, which cause errors that may exceed these limits significantly.
Products: Weekly dark frames delivered to CDBS and monthly tables of hot pixels on the
Web.
12
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 131 occultation periods.
Accuracy Achieved: Typical superdark accuracy is ~0.05 e-/hour.
Products: Dark reference files are regularly delivered to CDBS; WWW hot pixel lists are
maintained, in STSDAS format for use with the STSDAS task ‘warmpix’, and in ASCII
format for use outside of IRAF (Wiggs et al.). An excerpt from one of the hot pixel lists is
shown in the table below.
Timeline: Cycle 6 dark frames were taken weekly and new calibration files delivered generally within two weeks (primarily dependent on archive turnaround); the warm pixel lists
are made available ~monthly, typically within 1 month of nominal date (Wiggs et al.).
Continuation Plan: The 5 dark frames per week continue in Cycle 7. In addition, daily
1000 sec darks (up to 3 frames per day) are taken on a non-interference, low-priority basis
as a service to the GO community, to help with hot pixel rejection. There is no plan to use
the supplemental darks for the standard pipeline products.
Table 4. Excerpt from a hot pixel list (decon_971013_971114.tab); dark current is given
in DN/sec at 7 electrons/DN. The hot pixel tables typically span the time interval between
decons and contain hot pixel information derived from the weekly dark files taken during
that period; the table section below is from the period Oct 13,1997 to Nov 14,1997. The
STSDAS warmpix task uses the locations and darkcounts to flag and/or fix hotpixels in
an image; pixels with darkcounts set to “-100” before and after the observation are considered to be fine and are not changed by warmpix in the image or in the data quality file. For
more details on warmpix, see the online help (type “help warmpix” at the IRAF prompt).
chip
X (pixels)
Y (pixels)
date (MJD)
darkcount(DN/sec)
1
83
82
50734.000000
-100.0000
1
83
82
50734.994603
0.00311
1
83
82
50735.427242
0.00329
1
83
82
50741.070992
0.00363
1
83
82
50748.146686
0.00331
1
83
82
50755.043908
0.00326
1
83
82
50762.178631
0.00302
1
83
82
50765.342520
0.00397
1
83
82
50766.000000
-100.0000
13
Proposal ID 6905: WFPC2 Cycle 6: Internal Monitor
Plan
Purpose: Verification of short-term instrument stability for both gain settings.
Description: The internal observations will consist of 8 biases (4 at each gain) and 4
intflats (2 at each gain). The entire set should be run once per week, except for decon
weeks), on a non-interference basis. This proposal is similar to the Cycle 5 Internal Monitor (6250), except that the K-spot images have been removed (these are being taken with
the Decon Proposal). The execution frequency during Cycle 6 has also been reduced,
from twice a week to once a week, although the total number of biases has been increased
to continue to provide an adequate number of frames for the generation of pipeline reference files.
Fraction of GO/GTO Programs Supported: 100%
Resources:
Observation: 39 internal orbits (occultation periods).
Special Requirements: None.
Accuracy: Approximately 120 bias frames will be used for each pipeline reference file;
accuracy is required to be better than 1.5 e-/pixel, and is expected to be 0.8 e-/pixel.
Products: Superbiases delivered ~every year to CDBS; TIPS reports on possible buildup
of contaminants on the CCD windows (worms) as well as gain ratio stability, based on
INTFLATs. An ISR will be issued if significant changes occur.
14
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 37 occultation periods.
Accuracy Achieved: Sets of 120 bias frames are used to generate the pipeline reference
files: the accuracy is ~0.5 electrons/pixel. Other bias-related results are detailed in the ISR
(O’Dea et al., ISR 97-04), and can be summarized as follows.
•
Superbiases: These are similar to previous superbiases; see table below for statistics.
•
Bias Overscan: The analysis also included a study of the overscan properties. In general, the overscans were found to be well-behaved and, to a good approximation, constant as a function of row number, confirming that subtraction of a single value for
even and odd columns, the BIASEVEN and BIASODD keywords, is appropriate.
•
Bias Jumps: these jumps, as detected in the .x0h by calwp2, were found to occur a significant fraction of the time in both gain settings (63% and 45% for gain 7 and 15,
respectively). PC tends to dominate the statistics in gain 7, while WF4 dominates in
gain 15. The average bias jump magnitudes were 0.127 (gain 7) and 0.147 (gain 15).
There is no evidence for any long-term changes in frequency of jumps, their mean or
median amplitude, or dispersion in amplitudes (O’Dea et al., TIR 97-11).
Products: Results presented at TIPS; updated bias reference files delivered to CDBS
(Gonzaga et al.); ISR 97-04 (O’Dea et al.) and TIR 97-11 (O’Dea et al.) completed.
Timeline:
Continuation Plan: Maintain current policies.
Table 5. Statistics of the two most recent sets of superbiases (h* were generated from
biases dating May 95 - July 96 while i* were generated from Aug 96 - Nov 97 biases).
Chip
CDBS File
Mean
RMS
Max
Min
CDBS File
Mean
RMS
Max
Min
1
h161240au
0.346
0.382
287.8
-0.057
i2i1201qu
0.344
0.221
73.941
0.004
2
(gain 7)
0.312
0.217
91.5
-0.197
(gain 7)
0.314
0.303
133.497
-0.121
3
0.301
0.654
494.2
-0.147
0.297
0.323
146.916
-0.032
4
0.330
0.183
59.5
-0.165
0.319
0.297
159.772
-0.083
1
h1612404u
0.176
0.105
53.4
-0.103
i2h1025iu
0.176
0.114
42.423
-0.072
2
(gain 15)
0.153
0.134
69.2
-0.232
(gain 15)
0.160
0.150
61.924
-0.077
3
0.146
0.295
223.6
-0.117
0.149
0.155
73.203
-0.109
4
0.170
0.100
19.7
-0.295
0.169
0.142
58.485
-0.169
15
Proposal ID 6906: WFPC2 Cycle 6: Visflat Monitor
Plan
Purpose: Monitor the stability of the camera and filter responses via the VISFLAT channel.
Description: Twice a month, internal flat fields (VISFLATs) will be obtained using the
visible cal-channel lamp with the photometric filter set plus one of the linear ramp filters.
The images will be used to monitor WFPC2’s flat field response as well as to build a database of high S/N flat fields, which will provide information on the pixel-to-pixel response
in the cameras and any possible long-term, contamination-induced changes. The linear
ramp filter (FR533N) exposures, one at each gain, taken after decon will provide a monitor
of the performance of the ADC. Histograms generated from the ramp filter flats will be
used to trace the ADC transfer curve. ON HOLD: In addition to the monitor observations,
an initial filter sweep is done to obtain VISFLATs in all visible filters; these will be compared to the Cycle 5 filter-sweep data to verify that none of the filters are developing any
problems and to provide a check of the cal-channel’s long-term stability.
Fraction of GO/GTO Programs Supported: 100%
Resources:
Observation: 62 internal orbits (occultation periods).
Special Requirements: Uses the VISFLAT calibration channel, whose Welch Allyn bulb
is apparently wearing out (see ISR 96-01; a back-up exists for the Welch Allyn bulb). The
Cycle 6 proposal has been redesigned to limit the number of ON/OFF cycles placed on
this channel to a level believed safe over 10-15 years. The sweep part of the proposal,
which puts the heaviest usage on the lamp, is on hold, pending verification of the lamp
health from the short monthly executions. The INTFLAT Monitor (Proposal 6907) can
obtain similar information if necessary.
Accuracy: The VISFLAT response is stable to about 0.3%, both in overall level (lamp
degradation aside) and in spatial variations. The point of this proposal is to verify this stability on a regular basis and to monitor the lamp degradation.
