Instrument Science Report WFPC2 01-06
WFPC2 Cycle 8 Closure Report
S. Baggett, S. Gonzaga, J. Biretta, S. Casertano, I. Heyer, A. M. Koekemoer,
J. Mack, M. McMaster, A. Riess, A. Schultz, M. S. Wiggs
June 11, 2001
ABSTRACT
This report describes in detail the WFPC2 observations used to maintain and improve the
quality of WFPC2 calibrations during Cycle 8 and their status as of May 2001. The results
from servicing mission 3a (December 1999) have been reported separately.
1. Introduction
Cycle 8 nominally spanned the time interval from July 1, 1999 to June 30, 2000. The
WFPC2 calibration program conducted during that period was aimed at maintaining the
calibration of WFPC2 via monitoring programs, continuing some proposals from previous
Cycles, and performing new tests to improve our understanding in several key areas, such
as the effects of CTE. Observing during Cycle 8 was interrupted from Nov 13,1999 to Dec
27, 1999, while HST was in Zero Gyro safemode due to the failure of a gyroscope. Servicing Mission 3A was performed in Dec 1999, followed by an Orbital Verification period;
WFPC2 science and Cycle 8 calibration observations were resumed on Jan 12, 2000. A
full report of WFPC2 Servicing Mission Orbital Verification calibration results can be
found in Instrument Science Report 00-02 (Casertano et al., ISR 00-02).
Monitors
As in previous cycles, a substantial part of the program consisted of routine monitors
and decontamination (decon) procedures. The decons were performed on a ~28 day basis
to remove UV contaminants and anneal hot pixels. The monitoring observations associated with the decons were similar to those from previous Cycles, allowing efficient
tracking of the overall long-term photometric throughput of the camera, the monthly
throughput decline rates due to contaminant buildup on the CCD windows and the return
to nominal throughput after the decons. We also monitored the PSF properties at different
wavelengths, the OTA focus, and the general health and performance of the cameras. One
new aspect of the monitoring program was to combine previously separate programs tied
1
to decons (internals, photometric monitor, focus check, UV throughput) into the decon
proposal itself, to help minimize scheduling problems. As this resulted in an excessively
long proposal, the decon proposal was split into two pieces (8441, 8459; see Table 1), one
to run before and one to run after SM 3a.
Other continuing programs consisted of the standard darks program (six darks per
week, used for reference files and hot pixel lists), the supplemental darks program (0-3
darks per day, low priority, for archive only), and the weekly internal monitor (biases and
kspots). The Earth flat program was also extended, to allow tracking and correction for
changes in the flatfield. Following the general plans of previous cycles, streak flats in a
subset of filters were obtained to construct superflats for generating the pipeline flats.
The monitoring proposals included the astrometric monitor, CTE monitor, intflat/visflat sweeps, and UV internal flats. Data from the astrometry program, which also included
internal kspots observations, are being used to measure chip position shifts and changes in
the astrometry (work in progress, Casertano et al., 2001). Observations from the CTE
monitor program are currently being analyzed, and two ISRs will be released shortly
(Heyer et al., 2001; Whitmore et al., 2001). Internal flats, taken for verification of the pixel
to pixel flatfield response, are also being analysed; some of these have been useful in
determining the repeatability of the shutter blade mechanism (Riess et al., TIR 01-01).
Many of these programs provided baseline comparison observations for the post-servicing
mission checks (Casertano et al., ISR 00-02).
Special Programs
Several special programs that were executed in previous cycles were run as shorter
versions in Cycle 8: the photometric and PSF characterization proposals, the polarization
check, and the linear ramp filter proposal. Data analysis for these programs is still in
progress.
Five new special programs, designed to address the remaining photometric issues
(CTE and long vs short) as well as user concerns from previous cycles were executed in
cycle 8. The noiseless preflash proposal was used to test whether illuminating the detectors prior to an exposure reduces the impact of the CTE and long vs short anomalies. The
preflashes were done using intflats that were read out prior to the external exposures,
thereby minimizing additional noise in the observations. Darks were also taken before the
visit and during occultations, to insure that no prior exposures will effectively preflash the
non-preflashed images. Analysis of this data has shown that the detected counts are
slightly enhanced (~3%) for point sources far from the horizontal shift register (at Y=800)
for the preflashed exposure. The second external image after a preflash showed a decrease
in the detected counts, i.e., the CCDs essentially returned to a previous sensitivity level.
(Schultz, Heyer, & Biretta, ISR 01-02).
2
The CTE for extended sources proposal was a first effort to directly measure the effect
of CTE on small (2-3”) extended sources. A galaxy cluster was positioned in chips 2 and
4, to obtain photometry of the galaxies at different Y-locations, low Y in one chip, high Y
in the other chip. The average profile of the galaxy residuals was found to be distinctly
asymmetric, confirming that most of the charge is lost on the amplifier side of the galaxy.
Since the leading edge of the galaxy fills the traps, the side of the galaxy away from the
amplifier suffers less charge loss (Riess, ISR 00-04). Analysis of the effect on aperture
photometry is still in progress (Baggett et al., 2001).
Observations to check the photometric calibration for very red stars (two late M
dwarfs, VB8 and VB10) in BVRI were also obtained in cycle 8. The current zeropoints
(based on a white dwarf UV standard and verified via solar analog data) and the color
transformations from HST BVRI to groundbased BVRI are highly uncertain for stars this
red; this program will provide straightforward empirical calibration. In addition, a short
single-orbit program will allow variations in the plate scale to be measured as a function of
wavelength, particularly in the UV, where the index of refraction in the MgF window
increases rapidly. Finally, a special program was developed to help improve the quality of
the UV flatfields: the Earth flats were obtained in a variety of UV filters as well as some
crossed filter combinations to account for any redleak contributions. The data for these
programs are in the archive and are candidates for “calibration outsourcing” (where external groups propose and are funded to perform the analysis).
2. Format
Table 1 summarizes the program as executed during Cycle 8, including proposal titles
and numbers, frequency with which the program was executed, orbits used (numbers provided by PRESTO), analysis products, accuracy of the results, and general notes. The
remainder of the report contains details for every proposal: the plan is presented on the left
of each page and results are summarized on the right. The proposal pages are intentionally
in landscape format, to faciliate comparison of the plan and results. Finally, a detailed bibliography is provided, listing any new documents since the last closure report as well as
pointers to items of general interest. As always, any of the Phase II versions of the proposals can be viewed at http://www.stsci.edu/public/propinfo.html.
3
Table 1: Summary of WFPC2 Cycle 8 Calibrations
Time (orbits)
ID
Proposal Title
Frequency
Scheduling
Accuracy
Products
Required
“External” “Internal” Required
Notes
Routine Monitoring Programs
8441 WFPC2 Decons & Associated Observations 1-2/4 wks 25 [32]
8459
80 [72]
every 28 d
Synphot,
CDBS
8442 Standard Darks
weekly
252 [324]
every 7 d
CDBS
8443 Supplemental Darks (8460, 8461)
0-3/day
808 [1308] anytime
n/a
31 [45]
every 7d
CDBS
-
141 [442]
mid-cycle
CDBS
8444 Internal Monitor
8445 Earth Flats
3/4 wks
continuous
8446 Astrometric Monitor
2/cycle
2
early & late ISR
8447 CTE Monitor
2/cycle
9 [4]
mid- & late ISR
8448 Intflat and Visflat Sweeps
1/cycle
8449 UV Flats Internal Monitor
1/cycle
23 [43]
2
1-2%
1 e-/hr
Includes decons, phot. monitor, focus
monitor, internals, UV throughput
Also hot pixel lists for WWW.
For archive only, no analysis provided
0.8e /pixel New superbiases, not run on decon wks
0.3%
Also LRF, Methane quads
0.05’’
Also K-spots & platescale check in red
0.01 mag Extra orbits needed taken from reserve.
mid-cycle
TIR
0.3%
Mostly intflats
mid-cycle
TIR
2-8%
Uses UV cal channel lamp.
Special Calibration Programs
8451 Photometric Characterization
1
2
mid-cycle
8452 PSF Characterization
1
4 [2]
8453 Polarization
1
6
2.5%
Subset of Cycle 7 proposal, as check.
late in cycle CDBS
10%
Extra needed due to lack of scans.
early in cyc CDBS
3-5%
Subset of Cycle 6, as check
8454 Linear Ramp Filters
1
11 [4]
late in cycle CDBS
3%
Incl. 7 orbits carried over from # 8054.
