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Here we recap the works of two posters presented at the 2002 NASA Laboratory Astrophysics Workshop. The first was Shortcomings of the R-Matrix Method for Treating Dielectronic Recombination. The second was Computation of Dielectronic Recombination Data for the Oxygen-Like Isoelectronic Sequence.
In the present work, we report an investigation of plasma environment effects on the atomic parameters associated with the K-vacancy states in highly charged iron ions within the astrophysical context of accretion disks around black holes. More particularly, the sensitivity of K-line X-ray fluorescence parameters (wavelengths, radiative transition probabilities, and Auger rates) in Fe XVII–Fe XXV ions has been estimated for plasma conditions characterized by an electron temperature ranging from 105 to 107K and an electron density ranging from 1018 to1022 cm−3. In order to do this, relativistic multiconfiguration Dirac-Fock atomic structure calculations have been carried out by considering a time averaged Debye-Hückel potential for both the electron–nucleus and electron–electron interactions.
Our research program is designed to carry out state-of-the-art atomic physics calculations crucial to advancing our understanding of fundamental astrophysical problems. We redress the present inadequacies in the atomic data base along two important areas: dielectronic recombination and inner-shell photoionization and multiple electron ejection/Auger fluorescence therefrom. All of these data are disseminated to the astrophysical community in the proper format for implementation in spectral simulation code.
The proposal has three major objectives. The first focuses on advanced neutron-transmutation-doped (NTD)-based microcalorimeter development. Our goal is to develop an array of microcalorimeters with sub- 5 eV energy resolution that can operate with pile-up-free throughput of at least 100 Hz per pixel. The second objective is to establish our microcalorimeter as an essential x-ray diagnostic for laboratory astrophysics studies. We propose to develop a dedicated microcalorimeter spectrometer for the EBIT (electron beam ion trap). This instrument will incorporate the latest detector and cryogenic technology that we have available. The third objective is to investigate innovative ideas related to possible flight opportunities. These include compact, long lived cryo-systems, ultra-low temperature cold stages, low mass and low power electronics, and novel assemblies of thin windows with high x-ray transmission.
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The extension of solar surface activity models to the domain of stellar activity, and the possibility of testing such extensions, are discussed. The extrapolation of three canonical solar activity indicators, sunspots, Ca II emission, and solar flares, to other stars is considered. The use of satellites to study stellar activity at wavelengths at which surface activity is most prominent is briefly reviewed. The correlation of stellar activity with intrinsic stellar parameters, especially those relating to rotation, is briefly considered, and the use of phenomenological models of stellar coronal X-ray emission to deduce the magnetic flux production rate for observed stars as a function of rotation rate is discussed.
The electron cyclotron maser instability is analyzed for a plasma which consists of a suprathermal electron component characterized by velocity-space anisotropies in directions both parallel and perpendicular to the ambient magnetic field, as well as a high-density thermal plasma in which omega sub e is approximately equal to Omega sub e (where omega sub e and Omega sub e are the electron plasma and cyclotron frequencies). The complete relativistic resonance condition is used and shown to result in a 'resonance ellipse' in momentum space. The instability is considered for both cold and warm suprathermal electron distributions, and for frequencies omega approximately equal to Omega sub e in the ordinary mode and omega approximately equal to 2(Omega sub e) in the fast extraordinary mode. It is shown that the growth rates are comparable for these harmonics over a wide range of parameters which, since they are escape modes of the plasma, can lead to comparable radiation intensities.
To improve the accuracy of thermal X-ray emission spectrum predictions, new computations of electron excitation rates, dielectric recombination rates, and updated codes were applied to existing data on supernova remnants and O star winds. Because of its general predominance along with low ionization and recombination rates, Fe(XVII) was analyzed with the inclusion of resonances to the excitation rate data. Corrections to the existing dielectric recombination rates based on detailed Fe (XVII) calculations and the more approximate Quantum Defect Method were accomplished. by using Distorted Wave ionization rates and reliable excitation rates, models for X-ray, ultraviolet, and optical emission line intensities of non-radiative shock wave can be constructed that supply data on shock velocity, preshock ionization states, and elemental abundances. The radiative driving force that drives the shock wave is calculated through line opacities of the shocked gas. X-ray emission spectra are also calculated for O star winds.
The formation of flux ropes in the magnetosphere of Venus due to velocity shear is examined in order to infer the properties of flux ropes in the earth magnetosphere. Observational data obtained by the International Sun-Earth Explorer (ISEE) spacecraft for the geometry of directed flows in the earth magnetosheath are compared with magnetometer measurements carried out on board Pioneer Venus Orbiter, and the results are discussed in detail. It is shown that the velocity shear is the dominant element shaping the magnetic structure of the magnetosheaths.
