scholarly journals Infrared variability due to magnetic pressure-driven jets, dust ejection and quasi-puffed-up inner rims

2020 ◽  
Vol 493 (3) ◽  
pp. 4022-4038 ◽  
Author(s):  
Kurt Liffman ◽  
Geoffrey Bryan ◽  
Mark Hutchison ◽  
Sarah T Maddison
Keyword(s):  
Accretion Rate ◽  
Jet Flow ◽  
Flow Speed ◽  
Magnetic Pressure ◽  
Scale Height ◽  
Time Dependent ◽  
Gas Flows ◽  
Centrifugal Acceleration ◽  
The Face ◽  
Disc Region

ABSTRACT The interaction between a YSO stellar magnetic field and its protostellar disc can result in stellar accretional flows and outflows from the inner disc rim. Gas flows with a velocity component perpendicular to disc mid-plane subject particles to centrifugal acceleration away from the protostar, resulting in particles being catapulted across the face of the disc. The ejected material can produce a ‘dust fan’, which may be dense enough to mimic the appearance of a ‘puffed-up’ inner disc rim. We derive analytical equations for the time-dependent disc toroidal field, the disc magnetic twist, the size of the stable toroidal disc region, the jet speed, and the disc region of maximal jet flow speed. We show how the observed infrared variability of the pre-transition disc system LRLL 31 can be modelled by a dust ejecta fan from the inner-most regions of the disc whose height is partially dependent on the jet flow speed. The greater the jet flow speed, the higher is the potential dust fan scale height. An increase in mass accretion on to the star tends to increase the height and optical depth of the dust ejection fan, increasing the amount of 1–8 µm radiation. The subsequent shadow reduces the amount of light falling on the outer disc and decreases the 8–40 µm radiation. A decrease in the accretion rate reverses this scenario, thereby producing the observed ‘see-saw’ infrared variability.

Dynamic Response of Sandwich Anisotropic Flat Panels to Explosive Pressure Pulses

2001 ◽  
Author(s):  
Terry Hause ◽  
Liviu Librescu
Keyword(s):  
Dynamic Response ◽  
Detailed Analysis ◽  
Fiber Orientation ◽  
Sandwich Structures ◽  
Sandwich Panels ◽  
Core Layer ◽  
Time Dependent ◽  
Pressure Pulses ◽  
The Face ◽  
Advanced Model

Abstract This paper addresses the problem of the dynamic response in bending of flat sandwich panels exposed to time-dependent external pulses. The study is carried out in the context of an advanced model of sandwich structures that is characterized by anisotropic laminated face sheets and an orthotropic core layer. A detailed analysis of the influence of a large number of parameters associated with the particular type of pressure pulses, panel geometry, fiber orientation in the face sheets and, presence of tensile uni/biaxial edge loads is accomplished, and pertinent conclusions are outlined.

scholarly journals Growth Rate of White Dwarf Mass in Binaries

1989 ◽  
Vol 114 ◽  
pp. 507-510
Author(s):  
Mariko Kato ◽  
Hideyuki Saio ◽  
Izumi Hachisu
Keyword(s):  
Growth Rate ◽  
Steady State ◽  
Star Formation ◽  
Neutron Star ◽  
Mass Loss ◽  
White Dwarf ◽  
Accretion Rate ◽  
Time Dependent ◽  
Type I ◽  
Wide Range

AbstractThe growth rate of a white dwarf which accretes hydrogen-rich or helium matter is studied. If the accretion rate is relatively small, unstable shell flash occurs and during which the envelope mass is lost. We have followed the evolutions of shell flashes by steady state approach with wind mass loss solutions to determined the mass lost from the system for wide range of binary parameters. The time-dependent models are also calculated in some cases. The mass loss due to the Roche lobe overflow are taken into account. This results seriously affects the existing scenarios on the origin of the type I supernova or on the neutron star formation induced by accretion.

