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Stothers, R., 1976: A new interpretation of luminous blue stars. Astrophys. J., 209, 800-815.
A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's (1976) radiative opacities are adopted in stellar models. Unlike earlier opacities, the new opacities exhibit a large "bump" due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot diffuse stellar envelopes (typically those in which L/M > 103 solar units). Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. Thus, the new stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures (which are yet to be observationally confirmed) for O stars, and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than ~20 M☉, beginning at MV = -4.5 and Sp = B1. They alo predict slower surface rotations for O stars compared with B stars; and, in binary systems, slower apsidal motions, closer rotational-revolutional synchronism, and smaller orbital eccentricities. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Radial pulsations of the models have been calculated by employing linearized non-adiabatic theory. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The new models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars. Ultrashort-period variability, observed in many classes of hot luminous stars, may be due, in part, to high radial overtone pulsations (or, possibly, to nonradial pulsational or convective modes).
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