Astronomers have observed a young star ringed by a
swirling disc that may spin off planets, marking the first
published science observation using two linked 10-meter (33-
foot) telescopes in Hawaii.

The linked telescopes at the W.M. Keck Observatory on Mauna
Kea, known as the Keck Interferometer, comprise the world’s
largest optical telescope system. The observation was made of
DG Tau, a young star that has not yet begun to burn hydrogen
in its core. Such stars are called T-Tauri objects.
Observations of DG Tau were made on October 23, 2002, and
February 13, 2003, and the findings will appear in an
upcoming issue of the Astrophysical Journal Letters.

“We’re trying to measure the size of the hot material in the
dust disc around DG Tau, where planets may form,” said Dr.
Rachel Akeson, leader of the study team and an astronomer at
the Michelson Science Center at the California Institute of
Technology in Pasadena. “Studies like this teach us more
about how stars form, either alone or in pairs, and how
planets eventually form in discs around stars.”

The Keck Interferometer observations revealed a gap of 18
million miles between DG Tau and its orbiting dust disc.
Akeson notes that of the extra-solar planets – planets
orbiting other stars – discovered so far, roughly one in four
lies within 10 million miles of the parent star. Since
planets are believed to form within a dust disc, either DG
Tau’s disc has a larger-than-usual gap, or the close-in
planets form farther from the star and migrate inward.

Since 1995, astronomers have detected more than 100 extra-
solar planets, many considered too large and close to their
hot, parent stars to sustain life. By measuring the amount of
dust around other stars, where planets may form, the Keck
Interferometer will pave the way for NASA’s Terrestrial
Planet Finder mission. Terrestrial Planet Finder will look
for smaller, Earth-like planets that may harbor life. The
Keck Interferometer and Terrestrial Planet Finder are part of
NASA’s Origins Program, which seeks to answer the questions:
Where did we come from? Are we alone?

“T-Tauri objects had been observed with other instruments,
but only the brightest ones were detectable until now,”
Akeson said. “With the larger telescopes and greater
sensitivity of the Keck Interferometer, we can look at
fainter T-Tauri objects, like this one.”

The Keck Interferometer gathers light waves with two
telescopes and then combines the waves so they interact, or
“interfere” with each other. It’s like throwing a rock into a
lake and watching the ripples, or waves, and then throwing in
a second rock. The second set of waves either bumps against
the first set and changes its pattern, or both sets join
together to form larger, more powerful waves. With
interferometry, the idea is to combine light waves from
multiple telescopes to simulate a much larger, more powerful

In its ability to resolve fine details, the Keck
Interferometer is equivalent to an 85-meter (279-foot)
telescope. “The system transports the light gathered by the
two telescopes to an optical laboratory located in the
central building,” said Dr. Mark Colavita of NASA’s Jet
Propulsion Laboratory (JPL), Pasadena, interferometer system
architect and lead author of the paper. “In the lab, a beam
combiner and infrared camera combine and process the
collected light to make the science measurement.”

To make these measurements, the interferometer’s optical
system adjusts the light paths to a fraction of a wavelength
of light, and adaptive optics on the telescopes remove the
distortion caused by Earth’s atmosphere.

“This research represents the first scientific application of
an interferometer with telescopes that use adaptive optics,”
said Dr. Peter Wizinowich, interferometer team lead for the
W.M. Keck Observatory and co-author of the paper.

The development of the Keck Interferometer is managed by JPL
for NASA’s Office of Space Science, Washington. JPL is a
division of the California Institute of Technology in
Pasadena. The W.M. Keck Observatory is funded by Caltech, the
University of California and NASA, and is managed by the
California Association for Research in Astronomy, Kamuela,

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