Instrument Science Report ACS 2001-11
HRC AND WFC FLAT
FIELDS: STANDARD
FILTERS, POLARIZERS,
AND CORONOGRAPH
R. C. Bohlin, G. Hartig, and Andre Martel
December 2001
ABSTRACT
Laboratory flats with simulated sky illumination of the CCD cameras have been obtained
for supported and many unsupported ACS modes. The ACS HRC flight detector shows a
typical sensitivity variation from center to edge of ~10%, while the large format WFC
minimum/maximum sensitivity variation is ~15%. The CEI specification of +-10% uniformity is met for WFC and HRC. The intrinsic rms variation of sensitivity in the pixel-topixel P-flat is 0.5-0.9%, so that observed flats with ~100,000 electrons/px and an rms of
~0.3% are required to improve the intrinsic S/N that is possible without a P-flat field reference file These high S/N flats are the P-flats combined with the low frequency L-flat sensitivity variation over the field. The 142 measured LP-flats include 13 and 17 single filter
flats for WFC and HRC, respectively, 78 polarizer mode flats, and 34 flats of all types for
the HRC coronographic mode. In addition, estimates are made for 15 supported modes
that were not measured directly. All 157 flats are now available as reference files for the
pipeline processing of ACS observations from Cycle 11.
1. INTRODUCTION
Longward of its ~3500Å optical cutoff, the Refractive Aberrated Simulator/Hubble OptoMechanical Simulator (RAS/HOMS) with a continuum light source was used in 2001
February-March to produce flat fields which include both the low frequency L-flat and the
high frequency pixel-to-pixel P-flat structure (Martel & Hartig 2001). These LP-flats
Instrument Science Report ACS 2001-11
should be appropriate for reduction of on-orbit data with the flight B1 HRC and B4 WFC
CCD detectors. The individual data frames are tabulated in Tables 1-5. The HRC flat field
observations with standard, non-polarizing filters in Table 1 include the pre-flight database
entry number of the first image of a set, the observation date, the exposure time in seconds,
the number of images in the set, the filter wheel 1 and 2 positions, the CCD temperature,
and the intrinsic 1σ rms pixel-to-pixel variation in sensitivity in a selected region of the
HRC CCD. The laboratory calibration images are stored on the STScI SNAP5 disk with
search and retrieval functionality provided by the ACS Instrument Definition Team (IDT)
software written in the IDL language. Table 2 contains the same information as Table 1,
but for the WFC. In addition, Table 2 specifies the filter wheel offset positions, the x-axis
size in pixels, and the CCD amplifier configuration, which determine the location of the
subarray within the 4096x4096 px detector. Subarray flats for the smaller filters are indicated by AXIS1=2048. The HRC flats for the polarizer modes are in Table 3, which has
the same columns as Table 1, except that the rms variation is omitted. Table 4 has the same
information as Table 2, but for the WFC polarizers. Similarly, Table 5 lists the coronographic flat field observations. Since the intrinsic rms variation is a property of the CCD,
the rms values for the polarizing and coronographic modes are similar to those tabulated in
Tables 1-2.
The LP-flats are produced by combining the set of images for each filter mode with a
cosmic ray rejection algorithm (acs_cr.pro). The physical overscan regions define the bias
level. To normalize to unity, the flats are divided by the average number of counts in the
central 1% of the combined frame. The acs_cr routine also produces the statistical uncertainty and data quality arrays for each flat. In the case of full WFC frames, the chip 2
images are divided by the chip 1 central value, in order to preserve the overall sensitivity
difference between the two CCD chips across the ~40 pixel gap that separates the two
independent pieces of the WFC detector. For display of the Figures in this presentation
only, the two pieces of the WFC LP-flats are separately renormalized to the averages of
strips along the adjacent edges of chips 1 and 2. Because of variation in the illuminating
lamp with time, a special keyword (norm) in acs_cr.pro normalizes the succeeding images
to the first one of a set by computing an effective exposure time. Without this renormalization, the typical lamp variation of ~3% causes most pixels in our high S/N flats to have at
least one rejection. A single pass with a 5σ rejection and no sky adjustment in acs_cr.pro
is used to combine the separate frames. In the case of the 2048x2046 pixel subimages that
are used for the small filters that cover just part of one quadrant of the WFC, an extra line
with unit value is added at the top and bottom of these flats to pad to a standard 2048x2048
size. These flats for the small filters are masked to unity below 90% of the central value of
the data, so that no flat field correction is done on the scattered light outside the physical
edge of the filter. The other two IDL routines used to derive the flats are a driver, lpall.pro,
and a subroutine, flatlp.pro, which calls acs_cr and does the normalization to unity, the
padding, the masking, and the header creation. Figures 1-3 are examples of flats for the
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Instrument Science Report ACS 2001-11
HRC, a WFC subarray, and the full field WFC, respectively. The low order structure of the
flats over the field of view (L-flat) is mostly due to the variations in the sensitivity of the
CCD detector assembly; but variations in the filter transmissions also contribute, because
the filters are close to the CCD focal plane.
A translucent mylar diffuser screen at the pupil plane of the RAS/HOMS produces the
same flat field as the sky through the OTA+ACS. See Sparks, et al.(2000) for a description
of the role of SKY-flats in the pipeline data reduction. The pipeline data reduction will
produce geometrically corrected images; but our LP-flats are observed sky-flats with no
geometric correction. A direct application of a sky flat would make objects with uniform
surface brightness show a uniform response per pixel. However, a star's total response
would vary over the field in proportion to the change in the product of the x and y plate
scales, i.e. in proportion to the geometric correction factor G of Bohlin et al. 1999, Bohlin
et al. 2000, & Sparks, et al.(2000) as archived in the Image Distortion Correction (IDC)
file.
2. WAVELENGTH DEPENDENCE
2.1 White Light
Both the low frequency (L-flat) and pixel-to-pixel (P-flat) structure of the flats change
with wavelength. This dependence of the flat field structure on the spectral distribution of
the source may be the limiting factor in the analysis of GO science data with high S/N.
