scholarly journals Analytic approximations to photoabsorption cross sections of once-ionized helium in magnetar atmospheres

2021 ◽  
Vol 2103 (1) ◽  
pp. 012030
Author(s):  
I V Demidov ◽  
A Y Potekhin
Keyword(s):  
Magnetic Field ◽  
Cross Sections ◽  
Binding Energies ◽  
Oscillator Strengths ◽  
Theoretical Studies ◽  
Centre Of Mass ◽  
Substantial Fraction ◽  
Analytic Approximations ◽  
Internal Motions ◽  
Analytic Expressions

Abstract Magnetar atmospheres can contain a substantial fraction of once-ionized helium. At the magnetic fields about 1014 −1015 G, typical of magnetars, Landau quantization is important not only for the electrons, but also for the centre-of-mass (CM) motion of the He+ ion. The CM and internal motions are mutually dependent, which complicates theoretical studies of the He+ characteristics. We present asymptotic analytic expressions for the binding energies, oscillator strengths, and photoionization cross sections of the moving hydrogenlike ions in an ultra-strong magnetic field, which can be used to construct approximate models of magnetar atmospheres.

scholarly journals Оптические сечения поглощения и силы осцилляторов двойного донора магния в кремнии

2021 ◽  
Vol 55 (4) ◽  
pp. 299
Author(s):  
Ю.А. Астров ◽  
Л.М. Порцель ◽  
В.Б. Шуман ◽  
А.Н. Лодыгин ◽  
Н.В. Абросимов ◽  
...  
Keyword(s):  
Cross Sections ◽  
Ionization Energy ◽  
Binding Energies ◽  
Oscillator Strengths ◽  
Group V ◽  
Deep Donor ◽  
Hall Effect Measurements ◽  
Substitutional Impurities ◽  
Electron Binding Energies ◽  
Intracenter Transitions

The optical properties of magnesium impurity in silicon, whose atoms at interstitial positions in the lattice are deep double donors with an ionization energy of 107.56 meV in the neutral state, were studied. For optical transitions from the ground state of a neutral center to the excited levels 2p0 and 2p, the absorption cross sections and oscillator strengths were determined. These parameters were calculated from the impurity absorption spectra that were measured at T  K in samples with different magnesium concentrations. The deep donor content in the samples was determined using Hall effect measurements in the temperature range 78–300 K. The obtained characteristics of intracenter transitions in magnesium were compared with the corresponding literature data for shallow Group V donors in silicon, which are substitutional impurities. It was found that the optical characteristics of the investigated transitions in magnesium are consistent with the dependences of the corresponding parameters on the ionization energy for shallow donors, extrapolated to the region of larger electron binding energies.

Analytic Approximations for Integrated Electron?Atom Excitations

1981 ◽  
Vol 34 (2) ◽  
pp. 135 ◽  
Author(s):  
IE McCarthy ◽  
BC Saha ◽  
AT Stelbovics
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Momentum Space ◽  
Optical Potential ◽  
Analytic Approximations ◽  
Maximum Contribution ◽  
Excitation Cross Sections ◽  
Analytic Expressions ◽  
Reaction Channels ◽  
Atomic Excitations

Accurate calculations of atomic excitations require estimates of the effect of higher excitations on the effective (optical) potential coupling various reaction channels. The total cross section for a particular excitation is proportional to the maximum contribution of that excitation to the imaginary part of the elastic momentum-space optical potential, and is typical of the contribution to the potential in general. Analytic expressions relevant to the calculation of optical potentials are given Their validity is estimated by comparison with more-accurate calculations and with experimental excitation cross sections.

