Non-Gaussian foreground residuals of the WMAP first-year maps     

João Medeiros  Carlo R. Contaldi 《Monthly notices of the Royal Astronomical Society》2006,367(1):39-45

We investigate the effect of foreground residuals in the WMAP ( Wilkinson Microwave Anisotropy Probe ) data by adding foreground contamination to Gaussian ensembles of cosmic microwave background (CMB) signal and noise maps. We evaluate a set of non-Gaussian estimators on the contaminated ensembles to determine with what accuracy any residual in the data can be constrained using higher-order statistics. We apply the estimators to the raw and cleaned Q -, V - and W -band first-year maps. The foreground subtraction method applied to clean the data in Bennett et al. appears to have induced a correlation between the power spectra and normalized bispectra of the maps which is absent in Gaussian simulations. It also appears to increase the correlation between the  Δℓ= 1  inter-ℓ bispectrum of the cleaned maps and the foreground templates. In a number of cases the significance of the effect is above the 98 per cent confidence level.  相似文献   

Low-Mass Young Stars in Cep OB2: Ages, Distribution and Accretion Disks     

Aurora Sicilia-Aguilar  Lee Hartmann  César Briceño  María Eugenia Contreras  James Muzerolle  Nuria Calvet 《Astrophysics and Space Science》2004,292(1-4):457-463

We are studying the young clusters Tr37 and NGC7160 in the Cep OB2 region as part of a program to understand the evolution of accretion disks at the ages of disk dissipation and planet formation. Here, we present the first identifications of low mass (spectral types K-M) members of the clusters and study the presence and characteristics of their accretion disks, finding evidences of disk evolution. Using optical photometry and spectroscopy, we have identified ～70 members in Tr37 and ～20 in NGC7160, confirming age estimates of 3 and 10 Myr respectively. Accretion rates are ～10^?8 M _⊙yr^?1 in Tr37. We have not found any accreting members in NGC7160, suggesting that disk accretion generally ends before the age of 10 Myr, which is consistent with the results from other populations.  相似文献   

Transition from debris flow to hyperconcentrated flow in a submarine channel (the Cretaceous Cerro Toro Formation, southern Chile)     

Y. K. Sohn  M. Y. Choe  H. R. Jo 《地学学报》2002,14(5):405-415

ABSTRACT It is important to understand the exact process whereby very large amounts of sediment are transported. This paper reports peculiar conglomerate beds reflecting the transition of submarine debris flows into hyperconcentrated flows, something that has been well documented only in subaerial debris-flow events until now. Voluminous debris flows generated along a Cretaceous submarine channel, southern Chile, transformed immediately into multiphase flows. Their deposits overlie fluted or grooved surfaces and comprise a lower division of clast-supported and imbricated pebble–cobble conglomerate with basal inverse grading and an upper division of clast- to matrix-supported, disorganized conglomerate with abundant intraformational clasts. The conglomerate beds suggest temporal succession of turbidity current, gravelly hyperconcentrated flow, and mud-rich debris flow phases. The multiphase flows resulted from progressive dilution of gravelly but cohesive debris flows that could hydroplane, in contrast to the flow transitions in subaerial environments, which involve mostly non-cohesive debris flows. This finding has significant implications for the definition, classification, and hazard assessment of submarine mass-movement processes and characterization of submarine reservoir rocks.  相似文献   

Nebular and stellar properties of a metal-poor H ii galaxy at z= 3.36     

M. Villar-Martín  M. Cerviño  R. M. González Delgado 《Monthly notices of the Royal Astronomical Society》2004,355(4):1132-1142

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Photometric evolution of N-body + SPH + star formation simulations of isolated disc galaxies     

Léo Michel-Dansac  Hervé Wozniak 《Astrophysics and Space Science》2003,284(2):921-924

We have calibrated self-consistent simulations of isolated disc galaxies including star, gas and star formation with the spectro-photometric evolutionary model GISSEL2000 (Bruzual and Charlot, 1993). With this approach we can compare morphologies studying mass and luminous distributions. We present an example about the evolution of bar ellipticity, which is simultaneously governed by dynamic and spectro-photometric evolution. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Kinematics of disc galaxies using photometrically calibrated N-body models     

Hervé Wozniak  Léo Michel-Dansac 《Astrophysics and Space Science》2003,284(2):707-710

We have studied the evolution of isolated galaxies over several Gyr using a self-consistent N-body code including stars, gas and star formation. The results of our simulations are calibrated using spectrophotometric evolution models. We thus simultaneously analyse kinematical and photometrical evolution of the various stellar populations born during the successive bursts of star formation. Our calibrated simulations show that the properties of stellar velocity dispersion drops observed in the centre of three barred active galaxies by Emsellem et al. (2001) could depend on the observational wavelength. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

The evolution of stars and gas in starburst galaxies     

Roberto Cid Fernandes  João R. S. Leão  Reiner Rodrigues Lacerda 《Monthly notices of the Royal Astronomical Society》2003,340(1):29-42

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Observations of comet impact by reflections from the Galilean satellites     

Dietmar W. Foryta  João L. Kohl-Moreira  Daniela Lazzaro 《Earth, Moon, and Planets》1994,66(1):137-142

Results of observations of the Galilean satellites during the week of the impact of comet Shoemaker-Levy 9 on Jupiter are reported. These observations have been carried out at the Pico dos Dias observatory, at Brasópolis, Brazil. The satellites's light flux was monitored with a photometer during the time of the predicted impact of fragments B, F, J and L. No conclusive flash was observed in any of the data adquired. This non-detection imposes an upper limit to the energy released during the impact of these fragments.Observations carried out at the Observatório do Pico dos Dias, operated by the Laboratório Nacional de Astrofísica/CNPq/MCT, Brazil  相似文献   

Relative current effect on short wave growth     

Guimarães  Pedro Veras  Ardhuin  Fabrice  Perignon  Yves  Benetazzo  Alvise  Bouin  Marie-Noëlle  Garnier  Valerie  Redelsperger  Jean-Luc  Accensi  Mickael  Thomson  Jim 《Ocean Dynamics》2022,72(8):621-639

Ocean Dynamics - Short waves growth is characterized by nonlinear and dynamic processes that couple ocean and atmosphere. Ocean surface currents can have a strong impact on short wave steepness and...  相似文献   

A method of downscaling temperature maps based on analytical hillshading for use in species distribution modelling     

Á.M. Felicísimo Pérez  M.Á. Martín-Tardío 《制图学和地理信息科学》2018,45(4):329-338

Climate maps have been widely used for the construction of species distribution models. These maps derive from interpolation of data collected by meteorological stations. The sparse distribution of stations generates maps with coarse spatial resolution that are unable to detect microclimates or areas that can serve as plant or animal refuges. This work proposes a method for downscaling temperature maps using the solar radiation falling upon hillsides as predictor for the influence of relief on local variability. Solar irradiance is estimated from a digital elevation model of the study area using a routine based on analytical hillshading. Some examples of downscaling from 1 km to 25 m spatial resolution are shown. The results are compared with the surface temperature maps from Landsat 8 satellite imagery.  相似文献