J.D. Landstreet: Observing Atmospheric Convection in Stars (Review, Tue, Aug. 22)

This review talk opened Session B of the Convection Symposium: “Observational Probes of Convection”. It gave an overview of the classical ways to detect convection in observations.

Convection reaches the photosphere in most stars of Teff 10000), the situation is confusing (see Lyubimkov et al. 2004 and Przybilla et al. 2006).

Bisector curvature (line profile asymmetry) is another way to detect convection. Gray and Nagel (1989) showed that bisectors are reversed for cool (K) vs. hotter stars (F), with the reversion taking place at about G0. A stars have reversed bisectors, late B stars have no curvature at all.

The use of 3D models is limited – if one disagrees with observation, testing changes is time consuming. On the other hand, MLT and other convection models can be used for testing.

Conclusions:

• Stellar atmosphere velocity fields are clearly detectable in the spectrum.
• The behaviour over the HR diagram is varied, the largest velocities are found in supergiants
• Modelling is making progress at connecting convection theory with observations.