A5090069358- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Geomagnetism and Paleomagnetism Studies
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Fluid Dynamics and Turbulent Flows
- Geology and Paleoclimatology Research
- Oceanographic and Atmospheric Processes
- Astrophysical Phenomena and Observations
- Ocean Waves and Remote Sensing
- Geophysics and Gravity Measurements
- Adaptive optics and wavefront sensing
- Advanced NMR Techniques and Applications
- Ionosphere and magnetosphere dynamics
- Crystallography and Radiation Phenomena
- Gamma-ray bursts and supernovae
- High-pressure geophysics and materials
- Atomic and Subatomic Physics Research
- Cyclone Separators and Fluid Dynamics
- Advanced Chemical Physics Studies
- Tropical and Extratropical Cyclones Research
- Meteorological Phenomena and Simulations
- Cavitation Phenomena in Pumps
- Coastal and Marine Dynamics
University of Leeds
2017-2024
Helmholtz-Zentrum Dresden-Rossendorf
2022
Abastumani Astrophysical Observatory
2022
Brandenburg University of Technology Cottbus-Senftenberg
2022
University of Cambridge
2008-2019
Northwestern University
2012-2014
Tidal friction is thought to be important in determining the long-term spin-orbit evolution of short-period extrasolar planetary systems. Using a simple model orbit-averaged effects tidal friction, we study close-in planets on inclined orbits, due tides. We analyse inclusion stellar magnetic braking by performing phase-plane analysis simplified system equations, including torque. The found important, and its neglect can result very different history. then present results numerical...
We study the fate of internal gravity waves, which are excited by tidal forcing a short-period planet at interface convection and radiation zones, approaching centre solar-type star. what amplitude these wave subject to instabilities. These instabilities lead breaking whenever exceeds critical value. Below this value, reflects perfectly from Wave results in spinning up central regions star, formation layer, acts as an absorbing barrier for ingoing waves. As waves absorbed, star is spun...
We study tidal dissipation in stars with masses the range $0.1-1.6 M_\odot$ throughout their evolution, including turbulent effective viscosity acting on equilibrium tides and inertial waves convection zones, internal gravity radiation zones. consider a of stellar evolutionary models incorporate frequency-dependent based latest simulations. compare flow obtained conventional tide, which is strictly invalid finding that latter typically over-predicts by factor 2-3. Dissipation computed using...
We perform one of the first studies into non-linear evolution tidally excited inertial waves in a uniformly rotating fluid body, exploring simplified model envelope planet (or convective solar-type star) subject to gravitational tidal perturbations an orbiting companion. Our contains perfectly rigid spherical core, which is surrounded by incompressible uniform density fluid. The corresponding linear problem was studied previous papers this work extends regime, at moderate Ekman numbers (the...
We explore the linear stability of astrophysical discs exhibiting vertical shear, which arises when there is a radial variation in temperature or entropy. Such are subject to "vertical-shear instability", recent nonlinear simulations have shown drive hydrodynamic activity MRI-stable regions protoplanetary discs. first revisit locally isothermal using quasi-global reduced model derived by Nelson et al. (2013). This analysis then extended global axisymmetric perturbations cylindrical domain....
We study thermal convection in a rotating fluid order to better understand the properties of zones stars and planets. first derive mixing-length theory for rapidly-rotating convection, arriving at results Stevenson (1979) via simple physical arguments. The predicts as function imposed heat flux rotation rate, independent microscopic diffusivities. In particular, it mean temperature gradient; rms velocity fluctuations; size eddies that dominate transport. test all these predictions with high...
Tidally distorted rotating stars and gaseous planets are subject to a well-known linear fluid instability -- the elliptical instability. It has been proposed that this might drive enough energy dissipation solve long-standing problem of origin tidal in planets. But nonlinear outcome yet be investigated parameter regime interest, resulting turbulent not quantified. We do so by performing three dimensional hydrodynamical simulations small patch tidally deformed planet or star show when...
I present results from the first global hydrodynamical simulations of elliptical instability in a tidally deformed gaseous planet (or star) with free surface. The is potentially important for tidal evolution shortest-period hot Jupiters. model as spin–orbit aligned or anti-aligned, and non-synchronously rotating, deformed, homogeneous fluid body. A companion paper presented an analysis modes instabilities such planet. Here focus on non-linear instability. This observed to produce bursts...
The combination of elliptical deformation streamlines and vorticity can lead to the destabilization any rotating flow via instability. Such a mechanism has been invoked as possible source turbulence in planetary cores subject tidal deformations. saturation instability shown generate composed nonlinearly interacting waves strong columnar vortices with varying respective amplitudes, depending on control parameters geometry. In this Letter, we present suite numerical simulations investigate...
Turbulent convection is thought to act as an effective viscosity ($ν_E$) in damping tidal flows stars and giant planets. However, the efficiency of this mechanism has long been debated, particularly regime fast tides, when frequency ($ω$) exceeds turnover dominant convective eddies ($ω_c$). We present results hydrodynamical simulations study interaction between a small patch zone. These build upon our prior work by simulating more turbulent larger horizontal boxes, here we explore wider...
