Number 26 May 2003


1) Error in the Application of the FUSE Flux Calibration for post June 2002 data
2) FUSE Cycle 5 NRA to be released in late June, 2003

1) Error in the Application of the FUSE Flux Calibration for post June 2002 data

        We have discovered an error in the way that the flux-calibration is 
applied in the CalFUSE pipeline.  This problem affects data taken after June 
2002.  A corrected algorithm has been devised and implemented. 

        The FUSE Science Operations Team performs regular observations of flux 
calibration targets to monitor the sensitivity of the instrument.  For reasons 
of work load and pipeline stability, not all of these observations are used
to produce flux calibration files for the CalFUSE pipeline.  This is in part
due to the fact that very little change has been seen in the sensitivity over
the first part of the mission.  The latest set of time-dependent 
flux-calibration files were released in June of 2002.  Analyses now indicate 
that the FUSE sensitivity has decreased by 1 to 7%, depending on the channel, 
since that time.  We have been begun work on a new set of flux-calibration 
files that will reflect these changes; we expect to release them by June 2003.

        For data obtained between the dates of two flux-calibration files, 
the pipeline interpolates between the two calibration files.  For data obtained 
after the most recent calibration file, however, the pipeline has been deriving 
its flux-calibration by linearly extrapolating from the last two calibration 
files.  This is an error; the program should simply use the most recent 
flux-calibration file.

        Our two latest flux-calibration files are dated March 2002 and June 
2002.  Therefore, the problem affects all exposures obtained after 06/19/2002.  
Two segments, LiF 1B and LiF 2A, are particularly affected, because the last 
two sensitivity curves for these segments differ by about 10%.  Moreover, the 
flux error grows linearly with time.  The effects are less significant for other 
segments, and it affects only the FLUX and ERROR arrays, not COUNTS and CNTSERR.

        We have developed a number of tools to correct this error.  These 
tools, together with more information on this error, are available from the web 
page, "An Error in the Application of the FUSE Flux Calibration" at the 
following URL:

        Among the available correction tools is a new version of the CalFUSE 
pipeline, CalFUSE v2.4, containing the corrected algorithms. This is
available at:

        We are currently installing CalFUSE v2.4 into the default processing 
stream.  All data processed after May 6 will be processed with the new pipeline
version.  We are also dedicating an extra CPU to reprocessing the affected 
data sets as quickly as possible.  We estimate that this will be completed 
within a month of the present date.

2) FUSE Cycle 5 NRA to be released in late June, 2003

        We would like to remind you that the NRA for FUSE Cycle 5 observations
is planned to be released in late June 2003.  The proposal deadline will be in
mid-September with cycle 5 observations starting on April 1, 2004.

The Observer's Electronic Newsletter is published by the FUSE project and is 
aimed at the FUSE user community.

Editor: B-G Andersson, FUSE Guest Investigator Officer.

The FUSE Project is managed by Johns Hopkins University's Center for 
Astrophysical Sciences in Baltimore, MD, for NASA's Goddard Space Flight 
Center.  The FUSE Principal Investigator is Dr. Warren Moos, the FUSE Project 
Manager at JHU is Mr. J.B. Joyce, and the NASA Project Scientist for FUSE 
is Dr. George Sonneborn.

Further information about the FUSE Guest Investigator Program can  be
obtained from:  Dr. George Sonneborn;

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