- 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.
- 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.
- The HEASARC EUVE Data Archive
The HEASARC EUVE activities are described on the web pages at http://euve.gsfc.nasa.gov/. 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://legacy.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).
- 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.
- 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.
- 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.
Proceed to the next article
Return to the previous article
Select another article