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201.
The physical nature of the material responsible for the high-velocity broad absorption line (BAL) features seen in a small fraction of quasar spectra has been the subject of debate since their discovery. This has been especially compounded by the lack of observational probes of the absorbing region. In this paper we examine the role of 'microlenses' in external galaxies in the observed variability in the profiles of BALs in multiply imaged quasars. Utilizing realistic models for both the BAL region and the action of an ensemble of microlensing masses, we demonstrate that stars at cosmological distances can provide an important probe of the physical state and structure of material at the heart of these complex systems. Applying these results to the macrolensed BAL quasar system H1413+117, the observed spectral variations are readily reproduced, but without the fine-tuning requirements of earlier studies which employ more simplistic models. 相似文献
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J. C. Pickering A. P. Thorne & J. K. Webb 《Monthly notices of the Royal Astronomical Society》1998,300(1):131-134
Strong ultraviolet resonance transitions are observed routinely both in the Galactic interstellar medium and in quasar absorption systems. The quality of the astronomical spectroscopic data now available demands more precise laboratory rest wavelengths. Of particular interest is the accuracy with which one can constrain space–time variations in fundamental constants using quasar spectra. A recent analysis by Webb et al. of 25 quasar spectra using Mg and Fe transitions tentatively suggests that the fine-structure constant was smaller at earlier epochs. To permit a check on this result, and to allow further more extensive investigations, we have carried out a new determination of the laboratory wavelengths of Mg i 2853 Å, Mg II 2796 Å and Mg II 2803 Å by high-resolution Fourier transform spectroscopy. Our results for Mg II 2796 Å are consistent with the value measured independently by two other groups. To our knowledge, no previous measurements of comparable precision exist for Mg I 2853 Å and Mg II 2803 Å. 相似文献
204.
A. Hofzumahaus U. Aschmutat U. Brandenburger T. Brauers H.-P. Dorn M. Hausmann M. Heßling F. Holland C. Plass-Dülmer D. H. Ehhalt 《Journal of Atmospheric Chemistry》1998,31(1-2):227-246
In-situ OH measurements by laser-induced fluorescence (LIF) spectroscopy and folded long-path differential optical absorption spectroscopy (DOAS) were carried out in a rural environment in North-East Germany as part of the field experiment POPCORN in August 1994. The large set of OH data obtained allowed an intercomparison of both techniques based on relative diurnal profiles and simultaneously measured absolute concentrations. Most of the time the two OH instruments encountered the same air and agreed well in the measured relative diurnal variations. Only on a few occasions the measurements significantly disagreed due to a perturbation of the DOAS measurements by a local OH source in the north-western wind sector. Excluding data from this wind direction, the statistical analysis of 137 data pairs yields a correlation coefficient of r = 0.90 and a weighted linear fit with a slope of 1.09 ± 0.12. The correlations are carefully analyzed. The comparison of both instruments is discussed in the light of newly published effective absorption cross-sections for H2O and O2 that affect the calibration of LIF. 相似文献
205.
应用地震波速CT和吸收CT相结合的方法对山东省招远市界河金矿隐伏采空区进行了联合探测研究.波速CT是利用地震波走时资料反演地质体内部波速结构;吸收CT是通过能量变化观测反演吸收系数分布.地震波速对岩性敏感,吸收系数与岩石的完整性关系更密切在界河金矿采空区探测中利用地震波速和吸收系数为层析物理量,在巷道和地表间进行透射观测,以优于2m的分辨率清楚地揭示了测区内采空区和断裂破碎带的分布,探测结果已被后期的采掘所证实.探测的成功为解决同类问题提供了一种可行的方案,对促进工程地球物理探测技术的发展也有重要意义. 相似文献
206.
É. Biémont K. Blagoev V. Fivet G. Malcheva R. Mayo M. Ortiz P. Quinet 《Monthly notices of the Royal Astronomical Society》2007,380(4):1581-1588
Absolute transition probabilities have been measured for lines originating from the 5d9 6d and 5d9 7s electronic configurations in the spectrum of singly ionized gold (Au ii ). The laser-induced breakdown spectroscopy has been applied to free gold atoms and ions produced by laser ablation. Absolute transition probabilities have been determined using the branching fraction and the Boltzmann plot methods. Theoretical branching fractions as well as radiative lifetime values have also been obtained by a relativistic Hartree–Fock method taking core polarization and configuration interaction effects into account. The new results are compared with previous results when available. 相似文献
207.
C. Mendoza M. J. Seaton P. Buerger A. Bellorín M. Meléndez † J. González L. S. Rodríguez F. Delahaye E. Palacios A. K. Pradhan C. J. Zeippen 《Monthly notices of the Royal Astronomical Society》2007,378(3):1031-1035
Codes to compute mean opacities and radiative accelerations for arbitrary chemical mixtures using the Opacity Project recently revised data have been restructured in a client–server architecture and transcribed as a subroutine library. This implementation increases efficiency in stellar modelling where element stratification due to diffusion processes is depth dependent, and thus requires repeated fast opacity re-estimates. Three user modes are provided to fit different computing environments, namely, a web browser, a local workstation and a distributed grid. 相似文献
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What is the origin of the soft excess in active galactic nuclei? 总被引:1,自引:0,他引:1
Magorzata A. Sobolewska Chris Done 《Monthly notices of the Royal Astronomical Society》2007,374(1):150-158