Products: ISR, TIPS reports.
16
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 36 occultation periods.
Accuracy Achieved:
Products: Analysis is still in progress and is part of the intflat study (proposal #6907,
O’Dea et al.). Final results will be presented, as usual, at TIPS meetings, STAN, WWW,
Instrument and Data Handbook updates, and Instrument Science Report.
Timeline:
Continuation Plan: Maintain current policy: minimize use of VISFLAT lamp to conserve
remaining lifetime.
17
Proposal ID 6907: WFPC2 Cycle 6: Intflat Monitor
Plan
Purpose: Provide backup database of INTFLATS if VISFLAT channel fails.
Description: This proposal consists of two parts: (1) an INTFLAT filter sweep and (2) a
series of exposures to test the linearity of the camera. (1) The sweep is a complete set of
internal flats cycling through both shutter blades and both gains. The signal-to-noise ratio
per pixel is estimated to be similar to the VISFLATs (0.6%) but the spatial and wavelength
variations in the illumination pattern are much larger. However, the INTFLATs will provide a baseline comparison of INTFLAT vs. VISFLAT, in the event of a cal-channel system failure, and track temporal variations in the flat fields at the 1% level. In addition,
these images will provide a good measurement (better than 1%) of the stability of the gain
ratios. (2) The linearity test portion is aimed at obtaining a series of INTFLATs with both
gains and both shutters. Since the INTFLATs have significant spatial structure, any nonlinearity would appear as a non-uniform ratio of INTFLATs with different exposure times.
Exposures are also taken with gain 7, shutter B, and clocks=YES to test these modes.
Fraction of GO/GTO Programs Supported: Backup.
Resources:
Observation: 18 internal orbits (occultation periods).
Special Requirements: None.
Accuracy: The signal-to-noise ratio per pixel is similar to that obtained in the VISFLAT
program (0.6%) but there are much larger spatial and wavelength variations in the illumination pattern. As a result, this dataset will not form any part of the pipeline calibration.
This baseline is necessary in case the VISFLAT channel fails and there are temporal variations in the camera flat fields at the 1% level.
Products: TIPS report, ISR if any significant variations are observed.
18
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 25 occultation periods.
Accuracy Achieved: Preliminary results were presented at TIPS (see figure below): the
lamp output has remained relatively stable and exposures repeatable since the start of the
WFPC2 mission. The jump early on (MJD~49500) is attributed to the change to cooler
CCD operating temperature in April 1994; since then, the lamps have slowly increased
their output by ~1%. The increase is attributed to the lamps because, 1) this sort of behavior is typical for Carley-type bulbs and, 2) observations of the photometric standard stars
exhibit no such trend.
Products: Analysis is still in progress; final results will be presented in the standard fashion: TIPS, STAN, WWW, Instrument and Data Handbook updates, and ISR.
Timeline:
Continuation Plan: Maintain current policy.
62
INTFLATS MEANC300/EXPTIME PC1
F555W Gain 7 Blade A
March 1994 to Feb 1998
60
58
56
Julian Day
Figure 4: Countrates for F555W INTFLAT exposures, from early 1994 until early 1998
(O’Dea et al.).
19
Proposal ID 6908: WFPC2 Cycle 6: UV Flat Field Monitor
Plan
Purpose: Monitor the stability of UV flat field.
Description: UV flat fields will be obtained with the cal-channel’s ultraviolet lamp
(UVFLAT) using the UV filters F122M, F170W, F160BW, F185W, and F336W. The UV
flats will be used to monitor UV flat field stability and the stability of the Woods filter
(F160BW) by using F170W as the control. The F336W ratio of VISFLAT (Cycle 6 proposal 6906) to UVFLAT will provide a diagnostic of the UV flat field degradation and tie
the UVFLAT and VISFLAT flat field patterns together. Two supplemental dark frames
must be obtained immediately after each use of the lamp, in order to check for possible
afterimages.
Fraction of GO/GTO Programs Supported: 10%
Resources:
Observation: 12 internal orbits (occultation periods).
Special Requirements: Uses the limited life UV lamp. In order to prevent excessive degradation of the lamp, the SU (scheduling unit) duration for each UVFLAT visit should be
kept the same as the durations used during Cycle 5 (proposal 6191); the lamp should not
remain on for periods of time longer than those used in Cycle 5. To be executed once
before and once after the refurbishment mission, shortly after a decontamination.
Accuracy: About 2-8% pixel-to-pixel expected (depending on filter).
Products: New UV flat fields if changes are detected.
20
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 8 internal orbits.
Accuracy Achieved: 2% on lamp level, 5-10% on pixel-to-pixel sensitivity variation,
depending on filter.
Products: Results presented at TIPS meeting; the figure below illustrates the UV lamp
decline since 1994.
Timeline: Observations executed in January and April 1997.
Continuation Plan: Maintain current policies.
F170W, UVFLATS
F336W, UVFLATS
1.1
PC
1.05
mean
mean
1.1
1
WF2
1.05
1
WF2
1.05
1
.95
1.1
WF3
1.05
mean
mean
.95
1.1
1
.95
1.1
WF3
1.05
1
.95
1.1
WF4
1.05
mean
mean
1
.95
1.1
mean
mean
.95
1.1
PC
1.05
1
.95
WF4
1.05
1
.95
49500
49750
50000
MJD
50250
50500
49500
49750
50000
MJD
50250
50500
Figure 5: Variation in UV flats over time in two filters for the four cameras. The countrates were averaged over the central 300x300 pixels and normalized to the October 1994
set of UV flats (MJD of 49500 is May 28,1994, MJD of 50500 is Feb 21,1997). The lamp
degradation in the far UV is apparent from the F170W data (Baggett).
21
Proposal ID 6909: WFPC2 Cycle 6: Earth Flats
Plan
Purpose: Monitor flat field stability.
Description: As in Cycle 5 program 6187, sets of 200 Earth-streak flats are taken to construct high quality narrow-band flat fields with the filters F160BW, F375N, F502N, F656N
and F953N. Of these 200 perhaps 50 will be at a suitable exposure level for destreaking.
The resulting Earth superflats map the OTA illumination pattern and will be combined
with SLTV data (and calibration channel data in case of variation) for the WFPC2 filter set
to generate a set of superflats capable of removing both the OTA illumination and pixel-topixel variations in flat field. The Cycle 4 plan is being largely repeated except: (1) UV filters are dropped because measurement is generally only of red leak. (2) F160BW is
retained in order to check for developing pinholes. (3) Crossed filters used as neutral densities are eliminated (illumination pattern is wrong). (4) Observations with the Methane
Quad filters will be taken to define its vignetting pattern. (5) Observations with crossed
narrow-band and ramp filters will be taken to verify the relative stability of their wavelength.
Fraction of GO/GTO Programs Supported: 100%
Resources:
Observation: 155 non-science-impacting orbits (during occultation periods).
Special Requirements: None.
Accuracy: The single-pixel noise expected in the flat field is 0.3%.
Products: New flat fields to CDBS if changes detected.
22
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 187 occultation periods.
Accuracy Achieved: Flat fields currently in CDBS are based primarily upon Cycle 5
Earth flats; errors are generally < 0.5% rms. Earth flats from this Cycle 6 proposal are now
being used to investigate possible improvements to the CDBS flat fields.
Products: Analysis is still in progress (Biretta & Wiggs); final results will be presented at
TIPS meetings, STAN, WWW, Instrument and Data Handbook updates, and ISR.
Timeline: CDBS file updates are estimated for later in 1998.
Continuation Plan: Maintain current policies.
23
Proposal ID 6934: WFPC2 Cycle 6: Photometric Zeropoint
Plan
Purpose: Verify synthetic zeropoint of WFPC2 filters.
