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Electron collision strengths for Fe XXIII have been obtained using the 'distorted wave' approximation. Previous results (Bhatia and Mason, 1981) were obtained including the configurations 2s(2), 2s2p, 2p(2), 2s3s, 2s3p, and 2s3d. In this paper, the correlation configurations 2p3s, 2p3p and 2p3d have also been included in the solution of the electron scattering problem.
The possibility that variable linear polarization in massive X-ray binaries is produced by electron scattering in an asymmetric stellar wind is investigated. The stellar wind is asymmetric because of the gravitational field of the secondary (X-ray source). The degree of asymmetry and the magnitude of the linear polarization are controlled by the degree to which the primary star fills its Roche lobe. For the well-observed X-ray binary Cyg X-1, the present model can produce the correct magnitude for the polarization. Provided that the inclination of the system is less than about 20 deg, the present model should also predict the correct phase dependence of the polarization. Modifications to the model are described which would enable it to apply to systems with higher inclination.
A summary is presented of theoretical and observational characterization of the physical properties of accreting objects which emit X-ray, such as binary systems, through polarimetry of the observed light from the objects. X-ray polarimetry focuses on the accretion disk around secondary object. The electron scattering within the disk was predicted by Chandrasekhar (1946) to be detectable as polarization that varies with the phase of the eclipse between the third and fourth contacts. A relationship is also known to exist between the behavior of the linear polarization and the inclination of the system to the line-of-sight. Sample polarization data from several accreting stellar objects, including suspected black holes, is discussed in terms of the possible physical characteristics of the sources of the radiation.
The local thermal stability of accretion disks around supermassive black holes in active galactic nuclei is examined. Such disks are unstable at radii where the surface temperature is several thousand degrees. Supermassive disks therefore should undergo limit-cycle outbursts similar to those believed to occur in dwarf novae. Operating on a time scale of about 10,000 to 10 million yr and at radii of about 10 to the 15th to 10 to the 16th cm, this mechanism will result in alternating periods of higher and lower accretion rate onto the black hole and, consequently, higher and lower luminosity. Quasi-periodic outbursts on this time scale may be recorded in the structure of extended radio sources, a possible example being 4C 29.47. For accretion rates greater than 0.1 solar masses/yr, the situation is complicated by instabilities caused by self-gravitation and by the dominance of radiation pressure and electron scattering opacity.
Electron-attachment cross sections are calcualted for the process e(-) + SF6 yields SF6(-) in the energy range 1-200 meV. An electron scattering approximation is used in which diatomiclike potential energy curves near the equilibrium SF6 ground state are constructed from recent spectroscopic data. Excellent agreement is found over the entire energy range with experimental attachment cross sections at a temperature of 300 K for s-wave (l = 0) scattering. The same calculation, with appropriate adjustment of the thermal populations, is used to calculate attachment rate constants in the range 50-600 K for both s- and p-wave scattering.
The degree of anisotropy in the anisotropic electron transport that has been observed in GaAs modulation-doped quantum wells grown by MBE on Al(0.3)Ga(0.7)As is related to the thickness and growth parameters of this substrate, which is grown just prior to the inverted interface. It is presently observed that the inverted interface has an anisotropic roughness which affects the 77 K low field electron transport parallel to the interface, and gives rise to anisotropic electron scattering in the GaAs modulation-doped quantum well.
Einstein MPC observations of the 5.2-h binary 4U 2129 + 47 are analyzed, and a type 1 X-ray burst with rise time 6.5 + or 1.5 s, peak 2-10-keV flux about 1 nerg/sq cm s, and peak color temperature 2.8 + 0.9 or - 0.7 keV is detected in data for 22:01:03 UT on December 15, 1978. It is inferred that the compact component of the binary is a neutron star, and anomalies in the burst (e.g., peak luminosity 500 times lower than the Eddington limit) are interpreted in terms of the accretion-disk-corona (ADC) model of McClintock et al. (1982). Assuming that the burst itself is normal, an ADC with temperature about 10 to the 8th K, radius 4 x 10 to the 10th cm, and electron-scattering optical depth about 2.5 is predicted, making this object the first neutron star with a mass (0.6 + or - 0.2 solar mass according to Horne et al., 1986) well below the Chandrasekhar limit.
The first X-ray spectrum of a classical Seyfert 2 galaxy, NGC 1068, measured by the Einstein Observatory, is presented. The small soft X-ray luminosity of about 9 x 10 to the 41st ergs/s, the lack of variability, and the Compton temperature of less than 10 to the 6th K are all consistent with the model of Antonucci and Miller (1985); these authors have suggested that NGC 1068 contains a hidden Seyfert 1 nucleus seen indirectly through the electron scattering. However, the steep spectral slope (alpha = 2.0 + or - 0.3) distinguishes the NGC 1068 from the vast majority of Seyfert 1 galaxies.
A multigroup flux-limited diffusion approximation to neutrino transport, correct to first order in material velocities, is described. The role of neutrino-electron scattering in determining core deleptonization is studied using a modified Fokker-Planck approximation in which adjacent neutrino energy groups are coupled. The moderate deleptonizaton obtained during infall restricts homologous core masses to less than 0.8 solar mass. With 0.6-0.8 solar mass of outer core to traverse, nuclear dissociation alone stalls the shock waves produced at core bounce. In addition, neutrino energy losses remove at least another 4 x 10 to the 51st ergs. In no case is matter ejected promptly as a direct result of the initial shock wave.
