2013
Study of the evolution of the ACS/WFC sensitivity loss (ISR 13-01)
We present a study of the sensitivity loss of the ACS/WFC CCDs for one medium-band, eight broad-band, and three narrow-band filters. This study was done using a calibration field lo- cated 6.7 arcmin West of the center of globular cluster 47 Tucanae. For pre-SM4 images, a comparison of the sensitivity loss rates found in this research with those calculated using stan- dard white dwarf stars by Bohlin, R. et al. (ISR ACS 2011-03) shows excellent agreement within the uncertainties of the two methods. We found that the sensitivity losses are less than ∼0.0004 mag/year. We also have a baseline of at least three years of post-SM4 observations of the 47 Tucanae calibration field. Our study shows that, on average, the sensitivity loss post- SM4 is negligible. This is a remarkable result considering that ACS is an instrument that has been in space for over ten years and subject to contamination.
Leonardo Ubeda & Jay Anderson
29 Jan 2013
2012
A new accurate CTE photometric correction formula for ACS/WFC (ISR 12-05)
We present a new CTE photometric correction formula based on observation of 47Tuc obtained during Cycles 17, 18 and 19. Images were taken with two filters and different exposure times, in order to sample a wide range of background levels. In addition, the Cycle 19 program included imaging of a denser field near the center of 47Tuc with the F502N filter. Thanks to the increased number of stars available for the analysis, we are able to characterize CTE losses down to the lowest background levels (down to ~0.2e-) without significant loss of accuracy with respect to higher sky levels. The data from these three Cycles allow us to derive a new form of the correction formula that is significantly more accurate that those previously published. The formula may be used to correct stellar photometry for CTE losses on drizzled images taken after SM4. We compare the results of our new CTE correction to previous versions of the correction formula for ACS/WFC, and with the pixel-based CTE correction that is currently available as part of CALACS. The formula presented in this ISR and the pixel-based correction are in substantial agreement at high stellar fluxes and for relatively high background levels. However, the former is significantly more accurate than the latter for faint stars superimposed to a low sky background.
M. Chiaberge
03 Oct 2012
Assessing ACS/WFC Sky Backgrounds (ISR 12-04)
This report compares the on-orbit sky background levels present in Cycle 18 ACS/WFC full- frame images against estimates provided by the Exposure Time Calculator (ETC). Backgrounds of over ~20 e- can alleviate charge-transfer efficiency (CTE) losses, which especially affect low S/N sources. HST observers can use these estimates to anticipate the natural background that should be present in their exposures, and can then determine whether they want to supplement that background with a post-flash to improve the CTE – at the cost of more background noise.
Sokol, Anderson, Smith
31 Jul 2012
Study of the evolution of the ACS/WFC charge transfer efficiency (ISR 12-03)
We perform a comprehensive and detailed study of the evolution of the effect of charge transfer
efficiency (CTE) of the Wide-Field Channel of the Advanced Camera for Surveys (ACS). The
study is based on the profiles of warm pixels in all the dark frames ever produced by ACS between
2002 and 2011. We apply the pixel-based empirical approach by Anderson&Bedin (2010,
PASP, 122, 1035) which restores flux, position and shape of sources in the original images. We
demonstrate that this image-restoration process properly accounts for the time and temperature
dependence for CTE in ACS, and that it works for all epochs: the original setting when the
camera was operated at -77C and also on the post-SM4 data obtained with the current temperature
set at -81C. We also demonstrate that the code has been successfully integrated in the
ACS calibration and reduction pipeline CALACS.
Leonardo Ubeda & Jay Anderson
12 Mar 2012
Pixel-based correction of the ACS/WFC signal-dependent bias shift (ISR 12-02)
Since the installation of the CCD Electronic Box Replacement (CEB-R) during Servicing
Mission 4, the ACS Wide Field Channel has exhibited two bias anomalies that have been linked
to the CCDs’ external preamplifiers and the CEB-R’s dual-slope integrators. One anomaly is a
temporally stable bias gradient of 5-10 DN across each quadrant; the other anomaly is a local
bias shift that depends on the pixel signal and has an e-folding time comparable to the serial
transfer of several hundred pixels. Although the bias shift is relatively small (0.02−0.3% of the
pixel signal), it can be an impediment to high-contrast science observations and to the removal
of other electronic anomalies (e.g., 1/f noise). We have developed a pixel-based algorithm for
correcting the signal-dependent bias shift in full-frame WFC images. We describe the
calibration and tuning of this algorithm for each WFC quadrant, and we discuss a strategy for
implementing this algorithm in the standard CALACS image processing pipeline.
Golimowski, David et al
16 Feb 2012
Flux Calibration of the ACS CCD Cameras IV. Absolute Fluxes (ISR 12-01)
ISRs I-III in this series define the charge transfer efficiency (CTE) for the CCD detectors, the encircled energy fractions, and the optical throughput degradation. This fourth ISR es- tablishes the absolute flux calibration for the photometry, as corrected with the algorithms specified in I-III. Synthetic photometry from the SEDs of three primary hot 30,000-60,000K WDs define these sensitivity calibrations for the standard HRC and WFC filters. Even though the external uncertainty for the absolute flux of the three primary WD flux standards is ~1%, the internal consistency of the sensitivities is ~0.3%. However, when these WD sensitivities are applied to the cooler F, G, and K stars, there are internal inconsistencies of 1-2% for the F775W, F814W, and F850LP filters. For the same cooler stars, the other broadband filters are internally consistent to better than the 1% ACS flux calibration goal after applying the corrections and calibrations specified here. One filter F435W requires a small shift of the long wavelength edge of the bandpass by 18Å toward longer wavelengths in order to reduce the cool star residuals from as much as 2% to <0.5%; but wavelength shifts cannot remedy the flux discrepancies for the F, G, and K stars in the three long wavelength filters.
For HRC, the sensitivities change by 0.5-2% as a monotonic function of wavelength because of improvements in data processing. Additional residual corrections for individual filters
are typically <0.5% for wide filters in both cameras. For the medium and narrow filters,
these residuals are as large as ~3% for the WFC F550M and ~4% for HRC F344N. After implementing these throughput updates, the synthetic predictions of the WFC and HRC count rates for the average of the three primary WD standard stars agree with the observations to 0.1% for every filter.
Bohlin, Ralph C.
07 Feb 2012
2011
Post-SM4 ACS/WFC Bias Striping: Characterization and Mitigation (ISR 11-05)
Images taken with the Advanced Camera for Surveys Wide Field Channel (ACS/WFC) after
Servicing Mission 4 newly exhibit a row-correlated noise imparted by the CCD Electronics
Box Replacement (CEB-R). We characterize the noise component and assess algorithms for
software mitigation.
Grogin, N. A., et. al.
27 Jul 2011
ACS after Servicing Mission 4: The WFC Optimization Campaign (ISR 11-04)
The ACS CCD Electronics Box Replacement (CEB-R) installed during SM4 features a Teledyne SIDECAR ASIC that permits optimization of the WFC via adjustment of CCD clock voltages, bias voltages, and pixel transmission timing. A built-in oscilloscope mode allows sensing of the analog signal from each output amplifier. An on-orbit campaign to optimize the performance of the WFC was undertaken at the start of the SMOV period. Initial tests with pre-SM4 default voltages and timing patterns showed that WFC’s performance matches or exceeds its pre-failure levels, notwithstanding the expected increases in dark current and hot pixels and the decline in charge-transfer efficiency due to prolonged exposure to HST’s radiation environment. The WFC2 CCD exhibited anomalous behavior when operated with nondefault settings of its amplifiers’ reset-drain voltage (VOD). The CCD again displayed normal behavior when VOD was restored to its default setting. Consequently, the Optimization Campaign was truncated after two iterations, and ACS science operations commenced with the pre-SM4 default configuration.
David Golimowski, et. al.
15 Dec 2011
Flux Calibration of the ACS CCD Cameras II. Encircled Energy Correction (ISR 11-02)
In order to convert a point source flux calibration into a surface brightness calibration, the total response to a point source in an infinite aperture is required. In practice, infinite is defined as an aperture with a radius of 5".5. However, aperture photometry for such a large radius is exquisitely sensitive to the measured sky background level. In order to minimize uncertainties, corrections from one arcsec to infinity (5".5) are derived from averages over as many heavily exposed, isolated stellar images as possible. Calibrations, such as the change in sensitivity with time or flux calibrations from specific standard stars, utilize the low noise photometry for one arcsec radius; and the average correction to infinite aperture is used only as required. This ISR deals with the ACS encircled energy for one arcsec relative to infinity for the HRC and WFC.
Ralph C. Bohlin
02 May 2011
ACS Instrument Science Reports
None
ITT
05 Jul 2012
Flux Calibration of the ACS CCD Cameras III. Sensitivity Changes over Time (ISR 11-03)
The flux calibration of HST instruments is normally specified after removal of artifacts such
as a decline in charge transfer efficiency (CTE) for CCD detectors and optical throughput degradation. This ACS ISR deals with the HRC and WFC losses in sensitivity from polymerization of contaminants on the optical surfaces. Prior to the demise of the ACS CCD channels on 2007 Jan. 27, the losses are less than ~0.003 mag/year, except for the two
short wavelength HRC filters F220W and F250W. The measurements of the sensitivity loss rates using a set of observations of WD flux standards has a precision of ~0.0008 mag/year, while the sensitivity loss rates using repeated observations of the globular cluster 47 Tuc are
probably consistent within their currently lower precision.
Following the revival of ACS WFC during the Servicing Mission 4 (SM4) in 2009 May, the gain of the new electronics was set so that the measured signal in electrons s^-1 matched the signal for the same 47 Tuc field as measured in 2002 with the F606W filter. However, a longer time baseline is required to reliably determine the post-SM4 loss rates.
Bohlin, R., Mack, J., Ubeda, L.
03 Jun 2011
Flux Calibration of the ACS CCD Cameras I. CTE Correction (ISR 11-01)
The flux calibration of HST instruments is normally specifed after removal of artifacts such
as a decline in charge transfer efficiency (CTE) for CCD detectors and optical throughput degradation. This ISR deals with ACS/WFC CTE losses, which had been considered negligible for bright stars prior to the demise of the ACS CCD channels on 2007 Jan. 27.
Following the revival of ACS WFC during the Servicing Mission 4 (SM4) in 2009 May, CTE corrections are now typically several tenths of a percent and should be included, even for our bright standard star observations that utilize a standard reference point which is only 512 rows from the CCD amplifier B readout corner. For such bright standard stars with negligible background signal, a simple correction algorithm with an accuracy of better than 0.1%
is derived, which eliminates the need to execute the CTE correction code for the complete image.
Bohlin, R. & Anderson, J.
19 Jan 2011
2010
We use an empirical approach to characterize the effect of charge-transfer efficiency (CTE) losses in images taken with the Wide-Field Channel of the Advanced Camera for Surveys (ACS). The study is based on profiles of warm pixels in 168 dark exposures taken between 2009 September and October. The dark exposures allow us to explore charge traps that affect electrons when the background is extremely low. We develop a model for the readout process that reproduces the observed trails out to 70 pixels. We then invert the model to convert the observed pixel values in an image into an estimate of the original pixel values. We find that when we apply this image-restoration process to science images with a variety of stars on a variety of background levels, it restores flux, position, and shape. This means that the observed trails contain essentially all of the flux lost to inefficient CTE. The Space Telescope Science Institute is currently evaluating this algorithm with the aim of optimizing it and eventually providing enhanced data products. The empirical procedure presented here should also work for other epochs (e.g., pre-SM4), though the parameters may have to be recomputed for the time when ACS was operated at a higher temperature than the current -81°C. Finally, this empirical approach may also hold promise for other instruments, such as WFPC2, STIS, the ACS's HRC, and even WFC3/UVIS.
Jay Anderson and Luigi Bedin
07 Sep 2010
ACS/WFC Crosstalk after Servicing Mission 4 (ISR 10-02)
The ACS/WFC detector consists of two CCDs, each of which is read out through two amplifiers. While reading each quadrant of the detector, the electronic crosstalk between the amplifiers induces faint, typically negative, mirror-symmetric ghost images on the other three quadrants. The effect is strongest for high-signal offending (source) pixels. Analysis of pre-SM4 crosstalk showed that its impact on ACS/WFC science is not significant and can be ignored in most science applications. In this report, we analyze crosstalk after SM4. Crosstalk due to low-signal offenders is much weaker than before SM4 and does not produce ghosts similar to those seen in pre-SM4 images. For high-signal offending pixels, we find substantial differences between the gain=1 eˉ/DN and gain=2 eˉ/DN cases. For the default gain setting of 2, the crosstalk is similar to what it was before the SM4, up to 5–8 eˉ per pixel on the same CCD. For gain=1, the crosstalk is ~100 eˉ per pixel for saturated offending pixels on the same CCD, which is more than an order of magnitude above the pre-SM4 level. The crosstalk from saturated pixels is ~20–30 eˉ per pixel on the other CCD, which is also much higher than it was before SM4.
Anatoly Suchkov, et al.
06 Apr 2010
2009
Charge Transfer Inefficiency (CTI) due to radiation damage above the Earth's atmosphere creates spurious trailing in Hubble Space Telescope (HST) images. Radiation damage also creates unrelated warm pixels - but these happen to be perfect for measuring CTI. We model CTI in the Advanced Camera for Surveys (ACS)/Wide Field Channel and construct a physically motivated correction scheme. This operates on raw data, rather than secondary science products, by returning individual electrons to pixels from which they were unintentionally dragged during readout. We apply our correction to images from the HST Cosmic Evolution Survey (COSMOS), successfully reducing the CTI trails by a factor of #30 everywhere in the CCD and at all flux levels. We quantify changes in galaxy photometry, astrometry and shape. The remarkable 97 per cent level of correction is more than sufficient to enable a (forthcoming) reanalysis of downstream science products and the collection of larger surveys.
