Kinematics of globular cluster systems and the formation of early-type galaxies     

K. Bekki  Michael A. Beasley  Jean P. Brodie  Duncan A. Forbes 《Monthly notices of the Royal Astronomical Society》2005,363(4):1211-1222

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The globular cluster kinematics and galaxy dark matter content of NGC 4649 (M60)     

Terry Bridges  Karl Gebhardt  Ray Sharples  Favio Raul Faifer  Juan C. Forte  Michael A. Beasley  Stephen E. Zepf  Duncan A. Forbes  David A. Hanes  Michael Pierce 《Monthly notices of the Royal Astronomical Society》2006,373(1):157-166

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Simultaneous modelling of the stellar halo and globular cluster system of NGC 5128     

Michael. A. Beasley  William E. Harris  Gretchen L. H. Harris  Duncan A. Forbes 《Monthly notices of the Royal Astronomical Society》2003,340(1):341-352

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UBRI photometry of globular clusters in the Leo group galaxy NGC 3379     

Shannon Whitlock  Duncan A. Forbes  Michael A. Beasley 《Monthly notices of the Royal Astronomical Society》2003,345(3):949-959

We present wide-area UBRI photometry for globular clusters around the Leo group galaxy NGC 3379. Globular cluster candidates are selected from their B -band magnitudes and their  ( U − B ) _o   versus  ( B − I ) _o   colours. A colour–colour selection region was defined from photometry of the Milky Way and M31 globular cluster systems. We detect 133 globular cluster candidates, which supports previous claims of a low specific frequency for NGC 3379.
The Milky Way and M31 reveal blue and red subpopulations, with  ( U − B ) _o   and  ( B − I ) _o   colours indicating mean metallicities similar to those expected based on previous spectroscopic work. The stellar population models of Maraston and Brocato et al. are consistent with both subpopulations being old, and with metallicities of  [Fe/H]∼−1.5  and −0.6 for the blue and red subpopulations, respectively. The models of Worthey do not reproduce the  ( U − B ) _o   colours of the red (metal-rich) subpopulation for any modelled age.
For NGC 3379 we detect a blue subpopulation with similar colours, and presumably age/metallicity, to that of the Milky Way and M31 globular cluster systems. The red subpopulation is less well defined, perhaps due to increased photometric errors, but indicates a mean metallicity of [Fe/H]∼−0.6.  相似文献   

Evolutionary history of the elliptical galaxy NGC 1052     

Michael Pierce  Jean P. Brodie  Duncan A. Forbes  Michael A. Beasley  Robert Proctor  Jay Strader 《Monthly notices of the Royal Astronomical Society》2005,358(2):419-431

We have obtained Keck spectra for 16 globular clusters (GCs) associated with the merger remnant elliptical NGC 1052, as well as a long-slit spectrum of the galaxy. We derive ages, metallicities and abundance ratios from simple stellar population models using the recently published methods of Proctor & Sansom , applied to extragalactic GCs for the first time. A number of GCs indicate the presence of strong blue horizontal branches that are not fully accounted for in the current stellar population models. We find all of the GCs to be ∼13 Gyr old according to simple stellar populations, with a large range of metallicities. From the galaxy spectrum we find NGC 1052 to have a luminosity-weighted central age of ∼2 Gyr and metallicity of  [Fe/H]∼+0.6  . No strong gradients in either age or metallicity were found to the maximum radius measured  (0.3  r _e≃ 1 kpc)  . However, we do find a strong radial gradient in α-element abundance, which reaches a very high central value. The young central starburst age is consistent with the age inferred from the H  i tidal tails and infalling gas of ∼1 Gyr. Thus, although NGC 1052 shows substantial evidence for a recent merger and an associated starburst, it appears that the merger did not induce the formation of new GCs, perhaps suggesting that little recent star formation occurred. This interpretation is consistent with 'frosting' models for early-type galaxy formation.  相似文献   

