Reflections of a Supergiant Wind

The Astronomy Department is pleased to announce that the December release from the Hubble Heritage Project features images and science by Illinois astronomers You-Hua Chu, Rosie Chen, Bryan Dunne, and Robert Gruendl, Illinois alumnus Sean Points, and collaborators Sally Oey, Charles Danforth, and Yaël Nazé. Narrow-band Hubble Space Telescope WFPC2 images reveal a bow-shock-like halo around the HII region N30B toward the B[e] supergiant Henize S22 located within the larger DEM L 106 nebula in the Large Magellanic Cloud.

Henize S22 belongs to a peculiar class of stars called B[e] stars: they have the spectral type of ordinary B stars, which are blue, hot (about 25,000 K for S22) and massive (about 12 solar masses for S22). In addition, they also show emission from warm, dense gas that most likely surrounds the star in a disk configuration. It is unknown whether the disk is formed of accreted material or excreted material. Normally, B stars have fast winds, and these are still associated with the polar regions of B[e] stars, but are suppressed by the disk in the equatorial regions, where a slow, dense wind is seen instead.

The disks of B[e] stars have never been directly imaged against the high luminosity of the parent stars. However, the reflection nebula N30 B is positioned so that different parts of the nebula "see" the star-disk system from different angles. So this reflection nebula offers a convenient and unique mirror to probe the properties of the star-disk system in a B[e] star. This will enhance our understanding of how and where these peculiar stars fit into the evolution of the most massive stars.

The full paper will be presented in the April 2003 issue of the Astronomical Journal. The preprint is currently available at the arXiv.org e-Print archive.