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THE INTERPLAY OF STARLIGHT, GAS, AND DUST IN THE LARGE MAGELLANIC CLOUD

Complex interactions of starlight with interstellar gas and dust in a nearby galaxy are revealed in a new image obtained by NASA's Hubble Space Telescope and presented by the Hubble Heritage team.

Hubble's Wide Field Planetary Camera 2 (WFPC2) was positioned on a small region within a gas cloud, or nebula, called DEM L 106. It belongs to the Large Magellanic Cloud, a galaxy lying 160,000 light-years from our own Milky Way galaxy. DEM L 106 appears in this image as the faint, glowing hydrogen gas that covers most of the picture. This nebula was originally cataloged in the 1970's by astronomers R. Davies, K. Elliot, and J. Meaburn, who created the "DEM" catalogs of both the Large and Small Magellanic Clouds.

The smaller and much brighter gas cloud near the top of the image, called N30B, was discovered in the 1950's by astronomer K. Henize, who later became a NASA astronaut. The N30B nebula surrounds a group of hot, blue stars that have recently formed through gravitational contraction of the gas. The ultraviolet radiation streaming out from these blue stars strips electrons off of the hydrogen atoms in the surrounding gas, causing the gas to glow through a process of fluorescence.

The very bright star near the upper left corner of the picture is cataloged as Henize S22; it is a very hot and luminous supergiant star, lying only 25 light-years from the N30B nebula. It is a rare and peculiar type of blue star that is believed to be surrounded by a dense, dusty disk. This disk reddens the light from the star, just as the dusty Earth atmosphere reddens sunlight at sunset. As viewed from N30B, S22 would appear some 250 times as bright as the planet Venus does in Earth's sky. This bright starlight illuminates interstellar dust particles in N30B, producing a faint glow around it, called a reflection nebula, that somewhat resembles the numeral 8 turned on its side. The band of gas across the bottom of the image is part of the shell wall of a giant superbubble created by the stellar wind of S22. The shroud of gas surrounding N30B also shows a bow shock from the S22 wind.

Lowell Observatory astronomer M.S. Oey and University of Illinois astronomer Y.-H. Chu are members of a science team studying DEM L 106. Along with their collaborators, Oey and Chu have made a clever use of the reflection nebula around N30B. By obtaining spectroscopic observations at various points across the nebula, they can study the spectrum of S22 from different angles. Remarkably, they have found that the star's spectrum changes with viewing angle, confirming that the star is surrounded by a flattened disk of gas, that is probably expelled from its equator. (See supplemental page for more information.)

Archived Hubble images of DEM L 106 taken in 1998 were combined with data taken by the Hubble Heritage Team in late 2001. The final image shows emission in hydrogen and ionized sulfur, as well as stellar colors at blue, visual and infrared wavelengths.

Credits: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: M.S. Oey (Lowell Observatory) and Y.-H. Chu (U. of Illinois)