The creation of the ACS/WFC superbias, superdark, and sink pixel reference files is discussed, with historical context of the reference data acquisition and hot pixel annealing of the ACS/WFC CCDs. We also describe several datasets that are no longer automatically reprocessed for the static archive due to the use of unsupported modes or non-standard test configurations. Finally we make recommendations for future reference file creation, matching of reference files in CRDS, and notices about supported ACS data in the archive.
T. D. Desjardins, N. D. Miles, J. E. Ryon, and D. C. Borncamp August 2018
The current generation of detectors on board the Hubble Space Telescope (HST) suffer from extreme optical distortion - some of them have deviations as high as 11% across their field of view. This large effect must be accurately calibrated to obtain high precision astrometry and accurate alignment of any HST images. Corrections for the geometric distortion in the form of high-order polynomial coefficients can be found in the Instrument Distortion Coefficients Table reference file. Here we describe the transformation of polynomial coefficients of geometric distortion from the raw detector coordinate system into the HST coordinate system in the context of the IDC table.
D. Borncamp, V. Kozhurina-Platais, C. Cox, W. Hack 01 July 2014
This TIR reproduces a similarly titled document presented in January 2014 to the HST Lifetime Extension Initiatives Forum at Goddard Space Flight Center in response to that group’srequestforanassessmentoftheimpactsonscience,engineering,andcalibration should a switch from the primary (Side 1) to the redundant (Side 2) of the ACS CEB-R and LVPS-R be required. Such a switch would yield small changes in CCD performance due to intrinsic manufacturing differences between corresponding electronic components in each side. These changes should have little or no impact on science. The operating temperature of the WFC and the performance of the SBC, lamps, and mechanisms would be unaffected by the switch. If the present temperature of -81°C is maintained, then new calibrations of the CCD dark current, hot pixel contamination, flat field uniformity, QE, and CTE are recommended but not mandatory. Actions for modifying the ground system and flight software to enable the switch are described, as are tests of aliveness, functionality, and calibration performed after the switch. D. Golimowski, M. Chiaberge, N. A. Grogin, et al. 10 June 2014
The read noise in the quadrant of the ACS/WFC detector read out by amplifier D rose suddenly from 3.8 to 5.0 electrons RMS on January 20, 2013. For the following month until the next CCD anneal, this read noise fluctuated between 4.5 and 5.0 electrons until settling at 5.0. This new value is comparable to pre-SM4 read noise levels (March 2002 — January 2007) and does not significantly affect most observations that are sky background limited. We measure no significant variation in the amplifier gain and verify that photometry has been stable over this time period. Only the amplifier D quadrant was affected. This anomaly does not appear to be related to the ASIC installed during SM4. A similar read noise jump occurred in ACS/WFC amplifier A on June 29, 2003. Both events were likely due to cosmic rays impacting the amplifiers on the detector.
D. Coe, et al. 31 Dec 2013
Historically, the HST headers have included the PHOTBW parameter, which is advertised as the root-mean-square (RMS) bandwith of the system throughput. However, the PHOTBW widths are much smaller than other conventional measures of a filter width, such as the full width at half maximum (FWHM). The formulae and current situation are reviewed, and a new method of calculating the filter widths based on cumulative throughput is proposed. This new width is recommended to be included in the HST data headers as the new keyword PHOTBW95.
R. C. Bohlin & N. A. Grogin 18 Jul 2013
In May of 2012, a new version of the calibration pipeline for ACS on the Hubble Space Telescope, CALACS 2012.2, was released. One of the major improvements in the new CALACS is the incorporation of the algorithm created by Anderson and Bedin (2010) to correct for the charge transfer efficiency (CTE) losses in WFC1 and WFC2. This algorithm is a pixel specific correction that is applied as one of the first steps in CALACS, before the subtraction of the dark reference file. In order to properly reduce any raw science images it was necessary to correct all the WFC dark reference files used in CALACS for CTE loss, about 1,600 files.
S. Ogaz et al. 07 Aug 2012
We describe the post-SM4 automated pipeline that creates reference files for bias and dark calibration of ACS/WFC data. This document is intended for those who would like to adopt our pipeline or understand the technical details of its implementation.
