| 
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). |
