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1.
Timothy Pietsch Justine Kemp Colin Pardoe Rainer Grün Jon Olley Rachel Wood 《第四纪科学杂志》2019,34(8):662-673
Kiacatoo Man, a large, rugged Aboriginal adult buried in the Lachlan riverine plains of southeastern Australia, was discovered in 2011. Laser‐ablation uranium series analysis on bone yielded a minimum age for the burial of 27.4 ± 0.4 ka (2σ). Single‐grain, optically stimulated luminescence ages on quartz sediment in which the grave had been dug gave a weighted mean age of 26.4 ± 1.5 ka (1σ). Luminescence samples from the grave infill and from sediment beneath the grave exhibit overdispersed dose distributions consistent with bioturbation or other disturbance, which has obscured the burial signal. The overlap between the minimum (U‐series) and maximum (luminescence) ages places the burial between 27.0 and 29.4 ka (2σ). Luminescence ages obtained from the channel belt of between 28 ± 2 and 25 ± 3 ka indicate that fluvial sedimentation was occurring before the Last Glacial Maximum, which is consistent with the broader geomorphic setting. Together, these results are internally and regionally consistent, and indicate that Kiacatoo Man was one of the more ancient individuals so far identified in Australia. His remains are important to our understanding of patterns of biological variation and other processes that have shaped people in the Murray‐Darling Basin through time. Copyright © 2019 John Wiley & Sons, Ltd. 相似文献
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Several physical and observational effects may contribute to the significant imbalances of magnetic flux that are often observed in active regions. We consider an effect not previously treated: the influence of electric currents in the photosphere. Electric currents can cause a line-of-sight flux imbalance because of the directionality of the magnetic field they produce. Currents associated with magnetic flux tubes produce larger imbalances than do smoothly-varying distributions of flux and current. We estimate the magnitude of this effect for current densities, total currents, and magnetic geometry consistent with observations. The expected imbalances lie approximately in the range 0–15%, depending on the character of the current-carrying fields and the angle from which they are viewed. Observationally, current-induced flux imbalances could be indicated by a statistical dependence of the imbalance on angular distance from disk center. A general study of magnetic flux balance in active regions is needed to determine the relative importance of other - probably larger -effects such as dilute flux (too weak to measure or rendered invisible by radiative transfer effects), merging with weak background fields, and long-range connections between active regions.Operated for the National Science Foundation by the Association of Universities for Research in Astronomy. 相似文献
4.
The occultation of Io by Ganymede as observed on 10 June 1985 is reported. The middle of the occultation minimum was found to occur at 14h 14m 5.7s UT. In the plane perpendicular to the line of sight the centres of the two satellite disks passed to within ~ 2530 km of each other, at a relative velocity, in this plane, of about 11 kms–1. The values of these last two quantities, however, depend on what assumptions are made about the light distribution over io's disk. 相似文献
5.
It is shown how the hard X-ray burst count rate and itse-folding ime can be used to estimate the minimum magnetic fieldB
min required in a flare magnetic reconnection site for the burst to be interpreted in terms of a thick target model. Application of the method to data from the Solar Maximum Mission (HXRBS) indicates absolute minimum fields well in excess of 100 G, and impossibly high values for some reconnection geometries. 相似文献
6.
K. Iwasawa A.C. Fabian S.W. Allen S. Ettori 《Monthly notices of the Royal Astronomical Society》2001,328(1):L5-L10
We report on the metal distribution in the intracluster medium around the radio galaxy 4C+55.16 observed with the Chandra X-ray Observatory . The radial metallicity profile shows a dramatic change at 10 arcsec (∼50 kpc) in radius from half solar to twice solar at inner radii. Also found was a plume-like feature located at ∼3 arcsec to the south-west of the centre of the galaxy, which is mostly accounted for by a strong enhancement of iron L emission. The X-ray spectrum of the plume is characterized by the metal abundance pattern of Type Ia supernovae (SNeIa), i.e. large ratios of Fe to α elements, with the iron metallicity being unusually high at solar (90 per cent error). How the plume has been formed is not entirely clear. The inhomogeneous iron distribution suggested in this cluster provides important clues to understanding the metal enrichment process of the cluster medium. 相似文献
7.
Steven J. Ostro Lance A. M. Benner Christopher Magri Jon D. Giorgini Randy Rose Raymond F. Jurgens Donald K. Yeomans Alice A. Hine Michael C. Nolan Daniel J. Scheeres Stephen B. Broschart Mikko Kaasalainen Jean‐Luc Margot 《Meteoritics & planetary science》2005,40(11):1563-1574
Abstract— We present June 2004 radar images of asteroid 25143 Itokawa (1998 SF36) that improve upon the longitude‐latitude coverage of images obtained in 2001 by Ostro et al. (2004) and use the 2001–2004 data to refine that paper's constraints on Itokawa's shape. The 2004 images, the first of the asteroid's southern side, look distinctly different from the 2001 images, revealing leading edges that are much more curved and rugged than the nearly convex leading edges seen at northern latitudes in 2001. Itokawa is shaped like a slightly asymmetrical, bent, lumpy ellipsoid with dimensions along the principal axes within 10% of 594 times 320 times 288 m. To illustrate the uncertainty space associated with shape reconstruction from images with suboptimal orientational coverage, we present two alternative three‐dimensional models of the object. 相似文献
8.
S. W. Allen R. W. Schmidt A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2002,334(2):L11-L15
We present precise measurements of the X-ray gas mass fraction for a sample of luminous, relatively relaxed clusters of galaxies observed with the Chandra observatory, for which independent confirmation of the mass results is available from gravitational lensing studies. Parametrizing the total (luminous plus dark matter) mass profiles using the model of Navarro, Frenk & White, we show that the X-ray gas mass fractions in the clusters asymptote towards an approximately constant value at a radius r 2500 , where the mean interior density is 2500 times the critical density of the Universe at the redshifts of the clusters. Combining the Chandra results on the X-ray gas mass fraction and its apparent redshift dependence with recent measurements of the mean baryonic matter density in the Universe and the Hubble constant determined from the Hubble Key Project, we obtain a tight constraint on the mean total matter density of the Universe, , and measure a positive cosmological constant, . Our results are in good agreement with recent, independent findings based on analyses of anisotropies in the cosmic microwave background radiation, the properties of distant supernovae, and the large-scale distribution of galaxies. 相似文献
9.
Guinevere Kauffmann Timothy M. Heckman Simon D. M. White Stéphane Charlot Christy Tremonti Jarle Brinchmann Gustavo Bruzual Eric W. Peng Mark Seibert Mariangela Bernardi Michael Blanton Jon Brinkmann Francisco Castander Istvan Csábai Masataka Fukugita Zeljko Ivezic Jeffrey A. Munn Robert C. Nichol Nikhil Padmanabhan Aniruddha R. Thakar David H. Weinberg Donald York 《Monthly notices of the Royal Astronomical Society》2003,341(1):33-53
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