The r-modes of slowly rotating, stratified neutron stars. Issue 2 (2nd March 2023)

• Record Type: Journal Article
• Authors: Gittins, Fabian; Andersson, Nils
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 2(2023)
• Page Start: 3043
• Page End: 3057
• Publication Date: 2023-03-02
• Subjects: equation of state -- instabilities -- stars: neutron -- stars: oscillations -- stars: rotation; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad672
• Languages: English
• ISSNs: 0035-8711

Abstract

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.