8450 Noiseless Preflash
1
6 [5]
early in cyc TIR
0.01 mag
Extra orbit approved for initial darks.
8455 Photometry of Very Red Stars
1
2
mid-cycle
ISR
2-5%
Outsourcing candidate.
8456 CTE for Extended Sources (2-3”)
1
4
mid-cycle
ISR
0.01 mag
Outsourcing candidate.
8457 UV Earth Flats
continuous
early in cyc CDBS
3-10%
Outsourcing candidate.
8458 Plate Scale Verification
1
1
mid-cycle
0.05%
Outsourcing candidate.
8800 Moving Observations of a
Fixed Star Cluster
1
4
late in cycle ISR
~10% reserve for unexpected items
TOTAL TIME (including all executions)
4 [10]
240 [720]
7
ISR
ISR
A new proposal initiated by director’s
office in spring 2000.
Placeholder.
90 [73] 1579[2964]
Orbits listed in Time column are orbits actually used; [] marks initial requested number when different from the used orbits. Differences are discussed under
each individual proposal’s summary.
Proposal ID 8441/8459: WFPC2 Cycle 8: WFPC2 Decontaminations and Associated Observations
Plan
Results
Purpose Monthly WFPC2 decons. Instrument monitors tied to decons:
Modifications Upon approval from TTRB (Telescope Time Review Board),
photometric stability check, focus monitor, pre- and post-decon
one extra internal orbit of uvflats was inserted into 8459. These
internals--bias, intflats, kspots, & darks, UV throughput checks.
uvflats were to provide a baseline dataset taken 4 weeks after a
decon (all archival uvflats had been done no more than a few
days after a decon). The baseline was necessary in order to be
prepared for a possible zero-gyro safemode; the uvflats may
possibly be useful as a rough measurement of the contamination
state of WFPC2, during time periods when external observations are not feasible.
Description Decontamination:UV-blocking contaminants removed and hot
pixels annealed, by warming the CCDs to +20C for 6 hours.
Internals: intflats, biases, darks & kspots, before/after decons.
Photometric and Focus Monitor: Standard star GRW+70d5824
is observed after each decon and before every other decon: (1)
F170W in all chips to monitor far UV contamination. (2) PC
focus monitor observations in F439W, F555W, F814W. (3)
F160BW, F218W, F255W, F336W, F439W, F555W, F814W
observed in a different chip each month.
Execution Some exposure time decreases or occasionally removal of exposures in the GRW+70d5824 visits were required once the actual
visibility windows were determined by the schedulers. Six visits
(including two externals) in 8812 and 23 visits (including six
externals) in 8459 were withdrawn due to HST zero-gyro safing
in December ‘99.
UV Throughput: PC & WF3 UV observations in all UV filters,
popular UV filters in all chips, to verify that the UV spectral
response curve is unchanged. Also check methane Quads.
Fraction 100%
GO/GTO
Programs
Supported
Resources 32 external orbits (13 decon cycles, 3 spare decons, + 2 extra for
Required: smooth Cycle 7 to 8 transition). Also includes 4 orbits for UV
Observation throughput and 1 orbit for methane quad photometry check.
Time-line Observations taken every month for post-decon data, and every
other month for pre-decon data.
Resources 25 external orbits (10 for 8441 and 15 for 8459)
Used: 80 internal orbits (44 for 8441 and 36 for 8459)
Observation
Plan
Results
Products SYNPHOT, CDBS, Instrument Handbook, TIPS meetings,
WWW reports,TIR, ISR.
Products Results were presented at TIPS (Telescope and Instrument Performance) meetings and included in WFPC2 Instrument Handbook updates. Tables and photometric monitoring plots are
updated regularly on WWW.
Darks from this program were used not only for dark reference
files and hot pixel tables but also for ISR 99-04, Time Dependence of CTE from Cosmic Ray Trails (Riess et al.) and ISR 0003, Update on Charge Trapping, and CTE Residual Images in
WFPC2 (Baggett et al.). These results are discussed in more
detail as part of the Standard Darks (8442) and Daily Darks programs.
The PC, F555W images of the standard star were used in monitoring focus and determining secondary mirror moves necessary
to maintain focus; results are regularly posted to WWW Observatory Support pages.
Decon dates are also posted regularly to WFPC2 History File on
WWW; list of all decons done to date can be found in Table 2.
Accuracy Photometry: less than 2% discrepancy btwn results, 1% rms
Goals expected. Focus measurement: 1.5 micron accuracy w/goal of 1
micron. UV throughput: better than 3%. Flatfield: temporal
variations monitored at 1% level. Gain ratios: stable to better
than 0.1%.
Accuracy Decon procedures were successful, restoring WFPC2 UV
Achieved throughput, fluctuations are 2% or less peak to peak longwards
of F336W (see Fig. 1, taken from WWW Photometric Monitoring memo; Gonzaga et al.) and annealing hot pixels. The focus
monitor results are routinely reported on the WWW Observatory Support pages (Lallo et al.; see also Fig. 2, below); typically, ~1 micron RMS of secondary mirror motion is achieved.
Scheduling& Decons required every 4 weeks. Observations tied to within +/Special 1 week of decons. Darks should be NON-INT to prevent residRequirements ual image problems.
Continuation Continue monitors in present form for cycle 9, adding extra
Plans F555W GRW+70D5824 PC observations for more focus
checks.
Figure 1: Photometric monitoring results for PC1 and WF3, from Feb 1994 to March 2001; plot is regularly updated online (WWW Photometric Monitoring
memo; Gonzaga et al.). Note the UV contamination effects in the bluer filters and restoration to nominal UV throughput after each decon (upper envelope of
points); long-term trends were investigated and reported in Cycle 7 (WFPC2 Long-Term Photometric Stability, ISR 98-03, Baggett & Gonzaga).
Figure 2: History of the PC focus since Jan 1994. The focus values have been corrected for breathing (single-orbit timescale) effects using the Hershey model;
dates indicated with short, vertical lines mark times of secondary mirror moves (magnitude of moves are in parentheses). Figure was taken from the Observatory Aperture and Pointing WWW pages (Lallo et al.).
Table 2: WFPC2 decontamination dates, taken from the WFPC2 History Memo on the WWW (Baggett & Wiggs). For length of time chips are kept warm,
please refer to the online memo.