Binding energies and photoionization cross-sections of donor and acceptor impurities in inverted core/shell ellipsoidal quantum dots: Effects of magnetic field, ellipsoid anisotropy and impurity position

2019 ◽  
Vol 33 (13) ◽  
pp. 1950131 ◽  
Author(s):  
Lei Shi ◽  
Zu-Wei Yan
Keyword(s):  
Magnetic Field ◽  
Quantum Dot ◽  
Cross Section ◽  
Cross Sections ◽  
Applied Magnetic Field ◽  
Photoionization Cross Section ◽  
Binding Energies ◽  
Core Shell ◽  
Perturbation Approach ◽  
Donor And Acceptor

Within the framework of the effective-mass approximation and by using a variational and perturbation approach, the binding energies and photoionization cross-sections of donor and acceptor impurities in an inverted core/shell ellipsoidal spherical quantum dot under an applied magnetic field have been studied. We have calculated the binding energies of both donor and acceptor impurities as a function of the core and shell sizes and shapes with different impurity positions under the applied magnetic field. In addition, the corresponding photoionization cross-section is calculated. Our results show that the binding energy of the acceptor impurity is larger than that of the donor impurity, and both of them with different impurity positions and quantum ellipsoid anisotropies will exhibit a nonmonotonic change. The peak value of the photoionization cross-section will reach a maximum with the increasing ratio R1/R2. It is found that the applied magnetic field can be an effective means of enhancing the photoionization cross-section of an impurity state in such core/shell quantum dot system.

SIMPLE MODEL FOR INTERFACE EXCITON WITH THE ELECTRON-HOLE SEPARATION IN A STRONG MAGNETIC FIELD

2000 ◽  
Vol 14 (25n26) ◽  
pp. 899-905 ◽  
Author(s):  
NGO VAN THANH ◽  
NGUYEN AI VIET
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
Binding Energies ◽  
Oscillator Strengths ◽  
Bohr Radius ◽  
Electron Hole ◽  
Simple Theoretical Model ◽  
Magnetic Length ◽  
Junction Plane ◽  
Good Agreement

A simple theoretical model for the interface exciton in a strong magnetic field is studied, in which the electrons are confined in the junction plane and the local hole in the quantum well (δ doping3). The main parameter of this model is the separation d between electron and hole, which are assumed to be confined in the two planes. By variational numerical calculations, we obtain its main parameters: binding energies, effective Bohr radius and oscillator strengths, which depend strongly on the magnetic length. We find good agreement with previous results.

MAGNETIC FIELD, PRESSURE AND TEMPERATURE DEPENDENT OPTICAL PROPERTIES IN A GaAs 9.0 P 1.0 QUANTUM DOT

2014 ◽  
Vol 6 (2) ◽  
pp. 1178-1190
Author(s):  
A. JOHN PETER ◽  
Ada Vinolin
Keyword(s):  
Magnetic Field ◽  
Optical Properties ◽  
Quantum Dot ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Photon Energy ◽  
Nonlinear Optical ◽  
Binding Energies ◽  
Nonlinear Optical Properties ◽  
Optical Rectification

Simultaneous effects of magnetic field, pressure and temperature on the exciton binding energies are found in a 9.0 1.0 6.0 4.0 GaAs P / GaAs P quantum dot. Numerical calculations are carried out taking into consideration of spatial confinement effect. The cylindrical system is taken in the present problem with the strain effects. The electronic properties and the optical properties are found with the combined effects of magnetic field strength, hydrostatic pressure and temperature values. The exciton binding energies and the nonlinear optical properties are carried out taking into consideration of geometrical confinement and the external perturbations.Compact density approach is employed to obtain the nonlinear optical properties. The optical rectification coefficient is obtained with the photon energy in the presence of pressure, temperature and external magnetic field strength. Pressure and temperature dependence on nonlinear optical susceptibilities of generation of second and third order harmonics as a function of incident photon energy are brought out in the influence of magnetic field strength. The result shows that the electronic and nonlinear optical properties are significantly modified by the applications of external perturbations in a 9.0 1.0 6.0 4.0 GaAs P / GaAs P quantum dot.

scholarly journals The Nature of the Chemical Anomalies of the Sirius A

1998 ◽  
Vol 11 (1) ◽  
pp. 391-391
Author(s):  
V. Leushin
Keyword(s):  
Magnetic Field ◽  
Oscillator Strengths ◽  
Helium Abundance ◽  
Surface Magnetic Field ◽  
Line Widths ◽  
Chemical Anomalies ◽  
Improved Accuracy

