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When STIS resumed operations in July 2001 using the redundant "Side-2"
electronics, the read-noise of the CCD detector appeared to have increased
by ~1 e− due to a superimposed and
highly variable "herring-bone" pattern noise. For many programs that aim to
detect signals near the STIS design limits, the impact of this noise is far
more serious than implied by a mere
1 e− increase in the amplitude of the
read-noise, as it is of a systematic nature. Peak-to-valley deviations on
spatial scales of only a few pixels can be as large as
~8 e−.
[left] A portion of a raw, gain=4 BIAS frame o6hn4x020, taken in
2002 February; [middle] the pattern-free cleaned version available here; [right]
move your cursor over the image to blink between the original and pattern-free
frames. The pattern noise is even more apparent in gain=1 frames.
We perfected a method to cleanly and robustly detect and remove this
pattern-noise from raw STIS CCD frames
(Jansen, Collins & Windhorst 2002). After removal of the pattern noise,
we successfully reproduce the nominal "Side-1" CCD read-noise as observed prior
to 2001 July. As part of an approved Cycle 16 Archival Calibration
Legacy program (AR 11258; PI: Rolf Jansen) we removed the pattern noise from
all 75345 raw, un-binned, full-frame "Side-2" STIS/CCD frames (47192
datasets) taken between 2001 July and the short that rendered STIS inoperable
early in 2004 August. A more detailed paper describing the method, the nature
of the noise, and trends therein over time is
Jansen et al. 2010 (in: 'The 2010 STScI
Calibration Workshop', Eds. S. Deustua & C. Oliveira, [STScI;
Baltimore], pp.449–455 ).
Through this preliminary web-portal, users may search for and download
cleaned datasets of interest via a series of (static) index pages. In
the near future, we may support dynamic searches through these data and
requests of multiple datasets at once. The data may also become available
through MAST and/or the Hubble Legacy Archive (HLA).
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