The Size, Structure, and Variability of Late-Type Stars Measured ...

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Figure 3.10: “Standard” Bowen Model Density vs. Radius Where the Atmosphere is Driven
With a Piston Velocity Amplitude of 0 (static), 1, 2, 4, and 6 km/s (reproduction of Figure 1
from Bowen (1988) [15])
model with a velocity discontinuity between 25 and 30 km/s. Unlike the Bowen model, there
is no temperature increase associated with the shocks. Shocks produce conditions very much
out of thermal equilibrium, and the interaction of these regions with 11 µm radiation will be
considered separately, later. Like in the Bowen model, the density of the driven atmosphere
becomes much greater than the initial hydrostatic model outside the photosphere. However,
the Bessell model predicts a departure from hydrostatic density stratification for densities
lower than about 10 −10 g/cm 3 (as opposed to 10 −13.5 g/cm 3 predicted by Bowen). The
monochromatic radii (radius at which τ λ = 1) predicited by the Bessell model at maximum
and minimum as a function of wavelength are shown in Figure 3.11 which is a reproduction
of Figure 8 from Bessell et al. (1989) [9]. The continuum bands have monochromatic radii
very near the “parent” radius at maximum, and 30% larger at minimum. The atmospheric