date
MJD
1994
date
MJD
date
MJD
date
MJD
date
MJD
17 Oct 09:43
50007.4053
21 Mar 03:35
50528.1494
Aug 21 12:23
51046.5161
23 Mar 04:53
51626.2035
Feb 22 11:37
49405.4840
15 Nov 08:53
50036.3706
05 Apr 08:50
50543.3681
Sep 15 02:18
51071.0963
Apr 18 19:37
51652.8174
Mar 24 11:08
49435.4639
14 Dec 07:03
50065.2929
25 Apr 23:00
50563.9583
Oct 14 02:39
51100.1104
May 17 22:08
51681.9225
Apr 24 00:49
49466.0340
1996
15 May 20:18
50583.8460
Nov 10 05:01
51127.2090
Jun 14 10:27
51709.4354
May 23 15:00
49495.6250
11 Jan 23:24
50093.9750
07 Jun 13:06
50606.5461
Dec 08 14:19
51155.5969
Jul 11 18:12
51736.7583
Jun 13 11:02
49516.4597
11 Feb 00:30
50124.0208
24 Jun 11:04
50623.4612
Dec 31 03:29
51178.1453
Aug 06 21:43
51762.9049
Jul 10 11:40
49543.4861
10 Mar 00:21
50152.0147
24 Jul 18:42
50653.7795
1999
Aug 10 23:58
51766.9992
Jul 28 07:12
49561.3000
02 Apr 00:16
50175.0111
20 Aug 02:17
50680.0952
Jan 28 01:06
51206.0458
Sep 7 07:09
51794.2986
Aug 27 09:46
49591.4069
04 May 17:09
50207.7146
17 Sep 17:24
50708.7256
Feb 23 22:43
51232.9471
Oct 4 01:49
51821.0758
Sep 25 00:46
49620.0319
28 May 06:16
50231.2614
13 Oct 18:00
50734.7506
Mar 25 20:15
51262.8441
Oct 6 16:14
51823.6767
Oct 21 00:41
49646.0285
22 Jun 22:15
50256.9277
14 Nov 05:19
50766.2217
Apr 20 23:47
51288.9910
Nov 2 11:50
51850.4931
Nov 19 17:29
49675.7285
28 Jul 13:34
50292.5653
10 Dec 09:40
50792.4027
May 19 08:28
51317.3528
Nov 8 00:00
51856.0000
Dec 18 06:00
49704.2500
23 Aug 10:10
50318.4242
1998
Jun 16 07:07
51345.2965
Nov 28 18:58
51876.7903
18 Sep 16:25
50344.6840
Jan 08 00:03
50821.0025
Jul 14 04:07
51373.1715
Dec 30 07:25
51908.3093
1995
13 Jan 16:14
49730.6764
18 Oct 07:46
50374.3236
Feb 01 19:15
50821.0025
Aug 10 04:00
51400.1667
2001
12 Feb 01:54
49760.0792
12 Nov 09:40
50399.4031
Mar 06 09:18
50878.3877
Sep 9 01:27
51430.0604
Jan 23 17:08
51932.7141
11 Mar 14:30
49787.6042
15 Dec 00:00
50432.0417
Mar 31 12:54
50903.5376
Oct 5 15:27
51456.6437
Feb 20 04:34
51960.1909
8 Apr 10:29
49815.4368
19 Dec 12:33
50436.5229
May 02 12:26
50935.5186
Nov 3 06:51
51485.2854
Mar 7 05:01
51975.2090
7 May 01:13
49844.0507
1997
Jun 07 21:01
50971.8757
Dec 28 19:43
51540.8215
Mar 21 12:23
51989.5163
2 Jun 18:30
49870.7708
07 Jan 23:41
50455.9875
Jun 09 23:59
50973.9993
2000
Apr 17 22:36
52016.9421
27 Jun 20:00
49895.8333
09 Feb 00:00
50488.0006
Jun 12 08:01
50975.3340
Jan 03 01:37
51546.0674
May 15 23:23
52044.9744
30 Jul 08:50
49928.3681
23 Feb 19:08
50502.7978
Jun 25 06:59
50989.2910
Jan 17 16:27
51560.6854
27 Aug 05:43
49956.2382
27 Feb 06:31
50506.2721
Jun 28 14:06
50992.5881
Jan 31 15:48
51574.6583
22 Sep 03:40
49982.1528
04 Mar 10:16
50511.4278
Jul 22 18:56
51016.7889
Feb 25 10:43
51599.4465
Proposal ID 8442: WFPC2 Cycle 8: Standard Darks
Plan
Purpose Measure dark current & identify of hot pixels.
Description Six 1800s exp/week with the shutter closed, five with clocks off,
one with clocks on. This frequency is required due to the high
formation rate of new hot pixels (several tens/CCD/day). Five
darks per week are required for cosmic ray rejection, counterbalancing losses due to residual images, & improving the noise
of individual measurements. Sometimes, no usable darks are
available for a given week due to residual images, resulting in a
longer-than-usual gap in the hot pixel lists, but in a decon week,
information on hot pixels that became hot and then annealed
would be lost irretrievably. As a result, pre-decon darks (see
Decon proposal) are executed NON-INT and at least 30 min
after any WFPC2 activity.
Fraction 90%
GO/GTO
Programs
Supported
Results
Modifications None.
Execution Some visits lost due to HST zero-gyro safing in December ‘99.
In the event of missing darks, additional information on hot pixels was occasionally obtained from the dark frames taken via the
Supplemental Darks program (8443, 8460, 8461). The supplemental darks are not used to generate dark reference files.
Time-line Observations taken every week, except for decon weeks.
Resources 324 internal orbits (occultation periods), enough 6-dark sets for
Required: Cycle 8 plus additional darks to ensure smooth Cycle 7 to 8
Observation transition.
Resources 252 internal orbits. Not all extra orbits requested to cover cycle
Used: transition period were needed; in addition, darks were not taken
Observation during the safing.
Products Weekly darks delivered to CDBS and monthly tables of hot pixels on the WWW. Superdark reference files.
Products New superdark and dark reference files for pipeline routinely
delivered to CDBS (Wiggs, Mack, & Baggett) and available via
Starview or WWW Reference File listing.
Monthly hot pixel lists are posted to WWW (Wiggs et al.) and
regular updates are made to WFPC2 History File on WWW
(Baggett & Wiggs).
ISR 01-01, Creating WFPC2 Dark Reference Files (Mack &
Wiggs), ISR 99-04, Time Dependence of CTE from Cosmic
Ray Trails (Riess et al.) and ISR 00-03, Update on Charge Trapping and CTE Residual Images in WFPC2 (Baggett et al.).
Updates to Instrument Handbook.
Plan
Accuracy Require ~1 e-/hour (single-pixel rms) accuracy for most science
Goals
applications. Expected accuracy in a typical superdark is 0.05 e/hour for normal pixels. The need for regular darks 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.
Scheduling& Do not schedule during decon weeks (those darks are in decon
Special proposal).
Requirements
Results
Accuracy The typical superdark (120 dark frames) accuracy is ~0.07 e-/
Achieved hour. Dark reference files are generated from a superdark plus
hotpixels identified from a weekly (5 dark frames) dark and
delivered for use in the OPUS pipeline. HISTORY keywords in
the dark reference file headers provide details on the generation
of each dark; in addition, ISR 01-01, Creating WFPC2 Dark
Reference files (Mack & Wiggs) provides scripts and instructions for observers who may wish to generate their own pipeline
dark.
As illustrated in Fig. 3, after steadily increasing over the first 5
years, the low-level dark current has now begun to stabilize
(Mack et al., ISR 01-05). The lack of increase in the dark current is presumed due to solar maximum and the associated
decrease in cosmic ray events (a major component of the dark
level stems from CCD window fluorescence due to cosmic
rays). Over the 6.5 year period, the dark current has increased
by a factor of ~2.0 in the WFC CCDs and by a factor of ~1.3 in
PC. The long-term increase is unlikely to impact adversely the
quality of WFPC2 observations (dark current is generally a
minor contributor to the total noise) except perhaps in special
cases, such as faint sources observed in AREA mode through
narrow-band or UV filters. The changes are included in the pipeline reference files.
The darks have also been used for some CTE studies. Riess et
al., (ISR 99-04) found that cosmic ray trails in darks can be used
to monitor CTE changes over time. Their analysis showed that
while the charge in the trails does not account for all observed
CTE losses, some charge is being trapped and released on short
timescales (~seconds or less). The CTE losses measured using
the trails show a steady growth, with some evidence for an
acceleration (see Fig. 4). The technique may provide a precise
way to monitor CTE with greater time sampling than is currently feasible and without the cost of additional pointed observations.
Continuation Continue same observations for cycle 9.
Plans
Figure 3: Dark levels for the central 400x400 pixels in each camera, at gain 7, as a function of time (figure from Mack et al., ISR 01-05) Each data point represents the mean of 5 1800 sec dark frames taken just after the monthly decons.
Figure 4: Change over time in counts detected in cosmic ray CTE-tails found in darks; each point represents a dark frame (Figure 6 from Reiss et al., ISR 0004).
Counts in CR tails @ pix=800 (DN)
8
WFPC2 CTE-tails vs. Time
6
E
T
C
Y-
4
E
X-CT
2
0 1994
1995
4.95•104
1996
1997
1998
1999
5.00•104
5.05•104
5.10•104
Modified Julian Date (days)
5.15•104
Proposal ID 8443/8460/8461: WFPC2 Cycle 8: Supplemental Darks
Plan
Purpose Obtain very frequent monitoring of hot pixels.
Description This program is designed to provide up to three short (1000s)
darks per day, to be used primarily for the identification of hot
pixels. Shorter darks are used so that observations can fit into
almost any occultation period, making automatic scheduling
feasible. Supplemental darks will be taken at low priority, and
only when there is no other requirement for that specific occultation period. This program is complementary with the higher
priority Standard Darks proposal that has longer individual
observations for producing high-quality pipeline darks and
superdarks. Note that hot pixels are often a cause of concern for
relatively short science programs, since they can mimic stars or
mask key features of the observations. (About 400 new hot pixels/CCD are formed between executions of the Standard Darks
program. These observations will be made available as a service
to the GO community, and there is no plan to use them in our
standard analysis and products.
