20 research outputs found
Magnetized Iron Atmospheres for Neutron Stars
Using a Hartree-Fock formalism, we estimate energy levels and photon cross
sections for atomic iron in magnetic fields B ~ 10^13 G. Computing ionization
equilibrium and normal mode opacities with these data, we construct LTE neutron
star model atmospheres at 5.5 < Log(T_eff) < 6.5 and compute emergent spectra.
We examine the dependence of the emergent spectra on T_eff and B. We also show
the spectral variation with the angle between the magnetic field and the
atmosphere normal and describe the significant limb darkening in the X-ray
band. These results are compared with recent detailed computations of neutron
star H model atmospheres in high fields and with low field Fe and H model
atmospheres constructed from detailed opacities. The large spectral differences
for different surface compositions may be discernible with present X-ray data;
we also note improvements needed to allow comparison of Fe models with high
quality spectra.Comment: 18 pages with 5 eps figures, accepted for publication in ApJ Replaced
due to clerical error only: one more author, no new conten
Equation of state of a strongly magnetized hydrogen plasma
The influence of a constant uniform magnetic field on the thermodynamic
properties of a partially ionized hydrogen plasma is studied. Using the method
of Green' s function various interaction contributions to the thermodynamic
functions are calculated. The equation of state of a quantum magnetized plasma
is presented within the framework of a low density expansion up to the order
e^4 n^2 and, additionally, including ladder type contributions via the bound
states in the case of strong magnetic fields (2.35*10^{5} T << B << 2.35*10^{9}
T). We show that for high densities (n=10^{27-30} m^{-3}) and temperatures
T=10^5 - 10^6 K typical for the surface of neutron stars nonideality effects
as, e.g., Debye screening must be taken into account.Comment: 12 pages, 2 Postscript figures. uses revtex, to appear in Phys. Rev.
Hydrogen Molecules In Superstrong Magnetic Field: II. Excitation Levels
We study the energy levels of H molecules in a superstrong magnetic field
(B\go 10^{12} G), typically found on the surfaces of neutron stars. The
interatomic interaction potentials are calculated by a Hartree-Fock method with
multi-configurations assuming electrons are in the ground Landau state. Both
the aligned configurations and arbitrary orientations of the molecular axis
with respect to the magnetic field axis are considered. Different types of
molecular excitations are then studied: electronic excitations, aligned (along
the magnetic axis) vibrational excitations, transverse vibrational excitations
(a constrained rotation of the molecular axis around the magnetic field line).
Similar results for the molecular ion H are also obtained and compared
with previous variational calculations. Both numerical results and analytical
fitting formulae are given for a wide range of field strengths. In contrast to
the zero-field case, it is found that the transverse vibrational excitation
energies can be larger than the aligned vibration excitation, and they both can
be comparable or larger than the electronic excitations. For B\go
B_{crit}=4.23\times 10^{13} G, the Landau energy of proton is appreciable and
there is some controversy regarding the dissociation energy of H. We show
that H is bound even for and that neither proton has a Landau
excitation in the ground molecular state.Comment: Revtex (45 pages), 3 postscript figures; Phys. Rev. A in pres
Quantum computation with trapped polar molecules
We propose a novel physical realization of a quantum computer. The qubits are
electric dipole moments of ultracold diatomic molecules, oriented along or
against an external electric field. Individual molecules are held in a 1-D trap
array, with an electric field gradient allowing spectroscopic addressing of
each site. Bits are coupled via the electric dipole-dipole interaction. Using
technologies similar to those already demonstrated, this design can plausibly
lead to a quantum computer with qubits, which can perform CNOT gates in the anticipated decoherence time of s.Comment: 4 pages, RevTeX 4, 2 figures. Edited for length and converted to
RevTeX, but no substantial changes from earlier pdf versio
Matter in Strong Magnetic Fields
The properties of matter are significantly modified by strong magnetic
fields, Gauss (), as are typically
found on the surfaces of neutron stars. In such strong magnetic fields, the
Coulomb force on an electron acts as a small perturbation compared to the
magnetic force. The strong field condition can also be mimicked in laboratory
semiconductors. Because of the strong magnetic confinement of electrons
perpendicular to the field, atoms attain a much greater binding energy compared
to the zero-field case, and various other bound states become possible,
including molecular chains and three-dimensional condensed matter. This article
reviews the electronic structure of atoms, molecules and bulk matter, as well
as the thermodynamic properties of dense plasma, in strong magnetic fields,
. The focus is on the basic physical pictures and
approximate scaling relations, although various theoretical approaches and
numerical results are also discussed. For the neutron star surface composed of
light elements such as hydrogen or helium, the outermost layer constitutes a
nondegenerate, partially ionized Coulomb plasma if , and may be in
the form of a condensed liquid if the magnetic field is stronger (and
temperature K). For the iron surface, the outermost layer of the
neutron star can be in a gaseous or a condensed phase depending on the cohesive
property of the iron condensate.Comment: 45 pages with 9 figures. Many small additions/changes. Accepted for
publication in Rev. Mod. Phy
Quantum Theory of Angular Momentum
This is the most complete handbook on the quantum theory of angular momentum. Containing basic definitions and theorems as well as relations, tables of formula and numerical tables which are essential for applications to many physical problems, the book is useful for specialists in nuclear and particle physics, atomic and molecular spectroscopy, plasma physics, collision and reaction theory, quantum chemistry, etc. The authors take pains to write many formulae in different coordinate systems thus providing users with added ease in consulting this book. Each chapter opens with a comprehensive list of its contents to ease the search for any information needed later. New results relating to different aspects of the angular momentum thoery are also included. Containing close to 500 pages this book also gathers together many useful formulae besides those related to angular momentum. The book also compares different notations used by previous authors.illustrato
Quantum Theory Of Angular Momentum
This is the most complete handbook on the quantum theory of angular momentum. Containing basic definitions and theorems as well as relations, tables of formula and numerical tables which are essential for applications to many physical problems, the book is useful for specialists in nuclear and particle physics, atomic and molecular spectroscopy, plasma physics, collision and reaction theory, quantum chemistry, etc. The authors take pains to write many formulae in different coordinate systems thus providing users with added ease in consulting this book. Each chapter opens with a comprehensive list of its contents to ease the search for any information needed later. New results relating to different aspects of the angular momentum thoery are also included. Containing close to 500 pages this book also gathers together many useful formulae besides those related to angular momentum. The book also compares different notations used by previous authors