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1.
Rapid variations of the radial velocities of absorption components of Ti II lines in CH Cyg are presented. The periods of these variations are determined to 1.89 and 41.07 days in 1982. The variations are interpreted through oscilliations in the mass transfer from the M component onto the accretion disk of the companion during periastron passage.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986. 相似文献
2.
Xavier?LurtonEmail authorView authors OrcID profile Dimitrios?Eleftherakis Jean-Marie?Augustin 《Marine Geophysical Researches》2018,39(1-2):183-203
The sediment backscatter strength measured by multibeam echosounders is a key feature for seafloor mapping either qualitative (image mosaics) or quantitative (extraction of classifying features). An important phenomenon, often underestimated, is the dependence of the backscatter level on the azimuth angle imposed by the survey line directions: strong level differences at varying azimuth can be observed in case of organized roughness of the seabed, usually caused by tide currents over sandy sediments. This paper presents a number of experimental results obtained from shallow-water cruises using a 300-kHz multibeam echosounder and specially dedicated to the study of this azimuthal effect, with a specific configuration of the survey strategy involving a systematic coverage of reference areas following “compass rose” patterns. The results show for some areas a very strong dependence of the backscatter level, up to about 10-dB differences at intermediate oblique angles, although the presence of these ripples cannot be observed directly—neither from the bathymetry data nor from the sonar image, due to the insufficient resolution capability of the sonar. An elementary modeling of backscattering from rippled interfaces explains and comforts these observations. The consequences of this backscatter dependence upon survey azimuth on the current strategies of backscatter data acquisition and exploitation are discussed. 相似文献
3.
Martin Sudmanns Dirk Tiede Stefan Lang Helena Bergstedt Georg Trost Hannah Augustin 《International Journal of Digital Earth》2020,13(7):832-850
ABSTRACT Turning Earth observation (EO) data consistently and systematically into valuable global information layers is an ongoing challenge for the EO community. Recently, the term ‘big Earth data’ emerged to describe massive EO datasets that confronts analysts and their traditional workflows with a range of challenges. We argue that the altered circumstances must be actively intercepted by an evolution of EO to revolutionise their application in various domains. The disruptive element is that analysts and end-users increasingly rely on Web-based workflows. In this contribution we study selected systems and portals, put them in the context of challenges and opportunities and highlight selected shortcomings and possible future developments that we consider relevant for the imminent uptake of big Earth data. 相似文献
4.
5.
A. Skopal 《Astrophysics and Space Science》1996,238(2):285-302
A quantitative model explaining a periodic wave-like variation in both the optical continuum and the emission line fluxes of the symbiotic binary V443 Her is presented. The model suggests that behaviour of spectrophotometric parameters is caused by a different projection of the circumstellar matter located mostly between the components of the binary, viewing the system at different orbital phases. Our model suggests that the inclination of the orbit is 18° (+12°, –3°) and the mass ratio of the cool to the hot component is 2(+1). It is shown that the previous interpretation in terms of a reflection effect is incorrect. 相似文献
6.
M.M. Crocker R.J. Davis S.P.S. Eyres M.F. Bode A.R. Taylor A. Skopal H.T. Kenny 《Monthly notices of the Royal Astronomical Society》2001,326(2):781-787
Very Large Array surface brightness and spectral index maps of the evolving extended emission of the triple symbiotic star CH Cygni are presented. These are derived from observations at 4.8, 8.4 and 14 GHz between 1985 and 1999. The maps are dominated by thermal emission around the central bright peak of the nebula, but we also find unambiguous non-thermal emission associated with the extended regions. Our observations confirm that this is a jet. The central region has been associated with the stellar components through Hubble Space Telescope imaging. If the jets are the result of ejection events at outburst, expansion velocities are consistent with those from other measurement methods. We propose that the non-thermal emission is caused by material ejected in the bipolar jets interacting with the circumstellar wind envelope. The resulting shocks lead to local enhancements in the magnetic field from the compact component of the order of 3 mG. 相似文献
7.
