IUE Project Electronic Newsletter

NASA-Goddard Space Flight Center (GSFC)

Vol. 5, No. 9 - September 1997

IUE Archive Support Moving to Space Telescope Science Institute

Starting in mid-October, support for the IUE archive will be provided by the Space Telescope Science Institute. Following the advice of the IUE Users Committee, and working jointly with GSFC Code 680, the IUE Project, and Goddard's National Space Science Data Center, we developed a concept proposal for providing long-term support for the IUE archive in conjunction with the HST archive. This proposal was submitted to NASA HQ earlier this summer. We have just received word from NASA HQ of their intent to fund this effort. At this time, arrangements are being made for the transfer of four members of the IUE Project staff to STScI to provide support for users of the IUE archive.

The primary activities for the IUE archive support group will include user support (answering questions and providing assistance with using the NEWSIPS data products and the IUE DAC analysis software), further organizing IUE documentation and converting much of the information into electronic form, and, in conjunction with the NSSDC, assuring the completion of the ingest of VILSPA data into NDADS. We plan to make IUE data available through the same WWW and StarView interfaces used for data in the Hubble Data Archive, and to enable users to locate, examine, and retrieve data from both HST and IUE with a single query. Owing to resource limitations, however, the archival support will not be at a level comparable to that which has been provided by the IUE Project. For example, we will not be able to support some of the traditional DAC services, such as user accounts or additional analysis software development.

I'm sure there will be a few rough edges as we transition staff and user support functions from GSFC to STScI, and we ask for patience from users of IUE data during the first month or so of the changeover. We will endeavor to keep current contact addresses -- e-mail and WWW links, for example -- active, or with pointers to new locations at STScI.

- Bob Hanisch, Data Systems Division, Space Telescope Science Institute

IUE Image Processing News

Status of NEWSIPS Processing

We are still on track to finish the NEWSIPS processing of all NASA images by the beginning of October. Here is how each data set stands, as of September 12, 1997.

SWP low dispersion: 98% processed and archived.
LWP low dispersion: 97%
LWR low dispersion: 93%
SWP high dispersion: 99%
LWP high dispersion: 99%
LWR high dispersion: 91%

The remaining images are primarily various types of problem images and engineering images. We are currently processing the remaining science images and the flat field and null images.

We note that the SWR images, as well as the FES images, are not being reprocessed as NEWSIPS data. The original IUESIPS versions of these data will continue to be available, if anyone wishes to use them.

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. Thanks!

- Cathy Imhoff

Evaluation of LWR Ripple Correction

The GSFC IUE staff conducted several analyses to evaluate the quality of the LWR ripple correction and absolute calibration derived by VILSPA. Some 11 LWR high-dispersion images were investigated. These images represented a wide range of camera temperature (THDA), telescope focus, and observation date, as well as both large and small-aperture spectra.

In brief, all of the images show overcorrections in the wings of the ripple corrected orders at short wavelengths (typically below ~2300 Ångstroms). The severity of the overcorrections is greatest for images obtained during early epochs, with bad focus, and through the small aperture. In general, these same images also exhibit the overcorrection persisting to longer wavelengths than images that are less severely overcorrected.

The general property of overcorrection at short wavelengths was previously also found for many LWP images, although not as extremely so. Comparison of these results to the IUESIPS processing of the same images shows that the character of the correction errors is completely different in IUESIPS and NEWSIPS: the IUESIPS processing tends to show mediocre ripple corrections at all wavelengths, and in general, an undercorrection.

The overall quality of the NEWSIPS ripple corrections appears poorer at short wavelengths, comparable at intermediate wavelengths, and better at long wavelengths, compared to the IUESIPS results. VILSPA is currently exploring options for deriving an improved LWR ripple correction. In the meantime, processing is proceeding as planned for the LWR data. Future improvements to the ripple correction could be applied to the extracted spectral files by the user, if desired.

- Myron Smith

Error in LWP, LWR High Dispersion Sensitivity Correction

Evaluation by the IUEDAC of LWR and LWP high-dispersion data processed with NEWSIPS has uncovered an error in the way the sensitivity degradation correction was applied. A hardcoded parameter value for the SWP camera was inadvertently used for both LW cameras, causing the wrong degradation correction to be applied for wavelengths longward of 2712 Ångstroms. The errors vary from one 5 Å bin to the next over the affected wavelength range. The errors range from a few percent at wavelengths shortward of 3000 Ångstroms, up to 20% or more beyond 3200 Ångstroms. Data which are currently in the archive are affected by this error.

