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IUE Project Electronic Newsletter

NASA-Goddard Space Flight Center (GSFC)

Vol. 5, No. 6 - June 1997


IUE Image Processing News

Acknowledgements for Problems Found

We are committed to producing the highest quality, uniformly processed IUE data set we can by October 1. Therefore, we greatly appreciate the reporting of any suspected problems with the IUE Final Archive data. It is our goal, at the very least, to document any problems and, if possible, to fix them before the project goes out of business. We had neglected to acknowledge them in the last Newsletter, but we are indeed grateful to two veteran IUE researchers, Ed Fitzpatrick and Derck Massa, who discovered problems which we are fortunate to have the time to correct. Fitzpatrick noticed the odd sigma vectors in processed LWR low-dispersion images which were due to a problem with the noise model extrapolation at high FNs (flux numbers). Massa noticed that the SWP sensitivity decreased a few percent faster than the correction model had predicted for the last two years of IUE operations.

Thanks for the help.

Fix of LWR Low-Dispersion Images Begins

As we noted last month, a problem with the noise model used in the extraction of some LWR low-dispersion spectra was uncovered. The problem occurs when the noise model is extrapolated to higher FN values than in the original data used to construct the noise model. In some cases, the extrapolated function decreases, incorrectly indicating that the noise decreases at higher signal levels. This extrapolation error affects the sigma values and, since they are used in the extraction, it can affect the flux levels that are derived where the spectrum is somewhat to very overexposed.

We have screened the LWR images to determine which ones are affected and have begun to reprocess the affected images (3665 images) with the corrected noise model. We are taking a very conservative approach in which if one pixel is affected, we are reprocessing the image. It is likely many of the reprocessed images will yield no significant changes (e.g., 550 images had 4 or fewer pixels affected). However, it is more time efficient just to reprocess the images in a batch mode rather than to analyze how much the extracted spectra were affected. This change has been implemented in NEWSIPS Release 2.5.3, and the new noise model is listed in the processing history as Version 1.1. Please contact us if you are concerned about any LWR spectra you are currently using. We expect to have all the affected LWR images reprocessed by mid-July. We also welcome priority processing requests at

http://hypatia.gsfc.nasa.gov/IUE/search/IUE_usrreq.html

For more information, please contact Cathy Imhoff.

Updated SWP Images For 1993-1996

As noted last month, the SWP sensitivity degradation correction has been updated for data obtained from 1993 onward. We are currently reprocessing the affected data, both high- and low-dispersion images. The new version of the data is identifiable from the processing history NEWSIPS version (2.5.3 for SWP low dispersion, 3.1.1 for SWP high dispersion) as well as the processing date (May 2, 1997).

What about the LWP? Testing shows that there is no need to change the sensitivity degradation correction. The extrapolation for later data works fine.

Coming Soon: LWP High-Dispersion Processing

The LWP high-dispersion processing system is nearly ready. We hope to start processing images in the next week or so. You are welcome to send us your requests for priority processing; however they will not be put into the system until processing begins. You can access the request form at:

http://hypatia.gsfc.nasa.gov/IUE/search/IUE_usrreq.html

Questions?

If you have any questions about IUE processing or the Final Archive, please feel free to contact me any time at imhoff@iuegtc.gsfc.nasa.gov or 301-794-1470

- Cathy Imhoff


Streak Spectra List Available

A list of LWP low dispersion sky background images taken at Goddard since the onset of the Streak has been compiled. This file is available from the website at

http://iuewww.gsfc.nasa.gov/pub/manuals/streak.txt

and will also be included in the manuals subdirectory of future DAC software releases.

These exposures were usually taken while the SWP was exposing on a particular target, so there was no (intended) target seen by the LWP. The file gives image particulars for streak exposures, images with no streak contamination, images that have some additional contamination, and images that don't fall cleanly into any given category.

- James Caplinger


IUEDAC Software Changes

06-May
A new version of asc_read was added to the experimental library which allows users to extract data as double precision rather than floating point numbers.
09-May
A new version of newcalib was implemented which applies the absolute flux calibrations for LWR low dispersion spectra extracted from the NEWSIPS SILO files. (The previous version was only compatible with LWP and SWP spectra.) Corrections were also made to newcalib which improve the agreement with NEWSIPS calibrations for SWP and LWP spectra by 2-3%.
13-May
The following experimental routines were implemented:
bins
allows binning in energy units (KEV).
asc_read
allows reading of double precision numbers.
asc_write
properly displays number of extracted points.
artifact
prolog change.
iuespec
checks camera number in .dat file.
iuefx
checks image numbers entered using optional file keyword.
readmx
clarifies user prompt for order numbers.
readri
extracts extension data added for partial read raw NEWSIPS files.
srplot
accepts SIHI files as input.
wfiraf
converts wavelengths and fluxes to IRAF compatible FITS files.
28-May
A new version of newcalib was implemented which applies the new sensitivity degradation correction for post-1993 SWP low dispersion point source spectra.
- Randy Thompson

Software Libraries Updated

The IUEDAC software library sets for the various supported platforms were updated on 14 May 1997. All routines that were created or modified prior to that date and since the last release in December 1996 are included in the new distributions. These can be retrieved from our website from

http://iuewww.gsfc.nasa.gov/iuedac/data_software.html

Any programs created or modified since then are available in a Beta software area, available from the same page. Included there is a readme file describing how these additional routines should be incorporated into the software.

- James Caplinger


The IUE Electronic Newsletter, edited by James Caplinger, is primarily intended to inform the numerous remote and local users of the IUEDAC software of recent software updates, as well as let them know about news relating to the IUE project in general. If you want your name to be added to, deleted from, or changed on our distribution list, please send us e-mail to

news@iuedac.gsfc.nasa.gov

or send a postcard to:

IUE Data Analysis Center (IUEDAC)
Code 686.9, NASA-GSFC
Greenbelt, MD 20771


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Mr. James R. Caplinger, Computer Sciences Corporation

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Dr. Don West, IUE Operations Scientist