Waves in Thin Oceans on Oblate Neutron Stars

Abstract

Waves in thin fluid layers are important in various stellar and planetary problems. Due to rapid rotation such systems will become oblate, with a latitudinal variation in the gravitational acceleration across the surface of the object. In the case of accreting neutron stars, rapid rotation could lead to a polar radius smaller than the equatorial radius by a factor $\sim 0.8$. We investigate how the oblateness and a changing gravitational acceleration affect different hydrodynamic modes that exist in such fluid layers through analytic approximations and numerical calculations. The wave vectors of $g$-modes and Yanai modes increase for more oblate systems compared to spherical counterparts, although the impact of variations in the changing gravitational acceleration is effectively negligible. We find that for increased oblateness, Kelvin modes show less equatorial confinement and little change in their wave vector. For $r$-modes, we find that for more oblate systems the wave vector decreases. The exact manner of these changes for the $r$-modes depends on the model for the gravitational acceleration across the surface.

arXiv comment10 pages, 8 figures Accepted for publication in MNRAS

References in corpus (19)

• The ATNF Pulsar Catalogue
• The ATNF Pulsar Catalogue
• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Detecting gravitational wave emission from the known accreting neutron stars
• Thermonuclear burst oscillations
• R-Modes on Rapidly Rotating, Relativistic Stars: I. Do Type-I Bursts Excite Modes in the Neutron-Star Ocean?
• Universality of the Acceleration Due to Gravity on the Surface of a Rapidly Rotating Neutron Star
• Magnetohydrodynamic Shallow Water Waves: Linear Analysis
• Surface Modes on Bursting Neutron Stars and X-ray Burst Oscillations
• Implications of burst oscillations from the slowly rotating accreting pulsar IGR 17480-2446 in the globular cluster Terzan 5
• Non-adiabatic tidal forcing of a massive, uniformly rotating star III: Asymptotic treatment for low frequencies in the inertial regime
• A uniform search for thermonuclear burst oscillations in the RXTE legacy dataset
• On parametrised cold dense matter equation of state inference
• The accretion rate dependence of burst oscillation amplitude
• R-Modes on Rapidly Rotating, Relativistic Stars : II. Blackbody Emission
• Evolution of the bursting-layer wave during a Type 1 X-ray burst
• Relativistic ocean $r$-modes during type-I X-ray bursts
• Burning in the tail: implications for a burst oscillation model
• The traditional approximation in general relativity

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• Multi-messenger Emission from Tidal Waves in Neutron Star Oceans
• Modelling Neutron-Star Ocean Dynamics
• Surface gravity wave on a neutron star ocean trapped around a magnetic pole