Solar Coronal Mass Ejections (CMEs) from the Sun are an important aspect of coronal physics, and a potentially important contributor to the solar wind mass flux. However, despite significant progress in studies of CMEs since their discovery in the early 70's, questions remain about their effects on the interplanetary medium. A study is done of the long-term variations of the occurrence rates of CMEs, of activity tracers related to CMEs, and of the solar wind particle flux. CMEs are most directly detected by scattered electron radiation in white light. To estimate their long-term occurrence frequency and their contributions to the in-ecliptic solar wind mass flux, observed CME rates must be corrected for instrumental duty cycles, detection efficiency out of the plane of the sky, mass detection thresholds, and geometrical considerations. These corrections are evaluated using data on solar CMEs from the spaceborne Skylab, SMM, and SOLWIND coronagraphs and on interplanetary plasma clouds from the HELIOS white light photometers. Variations in the CME rate and the contribution of CMEs to the solar wind mass flux are traced over nearly a complete solar activity cycle.
The warm electron scattering region posited in 1985 by Antonucci and Miller to exist in NGC 1068 may be a characteristic feature of Seyfert galaxies. Whenever it exists, it presents a unique signature in Fe X-ray features. Predictions of the strength of the Fe K-edge and K-alpha line in both type 1 and type 2 Seyfert galaxies are presented and interpreted.
The simplest accretion-disk models have difficulties explaining the optical/UV/soft-X-ray 'big bump' in quasars. Here more realistic models are investigated, incorporating opacity and inclination effects while retaining an analytic form for ease of computation. It is found that opacity effects can explain the uniform 20,000-30,000 K 'maximum disk temperature' derived by previous workers. The observed spectral turndown would be the result of the onset of electron scattering and should not be identified with the hottest part of the disk. The frequency at which this spectral turndown occurs is only weakly dependent on the accretion-disk parameters. These opacity effects also allow high-frequency EUV and soft-X-ray extensions of the big bump without exceeding the Eddington limit strongly. For a wide range of disk parameters, the EUV spectra of quasar disks should have spectral slopes near -1.
Theoretical calculations of linear polarization of thermal radiation from accretion disks in nova-like variables and dwarf novae in eruption are presented. The primary source of polarization is due to electron scattering in the disk's photosphere. It is shown that the degree of polarization can be used as a powerful probe of the structure and evolution of the disk atmosphere. The degree of polarization is considerably higher in the ultraviolet than at optical wavelengths, and the degree of polarization may be higher in an eclipsing system when the central region of the disk is eclipsed. The orbital phase dependence distinguishes intrinsic polarization from the disk to that due to interstellar medium.
The thin accretion disk spectrum, including the effect of electron scattering, is calculated for a grid of the accretion parameters. It is shown that the luminosity and spectral slope in the UV and optical bands are uniquely determined by these parameters and depend only weakly on the viscosity parameter. When the model calculations are compared with observations of a sample of QSOs and Seyfert 1 nuclei, the black hole mass is in the range 10 to the 8th to 10 to the 9.5 solar for the QSOs and 10 to the 7.5 to 10 to the 8.5 solar for the Seyferts and for low-luminosity objects. The correlation between the spectral slope and luminosity of QSOs in the UV can be explained by evolution along curves of constant black hole mass and decreasing accretion rate. The relation between the spectrum and the accretion parameters can be used to constrain the cosmological evolution of the objects and imposes severe constraints on the pure luminosity evolution interpretation function for QSOs and Seyferts.
The major activities on the Spartan Ultraviolet Coronal Spectrometer project include both scientific and experimental/technical efforts. In the scientific area, a detailed analysis of the previously reported Doppler dimming of HI Ly-alpha from the July 1982 rocket flight has determined an outflow velocity at 2 solar radii from sun center to be between 153 and 251 km/s at 67 percent confidence. The technical activities include, several improvements made to the instrument that will result in enhanced scientific performance or in regaining a capability that had deteriorated during the delay time in the launch date. These include testing and characterizing the detector for OVI radiation, characterizing a serrated occulter at UV and visible wavelengths, fabricating and testing telescope mirrors with improved edges, testing and evaluating a new array detector system, modifying the slit mask mechanism and installing a mask in the instrument to block the Ly-alpha resonance line when the electron scattered component is being observed.
The prime objects of the present self-consistent model of a line-emitting accretion disk able to account for the properties observed in a small class of AGNs are Arp 102B and 3C 390.3, whose double-peaked emission lines have been attributed to a Keplerian disk. Improved calculations of the line profile of a relativistic Keplerian disk, generalized to include a variety of emissivity laws as well as local broadening due to electron scattering or turbulence, are noted to fit Arp 102B; analytic and numerical calculations of the solid angle presented by the outer thin disk to an extended isotropic source of illumination demonstrate that the energy budget requirements for line emission from the disk are also satisfied.
Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous, or short-range ordered, carbon identified by conventional TEM imaging and SAED may show evidence for sp(3) bonds in EELS spectra. It is suggested that complex, nanometer-scale, mineralogical interrelations are common to all elemental carbons irrespective of their origin. The subsequent thermal history, or energy balance, will determine the ultimate microstructure.
The new R-matrix package for comprehensive close-coupling calculations for electron scattering with the first three ions in the boron isoelectronic sequence, the astrophysically significant C(+), N(2+), and O(3+), is presented. The collision strengths are calculated in the LS coupling approximation, as well as in pair-coupling scheme, for the transitions among the fine-structure sublevels. Calculations are carried out at a large number of energies in order to study the detailed effects of autoionizing resonances.