2.1.1 Cosmetic Artifacts
2.1.1.1 The Blob
Figure 4 is the white light flat for the F814W filter and shows a more uniform response
than the F435W flat in Figure 3. The prominent extended doughnut of enhanced sensitivity at F435W has disappeared in F814W, while the blob at the lower left central part of
chip 1 changes from a ~10% deficiency to an enhanced response of ~5%. Even for the
adjacent filters, F435W and F475W, the ratio in the region of the blob still shows a relative
enhancement of almost 10% in parts of the white region that are off-scale in the
1024x1024 WFC subsection in Figure 5. For HRC, the F475W/F435W ratio changes
smoothly by <2%, over the full field of view.
2.1.1.2 The Dust Motes
Several circular patterns of a dark ring with a central brightening are visible on Figures
1-4 with typical diameters of ~30px on HRC and ~100px on WFC. These artifacts are
shadows of dust on the CCD windows and are weaker on the f/25 WFC than at f/68 for
HRC. Several of these dust motes can be seen at the same positions on Figures 3 and 4.
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Instrument Science Report ACS 2001-11
Since the shapes and depths of these motes are almost independent of wavelength, their
effects will be removed by the flats to <<1%, unless any of these particulate contaminants
move to different positions on the CCD windows.
2.1.1.3 The Freckles
The small black spots (freckles) with a size of a few pixels can be seen on Figures 1-4;
and a few have depths of more than 50%. The depth of the freckles decreases with increasing wavelength. However, the ratio of the adjacent wavelength HRC flats F475W/F435W
has only 51 pixels that are more than 1.05. The worst HRC freckle includes pixels 486,608
and 488,607 near the image center and might create a false signal in a source with a
slightly different spectral distribution than the tungsten lamp used for the white light laboratory flats. On the WFC, freckles are even less of a problem over most of the CCD area,
as illustrated by the sparsity of small white dots on Figure 5.
The data quality flag 'dq' in third extent of the flat field reference files. is set to 175 for
pixel values in the flats of <0.1 or >2.0. Low sensitivity pixels also have an anomalous
value in the uncertainty image 'err' in the second extent of the reference files.
2.1.2 P-Flat: Pixel-to-Pixel Fine Structure
A relatively blemish free region at (590:690,434:534) on the HRC, at
(590:690,1458:1558) on chip 1 of the full frame WFC, or at the same pixel range on the
subarray flats of the WFC is used to study the pixel-to-pixel fine structure of the flats. The
rms scatter is calculated in these regions, corrected for the small effect of the counting statistics, and tabulated in the final columns of Tables 1-2 as the intrinsic pixel-to-pixel rms
structure of the detectors. In order to avoid any significant loss of S/N when applying flats
to science data, the Poisson counting statistics of the flats are in the 0.2 to 0.3% range, i.e.
at least 110,000 electrons per pixel. Table 1 shows that the intrinsic rms structure is as
small as 0.5% in the longer wavelength filters on HRC. This intrinsic fine structure is
always <1%; and generally decreases with wavelength, except for the fringing pattern in
F892N and except for the longest wavelength F850LP filter on HRC.
In white light, fringing in standard filters is observed only for F892N (see Figure 2).
For all astrophysical sources where the continuum flux dominates the line emission within
the narrow 150Å bandpass of F892N, the typical fringe amplitude is <1% and should be
removed to a small fraction of a percent, because the fringe pattern is stable in monochromatic images. (See 2.2.1.2 below for a measurement of monochromatic fringe stability.)
Small differences in the effective wavelength of the source spectrum cause only small
residual noise in flat fielded data. For example, in the standard regions of HRC and WFC
the residuals for F475W/F435W are only 0.12% and 0.15%, respectively, after correcting
for the expected scatter due to counting statistics of 0.32 and 0.37%, respectively.
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Instrument Science Report ACS 2001-11
2.2 Monochromatic Light
Several monochromatic flats were obtained to compare with the broad band white light
flats that are used in the pipeline ACS data processing.
2.2.1 P-Flat
2.2.1.1 Wavelengths below 6400Å
Table 6 quantifies the rms errors accrued by a monochromatic source after dividing by
the white-light pipeline-reference flat for a selection of the standard broadband filters on
WFC. The standard 101x101 pixel regions defined in 2.1.2 are used to compute the Poisson counting statistics, the actual one σ rms scatter, the intrinsic rms variation (Sigma
Flat), and the minimum and maximum value of the flat. The Poisson scatter is removed
from the 'Actual sigma' to calculate the 'Sigma Flat', which is the intrinsic rms variation of
the flat itself. The RATIO section of the Table shows the result of correcting the numerator
flat by the denominator flat, where the Poisson statistics are the numerator and denominator Poisson statistics combined in quadrature. The 'Actual sigma' entries are the standard
deviations within the ratio sub-images.
At the shortest monochromatic wavelength of 3880Å in Table 6, the residual of 0.63%
is the poorest, because the pixel-to-pixel P-flat structure increases rapidly below ~4000Å.
However, the impact is only for monochromatic sources below 4000Å when a S/N ~200
per pixel is required. Monochromatic data for HRC in the range 4751-6300Å shows residuals similar to the WFC residuals in Table 6 for the same wavelength range. Except for the
shortest wavelength of 3880Å, the intrinsic rms structure in the monochromatic flats is
<0.9%. This intrinsic scatter is reduced to ~0.2% by application of the broadband flat that
includes the monochromatic wavelength in its bandpass. Below 6400Å and probably up to
7300 or 7400Å, the broadband P-flats obtained with the continuum lamp in the laboratory
are adequate for astronomical objects with any flux distribution.