Description: Standard stars are observed through all filters longward of F336W (inclusive) with the limit of one orbit per target. Targets include: the spectrophotometric standard grw+70d5824 in PC and WF3; the solar-type standards P041-C and P330-E selected
by the NICMOS team (P177-D was observed in Cycle 5); and the Landolt standard fields
SA98 and Rubin 149, containing 5 and 7 useful targets, respectively. Observations of
grw+70d5824 will be directly comparable to the corresponding observations for cycles 4
and 5 (programs 5572 and 6179) and will verify the stability of the filters as well as
improve the accuracy of the calibration. The other standards are observed to provide
cross-instrument calibration and to increase the range of colors used for photometric verification. This proposal will help all observers who want to do quantitative photometry at
the 2% level.
Fraction of GO/GTO Programs Supported: 70%
Resources:
Observation: 6 pointed orbits.
Special Requirements: Specific orientations will be required for the two fields of standards in order to fit the maximum number of stars. All observations should be executed
within a week after decontamination.
Accuracy: 2% required, 1% expected for our main spectrophotometric standard
grw+70d5824. Expected accuracy for the other standards is between 2% and 5%, depending on spectral type and filter; most of the error derives from limited knowledge of the
transformations between ground-based and WFPC2 photometric systems.
Products: TIPS report, SYNPHOT updates if necessary, ISR.
24
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 6 pointed orbits.
Accuracy Achieved: The data have been used to verify the current SYNPHOT tables
(Casertano et al.): the SYNPHOT predictions for the photometric filter set are within 1-2%
of the observations (see Table 6 below), slightly higher for F555W (consistent with the
absolute flux scale from the FOS measurements), and ~3% level for the other filters. Small
adjustments to the SYNPHOT tables to further improve the predictions will be made later
this year (Baggett et al.).
Products: Progress reports have been made at the TIPS meeting and 1997 Calibration
workshop (Casertano, 1997).
Timeline: Observations completed Nov 1996, May, August, and December 1997.
Continuation Plan: Continuing monitoring with grw+70D5824 standard only.
Table 6. Ratio of SYNPHOT predictions to observed countrates (from Casertano, 1997).
filter
HZ-44
P041-C
P177-D
P330-E
photometric filter set
F336W
0.997
1.009
1.022
0.983
F439W
0.992
1.007
1.006
0.989
F555W
0.994
1.031
1.030
1.017
F675W
0.993
1.006
1.005
1.006
F814W
0.000
1.019
1.018
1.012
other filters
F380W
1.000
1.042
1.045
1.024
F410M
1.018
0.996
1.003
0.986
F450W
1.008
1.027
1.022
1.014
F467M
0.992
1.032
1.034
1.023
F547M
0.987
1.049
1.045
1.061
F606W
0.973
1.032
1.026
1.011
F622W
0.000
1.030
0.000
0.000
F702W
1.005
1.022
1.008
1.004
F785LP
0.000
1.044
1.031
1.011
25
Proposal ID 6935: WFPC2 Cycle 6: Photometric Transformation
Plan
Purpose: (1) Update photometric transformations to Johnson-Cousins system and
Stromgren system; (2) Determine spatial dependence of contamination; (3) Check the
astrometric solution using M67; (4) Spot check of gain = 7 vs. gain = 15 ratios; (5) Spot
check short vs. long exposure zeropoints; (6) Determine cross-chip zeropoint differences
in UV for point-source photometry; (7) Determine the vignetting function in rotated filters.
Description: Three photometric standard star fields in ω Cen (Galactic globular cluster),
M67 (old open cluster), and NGC 2100 (young LMC globular cluster) are observed before
and after a decontamination. Four different filter sets are used:
(1) The five filters generally used to match the Johnson-Cousins system (F336W,
F439W, F555W, F675W, F814W).
(2) The wide-band equivalents for the Johnson-Cousins system (F300W, F380W,F450W,
F606W, F702W).
(3) The Stromgren equivalents (F336W, F410M, F467M, F547M).
(4) Two filters farther toward the UV (F255W, F170W), so that contamination over the
full field of view can be measured. F255W is not used for the reddest cluster (ω Cen).
F170W is only used for the bluest cluster (NGC 2100).
For the brighter clusters (M67 and NGC 2100) long and short exposures are taken in the
UBVRI equivalents both to extend the dynamic range and to check for differences in photometric zeropoints.
A spot check to compare gain=7 and gain=15 is also included for ω Cen and M67, and an
observation of ω Cen with a 60o change in orientation - which moves individual stars
across chips - is used to test the cross-chip zero-point calibration.
Finally, NGC 2100 is observed in F160BW in both normal and rotated (N15) position in
order to determine the vignetting function of the latter.
Fraction of GO/GTO Programs Supported: 40%
Resources:
Observation: 12 pointed orbits.
Special Requirements: The first visit for each target must be taken within 3 days after a
decontamination. The second visit, including only the UV filters, must be taken more than
25 days after the first visit, but before the next decontamination.
Accuracy: The photometric transformations should be accurate to 2-5%. The stability of
these transformations will be measured to the 1% level. The astrometry should be good to
0.1” (absolute) and 0.05” (relative).
Products: ISR, Instrument Handbook, and part of a planned paper on 1% photometry.
26
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 13 pointed orbits.
Accuracy Achieved:
Products: Analysis is still in progress (Whitmore et al.); final results will be presented at
TIPS meetings, STAN, WWW, Instrument and Data Handbook updates, and ISR.
Timeline: Data taken Sep/Oct 96 and Jun/Oct 97.
Continuation Plan: Repeat a shorter version (merging of 6934 and 6935) in Cycle 7, in
order to monitor any time-variable effects in the zeropoint, spatial dependence of
zeropoint, or contamination. May also include a new globular cluster target to aid in photometric transformations.
27
Proposal ID 6936: WFPC2 Cycle 6: UV Throughput and Lyman α Verification
Plan
Purpose: Verify throughput for all UV filters, including Lyman α test to monitor possible
contamination on pick-off mirror.
Description: Spectrophotometric standards are observed shortly before and after a
DECON through all the UV filters in each chip and through F160BW crossed with
F130LP, F185LP, and F165LP to determine the wavelength dependence of the throughput
across the bandpass (for color terms). This proposal is based on the Cycle 5 UV Throughput proposal (6186) but includes also the standard BD+75d325 used in Cycle 4 (proposal
5778) to establish the Lyman α throughput calibration. Some of the observations will be
repeated after the servicing mission to verify the stability of the camera.
Fraction of GO/GTO Programs Supported: 10% + check for contamination on pick-off
mirror.
Resources:
Observation: 12 pointed orbits.
Special Requirements: Timing requirements with respect to decontaminations.
Accuracy: The UV throughput will be measured to better than 3%. Accuracy in Lyman α
throughput is expected to be between 5 and 10%, because of the residual uncertainty of the
red leak correction after observations with crossed F122M and F130LP.
Products: TIPS, SYNPHOT update if necessary, ISR.
28
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 11 pointed orbits.
Accuracy Achieved: Analysis is currently in progress, in conjunction with the solar analog standard star data from proposal 6934 (Baggett et al.).
Products: Results will be reported in the standard fashion, via TIPS meetings, STANs,
WWW memos, and Instrument and Data Handbooks updates. Any necessary SYNPHOT
updates will be implemented later in 1998.
Timeline: Data taken in spring and fall of 1997.
Continuation Plan: UV throughput check will be cut back to just one iteration, midway
through the next cycle.
29
Proposal ID 6937: WFPC2 Cycle 6: CTE Calibration
Plan
Purpose: (1) Test whether the exposure-time dependence of the photometric calibration is
due to CTE (long vs. short exposure problem); (2) refine flux and background-level dependent aperture corrections.
