+--------------------------------------------------------+ | STScI Analysis Newsletter (STAN) | ACS+WFPC2 | 7 February 2008 +--------------------------------------------------------+ CONTENTS: 1. ACS-Repair Status 2. ACS SBC Bright Object Limit Revisions 3. Calibration Outsourcing 4. Plans for WFPC2 Data Reprocessing 5. Update on WFPC2 - WF4 Anomaly 6. Recent Instrument Science Reports 7. Recent Refereed Publications 8. Recent Press Releases +--------------------------------------------------------+ 1. ACS-Repair Status In January 2007 ACS lost its Wide Field Channel and High Resolution Channel due to a failure in the low voltage power supply of the Side-2 Electronics. ACS was operating on side-2 because of the previous failure of the side-1 electronics in 2006. Soon after the failure the HST Project rapidly assembled a team to determine if the ACS could be repaired as part of HST Servicing Mission 4 (SM4). This team includes contributors from NASA's Goddard Space Flight Center, Ball Aerospace, Teledyne Imaging Sensors and STScI. It determined that all of the capabilities of the ACS could be restored and created a concept for the ACS-Repair (ACS-R) component of SM4. ACS-R is designed to restore full, non-redundant operation to ACS by replacing the original WFC CCD electronic box (CEB) with the CEB-Replacement (CEB-R) and providing power from a new Low Voltage Power Supply Replacement (LVPS-R). The new LVPS-R will also attempt to restore the HRC function by providing power to the original HRC CEB through the original power bus (backpowering). The repair is designed so that failure of HRC backpowering does not pose risk to the success of the WFC repair. As of January 2007, the ACS-R development is proceeding well and is on-track for SM4. The team has successfully demonstrated that the ACS-R design can deliver the expected performance from the CCDs, and is integrating and testing a fully flight- representative engineering model. This testing will be completed shortly, and fabrication of the flight hardware will begin. A successful repair will restore the full functionality of ACS after SM4. All the three channels of ACS are available for the Cycle 17 Call for Proposals. More information will be available at the ACS WEB SITE: http://www.stsci.edu/hst/acs/performance/ACSR_status +--------------------------------------------------------+ 2. ACS SBC Bright Object Limit Revisions As discussed in the ACS Instrument Handbook for Cycle 17, Sections 4.4.2 and 5.5.2, during 2007 it was found that the SBC sensitivity to near-UV and optical light (the "red leak") is significantly greater than previously recognized (or alternatively, it has increased with time). Since the release of the current Handbook, further analysis has shown that the effect is somewhat less than specified there, but still much larger than previously recognized. Further details will be provided by Boffi et al. in ACS ISR 2008-02. A revised sensitivity curve has been delivered to the calibration database, and since November 2007, that has been reflected in the ETC. Hence, the V-magnitude screening limits in Table 7.4, Section 7.2.2 of the Handbook are now fainter for stars later than type F0 V. Revised values are given in the following table. Revised bright-limit V-band magnitudes for observations with the SBC filters and prisms (no reddening). ---------------------------------------------------------- Spec F122M F115LP F125LP F140LP F150LP F165LP PR110L PR130L ---- ----- ------ ------ ------ ------ ------ ------ ------ F0 V 4.8 10.1 10.0 10.0 10.0 9.9 8.3 8.3 F2 V 4.0 9.3 9.3 9.2 9.2 9.1 7.6 7.5 F5 V 2.2 7.7 7.6 7.6 7.6 7.5 5.9 5.9 F8 V 0.9 6.8 6.8 6.7 6.7 6.7 4.7 4.7 G2 V 2.2 6.3 6.0 6.0 5.9 5.8 3.2 3.1 G8 V ... 5.6 5.6 5.4 5.2 4.8 2.2 2.1 K2 V ... 5.7 5.7 5.2 5.0 4.3 3.2 3.0 KM III ... 4.5 4.5 4.2 4.0 3.6 2.7 2.3 ---------------------------------------------------------- All values have been calculated with the ETC to satisfy the local countrate screening limit of 50 counts/second/pixel (Table 7.3), and all other input sources are also as specified in the Handbook, except that the KM III values are now the faintest for each spectral element among IUE data for 8 objects with spectral types from G8 through M5. +--------------------------------------------------------+ 3. Calibration Outsourcing The Call for Proposals for Cycle 17 specifies a category of "Calibration GO Programs" in Section 3.2.4 defining how community members may apply for support of activities, observations, and/or archival research, to advance instrument calibration. We urge careful consideration of this prospect. By definition WFPC2 calibrations may only utilize archival data, while ACS may also request new observations as relevant. The large number of WFPC2 'close-out' calibrations obtained in the past year, see: http://www.stsci.edu/hst/wfpc2/analysis/WFPC2_cyc1516_cal_plan_final.pdf present opportunities for community involvement. If interested in exploring specific calibrations please initiate exchanges (e.g. understand our plans) with the instrument team by 25 February via 'help@stsci.edu'. +--------------------------------------------------------+ 