Nonradial Pulsations
Description
Nonradial stellar pulsations are characterized by their frequency and
three quantum numbers. The radial dependence of the variations is specified
by the radial order n which usually equals the number of nodes
between the center and surface of the star. The angular dependence of the
variations is described by spherical harmonics and is specified by:
the azimuthal order m, where 2 |m| specifies the number of
nodes in longitude, and the nonradial degree l, where
l - |m| specifies the number of nodal lines in planes parallel to
the equator. The azimuthal order may take on the values
m = -l, -l+1,..., l. For rotating stars, modes with negative orders
conventionally propagate in a prograde sense. Some patterns of velocity
variation resulting from nonradial oscillations with various combinations
of l and m are illustrated below.
Velocity Maps of Surface Oscillations. The line-of-sight
component of the surface velocity variations resulting from nonradial
oscillations is illustrated for modes with: a) l=3, m=0, b)
l=10, m=2, c) l=3, m=3, d) l=10, m=0, e)
l=10, m=6, and f) l=10, m=10. Dark areas represent motion
away from the observer; light areas represent motion towards the
observer.
More Illustrations
The pattern of nonradial pulsations may also arise as temperature
variations. For white dwarf variables, it is changes in the temperature
distribution across the stellar surfare that cause variations in the
brightness of the stars. The WET (Whole Earth Telescope) page has
included some very nice
amimations
to illustrate these variations.
____________________________________________
Edward J. Kennelly (kennelly@hao.ucar.edu)
Last modified: Thu May 1 17:41:12 1997