Granulation in Supergiants

• There are large cells (global long-lived + small short-lived).
• Schwarzschild's scaling arguments were OK, only Sun is not a good reference.
• Better correspondence: stars with more efficient radiation:
  • stars near the "granulation boundary":
  • Cepheids, A-type stars with inverse bisectors (Gray 2008)
• Reason for relatively large cells:
  • Bifurcation of cell sizes
  • Pressure scale height below the surface
  • Sphericity effects

Consequences for RHD Simulations

• Basic mechanism that drives atmospheric flows is no longer certain.
• Our benchmark star, the Sun, is no longer useful. We need new references.