Stellar winds and circumstellar disks of massive stars

Hot massive stars are known to possess radiatively driven winds. When the stars cool during their course of evolution, these winds stop because the stars are too cool to drive a wind radiatively. Nevertheless, especially during the cool phases of stellar evolution, e.g., during the red supergiant (RSG) phase, the stars eject a lot of material in form of rings of shells. The mechanism responsible for the mass ejection is not well known, but surface instabilities caused by pulsations seems to be promising in driving large mass ejections in combination with dust driving of the released material. Due to the cool effective temperatures of the RSGs, dust and molecules can relatively easily condensate in this high-density circumstellar material. Hence, the ejecta can be detected via imaging especially in the infrared spectral region. These images usually show beautiful dust shells and rings around these stars.

Surprisingly, not only the cool RSGs show dusty rings or shells of ejected material, but also the much hotter luminous blue variables (LBVs) and, even more surprisingly, the B[e] supergiants are surrounded by huge amounts of cool molecular and dusty material. In the case of the B[e] supergiants it is even assumed that they form extended circumstellar rings or disks. And since B[e] supergiants are eligible to maintain strong line-driven winds, it is speculated that these disk or disk-like structures are formed by some non-spherically symmetric mass loss. Such non-spherical mass loss could be linked to the (rapid) rotation of the stars. Rapid rotation seems also to act in shaping the asymmetric so-called LBV nebulae. It is thus important to understand the influence of (rapid) rotation on the shaping of the winds of hot, luminous stars.

Our studies concentrate on the structure and kinematics of both the winds and disks for stars in different evolved stages.

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Last modified 11.2.2011