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USING MASKS TO SEE CLEARER

Astronomers using the 10-meter Keck I telescope atop Mauna Kea, Hawaii, were able to improve the telescope's resolution by blocking most of the starlight it collects. Peter G. Tuthill (University of Sydney), John D. Monnier (Harvard-Smithsonian Center for Astrophysics), and William C. Danchi (NASA/Goddard Space Flight Center) put a mask on Keck's 1.4-m secondary mirror that eliminated 90 percent of incoming light. The light from the unblocked areas were combined into a single image using a technique called interferometry to make pictures with four times the resolution of the Hubble SpaceTelescope.

The astronomers used an infrared camera to peer at the young star LkHa 101 that is surrounded by a warm envelope of dust. Tuthill and his colleagues presented images in yesterday's issue of Nature that resolve the dust cloud into a doughnut-shaped disk, clearly showing a central clearing. The disk has a crescent shape because we see it slightly tipped from face-on; the side closer to Earth appears brighter. Their observations also revealed a companion star some 4 billion kilometers from LkHa 101 (not pictured above). These results demonstrate the power of optical interferometry.

Astronomers hope to be able to use the technique with widely separated telescopes, such as the twin Keck reflectors. Tuthill explains, "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."