X Rays From the Solar System and Beyond I
Presiding: A Bhardwaj, NASA Marshall Space Flight Center; V A Kharchenko, Harvard-Smithsonian Center for Astrophysics
P41A-01 INVITED 08:30h
Charge Exchange X-Rays Beyond the Solar System
Solar-wind charge exchange X-rays are emitted throughout the solar system, and this heliospheric emission contributes a significant fraction of the apparent cosmic soft X-ray background. The same phenomenon must occur around other stars with highly ionized stellar winds, which offers the possibility of measuring properties of other stars' astrospheres such as stellar mass-loss rate, local neutral gas density, and stellar-wind composition, velocity, and geometry. Such measurements are just beyond the capabilities of current X-ray telescopes, although useful mass-loss limits have been obtained from a few Chandra observations. The prospects for astrospheric studies using future X-ray missions such as Constellation-X and XEUS are bright, although not immediate. Moving beyond the local stellar neighborhood, charge exchange emission may be an important contributor to the diffuse line emission seen in the Galactic Ridge and Galactic Center. Observations with current X-ray telescopes should be able to address this more controversial hypothesis.
P41A-02 INVITED 08:50h
Heliospheric and Geocoronal X-rays
X-rays are generated throughout the heliosphere and the terrestrial magnetosheath as a consequence of charge transfer collisions between neutrals and heavy solar wind ions. Near Earth the highest production rate of this type of radiation is in the magnetosheath and particularly in the cusp regions. Due to its variability this radiation could be observable from suitable platforms and would be a valuable tool for monitoring space weather at Earth. Charge exchange also takes places between heavy solar wind ions and interstellar neutrals. The time variable component of this mechanism explains the long term enhancement contributions to the soft X-ray background seen in the ROSAT all-sky survey. Both types of X-ray emissions will be discussed.
P41A-03 09:10h
Emission Maps of Charge-transfer Induced Heliospheric X-rays
Model distributions of interstellar neutral hydrogen and helium in the heliosphere are combined with minimum and maximum activity 3D solar wind fluxes and compositions. Using updated charge-transfer cross-sections we derive maps and spectral properties of the soft X-ray emission as seen from different vantage points and at different solar cycle phases.
P41A-04 09:25h
Solar-cycle dependent heliospheric x-ray emission
The numerical modeling of the self-consistent interaction of the partially ionized local interstellar medium with the solar wind yields detailed estimates of the distribution of neutral particles throughout the heliosphere. The solar wind, and consequently the neutrals, change over the 11 year solar activity cycle. Charge exchange between the neutrals of interstellar origin (and secondary neutrals) and solar wind heavy ions produces characteristic x-ray emission. We calculate a time-dependent global heliospheric model, assuming an idealized 11 year solar wind variation. From this model, we evaluate the time-dependent x-ray (volume) emission and present line-of-sight integrated x-ray intensity predictions. The integration will mix features from different phases in the solar cycle. We also briefly touch on the consequences that ISM variations might have on the x-ray emissions.
P41A-05 INVITED 09:40h
Atomic Physics of X-Ray Emissions
Atomic Physics is an essential element in the interpretation of observations of X-rays,in the identification of the mechanisms that produce X-rays and in the prediction of the spectra. The spectra serve as powerful diagnostics of the origin of the X-rays and the nature of the astrophysical environments in which the sources are embedded. Atomic processes that lead to the emission of X-rays will be discussed with particular attention to charge transfer in collisions of highly-stripped ions with neutral material. Following electron capture radiative cascade occurs involving many transitions in which X-rays and extreme ultraviolet radiation are emitted. The charge transfer cross sections depend on velocity, on the charge state of the ions and on the target, and the transition rates depend on the atomic system formed by elcetron capture. These data can be used to separate out the different contributions to the soft X-ray background.