4. Plans for WFPC2 Data Reprocessing In preparation for the decommissioning of WFPC2, we have undertaken a series of calibration and software enhancements to the CALWP2 calibration pipeline. These enhancements include improved photometric calibrations, geometric-distortion coefficients, and flat fields; an improved UV-throughput correction; removal of the streaks and correction of the photometric errors caused by the WF4 anomaly; and the production of a PyDrizzled image for each WFPC2 data set. Once these enhancements have been incorporated into CALWP2, we will reprocess all WFPC2 data in the HST archive. The resulting data products, available in both waiver and multi-extension FITS formats, will provide a uniformly- calibrated WFPC2 data set, readily accessible to the Virtual Observatory and related projects. On-the-fly recalibration (OTFR) will be discontinued, dramatically improving data delivery speeds. We expect reprocessing to begin in the summer of 2008. +--------------------------------------------------------+ 5. Update on WFPC2 - WF4 Anomaly Since early 2002, the WF4 detector has exhibited an anomaly characterized by low or zero bias levels, faint horizontal streaks, and low count levels. The problem is thought to be caused by a failing amplifier in the WF4 signal-processing electronics. The anomaly is temperature dependent and since 2006 January has been mitigated by reducing the temperature of the instrument at regular intervals. The next temperature adjustment, scheduled for 2008 February 26, should ensure normal bias levels through SM4. To correct archival data for the effects of the anomaly, two new calibration steps have been added to CALWP2. The first rescales the counts in each image pixel, correcting the photometry and restoring the bias to its normal level. The second removes the streaks seen in low-bias WF4 images. Testing of both programs is ongoing, and we expect them to be completed in time for the WFPC2 data reprocessing this summer. +--------------------------------------------------------+ 6. Recent Instrument Science Reports ACS: Updated Flux Calibration and Fringe Modelling for the ACS/WFC G800L Grism (ACS ISR 08-01) http://www.stsci.edu/hst/acs/documents/isrs/isr0801.pdf ACS PSF Variations with Temperatures (ACS ISR 07-12) http://www.stsci.edu/hst/acs/documents/isrs/isr0712.pdf Calibration of Ramp Filters Using the ACS Grism (ACS ISR 07-11) http://www.stsci.edu/hst/acs/documents/isrs/isr0711.pdf ACS Polarization Calibration - Data, Throughput, and Multidrizzle Weighting Schemes (ACS ISR 07-10) http://www.stsci.edu/hst/acs/documents/isrs/isr0710.pdf Two Astrometric Fields for UV Observations (ACS ISR 07-09) http://www.stsci.edu/hst/acs/documents/isrs/isr0709r.pdf Variation of the Distortion Solution of the WFC (ACS ISR 07-08) http://www.stsci.edu/hst/acs/documents/isrs/isr0708.pdf Calibration of ACS/WFC Absolute Scale and Rotation for Use in Creation of a JWST Astrometric Reference (ACS ISR 07-07) http://www.stsci.edu/hst/acs/documents/isrs/isr0707.pdf Photometric Calibration of the ACS CCD Cameras (ACS ISR 07-06) http://www.stsci.edu/hst/acs/documents/isrs/isr0706.pdf Detection of Optical Ghost in the HST ACS Solar Blind Channel Filter 122M (ACS ISR 07-05) http://www.stsci.edu/hst/acs/documents/isrs/isr0705.pdf ACS/WFC: Differential CTE Corrections for Photometry and Astrometry from non-drizzled Images (ACS ISR 07-04) http://www.stsci.edu/hst/acs/documents/isrs/isr0704.pdf ACS CCDs UV and Narrow-band Filters Red Leak Check (ACS ISR 07-03) http://www.stsci.edu/hst/acs/documents/isrs/isr0703.pdf WFC Zeropoints at -80C (ACS ISR 07-02) http://www.stsci.edu/hst/acs/documents/isrs/isr0702.pdf Pixel-to-pixel Flat Field Changes on the WFC (ACS ISR 07-01) http://www.stsci.edu/hst/acs/documents/isrs/isr0701.pdf For a list of all ACS ISRs please see: http://www.stsci.edu/hst/acs/documents/isrs WFPC2: Temperature Reductions to Mitigate the WF4 Anomaly (WFPC2 ISR 07-01) http://www.stsci.edu/hst/wfpc2/documents/isr/wfpc2_isr0701.html For a list of all WFPC2 ISRs please see: http://www.stsci.edu/hst/wfpc2/documents/isrs +--------------------------------------------------------+ 7. Recent Refereed Publications A list of refereed publications for ACS or WFPC2 may be obtained using the STScI Library associated STEPsheet: http://stepsheet.stsci.edu/ A more complete list can be found through the ADS abstract service by using the standard search parameters: http://adsabs.harvard.edu/abstract_service.html +--------------------------------------------------------+ 8. Recent Press Releases Press releases, many of which are based on data from WFPC2 and/or ACS may be identified 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/hst/wfpc2 | Need help? http://www.stsci.edu/hst/acs/help.html | or http://www.stsci.edu/hst/wfpc2/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/hst/wfpc2/documents/newsletters +----------------------------------------------------------+ | The Space Telescope Science Institute is operated by the | Association of Universities for Research in Astronomy, | Inc., under NASA contract NAS5-26555. +----------------------------------------------------------+