Description: The globular cluster NGC 2419 will be observed through F555W with a
combination of exposure times (between 5 and 1400 s) and preflash levels (0 to 500 e-).
Analysis of cycle 5 CTE calibration data (proposal 6192) suggests that magnitude errors
due to charge transfer effects are greatly reduced (if not entirely eliminated) at background
levels of 160 e- or greater. CTE effects have been proposed as the solution to reported differences in the magnitudes of stars measured on frames with short exposures vs. long
exposures. If CTE is the cause, then the differences should disappear with preflash. We
will reobserve the cluster NGC 2419 with and without preflash to test this hypothesis. This
data set will also provide a large number of stars with which to refine existing measurements of the effects of CTE on the wings of the PSF. A range of preflash levels will be
explored at the 60 sec exposure time.
Fraction of GO/GTO Programs Supported: 30%
Resources:
Observation: 2 pointed orbits.
Special Requirements: Observations should be made at the same position and roll angle
as the previous NGC 2419 “long” exposures (proposal GO 5481).
Accuracy: The reported short vs. long effect is ~0.05 mag. We wish to reduce this to less
than 0.01 mag.
Products: ISR; if appropriate, a special task to correct the CTE effect will be generated.
30
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 2 pointed orbits.
Accuracy Achieved: The long vs. short anomaly, or nonlinearity, is characterized by
shorter exposures, with less total signal, providing lower countrates than long exposures
with more total signal (see Figures 6 and 7 on following page). For more details about previous studies, see the WFPC2 WWW Clearinghouse page and the CTE WWW memo.
The magnitude discrepancies are ~0 for well-exposed stars (>2000 DN in short exposure)
and >0.10 mag for faint sources (~100 DN). The total signal in the short exposure appears
to determine the discrepancy, i.e., nonlinearity is determined by total amount of signal, not
the exposure length, and the discrepancy increases with increasing disparity of exposure
times. An empirical correction (adding ~2-2.5 electrons per pixel in the target aperture),
although unphysical, appears to remove the effect (see WWW memo).
Despite the superficial similarity with the CTE problem, the long vs. short nonlinearity is
different: it is not affected by the background level and there is no apparent dependence on
position on the chip. Analysis of the data from this proposal (Casertano, 1997, Calibration
Workshop) showed that:
•
there have been no longterm changes in the long vs. short nonlinearity behavior (the
problem exists at the same level as it did back in 1994), and
•
preflashing at 200 e-/pixel has no measurable effect (see Figure 7 on next page).
Products: Preliminary results were presented at TIPS and at 1997 Calibration Workshop
(Casertano). The analysis is still in progress (Casertano et al.); final results will be presented in the standard fashion, via TIPS meetings, STAN, WWW, Instrument and Data
Handbook updates, and ISR.
Timeline:
Continuation Plan: More data is planned for Cycle 7 (proposal 7630) in order to allow a
more detailed characterization of the anomaly.
31
Figure 6: Long vs. Short Effect. Plotted is the difference in magnitude between the short
and long exposures (60 and 1400 seconds), without preflash, as a function of the long
exposure magnitude (Casertano & Mutchler).
Figure 7: Same as Figure 6, but data has been preflashed at ~250e- level.
32
Proposal ID 6938: WFPC2 Cycle 6: PSF Characterization
Plan
Purpose: Provide a subsampled PSF over the full field to allow PSF fitting photometry,
test PSF subtraction as well as dithering techniques (cf. effects of the OTA breathing and
CCD gain).
Description: Measure PSF over full field in photometric filters in order to update the TIM
and TINYTIM models and to allow accurate empirical PSFs to be derived for PSF fitting
photometry. These observations will also be useful in order to test PSF subtraction and
dithering techniques at various locations on the CCD chips. With one orbit per photometric filter, a spatial scan is performed over a 4x4 grid on the CCD. The step size is 0.125
arcseconds; this gives a critically sampled PSF over most of the visible range. This program uses the same specially chosen field in ω Cen as the Cycle 5 proposal 6193, but with
a few arcsec shift in order to better map the PSF variation. The standard ‘photometric’ filters are used. Two additional orbits are used to explore the effects of OTA breathing and
CCD gain on dithering and PSF subtraction techniques. Data volume will be a problem,
so special tape recorder management will be required. The proposal also allows a check
for subpixel phase effects on the integrated photometry.
Fraction of GO/GTO Programs Supported: 15%
Resources:
Observation: 7 pointed orbits.
Special Requirements: Needs same pointing and orientation as Cycle 5 observations for
proposal 6193, thus should be scheduled within a similar time frame.
Accuracy: Provides measurement of pixel phase effect on photometry (sub-pixel QE variations exist). The chosen field will have tens of well exposed stars in each chip. Each star
will be measured 16 times per filter at different pixel phase. The proposal therefore provides, in principle, a high signal-to-noise, critically sampled PSF. This would leave PSF
fitting photometrists in a much better position than now, where pixel undersampling
clearly limits the results. The result will be largely limited by breathing variations in focus.
It is difficult to predict the PSF accuracy that will result. If breathing is less than 5 microns
peak to peak, the resulting PSFs should be good to about 10% in each pixel. Breathing
effects will be investigated (1 additional orbit) as well as the gain dependence (1 additional
orbit). PSF fitting results using this calibration would of course be much more accurate. In
addition, the test gives a direct measurement of sub-pixel phase effects on photometry,
which should be measured to better than 1%.
Products: PSF library (CDBS); ISR
-----------------------------------------------------------------------------------------------------------Results Current status: Not yet executed; in the Long Range Plan, observations are set for June/
July 1998.
33
Proposal ID 6939: WFPC2 Cycle 6: Linear Ramp Filters
Plan
Purpose: Verify wavelength and throughput calibration for Linear Ramp Filters at
selected wavelengths.
Description: The throughput calibration is obtained by observing the spectrophotometric
standard grw+70D5824 at several filter rotations and wavelengths. This completes the
program carried out in Cycle 5, in which some wavelength ranges and rotations could not
be covered. The stability of the wavelength calibration is verified by observing an
extended line source (the Orion nebula) and checking the position of the bright spots corresponding to the bright nebular emission. An additional verification is obtained through
crossed narrow-band and linear ramp filters (see Proposal 6909).
Fraction of GO/GTO Programs Supported: 7%
Resources:
Observation: 6 pointed orbits.
Special Requirements: None.
Accuracy: Throughput accuracy should be verified to ~3%. Wavelength variations of
more than 0.2% (0.6-1.4 nm), or about 15% of the filter width, should be detectable; a factor of 2 better can be expected.
Products: Update SYNPHOT throughput tables if necessary.
34
Results (based on data from Cycle 5 Proposal 6194)
Modifications: Proposal 6939 was initially a placeholder, with proposal development
pending results from Cycle 5 Polarizer and Ramps Proposal (6194). Because of the delay
in executing 6194, the Cycle 6 version (6939) has now been withdrawn, in favor of a
Cycle 7 ramps proposal.
Execution: Observations near 7400Å and those between 8500 and 8600Å were lost due to
an error in the proposal.
Resources Used:
Observation: 8 pointed orbits for LRF portion of 6194.
Accuracy Achieved: A recent analysis of the ramp data taken as part of Proposal 6194
showed that, on average, there is 1% agreement between the ground-based calibration and
new on-orbit data, but there also ~8% RMS scatter between individual data points which
is not completely understood (O’Dea & McMaster).
Products: Work is still in progress; results will be reported as usual, at the TIPS meetings,
in STANs, on WWW, in Instrument & Data Handbooks and possibly a SYNPHOT update.
Timeline: Ramp portion of 6194 executed April-June 1997.
