The r -modes of slowly rotating, stratified neutron stars

Gittins, Fabian; Andersson, Nils

doi:10.1093/mnras/stad672

The r -modes of slowly rotating, stratified neutron stars

Journal Article · Thu Mar 02 00:00:00 EST 2023 · Monthly Notices of the Royal Astronomical Society

DOI:https://doi.org/10.1093/mnras/stad672· OSTI ID:1962881

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ABSTRACT

The only r-modes that exist in a globally barotropic, rotating, Newtonian star are the fundamental l = |m| solutions, where l and m are the indices of the spherical harmonic $$Y_l^m$$ that describe the mode’s angular dependence. This is in stark contrast to a stellar model that is non-barotropic throughout its interior, which hosts all the l ≥ |m| perturbations including radial overtones. In reality, neutron stars are stratified with locally barotropic regions. Therefore, we explore how stratification alters a star’s ability to support r-modes. We consider the globally stratified case and examine the behaviour of the modes as the star gets close to barotropicity. In this limit, we find that all but the fundamental l = |m| perturbations change character and become generic inertial modes. Restricting the analysis to l = |m| perturbations, we develop the r-mode equations in order to consider stellar models that exhibit local barotropicity. Our results for such models show that the r-mode overtones diverge and join the inertial modes. In order to see which r-modes persist and retain their character in realistic neutron stars, these calculations will need to be brought into full general relativity.

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Research Organization:: Univ. of Washington, Seattle, WA (United States)

Sponsoring Organization:: National Science Foundation (NSF); STFC; USDOE; USDOE Office of Science (SC)

Grant/Contract Number:: FG02-00ER41132

OSTI ID:: 1962881

Alternate ID(s):: OSTI ID: 2418911

Journal Information:: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 2 Vol. 521; ISSN 0035-8711

Publisher:: Oxford University PressCopyright Statement

Country of Publication:: United Kingdom

Language:: English

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