Richard Massey, Chris Stoughton, Alexie Leauthaud, Jason Rhodes, Anton Koekemoer, Richard Ellis, and Edgar Shaghoulian
26 Jan 2010
ACS after SM4: Relative Gain Values Among the Four WFC Amplifiers (ISR 09-03)
For the default setting of gain=2, the individual gain values of the four WFC amplifiers are determined from internal flat field observations. The average absolute gain remains unchanged, but matching the flat fields at the boundaries of the four quadrants provides a more accurate determinations of the relative gains among the four separate amplifiers.
R. C. Bohlin, A. Maybhate, and J. Mack
12 Oct 2009
Re-measurement of ACS/SBC dark images (ISR 09-02)
New measurements were made of the SBC dark rate in December 2008. As a function of temperature, the dark
rate was found not to have changed over the two year period. A few images were found to have abnormally high count rates. The effect was traced to a flight passage within the outer edges of the South Atlantic Anomaly. The effect of detector temperature on the dark rate is discussed.
Colin Cox
01 May 2009
Updated CTE photometric correction for WFC and HRC (ISR 09-01)
Observations for the ACS external CTE monitoring program were performed in Cycles
11 through 14 using both WFC and HRC. The aim of the program is to monitor the
change in CTE in both cameras, and provide correction formulae for stellar photometry.
Here we present the results of the data analysis, and we provide correction formulae for
photometry on drizzled images for both HRC and WFC. The correction formulae we
present here are significantly more accurate than those previously published, both
because of the larger amount of data available and because of a more advanced analysis
strategy. Observers are encouraged to use the new formulae to correct photometry,
especially in presence of faint stars on a low sky background.
M. Chiaberge
07 Apr 2009
2008
ACS CCD Image Anomalies in the Hubble Legacy Archive (HLA ISR 08-01)
The Hubble Legacy Archive (HLA) was created to make high-quality calibrated HST image products easily available to the astronomy research community. In its first public release, the HLA database has been populated with calibrated images from the Advanced Camera for Surveys (ACS). This report serves as a guide to identify ACS image anomalies that cannot currently be corrected in the HLA calibration pipeline.
M. Stankiewicz
05 Dec 2008
A New Geometric Distortion Solution for the ACS/SBC (ISR 08-02)
We have used ACS/SBC observations of two UV astrometric fields derived from ACS/HRC data to create a new geometric distortion solution for the Solar Blind Channel. The new solution consists of three components: (a) a filter-dependent linear part that takes into account the existence of three epoch ranges in the SBC alignment; (b) the remaining 24 higher-order components of a 4th degree polynomial; and (c) a fine-correction look-up table. Some of the previous solutions introduced possible errors of several pixels when producing mosaics due to an incorrect orientation. That issue has been solved and the accuracy due to the solution itself (excluding rotation) has been improved by an additional factor of 1.5-2.0. As a result, it is now possible to measure positions of medium to high S/N stars with a relative astrometric accuracy of 3-4 mas.
Jesus Maiz Apellaniz
10 Apr 2008
HST Focus Variations with Temperature (ACS ISR 08-03)
One of the main advantages of space observatories is the quality and stability of the point spread function that allows programs not feasible from the ground. However, when pushed to the limits, even the Hubble Space Telescope exhibits variations in the PSF that can be problematic for studies like weak lensing or identification of the host halos of bright quasars at high redshift. These variations are primarily due to small displacements in the focus of the telescope, which to a first approximation can be ascribed to temperature variations. The aim of this report is to characterize the variation of the focus position for HST in terms of the average temperature sensor values of the telescope. We propose a comprehensive temperature-focus model able to predict the position of the focus at the micron level over a dynamic range that extends from sub-orbital variations (< 1 hour) to seasonal and yearly variations. This allows us to predict the focus position significantly more accurately than using interpolation of the monthly direct measurements. Our model is also at least as accurate as the previously proposed breathing model for sub-orbital variations and it is the first one that describes longer term variations, potentially helping the determination of the model point spread function for observations lacking reference point sources.
Daiana Di Nino
08 May 2008
Updated Flux Calibration and Fringe Modelling for the ACS/WFC G800L Grism (ISR 08-01)
A revised flux calibration is presented for the G800L grism with the ACS Wide Field Channel.
H. Kuntschner, et al
25 Jan 2008
2007
Two astrometric fields for UV observations (ACS ISR 07-09)
I present the data for two fields that can be used to obtain accurate astrometric calibrations in the UV. The two
fields are located in NGC 604 (a Scaled OB Association in M33) and NGC 6681 (a Galactic globular cluster).
The coordinates are derived from multiple ACS/HRC exposures, use the Anderson and King (2004) geometric
distortion solution, have typical relative uncertainties of 1 mas, and can be used to derive geometric distortion
solutions for detectors with a field of view smaller than 1′. In the process of generating the astrometric fields,
the long-term stability of the HRC geometric distortion solution has been successfully tested. In two future ISRs
these results will be used to derive new geometric distortion solutions for the STIS NUV- and FUV-MAMA and
for the ACS SBC(Revised on 4 Oct 2007).
Jesus Maiz Apellaniz
19 Nov 2007
ACS PSF Variations with Temperatures (ISR 07-12)
We have used the HST ACS/WFC observations of a Galactic bulge field taken over a continuous interval of 7 days (Prop 9750) to investigate the possible dependence of the ACS focus with the external temperatures. This dataset allows us to investigate possible focus variations over timescales of a few hours to a few days. The engineering data related to the external temperatures for this duration show that the maximum temperature change occurred over the first 1.5 days. Among all the different temperatures recorded, the truss diametric differential and the truss axial temperatures are the only two temperatures which have the same timescale of variation as the PSFwidth variations. The PSF-widths also strongly correlate with these two temperatures during this time interval. We empirically fit the PSF-width variations with these 2 temperature sensor values. This suggests that the focus has a similar dependence, and we recommend that this finding be followed up with the determination of actual focus values to check if the focus values indeed have the same correlation. If so, the temperature data can be useful in estimating the focus values, which can then be used to predict the PSFs to a first order.
K.C.Sahu
18 Sep 2007
Calibration of Ramp Filters Using the ACS Grism (ISR 07-11)
Ramp filters provide ACS users with the equivalent of tunable narrow and medium-width passband filters. Here we analyze images taken under calibration programs CAL 9671 and CAL 10742 to measure the wavelength calibration of the ACS ramp filters by observing standard stars with the ramp filters crossed with the ACS G800L grism. We find that the tested HRC ramp filters are relatively well centered on the requested wavelengths. A number of the WFC filters, however, display significant o sets from the desired central wavelength. While the WFC direct images show large image o sets (wedges) due to the crossed filters, we have attempted to remove these o sets. Our results suggest we have reduced these o sets to one pixel or less both in images taken with the ramps crossed with wideband filters and in the spatial direction of images taken with the ramps crossed with the grism. O sets in the spectral direction of the grism images cannot be distinguished from a wavelength miscalibration. Data taken of line emission from an astrophysical source through the FR782N filter and compared to ground-based imaging suggest that this filter is well calibrated, in contrast to the result of the crossed filter observations reported here. Ray tracing simulations, deeper second order grism spectra, and further observations of astrophysical targets with known strong spectral features should be able to determine the extent to which the wavelength o sets reported here are real or an artifact of the calibration method.
A.S.Fruchter
18 Sep 2007
ACS Polarization Calibration - Data, Throughput, and Multidrizzle Weighting Schemes (ISR 07-10)
A subset of the polarized images from calibration proposals 9586, 9661, and 10055 were
analyzed to help determine the polarization calibration accuracy level of the ACS camera.
The polarization values found here are shown to be accurate to better than 1%. Differences in Multidrizzle weighting schemes are examined.
M. Cracraft, B. Sparks
20 Aug 2007
Variation of the Distortion Solution of the WFC (ACS ISR 07-08)
The linear skew terms have changed monotonically since ACS was installed 2002. These skew terms cancel out when relating data sets taken at the same epoch and same orientation, but they must be accounted for when dealing with observations taken at different roll angles.
J. Anderson
18 Sep 2007
Astrometric calibrations of JWST will use observations of a reference field in the Large Magellanic Cloud. This field will itself be astrometrically calibrated using observations with ACS/WFC on HST. The understanding of the ACS/WFC scale and rotation obtained through these analyses is sufficiently accurate to meet the JWST astrometric requirements.
R. P. van der Marel, et al.
05 Jul 2007
Photometric Calibration of the ACS CCD Cameras (ISR 07-06)
The absolute flux calibration of the standard WFC and HRC filters is derived from the available constraining observations of spectrophotometric standard stars. Values for the encircled energy (EE) of one arcsec radius relative to an infinite aperture radius are derived for hot stars and compared to the EE for cooler stars. The sensitivity degradation for five year ACS lifetime is defined and used to correct the ACS photometry before deriving revised quantum efficiency (QE) curves for the CCD detectors. Broad band EQ changes with a maximum of 2.3% for WFC are also included in the revised QE curves for both CCD cameras. Revisions of the average filter transmissions of up to 4% are required to bring both broad and narrow band photometry into exact agreement with synthetic photometry from the primary white dwarfs (WD) stars.
R.C. Bohlin
12 Jun 2007
Detection of Optical Ghost in the HST ACS Solar Blind Channel Filter 122M (ISR 07-05)
We report the detection of an optical ghost in the Advanced Camera for Surveys (ACS)
Solar Blind Channel (SBC). The ghost was first detected in deep imagery of two Herbig
Ae stars, HD 169142 and HD 100453, using filter F122M in April and June of 2006,
respectively.
K.A. Collins et. al.
04 Jun 2007
We present an analysis of the CTE correction for a science project using high-precision photometry in a crowded field derived with the ``effective PSF'' (ePSF) method of Anderson & King (2006) on ACS/WFC non-drizzled images. We present
a CTE correction technique which can be used for data sets where
images of a given field with different exposure times are compared or combined. The CTE-induced photometric losses and centroid shifts are parameterized in terms of the location of the source on the ACS/WFC CCD chips and the magnitudes of sources.
V.Kozhurina-Platais et al.
08 Jun 2007
ACS CCDs UV and narrow-band filters red leak check (ISR 07-03)
We present results of the observations of the star 15 Mon, obtained with the aim of checking the impact of red leaks in the UV (and U-band) and two narrow-band filters on ACS CCDs. We derive updated passbands for the three filters and we present the updated correction table for different spectral types.
M. Chiaberge and M. Sirianni
16 May 2007
WFC Zeropoints at -81C (ISR 07-02)
Following the recovery of ACS with the side-2 electronics in July 2006, the temperature of the WFC detector was lowered from -77C to -81C in order to mitigate CTE and hot pixels. A revised detector QE curve and a new set of photometric zeropoints have been computed for all WFC observations obtained at the new operating temperature. These zeropoints must be applied manually until the new QE curves are implemented in SYNPHOT.
J.Mack
02 Oct 2009
Pixel-to-pixel Flat Field Changes on the WFC (ACS ISR 07-01)
The pixel-to-pixel flat field changes noted by Bohlin and Mack (2005) for the WFC are further quantified. During each period between anneals, a population of pixels with lowered sensitivity develops which is largely reset by the next anneal.The sensitivity deficits are twice as large in the blue as in the red.The low QE pixels recover 90% of their losses on a time scale of a few monthly anneals, but never return fully.
R. Gilliland, R. Bohlin
22 Jan 2007
2006
SBC FLATS: PRISM P-FLATS and IMAGING L-FLATS (ACS ISR 06-08)
The internal deuterium lamp was used to illuminate the SBC detector through the PR110L and PR130L prisms for 12.2 hours each to produce a total of ~12,000 counts/pixel. This illumination does not simulate the OTA optics and, therefore, is not suitable for the production of a low frequency L-flat. However, the pixel-to-pixel P-flat is an improvement over the laboratory SBC P-flat currently used in the ACS pipeline for the two dispersing modes. In addition, short exposure internal lamp flats were obtained in the standard imaging filters. These flats have sufficient signal to define the low frequency L-flat field for five filters relative to the high signal F125LP flat, assuming that the relative lamp illumination does not vary with wavelength. These five ratio L-flats are smoother than the ratios of the current pipeline L-flats; but there is evidence for variation of the internal lamp illumination with wavelength. Thus, the current SBC L-flats may have some errors of a few percent due to local inappropriate lumpiness; but the alternative flats defined by the internal illumination may also have errors.
R.C. Bohlin, J. Mack
12 Dec 2006
WFC L-flats Post Cooldown (ISR06-06)
Following the recovery of ACS with Side 2 electronics, the temperature setpoint for WFC was lowered from -77C to -81C. By comparing internal tungsten exposures taken before and after cooldown, spatial changes in the WFC sensitivity (L-flats) have been computed for all filters with a unique useafter of July 4, 2006.
Gilliland, Bohlin, & Mack
31 Oct 2006
ACS Post Flash Measurements (ACS ISR 06-07)
The ACS CCDs are equipped with LEDs that can illuminate the chips with a controllable short exposure added to an image. The purpose of this is to counteract the loss of efficiency due to charge traps which develop from exposure to ionizing radiation causing a readout loss or redistribution of charge in science images. The LED post-flash exposure fills these traps but adds statistical noise. Mainly because of this noise, the mechanism has not been used yet on science data, but might come into play as radiation damage accumulates. Once a year the procedure has been tested to confirm that it is in working order and to measure its stability. Over a four year period the mechanism has continued to function and shows no variation in output.
