National Aeronautics and Space Administration

1. History of the Mission

Since its launch in June, 1992, NASA's Extreme Ultraviolet Explorer (EUVE) spacecraft has obtained sky survey and pointed spectroscopic observations at 70-760 Angstroms, between traditional UV and X-ray bands. The EUVE science and data management effort has been focussed at the Center for EUV Astrophysics (CEA: http://www.cea.berkeley.edu/) of the University of California, Berkeley (UCB), under the leadership of Dr. Roger Malina.

The first six months of the mission were dedicated to mapping the sky in a set of four EUV bands using a set of telescopes mounted perpendicular to the spacecraft spin axis. At the same time, it also carried out a deep survey of the ecliptic plane, using the main telescope which views the sky along the spin axis. Once the survey was complete, the mission entered a Guest Observer phase, carrying out pointed spectroscopy observations.

2. The Evolution of the EUVE Public Data Archive

The EUVE team had been providing public access to EUVE data from facilities at UCB/CEA via network and via the production of CD-WO disks; such access to the public data archive at CEA was recently terminated owing to resource constraints. (Notice that the CEA will continue to deliver proprietary data in the medium of CD-Wos to EUVE Principal Investigators within a few weeks of the end of an observation: the current article discusses the archival and dissemination of EUVE data for which the 6-month proprietary period has ended). As part of its preparation for its future cessation, the UCB team has started providing two data products to NSSDC on DLT tape: the "science archive" consisting of images and photon lists ("events") and the "telemetry archive" containing all the raw telemetry.

In the framework of the emerging Space Science Data Services (http://ssds.nasa.gov/ ), with its emphasis on "active archiving" at sites of major science discipline expertise, NSSDC has been interacting with the High Energy Astrophysics Science Archive Research Center (HEASARC) at Goddard and with the Space Telescope Science Institute (STScI) on optimal roles for each in the management, dissemination, and user support for these EUVE data. These organizations have primary active archive responsibilities in the X-ray (HEASARC) and UV (STScI) bands that bound the EUVE wavelength range. As a result of these interactions and under the guidance of NASA Headquartere, it was decided that access to the science archive data will be supported by both the HEASARC (http://heasarc.gsfc.nasa.gov/ ) and the STScI (http://archive.stsci.edu/ ) through interfaces familiar to those entities' traditional X-ray and optical/UV user communities, respectively. In early 1998, the science archive data were made available for immediate network access via the HEASARC, with links from both STScI and NSSDC, as is discussed in more detail below.

Since the primary mode of EUVE data dissemination support provided by CEA was through the creation and mailing of CD-Recordable disks, and as some EUVE data users may have a continuing preference for this mode of data access, NSSDC will respond to requests for observations from the science archive to be written to CD-WO disks. We encourage users who desire large amounts (Gigabytes) of EUVE data to use this method of obtaining science archive data.

3. The HEASARC EUVE Data Archive

The HEASARC EUVE activities are described on the web pages at http://heasarc.gsfc.nasa.gov/docs/euve/euvegof.html/. The HEASARC EUVE archive contains both proprietary and non-proprietary observations from the EUVE guest observer program through the end of 1997. The data in the EUVE archive will be supplemented periodically with additional observations from the Center for Extreme Ultraviolet Astronomy (CEA) as they are processed. The contents as of April 1998 comprise a total of 26 GB of compressed data on 244 distinct targets (including calibrations). Data are online for immediate download and may currently be retrieved though anonymous FTP or the Web at ftp://heasarc.gsfc.nasa.gov/euve/data/fits, or http://heasarc.gsfc.nasa.gov/FTP/euve/data/fits. These are the same data referenced by different servers. Proprietary data are also stored on-line but are not readable by the public (or most HEASARC personnel). The HEASARC has developed an EUVE observation log (called EUVEMASTER in the HEASARC's database systems) based on logs provided by Mark Abbott of CEA. As of May 1, 1998, users can query EUVEMASTER using either W3Browse or the xray account Browse interfaces, and are able to select observation based on names, observation times, positions, etc. Once the specific observations and data types (images or events files) have been selected, these data products can be obtained by the user using either the W3BRowse data products capability or anonymous ftp (at present the xray account Browse interface does not have access to the EUVE data products).

4. The STScI EUVE Archive

Access to EUVE data at STScI http://archive.stsci.edu/euve is available through the same WWW interfaces used for the Hubble Data Archive. Links are provided for users to search the EUVE catalog and retrieve the data, obtain help, and get information about data analysis. Once the search is done, the user is presented with a list of all datasets matching the query parameters. These can be then retrieved via ftp from HEASARC by using the two hyperlinks available in the "Data Files" column: EVT, which points to the event file, and IMG, which points to the image file. Support of the IRAF-based EUVE software will be from the STScI, after CEA completes the upgrade to IRAF V2.11.

5. The NSSDC EUVE Data Archive

NSSDC will provide a permanent archive of both the EUVE science archive data and the telemetry data. The NSSDC will also service requests from users who want copies of EUVE datasets on CD-WO disks. At present, notice, the EUVE telemetry data are not well-supported, as the UCB/CEA software needed to access and process observation-specific data from the telemetry tapes was highly specific to the CEA ADP environment, and is no longer supported there or elsewhere. Most of the science potential of the EUVE data are at the science-archive level, and only under extreme circumstances should it be necessary to access the telemetry archive.

6. Conclusions

The EUVE Science Archive is now available for browsing and for data retrieval at both the HEASARC and the STScI. The NSSDC will act as a deep archive for this important dataset, with particular responsibility for servicing requests for data on CD-WO disks.

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