Showing papers by "Garrelt Mellema published in 1994"

From the Owl to the Eskimo: the Radiation-Gasdynamics of Planetary Nebulae IV

Abstract: We present the results of two-dimensional radiation-gasdynamic simulations of aspherical Planetary Nebulae (PNe) evolution. These simulations were constructed using the Generalized Interacting Stellar Winds (GISW) scenario of Balick (1987) where a fast, tenuous wind from the central star expands into a toroidal, slow, dense wind. We demonstrate that the GISW model can produce a wide range of aspherical flow patterns. We have constructed self-consistent synthetic observations of the models from forbidden line emissivities used in the energy loss term. We present integrated intensity and long-slit spectrum, (Position-Velocity) maps of the models projected at different angles on the sky. These synthetic observations are compared with real intensity and Position-Velocity maps of PNe. We find that there is a very good match between the synthetic and real observations in terms of morphologies, kinematics, and physical conditions. From the results of these simulations we conclude that the GISW scenario can account for most, if not all, PNe morphologies, thus confirming Balick's (1987) conjecture.

General Relativistic Hydrodynamics with a Roe solver

Abstract: We present a numerical method to solve the equations of general relativistic hydrodynamics in a given external gravitational field. The method is based on a generalization of Roe's approximate Riemann solver for the non relativistic Euler equations in Cartesian coordinates. The new method is applied to a set of standard test problems for general relativistic hydrodynamics, and is shown to perform well in comparison to existing numerical schemes. In contrast to existing explicit methods the present method can cope with strong relativistic shocks. By-products are: the characteristic form of the general relativistic Euler equations, a numerical method for special relativity that can deal with strong discontinuities, a numerical scheme for the integration of the Euler equations in an arbitrary coordinate system, possibly under the influence of (external) gravity, and a novel method to incorporate source terms in numerical schemes.

Special relativistic jet collimation by inertial confinement

Abstract: We present an explicit numerical method to handle problems in special relativistic hydrodynamics. This method is a special relativistic extension of a Roe solver method for nonrelativistic flow. The method is used to simulate the collimation of an initially spherical outflow by a thickened disk (i.e. collimation by inertial confinement). Previous nonrelativistic results indicated that this is a mechanism to form jets. Here we show that this mechanism can also generate relativistic jets. The highest Lorentz factor achieved in these simulations is 15. We discuss the differences between the relativistic and nonrelativistic flow

The gasdynamic evolution of spherical planetary nebulae. Radiation-gasdynamics of PNe III.

Abstract: Using a radiation-gasdynamics code the evolution of spherical planetary nebulae is followed, while taking into account the evolution of central star and the fast wind. These models show the importance of ionization fronts for the structure of planetary nebulae, especially for the so called multiple shell nebulae (MSPNe). It is shown that the outer shell is formed by the ionization front while the inner shell is swept-up by the fast wind. These models explain the emission profiles of the outer shells as well as their various kinematic properties. Because they are shaped by the ionization front these outer shells only give indirect information on the AGB mass loss history. The models indicate that typical MSPN structures point to mass loss variations during the AGB phase. The ionization also leads to a stalling of the expansion of the nebula, leading to nebulae with expansion ages lower than their evolutionary age. Values for ionized mass and Zanstra temperatures are derived from the models.

Numerical models and our understanding of aspherical Planetary Nebulae

Abstract: The status of numerical hydrodynamical models for Planetary Nebulae is reviewed. Since all of the numerical work is based on the interacting winds model, we start with a description of this model and give an overview of the early analytical and numerical models. Subsequently we address the numerical models which include radiation effects, first of all the ones which neglect any effects of stellar evolution. These `constant environment' models are shown to closely match typical observed nebulae, both in images and kinematic data. This shows that the basic generalized interacting winds model gives a good description of the situation in aspherical PNe. Next we discuss models that do include the effects of stellar and fast wind evolution. This introduces several new effects, the most important of which are the formation of a surrounding attached envelope, and the modification of the expansion of the nebula, which helps in creating aspherical PNe very early on in their evolution. The ionization of the slow wind also leads to a gradual smoothing out of its aspherical character, working against aspherical PNe forming in later stages. Finally we discuss some applications of the model to nebular problems.

Numerical models and our understanding of aspherical Planetary Nebulae

Abstract: The status of numerical hydrodynamical models for Planetary Nebulae is reviewed Since all of the numerical work is based on the interacting winds model, we start with a description of this model and give an overview of the early analytical and numerical models Subsequently we address the numerical models which include radiation effects, first of all the ones which neglect any effects of stellar evolution These `constant environment' models are shown to closely match typical observed nebulae, both in images and kinematic data This shows that the basic generalized interacting winds model gives a good description of the situation in aspherical PNe Next we discuss models that do include the effects of stellar and fast wind evolution This introduces several new effects, the most important of which are the formation of a surrounding attached envelope, and the modification of the expansion of the nebula, which helps in creating aspherical PNe very early on in their evolution The ionization of the slow wind also leads to a gradual smoothing out of its aspherical character, working against aspherical PNe forming in later stages Finally we discuss some applications of the model to nebular problems

General Relativistic Hydrodynamics with a Roe solver

Abstract: We present a numerical method to solve the equations of general relativistic hydrodynamics in a given external gravitational field. The method is based on a generalization of Roe's approximate Riemann solver for the non relativistic Euler equations in Cartesian coordinates. The new method is applied to a set of standard test problems for general relativistic hydrodynamics, and is shown to perform well in comparison to existing numerical schemes. In contrast to existing explicit methods the present method can cope with strong relativistic shocks. By-products are: the characteristic form of the general relativistic Euler equations, a numerical method for special relativity that can deal with strong discontinuities, a numerical scheme for the integration of the Euler equations in an arbitrary coordinate system, possibly under the influence of (external) gravity, and a novel method to incorporate source terms in numerical schemes.