scholarly journals Dynamical Effects in Solar Photospheric Flux Tubes

1996 ◽  
Vol 154 ◽  
pp. 155-158
Author(s):  
S.S. Hasan
Keyword(s):  
Flux Tube ◽  
Ambient Medium ◽  
Resonant Interaction ◽  
Scale Height ◽  
Mhd Equations ◽  
Time Dependent ◽  
Radiative Transport ◽  
Local Pressure ◽  
Flux Tubes ◽  
Pressure Scale

AbstractThe interaction of an intense flux tube, extending vertically through the photosphere, with p-modes in the ambient medium is modelled by solving the time dependent MHD equations in the thin flux tube approximation. It is found that a resonant interaction can occur, which leads to the excitation of flux tube oscillations with large amplitudes. The resonance is not as sharp as in the case of an unstratified atmosphere, but is broadened by a factor proportional to H−2, where H is the local pressure scale height. In addition, the inclusion of radiative transport leads to a decrease in the amplitude of the oscillations, but does not qualitatively change the nature of the interaction.

scholarly journals Hydrodynamics of Accretion Columns

1987 ◽  
Vol 93 ◽  
pp. 591-594
Author(s):  
H. Herold ◽  
K. Wolf ◽  
H. Ruder
Keyword(s):  
Accretion Rate ◽  
Radiation Transport ◽  
Critical Value ◽  
Stationary Solutions ◽  
Time Dependent ◽  
Physical Parameters ◽  
High Luminosity ◽  
Accretion Flows ◽  
Accretion Rates ◽  
Parameter Ranges

AbstractA detailed understanding of how the infalling matter in accretion columns is decelerated is essential for the calculation of the emitted radiation. On neutron stars, the deceleration takes place mainly by the interaction of the plasma with radiation, at least for the high-luminosity sources. We report on our two-dimensional calculations of the hydrodynamic flow in such accretion columns. The radiation transport is treated in the diffusion approximation, and we are looking for a stationary solution for the velocity field. The dependence of the results on physical parameters, especially on the accretion rate is discussed. Due to the non-linearity of the problem it turns out that only in certain parameter ranges stationary solutions seem to exist. For accretion rates higher than a critical value there are no stationary accretion flows. This leads us to the conclusion that a time-dependent picture for the accretion is unavoidable.

scholarly journals Accretion of Protobinary and Evolution of the Mass Ratio

2004 ◽  
Vol 191 ◽  
pp. 163-167
Author(s):  
Tomoyuki Hanawa ◽  
Yasuhiro Ochi ◽  
Kanako Sugimoto
Keyword(s):  
Angular Momentum ◽  
Surface Density ◽  
Accretion Rate ◽  
Orbital Plane ◽  
Gas Flows ◽  
Lagrangian Point ◽  
Mass Ratio ◽  
Fall Velocity ◽  
Rotation Periods ◽  
The Masses

AbstractWe have reexamined accretion in a protobinary system with two dimensional numerical simulations. We consider protostars which rotate around the center of the mass with circular orbits. The accreting gas is assumed to flow in the orbital plane. It is injected from a circle whose radius is 5 times larger than the orbital separation of the binary. The injected gas has constant surface density, in fall velocity, and specific angular momentum. The accretion depends on the specific angular momentum of the injected gas, jinf. When jinf is small, the binary accretes the gas mainly through two channels: one through the Lagrangian point L2 and the other through L3. When jinf is large, the binary accretes the gas only through the L2 point. The primary accretes more than the secondary in both cases, although the L2 point is closer to the secondary. After flowing through the L2 point, the gas flows half around the secondary and through the L1 point to the primary. Only a small amount of gas flows back to the secondary and the rest forms a circumstellar ring around the primary. The accretion decreases the mass ratio, q = M2/M1, where M1 and M2 denote the masses of the primary and secondary, respectively. The accretion rate increases with time. When jinf is large, it is negligibly small in the first few rotation periods.

Sign in / Sign up

Export Citation Format

Share Document