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Hubble Space Telescope
December 2014 STAN

| STScI Analysis Newsletter (STAN) 
| Space Telescope Imaging Spectrograph (STIS) 
| December 2014

In this Newsletter we provide some updates of interest to 
STIS users:



A 3% Increase in the STIS CCD Readnoise at GAIN=4

Recent monitoring of the STIS CCD readnoise for GAIN=1
revealed a sudden increase of roughly 10% to 6.25e- per
read that began in mid-May 2014. We now also report that
an increase of 3% for observations performed with GAIN=4,
began within the same timeframe. For most users, this impact
will be negligible, with the exception of science programs
that require multiple reads of objects with low signal-to-noise
in individual reads (such as high contrast imaging or
spectroscopy of objects with highly wavelength variable spectral
energy distributions). The STIS team is in the process of
updating the read noise values used in both the ETC and the
STIS calibration pipeline, CalSTIS. There will also be
continued investigation into the potential reason for this
increase. PIs of pending STIS CCD programs that use GAIN=4 should
verify that their science programs are not adversely affected by
this change. If so, they should contact their program point of
contact or the STScI help desk at

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