1,121 research outputs found
Hydrogen atom in a magnetic field: The quadrupole moment
The quadrupole moment of a hydrogen atom in a magnetic field for field
strengths from 0 to 4.414e13 G is calculated by two different methods. The
first method is variational, and based on a single trial function. The second
method deals with a solution of the Schroedinger equation in the form of a
linear combination of Landau orbitals.Comment: 4 pages, 1 figure, 1 table; RevTeX. Final (proofs-stage) version of
the text; corrected numbers in Table 1 and in Eq.(15
Testing cosmological variability of fundamental constants
One of the topical problems of contemporary physics is a possible variability
of the fundamental constants. Here we consider possible variability of two
dimensionless constants which are most important for calculation of atomic and
molecular spectra (in particular, the X-ray ones): the fine-structure constant
\alpha=e^2/\hbar c and the proton-to-electron mass ratio \mu=m_p/m_e. Values of
the physical constants in the early epochs are estimated directly from
observations of quasars - the most powerful sources of radiation, whose spectra
were formed when the Universe was several times younger than now. A critical
analysis of the available results leads to the conclusion that present-day data
do not reveal any statistically significant evidence for variations of the
fundamental constants under study. The most reliable upper limits to possible
variation rates at the 95% confidence level, obtained in our work, read:
|\dot\alpha/\alpha| < (1.4e-14)/yr,
|\dot\mu/\mu| < (1.5e-14)/yr
on the average over the last ten billion years.Comment: 9 pages, 2 figures, 2 tables, LaTeX using aipproc.sty (included). In:
X-ray and Inner-Shell Processes, R.W. Dunford, D.S. Gemmel, E.P. Kanter, B.
Kraessig, S.H. Southworth, L. Young (eds.), AIP Conf. Proc. (AIP, Melville,
2000) vol. 506, p. 50
A hydrogenic molecular atmosphere of a neutron star
A model of a hydrogenic content of atmosphere of the isolated neutron star
1E1207.4-5209 is proposed. It is based on the assumption that the main
component in the atmosphere is the exotic molecular ion and that
there exists a magnetic field in the range of G.
Photoionization H_3^{2+} \rar e + 3p and photodissociation H_3^{2+} \rar H +
2p correspond to two absorption features at 0.7 KeV and 1.4 KeV, respectively,
discovered by {\it Chandra} observatory (Sanwal et al, 2002). The model
predicts one more absorption feature at 80-150 eV corresponding to
photodissociation H_3^{2+} \rar H_2^+ + p.Comment: 8 pages, 1 figur
Neutrino-pair bremsstrahlung by electrons in neutron star crusts
Neutrino-pair bremsstrahlung by relativistic degenerate electrons in a
neutron-star crust at densities (10^9 - 1.5x10^{14}) g/cm^3 is analyzed. The
processes taken into account are neutrino emission due to Coulomb scattering of
electrons by atomic nuclei in a Coulomb liquid, and electron-phonon scattering
and Bragg diffraction (the static-lattice contribution) in a Coulomb crystal.
The static-lattice contribution is calculated including the electron
band-structure effects for cubic Coulomb crystals of different types and also
for the liquid crystal phases composed of rod- and plate-like nuclei in the
neutron-star mantle (at 10^{14} - 1.5x10^{14} g/cm^3). The phonon contribution
is evaluated with proper treatment of the multi-phonon processes which removes
a jump in the neutrino bremsstrahlung emissivity at the melting point obtained
in previous works. Below 10^{13} g/cm^3, the results are rather insensitive to
the nuclear form factor, but results for the solid state near the melting point
are affected significantly by the Debye-Waller factor and multi-phonon
processes. At higher densities, the nuclear form factor becomes more
significant. A comparison of the various neutrino generation mechanisms in
neutron star crusts shows that electron bremsstrahlung is among the most
important ones.Comment: 17 pages, 13 figures, LaTeX using aa.cls and epsf.sty. A&A, in pres
Basic Chemical Models of Nonideal Atomic Plasma
The concept of basic chemical models is introduced, which is new from the
standpoint of the physics of nonideal atomic plasma. This concept is based on
the requirement of full conformity of the expression for free energy in the
chemical model of plasma to exact asymptotic expansions obtained in the grand
canonical ensemble within the physical model of plasma. The thermodynamic
functions and equations of state and ionization equilibrium are obtained for
three basic chemical models differing from one another by the choice of the
atomic partition function. Comparison is made with the experimental results for
nonideal plasma of cesium and inert gases. It is demonstrated that the best fit
to experiment is shown by the results obtained using a basic chemical model
with atomic partition function in the nearest neighbor approximation with
classical determination of the size of excited atom.Comment: 18 pages, 10 gigure
Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
We review the theory of electron-conduction opacity, a fundamental ingredient
in the computation of low-mass stellar models; shortcomings and limitations of
the existing calculations used in stellar evolution are discussed. We then
present new determinations of the electron-conduction opacity in stellar
conditions for an arbitrary chemical composition, that improve over previous
works and, most importantly, cover the whole parameter space relevant to
stellar evolution models (i.e., both the regime of partial and high electron
degeneracy). A detailed comparison with the currently used tabulations is also
performed. The impact of our new opacities on the evolution of low-mass stars
is assessed by computing stellar models along both the H- and He-burning
evolutionary phases, as well as Main Sequence models of very low-mass stars and
white dwarf cooling tracks.Comment: 11 pages, 6 figures, ApJ in pres
Thomas-Fermi Calculations of Atoms and Matter in Magnetic Neutron Stars II: Finite Temperature Effects
We present numerical calculations of the equation of state for dense matter
in high magnetic fields, using a temperature dependent Thomas-Fermi theory with
a magnetic field that takes all Landau levels into account. Free energies for
atoms and matter are also calculated as well as profiles of the electron
density as a function of distance from the atomic nucleus for representative
values of the magnetic field strength, total matter density, and temperature.
The Landau shell structure, which is so prominent in cold dense matter in high
magnetic fields, is still clearly present at finite temperature as long as it
is less than approximately one tenth of the cyclotron energy. This structure is
reflected in an oscillatory behaviour of the equation of state and other
thermodynamic properties of dense matter and hence also in profiles of the
density and pressure as functions of depth in the surface layers of magnetic
neutron stars. These oscillations are completely smoothed out by thermal
effects at temperatures of the order of the cyclotron energy or higher.Comment: 37 pages, 17 figures included, submitted to Ap
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