The interaction between collisionless shocks, such as may arise in a number of situations in space plasmas, is examined by means of hybrid numerical simulations. The production of energetic particles by shock collisions is investigated. When the shocks are quasi-perpendicular, ions with energies greater than 10E(0) are produced, where E(0) is the kinetic energy of the unshocked ions. The effect is optimized when the two colliding shocks have roughly equal strengths. As the shocks become closer to quasi-parallel, the number and energy of the accelerated ions increases. Energies in excess of 30E(0) are obtained in the quasi-parallel regime, with a small fall-off when the shocks are exactly parallel. For quasi-parallel collisions, the ion energization can be attributed to the interaction of hot ions with both strong electromagnetic waves and the motional electric field located at the shocks. These results are applied to shock collisions in the distant solar wind, at planetary bow shocks, as well as to the impulsive phase of solar flares.
Theoretical values of the emission-line ratio R are derived for the transitions 3s2 1S-3s3p 3P2 and 3s2 1S-3s3p 3P1 in Al II, at 2660 and 2669 A, respectively. These ratios are compared with IUE observations of the planetary nebula NGC 7027 and the symbiotic star RR Tel, to illustrate the usefulness of the R as an electron density diagnostics. A value of R = 0.72 was deduced for NGC 7027, which implies log Ne = 4.2 for Te = 14,000 K. This is consistent with densities deduced earlier for this planetary nebula.
Environments where the presence of dust is primarily inferred from its collisional interactions with the ambient gas are reviewed with emphasis on environments typically encountered behind fast (100 km/s or greater) shocks and in hot (few 10 exp 5 K) plasmas in galactic halos, some elliptical galaxies, or the intergalactic medium of galaxy clusters. The discussion covers interactions between dust grains and a hot gas, grain temperatures and infrared emission, supernova remnants and supershells, and dust and hot gas in, around, and between galaxies. Finally, future prospects in the field are briefly discussed.
There are many differences and also remarkable similarities between the ion chemistry and physics of planetary ionospheres and the ion chemistry and physics of astronomical environments beyond the solar system. In the early Universe, an expanded cooling gas of hydrogen and helium was embedded in the cosmic background radiation field and ionized by it. As the Universe cooled by adiabatic expansion, recombination occurred and molecular formation was driven by catalytic reactions involving the relict electrons and protons. Similar chemical processes are effective in the ionized zones of gaseous and planetary nebulae and in stellar winds where the ionization is due to radiation from the central stars, in the envelopes of supernovae where the ionization is initiated by the deposition of gamma-rays, in dissociative shocks where the ionization arises from electron impacts in a hot gas and in quasar broad-line region clouds where the quasar is responsible for the ionization. At high altitudes in the atmospheres of the Jovian planets, the main constituents are hydrogen and helium and the ion chemistry and physics is determined by the same processes, the source of the ionization being solar ultraviolet radiation and cosmic rays. After the collapse of the first distinct astronomical entities to emerge from the uniform flow, heavy elements were created by nuclear burning in the cores of the collapsed objects and distributed throughout the Universe by winds and explosions. The chemistry and physics became more complicated. Over 90 distinct molecular species have been identified in interstellar clouds where they are ionized globally by cosmic ray impacts and locally by radiation and shocks associated with star formation and evolution. Complex molecules have also been found in circumstellar shells of evolved stars. At intermediate and low altitudes in the Jovian atmospheres, the ion chemistry is complicated by the increasing abundance of heavy elements such as carbon, and an extensive array of complex molecules has been predicted. Reactions involving heavy elements dominate the structure of the ionspheres of the terrestrial planets and the satellites Titan and Triton.
This grant primarily covered the development of the thermal X-ray emission model code called APEC, which is meant to replace the Raymond and Smith (1977) code. The new code contains far more spectral lines and a great deal of updated atomic data. The code is now available (http://hea-www.harvard.edu/APEC), though new atomic data is still being added, particularly at longer wavelengths. While initial development of the code was funded by this grant, current work is carried on by N. Brickhouse, R. Smith and D. Liedahl under separate funding. Over the last five years, the grant has provided salary support for N. Brickhouse, R. Smith, a summer student (L. McAllister), an SAO predoctoral fellow (A. Vasquez), and visits by T. Kallman, D. Liedahl, P. Ghavamian, J.M. Laming, J. Li, P. Okeke, and M. Martos. In addition to the code development, the grant supported investigations into X-ray and UV spectral diagnostics as applied to shock waves in the ISM, accreting black holes and white dwarfs, and stellar coronae. Many of these efforts are continuing. Closely related work on the shock waves and coronal mass ejections in the solar corona has grown out of the efforts supported by the grant.
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