X Rays From the Solar System and Beyond III Posters
Presiding: A Bhardwaj, NASA Marshall Space Flight Center; T E Cravens, University of Kansas; C M Lisse, University of Maryland/Applied Physics Laboratory, Johns Hopkins University; V A Kharchenko, Harvard-Smithsonian Center for Astrophysics; R Hoekstra, University of Groningen; P Beiersdorfer, Lawrence Livermore National Laboratory
P43A-01 1330h
High-resolution Crystal Spectroscopy of Charge-Exchange Produced K-shell X-ray Emission Lines
Charge-exchange spectral models needed to describe and predict the X-ray emission of cometary and planetary atmospheres interacting with solar wind heavy ions are under development and require laboratory data for guidance. The relative intensity of the four K-shell emission lines in heliumlike ions is particularly uncertain, as the individual lines have not yet been fully resolved in charge-exchange-produced spectra. Using a high-resolution crystal spectrometer, we have measured the charge exchange induced K-shell X-ray emission from Ar16+ following the interaction of Ar17+ ions with fast, 40 keV/amu deuterium atoms. The measurement was performed on the National Spherical Torus Experiment (NSTX). The Ar17+ ions were constituents of the plasma, while deuterium was injected via a 80 keV neutral beam. During the brief, 20 ms neutral beam injection emission from electron-impact collisions ceases, and X-ray line emission is solely due to charge exchange. The measurement fully resolves the resonance, intercombination, and forbidden lines. We have constructed a complete radiative cascade model of Ar16+ that includes electron capture into levels as high as n=29 and all E1, M1, E2, and M2 radiative transitions. We find excellent agreement between the model and the NSTX crystyal spectrum. We will present these findings as well as our predictions of the emission in other spectral bands from the optical and extreme ultraviolet to the soft X-ray region. This work was performed under the auspices of the U.S. DOE by UC-LLNL under contract W-7405-Eng-48, by UMR under contract DE-FG02-84ER53175, and by PPPL under contract DE-AC02-76CHO3073.
P43A-02 1330h
Laboratory measurement of charge exchange X-ray emission for diagnosing the Solar wind and planetary and cometary atmospheres
We have used the EBIT-I electron beam ion trap located at the University of California Lawrence Livermore National Laboratory and a microcalorimeter array to create and measure the X-ray emission from charge exchange recombination reactions. The microcalorimeter array, dubbed the XRS/EBIT, was built by the NASA-Goddard Space Flight Center/University of Wisconsin collaboration and is in operation at the LLNL EBIT-I facility. It consists of 32 independent microcalorimeter elements that work in concert to provide a large collection area, high-resolution, large bandwidth x-ray spectrometer. Our studies have focussed on X-ray emission from charge exchange reactions that occur after Solar wind ions interact with cometary or planetary atmospheres. Here we present an overview of our measurement techniques and capabilities, and the utility of our results. This work is especially timely in light of the upcoming launch of the Astro-E2 X-ray observatory which will provide the first ever high resolution X-ray spectrum emitted from a comet. This work was performed under the auspices of the Department of Energy by UC-LLNL under contract W-7405-ENG-48 and supported by NASA's Planetary Atmospheres Program under Work Order W-19,938.
P43A-03 1330h
EXSAA: Environmentally-Induced X-ray Spectral Analysis Automation
X-ray fluorescence (XRF) spectrometry is one of the principal means of compositional analysis in the lab and in the field: it will be a central tool in NASA's Exploration Initiative (EI) missions. No currently available XRF software has the generic functionality to provide the basis for XRF experiment design, instrument development, and data interpretation for the suite of prospective EI missions. In response to this need, we have developed EXSAA (Environmentally-induced X-ray Spectral Analysis Automation), a generic, fast, interactive spectral simulation tool which can be used in assessing broadband continuous spectra being generated and detected during reconnaissance missions and field campaigns involving planetary surfaces. The software produces model spectra of detectable environmentally-induced X-ray spectra from fundamental principles for target characteristics and conditions likely to be experienced in remote or in situ planetary missions. Fluorescence is modeled following Jenkins and DeVries (1967); coherent and Compton scattering following Hubbell (1969). The modeling provided is extensible, and a user interface provides for selection of source, detector characteristics, compositional components, and geometry for known targets. An immediate application of the tool is the prediction for mission planning purposes of X-ray flux to be expected for a range of targets and instrumentation. A longer-term application is the model basis for the recovery of surface composition from actual missions, where some parameters (e.g. source flux) will be known, and others obtained from a Bayesian analysis of the observations. Ultimately, EXSAA could function as part of the agent-based SAA Toolkit being developed by a group of physical scientists, systems engineers, and AI practitioners to automate portions of the spectral analysis process. EXSAA could be called on by human or machine agents to provide an understanding of XRF phenomena for tasks including specifically (1) instrument and mission design and planning, or (2) model-based data analysis. Thus EXSAA could support traditional design methods and enable a variety of experiments in automated design and operation. The far term objective is to develop a toolkit for use at the human/robotic interface during exploration of lunar or Martian surfaces.
