Linking jet emission and X-ray properties in the peculiar neutron star X-ray binary Circinus X-1     

Paolo Soleri  Valeriu Tudose  Rob Fender  Michiel van der Klis  Peter G. Jonker 《Monthly notices of the Royal Astronomical Society》2009,399(1):453-464

We present the results of simultaneous X-ray and radio observations of the peculiar Z-type neutron star X-ray binary Cir X-1, observed with the Rossi X-ray Timing Explorer satellite and the Australia Telescope Compact Array in 2000 October and 2002 December. We identify typical Z-source behaviour in the power density spectra as well as characteristic Z patterns drawn in an X-ray hardness–intensity diagram. Power spectra typical of bright atoll sources have also been identified at orbital phases after the periastron passage, while orbital phases before the periastron passage are characterized by power spectra that are typical neither of Z nor of atoll sources. We investigate the coupling between the X-ray and the radio properties, focusing on three orbital phases when an enhancement of the radio flux density has been detected, to test the link between the inflow (X-ray) and the outflow (radio jet) to/from the compact object. In two out of three cases, we associate the presence of the radio jet to a spectral transition in the X-rays, although the transition does not precede the radio flare, as detected in other Z sources. An analogous behaviour has recently been found in the black hole candidate GX 339-4. In the third case, the radio light curve shows a similar shape to the X-ray light curve. We discuss our results in the context of jet models, considering also black hole candidates.  相似文献   

The Class 0 source Barnard 1c     

Brenda Matthews  Edwin Bergin  Antonio Crapsi  Michiel Hogerheijde  Jes Jørgensen  Dan Marrone  Ramprasand Rao 《Astrophysics and Space Science》2008,313(1-3):65-68

We present our most recent results from an ongoing study of the Class 0 source Barnard 1c in Perseus. This source is of particular interest because it exhibits evidence of strong alignment of grains all the way to the core’s centre, which is contrary to all other low-mass protostellar cores observed to date. Our goal is to clarify the source of poor alignment in other sources by identifying the source of strong alignment in B1c. A central cavity has been identified in N₂H⁺ emission; its anticorrelation with C¹⁸O emission suggests that heating in the centre has released CO from grain mantles, in turn destroying N₂H⁺. We present sensitivity-limited, high spatial resolution polarimetry data from the SubMillimeter Array and discuss the potential implications of these data.  相似文献   

A 40-year accumulation dataset for Adelie Land, Antarctica and its application for model validation   总被引：1，自引：0，他引：1  

Cécile Agosta  Vincent Favier  Christophe Genthon  Hubert Gallée  Gerhard Krinner  Jan T. M. Lenaerts  Michiel R. van den Broeke 《Climate Dynamics》2012,38(1-2):75-86

The GLACIOCLIM-SAMBA (GS) Antarctic accumulation monitoring network, which extends from the coast of Adelie Land to the Antarctic plateau, has been surveyed annually since 2004. The network includes a 156-km stake-line from the coast inland, along which accumulation shows high spatial and interannual variability with a mean value of 362?mm water equivalent a^?1. In this paper, this accumulation is compared with older accumulation reports from between 1971 and 1991. The mean and annual standard deviation and the km-scale spatial pattern of accumulation were seen to be very similar in the older and more recent data. The data did not reveal any significant accumulation trend over the last 40?years. The ECMWF analysis-based forecasts (ERA-40 and ERA-Interim), a stretched-grid global general circulation model (LMDZ4) and three regional circulation models (PMM5, MAR and RACMO2), all with high resolution over Antarctica (27–125?km), were tested against the GS reports. They qualitatively reproduced the meso-scale spatial pattern of the annual-mean accumulation except MAR. MAR significantly underestimated mean accumulation, while LMDZ4 and RACMO2 overestimated it. ERA-40 and the regional models that use ERA-40 as lateral boundary condition qualitatively reproduced the chronology of interannual variability but underestimated the magnitude of interannual variations. Two widely used climatologies for Antarctic accumulation agreed well with the mean GS data. The model-based climatology was also able to reproduce the observed spatial pattern. These data thus provide new stringent constraints on models and other large-scale evaluations of the Antarctic accumulation.  相似文献   

Climate simulation of the twenty-first century with interactive land-use changes   总被引：5，自引：0，他引：5  

Aurore Voldoire  Bas Eickhout  Michiel Schaeffer  Jean-François Royer  Fabrice Chauvin 《Climate Dynamics》2007,29(2-3):177-193

