Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonlinearity of nonradial modes in evolved stars   We show that in evolved stars, even at relatively low surface amplitudes,
nonradial modes become strongly nonlinear in the hydrogen shell source, where
the Brunt-Vaisala frequency has its absolute maximum. The measure of
nonlinearity is the product of horizontal displacement times the radial
wavenumber. It becomes large already in evolved delta-Scuti stars. This
nonlinearity presents a major problem for interpretations of amplitude
modulation in RR Lyrae stars in terms of nonradial mode excitation.

16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat