[Fwd: NEW ACS + WFPC2 STAN 30 November 2006] For those of you who haven't already received this directly.

From: Saul Perlmutter (saul@lbl.gov)
Date: Thu Nov 30 2006 - 09:42:00 PST

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    +--------------------------------------------------------+
    | STScI Analysis Newsletter (STAN)
    | ACS+WFPC2
    | 30 November 2006
    +--------------------------------------------------------+

    CONTENTS:

    1. New ACS Bulletin Board Online

    2. HRC Relay Anomaly

    3. SBC Operations

    4. ACS Calibration Status

    5. Calibration Outsourcing

    6. Optical Redleak in the ACS SBC Detector

    7. New MultiDrizzle Release and Improved Distortion Solutions

    8. WFPC2 WF4 CCD Anomaly

    9. WFPC2 Closeout Plans

    10. Recent Instrument Science Reports

    11. Recent Refereed Publications

    12. Recent Press Releases

    +--------------------------------------------------------+

    1. New ACS Bulletin Board Online

    STScI has established an online ACS bulletin board to allow
    staff and HST observers to correspond with each other on
    ACS-related topics. Feel free to peruse ongoing discussions,
    post a reply to an existing thread, or start a new message
    of your own. Your participation is needed to establish a useful
    dialogue, and the postings will be moderated to ensure maximum
    utility for users and to prevent misuse. To be able to post
    messages, you must first register with the bulletin board
    moderators. This is a quick one-time process - simply click
    on the "Register" link on the bulletin board webpage and follow
    the instructions. No registration is required to view the ongoing
    discussions. The bulletin board gives the STScI ACS Team a more
    efficient method to disseminate late-breaking news, and
    to respond in a more widely visible way to common questions
    often handled via the e-mail Help Desk. We look forward
    to communicating with you.

    http://forums.stsci.edu/

    +--------------------------------------------------------+

    2. HRC Relay Anomaly

    The ACS suspended on September 23, 2006 because of a problem
    with one of the relays on a signal processing chain board in
    the High Resolution Channel [HRC] CCD detector electronics.
    Analysis of the condition by an ACS Anomaly Review Board
    concluded that the most likely cause of the problem was a bit
    of non-conductive debris between two relay contacts that must
    meet to make a proper electrical connection. The missing
    voltage resulting from this problem did not affect the ACS Wide
    Field Channel [WFC], which was brought back into service on
    October 2, or the Solar Blind Channel [SBC], which will be
    brought back into service on November 27.

    After a thorough assessment of the risk to the HRC and other
    ACS hardware, the Anomaly Review Board recommended that the
    problematic relay be toggled open to clear the debris and then
    closed to reestablish the electrical connection. The relay was
    toggled open and closed on October 9. This procedure evidently
    cleared the debris because the missing connection was restored
    when the low voltage power supply for the the CCDs was turned
    on again. The HRC was configured for science operations and
    resumed service on October 16.

    The Anomaly Review Board recommended that the problematic HRC
    relay be left in its present (working) position. The WFC and
    HRC will be left powered during routine operations, except when
    monthly anneals are performed. Presently, all three ACS channels
    are operating nominally and may be requested for use in Cycle 16
    observing proposals.

    +--------------------------------------------------------+

    3. SBC Operations

    The Anomaly Review Board's recommendation to leave the HRC
    relay in its present position required changes to the instrument
    commanding used to operate the SBC. Previously, SBC use has been
    tied to a set of commands used to toggle the HRC relay so that the
    HRC and SBC were not on simultaneously. After studying the
    electrical current, power, and thermal implications of having all
    three ACS channels powered simultaneously during SBC operations,
    approval was given to implement SBC operations with both CCDs
    powered. The SBC will be powered only when it is being used for
    science or calibration observations. As before, the SBC cannot be
    used in parallel with the other ACS channels. For all practical
    purposes, the changes to the commanding of the SBC are transparent
    to observers. The SBC observing capabilities now are the same as
    those that have been available in the past.

    +--------------------------------------------------------+

    4. ACS Calibration Status

    Details for the Cycle 15 calibration plans may be found at:
    http://www.stsci.edu/hst/acs/analysis/calib_plan/index_html#Section7
    These programs support the annual science cycle. Emphasis
    this cycle includes maintaining up-to-date standard reference
    files, responding to any changes after the switch to Side 2
    electronics and 4 degree C cooldown of WFC last July, and
    providing additional SBC specific calibrations.

    The WFC temperature decrease, and Side 2 switch in July led
    to minor calibration changes. New biases and darks were
    put in place in July with standard releases of these since.
    The WFC flat fields have changes of ~0.6% in the blue to
    ~0.15% at F814W, new flat fields for filters with wavelengths
    between those corresponding to F435W and F814W were delivered
    November 2, 2006 -- see ACS/ISR 2006-06. The WFC detector
    sensitivity table will be updated to account for the
    -2.5% at F435W to about 1% drop for redder filters as a
    result of the lower operating temperature. We will provide
    documentation quantifying limits to existing performance
    changes for the HRC and SBC for which updates are not expected
    to be necessary.

    +--------------------------------------------------------+

    5. Calibration Outsourcing

    The Call for Proposals for Cycle 16 specifies categories of
    "Calibration GO and AR Programs" in Sections 3.2.4 and
    3.4.3 respectively 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. In addition to general
    areas mentioned in the CP, a candidate for such work
    includes polarimetry calibration for ACS/WFC for which
    significant calibration data exists that could be analyzed
    by an interested GO.

    +--------------------------------------------------------+

    6. Optical Redleak in the ACS SBC Detector

    Recent observations of cool stars using the ACS SBC PR110L prism
    have revealed that the sensitivity of the ACS Solar Blind Channel
    to optical and near-UV light is apparently much larger than was
    measured during ground testing. The throughput given in the standard
    reference files for the SBC detector at 3500 angstroms is about
    9.5e-9. Preliminary estimates suggest that the real SBC detector
    throughput at this wavelength is approximately 3.4e-6, or about 2.5
    orders of magnitude larger than the existing estimate.

    For a solar-type spectrum, this means that about 1/2 of the total
    counts detected are due to optical and near-UV photons rather than
    from the expected FUV photons. There is also some evidence that
    the amplitude of this 'red leak' changes as the SBC detector warms
    up, increasing by as much as 30% over the course of 5 orbits. It is
    not yet clear whether this red leak has also been increasing
    secularly over time. Imaging data taken with the STIS FUV-MAMA
    detector (for which the ACS SBC was the backup detector) seem to
    show a similar, although perhaps somewhat smaller effect.

    For dispersed PR110L and PR130L observations, it is straightforward
    to identify this extra red light; however, it clearly also affects
    SBC imaging observations done with the long-pass filters. The ACS
    team is undertaking efforts to obtain a better calibration of the
    red leak effect. Until this better characterization is in place,
    extreme caution should be exercised when interpreting FUV imaging
    observations of red targets. Observers conducting FUV imaging of red
    targets with the SBC may wish to consider interleaving observations
    with two different long-pass filters (e.g., F140LP and F165LP), so
    that the difference in the count rates can be used to isolate the
    true FUV flux.

    +--------------------------------------------------------+

    7. New MultiDrizzle Release and Improved Distortion Solutions

    We announce the release of updated MultiDrizzle/PyDrizzle software,
    together with improved polynomial distortion solutions ("IDCTABs")
    as well as improved distortion residual images ("DXY" files). The
    new software (MultiDrizzle v.2.7.2, PyDrizzle v5.7.0) is available
    at http://www.stsci.edu/resources/software_hardware/pyraf
    and has also been incorporated into the HST archive pipeline.
    The new distortion solutions were provided by J. Anderson and will
    be available from the archive, and from the reference file webpage:
    http://www.stsci.edu/hst/observatory/cdbs/SIfileInfo/reftablequeryindex
    Together, the distortion files and updated software are capable of
    providing an astrometric precision of about 0.01 pixels for data
    obtained during the first few years of ACS operation, thereby
    correcting pixel shift problems that had been previously reported.

