Open AccessEkman layer damping of r modes revisited
Author(s) -
Glampedakis Kostas,
Andersson Nils
Publication year - 2006
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 - 10.1111/j.1365-2966.2006.10749.x
Subject(s) - physics , neutron star , ekman number , ekman layer , boundary layer , stratification (seeds) , mechanics , instability , ekman transport , classical mechanics , convection , astrophysics , germination , geology , oceanography , upwelling , seed dormancy , botany , dormancy , biology
We investigate the damping of neutron star r modes due to the presence of a viscous boundary (Ekman) layer at the interface between the crust and the core. Our study is motivated by the possibility that the gravitational wave driven instability of the inertial r modes may become active in rapidly spinning neutron stars, for example, in low‐mass X‐ray binaries, and the fact that a viscous Ekman layer at the core–crust interface provides an efficient damping mechanism for these oscillations. We review various approaches to the problem and carry out an analytic calculation of the effects due to the Ekman layer for a rigid crust. Our analytic estimates support previous numerical results, and provide further insight into the intricacies of the problem. We add to previous work by discussing the effect that compressibility and composition stratification have on the boundary‐layer damping. We show that, while stratification is unimportant for the r‐mode problem, composition suppresses the damping rate by about a factor of 2 (depending on the detailed equation of state).