Continuation Plan: While the 8% accuracy reported could be considered "acceptable" for
ground-based narrow band imaging, the expectation is that ~3% accuracy should be possible for WFPC2; additional ramp filter observations are being planned for Cycle 7.
Figure 8: Countrates of ramp observations compared to SYNPHOT predictions (O’Dea &
McMaster).
35
Proposal ID 6940: WFPC2 Cycle 6: Polarizers
Plan
Purpose: Verify stability of polarization calibration.
Description: The goal of this proposal is to check for any changes in the polarization calibration since Cycle 5. Observations are made in F555W+POLQ of both polarized and
unpolarized stars, in addition to VISFLATs. Data are taken in all four quads of the polarizer, as well as in three rotated positions of the POLQ.
Fraction of GO/GTO Programs Supported: 5%
Resources:
Observation: 4 pointed orbits.
Special Requirements: Requires specific orientations.
Accuracy: The error in the polarization calibration is dominated by systematic instrumental effects. The Cycle 5 observations will be taken shortly and will allow a better assessment of the systematics. The practical limit for useful polarization observations is
probably around 3%; sources with smaller polarization probably cannot yield reliable
polarization measurements.
Products: Update SYNPHOT throughput tables if necessary.
36
Results (from Cycle 5 Proposal 6194)
Modifications: Cycle 6 Proposal 6940 is a placeholder pending completion of the analysis
of 6194. Here, we present results from the Cycle 5 Polarization Proposal 6194. The scope
of the polarization section of 6194 was expanded (to include multiple combinations of filter, aperture, and telescope roll) after Cycle 4 observations showed that significant instrument polarization was present.
Execution: Observations from visit 2 (target G191B2B) failed due to error in proposal.
Resources Used:
Observation: 16 pointed orbits, 76 occultation periods (24 VISFLATs and 52 Earth
flats).
Accuracy Achieved: A model of the polarization effects of the WFPC2 optics has been
developed, including effects of the pick-off mirror as well as the polarizer filters. Countrates predicted by this model agree with on-orbit data to ~1.5% RMS (Biretta & McMaster, ISR 97-11).
Products: ISR 97-11 and WWW tools for use in calibrating GO polarization data (Biretta
& McMaster).
Timeline: Last 6194 polarizer visit executed in December 1997; other portions of proposal were completed Nov/Oct 1996, and Jan, Apr-Aug, and October 1997.
Continuation Plan: The present model and tools should be sufficient for most GOs.
Areas for future work include the following (details in ISR 97-11, Biretta & McMaster).
- Obtain additional flat fields in more filters using VISFLAT lamp (Earth flats are too
bright); however, the degradation of the VISFLAT lamp (see results from proposal 6906)
has limited its use, so these flats are competing with other VISFLAT calibrations.
- Obtain additional on-orbit data to verify the model in more filters and apertures; this may
reduce calibration errors to < 1%; these are in the queue for early 1998 (proposal 6194).
- Study possible distortion effects due to polarized filters when using large apertures
(>20”) and possible spurious reflections against the filters (effects estimated ~1-2%).
- Since polarization studies rely on measuring small differences between observations
made at different chip locations, CTE is likely to have substantial effect on polarization
observations and may be the largest remaining error source.
- The existing WWW tools would benefit from additional testing using a larger variety of
targets as well as improvements in the least squares solution (to allow >4 apertures).
- A long-term goal is to develop an advanced STSDAS tool to handle the image alignments, distortion corrections, and computation of the Stokes vector components.
37
Proposal ID 6941: WFPC2 Cycle 6: Astrometry Verification
Plan
Purpose: Verify accuracy and stability of geometric transformation and relative astrometry solution.
Description: A very rich star field in ω Cen will be observed in five different positions
with relative shifts of 40’’ in each coordinate. Positions of more than 2000 stars per chip
will be compared between pointings using the three different astrometric solutions provided by Gilmozzi, Holtzman, and Trauger, in order to verify and refine their accuracy.
(Differences of up to 1 PC pixel exist in some regions of the field of view.) A very densely
populated field is chosen in order to achieve better coverage of the field of view, even if at
the expense of the accuracy of individual position measurements. Observations will be
carried out in three filters, F555W, F300W, and F814W, to provide a verification and/or
correction of the wavelength dependence of the solution. The F555W observation is
repeated with smaller shifts of 15’’ to ensure a better coverage of the PC. K-spot observations will be taken at the same time, in order to assess the relation between K-spot position
and astrometry.
Fraction of GO/GTO Programs Supported: 20% - also supports WFPC2-assisted target
acquisitions for other instruments.
Resources:
Observation: 4 pointed orbits.
Special Requirements: None.
Accuracy: Expected better than 0.01’’; required better than 0.05’’ (full field of view).
Products: Improvements in the STSDAS task metric and in the aperture reference file if
required; ISR.
38
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 4 pointed orbits.
Accuracy Achieved:
Products: The analysis is currently in progress (Fruchter et al.); preliminary results show
that over the longterm, there have been small motions (~0.1”) between the chips. Final
results will be reported via TIPS meeting, Instrument and Data Handbooks, STAN, and
WWW memo.
Timeline: Observations taken June 1997.
Continuation Plan: A subset of the program will be repeated twice during Cycle 7, as a
monitor of the relative positions of the chips.
39
Proposal ID 6942: WFPC2 Cycle 6: Camera Electronics Verification
Plan
Purpose: Verify several aspects of the WFPC2 camera electronics: linearity, gain ratios,
effect of CLOCKS, and effect of CTE on extended sources.
Description: A very extended non-uniform target (the giant elliptical galaxy NGC 4472)
will be observed with different exposure times and electronic configurations. The linearity
test is carried out by taking exposures of NGC 4472, centered in WFALL, with multiple
exposure times. Since the galaxy is non-uniform, the ratio of these exposures is directly
related to the camera linearity. The exposures will be taken with GAIN=7. However, one
exposure will also be taken with GAIN=15. Additional exposures will be taken with
CLOCKS=YES and with a preflash. These observations complement those of the internal
calibration proposal 6907. The two major advantages of these observations compared to
the 6907 ones are the possibility of studying the effect of preflash (since the light distribution of the preflash is different from that of NGC 4472) and the possibility of measuring an
absolute response curve, since NGC 4472, unlike the INTFLAT lamp, does not have temporal variations in luminosity. NGC 4472 has been chosen as target galaxy because it is
large enough to produce significant signal in all chips and bright enough to allow us to
explore the highest counts without excessive integration times.
Fraction of GO/GTO Programs Supported: 100%
Resources:
Observation: 1 pointed orbit.
Special Requirements: None.
Accuracy: expected: 0.5% for linearity and CTE, 0.1-0.2% for gain ratios and CLOCKS.
Required: less than 1% on each item.
Products: ISR, TIPS reports.
40
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 1 pointed orbit.
Accuracy Achieved: ISR (Stiavelli & Mutchler, ISR 97-04) details the results achieved
with the observations from this proposal. In summary:
•
Linearity: For countrates exceeding 0.5DN/sec, the linearity is better than 0.5% (see
Figure 9 below). Due to low S/N, results at the lowest countrates are less conclusive:
the formal errors of ~1% assume that nearby pixels are uncorrelated, which is probably incorrect (due to pixel response function and/or transfer inefficiencies).
•
Clocks on: although there is no trend with countrate, there is a 0.3% shift when comparing clocks on to off (see Figure 10 below). The exposure shortening effect due to
the shutter (see WFPC2 Handbook Section 2.6), is not large enough (at 0.125%) to
account for the shift. There may be some residual, as yet unknown, effect which is
shortening the clocks ON exposures.
