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NASA NTRS1975

Constant energy partitioning in the photoionization of NO and O2

Published data on the photoelectron spectra of NO and O2 are analyzed, and the energy distributions are found to have averages proportional to the available energy. Hence, vibration takes a constant fraction of the energy. Average distributions are found as a function of the fraction of available energy.

Lawrence, G. M.↗
NASA NTRS1984

Photoionization Structure of the Orion Nebula

The O III lines at 52 and 88 micro m and the N III line at 57 micro m were observed at 6 positions in the Orion Nebulae to probe the ionization structure of the nebula. The six positions form a line or cut south from and including the Trapezium. Electron densities and abundance ratios of N(++) were calculated and compared together with radio and optical observations. The predictions that the effects of heavy capacity in the ionized gas can cause the N(++) zone to extend appreciably beyond the O(++) zone are confirmed.

Simpson, J. P.↗
NASA NTRS1985

Polar cap photoionization and the ten-hour clock at Jupiter

It is shown that the clock-like modulation of the spectral index of energetic electrons (greater than 2 MeV) in the outer Jovian magnetosphere is due to a periodic shift of the particle energy spectrum toward higher and lower energies. This shift results in a modulation of the spectral index when the spectrum is not a pure power law in energy. It is suggested that the periodic energization is due to a periodic modulation of the magnetic field in the outer magnetosphere. This modulation is caused by a variation of the longitudinally averaged Pedersen conductivity due to the asymmetric solar illumination of the trace of the magnetodisk in the high-latitude ionospheres. Such a modulation requires the presence of a surface magnetic anomaly.

Goertz, C. K.↗
NASA NTRS1986

On star formation in stellar systems. I - Photoionization effects in protoglobular clusters

The progressive ionization and subsequent dynamical evolution of nonhomogeneously distributed low-metal-abundance diffuse gas after star formation in globular clusters are investigated analytically, taking the gravitational acceleration due to the stars into account. The basic equations are derived; the underlying assumptions, input parameters, and solution methods are explained; and numerical results for three standard cases (ionization during star formation, ionization during expansion, and evolution resulting in a stable H II region at its equilibrium Stromgren radius) are presented in graphs and characterized in detail. The time scale of residual-gas loss in typical clusters is found to be about the same as the lifetime of a massive star on the main sequence.

Tenorio-Tagle, G.↗
NASA NTRS1991

High-resolution threshold photoionization of N2O

Pulsed field ionization (PFI) has been used in conjunction with a coherent VUV source to obtain high-resolution threshold photoelectron spectra for the (000), (010), (020), and (100) vibrational states of the N2O(+) cation. Simulations for the rotational profiles of each vibronic level were obtained by fitting the Buckingham-Orr-Sichel equations using accurate spectroscopic constants for the ground states of the neutral and the ion. The relative branch intensities are interpreted in terms of the partial waves of the outgoing photoelectron to which the ionic core is coupled and in terms of the angular momentum transferred to the core.

Wiedmann, R. T.↗
NASA NTRS1992

A photoionization instability in the early intergalactic medium

It is argued that any fairly uniform source of ionizing photons can be the cause of an instability in the pregalactic medium on scales larger than a photon path length. Underdense regions receive more ionizing energy per atom and reach higher temperature and entropy, driving the density down still further. Fluctuations created by this instability can lead to the formation of structures resembling protogalaxies and intergalactic clouds, obviating the need for gas clouds or density perturbations of earlier cosmological provenance, as is usually assumed in theories of galaxy and structure formation. Characteristic masses for clouds produced by the instability, with log mass in solar units plotted against log radius in kpc, are illustrated.

Hogan, Craig J.↗