Fraction 30%
GO/GTO
Programs
Supported
Resources Total of 1308 internal orbits (occultation periods), which allows
Required: for a maximum of 3 darks per day plus enough extra to ensure a
Observation smooth transition between Cycle 7 and 8.
Products None.
Results
Modifications None.
Execution No anomalies. A few observations were occasionally dropped
by the scheduling system, which was not a problem as these
darks are to be scheduled as low-priority. Some visits lost due to
HST zero-gyro safing in December ‘99.
Time-line Observations taken three times a day and archived. No analysis
performed.
Resources 808 (333 + 412 + 63) internal orbits.
Used:
Observation
Products Archived daily darks are available to GOs via Starview. Very
occasionally, when the standard darks are lost (e.g., due to the
telescope safing), some of the daily darks are used to generate
the hot pixel lists. However, dark reference files for the pipeline
are always generated from the longer exposure-time standard
darks, never from these shorter daily darks.
Some of the daily darks were also used in ISR 99-04, Time
Dependence of CTE from Cosmic Ray Trails (Riess, et al.); discussed in more detail under the Standard Darks program) and
ISR 00-03, Update on Charge Trapping and CTE Residual
Images in WFPC2 (Baggett et al.), discussed below.
Plan
Results
Accuracy For archive only, no STScI analysis provided.
Goals
Accuracy The daily darks are archived only.
Achieved Some of these daily darks (as well as some standard darks) were
used to follow-up on a study of charge trapping as measured in
residual images found in darks (Baggett et al., ISR 00-03); Fig.
5 illustrates the effect. The new data support the original finding
that the amount of charge trapped appears correlated with the
maximum intensity clocked through the pixel during readout
(Biretta & Mutchler, ISR 97-05). Furthermore, the amount of
charge seen in the residual images appears to have been stable
over the six years, in marked contrast to the evolving CTI
(charge transfer inefficiency) found via photometry of external
stellar images (e.g., Whitmore et al., 1999) and analysis of cosmic ray tails in dark frames (Riess et al., ISR 99-04). Finally,
evidence was found that these residuals can be relatively longlived: some residuals appeared in darks started more than 20
minutes after the external image was read out.
Scheduling& Scheduled at low priority, non-interference basis, maximum of
Special 3/day. Will require 3 proposal IDs due to large number of visits
Requirements (1 dark/visit to maximize scheduling flexibility).
Continuation Continue program through cycle 9.
Plans
Figure 5: Left: the maximum intensity in each column of an external image of Mars (solid line), plotted as a function of column, and the average intensity distribution over the target only (dashed line). Right: the average of the residual charge rows in the median-filtered dark that followed the external image (Figure
1 from Baggett et al., ISR 00-03).
medu477cg01r
2000
1.5
1500
1.25
DN
max DN
u58r010fr
1000
500
1
.75
0
200
400
column
600
.5
200
400
column
600
Proposal ID 8444: WFPC2 Cycle 8: Internal Monitor
Plan
Purpose Verify the short-term instrument stability at both gain settings.
Description Each set of internal observations consists 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.
Fraction 100%
GO/GTO
Programs
Supported
Resources 45 internal orbits (occultation periods), plus existing Cycle 7
Required: visits, will provide sufficient repetions for Cycle 8.
Observation
Results
Modifications None.
Execution No anomalies other than some visits lost due to HST zero-gyro
safing in December ‘99.
Time-line Executed weekly, except on decon weeks.
Resources 31 internal orbits. Not all extra orbits requested to cover cycle
Used: transition period were needed; in addition, internals were not
Observation taken during the safing.
Products Superbiases delivered annually to CDBS; TIPS reports on possible buildup of contaminants on the CCD windows (worms) as
well as gain ratio stability, based on intflats. A Science Instrument Report will be issued if significant changes occur.
Products Updated bias files have been installed in CDBS (Gonzaga et al.)
and are accessible via Starview or WWW Reference File listing.
Some data was used as baseline data for SM3a verification
(O’Dea et al., TIR 00-04; Casertano et al., ISR 00-02) and are
also being used in a long-term study Gonzaga et al. (in
progress). Updates have also been included in the WFPC2
Instrument Handbook.
Accuracy Approximately 120 bias frames are used for each superbias
Goals pipeline reference file, generated once a year; accuracy is
required to be better than 1.5 e-/pixel, and is expected to be 0.8
e-/pixel.
Accuracy No significant differences were found between the old and new
Achieved biases. Statistics for these files are listed in Table 3.
The intflat analyses have found small (few tenths of a percent)
changes in the intflat lamp brightness across cycle 8, well within
the gradual long-term trends (see Fig. 6). There are also small
changes in the illumination patterns: ratios of intflats taken in
mid-99 and Jan. 2000 show small amplitude (0.1 - 1%) large
scale variations which are chip and wavelength dependent
(O’Dea et al., TIR 00-04). These variations are somewhat larger
than those seen in a similar time interval from Jan. 99 to mid-99.
The four Carley bulbs may not be varying in the same manner,
which would induce the observed changes in the illumination
pattern of the intflats. The variation in the lamp brightness may
be associated with changes in temperature.
Plan
Results
Scheduling& Do not schedule on decon weeks (internals for those weeks are
Special in decon proposal).
Requirements
Continuation Cycle 9 will use the same program structure but include new
Plans visits of F502N intflats that execute only during decon weeks
(intflats intended for preflash corrections).
Table 3: Statistics (in DN) of superbias files delivered to CDBS (Gonzaga et al.); pedigree column lists epoch of bias frames used in the superbias.
PC
WF2
WF3
WF4
pedigree
name
gain
of superbias reference file
mean stddev mean stddev mean stddev mean steddev dates of bias frames used to generate reference files
i2i1201qu
7
0.343 0.128
0.313 0.154
0.295 0.134
0.318 0.146
31/07/96-30/11/97
i9817383u
7
0.347 0.149
0.327 0.254
0.314 0.494
0.344 0.306
01/12/97-13/08/98
j9a1612mu
7
0.345 0.141
0.336 0.267
0.330 0.533
0.351 0.388
29/08/98-21/08/99
kcd1557lu
7
0.350 0.139
0.335 0.188
0.326 0.523
0.342 0.278
26/08/99 - 29/08/00
i2h1025iu
15
0.176 0.075
0.160 0.085
0.149 0.079
0.169 0.090
22/08/96-30/11/97
j3f1747qu
15
0.183 0.084
0.163 0.131
0.168 0.087
0.185 0.161
01/12/97-13/08/98
j9a1612nu
15
0.188 0.081
0.162 0.137
0.154 0.267
0.181 0.205
29/08/98-21/08/99
kci1424gu
15
0.183 0.080
0.172 0.101
0.159 0.266
0.169 0.146
26/08/99 - 29/08/00
Figure 6: Observed counts in the inner 300x300 pixels of the F555W intflats as a function of Modified Julian Date, one plot per camera. Open and closed circles are for gains 15 and 7, respectively; Servicing Missions are marked with short vertical lines while the Cycle 8 time span is delineated with long dashed
lines. Plots were generated from MEANC300 header keyword values, after subtracting an average bias level (DEZERO keyword); figure is from Gonzaga et
al. (in prep).
Proposal ID 8445: WFPC2 Cycle 8: Earth Flats
Plan
Purpose Monitor flatfield stability.
Description As in Cycle 7 programs 7625 & 8053 , sets of 200 Earth streak
flats are taken to construct high quality narrow-band flatfields
with the filters 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 are 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-to-pixel variations in the flatfields. The same
strategy used in Cycles 5, 6, and 7 is implemented here.
Fraction 100%
GO/GTO
Programs
Supported
Resources 442 internal orbits (occultation periods).
Required:
Observation
Results
Modifications No modification.
Execution No anomalies.
Time-line Observations taken throughout cycle.
Resources 141 internal orbits. Requested resources were for number of
Used: Earth flats; as typically 2-6 Earth flats could be packed into each
Observation visit, the final visits required were only 141 instead of 442.
Products New flatfields generated and delivered to CDBS if changes
detected.
Products Reference file generation and delivery are planned for later in
2001. Some Cycle 8 images were used as a baseline for SM3a
flatfield verification (TIR 00-01, Koekemoer et al.; Casertano et
al., ISR 00-02) and results have been presented posters at AAS
meetings.
Accuracy The single-pixel signal-to-noise ratio expected in the flatfield is
Goals 0.3%.
Accuracy Some Earth flats were used in the SM3a flatfield check (TIR 00Achieved 01, Koekemoer et al.). A comparison of Earth flats taken before
and after the 1999 Servicing Mission 3A found that most of the
field-of-view showed no change (<0.3%) in flat field calibration.
The largest changes were seen only near the CCD corners, particularly near the apex, reaching ~1.5%; they were attributed to
long-term changes in the camera geometry, rather than SM3a.
Scheduling& None.
Special
Requirements
Continuation Continue same observations for cycle 9.
Plans
Proposal ID 8446: WFPC2 Cycle 8: Astrometric Monitor
Plan
Purpose Verify relative positions of WFPC2 chips with respect to one
another.
Description The rich field in ω Cen (same positions as cycle 7 proposal
7627) is observed with large shifts (35’’) in F555W only, at two
different times during Cycle 8. This will indicate whether there
are shifts in the relative positions of the chips or changes in the
astrometric solution at the sub-pixel level. Kelsall spot images
will be taken in conjunction with each execution. The K-spots
data and some external data indicate that shifts of up to 1 pixel
may have occurred since mid-1994.
Fraction 20%
GO/GTO
Programs
Supported
Resources 2 pointed orbits and 2 occultation periods
Required:
Observation
Results
Modifications None.
Execution No anomalies.
Time-line Executed Jun 22, 1999 & Feb 15, 2000.
Resources 2 external orbits; 2 occultation periods (1 immediately after
Used: each 1 external orbit).
Observation
Products TIPS, Technical Instrument Report, update of chip positions in
PDB and of geometric solution in STSDAS tasks metric and
wmosaic if significant changes are found.
Products ISR is in progress (Casertano et al.).
Accuracy At least 0.01’’ in relative shifts; 0.05” or better for absolute
Goals astrometry.
Accuracy
Achieved
Scheduling& None.
Special
Requirements
Continuation Execute same observations, each visit spaced 6 months apart.
Plans
Proposal ID 8447: WFPC2 Cycle 8: CTE Monitor
Plan
Purpose Monitor CTE changes during cycle 8.
Description Observations of ω Cen (NGC 5139) are taken every 6 months
during cycle 8 to monitor changes in Charge Transfer Efficiency
(CTE) of the WFPC2 (extension of cycle 7 proposal 7629). The
principal observations will be in F814W at gain 15 in WF2 and
WF4. Supplemental observations at gain 7, and in the WF3 will
be performed if time permits, along with observations in F439W
and F555W. For each visit, observations will be done in single
guide star mode.
Fraction 30%
GO/GTO
Programs
Supported
Resources 4 orbits total (twice per cycle, 2 orbits each).
Required:
Observation
Results
Modifications Added a visit from cycle 7 (7929).
Execution No anomalies.
Time-line Observations taken Aug ‘99, Mar ‘00, and Aug. ‘00.
Resources 9 orbits. One of the extra orbits was carried forward from cycle
Used: 7; the other 4 extra orbits needed were taken from the 10%
Observation reserve pool.
Products Instrument Science Report
Products ISR in progress (Heyer et al., 2001); results incorporated into
the WFPC2 Instrument Handbook as well as presented in posters at AAS meetings (Biretta et al., Jan 2001, June 2000, Jan
2000, and Heyer et al., Jan 1999), in WFPC2 STANs (electronic
Space Telescope Analysis Newsletter), and at the CTE workshop held in Jan. 2000. CTE Estimation tool on WWW.
Accuracy 0.01 magnitude.
Goals
Accuracy The monitor observations indicate that for very faint stars on a
Achieved very faint background, the CTE loss from the top to the bottom
of the chip has increased from about 3% shortly after the
cooldown of WFPC2 (April 1994) to about 52% in August 2000
(see Fig. 7). In general, typical WFPC2 exposures are much
longer than these short calibration images, resulting in higher
background which significantly reduces the CTE loss and minimizes the CTE problem for most science exposures. Observers
interested in minimizing CTE losses should consider placing
their targets near the readout amplifier (low X,Y), applying corrections after their observations, possibly preflashing in certain
situations, and avoiding very short exposures (i.e., low background).
Plan
Scheduling& For each visit, use the same guide star for the small angle
Special maneuvers between the chips.
Requirements
Results
Continuation More detailed analysis, using 2 additional clusters and groundPlans based observations, will be done. Monitor portion will be continued as is, to allow tracking of changes in CTE losses over
time.
Figure 7: Change in CTE losses, from 1994 to 2000, for a range of target brightnesses, background levels, and filters (figure from Heyer et al., in prep).
Proposal ID 8448: WFPC2 Cycle 8: Intflat and Visflat Sweeps
Plan
Results
Purpose Monitor the pixel to pixel flatfield response and the visflat lamp Modifications Some rescheduling done due to Nov - Dec 1999 HST Safemode.
degradation, as well as detect any possible changes due to contamination. The linearity test obtains a series of intflat with both
gains and both shutters. Since the intflats have significant spatial
structure, any non-linearity would appear as a non-uniform ratio
of intflats with different exposure times.
Description Visflat mini-sweep: pre- and post-decon observations using the
photometric filter set at gain 7, and FR533N at both gains to test
the camera linearity. Intflat sweep: taken within a two-week
period. Almost all filters used, some with both blades and gains,
others with just one blade and gain. Linearity test: done at both
gains and blades using F555W, and an additional set with one
blade and gain with clocks=on.
Fraction 100%
GO/GTO
Programs
Supported
Resources 43 internal orbits (occultation periods)
Required:
Observation
Products TIPS, TIR if any significant variations are observed.
Execution No anomalies.
Time-line Observations taken in April 2000.
Resources 23 internal orbits, fewer than requested due to efficient packing
Used: of orbits.
Observation
Products Analysis of long-term trends in the intflats, visflats, and uvflats
is in progress (Gonzaga et al.); an anomaly in the FR533N filter
rotation found during that study has already been reported
(Gonzaga et al., ISR 01-04).Cycle 8 visflats and intflats were
also used as baseline images for SM3a verification (O’Dea et
al., TIR 00-04, Casertano et al., ISR 00-02).
Plan
Accuracy Visflats: stable to better than 1% in overall level and spatial variGoals ations (after correcting for lamp degradation). Contamination
effects should be < 1%. Intflats: SNR per pixel similar to the
visflats, but spatial and wavelength variations in the illumination
pattern are much larger. (intflats will provide a baseline comparison of intflat vs visflat if the CAL channel system fails.)
Results
Accuracy Gain ratios as measured from FR533N visflats are stable to betAchieved ter than 1% (see Fig. 8, taken from Gonzaga et al., ISR 01-04).
The apparent gain quantization seen in the early data is not real
but an artifact of an apparently randomly occuring rotational
offset in the filter wheel positioning of about 0.5 degrees in
some images (corresponding to one filter step). The pivot point
of the rotation implicates the filter wheel as the source of the
inconsistency. The photometric effect of the FR533N filter
anomaly has been estimated at less than 1% (Gonzaga et al., ISR
01-04). A cursory check of several filters on other filter wheels
shows no similar problem. At this time, the source of this problem (mechanical or software) is unknown.
Scheduling& Intflat sweeps should be scheduled within a 2-week period. Vis- Continuation To minimize the lamp degradation, the number of visflats taken
Special flat sweep must be done with minimum lamp cycles to prevent
Plans was dramatically reduced after Nov 1996 (MJD=50400). Same
Requirements further degradation of the lamp.
minmal set of observations to be done for cycle 9.
Figure 8: Gain ratio as a function of time, measured from FR533N visflats in PC; the dotted lines mark the Cycle 8 boundaries (from Gonzaga et al., in prep).
Counts were taken from the mean of the good central 300x300 pixels (MEANC300 keyword), with a zero-level bias (DEZERO keyword) removed.
Proposal ID 8449: WFPC2 Cycle 8: UV Flats Internal Monitor
Plan
Purpose Monitor the stability of UV flatfield.
Description UV flatfields obtained with the CAL channel’s ultraviolet lamp
(uvflat) using the UV filters F122M, F170W, F160BW, F185W,
& F336W. The UV flats are used to monitor UV flatfield stability and the stability of the F160BW filter by using F170W as the
control. The F336W ratio of visflat to uvflat provides a diagnostic of the UV flatfield degradation & ties the uvflat and visflat
flatfield patterns. Two supplemental dark frames must be
obtained immediately after each use of the lamp to check for
possible after-images.
