Low T/|W| dynamical instability in differentially rotating stars: Diagnosis with canonical angular momentum

Saijo, Motoyuki; Yoshida, Shin'ichirou

Low T/|W| dynamical instability in differentially rotating stars: Diagnosis with canonical angular momentum

Authors

Description

We study the nature of non-axisymmetric dynamical instabilities in differentially rotating stars with both linear eigenmode analysis and hydrodynamic simulations in Newtonian gravity. We especially investigate the following three types of instability; the one-armed spiral instability, the low T/|W| bar instability, and the high T/|W| bar instability, where T is the rotational kinetic energy and W is the gravitational potential energy. The nature of the dynamical instabilities is clarified by using a canonical angular momentum as a diagnostic. We find that the one-armed spiral and the low T/|W| bar instabilities occur around the corotation radius, and they grow through the inflow of canonical angular momentum around the corotation radius. The result is a clear contrast to that of a classical dynamical bar instability in high T/|W|. We also discuss the feature of gravitational waves generated from these three types of instability.
v1: 15 pages with 13 figures, mn2e.cls. Submitted to the Monthly Notices of the Royal Astronomical Society; v2: 16 pages with 17 figures, mn2e.cls. Monthly Notices of the Royal Astronomical Society (2006) in press