•
Preflash: preflashed images do not show any effect as a function of countrate. There is,
however, a uniform shift of 13 electrons per pixel (possibly due to higher than normal
sky background, e.g., from Earth limb?).
Products: TIPS presentations and ISR 97-07 (Stiavelli & Mutchler).
Timeline: Observations executed in February 1997.
Continuation Plan: None for Cycle 7.
41
Proposal ID 6943: WFPC2 Cycle 6: Throughput Verification for Narrow Band Filters
Plan
Purpose: Direct verification of throughput of narrow band filters through observations of
emission line objects.
Description: The current throughput calibration of narrow-band filters is based on filter
profiles from data obtained before launch and on observations of continuum sources. This
program will verify the accuracy of the calibration, and indirectly the stability of the filters, by observing compact planetary nebulae with well-established line fluxes. The targets, chosen for consistency across instruments, are the FOS standard NGC 6833 and the
six planetary nebulae selected for the NICMOS calibration of narrow-band filters. In
addition, two PN with existing Cycle 4 observations will be included to verify the stability
of the narrow-band filters. The observations can be executed in SNAPSHOT mode since
they will be short and none is specifically required.
Fraction of GO/GTO Programs Supported: 20%
Resources:
Observation: 10 SNAP orbits.
Special Requirements: None.
Accuracy: Expected 2%, required 3%.
Products: Update SYNPHOT tables if required; ISR.
42
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 9 SNAPs.
Accuracy Achieved: Work is still in progress(Casertano & Gonzaga). Preliminary results
have shown that there is no measurable time dependence to the narrowband throughput
and that the derived WFPC2 narrowband fluxes are in good agreement with ground-based
observations. In more detail:
•
Second-epoch observations of NGC 6543 were compared with first-epoch observations obtained in 1994. The narrow-band fluxes did not vary measurably. The measurements have an uncertainty of about 5%, dominated by actual changes in the
nebular structure - NGC 6543 turned out to be closer than previously thought, and we
detected a measurable expansion in the nebula.
•
The narrow-band flux measured for three planetary nebulae, M4-16, K3-15, and NGC
6833, was found in agreement with available ground-based measurements, generally
within 5-10%. Ground-based measurements have a catalog uncertainty of 25%. A
detailed analysis of the differences will be carried out after the last observation of this
program is executed.
Products: In progress.
Timeline: Of the 10 SNAPs, 9 were completed by Dec 1997. Visit 2 (target K3-69) is tentatively scheduled for next year, Feb 1999.
Continuation Plan: None for Cycle 7.
43
Figure 9: WFPC2 Linearity (taken from Figure 1 in ISR 97-07, Stiavelli & Mutchler).
Open squares are 350 sec vs. 50 sec data, filled triangles are 200 sec vs. 50 sec data, and
stars correspond to 350 sec vs. 100 sec data. Lowest bin is < 3 electrons/sec.
Figure 10: Effect of CLOCKS=YES (from ISR 97-07, Stiavelli & Mutchler). The data
point at a countrate of ~130 electrons/sec corresponds to pixels in the WF3 saturated star.
44
filter
PC1
WF2
WF3
WF4
new/
old
new
PHOT
FLAM
conv
Vega
ZP
new
PHOT
FLAM
Vega
ZP
new/
old
new
PHOT
FLAM
Vega
ZP
new
PHOT
FLAM
Vega
ZP
F160BW
1.113
5.212e-15
0.378
14.985
4.563e-15
15.126
1.168
5.418e-15
14.946
5.133e-15
15.002
F170W
1.044
1.551e-15
0.412
16.335
1.398e-15
16.454
1.072
1.578e-15
16.313
1.531e-15
16.350
F185W
1.074
2.063e-15
0.411
16.025
1.872e-15
16.132
1.095
2.083e-15
16.014
2.036e-15
16.040
F218W
1.051
1.071e-15
0.232
16.557
9.887e-16
16.646
1.058
1.069e-15
16.558
1.059e-15
16.570
F255W
1.071
5.736e-16
0.015
17.019
5.414e-16
17.082
1.063
5.640e-16
17.037
5.681e-16
17.029
F300W
1.035
6.137e-17
-0.024
19.406
5.891e-17
19.451
1.019
5.985e-17
19.433
6.097e-17
19.413
F336W
0.980
5.613e-17
-0.098
19.429
5.445e-17
19.462
0.961
5.451e-17
19.460
5.590e-17
19.433
F380W
1.008
2.558e-17
0.559
20.939
2.508e-17
20.959
0.987
2.481e-17
20.972
2.558e-17
20.938
F439W
0.984
2.945e-17
0.657
20.884
2.895e-17
20.903
0.965
2.860e-17
20.916
2.951e-17
20.882
F450W
1.008
9.022e-18
0.475
21.987
8.856e-18
22.007
0.992
8.797e-18
22.016
9.053e-18
21.984
F547M
0.996
7.691e-18
-0.023
21.662
7.502e-18
21.689
0.993
7.595e-18
21.676
7.747e-18
21.654
F555W
0.998
3.483e-18
-0.000
22.545
3.396e-18
22.571
0.995
3.439e-18
22.561
3.507e-18
22.538
F569W
0.995
4.150e-18
-0.114
22.241
4.040e-18
22.269
0.995
4.108e-18
22.253
4.181e-18
22.233
F606W
1.010
1.900e-18
-0.316
22.887
1.842e-18
22.919
1.013
1.888e-18
22.896
1.914e-18
22.880
F622W
0.994
2.789e-18
-0.424
22.363
2.700e-18
22.397
1.000
2.778e-18
22.368
2.811e-18
22.354
F675W
0.998
2.899e-18
-0.703
22.042
2.797e-18
22.080
1.007
2.898e-18
22.042
2.919e-18
22.034
F702W
1.001
1.872e-18
-0.791
22.428
1.809e-18
22.466
1.008
1.867e-18
22.431
1.883e-18
22.422
F791W
1.009
2.960e-18
-1.224
21.498
2.883e-18
21.529
1.003
2.913e-18
21.512
2.956e-18
21.498
F814W
1.002
2.508e-18
-1.263
21.639
2.458e-18
21.665
0.988
2.449e-18
21.659
2.498e-18
21.641
Table 7. PHOTFLAMs and zeropoints for the more popular observing modes; the above
values should be applied to counts referenced to a nominal “infinite” aperture, defined by
an aperture correction of 0.10 mag with respect to 0.5” radius standard aperture. The full
table is available on WWW Documentation page as well as in ISR 97-10 (Baggett et al.).
PHOTFLAM values for gain=15 can be obtained by multiplying by the gain ratio: 1.987,
2.003, 2.006, and 1.955 for PC, WF2, WF3, and WF4, respectively (from Holtzman et al.
1995). Zeropoints are given in the Vega system; the required conversion factor used for
transforming ST magnitudes1 to Vega magnitudes is provided in the ‘conv’ column. The
size of the SYNPHOT changes are given for PC1 and WF3 in the new/old columns.
1.
ST magnitudes are defined as -2.5*log10(PHOTFLAM)-21.1 and result in constant magnitudes for
spectra having constant flux per unit wavelength. See STSDAS Synphot User’s Guide for more
details.
45
Proposal ID 6186: WFPC2 Cycle 5: UV Throughput
Plan
Purpose: Update SYNPHOT database for UV throughput.
Description: Grw+70d5824 is observed shortly before and after a decontamination
(decon) through all the UV filters in each chip and through F160BW crossed with F130LP,
F185LP and F165LP (where applicable) to determine the wavelength dependence of the
throughput across the bandpass (hence color terms). This program is designed to better
characterize the spectral response curve in the UV, and the spectral shape introduced by
the contamination.