Fraction 10%
GO/GTO
Programs
Supported
Resources 2 orbits (non-pointed, but displaces WFPC2 science because of
Required: timing requirements), plus occultation periods before and after
Observation each orbit.
Results
Modifications Some rescheduling done due to Nov - Dec 1999 HST Safemode
Execution No anomalies.
Time-line Data obtained in Apr. 2000.
Resources 2 internal orbits for the flats and 2 external orbits due to the disUsed: placement of WFPC2 science.
Observation
Products New UV flatfields if changes are detected.
Products
Accuracy About 2-8% pixel-to-pixel expected (depending on filter).
Goals
Accuracy
Achieved
Scheduling& To prevent excessive degradation of the UV lamp, the SU duraSpecial tion for each uvflat visit should be kept the same as that in cycle
Requirements 7 (prop. 7624); the lamp should not remain on for periods of
time longer than those used in Cycles 6 & 7. Due to timing
requirements, each visit covers a 2-hour time span--one visibility period and two occultation periods. Note that other instruments can be used during this period. Execute once during
Cycle 8, after a decontamination.
Continuation Continue observations for cycle 9.
Plans
Figure 9: UV flat field statistics from April 1994 through April 2000, in four filters for the four cameras (Baggett). Countrates are averages of all good pixels,
normalized to the October 1994 set of UV flats (F185W images are normalized to Aug 1995 data due to lack of F185W data in Oct 1994). UV flats taken more
than 10 days after a decon procedure are not included.
mean
F185W, UVFLATS
mean
mean
PC
WF4
49500
50000
50500
MJD
51000
mean
mean
mean
mean
mean
F160BW, UVFLATS
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
51500
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
PC
WF4
49500
50000
mean
mean
mean
PC
WF4
49500
50000
50500
MJD
51000
51000
51500
F336W, UVFLATS
51500
mean
mean
mean
mean
mean
F170W, UVFLATS
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
50500
MJD
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
1.05
1
.95
.9
.85
PC
WF4
49500
50000
50500
MJD
51000
51500
Proposal ID 8450: WFPC2 Cycle 8: Noiseless Preflash
Plan
Purpose Test effectiveness of "Noiseless" preflash in reducing CTE and
long vs. short Photometric effects.
Description A globular cluster is observed both before and after a preflash
that has been read out (i.e. noiseless). The preflash will be tailored to expose the CCDs to about 3000 DN without saturation.
The hypothesis is that the traps in the CCD will remain filled
even though the preflash has been read out, thereby minimizing
the effects of CTE.
Results
Modifications An extra orbit was approved by the TTRB (Telescope Time
Review Board at STScI), needed to cover the initial dark.
Execution Most observations on Jul 28 ‘99 failed due to guide star acquisition problems. A repeat successfully executed on Feb 2000.
The observation sequence is repeated at two detector positions
and exposure times, so as to test for CTE and long vs. short
effects. The four orbits are done in one non-int visit, which is
preceded by a pair of 1800s darks and includes single darks during occultation periods to insure no prior exposures will effectively preflash the non-preflash exposures.
Fraction 20%
GO/GTO
Programs
Supported
Resources 5 orbits
Required:
Observation
Products Improved observing strategies; ISR.
Time-line Most observations on Jul 28 ‘99 failed due to guide star acquisition problems. A repeat successfully executed on Feb 2000.
Resources 6 orbits.
Used:
Observation
Products Presentations at TIPS and posters at AAS meetings., as well as
ISR 01-02, Noiseless Preflashing of the WFPC2 CCDs (Schultz
et al.) , TIR 99-02, Preliminary Results of the Noiseless Preflash
Test (Schultz et al.) and updates to the WFPC2 Instrument
Handbook. Recommendations made to observers regarding
placement of faint targets to minimize CTE losses published via
WFPC2 STANs, WWW, and AAS posters.
Plan
Results
Accuracy A crowded field in the globular cluster ω Cen was observed at a
Achieved variety of exposure times, using the WFPC2 calibration lamp as
a preflash source for the cameras. The preflash was readout prior
to imaging the external field (i.e., noiseless preflash). Schultz et
al. (ISR 01-02) found that the preflash increased stellar counts at
Y=800 by only ~3%, independent of the length of the science
exposure (see Table 4). The measured Y-CTE loss was ~8 times
this amount. They conclude that the preflash electrons are not
held in the traps long enough to significantly reduce the CTE
losses in aperture photometry of faint stellar targets.
The preflash appears to help only the image following it; the
second image after it suffers normal CTE losses.
Accuracy 1% photometry
Goals
Scheduling& Will require manual work to hide DARKS during occultation.
Special Would be most useful if scheduled as early as possible in, or
Requirements prior to, Cycle 8.
Continuation No plans to repeat this test for cycle 9.
Plans
Table 4: Results from the analysis of the 16 sec, 80 sec, and 400 sec exposure data. Shown are percentage increases, in counts, over 800 pixels of noiseless
preflashed image vs non-preflashed image (Table 6 from Schultz, Heyer, & Biretta, ISR 01-02).
CCD
16 sec.
80 sec.
400 sec.
average
WF2
2.2 +/- 1.5%
2.1 +/- 1.1%
2.3 +/- 0.8%
2.2 +/- 0.1%
WF3
2.5 +/- 1.6%
-
-
-
WF4
3.0 +/- 1.3%
3.6 +/- 1.3%
3.7 +/- 1.0%
3.4 +/- 0.3%
average
2.5+/- 12.8%
2.8 +/- 26.3%
3.0 +/- 23.3%
2.8 +/- 21.4%
Proposal ID 8451: WFPC2 Cycle 8: Photometric Characterization
Plan
Purpose Determine whether any changes in the zeropoint, the spatial
dependence of the zeropoint, or contamination rates have
occurred, by comparing with the baseline measurements for
GRW+70D5824 (single photometric standard with 13 filters)
Description Observe the standard star GRW+70D5824 in PC1 and WF3
using filters F380W, F410M, F450W, F467M, F547M, F569W,
F606W, F622W, F702W, F785LP, F791W, F850LP, and
F1042M. Observations should be done within 7 days after a
decon. These observations will be compared with data from the
cycle 7 program 7628.
Fraction 100%
GO/GTO
Programs
Supported
Resources 2 orbits.
Required:
Observation
Results
Modifications None.
Execution No anomalies.
Time-line Executed Feb. 2000.
Resources 2 orbits
Used:
Observation
Products TIR, SYNPHOT update if necessary.
Products Not yet analyzed.
Accuracy 2% photometry.
Goals
Accuracy
Achieved
Scheduling& Within 7 days of decon.
Special
Requirements
Continuation Repeat test in cycle 9, using all 4 chips.
Plans
Proposal ID 8452: WFPC2 Cycle 8: PSF Characterization
Plan
Purpose Provide a check of the subsampled PSF over the full field.
Description Observations using just two of the standard broadband filters
(F555W & F814W). With one orbit per photometric filter,
DITHER-LINE and POS TARG observations are performed in a
4x4 parallelogram. The dither-line-spacing=0.177, and POS
TARG steps are 0.125; this gives a critically sampled PSF over
most of the visible range. Each star is measured 16 times per filter at different pixel phase, providing a high S/N, critically sampled PSF. This will improve the quality of PSF fitting
photometry.
Fraction 15%
GO/GTO
Programs
Supported
Resources 2 pointed orbits.
Required:
Observation
Results
Modifications None.
Execution No anomalies.
Time-line Executed July 2000.
Resources 4 orbits. The two extra orbits, approved by the TTRB (Telescope
Used: Time Review Board), were needed to complete the necessary
Observation pattern using dither-line and pos targs, as the efficient spatial
scan capability is no longer available.
Products PSF library (WWW). Updates for TIM and TINYTIM. Accurate empirical PSFs to be derived for PSF fitting photometry.
Products Images are available via Starview though not archived into the
WWW PSF library yet.
Accuracy Results will be limited by breathing variations in focus, so preGoals dicting PSF accuracy is difficult. (For breathing < 5 micron
peak-to-peak, PSFs should be good to ~10% in each pixel.)
