Mode identification in pulsating stars is challenging because the modes that are predicted to be excited and visible are not all observed, and because sometimes modes that are not expected are observed. In principle, finding rotationally split multiplets can assist mode identification, but often not all of the components are observed, and rapid and differential rotation complicates the interpretation. Other challenges include distinguishing pulsations from star spots, identifying frequencies that are linear combinations of other (perhaps invisible) intrinsic modes, mode coupling, and variable mode amplitudes and frequencies. For brighter stars and modes with high signal-to-noise, spectroscopic and photometric techniques have had some success in separating l = 0, 1 and 2 modes and in identifying the azimuthal orders. The nearly equal frequency (period) spacings for high order p- (g-) mode pulsators expected from asymptotic theory can guide mode identifications. We review theoretical expectations for pulsation mode driving and damping, focusing on main-sequence variables, and compare with observational examples. Insights into mode selection and amplitudes may be possible by examining the energy partition between various processes in these stars and their contributions to driving and damping of the oscillation modes. Future progress will require two- and three-dimensional stellar models and nonadiabatic, nonlinear, and nonradial pulsation modeling.
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