P. L. Lim et al 11 Apr 2012
We detail the format and contents of the images taken during thermal vacuum testing of the ACS CCD Electronics Box Replacement (CEB-R). Testing of the CEB-R took place in August 2008 at Goddard Space Flight Center in preparation for installation during HST Servicing Mission 4. A series of flat, bias, and dark frames were taken in full-frame, subarray, and EPER formats with different settings to explore the stability of the new electronics by connecting them to the Build 5 flight-spare WFC detector. We identify all of the files and state their location in storage for future reference.
T. Desjardins et al. 23 Jun 2009
This TIR complements the ACS TIR 2008-03, ACS-R SMOV Optimization Plan & Rationale and Strategy by Ed Cheng. We present the implementation of the CEB-R optimization plan and a summary of the data analysis plan. This document should be used as guideline during the analysis of the data acquired during the ACS-R Optimization Campaign. The instructional details of the analysis reflect the state of the software on the date printed above and are subject to change as the software is modified.
M. Sirianni 28 May 2009
During normal operations, ACS/HRC Coronagraphic Spot Tables are produced
periodically in order to update the current location of the coronagraphic spot since there is
some variation in this over time. The automated regression testing of these files makes it
easier to perform quality control and to ensure that the process is performed consistently
from time to time, and that the new CSP tables (SPOTTAB) to be given to CDBS are
correct and in acceptable format, etc. This TIR briefly describes how the new spot position
is determined using an IDL program by Colin Cox (adapted from one by John Krist), and
then concentrates on the process of regression testing in ”cookbook” fashion, starting from
the notice of availability of a new file. The procedure as of the time of the cessation of
normal CCD operations in early 2007 is documented here in anticipation of its resumption
R. Lucas et al. Nov 2008
The repaired ACS WFC will undergo a three-week Optimization Campaign during early SMOV with read noise being the primary target for improvements through testing adjustments of a large number of detector control, voltage and timing patterns. A large number of factors, in addition to read noise, contribute to the utility of science data from ACS WFC. In this TIR we enumerate several such factors including Charge Transfer Efficiency (CTE), Full Well Depth (FWD), Linearity, Cross talk, gain stability and bias drift. For each we quantify values that existed when WFC was last used in January 2007 and provide extrapolation that we believe would have existed with a continuously operable instrument to May 2009. For each factor we provide qualitative discussion of how changes would impact science in order to provide a framework for considering changes that may arise during the Optimization Campaign.
In many cases, e.g. for CTE, significant deterioration of performance from nominal expectations as a result of changes during the optimization campaign would provide support for adjusting the optimization to lessen this, even at the cost of some increase of read noise.
R. L. Gilliland et al. Dec 2008
The document provides the optimization plan for the HST/ACS Replacement (ACS-R) flight hardware. It specifies the rationale for and types of activities required during SMOV to optimize the on-orbit performance of the hardware. The new flight hardware uses internal interfaces of the instrument that were not described or characterized in detail during the original build of the ACS. This optimization is planned in order to mitigate the risk of the ground (test) hardware not emulating these flight instrument interface well enough.
E. S. Cheng 26 Aug 2008
On November 12th, 2007 a new ACS SBC throughput curve was implemented in CDBS, OPUS and DADS. This new curve is an improved version and accounts for SBC red leak. The red leak portion is based on a spectrum of HD 209458 prepared by Paul Goudfrooij.
Boffi, F.R. 18 Apr 2008
The repaired ACS WFC may have initial readout noise values that could be improved either through extensive on-orbit tweaking, or through adoption of an alternate readout mode. To help guide trades in potentially implementing a Slow Readout Mode (SRM) we explore the relative trade space ar different readout noise levels of adopting this mode for science observations. Devoting three weeks of early SMOV to an "oscilloscope" mode is always found to be worthwhile if the resulting readout noise improvement exceeds 10%.
R. L. Gilliland et al. Apr 2008
Since the process of creating ACS biases and darks is now automated, it can be difficult
to know how to intervene in the process or else to manually manipulate it for purposes of
trouble-shooting or making special-purpose superbiases and superdarks, etc. This brief
cookbook documents and gives some insight into the crucial steps in this process. It assumes
that the user already has good familiarity with the steps, tools, and procedures described in
the ACS TIR 07-04 (Lucas et al., 2007) on the normal production and checking of bias and
dark pipeline products, as well as other general and historical knowledge documented in
that TIR. As an example, it uses a case study in making special biases and darks which use
non-standard combinations of amplifier, gain, and detector, etc. which were created when
studying the effects of the ACS side-switch in the Summer of 2006. Consequently, some
particulars may vary a bit for your own future use, but the general ideas and principles and
many of the particulars will still be the same. As such, it may be useful to the ACS group
in the future, and to others with similar detectors and pipelines such as the WFC3 group
and their UVIS detectors.
