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Hubble Space Telescope
January 2011 STAN

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| STScI Analysis Newsletter (STAN) 
| Cosmic Origins Spectrograph (COS)
| Space Telescope Imaging Spectrograph (STIS) 
| January 2011
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In this Newsletter we provide some updates of interest to
COS and STIS users who will be drafting and submitting Phase 1
HST programs over the next several weeks.


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Obtaining COS FUV spectra with a S/N > 100/1 per resolution element

Because the COS FUV detectors are subject to position and time dependent 
fixed pattern noise, we do not foresee producing routine pipeline 
processed data with a S/N much larger than 30.  However, S/N > 100 (per 
resolution element) spectra can be achieved by using the iterative FPPOS 
technique (e.g., Bagnulo & Gies, 1991, ApJ, 376, 266, and Lambert et al., 
1994, ApJ, 470, 756) as long as the source spectrum and the observational 
sequence meet certain conditions.  

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Incorrect Resolution Element Used by COS ETC for new G130M Modes

The resolution element used in the calculations performed with the COS 
spectroscopic ETC for the new FUV/G130M modes (cenwave=1055 and 
cenwave=1096) does not correspond to the real resolution element of the 
two new modes. To calculate the correct exposure time per real resolution 
element, divide the exposure time returned by the ETC by 5 (for calculations
at 950 Å) or 19 (for calculations at 1150 Å). 
To calculate the correct S/N per real resolution element, multiply the S/N 
returned by the ETC by 2.2 (for calculations at 950 Å) or 4.4 (for
calculations at 1150 Å). 

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Gain Sagged Regions on the COS FUV Detector

The gain sag on the COS FUV detector can lead to artifacts 
(absorption-like features) in the extracted spectra. The locations of the 
most seriously affected regions are listed.  Users should inspect their data 
for these effects.

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Gain Sag and FUV Dispersed Light Target Acquisitions

The gain sag of the COS FUV detector leads to mis-registration of events 
along the cross-dispersion or y-direction (y-walk) which can affect the 
centering of the target on the aperture when FUV dispersed light target 
acquisitions are used. 
Users preparing Cycle 19 phase I proposals are strongly encouraged to 
consider target acquisition strategies that do not use FUV dispersed light, 
such as Imaging TA or NUV dispersed light TA. 

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Release of CALCOS v2.13.6

CALCOS v2.13.6 was released as part of STSDAS 3.13 in December 2010 and was 
installed in the Operations Archive on January 19, 2011 (OPUS Release 2010.4). 
A detailed list of changes related to CALCOS v2.13.6 can be 
found on the "CALCOS Release Notices" web page at 
http://www.stsci.edu/hst/cos/pipeline/CALCOSReleaseNotes/notes/). 


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COS NUV Dark Rate Update

The dark rate of the COS NUV detector has been increasing
with time following an approximately linear trend. At the present
date, the mean dark rate is about 4.5 x 10^-4 cts/sec/pix, but if
the established trend continues, by April 2012, (approximately
the mid-point of Cycle 19), the mean dark rate will have reached a
level of about 7.3 x 10^-4 cts/sec/pix.  Users with active Cycle 17
and Cycle 18 programs using the COS NUV detector should evaluate 
whether this increasing dark rate will have an impact on their 
planned program.

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Verification of Proper Motion Specifications

We continue to experience some HST observation failures caused by erroneous 
proper motion entries. We remind proposers that the specification of correct 
HST pointing information is their responsibility and observations that fail 
because of incorrect pointing specifications will not be repeated. Changes 
to APT and acceptable units are discussed.  

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