C. Cox
24 Oct 2006
Relative Astrometry Within ACS Visits (ACS ISR 06-05)
The log files from APSIS, the ACS science team's image processing pipeline, have been analyzed to determine the relative astrometric scatter among ACS images observed within a single visit.
R. White
07 Aug 2006
Policy and Procedure for MAMA Targets Subject to Unpredictable Outbursts (ACS ISR 06-04)
The policy and procedure are described for the implementation of MAMA (currently, ACS/SBC) observations of targets subject to infrequent and unpredictable large outbursts, that would exceed the countrate limits should they occur during the observations.
N. Walborn, I. Dashevsky, A. Welty, J. Biretta
21 Apr 2006
Wavelength and Flux Calibration of the ACS/HRC PR200L prism (ISR 06-03)
Calibrations derived from cycle 13 observations for the PR200L prism are available as configuation files to aXe software.
S.S.Larsen, J. Walsh, M. Kummel
21 Mar 2006
Wavelength and Flux Calibration of the ACS/SBC PR110L and PR130L prisms (ISR 06-02)
Calibrations derived from cycle 13 observations are available as configuation files to aXe software.
S. Larsen
06 Mar 2006
PSFs, Photometry, and Astrometry for the ACS/WFC (ISR 06-01)
The effective PSF for 6 filters is presented.
J. Anderson, I. King
20 Feb 2006
2005
SBC L-flat Corrections and Time-Dependent Sensitivity (ISR 05-13)
Corrections to the SBC flatfields are described as well as the time-dependent component. Six new flats were delivered to the pipeline, the resulting photometric accuracy is now +/-1% for F115LP F122M, F125LP, and F140LP and +/-2% for F150LP and F165LP.
J. Mack et al.
18 Nov 2005
These HRC earth flats are not available in the routine pipeline, but may be more appropriate than the regular pipeline flats for observations of some large, diffuse objects such as the Moon, Jupiter, or the Orion Nebula, for example.
R. Bohlin et al.
28 Oct 2005
ACS/HRC Polarimetry Calibration IV. Low-Frequency Flat-Fields for Polarized Filters (ISR 05-10)
The goal of polarimetry calibrations for the ACS/HRC polarizer filters is to obtain photometric accuracy from polarized images at the level of 1%. So far such calibration has been done only for the standard wide-band filters. Thus, observations of the globular cluster 47 Tuc exposured through the filters F220W, F250W, F330W, F435W crossed with three blue-optimized UV polarizers, and F475W, F606W, F658N, F775W crossed with three visible-light-optimized polarizers have been used to examine how the sensitivity varies across the detector.
V.Kozhurina-Platais & J.Biretta
15 Aug 2005
The Internal CCD Flat Fields (ISR 05-09)
The internal flat field lamp has been used since launch to monitor the stability of the ACS HRC and WFC flat fields. The only ubiquitous change observed in these flat fields is an excess of pixel responses that are low. This excess of values that are low by more than 3 ? varies from factors of two to several over what is expected from the tail of the Gaussian distribution of Poisson statistics.
Occasionally, a pattern resembling the growth rings of a tree are seen on the WFC with an amplitude of ~1%; but this anomaly is sufficiently rare and short lived, so that the monitoring frequency can be decreased.
Ralph Bohlin & Jennifer Mack
20 Jul 2005
Updated Wavelength Calibration for the WFC/G800L Grism (ISR 05-08)
A revised wavelength calibration is presented for the G800L grism used with the ACS Wide Field Channel.
S. S. Larsen, J. R. Walsh
12 Jul 2005
Two-Gyro Pointing Stability of HST Measured with ACS (ISR 05-07)
We present the results of the pointing stability tests for HST as measured with the ACS/HRC during the two-gyro test program conducted in February 2005.
A. Koekemoer et al.
13 Jul 2005
Demonstration of a Significant Improvement in the Astrometric Accuracy of HST Data (ISR 05-06)
We demonstrate a technique that can significantly improve the absolute astrometric accuracy of HST data.
A. Koekemoer, B. McLean, M. McMaster, H. Jenker
13 Jul 2005
ACS Coronograph Performance in Two-Gyro Mode (ISR 05-05)
An analysis of the coronographic data quality during the February 2005 two-gyro test.
C. Cox & J. Biretta
29 Jun 2005
Flats: SBC Internal Lamp P-Flat (ISR 05-04)
The internal deuterium lamp was used to illuminate the SBC detector through the F125LP filter. This illumination does not simulate the OTA optics and, therefore, is not suitable for the production of a low frequency L-flat. However, the pixel-to-pixel P-flat is an improvement over the laboratory SBC flat currently used in the ACS pipeline for the six SBC imaging filters.
R.C.Bohlin & J.Mack
23 May 2005
Internal monitoring of ACS charge transfer efficiency (ISR 05-03)
We present the results of over two years of inflight charge transfer efficiency (CTE) monitoring of the CCDs in the Advanced Camera for Surveys (ACS), based on two internal tests: Extended Pixel Edge Response (EPER), and First Pixel Response (FPR). In general, we find that CTE losses are worst at the lowest signal levels, and at each signal level, CTE declines linearly over time, at a rate which is consistent with results from external photometric tests (Riess, 2004). We compare our inflight results to similar pre-flight baseline data, and to predictions for inflight performance, which were based on radiation tests.
Max Mutchler
08 Apr 2005
Flat-field and Sensitivity Calibration for ACS G800L Slitless Spectroscopy Modes (ISR 05-02)
The flat-fielding of the ACS WFC
and HRC for the G800L grism is
described. The efficacy of this
flat-field cube has been
investigated from observations of
a spectrophotometric standard at
different positions in the field.
By requiring the extracted spectra
from different positions over the
field to match in flux, a smooth
function was derived and applied
to the flat-field cube. The single
sensitivity curve for the whole
detector area is then determined
from the mean spectrum at the
different positions. Flat-fields
and sensitivity curves are
supplied for routine spectral
extraction of ACS slitless
spectral data as part of the aXe
package.
J. R. Walsh and N. Pirzkal
03 Mar 2005
Switching ACS from Side 1 to Side 2 electronics (ISR 05-01)
This ISR describes the steps taken to switch from MEB1 to MEB2 including detector startup procedures and recalibration requirements.
C. Cox
10 Feb 2005
2004
The Photometric Stability of ACS: Revisiting the Hubble Deep Field (ISR 04-17)
We utilized 10 epochs of 15-tile ACS WFC mosaics imaging the HDFN in the F850lp filter
over two years, and originally obtained for the science goal of finding type Ia supernovae
at z>1, to examine the photometric stability of the WFC (with at least filter f850lp).
Using repeated measurements of 371 stars, we performed a multi-variate linear regression
to determine the dependence of photometric variations on the time-dependent components
of parallel and serial CTE degradation as well as an overall time-dependence which
would indicate a change in the WFC?s sensitivity. Despite important differences between
the HDFN scenes and those in the original calibration field of 47 Tuc (i.e., source crowding
and sky level), we find the losses due to imperfect CTE to be consistent between the
two independent calibrations. Interestingly, we also find a decrease in the overall sensitivity
of the ACS WFC at a rate of 0.004 +/- 0.001 magnitudes per year (consistent with findings
based on 47 Tuc data from work in progress by Mack et al. 2005, in prep.).
A. Riess
27 Dec 2004
ACS coronographic flat fields (ISR04-16)
The effects of vignetting by the Lyot stop and the presence of the occulting spots and their time dependent motion on the ACS coronographic flat fields.
John Krist
30 Aug 2004
Multi-filter PSFs and Distortion Corrections for the HRC (ISR 04-15)
Fitting the low frequency and high frequency components of the HRC geometric distortion.
J. Anderson, I. King
23 Feb 2006
SBC Dark and Cumulative Images (ISR 04-14)
SBC dark images have been collected to provide dark current subtraction for science images and to monitor the instrument health and performance. Cumulative images which add counts from the whole history of the detector's use are also generated to anticipate any long-term degradation in performance. Images collected to date show no loss of efficiency or indications of any problem.
Colin Cox
23 Aug 2004
Cross-Talk in the ACS WFC Detectors. II: Using GAIN=2 to Minimize the Effect (ISR 04-13)
Cross talk is observed when using ACS/WFC. A strategy using GAIN=2 is described to minimize cross talk in ACS.
Mauro Giavalisco
10 Aug 2004
Cross-Talk in the ACS WFC Detectors. I: Description of the Effect (ISR 04-12)
Images acquired with ACS/WFC are affected by cross talk which is observed as negative ghost images. The phenomenology is described and its effect on photometry.
Mauro Giavalisco
10 Aug 2004
ACS/HRC Polarimetry Calibration III: Astrometry of Polarized Filters (ISR 04-11)
The goal of the astrometric calibration of the ACS/HRC polarizer filters is to obtain
a coordinate system free of distortion to a precision level of 1 mas.
Vera Kozhurina-Platais and John Biretta
12 Jul 2004
ACS Polarization Calibration - II. The POLV Filter Angles (ISR 04-10)
Describes the discovery, possible cause and POLV filter geometry of the anisotropy between polarized and non-polarized images.
J. Biretta, V.Kozhurina-Platais
17 Jun 2004
ACS Polarization Calibration I. Introduction and Status Report (ISR 04-09)
A status review of the ACS polarization calibration begins with a brief
description of the instrument and the GO science program, reviews the pre-flight calibration and on-orbit data. Various key parameters are derived and discussed. Closes with a summary of remaining issues, advice for observers, and a summary of future plans.
J. Biretta, V. Kozhurina-Platais, F. Boffi, W. Sparks, and J. Walsh
15 Jun 2004
Detector Quantum Efficiency and Photometric Zero Points of the ACS (ISR 04-08)
Characterizes the on-orbit sensitivity of the ACS CCDs cameras via
observations of spectrophotometric standard stars including updates to SYNPHOT. Photometric zero points are calculated for the WFC and HRC in VEGAmag, STmag and ABmag.
G. De Marchi, M. Sirianni, R. Gilliland, R. Bohlin,C. Pavlovsky, M. Jee, J. Mack, R. van der Marel & F. Boffi
15 Jun 2004
Bias and dark calibration of ACS data (ISR 04-07)
Production of the routine superbias and superdark reference files is explained.
We describe the primary features contained in these files, and provide
some guidance on how ACS users can produce even higher signal-to-noise calibrations
for datasets with extraordinary calibration requirements (e.g. deep field
observations).
Mutchler, Sirianni, Van Orsow, and Riess
24 May 2004
Time Dependence of ACS WFC CTE Corrections for Photometry and Future Predictions (ISR 04-06)
We see evidence for a modest increase in these photometric losses with time. We provide a global fitting formula to correct for CTE losses for all flux levels, sky values, and times. We extrapolate our time-dependent correction formula to the end of the decade and predict that the vast majority of science applications will retain their precision of flux measurements to better than a few percent.
A. Riess and J. Mack
05 May 2004
Results of UV Contamination Monitoring of the Advanced Camera for Surveys (ISR 04-05)
The UV performance and contamination of the HRC and SBC are discussed.
F. R. Boffi, R. C. Bohlin, G. De Marchi
08 Apr 2004
Elevated temperature measurements of ACS charge transfer efficiency(CTE) (ISR 04-04)
The ACS charge transfer efficiency (CTE) is analyzed during
March 2003 when the elevated temperature program was executed.
Max Mutchler and Adam Riess
01 Mar 2004
Best Gyroscope Usage to Maximize the HST Mission Lifetime (ISR04-03)
Without SM4, gyroscope survival is a critical factor for the HST Mission lifetime. A simple Monte-Carlo model is presented to calculate the survival probabilities for various scenarios. Predictions are made for the HST Mission end date (~2007) based on current gyroscope usage. Recommendations are made for alternative usage strategies that will maximize the overall HST mission lifetime. Such strategies have the potential to push forward the HST Mission end date by as much as 10 months.
R. van der Marel
21 Jan 2004
Lossy Compression of ACS images (ISR 04-02)
The Lossy Compression of ACS images
is analyzed and discussed.
Colin Cox
20 Jan 2004
ACS CCD Gains, Full Well Depths, and Linearity up to and Beyond Saturation (ISR 04-01)
Corrections to the supported gain values,
maps of the full well depth saturation and
linearity at different levels are presented.
R. L. Gilliland
05 Jan 2004
2003
Modelling the fringing of the ACS WFC and HRC chips (ISR 03-12)
Modelling of the layer structure of the ACS HRC and WFC CCD's is described.
Application of a fringe model to the correction of extracted spectra is outlined.
J. R. Walsh, W. Freudling, N. Pirzkal, A. Pasquali
10 Dec 2003
Flat Fields for Filter Wheel Offset Positions (ISR 03-11)
The ACS filter wheel movements are accurate to one motor step, which leads to errors that exceed one percent in the flat fields over small regions for a few filter combinations. For seven of these filter modes on the WFC and six on HRC with the worst blemishes, flat fields are available as a function of filter wheel offset step; and the pipeline data processing will select the flat corresponding to the offset step of each observation.
Bohlin, Wheeler, Mack
29 Oct 2003
A method is presented for determination of the low-frequency
flat-field (L-flat) structure from photometry of a stellar field that
is imaged multiple times with different pointing or roll. A numerical
implementation of the algorithm is presented and its accuracy verified
using tests with artificially generated data. The software was used to
generate the L-flats currently in the ACS pipeline. Newly implemented
features in the software should allow further improvements in these
L-flats.
