Statistical Properties of Fermionic Molecular Dynamics

Statistical properties of Fermionic Molecular Dynamics are studied. It is shown that, although the centroids of the single--particle wave--packets follow classical trajectories in the case of a harmonic oscillator potential, the equilibrium properties of the system are the quantum mechanical ones. A system of weakly interacting fermions as well as of distinguishable particles is found to be ergodic and the time--averaged occupation probabilities approach the quantum canonical ones of Fermi--Dirac and Boltzmann statistics, respectively.Comment: 16 pages, several postscript figures, uses 'epsfig.sty'. More information is available at http://www.gsi.de/~schnack/fmd.htm

Runaway of Line-Driven Winds Towards Critical and Overloaded solutions

Line-driven winds from hot stars and accretion disks are thought to adopt a unique, critical solution which corresponds to maximum mass loss rate and a particular velocity law. We show that in the presence of negative velocity gradients, radiative-acoustic (Abbott) waves can drive shallow wind solutions towards larger velocities and mass loss rates. Perturbations introduced downstream from the wind critical point lead to convergence towards the critical solution. By contrast, low-lying perturbations cause evolution towards a mass-overloaded solution, developing a broad deceleration region in the wind. Such a wind differs fundamentally from the critical solution. For sufficiently deep-seated perturbations, overloaded solutions become time-dependent and develop shocks and shells.Comment: Latex, 2 postscript figures Astrophysical Journal Letters, in pres

Nuclear Structure based on Correlated Realistic Nucleon-Nucleon Potentials

We present a novel scheme for nuclear structure calculations based on realistic nucleon-nucleon potentials. The essential ingredient is the explicit treatment of the dominant interaction-induced correlations by means of the Unitary Correlation Operator Method (UCOM). Short-range central and tensor correlations are imprinted into simple, uncorrelated many-body states through a state-independent unitary transformation. Applying the unitary transformation to the realistic Hamiltonian leads to a correlated, low-momentum interaction, well suited for all kinds of many-body models, e.g., Hartree-Fock or shell-model. We employ the correlated interaction, supplemented by a phenomenological correction to account for genuine three-body forces, in the framework of variational calculations with antisymmetrised Gaussian trial states (Fermionic Molecular Dynamics). Ground state properties of nuclei up to mass numbers A<~60 are discussed. Binding energies, charge radii, and charge distributions are in good agreement with experimental data. We perform angular momentum projections of the intrinsically deformed variational states to extract rotational spectra.Comment: 32 pages, 15 figure

Clusters, Halos, And S-Factors In Fermionic Molecular Dynamics

In Fermionic Molecular Dynamics antisymmetrized products of Gaussian wave packets are projected on angular momentum, linear momentum, and parity. An appropriately chosen set of these states span the many-body Hilbert space in which the Hamiltonian is diagonalized. The wave packet parameters - position, momentum, width and spin - are obtained by variation under constraints. The great flexibility of this basis allows to describe not only shell-model like states but also exotic states like halos, e.g. the two-proton halo in 17Ne, or cluster states as they appear for example in 12C close to the \alpha-breakup threshold where the Hoyle state is located. Even a fully microscopic calculation of the 3He(\alpha,\gamma)7Be capture reaction is possible and yields an astrophysical S-factor that compares very well with newer data. As representatives of numerous results these cases will be discussed in this contribution, some of them not published so far. The Hamiltonian is based on the realistic Argonne V18 nucleon-nucleon interaction.Comment: Presented at HIAS 2013, 8.-12. April 2013, Canberr

Fermionic Molecular Dynamics

A quantum molecular model for fermions is investigated which works with antisymmetrized many-body states composed of localized single-particle wave packets. The application to the description of atomic nuclei and collisions between them shows that the model is capable to address a rich variety of observed phenomena. Among them are shell effects, cluster structure and intrinsic deformation in ground states of nuclei as well as fusion, incomplete fusion, dissipative binary collisions and multifragmentation in reactions depending on impact parameter and beam energy. Thermodynamic properties studied with long time simulations proof that the model obeys Fermi-Dirac statistics and time averaging is equivalent to ensemble averaging. A first order liquid-gas phase transition is observed at a boiling temperature of $T \approx 5 MeV$ for finite nuclei of mass $16...40$.Comment: 61 pages, several postscript figures, uses 'epsfig.sty'. Report to be published in Prog. Part. Nucl. Phys. 39. More information available at http://www.gsi.de/~schnack/fmd.htm

X-ray photoionized bubble in the wind of Vela X-1 pulsar supergiant companion

Vela X-1 is the archetype of high-mass X-ray binaries, composed of a neutron star and a massive B supergiant. The supergiant is a source of a strong radiatively-driven stellar wind. The neutron star sweeps up this wind, and creates a huge amount of X-rays as a result of energy release during the process of wind accretion. Here we provide detailed NLTE models of the Vela X-1 envelope. We study how the X-rays photoionize the wind and destroy the ions responsible for the wind acceleration. The resulting decrease of the radiative force explains the observed reduction of the wind terminal velocity in a direction to the neutron star. The X-rays create a distinct photoionized region around the neutron star filled with a stagnating flow. The existence of such photoionized bubbles is a general property of high-mass X-ray binaries. We unveiled a new principle governing these complex objects, according to which there is an upper limit to the X-ray luminosity the compact star can have without suspending the wind due to inefficient line drivingComment: accepted for publication in ApJ, 6 pages, 4 figure

The Hoyle state and its relatives

The Hoyle state and other resonances in the continuum above the 3 alpha threshold in 12C are studied in a microscopic cluster model. Whereas the Hoyle state is a very sharp resonance and can be treated reasonably well in bound state approximation, the other higher lying states require a proper treatment of the continuum. The model space consists of an internal region with 3 alpha particles on a triangular grid and an external region consisting of the 8Be ground state and excited (pseudo)-states of 8Be with an additional alpha. The microscopic R-matrix method is used to match the many-body wave function to the asymptotic Coulomb behavior of bound states, Gamow states and scattering states. 8Be-alpha phase shifts are analyzed and resonance properties like radii and transition strengths are investigated.Comment: 7 pages, Talk given at SOTANCP3, 3rd International Workshop on State of the Art in Nuclear Cluster Physics, Yokohama, Japan, May 26-30, 201

The nuclear liquid-gas phase transition within Fermionic Molecular Dynamics

The time evolution of excited nuclei, which are in equilibrium with the surrounding vapour, is investigated. It is shown that the finite nuclear systems undergo a first oder phase transition. The caloric curve is presented for excited Oxygen, Magnesium, Aluminum and Calcium and the critical temperature is estimated for Oxygen.Comment: 8 pages, 3 postscript figures, uses 'epsfig.sty'. Submitted to Phys. Lett. B. More information available at http://www.gsi.de/~schnack/fmd.htm