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Roberto F. Viotti Lucio Angelo Antonelli Sonja Rebecchi Corinne Rossi 《Journal of Astrophysics and Astronomy》2002,23(1-2):19-22
We have investigated with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary
system η Car along its 5.52 year cycle. We have found that in March 1998 during egress from the last December 1997 eclipse,
this component was the same as outside eclipse, but for a large (×3.5) increase of NH
h
, that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly,
at that time the iron 6.7 keV emission line was 40% stronger. BeppoSAX has for the first time found ahard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2–100 keV
spectrum of η Car is instead well fitted with an absorbed powerlaw spectrum with photon index 2.53, suggesting non-thermal
emission as an alternative model for the core source. 相似文献
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Simon J. Woodings rew J. Williams Ralph Martin Ronald R. Burman & David G. Blair 《Monthly notices of the Royal Astronomical Society》1998,301(1):L5-L9
Following the proposal by Damineli that the central object of Eta Carinae may be an early-type binary, we perform numerical simulations of the X-ray emission from colliding stellar winds. A synthetic light curve has been generated which qualitatively agrees with the recent X-ray variability, and provides further support for the binary model. In particular, the model predicts a rise in the observed X-ray emission towards periastron, followed by a sharp drop and subsequent recovery. This is indeed what is seen in the RXTE light curve, although some problems concerning the X-ray spectrum at periastron still need to be explained. The simulations suggest that the width of the periastron dip will provide strong constraints on the binary and stellar wind properties of the components of Eta Car. 相似文献
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Discovering spatial and temporal patterns from taxi-based Floating Car Data: a case study from Nanjing 总被引：1，自引：0，他引：1
Floating Car Data (FCD) refers to the trajectories of vehicles equipped with Global Positioning System-enabled devices that automatically record location-related data within a short time interval. As taxies in Chinese cities continually drive along the streets seeking passengers, FCD can easily traverse the entire street network in a city on a daily basis. Taking advantage of this situation, this study extracted passenger pickup and drop-off locations from FCD sourced from 6445 taxis over a 2-week period in Nanjing, China to discover human behavioral patterns and the dynamics behind them. In this study, road nodes are converted to the points, based on which Thiessen polygons are generated to divide the study area into small areas with the goal of exploring the spatial distribution of pickup and drop-off locations. Moran’s I index is used to calculate the spatial autocorrelation of the spatial distribution of pickup and drop-off locations, and hot spot analysis is used to identify statistically significant spatial clusters of hot and cold spots. The spatial and temporal patterns of FCD in the study area are investigated, and the results show that: (1) the temporal patterns show a strong daily rhythm, (2) the spatial patterns show that the number of pickup and drop-off locations gradually diminish from the downtown areas to the outer suburbs, (3) the spatiotemporal patterns exhibit large differences over time, and (4) the driving forces explored by regression models indicate that population density and transportation density are consistent with the population distribution, but per capita disposable income is not consistent with the population distribution. 相似文献
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A merger tree with microsolar mass resolution: application to γ-ray emission from subhalo population
Carlo Giocoli Lidia Pieri Giuseppe Tormen Jorge Moreno 《Monthly notices of the Royal Astronomical Society》2009,395(3):1620-1630
Observations of the southern Cepheid ℓ Car to yield the mean angular diameter and angular pulsation amplitude have been made with the Sydney University Stellar Interferometer at a wavelength of 696 nm. The resulting mean limb-darkened angular diameter is 2.990 ± 0.017 mas (i.e. ± 0.6 per cent) with a maximum-to-minimum amplitude of 0.560 ± 0.018 mas corresponding to 18.7 ± 0.6 per cent in the mean stellar diameter. Careful attention has been paid to uncertainties, including those in measurements, in the adopted calibrator angular diameters, in the projected values of visibility squared at zero baseline, and to systematic effects. No evidence was found for a circumstellar envelope at 696 nm. The interferometric results have been combined with radial displacements of the stellar atmosphere derived from selected radial velocity data taken from the literature to determine the distance and mean diameter of ℓ Car. The distance is determined to be 525 ± 26 pc and the mean radius 169 ± 8 R⊙ . Comparison with published values for the distance and mean radius shows excellent agreement, particularly when a common scaling factor from observed radial velocity to pulsation velocity of the stellar atmosphere (the p -factor) is used. 相似文献
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We study the usage of the X-ray light curve, column density towards the hard X-ray source, and emission measure (density square times volume), of the massive binary system η Carinae to determine the orientation of its semimajor axis. The source of the hard X-ray emission is the shocked secondary wind. We argue that, by itself, the observed X-ray flux cannot teach us much about the orientation of the semimajor axis. Minor adjustment of some unknown parameters of the binary system allows to fit the X-ray light curve with almost any inclination angle and orientation. The column density and X-ray emission measure, on the other hand, impose strong constrains on the orientation. We improve our previous calculations and show that the column density is more compatible with an orientation where for most of the time the secondary – the hotter, less massive star – is behind the primary star. The secondary comes closer to the observer only for a short time near periastron passage. The 10-week X-ray deep minimum, which results from a large decrease in the emission measure, implies that the regular secondary wind is substantially suppressed during that period. This suppression is most likely resulted by accretion of mass from the dense wind of the primary luminous blue variable star. The accretion from the equatorial plane might lead to the formation of a polar outflow. We suggest that the polar outflow contributes to the soft X-ray emission during the X-ray minimum; the other source is the shocked secondary wind in the tail. The conclusion that accretion occurs at each periastron passage, every five and a half years, implies that accretion had occurred at a much higher rate during the Great Eruption of η Car in the 19th century. This has far reaching implications for major eruptions of luminous blue variable stars. 相似文献
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With its wide coverage of economic spheres and the variety of trade and investment measures currently under negotiation, the Transatlantic Trade and Investment Partnership opens windows of opportunity for advancing action on climate change. We examine possible avenues and international trade law implications for an alignment of carbon-related standards between the EU and the US. We compare EU and US carbon emissions standards for cars and argue that negotiators should strive for a mutual recognition of their equivalence for a transitional period, while pursuing the goal of full harmonization at the level of the highest standards of two parties at some date in the future. This could be a way to balance between economic and environmental interests and harness economic incentives for the benefit of climate. 相似文献
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Antonio Bianchini † Brian Alford ‡ Ronald Canterna Massimo Della Valle ‡ 《Monthly notices of the Royal Astronomical Society》2001,321(4):625-628
Low-resolution spectra, taken at La Silla (ESO), identify the old nova RS Car (1895) as a ∼18 mag star located 7 arcsec southwest from the previous published position. This suggests a much brighter absolute magnitude of the old nova, M v ∼5.4, than previously suspected. The spectrum reveals a continuum energy distribution typical of optically thick accretion discs and quite a high excitation state of the gas. The possible detection of the AlO λ 4843 emission band is discussed. 相似文献
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