2.2.1.2 Wavelengths above 7400Å
Fringing patterns with modulations up to ~20% for monochromatic light (see Figures
10-11 of Bohlin, Hartig, and Tsvetanov 2000) prevent verification of the above generalization at longer wavelengths. However, the default external tungsten flats should be
adequate, because the P-flats generally show weaker wavelength dependencies at the
longer wavelengths. In any case, fringing will probably limit the measurement precision of
small structure in monochromatic sources beyond ~7400Å. Any attempts to remove the
fringing signature from images of monochromatic sources will be based on the results of
the ESA-ECF effort to model and remove fringing effects in the ACS spectral modes. Stability of the fringing pattern is good: At 9200Å, where the modulation is ~20% and the
intrinsic rms scatter is 5-6%, the rms of the residual pattern is only ~0.5% when comparing fringe flats taken at CCDTEMP1 temperatures that differ by 2C. Further quantification
5
Instrument Science Report ACS 2001-11
of fringing residuals in monochromatic images must await completion of the ESA-ECF
modeling work.
2.2.2 L-Flats
The large scale error introduced by correcting the monochromatic flats of section 2.2.1
by the white light flats with the same filter is often less than 1-2%. However, errors
exceeding 20% occur in the WFC blob region at 3880Å. At 4330Å, the blob error has
dropped to ~5%; but 4330Å is still the worst case of overall L-flat error, as illustrated in
Figure 6. The L-flat ratio for monochromatic light at 4300Å is 0.95 in the top left corner,
and 1.11 in the bottom right corner. In addition, errors exceeding 5% occur at the bottom
right for 3880Å, in the blob for 4551Å, at the bottom right for 4770Å, and at the top left
for 6141 and 6320Å. The HRC monochromatic L-flats divided by the white light flats are
within ~1% of unity for the seven wavelengths measured between 4751 and 6300Å.
In the IR at 9000Å with the F814W filter, Figure 7 illustrates a ~4% enhancement in
the L-flat at the center of the doughnut and a ~4% drop in the doughnut ring region. Also,
illustrated in Figure 7 is the intricate fringe pattern for 9000Å monochromatic light where
the typical fringe amplitude is +-7%.
In summary, an observer should be wary of errors >2% for the WFC in the blob region,
in the doughnut ring in the IR, and at the extremes of the field for all wavelengths. The
amount of possible error depends on the amount of deviation of source spectrum from that
of the smooth continuum of the tungsten filament lamp used in the laboratory flat field calibration program.
3. SHORT WAVELENGTH HRC FLATS WITH THE RAS/CAL
Because the RAS/HOMS optics are opaque below 3500Å, the RAS/CAL system is
used with a UV-bright deuterium lamp shining on a piece of reflective diffusing Spectralon, which is placed in front of a mirror in RAS/CAL to simulate OTA sky illumination
for the HRC UV flats. For the one filter in common, F435W, the L-flat from RAS/CAL
drops below the RAS/HOMS L-flat by up to ~10% in the upper right hand corner, while
the deuterium flats are brighter than the RAS/HOMS baseline by ~10% in a region at the
lower right side of the field. Thus, 10-20% of the area of the deuterium flats are apparently
in error by >5%. A RAS/CAL flat with the same setup, except for a tungsten lamp like the
one used in RAS/HOMS, shows a similar drop at the upper right but no bright patch. The
deuterium RAS/CAL flats probably suffer from a specular reflection that causes a spurious
bright patch and from a mis-alignment that causes lower illumination at the upper right.
If the L-flat illumination error for the deuterium lamp is independent of wavelength
down to the shortest wavelength F220W filter, then these flats can be corrected by the deuterium illumination error as measured by the ratio D/T of the deuterium F435W flat
divided by the tungsten baseline F435W flat. The pixel-to-pixel intrinsic structure is the
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Instrument Science Report ACS 2001-11
same for both lamps in F435W. The only fine structure in D/T at F435W is in the dust
motes, where the deuterium illumination causes a typical 1-2% and maximum of 6% error
in a few pixels around the dust motes. Since the dust motes exhibit diffraction rings, D/T
should show some wavelength dependence in the regions of the dust motes. To estimate
the error in correcting the shortest wavelength F220W filter flat with D/T, the tungsten
baseline flats over a similar factor of two in wavelength from F435W to F814W are compared. The two worst motes from dust on the HRC window are at (20,910) and (280,210).
There are several pixels within ~10 pixels of these two positions that differ by up to +-3%
at the first diffraction ring in the F814W/F435W ratio.
Another complication to the D/T correction technique is that the deuterium F435W flat
has a low S/N corresponding to only ~20,000 electrons or a rms Poisson noise of 0.7%,
which is comparable to the intrinsic rms structure of 0.8% for the HRC UV flats. In order
to improve the statistics of the D/T correction, both the numerator and denominator
F435W flats are smoothed via a 3x3 pixel box. Since the Poisson statistics of the F220W,
F250W, and F330W observations are ~0.35%, the 0.7/3=0.23% noise of the smoothed D/T
correction increases their Poisson noise to only ~0.4%. The ~0.9% statistical uncertainty
of the F344N flat is determined by its ~13,000 total counts, i.e. electrons. These four UV
flats for HRC are generated by flatfix.pro.
In summary, the extra uncertainty in the P-flats for the four HRC UV filters is limited
to a few percent for a few pixels in the dust mote regions. Evidence that the UV L-flats are
correct to <5% is provided by the fact that the observed L-flat structure in the original
RAS/CAL deuterium flats is the same to <5% from F220W to F435W.
There are a few supported modes for which no laboratory flat field measurement was
done. The missing flats are for the three HRC UV filters, F220W, F250W, and F330W in
combination with PolUV and with the coronograph. The UV flats with the coronograph+PolUV are also missing but are not supported modes. Since the UV transmission as
a function of position on the PolUV filters and on the coronograph mask is likely to vary
and is unconstrained by measurement, a good estimate for the missing UV flats cannot be
made. These UV flats are crudely estimated by correcting the corrected UV flats of section
3 by the ratio (PolUV+F435W)/F435W or by (CORON+F435W)/F435W. Although the
POLUV and CORON transmissions change little over the longer wavelength ranges, the
UV transmission may change by larger amounts that cannot be estimated in the absense of
actual UV transmission measurements. Perhaps, the missing UV lab flats can be obtained
by observing the bright earth after launch.
