CO band emission from circumstellar material: Tracer for Keplerian rotating disks, molecular outflows, and evolutionary states
CO bands arise from coupled rotation-vibrational transitions within this
diatomic molecule. Their emission can be observed in the near-infrared
spectra of various objects, which possess a high-density circumstellar
environment. And especially the shape of the first CO band-head of the
first-overtone bands is known since long to be an ideal tracer for
Keplerian rotation. However, recent development in stellar wind theories
of rapidly rotating stars indicate that slow but high density winds occur, which
seem to be capable to create outflowing disk-like structures as observed, e.g.,
around B[e] supergiants. After a short introduction into the physics of the
CO bands, I will discuss the suitability of the CO bands as ideal tracer of
the kinematics of the circumstellar material (winds and disks). In addition,
I will discuss the problematics in classifying stars with high-density
circumstellar material and present the first reliable method for an
unambiguous discrimination between a young and an evolved star.
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