R. van der Marel
30 Sep 2003
On-orbit Calibration of ACS CTE Corrections for Photometry (ISR 03-09)
A preliminary on-orbit calibration of the photometric losses due to
imperfect CTE.
The characterization of the WFC CTE in this report has been superseded by ACS ISR 04-06.
Adam Riess
21 May 2004
The verification tests for the Astronomer's Proposal Tool (APT) Exposure Time Calculator (ETC) for the Advanced Camera for Surveys (ACS) are presented.
F.R. Boffi et al.
10 Jul 2003
The in-orbit wavelength calibration of the HRC G800L grism (ACS ISR 03-07)
G800L grism spectra of the Wolf-Rayet star WR45, obtained with the High Resolution
Channel (HRC) during the Servicing Mission Orbital Verification (SMOV) tests, are presented.
The target has been observed in five different positions across the HRC field of
view in order to quantify the field dependence of the grism physical properties and wavelength
solution.
A. Pasquali, N. Pirzkal, J. R. Walsh
09 Jul 2003
The ACS point spread function remains fairly stable over its field of view, compared to the
PSFs in WFPC2 or STIS. However, ACS/WFC PSF core width and ellipticity variations
are large enough to be of concern to those undertaking very small aperture photometry or
measuring small, bright-nucleus galaxy ellipticities.
J. Krist
25 Jun 2003
ACS Background Light vs. Bright Earth Limb Angle (ACS ISR 03-05)
The background contributed by scattered
Earth light at various angles is discussed
along with flat field artifacts.
John Biretta et al.
23 Jun 2003
Elevated Temperature measurements of Hot Pixels (ACS ISR 03-04)
We have investigated the dark rates and hot pixel counts by raising
the WFC temperature. We find that the
predominant effect of a change in temperature is a simple scaling
of the dark rate in each pixel. These results are applicable to the
effects of the Aft Shroud Cooling System installation in
in Servicing Mission 4.
C. Cox, M. Mutchler, D. van Orsow
23 Jun 2003
Stability and Accuracy of HRC and WFC Shutters (ACS ISR-03-03)
Calibration observations (9662) have been used to quantify precise exposure time values, stability and shading effects down to the shortest allowed exposures (0.1s HRC, 0.5s WFC).
Gilliland R.L., Hartig G.
03 Jun 2003
NUV Earth Flats (ACS ISR 03-02)
Creation of Earth flats for ACS/HRC modes
are described including red leak and dust mote
information.
R.C. Bohlin, J. Mack
21 Apr 2003
Wavelength calibration of the WFC G800L grism (ACS ISR 03-01)
We present the G800L grism spectra of Wolf-Rayet
stars acquired with the ACS/WFC during SMOV
and early Cycle 11. We discuss the procedure for
fitting the dispersion correction of the grism. We also
describe the calibration files derived from these data
which are used by the ST-ECF extraction package
"aXe".
Pasquali, Pirzkal, Walsh (ST-ECF)
05 Mar 2003
2002
ACS Coronagraph Update for Cycle 12 Proposers (ISR 02-11)
Small time-and-initialization-dependent instabilities
in the ACS coronagraph have led to revisions of the
coronagraph commanding procedures and to the suggested
methods for optimizing coronagraphic observations. An
example optimized sequence is given.
J. Krist
18 Dec 2002
ACS software tool development (ISR 02-10)
We describe the anticipated software tool
development requirements for ACS for the
period September 2002 to mid-2003, including
issues related to image registration and
combination.
W.B. Sparks, W.J. Hack, R.N. Hook, A. Koekemoer
16 Dec 2002
The Projected Growth of Hot Pixels on ACS WFC (ISR 02-09)
The anneal rate of hot pixels on the ACS WFC is discussed.
A fitted, successive annealing function is used to project
forward in time the expected fractional coverage of the CCD by hot pixels.
A. Riess
13 Dec 2002
ACS L-Flats for the WFC (ISR 02-08)
The uniformity of the WFC detector response has been assessed by using multiple dithered pointings of dense stellar fields.
The original WFC laboratory flat fields produce photometric errors of +-5 to +-9 percent from corner-to-corner.
J. Mack
21 Aug 2002
A first look at cosmic rays on ACS (ISR 02-07)
We have made an initial study of the characteristics of cosmic ray impacts on the two ACS
imaging cameras, HRC and WFC. Distributions of sizes and anisotropies are determined for
both cameras, characteristics which can be useful for distinguishing cosmic rays from
astrophysical sources in a single image.
Riess
06 Jun 2002
A first look at hot pixels on ACS (ISR 02-06)
We have made an initial study of hot pixels on the ACS CCD s, i.e.those with elevated
dark current. The characteristics of these pixels are similar to those seen on previous
CCD s flown on HSTand are likely caused by radiation damage.
Riess, Mutchler, Van Orsow
06 Jun 2002
HRC and WFC Flat Fields: Dispersors, Anomalies, and Photometric Stability (ISR 02-04)
The flat field correction scheme for the ACS prism (PR200L) and grism (G800L)
is discussed.
R. Bohlin
18 Mar 2002
HRC and WFC Flat Fields: Ramp Filters (ISR 02-01)
Discusses the ground flats for HRC and WFC ramp filters.
Bohlin
15 Jan 2002
2001
HRC and WFC Flat Fields: Standard Filters, Polarizers, and Coronograph (ISR 01-11)
Laboratory flats with simulated sky illumination of the CCD cameras have been obtained for supported and many unsupported ACS modes.
All 157 flats are now available as reference files for the pipeline processing of ACS observations from Cycle 11.
Ralph Bohlin
17 Dec 2001
ACS dither and mosaic pointing patterns (ISR 01-07)
We provide some background on pointing the ACS, and present the
dither and mosaic patterns that will be provided as a convenience for HST
Cycle 11 Phase II proposal writers.
Max Mutchler
21 Dec 2001
ACS thermal control with ASCS (ISR 01-05)
The components of the ACS need to be maintained within certain temperature limits for health and safety considerations and for the optimal scientific use of the cameras. Current planning calls for the NICMOS cryolcooler to be installed at the same time as the ACS but the ASCS to be placed on a later mission. The ACS will operate for at least a year without the cooling benefit of the ASCS.
C. Cox
08 Jun 2001
Initial Implementation Strategy for Drizzle with ACS (ISR 01-04)
In order to provide geometric correction for single pointing ACS images, and to provide geometric correction together with simple image combination for associations of ACS images, we describe plans to implement the "drizzle" code by means of a python wrapper, and to use this wrapper in calacs.
W. Sparks
08 Jun 2001
ACS Grism Simulations using SLIM 1.0 (ISR 01-03)
We introduce SLIM, a slitless spectroscopy simulator written in Python which can be used to simulate the ACS grism and prism modes. Here, we outline the features of SLIM and present some WFC and HRC grism simulations of emission line objects.
N. Pirzkal
08 Jun 2001
The Effective Spectral Resolution of the WFC and HRC Grism (ISR 01-02)
We present SLIM simulations of the WFC and HRC grism, obtained by varying the object size and orientation with respect to the dispersion axis. Our aim is to quantify the extent by which the object extension along the dispersion axis can degrade the nominal spectral resolution of the grism.
A. Pasquali
08 Jun 2001
2000
Geometric Distortion Table: IDCTAB (ISR 00-11)
The new reference table, IDCTAB, will support the description of geometric distortion models for instruments. This report describes the columns in the table and how the coefficients in the table can be used.
W. Hack
08 Jun 2001
Flats: Preliminary WFC Data and Plans for Flight Flats (ISR 00-10)
The ACS WFC pixel-to-pixel P-flats with the build-3 detector are discussed and compared to the HRC build-2 P-flats. The goals for these WFC and HRC ground flats are stated.
R. Bohlin
08 Jun 2001
ACS WFC CCD Radiation Test: The Radiation Environment (ISR 00-09)
The space environment is a complex, orbit dependent phenomenon. CCD detectors are particularly vulnerable to damage by ionizing radiation. This document summarizes the modeling and analysis that was performed to determine the appropriate exposure level for ground testing of the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) Charge-Coupled Device (CCD) detector.
M. Jones
08 Jun 2001
Our baseline suite of test cases for the Spectroscopic Exposure Time Calculator are documented for all five spectroscopic modes with a variety of point source flux distributions.
F. R. Boffi
08 Jun 2001
The verification tests for the ACS Ramp Filter Exposure Time Calculator are presented. Our baseline suite of test cases includes one calculation for all filter modes with the same target, plus one subset for all kinds of targets through the same filter.
D. Van Orsow
08 Jun 2001
The verification tests for the Imaging Exposure Time Calculator for the Advanced Camera for Surveys are presented. Our baseline suite of test cases includes one calculation for all filter modes with the same target, plus one subset for all kinds of targets through the same filter.
F. Boffi
08 Jun 2001
Measured Throughput and Bandpass of the RAMP Filters (ISR 00-05)
The ACS ramp filters are characterized by transmission curves which populate the STScI Synphot database for use in the Exposure Time Calculator.
R. Bohlin
08 Jun 2001
Software tools for ACS: Geometrical Issues and Overall Software Tool Development (ISR 00-03)
We describe the issues relating to internal geometrical distortions in the ACS. A software tool development route is outlined and we describe other software tool development activities.
W. Sparks
08 Jun 2001
ACS Default (Archival) Pure Parallel Program (ISR 00-02)
We describe the initial default non-proprietary pure parallel program for the Advanced Camera for Surveys. We describe the observing sequence and outline scientific questions that may be addressed with the data.
W. Sparks
08 Jun 2001
Predicted Sensitivity and Dispersion of the Prisms and Grism (ISR 00-01)
The three prisms and grism in ACS are characterized in terms of dispersion relations and sensitivity.
R. Bohlin
08 Jun 2001
1999
ACS Quicklook PDF products (ISR 99-10)
This report details the features of the ACS quicklook PDF products produced by the HST data pipeline.
A. Suchkov
08 Jun 2001
ACS calibration pipeline testing: cosmic ray rejection (ISR 99-09)
We describe the testing that was done to ensure that CALACS properly rejects cosmic ray contamination when combining multiple images.
M. Mutchler
08 Jun 2001
CALACS reference files (ISR 99-08)
This report describes the reference files used by CALACS to calibrate ACS observations.
W. Hack
08 Jun 2001
The Solar Blind Channel Bright Object Limits for Astronomical Objects (ISR 99-07)
Tables of limiting magnitudes for
all observation modes of the ACS
Solar Blind Channel are calculated
for a range of stellar energy
distributions, using Kurucz model
fluxes and observed standard stars.
F.R. Boffi and R.C. Bohlin
25 Oct 2004
ACS calibration pipeline testing: error propagation (ISR 99-06)
This report details how CALACS produces ERR (error) array output.
D. VanOrsow
08 Jun 2001
Design of the ACS science headers (ISR 99-05)
The decisions made in the design of the data format and packaging of the ACS science headers.
R. Jedrzejewski
08 Jun 2001
ACS calibration pipeline testing: basic image reduction (ISR 99-04)
This report describes the basic testing that was done to ensure that CALACS properly reduces raw ACS images and makes the corresponding modifications to their headers.
M. Mutchler
08 Jun 2001
CALACS operation and implementation (ISR 99-03)
This report describes the usage and implementation of CALACS. Instructions for using stand-alone tasks and the format of the input data are described in this paper. Furthermore, the processing steps for ACS data and the functional flow of the entire pipeline is outlined, along with descriptions of how the memory model was implemented.
W. Hack
08 Jun 2001
Flats: SBC Data from Thermal Vacuum Testing (ISR 99-02)
SBC flats for the six filters and two prisms taken during thermal vacuum testing at GSFC in 1999 March are characterized.
R.C. Bohlin
16 May 2002
Flats: Preliminary HRC Data and On-Orbit Plans (ISR 99-01)
The flat field baseline goal is to obtain a complete set of pixel-to-pixel P-flats before launch and to use the onboard lamps to track changes. A second goal of the ground calibration program is to obtain the low fre-quency L-flat variation over the field of view.
R. Bohlin
08 Jun 2001
Performance of the onboard compression algorithm for ACS (ISR 98-04)
An extensive set of experiments was performed to test the performance of the onboard compression algorithm created for ACS by R. White.
F. Boffi
08 Jun 2001
1998
Bright object protection for the ACS MAMA detector (ISR 98-03)
Bright object protection for the ACS MAMA is similar in concept to that for the STIS FUV MAMA, but several mechanisms are discussed which provide better protection for the ACS MAMA.
C. Cox
08 Jun 2001
Dithering strategies for ACS (ISR 98-02)
We review the motivations for dithering exposures with the ACS, discuss possible strategies for combining dithered exposures automatically and the implementation of dither patterns in RPS2.
M. Stiavelli
08 Jun 2001
CALACS Design: Lessons Learned from CALSTIS (ISR98-01)
This report documents the basic design of those parts of CALSTIS relevant for CALACS.
W.Hack
13 Dec 2006
1997
Data Compression for ACS (ISR 97-02)
The algorithm for on-board compression on the fly of ACS data is briefly reviewed and its benefits discussed.
M. Stiavelli
08 Jun 2001
HST Cycle 9 reference mission (ISR 97-01)
We describe the expected usage of the ACS during Cycle 9 and estimate ground system requirements for the full complement of HST instruments available for Cycle 9. We recommend that the current ground system throughput capacity be doubled to support an average daily capacity of 12 Gbits/day and a peak capacity of 18 Gbits/day following the third servicing mission.
