Wednesday, January 4, 2012

Dusty planetesimal ring orbiting star HR 4796 A

This image of a circumstellar dust ring was recently acquired by C. Thalmann and colleagues at the 8 meter Subaru telescope that the Japanese operate on the summit of mount Mauna Kea in Hawaii. Although the dust ring is nearly circular, the line-of-sight to the ring is oblique which makes the ring appear elongated. To reveal the faint ring, the astronomers must subtract a model image of the very bright central star, but imperfections in the star-subtraction results in the radial residuals seen in the image. Nonetheless the dust ring is still quite prominent despite those residuals, and its radius is about 80 AU. This dust is thought to be the result of collisions occurring among unseen planetesimals also orbiting within the ring. These planetesimals probably resemble the comets that inhabit our Kuiper Belt, which is the Sun's outermost debris belt that is of radius 45 AU. Another interesting feature of this image is that the dust ring's center is offset slightly from the star. Although the origin of this offset is uncertain, an unseen extra-solar planet is implicated, because its gravitational influence can displace the ring's center. But if there is an exoplanet here, it is too faint to be seen or is obscured by the residual starlight. For more information about this circumstellar dust ring, see this press release.

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