4. HRC CORONOGRAPH
Because the coronographic mode has an apodizer mask that changes the instrumental
PSF, the blemishes have a different diffraction structure, as illustrated in Figures 8-9. The
F475W coronograhic flat with the POL0V filter from Figure 8 is divided by the same flat
without the coronographic mask to produce Figure 9. Figure 9 shows that the dust mote
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Instrument Science Report ACS 2001-11
and L-flat structure of a coronograph flat does not match the corresponding mode without
the coronographic mask because of the different PSF for the coronograph and because of
the substrate transmission properties of the mask. The worst case differences in the small
dust motes are +-5% for the motes at (278,208) and (672,618). The large blemish on the
left side of Figure 8 with a deviation of +-3% in Figure 9 is the worst case of the bubbles
in the optical cement that bonds the two pieces of the curved polarizing filters. However,
outside of the bubble and dust mote regions, the coronograph does not change the P-flat
structure, as demonstrated by the reduction of the intrinsic rms structure from ~1% in Figure 8 to 0.4% in Figure 9.
Observations were inadvertently omitted for the HRC coronographic flats for F606W
in combination with the three PolV filters with polarization angles of 0, 60, and 120
degrees. Since the transmission properties of the coronograph subtrate do not change rapidly over the 5000-7000Å range, the coronographic contribution to the flats can be
estimated by the ratios, R, for the three F555W+PolV filters with the coronograph divided
by the F555W+PolV flats without the coronograph. Substitutes for the missing coronographic flats are manufactured by multiplying the existing HRC F606W+PolV flats by the
R image for each of the three corresponding polarization angles. To estimate the error for
these three missing flats, the F658N+PolV is corrected by R and compared with the flats
that are actually measured with the coronograph. The error in the L-flat structure of this
manufactured flat is <1%; and the manufactured coron+F606W+PolV flats should also be
good to <1%. The F625W filter could not be used in this process because of a dust particle
on the F625W filter, which causes a prominent large feature in the ratios for
(coron+F625W+PolV)/(F625W+PolV). Fortunately, the HRC regions for both the F606W
and the neighboring F555W are clean.
5. FUTURE ANALYSIS OF THE LABORATORY FLAT FIELDS
Subsequent publications will deal with the ramp filters and the dispersing modes. The
anomalous results and stability of the flat fields are also deferred to later discussions.
REFERENCES
Bohlin, R. C., Hartig, G., Lindler, D. J., Meurer, G., & Cox, C. 1999, Instrument
Science Report, ACS 99-01, (Baltimore:STScI)
Bohlin, R. C., Hartig, G., & Tsvetanov, Z. 2000, Instrument Science Report,
ACS 00-10, (Baltimore:STScI)
Martel, A. & Hartig, G. 2001,
http://acs.pha.jhu.edu/instrument/calibration/plans/ rashoms_feb2001/
Sparks, W. B., Jedrzejewski, R., Clampin, M., & Bohlin, R.C. 2000, Instrument
Science Report, ACS 00-03, (Baltimore:STScI)
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Instrument Science Report ACS 2001-11
Figure 1 Flat field for F435W on HRC with a stretch from 0.90 to 1.05, as indicated on
the reference calibration bar at the top right. The HRC CCD is 1024x1024 pixels. The
Fastie occulting finger is at the top and is masked to unit value on the flat. The numerous
~30 px size dark rings with a central bright spot are caused by dust particles on the CCD
window. The primary filter F435W is written at the top, followed by the secondary filter.
The next line of text "rms(%)=" indicates one-σ values in the 101x101 standard region
(square outlined by dashed line) for the total pixel-to-pixel scatter, the Poisson counting
statistic, and the intrinsic rms variation of the flat. The fourth line of text is the file name
indicating an LP-flat (lp), h for HRC, e for external illumination, 01057 for the date of
observation: day 57 in 2001,sm02 for the sum of 2 images taken for cosmic ray rejection,
and the filtername f435w.
0.900
ACS HRC LP Flat
F435W CLEAR1S
1.050
rms(%)= 0.85 0.22 0.82
lphe01057sm02f435w
Bohlin: prtimg 12-Nov-2001 15:10
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Instrument Science Report ACS 2001-11
Figure 2 Flat field in continuum light for the small F892N narrow band filter on WFC.
This subarray is 2048x2048 px and is from Amp B for the right hand half of chip 1 of the
two 4096x2048 CCD chips that are butted together in the WFC. The fringe pattern with
~1% amplitude is caused by interference of light in semi-transparent layers of the CCD
substrate.
0.900
ACS WFC LP Flat
F892N CLEAR2L
1.050
rms(%)= 0.81 0.30 0.75
lpwe01058sm03f892n chip=1
Bohlin: prtimg 12-Nov-2001 16:19
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Instrument Science Report ACS 2001-11
Figure 3 Flat field for F435W on WFC. The prominent cosmetic features are a white
doughnut of enhanced sensitivity with a black blob of reduced sensitivity near the center
of the doughnut. The doughnut and blob are coherent across the ~40 pixel crack that separates the two 4096x2048 pixel chips, because the two wafers are adjacent cuts of the
same silicon boule and are intentionally butted to produce the observed continuity. Small
errors in the measured relative gain of the two amplifiers used to read each chip cause the
weak discontinuity across a vertical line at the center of the image.
0.900
ACS WFC
CLEAR1L F435W
rms(%)= 0.95 0.25 0.91
lpwe01058sm03f435w
1.050
Bohlin: prtimg 11-Dec-2001 14:57
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Instrument Science Report ACS 2001-11
Figure 4 Flat field for F814W on WFC. In comparison to the F435W filter in Figure 3, the
doughnut has disappeared, while the blob has morphed from a low to a high sensitivity relative to the rest of the field. Several weak motes with a ~100px diameter are visible and
result from dust particles on the CCD window. A few of these same motes can be distinguished in Figure 3.
