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Hubble Space Telescope
April 2011 STAN

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| STScI Analysis Newsletter (STAN) 
| Cosmic Origins Spectrograph (COS)
| Space Telescope Imaging Spectrograph (STIS) 
| April 2011
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In this newsletter we provide information on reference files, 
updates to the STIS NUV TDC Table, the COS FUV TDS Table, 
the COS NUV Flat Field, the COS Dispersion and Lamp Tables, 
and the delivery of a COS FUV Flat Field. Additionally, changes 
to the COS PeakXD Target Acquisition Strategy and the results 
of the alignment of two STIS modes are discussed. Finally we 
present updates to the calibration software.

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Changes to PEAKXD Acquisitions with COS

To combat the effects of gain sag, we have modified the 
algorithm used for PEAKXD acquisitions with the COS FUV 
detector.  The new algorithm will require no changes to 
(most) Phase II proposals already in the system.  It has the
added benefit of enabling the use of all FUV gratings for 
target acquisitions.

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Partial flat field corrections for G130M and G160M spectra 
and their limiting signal-to-noise.

This article describes the newly implemented COS FUV grid- 
wire flats, which correct the largest contribution to fixed- 
pattern noise in COS FUV spectra.  It also provides 
estimates for the remaining fixed-pattern noise and the 
limiting S/N that can be achieved with standard pipeline
processed data.

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New COS Far Ultraviolet Time-Dependent Spectroscopic 
Sensitivity Reference File 

As part of routine monitoring of spectrophotometric white 
dwarf standard stars, a change in the time dependence of the 
spectroscopic sensitivity of the COS FUV detector has been 
determined. A new reference file has been delivered and is 
now routinely used in pipeline processing of data.

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Vignetting Removed from COS NUV Flat Field

The vignetting on the COS NUV detector has been shown to vary
with time. The static vignetting correction has therefore 
been removed from the NUV flat field. The new NUV flat field
(v2e20129l_flat.fits) was delivered to CDBS on 
February 14, 2011.

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Updated Wavelength Dispersion Solutions for G140L/1280 
setting

COS/FUV wavelength dispersion (v3g18194l_disp.fits) and lamp 
template (v3g18195l_lamp.fits) reference files were delivered 
to CDBS on Mar 16 2011. These files contain updated 
zero-point offsets for the G140L/1280 dispersion solutions, 
based on Cycle 17 on-orbit data obtained in September 2010. 
The lamp template reference file was also updated with lamp 
spectra obtained on-orbit for all FP-POS positions of the 
G140L/1280 setting.


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New TDC Reference File Delivered for STIS NUV

The dark rate of the STIS NUV MAMA detector was surprisingly high
after SM4, and its decline over time has been complicated
by another surge in the Fall of 2010 due to the STIS MAMA hiatus.
A new TDC (temperature dependent dark correction table) reference
file was delivered in February, to provide accurate dark 
subtraction within ~5% for the NUV MAMA.

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Adjustment to the Alignment of Two STIS Central Wavelength 
Settings

In March 2010, errors in the cross-dispersion alignment of 
the STIS G430M 5216 and G750M 6094 settings were corrected. 
Previously these offsets could cause problems when attempting 
to center the target in small subarrays, requiring awkward 
workarounds in the phase 2 implementation. These workarounds
should no longer be necessary, and the alignment of these 
central wavelength settings is now comparable to that of 
other STIS modes.

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CALCOS Version 2.14.4 Available for Download

CALCOS v2.14.4 was installed in STSCI_PYTHON 2.11 Patch 1 on 
April 4, 2011. The rest of STSCI_PYTHON remains unchanged. 
Some of the changes in this version include a fix to a bug 
that prevented using a corrtag file as input to CALCOS. It 
also adds a TIMELINE extension to corrtag files, giving the 
altitude of the Sun, the longitude and latitude of HST, and
other information at one-second intervals throughout the 
exposure. This new extension can be used to filter COS data
based on orbital day or night, which can be used to decrease 
the contamination of spectra by geocoronal emission lines.  
For a complete list of the changes and instructions
on how to download this version go to 
www.stsci.edu/institute/software_hardware/pyraf/stsci_python/current/stsci-python-download
/patch_install

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Development version of the STScI STSDAS software now 
available to the community

The development version of STScI STSDAS (called IRAFX), 
with the latest improvements to the HST calibration 
software, is currently available to the general astronomical 
community. IRAFX is presumed to be fairly reliable, but 
anyone using this software should be aware that it is 
not supported and has not been fully tested.

For more information and details on how to download the 
software go to http://stsdas.stsci.edu/irafx/
  
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