M. Stiavelli
08 Jun 2001
Related ISRs from the Telescopes Branch
2013
Study of the evolution of the ACS/WFC sensitivity loss (ISR 13-01)
We present a study of the sensitivity loss of the ACS/WFC CCDs for one medium-band, eight broad-band, and three narrow-band filters. This study was done using a calibration field lo- cated 6.7 arcmin West of the center of globular cluster 47 Tucanae. For pre-SM4 images, a comparison of the sensitivity loss rates found in this research with those calculated using stan- dard white dwarf stars by Bohlin, R. et al. (ISR ACS 2011-03) shows excellent agreement within the uncertainties of the two methods. We found that the sensitivity losses are less than ∼0.0004 mag/year. We also have a baseline of at least three years of post-SM4 observations of the 47 Tucanae calibration field. Our study shows that, on average, the sensitivity loss post- SM4 is negligible. This is a remarkable result considering that ACS is an instrument that has been in space for over ten years and subject to contamination.
Leonardo Ubeda & Jay Anderson
29 Jan 2013
2012
A new accurate CTE photometric correction formula for ACS/WFC (ISR 12-05)
We present a new CTE photometric correction formula based on observation of 47Tuc obtained during Cycles 17, 18 and 19. Images were taken with two filters and different exposure times, in order to sample a wide range of background levels. In addition, the Cycle 19 program included imaging of a denser field near the center of 47Tuc with the F502N filter. Thanks to the increased number of stars available for the analysis, we are able to characterize CTE losses down to the lowest background levels (down to ~0.2e-) without significant loss of accuracy with respect to higher sky levels. The data from these three Cycles allow us to derive a new form of the correction formula that is significantly more accurate that those previously published. The formula may be used to correct stellar photometry for CTE losses on drizzled images taken after SM4. We compare the results of our new CTE correction to previous versions of the correction formula for ACS/WFC, and with the pixel-based CTE correction that is currently available as part of CALACS. The formula presented in this ISR and the pixel-based correction are in substantial agreement at high stellar fluxes and for relatively high background levels. However, the former is significantly more accurate than the latter for faint stars superimposed to a low sky background.
M. Chiaberge
03 Oct 2012
Assessing ACS/WFC Sky Backgrounds (ISR 12-04)
This report compares the on-orbit sky background levels present in Cycle 18 ACS/WFC full- frame images against estimates provided by the Exposure Time Calculator (ETC). Backgrounds of over ~20 e- can alleviate charge-transfer efficiency (CTE) losses, which especially affect low S/N sources. HST observers can use these estimates to anticipate the natural background that should be present in their exposures, and can then determine whether they want to supplement that background with a post-flash to improve the CTE – at the cost of more background noise.
Sokol, Anderson, Smith
31 Jul 2012
Study of the evolution of the ACS/WFC charge transfer efficiency (ISR 12-03)
We perform a comprehensive and detailed study of the evolution of the effect of charge transfer
efficiency (CTE) of the Wide-Field Channel of the Advanced Camera for Surveys (ACS). The
study is based on the profiles of warm pixels in all the dark frames ever produced by ACS between
2002 and 2011. We apply the pixel-based empirical approach by Anderson&Bedin (2010,
PASP, 122, 1035) which restores flux, position and shape of sources in the original images. We
demonstrate that this image-restoration process properly accounts for the time and temperature
dependence for CTE in ACS, and that it works for all epochs: the original setting when the
camera was operated at -77C and also on the post-SM4 data obtained with the current temperature
set at -81C. We also demonstrate that the code has been successfully integrated in the
ACS calibration and reduction pipeline CALACS.
Leonardo Ubeda & Jay Anderson
12 Mar 2012
Pixel-based correction of the ACS/WFC signal-dependent bias shift (ISR 12-02)
Since the installation of the CCD Electronic Box Replacement (CEB-R) during Servicing
Mission 4, the ACS Wide Field Channel has exhibited two bias anomalies that have been linked
to the CCDs’ external preamplifiers and the CEB-R’s dual-slope integrators. One anomaly is a
temporally stable bias gradient of 5-10 DN across each quadrant; the other anomaly is a local
bias shift that depends on the pixel signal and has an e-folding time comparable to the serial
transfer of several hundred pixels. Although the bias shift is relatively small (0.02−0.3% of the
pixel signal), it can be an impediment to high-contrast science observations and to the removal
of other electronic anomalies (e.g., 1/f noise). We have developed a pixel-based algorithm for
correcting the signal-dependent bias shift in full-frame WFC images. We describe the
calibration and tuning of this algorithm for each WFC quadrant, and we discuss a strategy for
implementing this algorithm in the standard CALACS image processing pipeline.
Golimowski, David et al
16 Feb 2012
Flux Calibration of the ACS CCD Cameras IV. Absolute Fluxes (ISR 12-01)
ISRs I-III in this series define the charge transfer efficiency (CTE) for the CCD detectors, the encircled energy fractions, and the optical throughput degradation. This fourth ISR es- tablishes the absolute flux calibration for the photometry, as corrected with the algorithms specified in I-III. Synthetic photometry from the SEDs of three primary hot 30,000-60,000K WDs define these sensitivity calibrations for the standard HRC and WFC filters. Even though the external uncertainty for the absolute flux of the three primary WD flux standards is ~1%, the internal consistency of the sensitivities is ~0.3%. However, when these WD sensitivities are applied to the cooler F, G, and K stars, there are internal inconsistencies of 1-2% for the F775W, F814W, and F850LP filters. For the same cooler stars, the other broadband filters are internally consistent to better than the 1% ACS flux calibration goal after applying the corrections and calibrations specified here. One filter F435W requires a small shift of the long wavelength edge of the bandpass by 18Å toward longer wavelengths in order to reduce the cool star residuals from as much as 2% to <0.5%; but wavelength shifts cannot remedy the flux discrepancies for the F, G, and K stars in the three long wavelength filters.
For HRC, the sensitivities change by 0.5-2% as a monotonic function of wavelength because of improvements in data processing. Additional residual corrections for individual filters
are typically <0.5% for wide filters in both cameras. For the medium and narrow filters,
these residuals are as large as ~3% for the WFC F550M and ~4% for HRC F344N. After implementing these throughput updates, the synthetic predictions of the WFC and HRC count rates for the average of the three primary WD standard stars agree with the observations to 0.1% for every filter.
Bohlin, Ralph C.
07 Feb 2012
2011
Post-SM4 ACS/WFC Bias Striping: Characterization and Mitigation (ISR 11-05)
Images taken with the Advanced Camera for Surveys Wide Field Channel (ACS/WFC) after
Servicing Mission 4 newly exhibit a row-correlated noise imparted by the CCD Electronics
Box Replacement (CEB-R). We characterize the noise component and assess algorithms for
software mitigation.
Grogin, N. A., et. al.
27 Jul 2011
ACS after Servicing Mission 4: The WFC Optimization Campaign (ISR 11-04)
The ACS CCD Electronics Box Replacement (CEB-R) installed during SM4 features a Teledyne SIDECAR ASIC that permits optimization of the WFC via adjustment of CCD clock voltages, bias voltages, and pixel transmission timing. A built-in oscilloscope mode allows sensing of the analog signal from each output amplifier. An on-orbit campaign to optimize the performance of the WFC was undertaken at the start of the SMOV period. Initial tests with pre-SM4 default voltages and timing patterns showed that WFC’s performance matches or exceeds its pre-failure levels, notwithstanding the expected increases in dark current and hot pixels and the decline in charge-transfer efficiency due to prolonged exposure to HST’s radiation environment. The WFC2 CCD exhibited anomalous behavior when operated with nondefault settings of its amplifiers’ reset-drain voltage (VOD). The CCD again displayed normal behavior when VOD was restored to its default setting. Consequently, the Optimization Campaign was truncated after two iterations, and ACS science operations commenced with the pre-SM4 default configuration.
David Golimowski, et. al.
15 Dec 2011
Flux Calibration of the ACS CCD Cameras II. Encircled Energy Correction (ISR 11-02)
In order to convert a point source flux calibration into a surface brightness calibration, the total response to a point source in an infinite aperture is required. In practice, infinite is defined as an aperture with a radius of 5".5. However, aperture photometry for such a large radius is exquisitely sensitive to the measured sky background level. In order to minimize uncertainties, corrections from one arcsec to infinity (5".5) are derived from averages over as many heavily exposed, isolated stellar images as possible. Calibrations, such as the change in sensitivity with time or flux calibrations from specific standard stars, utilize the low noise photometry for one arcsec radius; and the average correction to infinite aperture is used only as required. This ISR deals with the ACS encircled energy for one arcsec relative to infinity for the HRC and WFC.
Ralph C. Bohlin
02 May 2011
ACS Instrument Science Reports
None
ITT
05 Jul 2012
Flux Calibration of the ACS CCD Cameras III. Sensitivity Changes over Time (ISR 11-03)
The flux calibration of HST instruments is normally specified after removal of artifacts such
as a decline in charge transfer efficiency (CTE) for CCD detectors and optical throughput degradation. This ACS ISR deals with the HRC and WFC losses in sensitivity from polymerization of contaminants on the optical surfaces. Prior to the demise of the ACS CCD channels on 2007 Jan. 27, the losses are less than ~0.003 mag/year, except for the two
short wavelength HRC filters F220W and F250W. The measurements of the sensitivity loss rates using a set of observations of WD flux standards has a precision of ~0.0008 mag/year, while the sensitivity loss rates using repeated observations of the globular cluster 47 Tuc are
probably consistent within their currently lower precision.
Following the revival of ACS WFC during the Servicing Mission 4 (SM4) in 2009 May, the gain of the new electronics was set so that the measured signal in electrons s^-1 matched the signal for the same 47 Tuc field as measured in 2002 with the F606W filter. However, a longer time baseline is required to reliably determine the post-SM4 loss rates.
Bohlin, R., Mack, J., Ubeda, L.
03 Jun 2011
Flux Calibration of the ACS CCD Cameras I. CTE Correction (ISR 11-01)
The flux calibration of HST instruments is normally specifed after removal of artifacts such
as a decline in charge transfer efficiency (CTE) for CCD detectors and optical throughput degradation. This ISR deals with ACS/WFC CTE losses, which had been considered negligible for bright stars prior to the demise of the ACS CCD channels on 2007 Jan. 27.
Following the revival of ACS WFC during the Servicing Mission 4 (SM4) in 2009 May, CTE corrections are now typically several tenths of a percent and should be included, even for our bright standard star observations that utilize a standard reference point which is only 512 rows from the CCD amplifier B readout corner. For such bright standard stars with negligible background signal, a simple correction algorithm with an accuracy of better than 0.1%
is derived, which eliminates the need to execute the CTE correction code for the complete image.
Bohlin, R. & Anderson, J.
19 Jan 2011
2010
We use an empirical approach to characterize the effect of charge-transfer efficiency (CTE) losses in images taken with the Wide-Field Channel of the Advanced Camera for Surveys (ACS). The study is based on profiles of warm pixels in 168 dark exposures taken between 2009 September and October. The dark exposures allow us to explore charge traps that affect electrons when the background is extremely low. We develop a model for the readout process that reproduces the observed trails out to 70 pixels. We then invert the model to convert the observed pixel values in an image into an estimate of the original pixel values. We find that when we apply this image-restoration process to science images with a variety of stars on a variety of background levels, it restores flux, position, and shape. This means that the observed trails contain essentially all of the flux lost to inefficient CTE. The Space Telescope Science Institute is currently evaluating this algorithm with the aim of optimizing it and eventually providing enhanced data products. The empirical procedure presented here should also work for other epochs (e.g., pre-SM4), though the parameters may have to be recomputed for the time when ACS was operated at a higher temperature than the current -81°C. Finally, this empirical approach may also hold promise for other instruments, such as WFPC2, STIS, the ACS's HRC, and even WFC3/UVIS.
Jay Anderson and Luigi Bedin
07 Sep 2010
ACS/WFC Crosstalk after Servicing Mission 4 (ISR 10-02)
The ACS/WFC detector consists of two CCDs, each of which is read out through two amplifiers. While reading each quadrant of the detector, the electronic crosstalk between the amplifiers induces faint, typically negative, mirror-symmetric ghost images on the other three quadrants. The effect is strongest for high-signal offending (source) pixels. Analysis of pre-SM4 crosstalk showed that its impact on ACS/WFC science is not significant and can be ignored in most science applications. In this report, we analyze crosstalk after SM4. Crosstalk due to low-signal offenders is much weaker than before SM4 and does not produce ghosts similar to those seen in pre-SM4 images. For high-signal offending pixels, we find substantial differences between the gain=1 eˉ/DN and gain=2 eˉ/DN cases. For the default gain setting of 2, the crosstalk is similar to what it was before the SM4, up to 5–8 eˉ per pixel on the same CCD. For gain=1, the crosstalk is ~100 eˉ per pixel for saturated offending pixels on the same CCD, which is more than an order of magnitude above the pre-SM4 level. The crosstalk from saturated pixels is ~20–30 eˉ per pixel on the other CCD, which is also much higher than it was before SM4.
Anatoly Suchkov, et al.
06 Apr 2010
2009
Charge Transfer Inefficiency (CTI) due to radiation damage above the Earth's atmosphere creates spurious trailing in Hubble Space Telescope (HST) images. Radiation damage also creates unrelated warm pixels - but these happen to be perfect for measuring CTI. We model CTI in the Advanced Camera for Surveys (ACS)/Wide Field Channel and construct a physically motivated correction scheme. This operates on raw data, rather than secondary science products, by returning individual electrons to pixels from which they were unintentionally dragged during readout. We apply our correction to images from the HST Cosmic Evolution Survey (COSMOS), successfully reducing the CTI trails by a factor of #30 everywhere in the CCD and at all flux levels. We quantify changes in galaxy photometry, astrometry and shape. The remarkable 97 per cent level of correction is more than sufficient to enable a (forthcoming) reanalysis of downstream science products and the collection of larger surveys.
Richard Massey, Chris Stoughton, Alexie Leauthaud, Jason Rhodes, Anton Koekemoer, Richard Ellis, and Edgar Shaghoulian
26 Jan 2010
ACS after SM4: Relative Gain Values Among the Four WFC Amplifiers (ISR 09-03)
For the default setting of gain=2, the individual gain values of the four WFC amplifiers are determined from internal flat field observations. The average absolute gain remains unchanged, but matching the flat fields at the boundaries of the four quadrants provides a more accurate determinations of the relative gains among the four separate amplifiers.
R. C. Bohlin, A. Maybhate, and J. Mack
12 Oct 2009
Re-measurement of ACS/SBC dark images (ISR 09-02)
New measurements were made of the SBC dark rate in December 2008. As a function of temperature, the dark
rate was found not to have changed over the two year period. A few images were found to have abnormally high count rates. The effect was traced to a flight passage within the outer edges of the South Atlantic Anomaly. The effect of detector temperature on the dark rate is discussed.
Colin Cox
01 May 2009
Updated CTE photometric correction for WFC and HRC (ISR 09-01)
Observations for the ACS external CTE monitoring program were performed in Cycles
11 through 14 using both WFC and HRC. The aim of the program is to monitor the
change in CTE in both cameras, and provide correction formulae for stellar photometry.
Here we present the results of the data analysis, and we provide correction formulae for
photometry on drizzled images for both HRC and WFC. The correction formulae we
present here are significantly more accurate than those previously published, both
because of the larger amount of data available and because of a more advanced analysis
strategy. Observers are encouraged to use the new formulae to correct photometry,
especially in presence of faint stars on a low sky background.
M. Chiaberge
07 Apr 2009
2008
ACS CCD Image Anomalies in the Hubble Legacy Archive (HLA ISR 08-01)
The Hubble Legacy Archive (HLA) was created to make high-quality calibrated HST image products easily available to the astronomy research community. In its first public release, the HLA database has been populated with calibrated images from the Advanced Camera for Surveys (ACS). This report serves as a guide to identify ACS image anomalies that cannot currently be corrected in the HLA calibration pipeline.
M. Stankiewicz
05 Dec 2008
A New Geometric Distortion Solution for the ACS/SBC (ISR 08-02)
We have used ACS/SBC observations of two UV astrometric fields derived from ACS/HRC data to create a new geometric distortion solution for the Solar Blind Channel. The new solution consists of three components: (a) a filter-dependent linear part that takes into account the existence of three epoch ranges in the SBC alignment; (b) the remaining 24 higher-order components of a 4th degree polynomial; and (c) a fine-correction look-up table. Some of the previous solutions introduced possible errors of several pixels when producing mosaics due to an incorrect orientation. That issue has been solved and the accuracy due to the solution itself (excluding rotation) has been improved by an additional factor of 1.5-2.0. As a result, it is now possible to measure positions of medium to high S/N stars with a relative astrometric accuracy of 3-4 mas.
Jesus Maiz Apellaniz
10 Apr 2008
HST Focus Variations with Temperature (ACS ISR 08-03)
One of the main advantages of space observatories is the quality and stability of the point spread function that allows programs not feasible from the ground. However, when pushed to the limits, even the Hubble Space Telescope exhibits variations in the PSF that can be problematic for studies like weak lensing or identification of the host halos of bright quasars at high redshift. These variations are primarily due to small displacements in the focus of the telescope, which to a first approximation can be ascribed to temperature variations. The aim of this report is to characterize the variation of the focus position for HST in terms of the average temperature sensor values of the telescope. We propose a comprehensive temperature-focus model able to predict the position of the focus at the micron level over a dynamic range that extends from sub-orbital variations (< 1 hour) to seasonal and yearly variations. This allows us to predict the focus position significantly more accurately than using interpolation of the monthly direct measurements. Our model is also at least as accurate as the previously proposed breathing model for sub-orbital variations and it is the first one that describes longer term variations, potentially helping the determination of the model point spread function for observations lacking reference point sources.
Daiana Di Nino
08 May 2008
Updated Flux Calibration and Fringe Modelling for the ACS/WFC G800L Grism (ISR 08-01)
A revised flux calibration is presented for the G800L grism with the ACS Wide Field Channel.
H. Kuntschner, et al
25 Jan 2008
2007
Two astrometric fields for UV observations (ACS ISR 07-09)
I present the data for two fields that can be used to obtain accurate astrometric calibrations in the UV. The two
fields are located in NGC 604 (a Scaled OB Association in M33) and NGC 6681 (a Galactic globular cluster).
The coordinates are derived from multiple ACS/HRC exposures, use the Anderson and King (2004) geometric
distortion solution, have typical relative uncertainties of 1 mas, and can be used to derive geometric distortion
solutions for detectors with a field of view smaller than 1′. In the process of generating the astrometric fields,
the long-term stability of the HRC geometric distortion solution has been successfully tested. In two future ISRs
these results will be used to derive new geometric distortion solutions for the STIS NUV- and FUV-MAMA and
for the ACS SBC(Revised on 4 Oct 2007).
Jesus Maiz Apellaniz
19 Nov 2007
ACS PSF Variations with Temperatures (ISR 07-12)
We have used the HST ACS/WFC observations of a Galactic bulge field taken over a continuous interval of 7 days (Prop 9750) to investigate the possible dependence of the ACS focus with the external temperatures. This dataset allows us to investigate possible focus variations over timescales of a few hours to a few days. The engineering data related to the external temperatures for this duration show that the maximum temperature change occurred over the first 1.5 days. Among all the different temperatures recorded, the truss diametric differential and the truss axial temperatures are the only two temperatures which have the same timescale of variation as the PSFwidth variations. The PSF-widths also strongly correlate with these two temperatures during this time interval. We empirically fit the PSF-width variations with these 2 temperature sensor values. This suggests that the focus has a similar dependence, and we recommend that this finding be followed up with the determination of actual focus values to check if the focus values indeed have the same correlation. If so, the temperature data can be useful in estimating the focus values, which can then be used to predict the PSFs to a first order.
K.C.Sahu
18 Sep 2007
Calibration of Ramp Filters Using the ACS Grism (ISR 07-11)
Ramp filters provide ACS users with the equivalent of tunable narrow and medium-width passband filters. Here we analyze images taken under calibration programs CAL 9671 and CAL 10742 to measure the wavelength calibration of the ACS ramp filters by observing standard stars with the ramp filters crossed with the ACS G800L grism. We find that the tested HRC ramp filters are relatively well centered on the requested wavelengths. A number of the WFC filters, however, display significant o sets from the desired central wavelength. While the WFC direct images show large image o sets (wedges) due to the crossed filters, we have attempted to remove these o sets. Our results suggest we have reduced these o sets to one pixel or less both in images taken with the ramps crossed with wideband filters and in the spatial direction of images taken with the ramps crossed with the grism. O sets in the spectral direction of the grism images cannot be distinguished from a wavelength miscalibration. Data taken of line emission from an astrophysical source through the FR782N filter and compared to ground-based imaging suggest that this filter is well calibrated, in contrast to the result of the crossed filter observations reported here. Ray tracing simulations, deeper second order grism spectra, and further observations of astrophysical targets with known strong spectral features should be able to determine the extent to which the wavelength o sets reported here are real or an artifact of the calibration method.
A.S.Fruchter
18 Sep 2007
ACS Polarization Calibration - Data, Throughput, and Multidrizzle Weighting Schemes (ISR 07-10)
A subset of the polarized images from calibration proposals 9586, 9661, and 10055 were
analyzed to help determine the polarization calibration accuracy level of the ACS camera.
The polarization values found here are shown to be accurate to better than 1%. Differences in Multidrizzle weighting schemes are examined.
M. Cracraft, B. Sparks
20 Aug 2007
Variation of the Distortion Solution of the WFC (ACS ISR 07-08)
The linear skew terms have changed monotonically since ACS was installed 2002. These skew terms cancel out when relating data sets taken at the same epoch and same orientation, but they must be accounted for when dealing with observations taken at different roll angles.
J. Anderson
18 Sep 2007
Astrometric calibrations of JWST will use observations of a reference field in the Large Magellanic Cloud. This field will itself be astrometrically calibrated using observations with ACS/WFC on HST. The understanding of the ACS/WFC scale and rotation obtained through these analyses is sufficiently accurate to meet the JWST astrometric requirements.
R. P. van der Marel, et al.
05 Jul 2007
Photometric Calibration of the ACS CCD Cameras (ISR 07-06)
The absolute flux calibration of the standard WFC and HRC filters is derived from the available constraining observations of spectrophotometric standard stars. Values for the encircled energy (EE) of one arcsec radius relative to an infinite aperture radius are derived for hot stars and compared to the EE for cooler stars. The sensitivity degradation for five year ACS lifetime is defined and used to correct the ACS photometry before deriving revised quantum efficiency (QE) curves for the CCD detectors. Broad band EQ changes with a maximum of 2.3% for WFC are also included in the revised QE curves for both CCD cameras. Revisions of the average filter transmissions of up to 4% are required to bring both broad and narrow band photometry into exact agreement with synthetic photometry from the primary white dwarfs (WD) stars.
R.C. Bohlin
12 Jun 2007
Detection of Optical Ghost in the HST ACS Solar Blind Channel Filter 122M (ISR 07-05)
We report the detection of an optical ghost in the Advanced Camera for Surveys (ACS)
Solar Blind Channel (SBC). The ghost was first detected in deep imagery of two Herbig
Ae stars, HD 169142 and HD 100453, using filter F122M in April and June of 2006,
respectively.
K.A. Collins et. al.
04 Jun 2007
We present an analysis of the CTE correction for a science project using high-precision photometry in a crowded field derived with the ``effective PSF'' (ePSF) method of Anderson & King (2006) on ACS/WFC non-drizzled images. We present
a CTE correction technique which can be used for data sets where
images of a given field with different exposure times are compared or combined. The CTE-induced photometric losses and centroid shifts are parameterized in terms of the location of the source on the ACS/WFC CCD chips and the magnitudes of sources.
V.Kozhurina-Platais et al.
08 Jun 2007
ACS CCDs UV and narrow-band filters red leak check (ISR 07-03)
We present results of the observations of the star 15 Mon, obtained with the aim of checking the impact of red leaks in the UV (and U-band) and two narrow-band filters on ACS CCDs. We derive updated passbands for the three filters and we present the updated correction table for different spectral types.
M. Chiaberge and M. Sirianni
16 May 2007
WFC Zeropoints at -81C (ISR 07-02)
Following the recovery of ACS with the side-2 electronics in July 2006, the temperature of the WFC detector was lowered from -77C to -81C in order to mitigate CTE and hot pixels. A revised detector QE curve and a new set of photometric zeropoints have been computed for all WFC observations obtained at the new operating temperature. These zeropoints must be applied manually until the new QE curves are implemented in SYNPHOT.
J.Mack
02 Oct 2009
Pixel-to-pixel Flat Field Changes on the WFC (ACS ISR 07-01)
The pixel-to-pixel flat field changes noted by Bohlin and Mack (2005) for the WFC are further quantified. During each period between anneals, a population of pixels with lowered sensitivity develops which is largely reset by the next anneal.The sensitivity deficits are twice as large in the blue as in the red.The low QE pixels recover 90% of their losses on a time scale of a few monthly anneals, but never return fully.
R. Gilliland, R. Bohlin
22 Jan 2007
2006
SBC FLATS: PRISM P-FLATS and IMAGING L-FLATS (ACS ISR 06-08)
The internal deuterium lamp was used to illuminate the SBC detector through the PR110L and PR130L prisms for 12.2 hours each to produce a total of ~12,000 counts/pixel. This illumination does not simulate the OTA optics and, therefore, is not suitable for the production of a low frequency L-flat. However, the pixel-to-pixel P-flat is an improvement over the laboratory SBC P-flat currently used in the ACS pipeline for the two dispersing modes. In addition, short exposure internal lamp flats were obtained in the standard imaging filters. These flats have sufficient signal to define the low frequency L-flat field for five filters relative to the high signal F125LP flat, assuming that the relative lamp illumination does not vary with wavelength. These five ratio L-flats are smoother than the ratios of the current pipeline L-flats; but there is evidence for variation of the internal lamp illumination with wavelength. Thus, the current SBC L-flats may have some errors of a few percent due to local inappropriate lumpiness; but the alternative flats defined by the internal illumination may also have errors.
R.C. Bohlin, J. Mack
12 Dec 2006
WFC L-flats Post Cooldown (ISR06-06)
Following the recovery of ACS with Side 2 electronics, the temperature setpoint for WFC was lowered from -77C to -81C. By comparing internal tungsten exposures taken before and after cooldown, spatial changes in the WFC sensitivity (L-flats) have been computed for all filters with a unique useafter of July 4, 2006.
Gilliland, Bohlin, & Mack
31 Oct 2006
ACS Post Flash Measurements (ACS ISR 06-07)
The ACS CCDs are equipped with LEDs that can illuminate the chips with a controllable short exposure added to an image. The purpose of this is to counteract the loss of efficiency due to charge traps which develop from exposure to ionizing radiation causing a readout loss or redistribution of charge in science images. The LED post-flash exposure fills these traps but adds statistical noise. Mainly because of this noise, the mechanism has not been used yet on science data, but might come into play as radiation damage accumulates. Once a year the procedure has been tested to confirm that it is in working order and to measure its stability. Over a four year period the mechanism has continued to function and shows no variation in output.