To include land-use dynamics in a general circulation model (GCM), the physical system has to be linked to a system that represents socio-economy. This issue is addressed by coupling an integrated assessment model, IMAGE2.2, to an ocean–atmosphere GCM, CNRM-CM3. In the new system, IMAGE2.2 provides CNRM-CM3 with all the external forcings that are scenario dependent: greenhouse gas (GHGs) concentrations, sulfate aerosols charge and land cover. Conversely, the GCM gives IMAGE changes in mean temperature and precipitation. With this new system, we have run an adapted scenario of the IPCC SRES scenario family. We have chosen a single scenario with maximum land-use changes (SRES A2), to illustrate some important feedback issues. Even in this two-way coupled model set-up, land use in this scenario is mainly driven by demographic and agricultural practices, which overpowers a potential influence of climate feedbacks on land-use patterns. This suggests that for scenarios in which socio-economically driven land-use change is very large, land-use changes can be incorporated in GCM simulations as a one-way driving force, without taking into account climate feedbacks. The dynamics of natural vegetation is more closely linked to climate but the time-scale of changes is of the order of a century. Thus, the coupling between natural vegetation and climate could generate important feedbacks but these effects are relevant mainly for multi-centennial simulations.  相似文献   

Effect of clouds on the photodissociation of NO2: Observations and modelling     

Michiel van Weele  Peter G. Duynkerke 《Journal of Atmospheric Chemistry》1993,16(3):231-255

The role of clouds in photodissociation is examined by both modelling and observations. It is emphasized that the photodissociation rate is proportional to the actinic flux rather than to the irradiance. The actinic flux concerns the energy that is incident on a molecule, irrespective of the direction of incidence. The irradiance concerns the energy that is incident on a plane.As far as the modelling aspect is concerned, a multi-layer delta-Eddington model is used to calculate irradiances, actinic fluxes, and photodissociation rates of nitrogen dioxide J(NO₂) as a function of height in inhomogeneous atmospheres. For the considered wavelength interval [290–420 nm], Rayleigh scattering, ozone absorption, and Mie scattering and absorption by cloud drops and aerosols should be taken into account.Further, a three-layer model is used to calculate the actinic flux above and below a cloud, relative to the incident flux, in terms of cloud albedo, zenith angle, and the albedo of the underlying and overlying atmosphere. Cloud albedo is mainly determined by cloud optical thickness. An expression for the incloud actinic flux is given as a function of in-cloud optical thickness. The three-layer model seems to be a useful model for the estimation of photodissociation rates in dispersion models.It is stressed that both models in their present form cannot handle partial cloudiness.It is shown that if no clouds are present, the actinic flux depends primarily on solar zenith angle. Further, the incident flux at the top of the atmosphere diminishes downward into the atmosphere due to the increasing effect of scattering. Therefore, the actinic flux usually increases with height, although above clouds the actinic flux sometimes decreases with height due to a large contribution of the upward scattered light.For cloudy atmospheres, another important parameter with respect to the actinic flux is added: cloud optical thickness. Cloud optical thickness determines cloud albedo. It can be shown that incloud characteristics and cloud height are less important while describing the effect of a cloud on the actinic flux (outside the cloud). The in-cloud values of the actinic flux can exceed the values outside the cloud.Finally, using the photostationary state relationship, a comparison is performed between model results and ground-based measurements as well as in-cloud air craft measurements.  相似文献   

Townscapes of power     

Michiel Wagenaar 《GeoJournal》2000,51(1-2):3-13

From the 1850s onward, the quest for an impressive capital city was answered by Haussmann's transformation of central Paris. His interventions combined the cutting of new arteries, slum clearance and embellishment.His approach had a great visual impact on foreign visitors. The Prefect made use of the proven instruments of axiality and proportion to create an awe-inspiring townscape. One of the highlights was the new Opera. Its surroundings were razed to place it in a proper perspective.The townscape of Paris soon found its emulators in Brussels, Budapest and Rome, which copied Haussmann's strategy. London and Amsterdam were tempted to follow. But most plans for new boulevards and slum clearance failed. In both cities, central areas fell prey to commercial land use, pockmarked with slums. Civic pride did provide the ingredients deemed necessary for a capital. But these lacked the scenography to place them in a proper perspective.Such a scenography required political, financial and legal tools to intervene in the built environment that were available in nations with a centralist and authoritarian political system. They were absent in liberal laissez-faire and decentralist nations such as Great Britain and The Netherlands.The lack of powerful intervention in central London and Amsterdam caused a flight to the city's fringes, where estate owners occasionally realised suburban design gems. In their colonies, however, both nations succeeded in creating impressive new capitals. La beauté d'un monument public doit être une émanation éclatante et directe du génie vivant de tous, une profession de foi esthétique de la race. Aussi l'architecte n'est-il, par moments, que la trompette sonore dans laquelle passe le souffle puissant d'une nation; il résonne alors des vibrations qui sortent des poumons de tout un peuple César DALY, L' architecture privée au XIX^e siècle (sous Napoléon III). Nouvelles maisons de Paris et ses Environs. Paris, 1864–1872. Pp. 11–12.  相似文献   

Morphological evolution of a barchan dune migrating past an offshore wind farm foundation     

Amelia J. Couldrey  Thomas Benson  Michiel A.F. Knaapen  Kerry V. Marten  Richard J.S. Whitehouse 《地球表面变化过程与地形》2020,45(12):2884-2896