R.Lucas & M. Swam Jun 2007
Although the process of creating routine ACS superbias and superdark calibration files is now automated, it is still very important that the products of this process be checked for quality before each hand-off to the CDBS group for their delivery of the files to OPUS and the pipeline and Archive. This document describes the process currently in use by the ACS/WFPC2 Team since it is important to know and understand what is done, and since this also may be useful to some other instrument groups, and especially for future similar instruments such as the UVIS channel of the WFC3.
R. Lucas et al. Jun 2007
The restored ACS WFC may have readout noise values that differ significantly from the
current 5.5 electrons in either a positive or negative sense. To help guide trades in
the potential electronics design the sensitivity to readout noise of time to reach given
signal-to-noise is explored for several illustrative cases. With reasonable assumptions about
an ACS WFC science program post SM4 we find that a lower readout noise of 3 electrons
could provide savings over an assumed 4 year lifetime equivalent to 650 orbits while 10
electrons would be a loss of 2250 orbits.
R. L. Gilliland et al. Jul 2007
The ACS suffered an electronics failure in Jan 2007 resulting in the loss of WFC and HRC use. The SBC was recovered in Feb 2007 and priority was given to testing its sensitivity, including Lyman alpha, as a check against internal contamination having occurred. F122M observations of NGC6681 from SMOV have been compared to similar observations in April 2007. Over this five year baseline the countrate averaged over 18 stars declined by 4.2+/-0.6% in F122M. To facilitate these analyes, a pixel area map was created for the SBC and verified by comparing FLT images corrected for PAM with pipeline DRZ images of the same field.
R. L. Gilliland et al. Jul 2007
We describe a revised set of procedures and software for creating finding charts and object catalogues which can be used to assess the risk to the STIS MAMA and ACS SBC detectors from bright blue objects in the vicinity of proposed planetary observations. These charts show the path of given planet, moon or comet across the background of stars, down to magnitude limit of the GSC2 digital sky survey plates. Associated object catalogues and color-magnitude diagrams are also produced showing which stars may violate bright object limits for the selected instrument mode.
C. Proffit et. al. 07 Jun 2007
In the ACS/HRC CCD a single UV photon may generate more than one photo-electron. We calculate the theoretical quantum yield and discuss the impact on the calculation of the S/N ratio for an observation in the UV. Without such correction the S/N can be overestimated up to ~18% in the F220W and ~26% at the bluest edge of PR200L. The implementation of the quantum yield correction in the ACS Exposure Time Calculator (ETC) is also described.
M. Sirianni & C. Pavlovsky 07 Nov 2006
The switchover of the Advanced Camera for Surveys to its Side-2 electronics in July 2006
presented an opportunity to combine calibration activities for the electronics switch with
those needed for a lowering of the Wide Field Channel CCD detector temperature
setpoint from -77 °C to -81 °C. This document, which was originally released as an
internal white paper to the HST Mission Office in June 2006, describes the rationale for
the temperature setpoint change. Future documentation will describe the implementation
and results of the calibration activities required to support the electronics switch and
temperature setpoint change.
M. Sirianni et al. 06 Sep 2006
The default gain for ACS/WFC has been changed from 1 e-/DN to 2 e-/DN in Cycle 14.
Existing photometric calibrations are based upon analyses of observations taken almost
exclusively at GAIN = 1. Any relative errors in the GAIN = 2 values as compared to GAIN
= 1 would appear as direct offsets in photometry for observations using the new default
gain. The current values for GAIN = 2 were given in Gilliland (2004) based upon analysis
of one image pair, the components of which had significantly different exposure times. This
TIR reports on results from Cycle 14 data taken to sensitively determine the current ratio
of these critical gain values.
R. Gilliland Feb 2006
With the probable permanent loss of STIS, the ACS SBC is in place to take over some of the activities of the FUV MAMA. The SBC was a spare STIS MAMA and so is identical to the original STIS model. It is noisier than the STIS MAMA, but seems to have become less noisy in space and has about twice the sensitivity of its counterpart.