    We caution that inherent uncertainties up to ~0.1 pixel or more
    may still exist in the observations. These can be introduced by
    guide star problems which cause errors in the commanded offsets,
    as well as long-term thermal changes and other effects resulting
    in evolution of the distortion solutions over time. The released
    versions of the software and distortion solutions do not yet
    contain time-dependent information, which will be available in
    a subsequent release. Meanwhile, it is possible to iteratively
    refine shifts, if necessary, as described in section 4.6 of the
    current ACS Data Handbook. Observers will be notified as soon as
    more updated time-dependent distortion solutions are available.

    +--------------------------------------------------------+

    8. WFPC2 WF4 CCD Anomaly

    The bias level in the WF4 CCD has begun to trend downwards again,
    mimicking its behavior in late 2004 and early 2005. We have not
    yet seen any further blank images in WF4, but a few blank images
    could occur if the trend accelerates during the next two months.
    We are tentatively planning another WFPC2 temperature adjustment
    in January or February 2007 to counteract the trend. Observers
    are reminded that WF4 images with low bias values (below about
    300 DN, and above about 5 DN) will have low photometric counts,
    but the photometry should be correctable. This information will
    be updated as needed at
    http://www.stsci.edu/hst/wfpc2.

    +--------------------------------------------------------+

    9. WFPC2 Closeout Plans

    A summary of the WFPC2 calibration observations for its
    remaining time onboard HST has been posted at
    http://www.stsci.edu/hst/wfpc2/analysis/WFPC2_cyc1516_cal_plan_final.pdf
    As always, observers are welcomed to suggest additional
    calibrations, or propose additional calibration observations via
    Calibration Outsourcing proposals. These Outsource proposals
    can also be of an archival nature, and utilize existing or planned
    WFPC2 calibration data. We would be happy to discuss current
    calibration plans and potential outsource projects with interested
    parties.

    +--------------------------------------------------------+

    10. Recent Instrument Science Reports

    ACS:

    ACS Post Flash Measurements (ACS ISR 06-07)
    http://www.stsci.edu/hst/acs/documents/isrs/isr0607.pdf

    WFC L-flats Post Cooldown (ACS ISR 06-06)
    http://www.stsci.edu/hst/acs/documents/isrs/isr0606.pdf

    Relative Astrometry Within ACS Visits (ACS ISR 06-05)
    http://www.stsci.edu/hst/acs/documents/isrs/isr0605.pdf

    Related ISR from the Telescopes branch:
    Modeling Aberrations in the Advanced Camera for Surveys(ISR TEL 06-01)
    http://www.stsci.edu/institute/org/telescopes/Reports/ISR-TEL-2006-01.pdf

    WFPC2:

    A list of the recent WFPC2 ISRs can be found at:
    http://www.stsci.edu/instruments/wfpc2/wfpc2_bib.html

    +--------------------------------------------------------+

    11. Recent Refereed Publications

    ACS:
    http://www.stsci.edu/hst/acs/documents/pub_acs_nov_06.ps

    WFPC2:
    http://www.stsci.edu/hst/acs/documents/pub_wfpc2_nov_06.ps

    The papers listed above are based on data from ACS and WFPC2.
    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/

    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

    +--------------------------------------------------------+

    12. Recent Press Releases

    ACS:
    http://www.stsci.edu/hst/acs/documents/press_acs_nov_06.html

    WFPC2:
    http://www.stsci.edu/hst/acs/documents/press_wfpc2_nov_06.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
    +----------------------------------------------------------+
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    | 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.
    +----------------------------------------------------------+



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