P43A-04 1330h
The Spatial Distribution Of Comet - Solar Wind X-ray Spectra
Charge exchange processes lead to characteristic X-ray emission spectra, which provide an excellent diagnostic tool for the interaction between comets and the solar wind. We have developed a model for the X-ray emission spectra of comets based upon measured charge exchange cross sections of astrophysically relevant ions. The results show that the differences in electron capture cross sections of solar wind carbon and oxygen ions result in distinctly different spatial distributions of X-ray emission from these species. Specifically, the ratio of the (OVIII+ OVII)/(CVI+CV) is shown to be a good measure of the solar wind velocity and cometary neutral density distribution. As such, this ratio opens a unique window on the interaction of the solar wind plasma and coma.
http://www.kvi.nl/~atf
P43A-05 1330h
A Comparative View of X-rays from the Solar System
With the advent of sophisticated X-ray observatories, viz., Chandra and XMM-Newton, the field of planetary X-ray astronomy is advancing at a faster pace. Several new solar system objects are now know to shine in X-rays at energies generally below 2 keV. Jupiter, Saturn, and Earth, all three magnetized planets, have been observed by Chandra and XMM-Newton. At Jupiter, both auroral and non-auroral disk X-ray emissions have been observed. The first soft X-ray observation of Earth's aurora by Chandra shows that it is highly variable. X-rays have been detected from Saturn's disk, but no convincing evidence of X-ray aurora has been seen. Several comets have been observed in X-rays by Chandra and XMM-Newton. Cometary X-rays are produced due to change exchange of solar wind ions with cold cometary neutrals. Soft X-rays have also been observed from Venus, Mars, Moon, Io, Europa, Io plasma torus, and heliosphere. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, and those from sunlit disk of Mars, Venus, and Moon are produced due to scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, heliosphere, darkside of Moon, and Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. The X-ray aurora on Earth is generated by electron bremsstrahlung and on Jupiter by precipitation of highly-ionized energetic heavy ions. In this paper we will present a comparative overview of X-ray emission from different solar system objects and make an attempt to synthesize a coherent picture.
P43A-06 1330h
X-Ray and EUV Spectra of Comets
Six comets have been observed using Chandra X-ray Observatory, and spectra of two comets, LINEAR S4 and McNaught-Hartley (MH), have been analyzed. A method was developed for processing, extraction, and analysis of the CXO/ACIS spectra of comets. This method differs from the standard CXO software and is based on a careful background correction (partially at the expense of the photon statistics) and extension of the spectrum down to 150 eV where the CXO/ACIS sensitivity is still significant. The x-ray luminosities of MH and prebreakup S4 are equal to 8.6 and 1.4× 1015 erg s-1 inside the apertures of 1.5 and 0.5× 104 km, respectively. (These boundaries are at 20% of the peak brightnesses.) Efficiencies of x-ray excitation corrected for the solar wind flow are similar and equal to 4.3× 1014 erg AU3/2, confirming the solar wind excitation of x-rays in comets. Spectra of MH and S4 consist of 10 and 8 emissions, respectively. Emissions at 380, 460, 560, 650, and 920 eV are present in both comets and identified as C+5, O+6, O+7, and Ne+8. These emissions and those at 780 and 850 eV in MH and 820 eV in S4 make it possible to determine some ion ratios in the solar wind: O+8/O+7 = 0.29 ± 0.04 and 0.14 ± 0.02, Ne+9/O+7 = (15± 6)× 10-3 and (19 ± 7)× 10-3 in MH and S4, respectively, and C+6/O+7 = 0.7 ± 0.2 in both comets. The observed Ne+8 emissions are the first data on Ne+9 in the solar wind. X-ray spectroscopy of comets may be used as a diagnostic tool to study the solar wind composition and its interaction with comets. Though the EUVE spectra of comet Hyakutake were measured with even better resolving power than the CXO spectra, their quantitative analysis is more difficult because of the great number of blended emissions. The most prominent lines are He+ 304 Ã…, O+4 215 Ã…, and C+4 249 Ã…. These lines were the first charge exchange emissions detected in comets. Although α-particles are much more abundant than heavy ions in the solar wind, the He+ emission consitutes a quarter of all charge exchange photons from comets because of a comparatively low charge exchange cross section for α-particles. The O+4 and C+4 lines are mostly from the secondary ions that appear in collisionally thick parts of comae. The O+ lines at 538, 617, and 430/442 Ã… are excited by photoionization of atomic oxygen, and the absense of Ne 630 Ã… confirms the formation of Oort cloud comets in the Jupiter-Neptune region of the solar nebula.
P43A-07 1330h
Charge-exchange x-rays from the heliospheric termination shock. An outside view.
The outer heliosphere, and the termination shock in particular, produces X-ray emission. This emission is due to the charge exchange process between highly ionized minor ions of the solar wind interacting with neutral hydrogen atoms from our local interstellar medium. In this work, we combine high-resolution 2D magnetohydrodynamic simulations with an X-ray emission mechanism in order to produce two-dimensional X-ray brightness maps of the heliosphere as seen from the outside. The model is capable of tracing the full evolution of solar wind ion species along the solar wind stream lines, and thus correctly treats both the collisionally thin and collisionally thick regimes. X-ray emission from charge transfer should also occur in the astrospheres of other stars, so that this technique may ultimately be used to probe the properties of stellar winds of nearby stars.
P43A-08 1330h
X-ray Production in Discharges of Non-Uniform Plasmas
New evidence indicates that comets are not dirty snow balls but are in fact asteroid rocky objects involved in the discharge of the non-uniform local plasma. The complete theory for this model for comet behavior was published in 1979, called the Plasma Discharge Comet Model, but until close range data was obtained it has not been recognized. One of the predictions of the model was the sunward side x-ray signature that was an inherent part of the model resulting from the pinched electron stream coming from the sun side and encountering both the coma material and also the electric field of the negatively charged comet nucleus. This model was presented also in a poster session of the 1997 AGU meeting. This effect is not limited to the environment of comets but occurs when any object discharges local or wide scale non-uniform plasmas. The effect is not limited to x-ray production and the resulting electromagnetic generation depends on numerous factors. The model and effects will be presented in relation to comets and the more general case.
http://www.jmccanneyscience.com