Fraction of GO/GTO Programs Supported: 20%
Resources:
Observation: 6 pointed orbits.
Special Requirements: Must be phased with decon cycle; one execution just before, one
just after decon.
Accuracy: Overall discrepancies between the updated synthetic photometric products and
the results of this test should be 1-2% rms. This does not mean that the UV throughput
will be known to this accuracy primarily because of uncertainties in the flux calibration of
the standard used (5%), uncertainties in the UV flat fields (maybe 3% near the chip center), and time dependent contamination corrections (3% error), and uncertainties in the
CTE correction (2%). The derived UV absolute photometric accuracy at the center of the
chips should therefore be about 10%.
Products: After pipeline processing, each image will be reduced by aperture photometry.
The throughput curves and their normalizations can be updated by trial and error.
Expected to run 8/95.
46
Results
Modifications: Some pre-decon exposures with crossed filters dropped to save orbits.
Execution: Nominal.
Resources Used:
Observation: 9 pointed orbits.
Accuracy Achieved: All UV filters shortward of F439W were updated, as well as some of
the more frequently-used broadband filters redward of F439W. With a few exceptions,
changes to non-UV filter modes were relatively minor: generally ~1-2% or less (changes
in F785LP, F850LP, and F1042M were higher: ~1-4%, ~1-6%, and ~2-15% respectively,
depending on the chip.). The UV filters required somewhat larger changes to bring SYNPHOT into agreement with the observations, ranging from ~2% (e.g., F255W and F300W)
to ~5% (F170W, F218W) to > 10% (F160BW, F375N). Full details of the update, including a table of the new zeropoints (PHOTFLAMs), are in ISR 97-10 (Baggett et al.).
Products: Updated SYNPHOT tables were installed May 1997; ASCII versions are on
WWW. Results were reported via TIPS, STAN, 1997 Calibration Workshop and ISR.
Timeline: Data and analysis are complete.
Continuation Plan: Repeat subset in Cycle 7.
Figure 11: Observed grw+70D5824 countrates compared to SYNPHOT predictions (from
ISR 97-10, Baggett et al.).
47
Proposal ID 6195: WFPC2 Cycle 5: Flat Field Check
Plan
Purpose: Check quality of flat fields and estimate errors.
Description: The crowded ω Cen field is positioned with a bright star at the center of each
CCD in turn. 40 sec images are taken through each of the photometric filters (F336W,
F439W, F555W, F675W, F814W) and as many supplementary filters (from F450W,
F606W, F702W and F547M) as can fit in the allotted time. If data volume is a problem,
single chip readout is acceptable, but should be avoided as much as possible. Based on
cycle 4 programs 5659 and 5646.
Fraction of GO/GTO Programs Supported: 60%
Resources:
Observation: 2 pointed orbits.
Special Requirements: Assumes that the CTE proposal has been run and gives satisfactory results; if CTE calibration fails, this proposal may need to be run with preflash.
Accuracy: Overall discrepancies between the synthetic photometric products and the
results of this test should be 1-2% rms. Part of the point of the test is to measure this accuracy.
Products: After pipeline processing, each image will be reduced by aperture photometry
to measure the RMS errors in the flat fields. The RMS error will be determined by the
additional noise in the independent measurements over the expected variance of less than
1% from photon statistics. The single bright star at the center of each chip independently
estimates the chip-to-chip normalization error.
48
Results
Modifications: None.
Execution: Nominal.
Resources Used:
Observation: 4 pointed orbits.
Accuracy Achieved: Conclusions from the data analysis (Whitmore & Heyer, ISR 97-08)
can be summarized as:
•
The flat fields are uniform to at least 1.5% across the chips (0.6% chip to chip), likely
better as remaining uncertainties may be due to other sources (e.g., variable PSF).
•
A 2% scatter exists in the normalization of the different chips, understood as differences in the gain ratios and aperture corrections.
•
Applying the new corrections for CTE, aperture corrections, and gain ratios reduces
the RMS scatter for a random observation from ~4-7% to 2-3%.
•
The CTE results from Holtzman et al. (1995) were confirmed with this new dataset:
- CTE loss is proportionally larger for fainter point sources.
- CTE loss is larger for images with low background.
- The 4% linear ramp provides a reasonable correction in many cases, although not all.
•
Analysis of this dataset also led to new results concerning the CTE problem:
- CTE loss is the same on all three WF chips and appears to be the same on PC.
- The CTE loss ranges from 2% (for bright stars on a bright background) to ~15%
(faint stars on a faint background). The filter dependence of the CTE loss is shown in
the figure below.
- The dependence on background has been quanitified (linear in log-log space).
- There appears to be weak CTE loss in X-axis (~1-5% level).
- Differences in CR-SPLIT exposure pairs can be understood as first exposure acting
as a ‘preflash’ for the second exposure.
•
Formulae for correcting the effects of the CTE problem have been developed (see Section 2.7 of ISR 97-08, Whitmore & Heyer); these depend upon X and Y position, the
background, the star brightness, and aperture size.
Products: Results reported in TIPS, STAN and ISR 97-08 (Whitmore & Heyer).
Timeline: Observations executed in June 1996.
Continuation Plan:
49
Figure 12: Values of CTE loss in units of % loss over 800 pixels vs. the brightness of the
star in DN (figure taken from ISR 97-08, Whitmore & Heyer); top plot is for 2-pixel radius
aperture, bottom is for 5-pixel radius aperture. A small horizontal offset has been made as
a function of the wavelength in order to reduce overlaps, and to show the dependence on
wavelength.
50
3. References
For more details on specific results, please refer to the documents listed below.
For paper copies of any documents listed here, please contact help@stsci.edu.
WWW
Advisories Documentation
Documentation:
Software
Tools
Software
Tools:
User
Support
User
Support:
Frequently
Asked
Questions
Frequently
Asked
Questions:
Astrometry
Calibration
WFPC2 Handbook
Calibration Reports
Instrument Science Reports
Calibration Monitoring
Memos
S.T.A.N.
WFPC2 Photometry
SYNPHOT
WFPC2 PSF Documentation
PSF Library Search
Tool
Dithering
Exposure Times
Exposure Time
Calculator
STScI Visits
Linear Ramp Filter
Calculator
WFPC2
Documentation
Miscellaneous
Polarizer
Calibration Tools
WFPC2 Group
Narrow Band
Photometry
WFPC2
Clearinghouse
Image Displays
Photometry
Proposal Preparation
PSFs
Other WFPC2 Documents
Other FAQ Lists
Figure 13: Overview and site layout of WFPC2 WWW pages (Wiggs). This map is accessible via WFPC2 homepage at the WFPC2 home page:
http://www.stsci.edu/ftp/instrument_news/WFPC2/wfpc2_top.html.
All topics listed on the roadmap are also direct links to the corresponding pages.