0.900
ACS WFC
CLEAR1L F814W
rms(%)= 0.74 0.28 0.69
lpwe01058sm03f814w
1.050
Bohlin: prtimg 11-Dec-2001 14:59
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Instrument Science Report ACS 2001-11
Figure 5 A 1024x1024px region of the WFC ratio image of the F475W/F435W flats. The
blob is prominent on the 0.97 to 1.03 stretch even for these neighboring bandpasses. Away
from the blob, the pixel-to-pixel residual scatter of 0.16% demonstrates that these two flats
have almost exactly the same P-flat structure.
0.97
ACS WFC RATIO
1.03
F475W CLEAR2L / F435W CLEAR1L
rms(%)= 0.40 0.37 0.14
lpwe01058sm03f475w / lpwe01058sm03f435w 1024x1024 center: 1512, 522
Bohlin: wbloup 13-Nov-2001 12:56
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Instrument Science Report ACS 2001-11
Figure 6 Ratio of a monochromatic 4330Å flat to a white-light tungsten flat for the
F435W on WFC. While the white-light flat provides an excellent (0.2% rms) correction of
the P-flat structure, the L-flat residuals are a worst case from our limited test set of monochromatic flats. About half of the image shows a residual of >2%, while substantial
regions differ from unity by >5%. Because of these differential variations in sensitivity
with the spectral flux distribution of the source, caution is advised when attempting to perform relative photometry over the large WFC field of view.
0.950
ACS WFC RATIO
F435W CLEAR1L / F435W CLEAR1L
1.050
rms(%)= 0.66 0.65 0.15
lp4330w01057sm02f435w / lpwe01058sm03f435w
Bohlin: prtimg 13-Nov-2001 13:02
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Instrument Science Report ACS 2001-11
Figure 7 Monochromatic flat at 9000Å divided by the broadband, white-light F814W flat
on WFC. The fringing pattern is prominent; and ~4% large scale L-flat residuals appear in
the doughnut and blob regions. Because of the small scale of the fringing, rms residuals in
the standard 101x101 pixel region are 3.8%.
0.950
ACS WFC RATIO
F814W CLEAR1L / F814W CLEAR1L
1.050
rms(%)= 3.87 0.86 3.78
lp9000w25691f814w / lpwe01058sm03f814w
Bohlin: prtimg 13-Nov-2001 15:00
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Instrument Science Report ACS 2001-11
Figure 8 White light flat for the coronograph combined with the F475W and POL0V filters. The regions of the coronographic spots and the Fastie finger are masked to unit value.
The "c" in the file name lphc... indicates that the coronograph is in the beam for this flat.
The square box outlined with a dashed line is the 101x101 pixel region where the statistics
are computed.
0.900
ACS HRC LP Flat
F475W POL0V
1.050
rms(%)= 1.06 0.22 1.03
lphc01058sm02f475wpol0v
Bohlin: prtimg 23-Oct-2001 11:30
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Instrument Science Report ACS 2001-11
Figure 9 Flat from Figure 8 divided by the same flat without the coronograph. Differences
in the small window dust motes and the large POL0V bubble blemishes are prominent
along with an overall gradient in the L-flat from top left to bottom right.
0.950
ACS HRC RATIO
F475W POL0V / F475W POL0V
1.050
rms(%)= 0.50 0.31 0.39
lphc01058sm02f475wpol0v / lphe01057sm02f475wpol0v
Bohlin: prtimg 23-Oct-2001 11:26
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Instrument Science Report ACS 2001-11
Table 1. Table 1. HRC Standard Filters with LP Illumination
ENTRY
DATE-OBS
EXP-TIME
N
FILTER1
FILTER2
CCD TEMP(C)
RMS(%)
33997
23/08/01
1000.0
2
CLEAR1S
F250W
-80.0
0.80
33999
23/08/01
1000.0
2
CLEAR1S
F220W
-80.1
0.75
34002
23/08/01
1000.0
2
CLEAR1S
F330W
-80.0
0.75
34009
23/08/01
1000.0
4
CLEAR1S
F344N
-80.0
