Open AccessMagnetic perturbations to the acoustic modes of roAp stars
Author(s) -
Cunha Margarida S.,
Gough Douglas
Publication year - 2000
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2000.03896.x
Subject(s) - physics , eigenfunction , stars , magnetic field , harmonics , excited state , azimuth , normal mode , mode (computer interface) , computational physics , spherical harmonics , astrophysics , helioseismology , classical mechanics , acoustics , atomic physics , eigenvalues and eigenvectors , optics , quantum mechanics , voltage , computer science , vibration , operating system
We study the effect of a large‐scale surface magnetic field on the non‐radial acoustic modes of roAp stars. Special attention is given to the use of a variational principle which is used for determining the shifts in the frequencies with relative ease, enabling us to avoid having to calculate the perturbed eigenfunctions. With knowledge of the frequency shifts we then estimate the eigenfunctions in a simpler, albeit approximate way. The results indicate frequency shifts of the order of few μHz, which depend on the order, degree and azimuthal order of the mode. The loss of energy through Alfvén waves is also estimated from the imaginary parts of the frequency shifts. The results indicate that the loss is particularly high near specific frequencies. This might indicate the presence of a selection effect, which could make some modes more likely to be excited than others. However, our results do not explain why the modes observed appear always to be aligned with the axis of the magnetic field. Finally, the estimated perturbed eigenfunctions contain strong components of spherical harmonics that differ from those of the original unperturbed modes.