C. Cox
24 Oct 2006
Relative Astrometry Within ACS Visits (ACS ISR 06-05)
The log files from APSIS, the ACS science team's image processing pipeline, have been analyzed to determine the relative astrometric scatter among ACS images observed within a single visit.
R. White
07 Aug 2006
Policy and Procedure for MAMA Targets Subject to Unpredictable Outbursts (ACS ISR 06-04)
The policy and procedure are described for the implementation of MAMA (currently, ACS/SBC) observations of targets subject to infrequent and unpredictable large outbursts, that would exceed the countrate limits should they occur during the observations.
N. Walborn, I. Dashevsky, A. Welty, J. Biretta
21 Apr 2006
Wavelength and Flux Calibration of the ACS/HRC PR200L prism (ISR 06-03)
Calibrations derived from cycle 13 observations for the PR200L prism are available as configuation files to aXe software.
S.S.Larsen, J. Walsh, M. Kummel
21 Mar 2006
Wavelength and Flux Calibration of the ACS/SBC PR110L and PR130L prisms (ISR 06-02)
Calibrations derived from cycle 13 observations are available as configuation files to aXe software.
S. Larsen
06 Mar 2006
PSFs, Photometry, and Astrometry for the ACS/WFC (ISR 06-01)
The effective PSF for 6 filters is presented.
J. Anderson, I. King
20 Feb 2006
2005
SBC L-flat Corrections and Time-Dependent Sensitivity (ISR 05-13)
Corrections to the SBC flatfields are described as well as the time-dependent component. Six new flats were delivered to the pipeline, the resulting photometric accuracy is now +/-1% for F115LP F122M, F125LP, and F140LP and +/-2% for F150LP and F165LP.
J. Mack et al.
18 Nov 2005
These HRC earth flats are not available in the routine pipeline, but may be more appropriate than the regular pipeline flats for observations of some large, diffuse objects such as the Moon, Jupiter, or the Orion Nebula, for example.
R. Bohlin et al.
28 Oct 2005
ACS/HRC Polarimetry Calibration IV. Low-Frequency Flat-Fields for Polarized Filters (ISR 05-10)
The goal of polarimetry calibrations for the ACS/HRC polarizer filters is to obtain photometric accuracy from polarized images at the level of 1%. So far such calibration has been done only for the standard wide-band filters. Thus, observations of the globular cluster 47 Tuc exposured through the filters F220W, F250W, F330W, F435W crossed with three blue-optimized UV polarizers, and F475W, F606W, F658N, F775W crossed with three visible-light-optimized polarizers have been used to examine how the sensitivity varies across the detector.
V.Kozhurina-Platais & J.Biretta
15 Aug 2005
The Internal CCD Flat Fields (ISR 05-09)
The internal flat field lamp has been used since launch to monitor the stability of the ACS HRC and WFC flat fields. The only ubiquitous change observed in these flat fields is an excess of pixel responses that are low. This excess of values that are low by more than 3 ? varies from factors of two to several over what is expected from the tail of the Gaussian distribution of Poisson statistics.
Occasionally, a pattern resembling the growth rings of a tree are seen on the WFC with an amplitude of ~1%; but this anomaly is sufficiently rare and short lived, so that the monitoring frequency can be decreased.
Ralph Bohlin & Jennifer Mack
20 Jul 2005
Updated Wavelength Calibration for the WFC/G800L Grism (ISR 05-08)
A revised wavelength calibration is presented for the G800L grism used with the ACS Wide Field Channel.
S. S. Larsen, J. R. Walsh
12 Jul 2005
Two-Gyro Pointing Stability of HST Measured with ACS (ISR 05-07)
We present the results of the pointing stability tests for HST as measured with the ACS/HRC during the two-gyro test program conducted in February 2005.
A. Koekemoer et al.
13 Jul 2005
Demonstration of a Significant Improvement in the Astrometric Accuracy of HST Data (ISR 05-06)
We demonstrate a technique that can significantly improve the absolute astrometric accuracy of HST data.
A. Koekemoer, B. McLean, M. McMaster, H. Jenker
13 Jul 2005
ACS Coronograph Performance in Two-Gyro Mode (ISR 05-05)
An analysis of the coronographic data quality during the February 2005 two-gyro test.
C. Cox & J. Biretta
29 Jun 2005
Flats: SBC Internal Lamp P-Flat (ISR 05-04)
The internal deuterium lamp was used to illuminate the SBC detector through the F125LP filter. This illumination does not simulate the OTA optics and, therefore, is not suitable for the production of a low frequency L-flat. However, the pixel-to-pixel P-flat is an improvement over the laboratory SBC flat currently used in the ACS pipeline for the six SBC imaging filters.
R.C.Bohlin & J.Mack
23 May 2005
Internal monitoring of ACS charge transfer efficiency (ISR 05-03)
We present the results of over two years of inflight charge transfer efficiency (CTE) monitoring of the CCDs in the Advanced Camera for Surveys (ACS), based on two internal tests: Extended Pixel Edge Response (EPER), and First Pixel Response (FPR). In general, we find that CTE losses are worst at the lowest signal levels, and at each signal level, CTE declines linearly over time, at a rate which is consistent with results from external photometric tests (Riess, 2004). We compare our inflight results to similar pre-flight baseline data, and to predictions for inflight performance, which were based on radiation tests.
Max Mutchler
08 Apr 2005
Flat-field and Sensitivity Calibration for ACS G800L Slitless Spectroscopy Modes (ISR 05-02)
The flat-fielding of the ACS WFC
and HRC for the G800L grism is
described. The efficacy of this
flat-field cube has been
investigated from observations of
a spectrophotometric standard at
different positions in the field.
By requiring the extracted spectra
from different positions over the
field to match in flux, a smooth
function was derived and applied
to the flat-field cube. The single
sensitivity curve for the whole
detector area is then determined
from the mean spectrum at the
different positions. Flat-fields
and sensitivity curves are
supplied for routine spectral
extraction of ACS slitless
spectral data as part of the aXe
package.
J. R. Walsh and N. Pirzkal
03 Mar 2005
Switching ACS from Side 1 to Side 2 electronics (ISR 05-01)
This ISR describes the steps taken to switch from MEB1 to MEB2 including detector startup procedures and recalibration requirements.
C. Cox
10 Feb 2005
2004
The Photometric Stability of ACS: Revisiting the Hubble Deep Field (ISR 04-17)
We utilized 10 epochs of 15-tile ACS WFC mosaics imaging the HDFN in the F850lp filter
over two years, and originally obtained for the science goal of finding type Ia supernovae
at z>1, to examine the photometric stability of the WFC (with at least filter f850lp).
Using repeated measurements of 371 stars, we performed a multi-variate linear regression
to determine the dependence of photometric variations on the time-dependent components
of parallel and serial CTE degradation as well as an overall time-dependence which
would indicate a change in the WFC?s sensitivity. Despite important differences between
the HDFN scenes and those in the original calibration field of 47 Tuc (i.e., source crowding
and sky level), we find the losses due to imperfect CTE to be consistent between the
two independent calibrations. Interestingly, we also find a decrease in the overall sensitivity
of the ACS WFC at a rate of 0.004 +/- 0.001 magnitudes per year (consistent with findings
based on 47 Tuc data from work in progress by Mack et al. 2005, in prep.).
A. Riess
27 Dec 2004
ACS coronographic flat fields (ISR04-16)
The effects of vignetting by the Lyot stop and the presence of the occulting spots and their time dependent motion on the ACS coronographic flat fields.
John Krist
30 Aug 2004
Multi-filter PSFs and Distortion Corrections for the HRC (ISR 04-15)
Fitting the low frequency and high frequency components of the HRC geometric distortion.
J. Anderson, I. King
23 Feb 2006
SBC Dark and Cumulative Images (ISR 04-14)
SBC dark images have been collected to provide dark current subtraction for science images and to monitor the instrument health and performance. Cumulative images which add counts from the whole history of the detector's use are also generated to anticipate any long-term degradation in performance. Images collected to date show no loss of efficiency or indications of any problem.
Colin Cox
23 Aug 2004
Cross-Talk in the ACS WFC Detectors. II: Using GAIN=2 to Minimize the Effect (ISR 04-13)
Cross talk is observed when using ACS/WFC. A strategy using GAIN=2 is described to minimize cross talk in ACS.
Mauro Giavalisco
10 Aug 2004
Cross-Talk in the ACS WFC Detectors. I: Description of the Effect (ISR 04-12)
Images acquired with ACS/WFC are affected by cross talk which is observed as negative ghost images. The phenomenology is described and its effect on photometry.
Mauro Giavalisco
10 Aug 2004
ACS/HRC Polarimetry Calibration III: Astrometry of Polarized Filters (ISR 04-11)
The goal of the astrometric calibration of the ACS/HRC polarizer filters is to obtain
a coordinate system free of distortion to a precision level of 1 mas.
Vera Kozhurina-Platais and John Biretta
12 Jul 2004
ACS Polarization Calibration - II. The POLV Filter Angles (ISR 04-10)
Describes the discovery, possible cause and POLV filter geometry of the anisotropy between polarized and non-polarized images.
J. Biretta, V.Kozhurina-Platais
17 Jun 2004
ACS Polarization Calibration I. Introduction and Status Report (ISR 04-09)
A status review of the ACS polarization calibration begins with a brief
description of the instrument and the GO science program, reviews the pre-flight calibration and on-orbit data. Various key parameters are derived and discussed. Closes with a summary of remaining issues, advice for observers, and a summary of future plans.
J. Biretta, V. Kozhurina-Platais, F. Boffi, W. Sparks, and J. Walsh
15 Jun 2004
Detector Quantum Efficiency and Photometric Zero Points of the ACS (ISR 04-08)
Characterizes the on-orbit sensitivity of the ACS CCDs cameras via
observations of spectrophotometric standard stars including updates to SYNPHOT. Photometric zero points are calculated for the WFC and HRC in VEGAmag, STmag and ABmag.
G. De Marchi, M. Sirianni, R. Gilliland, R. Bohlin,C. Pavlovsky, M. Jee, J. Mack, R. van der Marel & F. Boffi
15 Jun 2004
Bias and dark calibration of ACS data (ISR 04-07)
Production of the routine superbias and superdark reference files is explained.
We describe the primary features contained in these files, and provide
some guidance on how ACS users can produce even higher signal-to-noise calibrations
for datasets with extraordinary calibration requirements (e.g. deep field
observations).
Mutchler, Sirianni, Van Orsow, and Riess
24 May 2004
Time Dependence of ACS WFC CTE Corrections for Photometry and Future Predictions (ISR 04-06)
We see evidence for a modest increase in these photometric losses with time. We provide a global fitting formula to correct for CTE losses for all flux levels, sky values, and times. We extrapolate our time-dependent correction formula to the end of the decade and predict that the vast majority of science applications will retain their precision of flux measurements to better than a few percent.
A. Riess and J. Mack
05 May 2004
Results of UV Contamination Monitoring of the Advanced Camera for Surveys (ISR 04-05)
The UV performance and contamination of the HRC and SBC are discussed.
F. R. Boffi, R. C. Bohlin, G. De Marchi
08 Apr 2004
Elevated temperature measurements of ACS charge transfer efficiency(CTE) (ISR 04-04)
The ACS charge transfer efficiency (CTE) is analyzed during
March 2003 when the elevated temperature program was executed.
Max Mutchler and Adam Riess
01 Mar 2004
Best Gyroscope Usage to Maximize the HST Mission Lifetime (ISR04-03)
Without SM4, gyroscope survival is a critical factor for the HST Mission lifetime. A simple Monte-Carlo model is presented to calculate the survival probabilities for various scenarios. Predictions are made for the HST Mission end date (~2007) based on current gyroscope usage. Recommendations are made for alternative usage strategies that will maximize the overall HST mission lifetime. Such strategies have the potential to push forward the HST Mission end date by as much as 10 months.
R. van der Marel
21 Jan 2004
Lossy Compression of ACS images (ISR 04-02)
The Lossy Compression of ACS images
is analyzed and discussed.
Colin Cox
20 Jan 2004
ACS CCD Gains, Full Well Depths, and Linearity up to and Beyond Saturation (ISR 04-01)
Corrections to the supported gain values,
maps of the full well depth saturation and
linearity at different levels are presented.
R. L. Gilliland
05 Jan 2004
2003
Modelling the fringing of the ACS WFC and HRC chips (ISR 03-12)
Modelling of the layer structure of the ACS HRC and WFC CCD's is described.
Application of a fringe model to the correction of extracted spectra is outlined.
J. R. Walsh, W. Freudling, N. Pirzkal, A. Pasquali
10 Dec 2003
Flat Fields for Filter Wheel Offset Positions (ISR 03-11)
The ACS filter wheel movements are accurate to one motor step, which leads to errors that exceed one percent in the flat fields over small regions for a few filter combinations. For seven of these filter modes on the WFC and six on HRC with the worst blemishes, flat fields are available as a function of filter wheel offset step; and the pipeline data processing will select the flat corresponding to the offset step of each observation.
Bohlin, Wheeler, Mack
29 Oct 2003
A method is presented for determination of the low-frequency
flat-field (L-flat) structure from photometry of a stellar field that
is imaged multiple times with different pointing or roll. A numerical
implementation of the algorithm is presented and its accuracy verified
using tests with artificially generated data. The software was used to
generate the L-flats currently in the ACS pipeline. Newly implemented
features in the software should allow further improvements in these
L-flats.