0.77
26107
26/02/01
14.5
2
CLEAR1S
F435W
-80.9
0.82
26119
26/02/01
35.0
2
CLEAR1S
F660N
-80.9
0.55
26105
26/02/01
3.0
2
CLEAR1S
F814W
-80.8
0.52
26103
26/02/01
3.5
2
F475W
CLEAR2S
-80.8
0.81
26115
26/02/01
86.0
2
F502N
CLEAR2S
-81.0
0.71
26111
26/02/01
3.8
2
F550M
CLEAR2S
-80.8
0.71
26093
26/02/01
2.3
2
F555W
CLEAR2S
-80.9
0.75
26101
26/02/01
0.7
2
F606W
CLEAR2S
-80.9
0.61
26643
28/02/01
0.7
1
F606W
CLEAR2S
-80.8
0.61
26097
26/02/01
0.9
2
F625W
CLEAR2S
-80.9
0.60
26117
26/02/01
15.0
2
F658N
CLEAR2S
-80.8
0.62
26095
26/02/01
2.8
2
F775W
CLEAR2S
-80.8
0.46
26099
26/02/01
15.5
2
F850LP
CLEAR2S
-80.8
0.89
26113
26/02/01
120.0
2
F892N
CLEAR2S
-80.8
0.93
18
Table 2. WFC Standard Filters with LP Illumination
DATE-OBS
EXP-TIME
N
FILTER1
FW1 OFF
FILTER2
FW2 OFF
AXIS1(px)
CCD AMP
CCD TEMP(C)
RMS(%)
26089
26/02/01
1.0
2
CLEAR1L
0
F435W
0
4096
ABCD
-78.8
0.92
26313
27/02/01
30.0
3
CLEAR1L
0
F435W
0
4096
ABCD
-78.9
0.91
26421
27/02/01
23.2
3
CLEAR1L
0
F660N
0
4096
ABCD
-78.8
0.80
26310
27/02/01
1.3
3
CLEAR1L
0
F814W
0
4096
ABCD
-78.9
0.69
26307
27/02/01
5.9
3
F475W
0
CLEAR2L
0
4096
ABCD
-78.8
0.92
26415
27/02/01
132.0
3
F502N
0
CLEAR2L
0
4096
ABCD
-78.8
0.94
26412
27/02/01
4.3
3
F550M
0
CLEAR2L
0
4096
ABCD
-78.8
0.88
26291
27/02/01
2.8
3
F555W
0
CLEAR2L
0
4096
ABCD
-78.8
0.90
26304
27/02/01
0.5
3
F606W
0
CLEAR2L
0
4096
ABCD
-78.8
0.81
26475
28/02/01
0.5
3
F606W
0
CLEAR2L
0
4096
ABCD
-78.7
0.80
26297
27/02/01
0.7
3
F625W
0
CLEAR2L
0
4096
ABCD
-78.8
0.84
26418
27/02/01
9.1
3
F658N
0
CLEAR2L
0
4096
ABCD
-78.8
0.79
26294
27/02/01
1.4
3
F775W
0
CLEAR2L
0
4096
ABCD
-78.8
0.70
26300
27/02/01
6.3
3
F850LP
0
CLEAR2L
0
4096
ABCD
-78.8
0.71
26426
27/02/01
77.0
3
F892N
57
CLEAR2L
0
2048
B
-78.8
0.75
26430
27/02/01
77.0
3
F892N
-61
CLEAR2L
0
2048
C
-78.7
0.72
Instrument Science Report ACS 2001-11
19
ENTRY
Instrument Science Report ACS 2001-11
Table 3. HRC Polarizer Filters with LP Illumination
ENTRY
DATE-OBS
EXP-TIME
N
FILTER1
FILTER2
CCD TEMP(C)
26123
26/02/01
11.0
2
26125
26/02/01
11.0
2
F475W
POL0V
-80.9
F475W
POL60V
-80.9
26127
26/02/01
11.0
2
F475W
POL120V
-80.9
26681
28/02/01
245.0
2
F502N
POL0V
-80.8
26683
26685
28/02/01
245.0
2
F502N
POL60V
-80.9
28/02/01
245.0
2
F502N
POL120V
-80.8
26657
28/02/01
11.6
2
F550M
POL0V
-80.9
26659
28/02/01
11.6
2
F550M
POL60V
-80.9
26661
28/02/01
11.6
2
F550M
POL120V
-80.9
26129
26/02/01
6.7
2
F555W
POL0V
-80.8
26131
26/02/01
6.7
2
F555W
POL60V
-80.8
26133
26/02/01
6.7
2
F555W
POL120V
-80.8
26675
28/02/01
2.0
2
F606W
POL0V
-80.9
26677
28/02/01
2.0
2
F606W
POL60V
-80.9
26679
28/02/01
2.0
2
F606W
POL120V
-80.9
26141
26/02/01
2.0
2
F625W
POL0V
-80.9
26143
26/02/01
2.0
2
F625W
POL60V
-80.9
26145
26/02/01
2.0
2
F625W
POL120V
-80.8
26147
26/02/01
39.0
2
F658N
POL0V
-80.9
26149
26/02/01
39.0
2
F658N
POL60V
-80.9
26151
26/02/01
39.0
2
F658N
POL120V
-81.0
26135
26/02/01
6.7
2
F775W
POL0V
-80.9
26137
26/02/01
6.7
2
F775W
POL60V
-80.9
26139
26/02/01
6.7
2
F775W
POL120V
-80.8
26663
28/02/01
21.5
2
F850LP
POL0V
-80.9
26665
28/02/01
21.5
2
F850LP
POL60V
-80.9
26667
28/02/01
21.5
2
F850LP
POL120V
-80.8
26669
28/02/01
250.0
2
F892N
POL0V
-80.9
26671
28/02/01
250.0
2
F892N
POL60V
-80.8
26673
28/02/01
250.0
2
F892N
POL120V
-80.9
26155
26/02/01
45.0
2
POL0UV
F435W
-80.9
26157
26/02/01
45.0
2
POL60UV
F435W
-80.8
26159
26/02/01
45.0
2
POL120UV
F435W
-80.9
26645
28/02/01
95.0
2
POL0UV
F660N
-80.9
26647
28/02/01
95.0
2
POL60UV
F660N
-80.9
26649
28/02/01
95.0
2
POL120UV
F660N
-80.9
26161
26/02/01
5.8
2
POL0UV
F814W
-80.9
26163
26/02/01
5.8
2
POL60UV
F814W
-80.9
26165
26/02/01
5.8
2
POL120UV
F814W
-80.9
20
