The influence of autoionizing states on absorption cross sections for atomic oxygen

Multi-channel expressions, in the dipole approximation, are used to calculate absorption cross sections for the ejection of an outer subshell electron from atomic oxygen. Autoionization levels have been included and the resulting resonances in the cross section are characterized by the dispersion formula. Averaged absorption cross sections are presented for wavelengths 911-754 Å and 705-675 Å.     

Magnetized particle capture cross section for braneworld black hole

Capture cross section of magnetized particle (with nonzero magnetic moment) by braneworld black hole in uniform magnetic field is studied. The magnetic moment of particle was chosen as it was done by de Felice and Sorge (Class. Quantum Gravity 20:469, 2003) and for the simplicity particle with zero electric charge is chosen. It is shown that the spin of particle as well as the brane parameter are to sustain the stability of particles circularly orbiting around the black hole in braneworld i.e. spin of particles and brane parameter try to prevent the capture by black hole.     

Upper limit on the radar cross section of the comet Kohoutek

An attempt to observe radar echoes from the comet Kohoutek was made at a radio frequency of 7840 MHz (λ ～- 3.8 cm) on 12 January 1974 using the Haystack Observatory radar in Massachusetts. A search for an echo over a range of band-widths covering 2Hz to 66kHz yielded no positive result. The upper limit on the radar cross section is therefore approximately $\text{10}{}^4\text{B}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{km}{}^2$, where B is the (unknown) bandwidth of the echo in Hertz. For $\text{B ? 100}\text{Hz}$, it follows that (i) the nucleus, if a perfect spherical reflector, must be less than 250 km in diameter, and (ii) the density of any millimeter-sized particles must be less than 1m^?3 for a coma of diameter 10⁴km.     

Effective radiative recombination coefficients of atomic oxygen

Effective radiative recombination coefficients are calculated for atomic oxygen using an atomic model potential to obtain accurate non-hydrogenic transition probabilities of singly excited states. Results are presented for many lines for temperatures up to 3000 K. Simple analytic fits are given which are accurate for most lines.     

Conjugate excitation of atomic oxygen emissions in the far ultraviolet

Thirty four objects appearing in the SharplessCatalogue of H ii Regions with radio flux densities below 0.1 fu^* at 1400 MHz, are studied. It is shown that two of them are planetary nebulae, two are reflection nebulae and two weak emission-reflection nebulae. From statistical arguments it is concluded that six may be evolved planetaries while the remaining are faint nearby Hii regions excited by stars of relatively advanced spectral type.     

The ionization of atomic oxygen by electron impact

The single and double ionization of atomic oxygen by electron impact has been studied, and the energy dependence of the specific ionization cross-section, σ(O⁺) and σ(O²⁺), has been measured from 40 to 300 eV using a high-density atomic oxygen source not contaminated by metastable O(¹D) or O(¹S) atoms.     

Double ionization of atomic oxygen by electron impact

Laboratory measurements of the cross-sections for double ionization of atomic oxygen by electrons are presented for energies from threshold to ～ 400 eV. A maximum cross-section of about 5.6 × 10^?18 cm² is observed at an electron energy of approx. 200 eV. Absolute cross-sections are obtained from measurements of the ratio of the cross-sections for double and single ionization, coupled with absolute cross-sections for single ionization previously measured by other investigators. The possible effects of excited oxygen reactants are examined, and the reported cross-sections are considered to be characteristic of ground state oxygen atoms.     

Association of atomic oxygen and airglow excitation mechanisms

An outline is presented of a method of calculating relative rates of association of oxygen atoms by energy transfer into the different bound states of molecular oxygen. The method takes account of the detailed form of the potential energy curves for the different states. Results are presented for seven bound states of O₂ at temperatures between 100 and 600 K and are compared with laboratory and airglow data. The ⁵Π_g state, not known experimentally, accounts for over 70% of the total association below 200 K. At higher temperatures it is redissociated, and the variation in its effective association rate is primarily responsible for the variation of the total rate of oxygen association with temperature. The ⁵Π_g state is probably involved in the production at night of the a¹Δ_g and b¹Σ_g⁺ states of O₂, and in the production of $\text{O(}{}^1\text{S)}$ in the airglow. It may also be produced by electron impact on O₂, and contribute to $\text{O(}{}^1\text{S)}$ production in aurorae.     

The effects of ablation on the cross section of planetary envelopes at capturing planetesimals

We explore the cross section of giant planet envelopes at capturing planetesimals of different sizes. For this purpose we employ two sets of realistic planetary envelope models (computed assuming for the protoplanetary nebula masses of 10 and 5 times the mass of the minimum mass solar nebula), account for drag and ablation effects and study the trajectories along which planetesimals move. The core accretion of these models has been computed in the oligarchic growth regime [Fortier, A., Benvenuto, O.G., Brunini, A., 2007. Astron. Astrophys. 473, 311-322], which has also been considered for the velocities of the incoming planetesimals. This regime predicts velocities larger that those used in previous studies of this problem. As the rate of ablation is dependent on the third power of velocity, ablation is more important in the oligarchic growth regime. We compute energy and mass deposition, fractional ablated masses and the total cross section of planets for a wide range of values of the critical parameter of ablation. In computing the total cross section of the planet we have included the contributions due to mass deposited by planetesimals moving along unbound orbits. Our results indicate that, for the case of small planetary cores and low velocities for the incoming planetesimals, ablation has a negligible impact on the capture cross section in agreement with the results presented in Inaba and Ikoma [Inaba, S., Ikoma, M., 2003. Astron. Astrophys. 410, 711-723]. However for the case of larger cores and high velocities of the incoming planetesimals as predicted by the oligarchic growth regime, we find that ablation is important in determining the planetary cross section, being several times larger than the value corresponding ignoring ablation. This is so regardless of the size of the incoming planetesimals.     