Proposal provides a measurement of pixel phase effect on photometry (sub-pixel QE variations exist), and gives a direct measurement of sub-pixel phase effects on photometry, measured to
better than 1%.
Accuracy
Achieved
Scheduling& Same pointing and orientation as Cycle 7 observations for proSpecial posal 7629. Visits should be completed within 2 week timeRequirements frame to minimize spacecraft temperature differences.
Continuation Observations may be repeated for cycle 9.
Plans
Proposal ID 8453: WFPC2 Cycle 8: Polarization
Plan
Purpose Verify stability of polarization calibration.
Description The data from this proposal will be used to identify any changes
that may have occurred since the polarizer calibration in Cycles
5 and 6. Two stars will be observed, G191B2B and
BD+64D106, a non-polarized and polarized standard star,
respectively. The unpolarized star will be observed in 2 visits
with the ORIENT changed by 90 degrees between visits, so as
to sample any residual polarization of the star. The polarized
star will be observed in 4 visits with the ORIENT changed by 45
degrees between visits, so as to fully sample the properties of
each polarizer quad. Each visit consists of F555W exposures in
PC1 and WF3, followed by F555W+POLQ exposures in PC1,
WF2, WF3, and WF4. Other popular broadband filters (F300W,
F439W, F675W, and F814W) will be checked using only the
unrotated polarizer. Finally, a small set of visflats (with a minimum of lamp cycles) will be included to check for flatfield
changes.
Fraction 5%
GO/GTO
Programs
Supported
Resources 6 external orbits, 10 internal orbits.
Required:
Observation
Results
Modifications Some rescheduling to accomodate visibility and orientation constraints.
Execution No anomalies.
Time-line Executed between Aug-Oct 1999, Nov & Dec 2000.
Resources 6 external, 4 internal.
Used:
Observation
Products TIR or ISR report. Update of SYNPHOT tables, WWW polarization calibration tools, and new CDBS flatfields if necessary.
Products In progress.
Accuracy Expected accuracy is <3%
Goals
Accuracy Analysis in progress (Biretta & McMaster).
Achieved
Scheduling& Requires use of POLQ and rotated POLQ filter. Visflat lamp
Special should be schedule to keep number of lamp cycles at a miniRequirements mum.
Continuation No plans to repeat observations in cycle 9.
Plans
Proposal ID 8454: WFPC2 Cycle 8: Linear Ramp Filter
Plan
Purpose Check wavelength and throughput calibration for LRFs at
selected wavelengths
Description A thorough check of the linear ramp filters (LRFs) was done as
part of the Cycle 7 calibration program, where the UV spectrophotometric standard (grw+70d5824) was observed at 75 different wavelengths and an extended source (Orion nebula) was
observed for an orbit as well. We anticipate requiring 4 orbits in
Cycle 8 to spot-check some of the more popular wavelengths as
well as cover any wavelengths requested by Cycle 8 GOs that
weren’t observed as part of the Cycle 7 calibration program.
Fraction 7%
GO/GTO
Programs
Supported
Resources 4 pointed orbits.
Required:
Observation
Results
Modifications None.
Execution No anomalies.
Time-line Observations obtained in March and April, 2000.
Resources 11 external orbits - four as originally requested for this Cycle 8
Used: proposal plus seven carried over from the Cycle 7 proposal 8054
Observation failed orbits (approved by Telescope Time Review Board).
Products Updates to SYNPHOT tables if necessary and an ISR.
Products In progress.
Accuracy Throughput accuracy should be better than 3%.
Goals
Accuracy Analysis is in progress. Initial results (O’Dea, McMaster, &
Achieved Biretta, priv.comm.) have shown ~1% agreement between the
ground-based calibration and the on-orbit data, though there
remains a 5-10% RMS scatter between individual data points
(the latter is still under investigation).
Scheduling& None.
Special
Requirements
Continuation None.
Plans
Proposal ID 8455: WFPC2 Cycle 8: Photometry of Very Red Stars
Plan
Purpose Verify the photometric calibration of WFPC2 filters and obtain
estimated color terms (HST to Johnson) for late M stars.
Description WFPC2 imaging (F439W, F555W, F675W, F814W) of two
well-known M dwarfs, VB8 and VB10, for which ground-based
measurements in the Johnson filters exist. Use two different
CCD Y positions to account for CTE. The current calibration is
based on white dwarf and solar analog data, which are insufficient to produce an accurate calibration for cool red stars (late
K and M) in broad-band filters. The calibration of cool stars is
especially difficult at the red end (F814W), because their spectra
can rise quickly where the DQE drops substantially (increasing
the uncertainty in the synthetic magnitude calibration). The
observations of two well-studied late M stars, VB8 and VB10,
will provide a direct empirical calibration of these effects and
reduce the uncertainties in the photometric response of WFPC2
for very red stars.
Fraction < 10%
GO/GTO
Programs
Supported
Resources 2 pointed orbits, one per star.
Required:
Observation
Results
Modifications None.
Execution No anomalies.
Time-line Executed October 1999.
Resources 2 orbits
Used:
Observation
Products N/A
Products None yet. Project may be outsourced.
Accuracy Better than 0.03 mag. Outsourcing candidate.
Goals
Accuracy
Achieved
Scheduling& None.
Special
Requirements
Continuation No plans to repeat these observations in cycle 9. For oursourcPlans ing.
Proposal ID 8456: WFPC2 Cycle 8: CTE for Extended Sources
Plan
Purpose Determine the effect of Charge Transfer Efficiency (CTE) on
small extended sources.
Description Previous CTE proposals have all focused on stellar targets. This
proposal is aimed at observing small (~2-3”) extended sources
in a suitable galaxy cluster. The target (tentatively cluster
135951+623105, at z=0.3) will be observed in WF2 and WF4,
in F606W and F814W. The filter F606W is chosen instead of
the F555W used for stellar CTE measurements, to allow a
comparison to archival images for estimating of any possible
time-dependence. One orbit is needed for each pointing for each
filter, for a total of four orbits.
Fraction 30%.
GO/GTO
Programs
Supported
Resources 4 pointed orbits.
Required:
Observation
Results
Modifications Exposure times reduced so visit would fit target visibility window.
Execution No anomalies.
Target switched from 135951+623105 to A1689-10, to allow it
to run earlier in the cycle rather than later.
Time-line Executed Feb 2000.
Resources 4 orbits.
Used:
Observation
Products ISR
Products ISR 00-04, How CTE Affects Extended Sources (Riess, 2000).
Updates to WFPC2 Instrument Handbook. Results have been
presented at TIPS meetings, at the CTE workshop held in Jan.
2000, and in posters at AAS meetings. Analysis of the CTE
effect on extended source aperture photometry is still in
progress (Baggett et al., 2001).
Accuracy 10%. Outsourcing candidate.
Goals
Accuracy This proposal was a first effort to directly measure the effect of
Achieved CTE on small (2-3”) extended sources. A galaxy cluster was
positioned in chips 2 and 4, such that the targets appeared in different Y-locations, low Y in one chip, high Y in the other chip.
Analysis by Riess (ISR 00-04) showed that the average profile
of the galaxy residuals was distinctly asymmetric (see Fig. 10),
confirming that most of the charge is lost on the amplifier side of
the galaxy. This is consistent with the leading edge of the galaxy
filling the traps and effectively shielding the side of the galaxy
away from the amplifier from CTE effects. A simple model of
the readout process is able to reproduce the observed results.
Plan
Results
Scheduling& TBD
Special
Requirements
Continuation No plans to repeat observations in cycle 9.
Plans
Figure 10: Composite galaxy residual profile, illustrating the charge loss on the leading edge of the targets (left) compared to the trailing edge (right); Figure
2 from Riess, ISR 00-04. The trailing edge exhibits a net gain, as trapped charge is released.
15
1-D Cut: Galaxy Difference
mean residual DN
10
CTE Loss
5
0
Read Direction
CTE Gain
-5
-10
Galaxy Peak
-5
0
y pixels
5
10
Proposal ID 8457: WFPC2 Cycle 8: UV Earth Flats
Plan
Purpose Improve quality of pipeline UV flatfields.
Description Earth streakflats are taken in UV filters (F170W, F185W,
F218W, F255W, F300W, F336W, and F343N). Those UV filters
with significant redleak will also be observed crossed with
selected broadband filters (F450W, F606W, F675W, and
F814W), in order to assess and remove the redleak contribution.
