Modeling X-Ray Photoionized Plasmas Produced at the Sandia Z-Facility     

P. A. M. Van Hoof  M. E. Foord  R. F. Heeter  J. E. Bailey  H.-K. Chung  M. E. Cuneo  W. H. Goldstein  V. Jonauskas  F. P. Keenan  R. Kisielius  D. A. Liedahl  C. Ramsbottom  S. J. Rose  P. T. Springer  R. S. Thoe 《Astrophysics and Space Science》2005,298(1-2):147-153

In experiments at the high-power Z-facility at Sandia National Laboratory in Albuquerque, New Mexico, we have been able to produce a low density photoionized laboratory plasma of Fe mixed with NaF. The conditions in the experiment allow a meaningful comparison with X-ray emission from astrophysical sources. The charge state distributions of Fe, Na and F are determined in this plasma using high resolution X-ray spectroscopy. Independent measurements of the density and radiation flux indicate unprecedented values for the ionization parameter ξ = 20–25 erg cm s⁻¹ under nearly steady-state conditions. First comparisons of the measured charge state distributions with X-ray photoionization models show reasonable agreement, although many questions remain.  相似文献   

The Optical Gravitational Lensing Experiment: catalogue of stellar proper motions in the OGLE-II Galactic bulge fields     

T. Sumi  X. Wu  A. Udalski  M. Szyma&#;ski  M. Kubiak  G. Pietrzy&#;ski  I. Soszy&#;ski  P. Wo&#;niak  K. &#;ebru&#;  O. Szewczyk  &#;. Wyrzykowski 《Monthly notices of the Royal Astronomical Society》2004,348(4):1439-1450

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Microboudin structures of piemontite along the Sambagawa metamorphic belt, Japan: implications for lateral variation of differential stress during regional metamorphism     

T. Masuda  T. Shibutani  T. Ochiai  S. Akagi  H. Yamaguchi  Y. Kugimiya  N. Kimura  T. Miyake 《Journal of Metamorphic Geology》2004,22(3):199-205

Evidence is presented of a lateral variation in differential stress during metamorphism along a regional metamorphic belt on the basis of the proportion of microboudinaged piemontite grains (p) in a quartz matrix in metacherts. It is proposed that p is a practical indicator of relative differential stress. Analysis of 123 metacherts from the 800 km long Sambagawa metamorphic belt, Japan, reveals that p‐values range from < 0.01 to 0.7 in this region. Most samples from Wakayama in the mid‐belt area have p‐values of 0.4–0.6, whereas those from western Shikoku have p‐values of < 0.1. This difference cannot be explained by variations in metamorphic temperature, and is instead attributed to a regional, lateral variation in differential stress during metamorphism.  相似文献   

Neutron background in large-scale xenon detectors for dark matter searches     

M. J. Carson  J. C. Davies  E. Daw  R. J. Hollingworth  V. A. Kudryavtsev  T. B. Lawson  P. K. Lightfoot  J. E. McMillan  B. Morgan  S. M. Paling  M. Robinson  N. J. C. Spooner  D. R. Tovey 《Astroparticle Physics》2004,21(6):667-687

Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10⁻⁹–10⁻¹⁰ pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector.  相似文献   

Fragmentation and the formation of primordial protostars: the possible role of collision-induced emission     

E. Ripamonti  T. Abel 《Monthly notices of the Royal Astronomical Society》2004,348(3):1019-1034

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Magnetic Reconnection and Extraplanar Diffuse Ionized Gas     

Guido T. Birk  Harald Lesch  Thomas Neukirch 《Astrophysics and Space Science》2004,289(3-4):359-362

Photoionization by stars cannot be the only cause for the diffuseionized gas component in the distant halos of galaxies.Quasistationary localized magnetic reconnection can efficientlycontribute to the ionization of the extraplanar halo gas. The gas isheated and re-ionized in numerous current filaments fast enough tocompensate recombination. The necessary magnetic energy is provided bythe disk activity.  相似文献   

Acceleration of anomalous cosmic rays at the heliospheric termination shock     

Berezhko  E. G.  Ksenofontov  L. T. 《Astronomy Letters》2005,31(12):836-843

Astronomy Letters - The acceleration of anomalous cosmic rays (ACRs) at the heliospheric termination shock and their influence on the shock structure and location are analyzed in terms of a...  相似文献   

The Hubble constant from the gravitational lens CLASS B0218+357 using the Advanced Camera for Surveys     

T. York  N. Jackson  I. W. A. Browne  O. Wucknitz  J. E. Skelton † 《Monthly notices of the Royal Astronomical Society》2005,357(1):124-134

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Emission-line outflows in PKS1549−79: the effects of the early stages of radio-source evolution?     

C. Tadhunter  K. Wills  R. Morganti  T. Oosterloo  R. Dickson 《Monthly notices of the Royal Astronomical Society》2001,327(1):227-232

We present new spectroscopic observations of the southern radio galaxy         . Despite the flat-spectrum character of the radio emission from this source, our optical spectra show no sign of the broad permitted lines and non-stellar continuum characteristic of quasar nuclei and broad-line radio galaxies. However, the high-ionization forbidden lines, including [O  iii ] λλ 5007, 4959, are unusually broad for a narrow-line radio galaxy     , and are blueshifted by 600 km s⁻¹ relative to the low-ionization lines such as [O  ii ] λλ 3726,3729. The [O  ii ] lines are also considerably narrower     than the [O  iii ] lines, and have a redshift consistent with that of the recently detected H  i 21-cm absorption-line system. Whereas the kinematics of the [O  iii ] emission lines are consistent with outflow in an inner narrow-line region, the properties of the [O  ii ] emission lines suggest that they are emitted by a more extended and quiescent gaseous component. We argue that, given the radio properties of the source, our line of sight is likely to be lying close to the direction of bulk outflow of the radio jets. In this case it is probable that the quasar nucleus is entirely obscured at optical wavelengths by the material responsible for the H  i absorption-line system. The unusually broad [O  iii ] emission lines suggest that the radio source is intrinsically compact. Overall, our data are consistent the idea that     is a radio source in an early stage of evolution.  相似文献   

Exposure history of the Torino meteorite     

R. Wieler  Th. Graf  P. Signer  S. Vogt  G. F. Herzog  C. Tuniz  D. Fink  L. K. Fifield  J. Klein  R. Middleton  A. J. T. Jull  P. Pellas  J. Masarik  G. Dreibus 《Meteoritics & planetary science》1996,31(2):265-272

Abstract— We determined He, Ne, Ar, ¹⁰Be, ²⁶Al, ³⁶Cl, and ¹⁴C concentrations, as well as cosmic-ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ～20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ～65 Ma. If the first-stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first-stage exposure ages when constructing two-stage histories.  相似文献