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Hubble Space Telescope
November 2010 STAN

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| STScI Analysis Newsletter (STAN) 
| Cosmic Origins Spectrograph (COS)
| Space Telescope Imaging Spectrograph (STIS) 
| November 2010
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In this Newsletter we provide information on the corrected STIS
NUV TDS file and the COS FUV gain sag.

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Gain Sag in the COS FUV Detectors

The COS FUV detector has exhibited gain sag in the regions
illuminated by the bright airglow lines. This causes calcos
to reject some target photons as background events and will eventually
lead to the loss of target photons. Short and long term
solutions have been developed by the team and are being implemented.


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New STIS NUV MAMA time-dependent sensitivity correction reference file.

It was recently discovered that some rows of the STIS TDS reference file 
(u7c1846io_tds.fits) that was delivered on July 12 for the NUV MAMA 
were corrupted, leading to an incorrect flux calibration for post-SM4 
observations using the STIS E230M, E230H, and G230M gratings. These files 
produced errors of 10-15% over much of the range of these gratings, and at 
some shorter wavelengths the errors were as large as 23%. Results for the 
STIS G230L were correct. Procedures for monitoring STIS time dependent 
sensitivity changes and for producing and testing these reference files 
have now been significantly revised to better ensure that final calibrated 
data products are scientifically correct. A new revised reference file that 
corrects the previous errors has now been delivered (ub920085o_tds.fits).  
For 1st order NUV MAMA modes, these revised files remove time dependent 
trends in the calibrated flux with about 2% accuracy.  For echelle modes, 
the accuracy is about 6% or better, and future revisions may allow the 
repeatability of these modes to be further improved.


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