General Documents
The WFPC2 Instrument Handbook (http://www.stsci.edu/ftp/instrument_news/
WFPC2/wfpc2_bib.html)
The HST Data Handbook (http://www.stsci.edu/ftp/documents/html/data-handbook.html)
The 1997 HST Calibration Workshop (http://www.stsci.edu/stsci/meetings/
cal97/)
51
STAN, the Space Telescope Analysis Newsletter (http://www.stsci.edu/ftp/
instrument_news/WFPC2/wfpc2_stan.html)
The list of Frequently Asked Questions (http://www.stsci.edu/ftp/
instrument_news/WFPC2/wfpc2_top_faq.html)
Proposals in Phase II format, page maintained by PRESTO, at
http://www.stsci.edu/public/propinfo.html
Some of the Memos and Reports on WWW
WFPC2 Clearinghouse, Whitmore et al., (http://www.stsci.edu/ftp/
instrument_news/WFPC2/Wfpc2_clear/wfpc2_clrhs.html)
WFPC2 History file, Whitmore, Baggett & Wiggs, updated regularly (http://
www.stsci.edu/ftp/instrument_news/WFPC2/Wfpc2_memos/
wfpc2_history.html)
Standard Star and UV Monitoring Memo, Gonzaga, et. al., October 1997 (http://
www.stsci.edu/ftp/instrument_news/WFPC2/Wfpc2_memos/
wfpc2_stdstar_phot3.html)
WFPC2 Reference Files Currently in the Calibration Database, Baggett and Wiggs,
updated regularly (http://www.stsci.edu/ftp/instrument_news/WFPC2/
Wfpc2_memos/wfpc2_reffiles.html)
WFPC2 IDT Reference Files (http://www.stsci.edu/ftp/instrument_news/WFPC2/
Wfpc2_memos/wfpc2_idtrefs.html)
WFPC2 Hot Pixel Lists for Use with Warmpix (http://www.stsci.edu/ftp/
instrument_news/WFPC2/wfpc2_warmpix.html)
Guide to WFPC2 Synphot Tables, Baggett, May 1997 (http://www.stsci.edu/ftp/
instrument_news/WFPC2/Wfpc2_phot/wfpc2_synphot.html)
Table of SYNPHOT Zeropoints, Baggett and Casertano, May 1997, (http://
www.stsci.edu/ftp/instrument_news/WFPC2/Wfpc2_phot/
wfpc2_photlam.html)
WFPC2 Photometry Cookbook, Whitmore, (http://www.stsci.edu/ftp/
instrument_news/WFPC2/Wfpc2_phot/wfpc2_cookbook.html)
The Performance and Calibration of WFPC2, Holtzman, J.A., et al., 1995a, PASP, 107,
156 (also at http://www.stsci.edu/ftp/instrument_news/WFPC2/
wfpc2_doc.html#Wcal).
Photometric Performance and Calibration of WFPC2, Holtzman, J.A., et al., 1995b,
PASP, 107, 1065 (also at http://www.stsci.edu/ftp/instrument_news/
WFPC2/wfpc2_doc.html#Wcal).
The CTE effect as a function of preflash levels, Ferguson, May 96 (http://
www.stsci.edu/ftp/instrument_news/WFPC2/Wfpc2_cte/cte.html)
The long vs. short exposure time problem, Casertano, May 96 (http://www.stsci.edu/
52
ftp/instrument_news/WFPC2/Wfpc2_cte/shortnlong.html)
Tiny Tim, Krist, (http://scivax.stsci.edu/~krist/tinytim.html)
Modelling HST Focal-Length Variations, Hershey, November 1997 (copy available at
http://www.stsci.edu/ftp/instrument_news/Observatory/focus/focus2.html)
HST Focus History, Lallo, November 1997 (http://www.stsci.edu/ftp/instrument_news/
Observatory/focus/focus2.html)
ISR OTA-18: WFPC2 Focus Report, Casertano, January 1995 (http://www.stsci.edu/
ftp/instrument_news/Observatory/postscript/ota18.ps)
HST Focus Page, Lallo (http://www.stsci.edu/ftp/instrument_news/Observatory/services.html)
WFPC2 Instrument Science Reports
(Postscript copies are available online at
http://www.stsci.edu/ftp/instrument_news/WFPC2/wfpc2_bib.html)
97-11: WFPC2 Polarization Calibration, Biretta and McMaster
97-10: WFPC2 Synphot Update, Baggett, et al., 10/97
97-09: Results of WFPC2 Post-Servicing Mission 97 Calibration, Biretta et al., 09/97
97-08: New Results on Charge Transfer Efficiency and Constraints on the Flat-Field,
Whitmore and Heyer, 09/97
97-07: WFPC2 Electronics Verification, Stiavelli and Mutchler, 07/97
97-06: WFPC2 Cycle 7 Calibration Plan, Casertano, et al., 08/97
97-05: WFPC2 CTE/Residual Images, Biretta and Mutchler (in progress)
97-04: Properties of WFPC2 Bias Frames, O’Dea et al., 06/97
97-03: Summary of WFPC2 SM97 Plans, Biretta et al., 02/97
97-02: WFPC2 Cycle 5 Calibration Closure Report, Casertano and Baggett, 02/97
97-01: Impact of Focus Drift on Aperture Photometry, Suchkov and Casertano, 01/97
96-08: WFPC2 Cycle 6 Calibration Plan, Casertano, et al., 07/96
96-07: WFPC2 Throughput Stability in the Ultraviolet, MacKenty and Baggett, 05/96
96-06: Photometric Calibration of WFPC2 Linear Ramp Filter Data in SYNPHOT,
Biretta, Baggett, and Noll, 07/96
96-05: Wavelength / Aperture Calibration of the Linear Ramp Filters, Biretta, et al., 05/96
96-04: Effects of Contamination on WFPC2 Photometry, Whitmore, et al., 06/96
96-02: Contamination Correction in SYNPHOT for WFPC2 and WF/PC-1, Baggett, et al.,
02/96
96-01: Internal Flat Field Monitoring, Stiavelli and Baggett, 01/96
95-07: WFPC2 Cycle 4 Calibration Summary, Baggett, Casertano, and Biretta, 12/95
53
95-06: A Field Guide to WFPC2 Image Anomalies, Biretta, Ritchie, and Rudloff, 08/95
95-04: A Demonstration Analysis Script for Performing Aperture Photometry, Whitmore
and Heyer, 07/95
95-03: Charge Transfer Traps in the WFPC2, Whitmore and Wiggs, 07/95
95-02: The Geometric Distortion of the WFPC2 Cameras, Gilmozzi, et al., 06/95
95-01: WFPC2 Polarization Observations: Strategies, Apertures, and Calibration Plans.,
Biretta and Sparks, 02/95
94-03: WFPC2 Pipeline Calibration, Burrows, 12/94
94-01: Large Angle Scattering in WFPC2 and Horizontal "Smearing" Correction, Krist
and Burrows, 10/94
93-01: Polarizer Quad Nomenclature, Mark Clampin, 3/93
92-06: WFPC2 CCDs, Mark Clampin, 12/92
92-05: WFPC2 AFM and POMM Actuation Algorithm, J.T. Trauger et al., 7/92
92-03: WFPC2 Science Observation and Engineering Modes, Trauger and Brown, 10/92
92-02: System Level Contamination Issues for WFPC2 and COSTAR, M. Clampin, 9/92
WFPC2 Technical Instrument Reports
These are informal, internal reports; paper copies available on request.
97-11: Long-term Study of Bias Jumps, O’Dea et al., 11/97
97-10: WFPC2 Photometry from Subtraction of Observed PSFs, Surdej et al., 10/97
97-09: WFPC2 PSF Library, Wiggs et al., 9/97
97-08: SMOV Flat Field Check (prop 7019), Biretta and Wiggs, 9/97
97-07: WFPC2 SM97 Internal Monitoring (prop 7022), Mutchler and Stiavelli, 7/97
97-06: SMOV2 Check of WFPC2 PSF Stability, Fruchter and McMaster, 9/97
97-05: Results of the WFPC2 SM-2 Lyman-α Throughput Check (prop 7018 and
7029), O’Dea, Baggett, and Gonzaga, 6/97
97-04: VISFLAT Channel Monitoring, Stiavelli, 5/97
97-03: OTA Focus During SMOV, Casertano et al., 5/97
97-02: SM-2 UV Monitoring and Cool-down Procedure (prop 7016 , 7122), Stiavelli
et al., 5/97
97-01: Results of the WFPC2 SMOV-97 Relative Photometry Check (prop 7020),
Whitmore, Gonzaga, and Heyer 4/97
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