C. Cox 05 Oct 2004
In analyzing the ACS photometry of the primary WD stars, Bohlin & Gilliland (2004)
found a 2.5% contribution to the predicted integrated HRC count rates due to the F660N
filter transmission rise at the shortest wavelength of the tabulation. Following discussions
with G. Hartig, the tabulated value of 0.00604 at 2500 Å was deemed a spurious artifact of
the measurement procedure (Leviton et al. 1998a, Leviton et al. 1998b). The ACS filters
generally use colored glass substrates to block short wavelengths and are not subject to the
kind of UV leak that is indicated by the original data supplied by the IDT. The signal
transmitted by the filter at 2500 Å in the lab measurement process was probably dominated
by stray light from longer wavelengths. Even though for normal stellar continua,
similar errors for other filters are less than 0.5% of the predicted count rate, all UV transmittance
curves with a similar suspicious rise in the UV are corrected to values typical of
the nearest measured values. Table 1 lists all of the changes that are implemented in Synphot
as a result of this investigation. These changes are also reflected in the ETC
F.R.Boffi & R. C. Bohlin 29 Jun 2004
The Advanced Camera for Surveys (ACS), installed in the Hubble Space Telescope in March 2002, has significantly
extended HST’s imaging capabilities. We describe the on-orbit optical alignment procedures and results, detailing the
excellent image quality performance achieved. Comparison is made with the instrument specifications, ground test
results and published performance expectations. The residual aberration content over the field of each channel is
described and compared with the optical model, and various other performance measures, including sharpness and
encircled energy are treated. The effects of the telescope focus oscillations due to thermal variations ("breathing") and
image positional stability are also discussed.
G. Hartig et al. 24 February 2003
We investigate the observed variation of commanded filter position for the ACS WFC/HRC filter wheels 1 and 2. We find the commanded filter position typically varies among 3 step or encoder positions. This variation leads directly to an inability to properly flat field images. For most filters, dust motes on the filter causes less than 0.1% variation in flux across the field of view, less than the 0.3% specification. An exception is seen for F606W which has a mote causing 2% variation in flux. Because the pattern of dust motes on the filters is not yet stationary, we do not recommend any additional calibration at this time.
However, permamnet bubble-like defects are present in the VISPOL0 and VISPOL60 filters causing 1% variations across the field of view necessitating the collection of additional flats corresponding to the discretly varying commanded position of the filters.
A. Riess et al. 05 Nov 2001
The appropriate flux transformation for ACS observations is calculated by CALACS and is written to the image header during calibration. This flux transformation is based on the instrument configuration during the observation and is derived from a combination of aperture and filter throughput curves. CALACS uses the throughput curves available in SYNPHOT to determine the appropriate photometric keywords for flux conversion. Therefore, we have tested the most recent version of CALACS to confirm that the photometric keywords generated using the pipeline software are in agreement with those calculated independently using SYNPHOT.
J. Mack et al. 01 Mar 2002
A brief investigation was made to assess the scatter properties of the gap between the two WFC chips. The geometry of this gap is complex and composed of materials, which present diffusive surfaces that might potentially scatter light in an undesired fashion. Nevertheless, this gap could provide a useful dump for the unwanted light from a bright point source in a field of fainter sources under study, minimizing the area of the image affected by blooming (along the CCD columns).
G. Hartig 18 Jan 2002
The Advanced Camera for Surveys offers a large selection of filter/detector combinations, including essentially continuously adjustable ramp filters and two sets of three polarizers, each of which may be crossed with standard filters. Obtaining flat-field calibrations for the scientifically useful modes is a vital element of ground calibration and requires careful planning given the large number of potential modes. This memo itemizes the combinations requiring calibration and hence serves as a basis for detailed ground calibration plan development, budgeting and prioritization.
W. Sparks et al. 04 Dec 2000
When the Advanced Camera for Surveys is installed in SM3B it will become the instrument which requires by far the greatest data volume. We expect to need to downlink about 14 Gigabits of science data per day, of which 70% to 80% will come from the ACS. The factors entering into this estimate are described, together with the effect of varying some operational conditions
C. Cox 17 Jul 2000
Compressed WFC data provided by Ball Aerospace from a WFC qualification unit detector (with a read noise of ~4 electrons) were run through a test version of generic conversion to verify that it is able to unpack and uncompress on-board compressed data. Testing of this first set of images has determined that generic conversion, as implemented, operates correctly. Further testing will be carried out as images with different gain values and compression parameters become available. A summary of the outstanding test requirements is presented.
