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Hubble Space Telescope
December 2010 STAN

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| STScI Analysis Newsletter (STAN) 
| Cosmic Origins Spectrograph (COS)
| Space Telescope Imaging Spectrograph (STIS) 
| December 2010
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In this Newsletter we provide information on the changes to the 
COS pulse height filtering, the effects of gain sag on dispersed
light target acquisitions for COS, COS airglow Observations, 
Reference file updates mailing lists for both COS and STIS,
and the delivery of a new FUV bad pixel table for STIS.

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Change to Pulse Height Filtering to Mitigate Effects of Gain Sag in the COS
FUV Detector

The gain sag experienced by the COS FUV detector in the regions illuminated
by bright airglow lines leads to artifacts (absorption-like features) in the
extracted spectra. In order to mitigate this effect we are lowering the
minimum threshold used for pulse height screening during calibration. This
change to the pulse height screening leads to an increase of ~7% in the
average value of the dark count rate and to a 5% overestimation of the
calibrated flux.

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Effect of COS FUV Gain Sag on FUV Dispersed Light Target Acquisitions

The gain sag of the COS FUV detector produces also mis-registration of
events along the cross-dispersion direction, leading to a "walk" of the
spectrum on the detector toward lower values of the cross-dispersion
direction.  While this walk has no effect in extracted spectra it can potentially
alter the accuracy of target acquisitions using FUV dispersed light.

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COS Airglow Observations

A list of non-proprietary COS observations that provide good examples of uncontaminated
geo-coronal airglow lines has been posted on the COS web site at
http://www.stsci.edu/hst/cos/calibration/airglow.html.

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COS and STIS Reference File Updates Mailing Lists

Every time a new COS or STIS reference file is delivered and the database updated, an email is
sent to the mailing lists cos_reffiles_upd@stsci.edu and stis_reffiles_upd@stsci.edu, respectively.
For example, to subscribe to the STIS list, send an e-mail to 
MajorDomo@stsci.edu with the
following in the body of the message: subscribe stis_reffiles_upd your_address .

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New STIS FUV Bad Pixel Table

On December 14, 2010, a new FUV bad pixel table for STIS (uce15153o_bpx.fits) was 
delivered to CDBS. This table adds an optical element column, enabling the correct 
marking of the repeller wire shadow for all FUV modes.

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