The IUEDAC software can be used to recalibrate the data correctly. In addition, the IUE Project plans to correct and re-archive the affected MXHI files. A correction procedure has been developed and is being tested. We expect to produce and archive the corrected MXHI files over the next several weeks. The NEWSIPS processing software has also been updated and corrected. Correct LWP and LWR MXHI files can be identified from their processing headers, where the version number will be Release 3.3.1_A_C, 3.3.2_A_C, (C signifies that the original archived data were corrected and rearchived, while A indicates the software version running on the Alpha OpenVMS system) or Release 3.3.3_A (the corrected NEWSIPS processing system). VILSPA data are not affected; VILSPA will process their data with the corrected software under Release 3.3.3.

- Cathy Imhoff

Possible Corrupted Data at the National Space Science Data Center

We recently discovered that some IUE Final Archive data were corrupted during the archival process at Goddard's National Space Science Data Center. There is an ongoing investigation to define the window of this problem, but the best estimate indicates that the problem occurred between June 8 and July 27, 1997. Most of the affected data processed at GSFC were LWP high dispersion data and LWR low dispersion data. A small subset of SWP and LWP low dispersion data were also affected. Good copies, from the PPARC archive set that is being constructed, exist for most of the data archived during this time with the exception of some vector displacement files (VD files). The IUE Project is reprocessing the images for which "good" copies do not exist. Good copies of the data will be rearchived as soon as possible with the exception of the VD files which will not be replaced.

IUE Final Archive data processed by GSFC that may have been affected will have processing time stamps between June 6, 1997 and July 25, 1997. In addition, some VILSPA data were ingested during this time. It will be harder for archive users to identify potentially corrupted VILSPA data, however; it included some LWP low dispersion data, some SWP low dispersion data, and some SWP high dispersion data. The affected VILSPA data were generally processed between March and May, 1997. If you have a critical need to know if data you have requested was archived during the critical window, please send me an e-mail message to levay@ndads.gsfc.nasa.gov and I will check the archive date for the image for you.

There is also the potential that any IUE data requested from the National Space Science Data Center NDADS facility, including but not restricted to IUEFX, IUE WWW SEARCH, WISARD, ARMS, and WWW ARMS during this time may have been corrupted during the read from the archive media. This potential problem has not yet been investigated, but we feel users should know of this potential problem. Current data requests, for data not archived during the window, should be uncorrupted.

The corruption did not affect every file. However, since the corruption is subtle and can only be reliably identified by comparing pristine files with the files on the archive media, the archive user should regard all files as potentially corrupt. The corruption follows the following pattern, but it occurred randomly. The 396th byte of each 1024 byte data segment is susceptible to OR with 64. In other words, starting at byte 396 of the file, every 1024th byte could have had 64 added to it. The bit modification (flip) did not occur for every data segment nor for every file.

- Karen Levay

IUEDAC Software Updates

04-Aug

The following routines were implemented:

readsi: add slit height information to output WAVE array (high dispersion only) for use with rdz
rdz: add new keyword option to superimpose NEWSIPS extraction slit on displayed SIHI images
iuefhrd: add test for SIMPLE = 'T' as first FITS keyword
ifitswrt: fix bug when data ends on a FITS record boundary
ismenu4: add information on L flag
isview: add information on L flag

10-Sep

The following routines were implemented:

iuefx: uses a different temporary file when the FILE keyword is used, and lists additional NEWSIPS data types
iuerip: includes NEWSIPS LWR ripple correction
newcalib: includes high dispersion absolute flux calibrations
mxcor: new routine for correcting error in LWR & LWP sensitivity degradation corrections (for wavelengths greater than 2712 Ångstroms)
corrcalib: subroutine of mxcor

11-Sep

The IUE merged log was updated. Processing information available through July 30th has been included.

- Randy Thompson

Webmaster

Mr. James R. Caplinger, Computer Sciences Corporation

Responsible NASA Organization/Official

Dr. Don West, IUE Operations Scientist