Table 4. WFC Polarizer Filters with LP Illumination
DATE-OBS
EXP-TIME
N
FILTER1
FW1 OFF
FILTER2
FW2 OFF
AXIS1(px)
CCD AMP
CCD TEMP(C)
26318
27/02/01
16.0
3
F475W
0
POL0V
-57
2048
B
-78.8
26324
27/02/01
16.0
3
F475W
0
POL120V
-57
2048
B
-78.8
26321
27/02/01
16.0
3
F475W
0
POL60V
-57
2048
B
-78.8
26869
01/03/01
360.0
3
F502N
0
POL0V
-57
2048
B
-78.8
26875
01/03/01
360.0
3
F502N
0
POL120V
-57
2048
B
-78.8
26872
01/03/01
360.0
3
F502N
0
POL60V
-57
2048
B
-78.8
26833
01/03/01
12.0
3
F550M
0
POL0V
-57
2048
B
-78.8
26839
01/03/01
12.0
3
F550M
0
POL120V
-57
2048
B
-78.7
26836
01/03/01
12.0
3
F550M
0
POL60V
-57
2048
B
-78.9
26327
27/02/01
7.4
3
F555W
0
POL0V
-57
2048
B
-78.8
26333
27/02/01
7.4
3
F555W
0
POL120V
-57
2048
B
-78.8
26330
27/02/01
7.4
3
F555W
0
POL60V
-57
2048
B
-78.7
26860
01/03/01
1.7
3
F606W
0
POL0V
-57
2048
B
-78.8
26866
01/03/01
1.7
3
F606W
0
POL120V
-57
2048
B
-78.8
26863
01/03/01
1.7
3
F606W
0
POL60V
-57
2048
B
-78.8
26345
27/02/01
1.7
3
F625W
0
POL0V
-57
2048
B
-78.8
26351
27/02/01
1.7
3
F625W
0
POL120V
-57
2048
B
-78.8
26348
27/02/01
1.7
3
F625W
0
POL60V
-57
2048
B
-78.8
26354
27/02/01
23.0
3
F658N
0
POL0V
-57
2048
B
-78.8
26360
27/02/01
23.0
3
F658N
0
POL120V
-57
2048
B
-78.7
26357
27/02/01
23.0
3
F658N
0
POL60V
-57
2048
B
-78.8
26336
27/02/01
2.9
3
F775W
0
POL0V
-57
2048
B
-78.9
26342
27/02/01
2.9
3
F775W
0
POL120V
-57
2048
B
-78.9
26339
27/02/01
2.9
3
F775W
0
POL60V
-57
2048
B
-78.8
26842
01/03/01
8.5
3
F850LP
0
POL0V
-57
2048
B
-78.8
26848
01/03/01
8.5
3
F850LP
0
POL120V
-57
2048
B
-78.9
26845
01/03/01
8.5
3
F850LP
0
POL60V
-57
2048
B
-78.7
26365
27/02/01
16.0
3
F475W
0
POL0V
61
2048
C
-78.8
26371
27/02/01
16.0
3
F475W
0
POL120V
61
2048
C
-78.9
26368
27/02/01
16.0
3
F475W
0
POL60V
61
2048
C
-78.7
26934
01/03/01
360.0
3
F502N
0
POL0V
61
2048
C
-78.9
26940
01/03/01
360.0
3
F502N
0
POL120V
61
2048
C
-78.8
26937
01/03/01
360.0
3
F502N
0
POL60V
61
2048
C
-78.8
26898
01/03/01
12.0
3
F550M
0
POL0V
61
2048
C
-78.8
26904
01/03/01
12.0
3
F550M
0
POL120V
61
2048
C
-78.9
26901
01/03/01
12.0
3
F550M
0
POL60V
61
2048
C
-78.8
26374
27/02/01
7.4
3
F555W
0
POL0V
61
2048
C
-78.8
26380
27/02/01
7.4
3
F555W
0
POL120V
61
2048
C
-78.7
26377
27/02/01
7.4
3
F555W
0
POL60V
61
2048
C
-78.8
Instrument Science Report ACS 2001-11
21
ENTRY
DATE-OBS
EXP-TIME
N
FILTER1
FW1 OFF
FILTER2
FW2 OFF
AXIS1(px)
CCD AMP
CCD TEMP(C)
26925
01/03/01
1.7
3
F606W
0
POL0V
61
2048
C
-78.9
26931
01/03/01
1.7
3
F606W
0
POL120V
61
2048
C
-78.7
26928
01/03/01
1.7
3
F606W
0
POL60V
61
2048
C
-78.8
26392
27/02/01
1.7
3
F625W
0
POL0V
61
2048
C
-78.8
26398
27/02/01
1.7
3
F625W
0
POL120V
61
2048
C
-78.9
26395
27/02/01
1.7
3
F625W
0
POL60V
61
2048
C
-78.8
26401
27/02/01
23.0
3
F658N
0
POL0V
61
2048
C
-78.8
26407
27/02/01
23.0
3
F658N
0
POL120V
61
2048
C
-78.9
26404
27/02/01
23.0
3
F658N
0
POL60V
61
2048
C
-78.9
26383
27/02/01
2.9
3
F775W
0
POL0V
61
2048
C
-78.7
26389
27/02/01
2.9
3
F775W
0
POL120V
61
2048
C
-78.7
26386
27/02/01
2.9
3
F775W
0
POL60V
61
2048
C
-78.8
26907
01/03/01
8.5
3
F850LP
0
POL0V
61
2048
C
-78.7
26913
01/03/01
8.5
3
F850LP
0
POL120V
61
2048
C
-78.8
26910
01/03/01
8.5
3
F850LP
0
POL60V
61
2048
C
-78.9
26916
01/03/01
90.0
3
F892N
-61
POL0V
61
2048
C
-78.9
26922
01/03/01
90.0
3
F892N
-61
POL120V
61
2048
C
-78.7
26919
01/03/01
90.0
3
F892N
-61
POL60V
61
2048
C
-78.8
26851
01/03/01
90.0
3
F892N
57
POL0V
-57
2048
B
-78.8
26857
01/03/01
90.0
3
F892N
57
POL120V
-57
2048
B
-78.8
26854
01/03/01
90.0
3
F892N
57
POL60V
-57
2048
B
-78.9
26456
27/02/01
81.0
3
POL0UV
-61
F435W
0
2048
C
-78.9
26462
28/02/01
81.0
3
POL120UV
-61
F435W
0
2048
C
-78.8
