Virtual observatory prototype produces surprise discovery

Early demo project identifies new brown dwarf

A new approach to finding undiscovered objects buried in immense astronomical databases has produced an early and unexpected payoff: a new instance of a hard-to-find type of star known as a brown dwarf.

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.

Note: Images of the newly identified brown dwarf from 2MASS and SDSS are available; contact Michael Purdy.

Acknowledgments: The NVO Project is funded by the National Science Foundation’s Information Technology Research Program, under Cooperative Agreement AST0122449 to The Johns Hopkins University. The development efforts build upon complementary projects and programs, including NSF’s National Partnership for Advanced Computational Infrastructure (NPACI) Digital Sky project (Caltech). Funding for the Sloan Digital Sky Survey has been provided by the Alfred P. Sloan Foundation, NASA, NSF, the U.S. Department of Energy, the Japanese Monbukagakusho, the Max Planck Society, and the participating institutions (The University of Chicago, Fermilab, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics , New Mexico State University, University of Pittsburgh, Princeton University, the United States Naval Observatory, and the University of Washington). The Two-Micron All-Sky Survey (2MASS) is a joint project of the University of Massachusetts and IPAC/Caltech, funded by NASA and NSF.