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991.
992.
M. J. Freyberg H. Bräuninger W. Burkert G. D. Hartner O. Citterio F. Mazzoleni G. Pareschi D. Spiga S. Romaine P. Gorenstein B. D. Ramsey 《Experimental Astronomy》2005,20(1-3):405-412
The Max-Planck-Institut für extraterrestrische Physik (MPE) in Garching, Germany, uses its large X-ray beam line facility PANTER for testing X-ray astronomical instrumentation. A number of telescopes, gratings, filters, and detectors, e.g. for astronomical satellite missions like Exosat, ROSAT, Chandra (LETG), BeppoSAX, SOHO (CDS), XMM-Newton, ABRIXAS, Swift (XRT), have been successfully calibrated in the soft X-ray energy range (< 15keV). Moreover, measurements with mirror test samples for new missions like ROSITA and XEUS have been carried out at PANTER. Here we report on an extension of the energy range, enabling calibrations of hard X-ray optics over the energy range 15–50 keV. Several future X-ray astronomy missions (e.g., Simbol-X, Constellation-X, XEUS) have been proposed, which make use of hard X-ray optics based on multilayer coatings. Such optics are currently being developed by the Osservatorio Astronomico di Brera (OAB), Milano, Italy, and the Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, MA, USA. These optics have been tested at the PANTER facility with a broad energy band beam (up to 50 keV) using the XMM-Newton EPIC-pn flight spare CCD camera with its good intrinsic energy resolution, and also with monochromatic X-rays between C-K (0.277 keV) and Cu-Kα (8.04 keV).
PACS: 95.55.Ka, 95.55.Aq, 41 50.+h, 07.85.Fv 相似文献
993.
994.
In previous papers we have published preliminary results on the stellar oxygen-abundance gradient in M33 by using B-type supergiants.
In the present study, we include one new B-supergiant and derive effective temperatures and gravities for these stars. The
determination of atmospheric parameters is based on analyses of silicon ionisation balance.
Detailed non-LTE model atmospheres and non-LTE line formation calculations were used for the abundance determination of Si
and O. Careful differential analyses are used to quantify the differences in metal abundances between M33 stars and MK spectral
standards in our Galaxy.
We compare our results with the abundances expected from studies of HII regions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
995.
S. P. Plunkett M. Delaney B. McBreen K. J. Hurley C. T. O'Sullivan 《Astrophysics and Space Science》1995,231(1-2):271-276
A small air shower array operating over many years has been used to search for ultra-high energy (UHE) gamma radiation ( 50 TeV) associated with gamma-ray bursts (GRBs) detected by the BATSE instrument on the Compton Gamma-Ray Observatory (CGRO). Upper limits for a one minute interval after each burst are presented for seven GRBs located with zenith angles < 20°. A 4.3 excess over background was observed between 10 and 20 minutes following the onset of a GRB on 11 May 1991. The confidence level that this is due to a real effect and not a background fluctuation is 99.8%. If this effect is real then cosmological models are excluded for this burst because of absorption of UHE gamma rays by the intergalactic radiation fields. 相似文献
996.
We have analysed X-ray spectra of 13 solar flares as obtained by the Bent Crystal Spectrometer (BCS) on the Solar Maximum Mission. In particular, we have examined the observed ratio of T
Fe/T
Ca where T
Fe and T
Ca are the temperatures obtained from the Fexxv and Caxix spectra, respectively. In order to simplify the investigation we have analysed only flares which reach quasi-steady-state during the decay. It turned out that the observed ratios cannot be explained by a model consisting of a single, uniformly heated loop, with a constant or variable cross-sectional area. We propose that this problem may be solved by introducing some distribution of the heating function across the flaring loop. This model has been tested by detailed calculations. 相似文献
997.
Spectral maps of Mimas’ daytime thermal emission show a previously unobserved thermal anomaly on Mimas’ surface. A sharp V-shaped boundary, centered at 0°N and 180°W, separates relatively warm daytime temperatures from a cooler anomalous region occupying low- to mid-latitudes on the leading hemisphere. Subsequent observations show the anomalous region is also warmer than its surroundings at night, indicating high thermal inertia. Thermal inertia in the anomalous region is , compared to < outside the anomaly. Bolometric Bond albedos are similar between the two regions, in the range 0.49-0.70. The mapped portion of the thermally anomalous region coincides in shape and location to a region of high-energy electron deposition from Saturn’s magnetosphere, which also has unusually high near-UV reflectance. It is therefore likely that high-energy electrons, which penetrate Mimas’ surface to the centimeter depths probed by diurnal temperature variations, also alter the surface texture, dramatically increasing its thermal inertia. 相似文献
998.
We investigate a dynamical model of prominence formation in a current sheet at the boundary between two regions of opposite magnetic polarity. Coupled nonlinear equations describing the temporal compression and condensation of plasma in the current sheet are set up as a natural extension of the usual equations for current sheet collapse (Imshennik and Syrovatskii, 1967). It is shown that under certain conditions the current sheet undergoes a nonlinear oscillation during the compression. The thermal instability with cooling is driven by a density enhancement produced during the current sheet formation stage. 相似文献
999.
IMP-6 spacecraft observations of low frequency radio emission, fast electrons, and solar wind plasma are used to examine the dynamics of the fast electron streams which generate solar type-III radio bursts. Of twenty solar electron events observed between April, 1971 and August, 1972, four were found to be amenable to detailed analysis. Observations of the direction of arrival of the radio emission at different frequencies were combined with the solar wind density and velocity measurements at 1 AU to define an Archimedean spiral trajectory for the radio burst exciter. The propagation characteristics of the exciter and of the fast electrons observed at 1 AU were then conpared. We find that: (1) the fast electrons excite the radio emission at the second harmonic; (2) the total distance travelled by the electrons was between 30 and 70% longer than the length of the smooth spiral defined by the radio observations; (3) this additional distance travelled is the result of scattering of the electrons in the interplanetary medium; (4) the observations are consistent with negligible true energy loss by the fast electrons. 相似文献
1000.
The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation. 相似文献