Lobel, A. ; de Jager, K. ; Nieuwenhuijzen, H.

published in 370 Years of Astronomy in Utrecht, 470, pp. 167 (2013)

Abstract: We discuss the spectral variability of three white (A-type) hypergiants (Ia+) near the region of atmospheric dynamical instability in the upper H-R diagram, called the Yellow Evolutionary Void. The Void represents an obstacle for the fast blueward evolution of the most massive cool hypergiant stars. Optical and near-IR spectra observed between 1993 and 2011 with several high-resolution spectrographs, including the WHT-Utrecht Echelle Spectrograph, Mercator-HERMES, NOT-Sofin, and Keck-HIRES, are compared to investigate the wind-physics and -dynamics of the hypergiants.

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