As the number of manmade structures installed on the seafloor is increasing rapidly, we seek to understand the impact of these immobile obstacles on marine geomorphological processes, such as the evolution of bedforms. A 5.8 m diameter monopile foundation was installed at the case study offshore windfarm approximately 30 m ahead of an approaching barchan (crescent-shaped) dune. The impact of the monopile on the dune's evolution was analysed using six multibeam bathymetry surveys spanning 20 years. To substantiate this analysis, coupled three-dimensional numerical modelling of flows and sediment was conducted in which the scour inducing bed shear stresses were calculated from the modelled turbulent kinetic energy. Following the installation of the monopile, the mid-section of the dune accelerated and stretched in the direction of the wake of the monopile. Four years after the monopile's installation the rest of the dune had caught up, flattening out the slip face within half the dune's length downstream of the monopile. Due to the modified flow field, the dune was scoured deeply at the base of the monopile to a depth of 6.8 m (supported by the model results that predicted a scour depth exceeding 2 m over a period of just a few days). The surveyed volume of material scoured amounted to 8% of the total dune volume. Whilst the process of scouring occurs at a timescale of days to weeks, the dune migrated on average by 25 m/yr. The difference in the timescale of the two processes allowed the scouring to occur through the full thickness of the dune. The scoured dune profile recovered rapidly once the dune migrated downstream of the monopile. This article demonstrates how large geomorphological features can intercept and migrate past a monopile foundation without long-lasting impacts on the integrity of the feature or the foundation. © 2020 John Wiley & Sons, Ltd.  相似文献   

Fractionation of Th, Pa, and Be induced by particle size and composition within an opal-rich sediment of the Atlantic Southern Ocean     

Sven Kretschmer  Walter Geibert  Michiel M. Rutgers van der Loeff  Sheng Xu 《Geochimica et cosmochimica acta》2011,75(22):6971-6987

This study centers on the question: How sensitive are ²³¹Pa/²³⁰Th and ¹⁰Be/²³⁰Th to sediment composition and redistribution? The natural radionuclides ²³¹Pa, ²³⁰Th and ¹⁰Be recorded in deep sea sediments are tracers for water mass advection and particle fluxes. We investigate the influence of oceanic particle composition on the element adsorption in order to improve our understanding of sedimentary isotope records. We present new data on particle size specific ²³¹Pa and ¹⁰Be concentrations. An additional separation step, based on settling velocities, led to the isolation of a very opal-rich phase. We find that opal-rich particles contain the highest ²³¹Pa and ¹⁰Be concentrations, and higher ²³¹Pa/²³⁰Th and ¹⁰Be/²³⁰Th isotope ratios than opal-poor particles. The fractionation relative to ²³⁰Th induced by the adsorption to opal-rich particles is more pronounced for ²³¹Pa than for ¹⁰Be. We conclude that bulk ²³¹Pa/²³⁰Th in Southern Ocean sediments is most suitable as a proxy for past opal fluxes. The comparison between two neighboring cores with rapid and slow accumulation rates reveals that these isotope ratios are not influenced significantly by the intensity of sediment focusing at these two study sites. However, a simulation shows that particle sorting by selective removal of sediment (winnowing) could change the isotope ratios. Consequently, ²³¹Pa/²³⁰Th should not be used as paleocirculation proxy in cases where a strong loss of opal-rich material due to bottom currents occurred.  相似文献   

Radially truncated galactic discs     

Richard de Grijs  Michiel Kregel  Karen H. Wesson † 《Monthly notices of the Royal Astronomical Society》2001,324(4):1074-1086

We present the first results of a systematic analysis of radially truncated exponential discs for four galaxies of a complete sample of disc-dominated edge-on spiral galaxies.
The discs of our sample galaxies are truncated at similar radii on either side of their centres. With the possible exception of the disc of ESO 416-G25, it appears that the truncations in our sample galaxies are closely symmetric, in terms of both their sharpness and the truncation length. However, the truncations occur over a larger region and not as abruptly as found in previous studies.
We show that the truncated luminosity distributions of our sample galaxies, if also present in the mass distributions, comfortably meet the requirements for longevity. The formation and maintenance of disc truncations are probably closely related to stability requirements for galactic discs.  相似文献   

Chemical Evolution of Protostars     

Michiel R. Hogerheijde 《Astrophysics and Space Science》2005,295(1-2):179-187

This review discusses the evolution of the chemical composition of the molecular gas throughout the process of star formation. It covers the initial stages of cloud-core formation, gravitational collapse and the formation of the star, the effects of stellar radiation and outflows on the surrounding cloud, and the composition of the circumstellar disk. A brief overview of relevant chemical processes sets the stage. The ensuing evolution of the chemistry is governed by several competing timescales and by energy input by the young star(s). Special attention is given to the role of molecular freeze-out on dust grains and to deuterium fractionation in cold gas.  相似文献