26459
27/02/01
81.0
3
POL60UV
-61
F435W
0
2048
C
-78.9
26889
01/03/01
42.0
3
POL0UV
-61
F660N
0
2048
C
-78.8
26895
01/03/01
42.0
3
POL120UV
-61
F660N
0
2048
C
-78.7
26892
01/03/01
42.0
3
POL60UV
-61
F660N
0
2048
C
-78.9
26465
28/02/01
2.4
3
POL0UV
-61
F814W
0
2048
C
-78.8
26471
28/02/01
2.4
3
POL120UV
-61
F814W
0
2048
C
-78.8
26468
28/02/01
2.4
3
POL60UV
-61
F814W
0
2048
C
-78.7
26436
27/02/01
81.0
3
POL0UV
57
F435W
0
2048
B
-78.8
26442
27/02/01
81.0
3
POL120UV
57
F435W
0
2048
B
-78.7
26439
27/02/01
81.0
3
POL60UV
57
F435W0
0
2048
B
-78.8
26824
01/03/01
42.0
3
POL0UV
57
F660N
0
2048
B
-78.9
26830
01/03/01
42.0
3
POL120UV
57
F660N
0
2048
B
-78.8
26827
01/03/01
42.0
3
POL60UV
57
F660N
0
2048
B
-78.7
26445
27/02/01
2.4
3
POL0UV
57
F814W
0
2048
B
-78.8
26451
27/02/01
2.4
3
POL120UV
57
F814W
0
2048
B
-78.8
26448
27/02/01
2.4
3
POL60UV
57
F814W
0
2048
B
-78.8
Instrument Science Report ACS 2001-11
22
ENTRY
Instrument Science Report ACS 2001-11
Table 5. HRC Coronographic LP-flat Data
ENTRY
DATE-OBS
EXP-TIME
N
FILTER1
FILTER2
CCD TEMP(C)
26169
26/02/01
4.6
2
F555W
CLEAR2S
-80.9
26171
26/02/01
5.6
2
F775W
CLEAR2S
-80.9
26173
26/02/01
1.8
2
F625W
CLEAR2S
-81.0
26175
26/02/01
31.0
2
F850LP
CLEAR2S
-80.9
26177
26/02/01
1.4
2
F606W
CLEAR2S
-80.9
26179
26/02/01
7.0
2
F475W
CLEAR2S
-80.9
26181
26/02/01
6.0
2
CLEAR1S
F814W
-80.9
26183
26/02/01
29.0
2
CLEAR1S
F435W
-80.8
26187
26/02/01
7.6
2
F550M
CLEAR2S
-80.8
26189
26/02/01
240.0
2
F892N
CLEAR2S
-80.9
26191
26/02/01
172.0
2
F502N
CLEAR2S
-80.9
26193
26/02/01
30.0
2
F658N
CLEAR2S
-80.8
26195
26/02/01
70.0
2
CLEAR1S
F660N
-80.9
26199
27/02/01
22.0
2
F475W
POL0V
-80.9
26201
27/02/01
22.0
2
F475W
POL60V
-80.9
26203
27/02/01
22.0
2
F475W
POL120V
-80.9
26205
27/02/01
13.4
2
F555W
POL0V
-80.9
26207
27/02/01
13.4
2
F555W
POL60V
-81.0
26209
27/02/01
13.4
2
F555W
POL120V
-80.9
26211
27/02/01
13.4
2
F775W
POL0V
-81.0
26213
27/02/01
13.4
2
F775W
POL60V
-80.9
26215
27/02/01
13.4
2
F775W
POL120V
-80.9
26217
27/02/01
4.0
2
F625W
POL0V
-80.9
26219
27/02/01
4.0
2
F625W
POL60V
-80.9
26221
27/02/01
4.0
2
F625W
POL120V
-80.9
26223
27/02/01
78.0
2
F658N
POL0V
-80.9
26225
27/02/01
78.0
2
F658N
POL60V
-80.9
26227
27/02/01
78.0
2
F658N
POL120V
-80.9
26242
27/02/01
90.0
2
POL0UV
F435W
-80.9
26244
27/02/01
90.0
2
POL60UV
F435W
-80.9
26246
27/02/01
90.0
2
POL120UV
F435W
-80.9
26248
27/02/01
11.6
2
POL0UV
F814W
-80.9
26250
27/02/01
11.6
2
POL60UV
F814W
-80.8
26252
27/02/01
11.6
2
POL120UV
F814W
-80.8
23
Instrument Science Report ACS 2001-11
Table 6. STATISTICS OF THE WFC MONOCHROMATIC FLATS VS. BROADBAND
FLATS
3880
4330
4551
4772
5076
5381
5672
5962
6141
6320
f435w
f435w
f475w
f475w
f475w
f555w
f606w
f606w
f625w
f625w
Poisson(%)
1.28
0.60
0.56
0.58
0.67
0.53
0.41
0.35
0.33
0.32
Actual sigma(%)
1.79
1.08
1.05
1.08
1.15
1.04
0.97
0.92
0.92
0.89
Sigma Flat(%)
1.26
0.90
0.89
0.91
0.93
0.90
0.88
0.85
0.86
0.83
Minimum
0.78
0.88
0.88
0.87
0.87
0.86
0.87
0.87
0.87
0.87
Maximum
1.06
1.02
1.02
1.02
1.03
1.03
1.02
1.03
1.03
1.02
f435w
f435w
f475w
f475w
f475w
f555w
f606w
f606w
f625w
f625w
Poisson(%)
0.29
0.29
0.26
0.26
0.26
0.26
0.28
0.28
0.26
0.26
Actual sigma(%)
0.97
0.97
0.96
0.96
0.96
0.93
0.85
0.85
0.87
0.87
Sigma Flat(%)
0.92
0.92
0.92
0.92
0.92
0.89
0.80
0.80
0.83
0.83
Minimum
0.89
0.89
0.86
0.86
0.86
0.87
0.87
0.87
0.85
0.85
Maximum
1.04
1.04
1.01
1.01
1.01
1.02
1.01
1.01
0.99
0.99
Poisson(%)
1.31
0.67
0.62
0.64
0.72
0.59
0.49
0.45
0.42
0.42
Actual sigma(%)
1.45
0.69
0.65
0.68
0.76
0.62
0.54
0.49
0.45
0.44
Resid. sigma(%)
0.63
0.20
0.22
0.24
0.24
0.19
0.21
0.20
0.15
0.16
NUMERATOR
DENOMINATOR
RATIO
24