The nature of the luminous X-ray emission of NGC 6240     

Stefanie Komossa  Hartmut Schulz 《Astrophysics and Space Science》1999,266(1-2):61-66

We briefly review and extend our discussion of the ROSAT detectionof the extraordinarily luminous (>10⁴² erg/s) partly extended(>30 kpc diameter) X-ray emission from the ultraluminous infrared galaxy NGC 6240.The `standard'-model of starburst outflow is contrasted with alternatives and a comparison with the X-ray properties of ellipticals is performed.  相似文献   

The solar abundance of calcium and collision broadening of Ca i- and Ca ii-Fraunhofer lines by hydrogen     

H. Holweger 《Solar physics》1972,25(1):14-29

An abundance analysis of the solar calcium spectrum is carried out using 46 lines with known f-values in the visible and near infrared spectral region. Resonance, forbidden and autoionizing lines are included. The solar abundance of calcium resulting from the 25 weaker, nearly damping-independent lines only is log _Ca=6.36±0.07, on the scale log H = 12. The great variety of transitions involved in the solar calcium spectrum, ranging from 0 eV lines of CaI to 7.5 eV lines of CaII and including autoionizing lines, are in reasonable agreement (Figure 1b). Therefore notable non-LTE effects on their equivalent widths can be excluded.Together with the sodium abundance log _Na = 6.30 determined earlier, the solar abundance ratio Ca/Na = 1.15 is obtained with an accuracy of 10%. Comparison with meteorites (carbonaceous chondrites I) shows that solar and meteoritic ratio agree within these limits.The line broadening by collisions with hydrogen atoms is determined empirically from a comparison of weak and strong Fraunhofer lines of CaI and CaII, thereby using the solar atmosphere as an absorption tube of comparatively well-known physical state. The damping half-widths H turn out to be larger than predicted from pure van der Waals interaction, the average enhancement factor being 3.0 for CaI and 1.7 for CaII, independent of term properties to a first approximation. Regardless of the reason for this enhancement — inaccurate van der Waals theory or predominance of repulsive interaction these results can be used in the spectroscopy of other stars.  相似文献   

The radioactive contamination of the Baltic Sea during the years 1983 to 1987 and its radiological consequences     

Dr. Hartmut Nies 《Ocean Dynamics》1988,41(1):39-44

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Seasonal and interannual variability of the planktic foraminiferal flux in the vicinity of the Azores Current     

David Storz  Hartmut Schulz  Joanna J. Waniek  Detlef E. Schulz-Bull  Michal Kučera 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):107-124

Planktic foraminiferal (PF) flux and faunal composition from three sediment trap time series of 2002–2004 in the northeastern Atlantic show pronounced year-to-year variations despite similar sea surface temperature (SST). The averaged fauna of the in 2002/2003 is dominated by the species Globigerinita glutinata, whereas in 2003/2004 the averaged fauna is dominated by Globigerinoides ruber. We show that PF species respond primarily to productivity, triggered by the seasonal dynamics of vertical stratification of the upper water column. Multivariate statistical analysis reveals three distinct species groups, linked to bulk particle flux, to chlorophyll concentrations and to summer/fall oligotrophy with high SST and stratification. We speculate that the distinct nutrition strategies of strictly asymbiontic, facultatively symbiontic, and symbiontic species may play a key role in explaining their abundances and temporal succession. Advection of water masses within the Azores Current and species expatriation result in a highly diverse PF assemblage. The Azores Frontal Zone may have influenced the trap site in 2002, indicated by subsurface water cooling, by highest PF flux and high flux of the deep-dwelling species Globorotalia scitula. Similarity analyses with core top samples from the global ocean including 746 sites from the Atlantic suggest that the trap faunas have only poor analogs in the surface sediments. These differences have to be taken into account when estimating past oceanic properties from sediment PF data in the eastern subtropical North Atlantic.  相似文献   

Comment on ‘Where are the halo stars?’     

Burkhard Fuchs  Hartmut Jahreiß 《New Astronomy》2002,7(8):541-542

We comment briefly on a recent paper by Fuhrmann which claims that about half of the sample of halo stars in the solar neighbourhood presented by Fuchs and Jahreiß [A&A 329 (1998) 81] are actually thick disc stars. By referring to star counts in the CADIS survey we argue that this is rather unlikely.  相似文献   

Testing thermal reprocessing in active galactic nuclei accretion discs     

Edward M. Cackett  Keith Horne  Hartmut Winkler 《Monthly notices of the Royal Astronomical Society》2007,380(2):669-682

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Center-to-limb analysis of the solar oxygen lines     

Edith A. Müller  Bodo Baschek  Hartmut Holweger 《Solar physics》1968,3(1):125-145

Several lines of neutral oxygen observed at various positions on the solar disk were used to study the influence of (1) the temperature distribution, (2) the velocity field, and (3) the damping on the line profiles and the abundance of oxygen in the photosphere. Theoretical profiles were calculated on the basis of four different model atmospheres in LTE. It was found that the model proposed by Holweger (1967) best reproduced the center-to-limb observations of the lines studied. The weighted mean of the oxygen abundance turned out to be log _O = 8.83 on the basis of log _H = 12.00.  相似文献   

Erratum to: A note on stokes production of turbulence kinetic energy in the oceanic mixed layer: observations in the Baltic Sea     

Lakshmi Kantha  Hans Ulrich Lass  Hartmut Prandke 《Ocean Dynamics》2010,60(3):629-629

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Poisson's ratio of eclogite: Implications for lower crustal delamination of orogens   总被引：5，自引：2，他引：3  

高山  Hartmut Kern  金振民  张宏飞  张本仁 《中国科学D辑(英文版)》2003,46(9):909-918

Eclogite is essentially a bi-mineralogic high-grade metamorphic rock consisting of garnet and omphacite and is the product of high-to-ultrahigh pressure metamorphism of basaltic rocks due to the subduction of oceanic crust or the thickening/subduction of …  相似文献   

Lightning evolution related to radar-derived microphysics in the 21 July 1998 EULINOX supercell storm     

Nikolai Dotzek  Hartmut Hller  Claire Thry  Thorsten Fehr 《Atmospheric Research》2001,56(1-4)

Results of a combined analysis of data from a C-band polarimetric Doppler radar and a 3D VHF interferometric lightning mapping system, as obtained during the European Lightning Nitrogen Oxides project (EULINOX) field campaign, are presented. For 21 July 1998, the lightning data from a supercell thunderstorm weakly indicate a tendency for a bi-level vertical distribution of lightning VHF emissions around the −15°C and −30°C temperature levels. Also, in some parts of the clouds, evidence is found for the presence of a lower positive charge center near the freezing level. However, where strong vertical motions prevail, VHF emissions are not organized in horizontal layers but in oblique or vertical regions. Correlation of VHF signals with radar quantities shows that in the growing storm, peak VHF activity is low and related to reflectivity factors around 30 dBZ, while after the mature stage, the peak VHF activity is about three times larger. The highest density of VHF signals is now found near reflectivity factors of 45 dBZ. A polarimetric hydrometeor classification indicates that during storm development, most lightning activity occurs where graupel and, secondarily, snow and small dry hail are present. In the decaying phase of the supercell hailstorm, however, most lightning VHF emissions stem from the region with hail and heavy rain. Furthermore, while the VHF signal frequency per cubic kilometer in the graupel and rain regions remains nearly constant throughout the supercell life cycle, the signal frequency in the hail region rises during storm decay.  相似文献