+----------------------------------------------------------+ | STScI Analysis Newsletter (STAN) | ACS+WFPC2 | 1 October 2004 +----------------------------------------------------------+ CONTENTS: 1. Addition of MultiDrizzle to the ACS Pipeline 2. ACS Data Handbook Version 3.0 3. HST Cycle 14 Phase I Proposal Deadline: Friday January 21, 2005 4. ACS and WFPC2 Instrument Handbooks for Cycle 14 5. ACS Geometric Distortion Corrections 6. ACS Zeropoints 7. ACS Bias and Dark Reference Files 8. Discontinuation of WFPC2 Supplemental Darks 9. Recent Instrument Science Reports 10. Recent Publications 11. Recent Press Releases +----------------------------------------------------------+ 1. Addition of MultiDrizzle to the ACS Pipeline As of September 22, 2004, the MultiDrizzle software has been incorporated into the ACS data reduction pipeline. This means that when data are requested from the HST Archive, a "*_drz.fits" image product will be delivered which consists of a cosmic-ray cleaned, combined, and geometrically corrected image. This image product will be created for all ACS associations, which are defined as groups of exposures within a single visit, obtained using the recommended dither patterns or CR-SPLITs as specified in the Phase II proposal instructions. The pipeline previously constructed drz.fits image products using PyDrizzle. The advantages of MultiDrizzle over PyDrizzle are described in Section 4.5 of the ACS Data Handbook. Section 4.6 describes how observers can run the MultiDrizzle software outside of the HST Archive to recalibrate the data if necessary. A future update to the ACS Data Handbook (scheduled to appear by the end of 2004) will include a full discussion of how the software was implemented into the ACS pipeline. In the meantime, users should refer to information at http://www.stsci.edu/hst/acs/analysis/multidrizzle for details about the implementation and the data products that are produced. +----------------------------------------------------------+ 2. ACS Data Handbook version 3.0 Version 3.0 of the ACS Data Handbook was released. It is available in various formats from http://www.stsci.edu/hst/acs/documents/documents/handbooks/DataHandbookv3/ACS_longdhbcover.html This new version has two entirely new Chapters. Chapter 5 covers ACS Error Sources, and discusses issues such as Readout Noise, A-to-D Conversion, Bias Subtraction, Dark Current, Hot Pixels, Cosmic Rays, Flat Fields, Image Anomalies, and Generic Detector and Camera Properties. Chapter 6 covers ACS Data Analysis and discusses issues such as Photometry, Astrometry, Polarimetry, Coronagraphy, Ramp Filters, and Grism/Prism Spectroscopy. +----------------------------------------------------------+ 3. HST Cycle 14 Phase I Proposal Deadline: Friday January 21, 2005 See the HST Call for Proposals and related information that will soon be made available at: http://www.stsci.edu/hst/proposing/docs/cycle14announce Proposers should note the new requirement for Cycle 14 to provide information on how the scheduling and science of a proposal would be affected by a potential transition of Hubble Space Telescope to a pointing mode with only two functional gyroscopes. A detailed description of this mode is contained in the Two-Gyro Handbook, which will be available from the aforementioned Cycle 14 announcement web page. Chapters 7 and 8 contain discussions of impacts unique to observations with ACS and WFPC2, respectively. +----------------------------------------------------------+ 4. ACS and WFPC2 Instrument Handbooks for Cycle 14 The ACS and WFPC2 Instrument Handbooks both have undergone revisions to update for Cycle 14. The new versions will soon be made available respectively at: http://www.stsci.edu/hst/acs/documents/ http://www.stsci.edu/instruments/wfpc2/ These new Handbooks reflect our current understanding of the instruments, and include calibrations and insights obtained during the past year. +----------------------------------------------------------+ 5. ACS Geometric Distortion Corrections ACS images have considerable geometric distortion. Until recently, the geometric distortion corrections applied in the ACS pipeline to create drizzled "*_drz.fits" files were based on fourth-order polynomial solutions. However, it was found that more accurate results can be obtained when corrections are applied that: (a) are dependent on the filter; and (b) contain higher frequency information than can be easily captured with a polynomial. The version of Multidrizzle that was installed in the ACS pipeline (see item 1 above) now applies such corrections for all of the most common filters on WFC and HRC. The corrections are based on the work of Anderson & King (2004; ACS ISR 04-15, hyperlink given under Item 9 below). For the corrections the pipeline uses new calibration reference files "*_dxy.fits". +----------------------------------------------------------+ 6. ACS Zeropoints Photometric zeropoints for ACS are available at the web page http://www.stsci.edu/hst/acs/analysis/zeropoints On May 10, 2004, we made minor updates to the VEGAmag zeropoints for ACS. The new zeropoints are based on the latest spectrophotometric calibration of Vega (Bohlin & Gilliland 2004, AJ 127, 3508). The new composite flux standard alpha_lyr_stis_002.fits (available at http://www.stsci.edu/hst/observatory/cdbs/calspec.html) consists of IUE data from 1256-1675A, STIS CCD fluxes from 1675-4200A, and a specially tailored Kurucz model longward of 4200A (Kurucz 2003) and from 900-1256A. The STmag and ABmag zeropoints have not been affected by this change. NOTE: From May 10, 2004 until August 23, 2004, the VEGAMAG zeropoints for filters F660N and F775W on ACS/HRC were erroneously listed on the aforementioned web page as 25.827 and 25.551. The