On the basis of the analysis of the observed equivalent line widths of FeI, FeII, and TiII in the spectra of Sirius A and Omicron Peg and calculation of abundances of these elements, the oscillator strengths of the lines used are refined. With the improved oscillator strengths, the iron and titanium abundances in the atmosphere of Sirius A are obtained with a higher accuracy than previously: lgN(FeI) = 7.899 ±0.011, lgN(FeII) = 7.908±0.010, lgN(TiII) =5.30±0.02. The improved accuracy allowed one to conclude that the surface magnetic field is absent in the atmosphere of Sirius A: H =3D 0±100 Gs. The equivalent widths of 7 helium lines of the red region of the spectrum are measured. The calculations of these lines (with allowance for their blending with lines of other elements) show normal helium abundance. Following a comparison of features of Sirius A and Omicron Peg, a suggestion is advanced on possible reasons for the existence of Am stars.

scholarly journals A New View on Young Pulsars in Supernova Remnants: Slow, Radio-quiet & X-ray Bright

2000 ◽  
Vol 177 ◽  
pp. 699-702 ◽  
Author(s):  
E. V. Gotthelf ◽  
G. Vasisht
Keyword(s):  
Magnetic Field ◽  
Neutron Stars ◽  
Supernova Remnants ◽  
Simple Explanation ◽  
Crab Pulsar ◽  
Radio Pulsars ◽  
Substantial Fraction ◽  
Subsequent Evolution ◽  
X Ray ◽  
Field Decay

AbstractWe propose a simple explanation for the apparent dearth of radio pulsars associated with young supernova remnants (SNRs). Recent X-ray observations of young remnants have revealed slowly rotating (P∼ 10s) central pulsars with pulsed emission above 2 keV, lacking in detectable radio emission. Some of these objects apparently have enormous magnetic fields, evolving in a manner distinct from the Crab pulsar. We argue that these X-ray pulsars can account for a substantial fraction of the long sought after neutron stars in SNRs and that Crab-like pulsars are perhaps the rarer, but more highly visible example of these stellar embers. Magnetic field decay likely accounts for their high X-ray luminosity, which cannot be explained as rotational energy loss, as for the Crab-like pulsars. We suggest that the natal magnetic field strength of these objects control their subsequent evolution. There are currently almost a dozen slow X-ray pulsars associated with young SNRs. Remarkably, these objects, taken together, represent at least half of the confirmed pulsars in supernova remnants. This being the case, these pulsars must be the progenitors of a vast population of previously unrecognized neutron stars.

FREQUENCY VARIATION IN IONOSPHERIC CYCLOTRON HARMONIC SERIES OBTAINED BY THE ALOUETTE I SATELLITE

1966 ◽  
Vol 44 (5) ◽  
pp. 987-994 ◽  
Author(s):  
R. E. Barrington ◽  
Luise Herzberg
Keyword(s):  
Magnetic Field ◽  
Cyclotron Frequency ◽  
Harmonic Series ◽  
Frequency Variation ◽  
Theoretical Studies ◽  
Experimental Accuracy ◽  
Laboratory Results ◽  
Cyclotron Harmonics ◽  
Cyclotron Harmonic ◽  
Recent Laboratory

Ionograms produced by the Alouette I topside sounder frequently show well-developed series of cyclotron harmonics. Their frequencies have been determined from A (amplitude) scans with an accuracy of ~0.02 Mc/s for the sweep range of 1 to 6 Mc/s. In all cases examined, the frequencies of all of the members of the harmonic series are, within the experimental accuracy, integral multiples of the cyclotron frequency derived from the best present estimates of the earth's magnetic field strength at the satellite height. This result is discussed in the light of recent laboratory results and theoretical studies.

Sign in / Sign up

Export Citation Format

Share Document