R. van der Marel
30 Sep 2003
On-orbit Calibration of ACS CTE Corrections for Photometry (ISR 03-09)
A preliminary on-orbit calibration of the photometric losses due to
imperfect CTE.
The characterization of the WFC CTE in this report has been superseded by ACS ISR 04-06.
Adam Riess
21 May 2004
The verification tests for the Astronomer's Proposal Tool (APT) Exposure Time Calculator (ETC) for the Advanced Camera for Surveys (ACS) are presented.
F.R. Boffi et al.
10 Jul 2003
The in-orbit wavelength calibration of the HRC G800L grism (ACS ISR 03-07)
G800L grism spectra of the Wolf-Rayet star WR45, obtained with the High Resolution
Channel (HRC) during the Servicing Mission Orbital Verification (SMOV) tests, are presented.
The target has been observed in five different positions across the HRC field of
view in order to quantify the field dependence of the grism physical properties and wavelength
solution.
A. Pasquali, N. Pirzkal, J. R. Walsh
09 Jul 2003
The ACS point spread function remains fairly stable over its field of view, compared to the
PSFs in WFPC2 or STIS. However, ACS/WFC PSF core width and ellipticity variations
are large enough to be of concern to those undertaking very small aperture photometry or
measuring small, bright-nucleus galaxy ellipticities.
J. Krist
25 Jun 2003
ACS Background Light vs. Bright Earth Limb Angle (ACS ISR 03-05)
The background contributed by scattered
Earth light at various angles is discussed
along with flat field artifacts.
John Biretta et al.
23 Jun 2003
Elevated Temperature measurements of Hot Pixels (ACS ISR 03-04)
We have investigated the dark rates and hot pixel counts by raising
the WFC temperature. We find that the
predominant effect of a change in temperature is a simple scaling
of the dark rate in each pixel. These results are applicable to the
effects of the Aft Shroud Cooling System installation in
in Servicing Mission 4.
C. Cox, M. Mutchler, D. van Orsow
23 Jun 2003
Stability and Accuracy of HRC and WFC Shutters (ACS ISR-03-03)
Calibration observations (9662) have been used to quantify precise exposure time values, stability and shading effects down to the shortest allowed exposures (0.1s HRC, 0.5s WFC).
Gilliland R.L., Hartig G.
03 Jun 2003
NUV Earth Flats (ACS ISR 03-02)
Creation of Earth flats for ACS/HRC modes
are described including red leak and dust mote
information.
R.C. Bohlin, J. Mack
21 Apr 2003
Wavelength calibration of the WFC G800L grism (ACS ISR 03-01)
We present the G800L grism spectra of Wolf-Rayet
stars acquired with the ACS/WFC during SMOV
and early Cycle 11. We discuss the procedure for
fitting the dispersion correction of the grism. We also
describe the calibration files derived from these data
which are used by the ST-ECF extraction package
"aXe".
Pasquali, Pirzkal, Walsh (ST-ECF)
05 Mar 2003
2002
ACS Coronagraph Update for Cycle 12 Proposers (ISR 02-11)
Small time-and-initialization-dependent instabilities
in the ACS coronagraph have led to revisions of the
coronagraph commanding procedures and to the suggested
methods for optimizing coronagraphic observations. An
example optimized sequence is given.
J. Krist
18 Dec 2002
ACS software tool development (ISR 02-10)
We describe the anticipated software tool
development requirements for ACS for the
period September 2002 to mid-2003, including
issues related to image registration and
combination.
W.B. Sparks, W.J. Hack, R.N. Hook, A. Koekemoer
16 Dec 2002
The Projected Growth of Hot Pixels on ACS WFC (ISR 02-09)
The anneal rate of hot pixels on the ACS WFC is discussed.
A fitted, successive annealing function is used to project
forward in time the expected fractional coverage of the CCD by hot pixels.
A. Riess
13 Dec 2002
ACS L-Flats for the WFC (ISR 02-08)
The uniformity of the WFC detector response has been assessed by using multiple dithered pointings of dense stellar fields.
The original WFC laboratory flat fields produce photometric errors of +-5 to +-9 percent from corner-to-corner.
J. Mack
21 Aug 2002
A first look at cosmic rays on ACS (ISR 02-07)
We have made an initial study of the characteristics of cosmic ray impacts on the two ACS
imaging cameras, HRC and WFC. Distributions of sizes and anisotropies are determined for
both cameras, characteristics which can be useful for distinguishing cosmic rays from
astrophysical sources in a single image.
Riess
06 Jun 2002
A first look at hot pixels on ACS (ISR 02-06)
We have made an initial study of hot pixels on the ACS CCD s, i.e.those with elevated
dark current. The characteristics of these pixels are similar to those seen on previous
CCD s flown on HSTand are likely caused by radiation damage.
Riess, Mutchler, Van Orsow
06 Jun 2002
HRC and WFC Flat Fields: Dispersors, Anomalies, and Photometric Stability (ISR 02-04)
The flat field correction scheme for the ACS prism (PR200L) and grism (G800L)
is discussed.
R. Bohlin
18 Mar 2002
HRC and WFC Flat Fields: Ramp Filters (ISR 02-01)
Discusses the ground flats for HRC and WFC ramp filters.
Bohlin
15 Jan 2002
2001
HRC and WFC Flat Fields: Standard Filters, Polarizers, and Coronograph (ISR 01-11)
Laboratory flats with simulated sky illumination of the CCD cameras have been obtained for supported and many unsupported ACS modes.
All 157 flats are now available as reference files for the pipeline processing of ACS observations from Cycle 11.
Ralph Bohlin
17 Dec 2001
ACS dither and mosaic pointing patterns (ISR 01-07)
We provide some background on pointing the ACS, and present the
dither and mosaic patterns that will be provided as a convenience for HST
Cycle 11 Phase II proposal writers.
Max Mutchler
21 Dec 2001
ACS thermal control with ASCS (ISR 01-05)
The components of the ACS need to be maintained within certain temperature limits for health and safety considerations and for the optimal scientific use of the cameras. Current planning calls for the NICMOS cryolcooler to be installed at the same time as the ACS but the ASCS to be placed on a later mission. The ACS will operate for at least a year without the cooling benefit of the ASCS.
C. Cox
08 Jun 2001
Initial Implementation Strategy for Drizzle with ACS (ISR 01-04)
In order to provide geometric correction for single pointing ACS images, and to provide geometric correction together with simple image combination for associations of ACS images, we describe plans to implement the "drizzle" code by means of a python wrapper, and to use this wrapper in calacs.
W. Sparks
08 Jun 2001
ACS Grism Simulations using SLIM 1.0 (ISR 01-03)
We introduce SLIM, a slitless spectroscopy simulator written in Python which can be used to simulate the ACS grism and prism modes. Here, we outline the features of SLIM and present some WFC and HRC grism simulations of emission line objects.
N. Pirzkal
08 Jun 2001
The Effective Spectral Resolution of the WFC and HRC Grism (ISR 01-02)
We present SLIM simulations of the WFC and HRC grism, obtained by varying the object size and orientation with respect to the dispersion axis. Our aim is to quantify the extent by which the object extension along the dispersion axis can degrade the nominal spectral resolution of the grism.
A. Pasquali
08 Jun 2001
2000
Geometric Distortion Table: IDCTAB (ISR 00-11)
The new reference table, IDCTAB, will support the description of geometric distortion models for instruments. This report describes the columns in the table and how the coefficients in the table can be used.
W. Hack
08 Jun 2001
Flats: Preliminary WFC Data and Plans for Flight Flats (ISR 00-10)
The ACS WFC pixel-to-pixel P-flats with the build-3 detector are discussed and compared to the HRC build-2 P-flats. The goals for these WFC and HRC ground flats are stated.
R. Bohlin
08 Jun 2001
ACS WFC CCD Radiation Test: The Radiation Environment (ISR 00-09)
The space environment is a complex, orbit dependent phenomenon. CCD detectors are particularly vulnerable to damage by ionizing radiation. This document summarizes the modeling and analysis that was performed to determine the appropriate exposure level for ground testing of the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) Charge-Coupled Device (CCD) detector.
M. Jones
08 Jun 2001
Our baseline suite of test cases for the Spectroscopic Exposure Time Calculator are documented for all five spectroscopic modes with a variety of point source flux distributions.
F. R. Boffi
08 Jun 2001
The verification tests for the ACS Ramp Filter Exposure Time Calculator are presented. Our baseline suite of test cases includes one calculation for all filter modes with the same target, plus one subset for all kinds of targets through the same filter.
D. Van Orsow
08 Jun 2001
The verification tests for the Imaging Exposure Time Calculator for the Advanced Camera for Surveys are presented. Our baseline suite of test cases includes one calculation for all filter modes with the same target, plus one subset for all kinds of targets through the same filter.
F. Boffi
08 Jun 2001
Measured Throughput and Bandpass of the RAMP Filters (ISR 00-05)
The ACS ramp filters are characterized by transmission curves which populate the STScI Synphot database for use in the Exposure Time Calculator.
R. Bohlin
08 Jun 2001
Software tools for ACS: Geometrical Issues and Overall Software Tool Development (ISR 00-03)
We describe the issues relating to internal geometrical distortions in the ACS. A software tool development route is outlined and we describe other software tool development activities.
W. Sparks
08 Jun 2001
ACS Default (Archival) Pure Parallel Program (ISR 00-02)
We describe the initial default non-proprietary pure parallel program for the Advanced Camera for Surveys. We describe the observing sequence and outline scientific questions that may be addressed with the data.
W. Sparks
08 Jun 2001
Predicted Sensitivity and Dispersion of the Prisms and Grism (ISR 00-01)
The three prisms and grism in ACS are characterized in terms of dispersion relations and sensitivity.
R. Bohlin
08 Jun 2001
1999
ACS Quicklook PDF products (ISR 99-10)
This report details the features of the ACS quicklook PDF products produced by the HST data pipeline.
A. Suchkov
08 Jun 2001
ACS calibration pipeline testing: cosmic ray rejection (ISR 99-09)
We describe the testing that was done to ensure that CALACS properly rejects cosmic ray contamination when combining multiple images.
M. Mutchler
08 Jun 2001
CALACS reference files (ISR 99-08)
This report describes the reference files used by CALACS to calibrate ACS observations.
W. Hack
08 Jun 2001
The Solar Blind Channel Bright Object Limits for Astronomical Objects (ISR 99-07)
Tables of limiting magnitudes for
all observation modes of the ACS
Solar Blind Channel are calculated
for a range of stellar energy
distributions, using Kurucz model
fluxes and observed standard stars.
F.R. Boffi and R.C. Bohlin
25 Oct 2004
ACS calibration pipeline testing: error propagation (ISR 99-06)
This report details how CALACS produces ERR (error) array output.
D. VanOrsow
08 Jun 2001
Design of the ACS science headers (ISR 99-05)
The decisions made in the design of the data format and packaging of the ACS science headers.
R. Jedrzejewski
08 Jun 2001
ACS calibration pipeline testing: basic image reduction (ISR 99-04)
This report describes the basic testing that was done to ensure that CALACS properly reduces raw ACS images and makes the corresponding modifications to their headers.
M. Mutchler
08 Jun 2001
CALACS operation and implementation (ISR 99-03)
This report describes the usage and implementation of CALACS. Instructions for using stand-alone tasks and the format of the input data are described in this paper. Furthermore, the processing steps for ACS data and the functional flow of the entire pipeline is outlined, along with descriptions of how the memory model was implemented.
W. Hack
08 Jun 2001
Flats: SBC Data from Thermal Vacuum Testing (ISR 99-02)
SBC flats for the six filters and two prisms taken during thermal vacuum testing at GSFC in 1999 March are characterized.
R.C. Bohlin
16 May 2002
Flats: Preliminary HRC Data and On-Orbit Plans (ISR 99-01)
The flat field baseline goal is to obtain a complete set of pixel-to-pixel P-flats before launch and to use the onboard lamps to track changes. A second goal of the ground calibration program is to obtain the low fre-quency L-flat variation over the field of view.
R. Bohlin
08 Jun 2001
Performance of the onboard compression algorithm for ACS (ISR 98-04)
An extensive set of experiments was performed to test the performance of the onboard compression algorithm created for ACS by R. White.
F. Boffi
08 Jun 2001
1998
Bright object protection for the ACS MAMA detector (ISR 98-03)
Bright object protection for the ACS MAMA is similar in concept to that for the STIS FUV MAMA, but several mechanisms are discussed which provide better protection for the ACS MAMA.
C. Cox
08 Jun 2001
Dithering strategies for ACS (ISR 98-02)
We review the motivations for dithering exposures with the ACS, discuss possible strategies for combining dithered exposures automatically and the implementation of dither patterns in RPS2.
M. Stiavelli
08 Jun 2001
CALACS Design: Lessons Learned from CALSTIS (ISR98-01)
This report documents the basic design of those parts of CALSTIS relevant for CALACS.
W.Hack
13 Dec 2006
1997
Data Compression for ACS (ISR 97-02)
The algorithm for on-board compression on the fly of ACS data is briefly reviewed and its benefits discussed.
M. Stiavelli
08 Jun 2001
HST Cycle 9 reference mission (ISR 97-01)
We describe the expected usage of the ACS during Cycle 9 and estimate ground system requirements for the full complement of HST instruments available for Cycle 9. We recommend that the current ground system throughput capacity be doubled to support an average daily capacity of 12 Gbits/day and a peak capacity of 18 Gbits/day following the third servicing mission.
M. Stiavelli
08 Jun 2001