F. Boffi et al. 31 May 2000
We address the question of how we will deal with differences between expected and after launch throughput estimates to be stored in STSDAS tables. We have considered various alternatives and decided to follow in WFPC-2 steps, i.e. to eventually update only detector and filter sensitivities as appropriate.
F. Boffi et al. 24 Feb 2000
Microchannel plates slowly lose gain with use as charge is extracted. The gain loss depends not only on the total charge but also on the rate at which this charge is extracted. At a fixed pulse height threshold this gain degradation translates to a loss of efficiency. To predict the efficiency loss of the ACS MAMA with use we will maintain cumulative images which express the total counts in each pixel and the expected loss of sensitivity. The strategy for maintaining these images is given together with the image formatting requirements. In the event of a loss in excess of a percent or so we could consider producing new photometry tables and flat fields or increasing the tube voltage. The experience with the STIS MAMAs does not lead us to expect a measurable decline over a five year period of normal operations.
C. Cox 29 Dec 1999
On-orbit experience with WFPC2 and, to a lesser degree, STIS has shown that Charge Transfer Efficiency (CTE) charge loss has a significant impact on the photometric precision of the CCD detectors. The magnitude of the error increases with time as displacement damage due to radiation exposure accumulates. In order to track the degradation of the ACS HRC and WFC CCD detectors, some on-board means of accurately and efficiently measuring CTE should be defined. To accomplish this goal, we advocate the development of a set of special clock timing patterns that will be used to measure CTE via the First Pixel Response (FPR) and Extended Pixel Edge Response (EPER) methods. We present a general description of how both methods work and delineate specific requirements for on-board implementation of the FPR and EPER tests.
M. R. Jones et al. 02 Nov 1999
A set of ACS apertures has been characterized using values derived from optical modelling software. This report describes the assumptions and calculations used to prepare the Science Instrument Aperture File which is included in the Science Operations Database. This revision corrects several typographical errors of sign on pages 4 and 5. The values in the spread sheets and those delivered to the SIAF were correct and have not been altered.
C. Cox et al. 14 Dec 1999
On April 19th 1999 commanding tests were run against the ACS to exercise the turning on of the MAMA and the fold analysis according to proposals 9008 and 9009. The instrument was not in vacuum and the Deuterium lamp was not turned on, so only dark counts were collected and a real fold analysis could not be performed. Voltages, currents and dark counts were monitored. The tests proceeded without problems. Some voltages were marginally outside ground software limits but well within flight software limits, The ground limits that were too restrictive have since been relaxed slightly so as to avoid spurious warnings. Note that, since the first ACS observations will be scheduled in cycle 10, these proposals will be renumbered later to be in the 10000 series.
C. Cox et al. 02 Aug 1999
Data from the ACS CCDs will be converted by Generic Conversion into a form that will be input to CALACS, and will be given to users as raw data. In this TIR we specify what the data output from Generic Conversion should look like. In particular, the orientation convention of the images with respect to the chip amplifiers and V2V3 is specified.
R. Jedrzejewski et al. 24 Sep 1998
The ACS filter set consists of six filters that may be used for near-UV, U and B observations: f220w, f250w, f330w, f435w and f475. The ACS red leaks for these filters were calculated using preliminary throughputs and are presented here and compared to their counterpart filters in the WFPC2 filter set.
C. M. Pavlovsky 03 Sep 1998
Based on the proceedings of the ACS Dithering WG, and on the results presented in the companion ISR “Dithering Strategies for ACS” we recommend here a set of dither patterns for use with the Advanced Camera for Surveys. These dither patterns allow the user to specify small scale dithers to remove defects and large scale mosaic patterns. The small scale dithers can be either user-tunable or optimized by the ACS Group on the basis of their instrument knowledge.
M. Stiavelli et al. 10 Jul 1998
Realistic simulated images of different astronomical fields were created to test the compression algorithm to be used on-board the ACS. The simulation process of such images is described step by step and some images are shown
F. Boffi & M. Stiavelli 08 Oct 1998
A summary of maximum exposure times and count rates through a select group of ACS filters for five current HST standard stars and eight white dwarfs that have been proposed as possible new standard stars for the more sensitive HST instruments.
C. Pavlovsky 28 Aug 1998