The gigantic interacting galaxy NGC 6872     

C. Horellou  B. Koribalski 《Astrophysics and Space Science》2003,284(2):499-502

The luminous barred galaxy NGC 6872 is one of the largest spiral galaxies known. Star formation is traced all along the arms, which extend over more than 100 kpc. The galaxy is likely to be affected by tidal perturbations from the nearby companion IC 4970 passing by on a low-inclination, prograde orbit. We have mapped the large-scale distribution and kinematics of the atomic gas in the NGC 6872/IC 4970 system and carried out N-body simulations. Our aim is to investigate the evolution of gas and stars in such close encounters, examine the influence of a dark matter halo on the length of the tidal tails, and test models of collisionally induced star formation. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Occurrence of varved lake sediment sequences in Varmland, west central Sweden: lake characteristics, varve chronology and AMS radiocarbon dating     

LOVISA ZILLÉN  IAN SNOWBALL  PER SANDGREN  TANIA STANTON 《Boreas: An International Journal of Quaternary Research》2003,32(4):612-626

Varved lake sediments can be used to set multiple environmental proxies within a calendar year time scale. We undertook a systematic survey of lakes in the Province of Värmland, west central Sweden, with the aim of finding continuous varved lake sediment sequences covering the majority of the Holocene. In Fennoscandia, such sediments have previously only been recorded in northern Sweden and in southern and central Finland. By following a selective process and fieldwork we discovered three new varved sites (i.e. Furskogstjärnet, Mötterudstjärnet and Kälksjön). We found that lakes with varved sediments have several common lake morphometry properties and lake catchment characteristics such as maximum water depth, maximum water depth/lake surface area ratio, catchment soil types, altitude and number of inflows. Varve chronologies, supported by AMS-¹⁴C dating and tephrochronology were established for two of the sediment profiles. These varve chronologies are the longest geological records with an annual resolution known to exist in Sweden. In Furskogstjärnet, the AMS- ¹⁴C dates based on terrestrial plant macrofossils at several levels deviate significantly from the varve based time-depth curve. In Motterudstjarnet, a fully reasonable time-depth model based on the ¹⁴C dates gives older ages in the lower part of the sequence compared to the varve chronology. These results highlight that seemingly acceptable AMS radiocarbon dates may be erroneous. They also point to the fact that varved lake sediments are reliable geological archives with respect to chronological control and accuracy. Thus, these archives should be of prime interest for studies of climate and environmental change undertaken with the aim of providing sub-decadal resolution proxy data sets.  相似文献   

High-resolution δ¹³C measurements on ancient air extracted from less than 10 cm³ of ice     

M. C. LEUENBERGER  M. EYER  P. NYFELER  B. STAUFFER  T. F. STOCKER 《Tellus. Series B, Chemical and physical meteorology》2003,55(2):138-144

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The evolution of binary fractions in globular clusters     

N. Ivanova  K. Belczynski  J. M. Fregeau  F. A. Rasio 《Monthly notices of the Royal Astronomical Society》2005,358(2):572-584

We study the evolution of binary stars in globular clusters using a new Monte Carlo approach combining a population synthesis code ( startrack ) and a simple treatment of dynamical interactions in the dense cluster core using a new tool for computing three- and four-body interactions ( fewbody ). We find that the combination of stellar evolution and dynamical interactions (binary–single and binary–binary) leads to a rapid depletion of the binary population in the cluster core. The maximum binary fraction today in the core of a typical dense cluster such as 47 Tuc, assuming an initial binary fraction of 100 per cent, is only ∼ 5–10 per cent. We show that this is in good agreement with recent Hubble Space Telescope observations of close binaries in the core of 47 Tuc, provided that a realistic distribution of binary periods is used to interpret the results. Our findings also have important consequences for the dynamical modelling of globular clusters, suggesting that 'realistic models' should incorporate much larger initial binary fractions than has usually been the case in the past.  相似文献   

Richtmyer-Meshkov Experiments on the Omega Laser     

R. M. Hueckstaedt  S. H. Batha  M. M. Balkey  N. D. Delamater  J. R. Fincke  R. L. Holmes  N. E. Lanier  G. R. Magelssen  J. M. Scott  J. M. Taccetti  C. J. Horsfield  K. W. Parker  S. D. Rothman 《Astrophysics and Space Science》2005,298(1-2):255-259

Observations of the interstellar medium reveal a dynamic realm permeated by shocks. These shocks are generated on a large range of scales by galactic rotation, supernovae, stellar winds, and other processes. Whenever a shock encounters a density interface, Richtmyer-Meshkov instabilities may develop. Perturbations along the interface grow, leading to structure formation and material mixing. An understanding of the evolution of Richtmyer-Meshkov instabilities is essential for understanding galactic structure, molecular cloud morphology, and the early stages of star formation. An ongoing experimental campaign studies Richtmyer-Meshkov mixing in a convergent, compressible, miscible plasma at the Omega laser facility. Cylindrical targets, consisting of a low density foam core and an aluminum shell covered by an epoxy ablator, are directly driven by fifty laser beams. The aluminum shell is machined to produce different perturbation spectra. Surface types include unperturbed (smooth), single-mode sinusoids, multi-mode (rough), and multi-mode with particular modes accentuated (specified-rough). Experimental results are compared to theory and numerical simulations.  相似文献   

The correlation of solar flare production with magnetic energy in active regions     

E. B. Mayfield  John K. Lawrence 《Solar physics》1985,96(2):293-305

An investigation of 531 active regions was made to determine the correlation between energy released by flares and the available energy in magnetic fields of the regions. Regions with magnetic flux greater than 10²¹ maxwell during the years 1967–1969, which included sunspot maximum, were selected for the investigation. A linear regression analysis of flare production on magnetic flux showed that the flare energy is correlated with magnetic energy with a coeificient of correlation of 0.78. Magnetic classification and field configuration also significantly affect the production of flares.This work was supported by the Aerospace Sponsored Research Program.  相似文献   

Effect of metamorphism and partial melting of host rocks on zircons     

L. N. GUPTA  W. JOHANNES 《Journal of Metamorphic Geology》1985,3(3):311-323

Abstract Zircons have been studied from different layers of migmatites (from Arvika, western Sweden and Nelaug, southern Norway) and from a paragneiss (from Arvika) associated with one of the migmatites. The main purpose of the investigation is to establish whether or not information about zircons can help in the elucidation of the parentage and rock-forming processes of migmatites.
The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence of characteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting.  相似文献   

The nature of Europa's dark non-ice surface material: Spatially-resolved high spectral resolution spectroscopy from the Keck telescope     

John R. Spencer  William M. Grundy  Robert W. Carlson  Gary B. Hansen 《Icarus》2006,182(1):202-210

We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra.  相似文献   

The induced turbulence effect on propagation of radio emission in pulsar magnetospheres     

Qinghuan Luo  D. B. Melrose 《Monthly notices of the Royal Astronomical Society》2006,371(3):1395-1404

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The Faint Sky Variability Survey – I. Goals and data reduction process     

P. J. Groot  P. M. Vreeswijk  M. E. Huber  M. E. Everett  S. B. Howell  G. Nelemans  J. van Paradijs  E. P. J. van den Heuvel  T. Augusteijn  E. Kuulkers  R. G. M. Rutten  J. Storm 《Monthly notices of the Royal Astronomical Society》2003,339(2):427-434

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