Augustin Skopal 《Astrophysics and Space Science》2005,296(1-4):421-425
We explain a complex behaviour of the light curves (LC) of symbiotic binaries on the basis of their spectral energy distribution
(SED) in the optical domain. During quiescent phases we observe a wave-like variation of the optical light as a function of
orbital phase. This is produced by the orbitally-related variation of the emission measure (EM) of the symbiotic nebula. During
active phases this type of variability disappears, the continuum level increases by 2–3 magnitudes in U and, in the case of
a highly inclined orbit, narrow minima – eclipses – in the LC can occur. These phenomena are connected with the creation of
a cool pseudo-photosphere around the hot star, whose contribution is significant in the optical, while the nebula practically
disappears. 相似文献
8.
Anne-Marie Lézine Augustin F.-C. Holl Judicaël Lebamba Annie Vincens Chimène Assi-Khaudjis Louis Février Émmanuelle Sultan 《Comptes Rendus Geoscience》2013,345(7-8):327-335
This paper discusses the relationship between patterns of human settlements and environmental change during the Holocene along the northwestern margins of the equatorial rain forest of central Africa. Palaeoenvironmental data from high-resolution sediment cores from lacustrine deposits, plant macro-remains from forest soils, and archaeological data are harnessed to discuss the differential impact of climate and/or humans on the central African rain forest. It is shown that climate change impacted the rain forest well before the widespread expansion of human settlements all over the study area. 相似文献
9.
10.
A. Krabbenhöft F. Böhm J. Fietzke N. Augustin M.N. Müller C. Horn N. Nolte 《Geochimica et cosmochimica acta》2010,74(14):4097-4109
We present strontium (Sr) isotope ratios that, unlike traditional 87Sr/86Sr data, are not normalized to a fixed 88Sr/86Sr ratio of 8.375209 (defined as δ88/86Sr = 0 relative to NIST SRM 987). Instead, we correct for isotope fractionation during mass spectrometry with a 87Sr-84Sr double spike. This technique yields two independent ratios for 87Sr/86Sr and 88Sr/86Sr that are reported as (87Sr/86Sr∗) and (δ88/86Sr), respectively. The difference between the traditional radiogenic (87Sr/86Sr normalized to 88Sr/86Sr = 8.375209) and the new 87Sr/86Sr∗ values reflect natural mass-dependent isotope fractionation. In order to constrain glacial/interglacial changes in the marine Sr budget we compare the isotope composition of modern seawater ((87Sr/86Sr∗, δ88/86Sr)Seawater) and modern marine biogenic carbonates ((87Sr/86Sr∗, δ88/86Sr)Carbonates) with the corresponding values of river waters ((87Sr/86Sr∗, δ88/86Sr)River) and hydrothermal solutions ((87Sr/86Sr∗, δ88/86Sr)HydEnd) in a triple isotope plot. The measured (87Sr/86Sr∗, δ88/86Sr)River values of selected rivers that together account for ∼18% of the global Sr discharge yield a Sr flux-weighted mean of (0.7114(8), 0.315(8)‰). The average (87Sr/86Sr∗, δ88/86Sr)HydEnd values for hydrothermal solutions from the Atlantic Ocean are (0.7045(5), 0.27(3)‰). In contrast, the (87Sr/86Sr∗, δ88/86Sr)Carbonates values representing the marine Sr output are (0.70926(2), 0.21(2)‰). We estimate the modern Sr isotope composition of the sources at (0.7106(8), 0.310(8)‰). The difference between the estimated (87Sr/86Sr∗, δ88/86Sr)input and (87Sr/86Sr∗, δ88/86Sr)output values reflects isotope disequilibrium with respect to Sr inputs and outputs. In contrast to the modern ocean, isotope equilibrium between inputs and outputs during the last glacial maximum (10-30 ka before present) can be explained by invoking three times higher Sr inputs from a uniquely “glacial” source: weathering of shelf carbonates exposed at low sea levels. Our data are also consistent with the “weathering peak” hypothesis that invokes enhanced Sr inputs resulting from weathering of post-glacial exposure of abundant fine-grained material. 相似文献