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About the HEASARC:
HEASARC Overview:
The Archive >
Science Results Using HEASARC Data
The Archive
The philosophy of the HEASARC from the beginning has been to provide
immediate access to the latest version of any data file from any
particular mission. This means making every file directly available via
FTP and the Web. This rapid
access to the data has been a major factor in
enabling large survey projects, where access to a significant fraction of
the archive is required. This instant access was achieved with re-writable
optical disk juke-boxes mounted as a Unix file system. These juke-boxes
proved to be a very cost effective way of providing online access to the
entire HEASARC data holding. As technology has advanced the HEASARC has
been able to keep up with the growth in the archive. Over the last year we
have started to replace the optical juke-boxes with a magnetic RAID
(Redundant Array of Inexpensive Disks), which provide even better
performance for a similar price.
As of April 2000 the HEASARC Archive contains 1600 Gigabytes (Gb) of data.
Files are compressed to save space and speed up network transfers. The
data volume would be ~ 3 times larger uncompressed. Electronic retrieval
is the main method of data distribution. Current network bandwidth appears
to be adequate to satisfy users' needs. From 1991 to 1996 the HEASARC made
CD-ROMs of ROSAT, CGRO, EXOSAT, and Einstein data. While these were
popular give-aways, network access to the archive has made them redundant.
Mirror archive sites have been established in Europe and Japan to improve
access for astronomers worldwide in exchange for data archives from
international missions. The HEASARC site itself sees data down-loads of
order 200 Gb/month, so the equivalent of the entire archive is retrieved
every eight months. As projects have gained confidence in the HEASARC
capabilities, they have elected to directly archive and distribute data
through the HEASARC. During the proprietary period the data files are
PGP-encrypted to ensure security and the PI is sent the key to decode
their data.
The HEASARC archive interface helps the user find the data and also
provides advanced catalog search capabilities. This was originally based
on the Browse system developed in the late 1980s for the
EXOSAT project
in Europe, using a home-grown database system. The initial access, via a
telnet account, provided a command line search-and-retrieval system and
data analysis software. The HEASARC quickly recognized the power of the
Web and in 1993 became one of the first astronomy archive sites to provide
a browser-based search-and-retrieval facility. The database system has
migrated to Sybase, which is better able to keep up with the increasing
demand. The Web-based Browse interface is now the main access point to the
archive. Through an AISRP-funded effort called Hera (link to this), the
HEASARC plans to make data analysis capability available over the Web.
In the interests of increasing the availability of high energy data to
a broader community it is the philosophy of the HEASARC to encourage
other archive centers and services to provide access to the HEASARC
data holding via their interfaces. The final disposition of the
EUVE
archive provided an opportunity to put this philosophy into
practice. The EUVE data are stored in the HEASARC FTP area and
accessed both from the HEASARC Browse and STScI/MAST user interfaces.
Following this example the ROSAT
archive has also been made
available via MAST. These are simple examples of the trend to move
away from the proliferation of archive interfaces and toward an open
archive access layer and fewer custom interfaces. As another step
along this path the HEASARC, in collaboration with STScI and CDS,
developed the Astrobrowse facility to demonstrate how Web technology
can be used to provide search facilities across many sites at minimal
effort. The HEASARC is now working within a larger consortium to
design a system that will extend the capabilities to more fully
integrate Web services.
The HEASARC also provides another interface to the archive called SkyView. This
provides an image of the sky in different wavebands (optical, IR, X-ray,
Gamma-ray, EUV, and radio) in any projection or equinox system. The Data Archive page provides a
central point where all the HEASARC Web services can be accessed.
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Last modified: Monday, 19-Jun-2006 11:24:57 EDT
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