Scientific
Applications:
VIRTUAL OBSERVATORY PROTOTYPE
PRODUCES SURPRISE DISCOVERY
Scientists working to create the National Virtual Observatory (NVO), an
online
portal for astronomical research unifying dozens of large astronomical
databases, confirmed discovery of the new brown dwarf recently. The star
emerged from a computerized search of information on millions of astronomical
objects in two separate astronomical databases. Thanks to an NVO prototype,
that search, formerly an endeavor requiring weeks or months of human
attention, took approximately two minutes.
NVO researchers emphasized that a single new brown dwarf added to a list of
approximately 200 known brown dwarfs isn't as scientifically exciting as the
timing of the new discovery and the tantalizing hint it offers to the
potential of NVO. The discovery came at a stage when organizers were simply
hoping to use NVO to confirm existing science, not make new findings.
"This was just supposed to be a feasibility demo. We just wanted it to find
all the brown dwarfs that others could find, to show that this was a valid
approach," said Alex Szalay, director of the NVO project and Alumni Centennial
Professor of Astronomy in the Johns Hopkins Krieger School of Arts and
Sciences. "This was the first time we turned the NVO devices on, and they
immediately yielded a new discovery from data that's been publicly available
for at least a year and a half."
According to Szalay, that's just the kind of finding organizers are hoping
will start pouring from the NVO in a few more years: revelations available in
data already gathered by observatories, probes and surveys, but left
undiscovered because new technology is pouring new data so rapidly into a
variety of different databases.
The new discovery came from one of three scientific prototypes NVO
scientists
presented at the January 2003 meeting of the American Astronomical Society.
NVO partners at the California Institute of Technology's Infrared Processing
and Analysis Center (IPAC) implemented the software for the prototype that
found the new brown dwarf. Principal contributors to the demonstration project
included Davy Kirkpatrick and Bruce Berriman, the demonstration project
leader, both from IPAC.
Different astronomical surveys and probes look at the sky with instruments
sensitive to different portions of the electromagnetic spectrum. Often, the
specific part of the spectrum measured by a particular instrument can be the
key to gaining insights to a particular class of objects or certain properties
of those objects. But some of the oddest characters in the cosmos, such as
brown dwarfs, only really start to stick out from the enormous background of
the universe when looked at by different instruments that show how the objects
appear at points across the electromagnetic spectrum.
Among the key ingredients NVO will provide for multiple database searches
is
a
standard way of delivering data, according to NVO co-director Roy Williams, a
senior scientist at Caltech.
"The brown dwarf emerged from looking at two independent surveys together,
and
it's the standard way of delivering the data from the surveys that enables
them to be federated and us to find out what's in there," Williams said. "It's
hard to identify the brown dwarfs in either survey, but if you put them
together, they start to come out."
"People can do these kinds of investigations without NVO," said Bob
Hanisch,
a
Space Telescope Science Institute astronomer and NVO project manager. "But
with the NVO, they'll run much more rapidly and effectively. Many projects
that astronomers can't take on now because of the sheer volume of sifting and
searching involved will suddenly become much more feasible." Astronomers and
computer scientists from 17 research institutions are currently collaborating
to build the framework for the NVO, which is funded by a five-year, $10
million Information Technology Research Grant from the National Science
Foundation.
For the brown dwarf project, researchers wanted to show that they could use
NVO connections they had built between two large databases -- the Sloan
Digital Sky Survey (SDSS) and the Two Micron All Sky Survey (2MASS) -- to
confirm brown dwarfs already identified through previous non-NVO comparison of
those databases.
Brown dwarfs were, for many years, a missing link in astronomers' model of
star formation. The first definitive detection of a brown dwarf didn't come
until 1995, when a team at Johns Hopkins and Caltech announced that they had
firmly identified one. Brown dwarfs are hard to detect because they're small,
cool stars, sometimes described as "failed stars," with less than 8 percent
the mass of the sun. That's still hundreds of times the mass of the gas giant
planet Jupiter, but not massive enough to create the self-sustaining nuclear
reaction that powers larger stars. As a result, a brown dwarf grows cooler and
dimmer as it ages, making it increasingly difficult for astronomers to
detect.
To find the new brown dwarf and two already-recognized brown dwarfs, the
NVO
project searched through information on 15 million astronomical objects in
SDSS and 160 million objects in 2MASS. The prototype found that in the region
of sky currently covered by both surveys (about 0.4 percent of the night sky)
the two databases had 300,000 astronomical objects in common or very likely to
be references to the same physical object.
Additional selection criteria based on the brightness differences of the
objects between the SDSS and 2MASS catalogs suggested that the NVO prototype
had found seven new brown dwarf candidates, but followup observations and
human analysis whittled that list down to three, yielding the confirmed brown
dwarf and two more candidates that have yet to be spectroscopically verified.
Szalay said that was a fine success rate, given the magnitude of the data
searched.
"We narrowed it down from tens of million of objects, to a few hundred
thousand, to a handful," Szalay explained. "This is truly remarkable."
"The discovery of the new brown dwarf is a wonderful example of what can be
done with powerful tools to mine large databases," said Rich Kron, astronomer
at Fermilab and the University of Chicago and an SDSS spokesperson.
"Correlating different maps of the sky greatly expands the 'discovery space'
of each survey. No doubt, many more remarkable objects still remain to be
found."
"The combined, multi-wavelength view of the universe is definitely more
than
the sum of its parts," says Roc Cutri, 2MASS project scientist and IPAC deputy
director. "The SDSS and 2MASS data sets are unprecedented resources for
astronomical discovery in their own right, but the synergy realized by
combining these massive data sets opens research possibilities that were only
dreamed of before."
Brown dwarf expert Kirkpatrick expressed eagerness to apply the new
NVO-based
search technique to larger patches of sky as the data becomes available.
"This method is fully capable of uncovering a colder brown dwarf than any
now
known, and I'm looking forward to working with NVO products in order to find
it," Kirkpatrick said.
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