R.H.M. Voors

Dust in LBV Nebulae

The upper part of the HR diagram is populated by massive, luminous stars that show strong stellar winds. These stellar winds have a profound effect on the evolution of the most massive stars, e.g. they lead to the formation of He-rich Wolf-Rayet (WR) stars. It was shown by Humphreys & Davidson (1979) that no red supergiants (RSG) exist with luminosity above Mbol ≈ -9.7, while there are many blue supergiants with luminosities that exceed this limit. This lack of luminous RSG can be explained if very massive stars go through a short-lived phase of extensive post-main-sequence mass loss, during which a significant fraction of the H-rich envelope is removed. The Luminous Blue Variables (LBVs) may represent this short-lived phase of very high mass loss. It has been suggested that a very brief (~ 103 yrs) phase as yellow or red supergiant precedes the LBV phase (Stothers & Chin 1996). For recent reviews see Luminous Blue Variables: massive stars in transition, eds. A. Nota & H.J.G.L.M. Lamers.

ISO-SWS spectroscopy of B[e] stars

We present ISO-SWS spectra of B[e] stars. We find a wide diversity of spectral characteristics of B[e] stars, suggesting different origins for the circumstellar matter. Most B[e] supergiants show hot dust with weak amorphous silicate emission. MWC 300 has a warm dust shell with strong crystalline silicate emission; its evolutionary status is unclear.