The α-Monocerotids meteor outburst: the cross section of a comet dust trail

One minute counts obtained during the meteor outburst of α-Monocerotids on November 22, 1995, are analyzed in order to examine the possibility of filamentary structure in the stream profile. None is found. It is argued that far-comet type outbursts are due to the Earth's passage through the dust trail of a long period comet, thus offering a direct means of studying such comet dust trails. Hence, the meteor stream activity curve is the first accurate cross section of dust densities through a comet dust trail.     

Inelastic cross section for antihelium on nuclei: an empirical formula for use in the experiments to search for cosmic antimatter

An empirical formula for the cross section for inelastic hadronic interaction of antihelium with nuclei for the projectile energy range from 0.3 GeV/n to 80 GeV/n and target atomic mass number A from 4 to 120 has been developed. It is based on the available experimental data of nucleon (antinucleon) — nucleus and helium — nucleus inelastic cross sections. Such a formula is needed by experiments designed to search for antihelium in cosmic rays. With this formula one can estimate the efficiency of antihelium detection and correct for antihelium attenuation in the atmosphere for the balloon-borne experiments. A byproduct of this work is an empirical formula for antiproton-nucleus inelastic cross.     

Spectroscopic anatomy of a meteor trail cross section with the European Southern Observatory Very Large Telescope

Abstract— A meteor spectrum was recorded serendipitously at the European Southern Obrervatory (ESO) Very Large Telescope (VLT) during a long exposure in long‐slit spectroscopic mode with FORS1. The ?8 magnitude fireball crossed the narrow 1Î × 7î slit during the observation of a high z supernova in normal service mode operation on May 12, 2002. The spectrum covered the range of 637–1050 nm, where the meteor's air plasma emissions from N₂, N, and O dominate. Carbon atom emission was not detected in the relatively unexplored wavelength range above 900 nm, but the observed upper limit was only 3 sigma less than expected from the dissociation of atmospheric CO₂. The meteor trail was resolved along the slit, and the emission had a Gaussian distribution with a dimension of FWHM = 7.0 (±0.4) * sin(α) * H (km)/90 m, where α is the unknown angle between the orientation of the meteor path and slit and H the assumed altitude of the meteor in km. To our knowledge, this is the first observation of a spatially resolved spectrum across a meteor trail. Unlike model predictions, the plasma excitation temperature varied only from about 4,300 to 4,365 K across the trail, based on the ratio of atomic and molecular nitrogen emissions. Unfortunately, we conclude that this was because the meteor at 100 km altitude was out of focus.     

Angular distribution of photoelectrons from atomic oxygen,nitrogen and carbon

The angular distributions of photoelectrons from atomic oxygen, nitrogen and carbon are calculated. Both Hartree-Fock and Hartree-Slater (Herman-Skillman) wave functions are used for oxygen and the agreement is excellent; thus only Hartree-Slater functions are used for carbon and nitrogen. The pitch angle distribution of photoelectrons is discussed and it is shown that previous approximations of energy independent isotropic or sin² θ distributions are at odds with our results, which vary with energy. This variation with energy is discussed as is the reliability of these calculations.     

Intensity variation of atomic oxygen red line in the day airglow with solar activity

Rates of production of O(¹ D) atoms in the upper atmosphere by photodissociation of O₂, dissociative recombination of O₂ ⁺, NO⁺ and electron impact excitation of O(³ P) have been calculated for low, medium and high levels of solar activity. Variations with solar activity, of neutral and ionic composition, electron and neutral temperatures of the upper atmosphere and solar extreme ultraviolet fluxes incident on it have been taken into consideration.Emission rates ofOi red line (6300Å) have been computed taking into account the deactivation both by molecular oxygen and nitrogen. It has been shown that the integrated intensity from low to high activity period varies by approximately an order of magnitude in agreement with the results of experimental observations.     

Decrease of ozone and atomic oxygen in the lower mesosphere during a PCA event

It is argued that ozone measurements made by Weeks et al. (1972) can be interpreted in terms of the enhanced ionization present. The conversion of O₂⁺ ions to oxonium, H₃O⁺ · (H₂O)_n, ions plus the dissociative recombination of these ions provides for an increased OH and/or H formation rate. The resulting enhanced OH and HO₂ concentrations reduce the ambient atomic oxygen and hence ozone populations. The net excess H + OH formation rate is found to lie between one and two times the ionization production rate at altitudes where oxonium ions are the dominant positive ion species.     

Determination of atomic oxygen density from rocket borne measurement of hydroxyl airglow

A rocket experiment was conducted which measured the infrared bands of the excited hydroxyl radical in the night airglow. The OH emission was found in a layer centered at 87 km having a half-width of 6 km and a total emission of 1.1 MR. The atomic oxygen altitude profile, ranging from 1.3 × 10¹⁰ atoms/cm³ at 83 km to 3 × 10¹¹ atoms/cm³ at 90 km is determined from the hydroxyl airglow measurements. This derivation is based on the steady state balance between ozone formation from atomic oxygen and its destruction by hydrogen which produces the OH infrared emission.