April 2015
Benoit Neichel
RCW 41:
Dissecting a Very Young Cluster
with Adaptive Optics
High-resolution observations of a Galactic star-forming region
with the Gemini Multi-conjugate adaptive optics System (GeMS),
in union with the Gemini South Adaptive Optics Imager (GSAOI),
have shed new light on how star-forming regions, and the young
stellar objects within them, evolve.
Figure 1.
The different
mechanisms that may
trigger the formation
of a new generation
of stars at the edges of
an ionized (HII) region
(from Deharveng
et al., 2010).
All stars are born from an original collapsing cloud of gas and dust. When the core of one
of these molecular clouds becomes unstable, it collapses and forms protostars. When the
protostars are massive, they achieve temp eratures hot enough to ionize the surrounding
gas (mostly hydrogen) causing it to glow; we call this glowing stellar nursery an emission
nebula or HII (H+) region.
Stellar Nurseries
Massive stars form HII regions that expand in the surrounding medium at supersonic
speeds. Once a sphere of ionized gas is far from the newborn stars, the outer boundary
(the ionization front) slows to subsonic speeds. Continued expansion of material ejected
from the nebula builds pressure behind the front, before it breaks through as a shock. This
second wave of expansion at the edges of the HII region can create a layer of cold neutral
material, which accumulates between the ionized and the shock fronts. This layer may
become unstable and form a new generation of stars through different physical mechanisms. Those mechanisms are summarized in Figure 1. These include small- and largescale instabilities (denoted as 1 and 2, respectively; also called “collect and collapse”); interaction with a pre-existing turbulent media (3; leading to the formation of pillars); and
interaction with pre-existing clumps (4).
16
GeminiFocus
2015 Year in Review
January 2016