Earth flats required: 100 for each of the 7 UV filters plus 20
with each of the crossed filter sets.
Fraction ~10%
GO/GTO
Programs
Supported
Resources 720 non-science impacting orbits (occultation periods).
Required:
Observation
Results
Modifications None.
Execution No anomalies.
Time-line Observations executed from August to October 1999, then
resumed after the November-December HST Safemode from
February to May, July 2000.
Resources 240 occultation periods. Requested resources were for total
Used: number of Earth flats required; as typically 2-6 Earth flats were
Observation packed into each visit, only 240 visits were needed.
Products Updated flatfields for pipeline via CDBS.
Products In progress. Project has been outsourced; flatfield reference files
to be delivered.
Accuracy 3-10%. Outsourcing candidate.
Goals
Accuracy
Achieved
Scheduling& None.
Special
Requirements
Continuation Observations to continue in cycle 9.
Plans
Proposal ID 8458: WFPC2 Cycle 8: Plate Scale Verification
Plan
Purpose Check of the WFPC2 plate scale in the UV and red.
Description UV and F953N observations of the bright cluster NGC2100.
Data will be taken in F170W, F218W, F300W, F555W (to allow
tie-in to previous observations) and F953N. To minimize orbits
required, the program is designed around short exposures in the
filters listed above; the data will provide a verification the plate
scale in the UV but exposure times will not be long enough to
allow a full distortion solution.
Fraction < 10%
GO/GTO
Programs
Supported
Resources 1 external orbit.
Required:
Observation
Results
Modifications None.
Execution No anomalies.
Time-line Observations executed in October 1999.
Resources 1 external orbit.
Used:
Observation
Products ISR.
Products None (outsourcing candidate). PC chip scale correction factors
have been determined from these data and published by Barstow
et al., MNRAS 322, 891.
Accuracy Better than 0.05% (0.4 pixels over 1 chip), or 0.05 mas/pixel in
Goals WF. Outsourcing candidate.
Accuracy N/A.
Achieved
Scheduling& None.
Special
Requirements
Continuation No plans to repeat this program in cycle 9.
Plans
Proposal ID 8800: Moving Observations of a Fixed Star Cluster
Plan
Purpose Slew HST across a star cluster while exposing with WFPC2.
Study the resulting trailed images.
Description Continuous scans at four different angles---two orthogonal
pairs--- are done of a region centered on the LMC globular cluster NGC 1850. Each position angle is expected to yield an accurate position perpendicular to the scan angle, thus each pair of
orthogonal scans will produce a full two-dimensional astrometric solution for the cluster. The comparison of the two solutions
based on independent scans will indicate the accuracy of the
photometry. Four scans are executed at each angle, with subpixel stepping to improve the sampling. The scans will execute
under gyro guidance because of the inefficiency of guide star
handoff; comparison of solutions using shorter scans will help
characterize the error induced by small drifts in the gyro position and scan rate. In addition, a single scan at an angle of 45
degrees (corresponding to the length of the FGS1 and FGS3
pickles) will be taken under guide star control. Finally, normal
100s exposures of the target will be taken corresponding to the
initial and final points of the scans, so that images of the target
will be available.
Fraction < 10%
GO/GTO
Programs
Supported
Resources 4 external orbit.
Required:
Observation
Products ISR
Results
Modifications None.
Execution The observations were taken largely as planned, thanks to the
dedicated effort by T. Roman and the scheduling team to finetune the program once it was on the schedule. Some of the
observations ended up slightly displaced in their initial and final
position, but were nonetheless useful for the purpose of the program.
Time-line Executed July 2000.
Resources 4 external orbits.
Used:
Observation
Products Initial analysis completed; report is in progress (Casertano &
Gonzaga).
Plan
Accuracy Better than 0.05% (0.4 pixels over 1 chip), or 0.05 mas/pixel in
Goals WF. Outsourcing candidate.
Scheduling& Special scheduling needed to “create” fake moving targets to
Special scan NGC 1850.
Requirements
Results
Accuracy The initial reduction procedure consisted of generating a large
Achieved mosaic of the pointed (untrailed) observations, and cross-identifying about 30 star trails between the mosaic and the drifted
(trailed) observations (Casertano & Gonzaga). The positions of
the trails were then measured in the cross-trail direction using a
custom-written IDL routine.
Unfortunately, this first effort was not very successful, in that
the routine used proved inadequate to measure a stable crosstrail position with an accuracy of better than 0.1 pixels (see Figure 11).
The reduced accuracy is most likely due to the undersampling of
the WFPC2 PSF. We expect that a better analysis will require a
proper model of the trail, obtained by generating a PSF at multiple positions along the trail and fitting it to the observed trail. It
is not clear whether this analysis can be done with the available
tools, or whether a new tool must be developed for this purpose.
Continuation None.
Plans
(pixels)
Figure 11: Position of a trailed star in the cross-trail direction (av_06), measured by fitting a simple functional form to the cross-trail profile, as a function of
position along the trail (xr_06); only a small segment of trail is shown here (x pixel 305-320). The measured position fluctuates by about +/- 0.1 pixels, in
phase with pixel boundaries; this fluctuation is due to residual pixellation effects in the star trail (figure from Casertano & Gonzaga, in progress).
(pixels)
References
General Documents
Site Map of WFPC2 WWW pages
WFPC2 Advisories
WFPC2 Documentation
WFPC2 Software Tools
WFPC2 User Support
Frequently Asked Questions
WFPC2 Clearinghouse
The WFPC2 Instrument Handbook
The Dither Handbook
The HST Data Handbook
STAN, the Space Telescope Analysis Newsletter -- To subscribe, send a message to majordomo@stsci.edu with the Subject: line blank and the following in the body: subscribe
wfpc_news)
Proposals in Phase II format, page maintained by PRESTO
WFPC2 PSF page
Workshop on Hubble Space Telescope CCD Detector CTE, Jan. 2000
New ISRs and other reports since the last closure report
01-05: WFPC2 Dark Current vs. Time, Mack, Biretta, Baggett, & Proffitt.
01-03: WFPC2 Cycle 10 Calibration Plan, Baggett, Gonzaga, Biretta, Heyer, Koekemoer,
Mack, McMaster, Schultz.
01-02: Noiseless Preflashing of the WFPC2 CCDs, Schultz, Heyer, & Biretta.
01-01: Creating WFPC2 Dark Reference Files, Mack & Wiggs.
00-04: How CTE Affects Extended Sources, Riess.
00-03: Update on Charge Trapping and CTE Residual Images in WFPC2, Baggett,
Biretta, & Hsu.
00-02: Results of the WFPC2 Observatory Verification after Servicing Mission 3, Casertano, Gonzaga, Baggett, Balleza, Biretta, Heyer, Koekemoer, O’Dea, Riess, Schultz, &
Wiggs.
00-01: WFPC2 Cycle 9 Calibration Plan, Baggett, Gonzaga, Biretta, Casertano, Heyer,
Koekemoer, McMaster, O’Dea, Riess, Schultz, Whitmore, & Wiggs.
99-05: WFPC2 Cycle 7 Closure Report, Baggett, Biretta, Casertano, Gonzaga, Heyer,
McMaster, O’Dea, Schultz, Whitmore, & Wiggs.
99-04: Time Dependence of CTE from Cosmic Ray Trails, Riess, Biretta, Casertano.
Charge-Transfer Efficiency of WFPC2, PASP 11,1559, Dec 1999, Whitmore, Heyer, &
Casertano.
41
Internal reports
01-01 Shutter Jitter History Measured from INTFLATs, Riess, Casertano, & Biretta.
00-05 Testing OTFC with WFPC2 Data, Wiggs & Baggett.
00-04 WFPC2 Internal Monitoring, O’Dea, Heyer, & Baggett.
00-03 SM3A WFPC2 Photometry Check, Schultz, Gonzaga, & Casertano.
00-02 Results of the WFPC2 SM3a Lyman-alpha Throughput Check (proposals 8492,
8494, and 8515), Baggett & Heyer.
00-01 SMOV3a Flat Field Stability Check, Koekemoer, Biretta, & Wiggs.
99-02 Preliminary Results of the Noiseless Preflash Test, Schultz, Heyer, Biretta, 12/99
For paper copies of any documents listed here, please contact help@stsci.edu.
42