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H II Regions, Reflection Nebulae and Circumstellar Disks

H-alpha Image of DEM L 106

The reflection nebula N30 B offers a unique opportunity to study the disk around Henize S22, and its relationship to the star. 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. We don't know 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 (Figure 1). So this reflection nebula offers a convenient and unique mirror for us to probe the properties of the star-disk system in a B[e] star. This will help us understand how and where these peculiar stars fit into the evolution of the most massive stars.

CTIO Curtis Schmidt images in red band and H-alpha line. Images courtesy of Charles Danforth (JHU) and You-Hua Chu (U. of Illinois).

Red Image of DEM L 106

Figure 1:Geometry of Viewing Angle for Reflection Nebula N30B in DEM L 106. Illustration courtesy of You-Hua Chu (U. of Illinois) and collaborators.

Members of the Science Team studying N30B in DEM L 106:

You-Hua Chu (U. Illinois)
Rosie Chen (U. Illinois)
Sally Oey (Lowell Observatory)
Charles Danforth (JHU)
Bryan Dunne (U. Illinois)
Robert Gruendl (U. Illinois)
Yaël Nazé (Institut d'Astrophysique et de Géophysique, Belgium)
Sean Points (Northwestern U.)