correct values are 20.827 and 24.551, respectively. +----------------------------------------------------------+ 7. ACS Bias and Dark Reference Files ACS bias and dark reference files (which are made from many contemporaneous bias and dark frames) are typically available in the HST Data Archive within a few weeks after any WFC or HRC observation. However, due to transitions in our reference file production processes and infrastructure over the summer, this turnaround time has been longer for most of the WFC and HRC data obtained between June 17 and August 25. We have now completed the process of creating and delivering the reference files for this period. WFC and HRC users who obtained data in this period are advised to re-retrieve their data from the HST Data Archive to obtain the optimal bias and dark calibration. More generally, users are advised to monitor our reference file webpages at http://www.stsci.edu/hst/acs/analysis/reference_files These list when the best reference files for any particular date of observation have become available. Once dark and bias frames for a particular date have become available, users should (re-)retrieve their data from the HST Archive. +----------------------------------------------------------+ 8. Discontinuation of WFPC2 Supplemental Darks We are attempting to reduce the number of low-priority exposures taken on HST in an effort to prolong the life of the radio transmitters which are used to down-link science data. Hence, we are discontinuing the WFPC2 supplemental dark calibration program, where typically three dark frames were taken per day. In principle these could be used to optimize removal of hot pixels from WFPC2 science images, since dark frames could be selected very close in time to the science data. However, in practice they were rarely used. We will of course be continuing the weekly dark calibration program, which provides reference files for the WFPC2 data reduction pipeline. +----------------------------------------------------------+ 9. Recent Instrument Science Reports ACS: ACS coronographic flat fields (ISR04-16) http://www.stsci.edu/hst/acs/documents/isrs/isr0416.pdf Multi-filter PSFs and Distortion Corrections for the HRC (ISR 04-15) http://www.stsci.edu/hst/acs/documents/isrs/isr0415.pdf SBC Dark and Cumulative Images (ISR 04-14) http://www.stsci.edu/hst/acs/documents/isrs/isr0415.pdf Cross-Talk in the ACS WFC Detectors. II: Using GAIN=2 to Minimize the Effect (ISR 04-13) http://www.stsci.edu/hst/acs/documents/isrs/isr0413.pdf Cross-Talk in the ACS WFC Detectors. I: Description of the Effect (ISR 04-12) http://www.stsci.edu/hst/acs/documents/isrs/isr0412.pdf ACS/HRC Polarimetry Calibration III: Astrometry of Polarized Stars (ISR 04-11) http://www.stsci.edu/hst/acs/documents/isrs/isr0411.pdf ACS Polarization Calibration - II. The POLV Filter Angles (ISR 04-10) http://www.stsci.edu/hst/acs/documents/isrs/isr0410.pdf ACS Polarization Calibration I. Introduction and Status Report (ISR 04-09) http://www.stsci.edu/hst/acs/documents/isrs/isr0409.pdf Detector Quantum Efficiency and Photometric Zero Points of the ACS (ISR 04-08) http://www.stsci.edu/hst/acs/documents/isrs/isr0408.pdf Bias and dark calibration of ACS data (ISR 04-07) http://www.stsci.edu/hst/acs/documents/isrs/isr0407.pdf Time Dependence of ACS WFC CTE Corrections for Photometry and Future Predictions (ISR 04-06) http://www.stsci.edu/hst/acs/documents/isrs/isr0406.pdf For a list of all ACS ISRs please see: http://www.stsci.edu/hst/acs/documents/isrs/ WFPC2: The Accuracy of WFPC2 Photometric Zeropoints (ISR 04-01) http://www.stsci.edu/instruments/wfpc2/Wfpc2_isr/wfpc2_isr0401.html For a list of all WFPC2 ISRs please see: http://www.stsci.edu/instruments/wfpc2/wfpc2_bib.html +----------------------------------------------------------+ 10. Recent Refereed Publications ACS: http://www.stsci.edu/hst/acs/documents/pub_acs_2004_10.pdf WFPC2: http://www.stsci.edu/hst/acs/documents/pub_wfpc2_2004_10.pdf WF/PC: http://www.stsci.edu/hst/acs/documents/pub_wfpc1_2004_10.pdf The papers listed above are based on data from ACS, WFPC2, and WF/PC. The lists include all refereed papers received and identified by the STScI Library during the current year. Please include our Library in your preprint distribution list. The listings were generated with STEPsheet: http://stepsheet.stsci.edu/ +----------------------------------------------------------+ 11. Recent Press Releases ACS: http://www.stsci.edu/hst/acs/documents/press_acs_2004_10.html WFPC2: http://www.stsci.edu/hst/acs/documents/press_wfpc2_2004_10.html The press releases listed above are based on data from WFPC2 and/or ACS. The listing was compiled from the collection of STScI Press Releases available at http://hubblesite.org/newscenter/newsdesk/archive/ . +----------------------------------------------------------+ | Visit the ACS and WFPC2 websites for more news: | ACS: http://www.stsci.edu/hst/acs | WFPC2: http://www.stsci.edu/instruments/wfpc2 | Need help? http://www.stsci.edu/hst/acs/help.html | or send your questions to the Help Desk: help@stsci.edu +----------------------------------------------------------+ | To subscribe or unsubscribe to this STAN, send a message | to majordomo@stsci.edu with a blank subject line and | the following in the body: [un]subscribe acs_wfpc2_news | Previous ACS and WFPC2 STANs are archived at: | ACS: http://www.stsci.edu/hst/acs/documents/newsletters | WFPC2: http://www.stsci.edu/instruments/wfpc2/wfpc2_stan.html +----------------------------------------------------------+ | The Space Telescope Science Institute is operated by the | Association of Universities for Research in Astronomy, | Inc., under NASA contract NAS5-26555. +----------------------------------------------------------+
