ASOCAM Observations of CYG X-3: Search for a Hot Stellar Wind     

R.N. Ogley  S.J. Bell Burnell  R.P. Fender 《Astrophysics and Space Science》1997,255(1-2):205-210

Six CAM observations have been made in the 4 - 14 μm wavelength region to search for further evidence of emission from a hot stellar wind. Initial results suggest that the spectrum detected by Fender et al. using UKIRT extends into the wavelength region covered by ISOCAM. There is also evidence that the source is variable on timescales of ≈ 70 seconds. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Nature and completeness of galaxies detected in the Two Micron All Sky Survey     

Daniel H. McIntosh  Eric F. Bell  Martin D. Weinberg  Neal Katz 《Monthly notices of the Royal Astronomical Society》2006,373(4):1321-1338

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Evolution and Morphodynamics of a Prograded Beach‐Ridge Foreland,Northern Baffin Island,Canadian Arctic Archipelago          下载免费PDF全文

Dominique St‐Hilaire‐Gravel  Donald L. Forbes  Trevor Bell 《Geografiska Annaler: Series A, Physical Geography》2015,97(3):615-631

Landward retreat (marine transgression) is a common response of coastal systems to rising relative sea level. However, given sufficient sediment supply, the coast may advance seaward. The latter response of gravel barriers has been recorded in parts of southeastern and northwestern Canada, where seaward‐rising sets of beach ridges are observed in areas of Holocene RSL rise. Cape Charles Yorke, northern Baffin Island, is a 5 km long gravel foreland characterized by seaward‐rising beach‐ridge crest elevations. The prograded morphology of the Cape Charles Yorke foreland is a prime example of coastal response to a combination of rising RSL and abundant sediment supply, an unusual and little‐documented pattern in the Canadian Arctic. The main gravel supply to Cape Charles Yorke is likely from eroding bedrock and raised marine deposits southwest of the foreland. Although not the dominant sediment source, the Cape Charles Yorke delta contributed to the formation of the foreland by sheltering it from easterly storm waves and providing an anchor point for the prograding ridges. The truncation of relict ridges by the modern shoreline suggests a recent regime shift from continuous deposition to predominant erosion. The cause and timing of this shift are unknown but could result from a recent dwindling in sediment supply, increased accommodation space, increased wave energy, and/or an accelerated rise of relative sea level.  相似文献   

Crystal chemistry of merrillite from Martian meteorites: Mineralogical recorders of magmatic processes and planetary differentiation          下载免费PDF全文

C. K. Shearer  P. V. Burger  J. J. Papike  F. M. McCubbin  A. S. Bell 《Meteoritics & planetary science》2015,50(4):649-673

Merrillite is a ubiquitous accessory phase in a variety of Martian meteorite lithologies. The Martian merrillites exhibit a positive correlation between Mg# and Na and a negative correlation between Mg# and both Mn and vacancies in the octahedral Na‐site. Their REE patterns are varied and range from LREE‐depleted to LREE‐enriched. The dominant cation substitutions in the Martian merrillites are Fe²⁺_{VI Mg‐site}?Mg²⁺_{VI Mg‐site} and Ca²⁺_{VI Na‐site} +  □_{VI Na‐site}?2Na⁺_{VI Na‐site}. The REE substitution into the 8‐fold coordinated Ca‐site is accommodated by the coupled substitution Ca_{VIII Ca‐site} + (Na)_{VI Na‐site} ?(Y³⁺ + REE³⁺)_{VIII Ca‐site} + □_{VI Na‐site}. The REE substitution is significantly more prevalent in lunar merrillite and can be used as a “fingerprint” to distinguish lunar from Martian meteorites. The substitution of OH^? (whitlockite) and/or F^? (bobdownsite) for O^2? on one of the phosphate tetrahedrons appears to be rather insignificant. The correlations among Na, Mg#, Mn, and Na‐site vacancies are linked to the premerrillite crystallization history of the melt and the crystal chemical behavior of the Mg‐ and Na‐sites. The former reflects the sequence and extent of plagioclase and pyroxene crystallization. The differences in REE pattern shapes among the merrillites reflect source regions for the Martian basalts and the shapes are not greatly perturbed by the crystallization history. The occurrence of merrillite does not imply low‐volatile component in the Martian magmas. However, the low whitlockite and bobdownsite contents suggest that these samples were not altered by hydrothermal fluids and therefore not reset owing to aqueous fluid interactions. Consequently, the young ages of the shergottites are probably true igneous crystallization ages.  相似文献   

Molecular line intensities as measures of cloud masses – I. Sensitivity of CO emissions to physical parameter variations     

