The Granulation Boundary in the H-R Diagram

A granulation boundary in the H-R diagram is found. The boundary runs smoothly from spectral type G1 Ib to near F0 on the main sequence. On the cool side of the boundary, the spectral line bisectors are of the classical type associated with granulation. On the hot side the bisectors show a reversed slope and curvature indicative of some other type of photospheric velocity field, possibly having velocities substantially larger than typical granulation velocities. 28 refs.