NEW TECHNOLOGY GIVES CLOSEST- EVER VIEW OF THE DUST "DONUT" SURROUNDING A MASSIVE YOUNG STAR AND A SURPRISE COMPANION

The innermost structure of the donut-shaped dust cloud surrounding a massive young star and the first glimpse of its previously unknown companion star was seen by applying new technology to the Keck telescope, Mauna Kea, Hawaii. The new technology, which uses an interferometer aperture mask in front of the telescope's secondary mirror, gives Keck at least four times greater ability to detect fine detail than the Hubble Space Telescope for small fields of view. With the aperture mask, a team of astronomers viewed regions in the surrounding dust cloud that are closer to the central star than anything previously seen, and imaged for the first time the central void in these clouds caused by the star's intense heat and radiation. The ability to see fine structure in these dust clouds is of interest to astronomers because the clouds are thought to provide the material for planet formation.

"We've seen the donut hole for the first time, and it's a lot bigger than people thought," said Dr. William Danchi of NASA's Goddard Space Flight Center in Greenbelt, Md., co-author of a paper describing the research to appear in the February 22 issue of Nature. "Matter falling onto a young star creates a donut-shaped cloud around the star, and in the middle, there should be a void because heat from the star vaporizes the dust. Prior observations of the star LkHa101, with instruments that do not make images, indicated that the central void was about ten times smaller than what we now see."

"These images allow us to look back in time to understand better the origins of our Sun and Solar system," said Dr. John Monnier of the Harvard-Smithsonian Center for Astrophysics (CfA), also a co-author of the paper.

The star, called LkHa101, is about 522 light-years away in the direction of the constellation Perseus. (A light-year is the distance traveled by light in one year, almost six trillion miles.) Less than about one million years old, LkHa101 is still relatively young, about one percent of its estimated lifespan of no more than 100 million years. It's at least 5 times as massive as the Sun and shines 40,000 times more brilliantly. The central void extends about 316 million miles from the star, more than three times the Earth's distance from the Sun. Prior observations did not have sufficient resolution to detect its companion star, which orbits around LkHa101 at a distance of about 2.6 billion miles.

Interferometer technology takes the light from two or more observing sources targeting the same object and combines it to create an interference pattern, similar to the ripple pattern in a puddle caused by rain. Although the aperture mask blocks 90 percent of the light collected by Keck's 32-foot (10 meter) primary mirror, it creates an interference pattern that preserves the spatial resolution information (ability to see fine detail) normally lost due to atmospheric distortion. A computer analyzes the interference pattern and constructs the image.

"The interferometer technology demonstrated by our aperture mask lets us detect extraordinarily fine detail, and is a first step in projects that will combine light from an array of telescopes to image planets around distant stars," said Dr. Peter Tuthill of Sydney University, Australia, primary author of the Nature paper.

The team used the Near Infrared Camera (NIRC) instrument on Keck, which receives infrared light from celestial objects and can make images of the hottest regions in the dust clouds around young stars. Infrared light is invisible to the human eye, but some types are perceived as heat. The dust cloud around LkHa101 is larger than the NIRC images indicate, because there is a great deal of outlying material that is cooler than what NIRC can see.

This work was funded primarily by the National Science Foundation and NASA, with contributions from the CfA.

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