We revisit the global modes and instabilities of homogeneous rotating ellipsoidal fluid masses, which are simplest models rotationally tidally deformed gaseous planets or stars. The tidal flow in a short-period planet may be unstable to elliptical instability, hydrodynamic instability that can drive evolution. perform (and local WKB) analysis study this using elegant formalism Lebovitz & Lifschitz. survey parameter space with harmonic orders $\ell\leq 5$, for spins purely aligned (prograde)...
The spin axis of a rotationally deformed planet is forced to precess about its orbital angular momentum vector, due the tidal gravity host star, if these directions are misaligned. This induces internal fluid motions inside that subject hydrodynamic instability. We study turbulent damping precessional motions, as result this instability, in simplest local computational model giant (or star), with and without weak magnetic field. Our aim determine outcome importance driving evolution...
Tidal dissipation is responsible for circularizing the orbits and synchronizing spins of solar-type close binary stars, but mechanisms are not fully understood. Previous work has indicated that significant enhancements to theoretically-predicted tidal rates required explain observed circularization periods ($P_\mathrm{circ}$) in various stellar populations, their evolution with age. This was based partly on common belief dominant mechanism stars turbulent viscosity acting equilibrium tides...
PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect characterise extrasolar planets perform asteroseismic monitoring a large number stars. will small (down <2 R_(Earth)) around bright stars (<11 mag), including terrestrial in the habitable zone solar-like With complement radial velocity observations from ground, be characterised for their radius, mass, age with high accuracy (5 %, 10 % an Earth-Sun combination respectively). provide us large-scale...
Stars and planets in close systems are magnetised but the influence of magnetic fields on their tidal responses (and vice versa) dissipation rates has not been well explored. We present exploratory nonlinear magnetohydrodynamical (MHD) simulations tidally-excited inertial waves convective envelopes. These probably provide dominant contribution to several astrophysical settings, including circularisation solar-type binary stars hot Jupiters, orbital migration moons Jupiter Saturn. model...
We investigate whether the elliptical instability is important for tidal dissipation in gaseous planets and stars. In a companion paper, we found that conventional results insufficient because it produces long-lived vortices then quench further instability. Here, study addition of magnetic field prevents those from forming, hence leads to enhanced dissipation. present magnetohydrodynamical simulations evolve local patch rotating planet or star, presence weak field. find fields do indeed...
We formulate a local dynamical model of an eccentric disc in which the dominant motion consists elliptical Keplerian orbits. The is generalization well known shearing sheet, and suitable for both analytical computational studies dynamics discs. It spatially homogeneous horizontal dimensions but has time-dependent geometry that oscillates at orbital frequency. show how certain averages stress tensor determine large-scale evolution shape mass distribution disc. simplest solutions are laminar...
The Kelvin-Helmholtz instability has been proposed as a mechanism to extract energy from magnetohydrodynamic (MHD) kink waves in flux tubes, and drive dissipation of this wave through turbulence. It is therefore potentially important process heating the solar corona. However, it unclear how influenced by oscillatory shear flow associated with an MHD wave. We investigate linear stability discontinuous presence horizontal magnetic field within Cartesian framework that captures essential...
Convection is thought to act as a turbulent viscosity in damping tidal flows and driving spin orbital evolution close convective binary systems. This should be reduced, compared mixing-length predictions, when the forcing (tidal) frequency $|{\omega}_t|$ exceeds turnover ${\omega}_{cv}$ of dominant eddies. However, two contradictory scaling laws have been proposed this issue remains highly disputed. To revisit controversy, we conduct first direct numerical simulations (DNS) convection...
Abstract Differentially rotating stars and planets transport angular momentum (AM) internally due to turbulence at rates that have long been a challenge predict reliably. We develop self-consistent saturation theory, using statistical closure approximation, for hydrodynamic driven by the axisymmetric Goldreich–Schubert–Fricke instability stellar equator with radial differential rotation. This arises when fast thermal diffusion eliminates stabilizing effects of buoyancy forces in system where...
We study the fate of internal gravity waves approaching centre a non-rotating solar-type star, by performing 3D numerical simulations using Boussinesq-type model. These are excited at top radiation zone tidal forcing short-period planet on circular, coplanar orbit. This extends previous work done in 2D Barker & Ogilvie. first derive linear wave solution, which is not exact 3D; however, reflection ingoing from close to perfect for moderate amplitude waves. Waves with sufficient cause...
Eccentric Keplerian discs are believed to be unstable three-dimensional hydrodynamical instabilities driven by the time-dependence of fluid properties around an orbit. These could lead small-scale turbulence, and ultimately modify global disc properties. We use a local model eccentric disc, derived in companion paper, compute nonlinear vertical ("breathing mode") oscillations disc. then analyse their linear stability locally axisymmetric disturbances for any eccentricity gradient using...
Tidal interactions are important in driving spin and orbital evolution planetary stellar binary systems, but the fluid dynamical mechanisms responsible remain incompletely understood. One key mechanism is interaction between tidal flows convection. Turbulent convection thought to act as an effective viscosity damping large-scale flows, there a long-standing controversy over efficiency of this when frequency exceeds turnover dominant convective eddies. This high regime relevant for many...