T. A. Bell  E. Roueff  S. Viti  D. A. Williams 《Monthly notices of the Royal Astronomical Society》2006,371(4):1865-1872

A reliable estimate of the molecular gas content in galaxies plays a crucial role in determining their dynamical and star-forming properties. However, H₂, the dominant molecular species, is difficult to observe directly, particularly in the regions where most molecular gas is thought to reside. Its mass is therefore commonly inferred by assuming a direct proportionality with the integrated intensity of the  ¹²CO( J = 1 → 0)  emission line, using a CO-to-H₂ conversion factor, X . Although a canonical value for X is used extensively in such estimates, there is increasing evidence, both theoretical and observational, that the conversion factor may vary by over an order of magnitude under conditions different from those of the local neighbourhood. In an effort to understand the influence of changing environmental conditions on the conversion factor, we derive theoretical estimates of X for a wide range of physical parameters using a photon-dominated region (PDR) time-dependent chemical model, benchmarking key results against those of an independent PDR code to ensure reliability. Based on these results, the sensitivity of the X factor to change in each physical parameter is interpreted in terms of the chemistry and physical processes within the cloud. In addition to confirming previous observationally derived trends, we find that the time-dependence of the chemistry, often neglected in such models, has a considerable influence on the value of the conversion factor.  相似文献   

Measurements of winds on Mars with Hubble Space Telescope images in 2003 opposition     

V.G. Kaydash  M.A. Kreslavsky  Yu.G. Shkuratov  J.F. Bell III 《Icarus》2006,185(1):97-101

The winds of Mars at the water cloud level are measured by tracking cloud features in sequential high-resolution Hubble Space Telescope UV images for 5 days during the perihelion season in 2003. Global circulation model (GCM) predictions are in general agreement with the observations for the zonal wind component, but reveal significant differences for the meridional component.  相似文献   

The interaction of cosmic rays and magnetized plasma     

A. R. Bell 《Monthly notices of the Royal Astronomical Society》2005,358(1):181-187

A large flux of cosmic rays streaming through a magnetized plasma creates cavities of low plasma density and low magnetic field. The magnetic field focuses the cosmic ray trajectories into the cavities with the possible formation of filaments or beams of high-energy cosmic rays.  相似文献   

The dark side of Iapetus     

D.P. Cruikshank  J.F. Bell  M.J. Gaffey  R.Hamilton Brown  R. Howell  C. Beerman  M. Rognstad 《Icarus》1983,53(1):90-104

This paper presents new photometric and spectrophotometric observations of the dark (leading) hemisphere of Saturn's satellite Iapetus. Spectrophotometry from 0.3–1.0 um (May 1979) shows the dark hemisphere to be very red, similar to a few asteroids and the Moon, but with no spectral features attributable to olivine or pyroxene. Near-infrared spectrophometry in the regions 1.4–2.5 um (May 1981) and 3.0–3.8 um (February 1981) reveals water ice absorption bands, probably resulting from the polar caps intruding onto the dark hemisphere. The reflectance of Iapetus is unlike that of carbonaceous chondrites or C-type asteroids and most closely resembles the reflectance (and low albedo) of carbonaceous (organic) residue from the Murchison C2 carbonaceous chondrite. The Murchison material has the same red slope and a probable spectral feature near 0.6 um seen in Iapetus data. Three hypotheses for the formation of the dark hemisphere are discussed in light of the observational data. The favored hypothesis is that debris from Phoebe or other unknown outer satellites of Saturn impacts the dark hemisphere of Iapetus as Poynting-Robertson drag causes the debris to spiral toward Saturn. The high-velocity impacts preferentially remove ice from the satellite's surface, causing enrichment of included carbonaceous material intrinsic to Iapetus. The reflectance of Phoebe itself is significantly different from that of Iapetus, suggesting that relatively little Phoebe debris lies on the dark hemisphere. There remains the possibility that the impacting debris originates from another body of composition similar to the Murchison residue and that this material is exposed on the surface of Iapetus.  相似文献   

The properties of spiral galaxies: confronting hierarchical galaxy formation models with observations     

Eric F. Bell  Carlton M. Baugh  Shaun Cole  Carlos S. Frenk  Cedric G. Lacey 《Monthly notices of the Royal Astronomical Society》2003,343(2):367-384

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Neutron monitor observations of high-energy solar particles during the new cycle     

G. A. Baird  G. G. Bell  S. P. Duggal  M. A. Pomerantz 《Solar physics》1967,2(4):491-501

After a lapse of five years, the first solar events in which particles were emitted with sufficiently high energies to produce intensity enhancements in ground-based neutron monitors occurred on July 7, 1966, and January 28, 1967. Although the magnitude of the first of these increases was too small (<2%) to permit detailed analysis, the later event, which exceeded 18% at sea-level stations in the polar regions, displayed unusual characteristics. The January 28 event is anomalous in that either it represents the first observation of solar particles reaching the earth from the back side of the sun, or it is associated with a feeble flare (1-) in the unfavored eastern hemisphere of the visible disk. The propagation of solar particles in this event was evidently controlled by a diffusion mechanism, and the observations are consistent with predictions based on alternative theoretical models of this process.This work was supported by the U.S. National Science Foundation and the U.S. Air Force Cambridge Research Laboratories, Office of Aerospace Research.  相似文献