A robust method for the analysis of integrated spectra from globular clusters using Lick indices     

Robert N. Proctor  Duncan A. Forbes  Michael A. Beasley 《Monthly notices of the Royal Astronomical Society》2004,355(4):1327-1338

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Widespread Neogene volcanism on Central Kerguelen Plateau,Southern Indian Ocean     

R. A. Duncan  T. J. Falloon  P. G. Quilty  M. F. Coffin 《Australian Journal of Earth Sciences》2016,63(4):379-392

We report new age determinations and compositions for rocks from 18 dredge hauls collected from eight submarine areas across Central Kerguelen Plateau (CKP). Sea knolls and volcanic fields with multiple small cones were targeted over a ～125 000 km² region that includes Heard and McDonald Islands. Large early Miocene (22–16 Ma) sea knolls rise from the western margin of the CKP and are part of a NNW–SSE line of volcanic centres that lie between Îles Kerguelen and Heard and McDonald Islands. These are probably related to hotspot activity now underlying the Heard Island area. We see evidence of much younger activity (5 Ma to present) in volcanic fields to the north of, and up to 300 km NE of, Heard Island. Compositions include basanite, basalt and trachybasalt, which are broadly similar to plateau lava flows from nearby Ocean Drilling Program Site 1138, lower Miocene lavas at Îles Kerguelen, dredged rocks from the early Miocene sea knolls, and Big Ben lavas from Heard Island. Geochemical data indicate decreasing fractions of mantle source melting with time. We propose that a broad region of the CKP became volcanically active in Neogene time owing to incubation of plume material at the base of the relatively stationary overlying plateau. The presence of pre-existing crustal faults gave access for melts from the Heard mantle plume to rise to the surface.  相似文献   

Consortium study of the unusual H chondrite regolith breccia,Noblesville     

Michael E. Lipschutz  Stephen F. Wolf  Stephan Vogt  Edward Michlovich  Marilyn M. Lindstrom  Michael E. Zolensky  David W. Mittlefehldt  Cecilia Satterwhite  Ludolf Schultz  Thomas Loeken  Peter Scherer  Robert T. Dodd  Derek W. G. Sears  Paul H. Benoit  John F. Wacker  Roger G. Burns  Duncan S. Fisher 《Meteoritics & planetary science》1993,28(4):528-537

Abstract— The Noblesville meteorite is a genomict, regolith breccia (H6 clasts in H4 matrix). Mössbauer analysis confirms that Noblesville is unusually fresh, not surprising in view of its recovery immediately after its fall. It resembles “normal” H4–6 chondrites in its chemical composition and induced thermoluminescence (TL) levels. Thus, at least in its contents of volatile trace elements, Noblesville differs from other H chondrite, class A regolith breccias. Noblesville's small pre-atmospheric mass and fall near Solar maximum and/or its peculiar orbit (with perihelion <0.8 AU as shown by natural TL intensity) may partly explain its levels of cosmogenic radionuclides. Its cosmic ray exposure age of ～ 44 Ma, is long, is equalled or exceeded by <3% of all H chondrites, and also differs from the 33 ± 3 Ma mean exposure age peak of other H chondrite regolith breccias. One whole-rock aliquot has a high, but not unmatched, ¹²⁹Xe/¹³²Xe of 1.88. While Noblesville is now among the chondritic regolithic breccias richest in solar gases, elemental ratios indicate some loss, especially of He, perhaps b; impacts in the regolith that heated individual grains. While general shock-loading levels in Noblesville did not exceed 4 GPa, individual clasts record shock levels of 5–10 GPa, doubtless acquired prior to lithification of the whole-rock meteoroid.  相似文献   

AN INVESTIGATION OF SOIL STATUS AND LANDUSE ON A STEEPLY SLOPING HILLSIDE, BLUE MOUNTAINS, JAMAICA     

Duncan F. M. McGregor  B.Sc.  Ph.D. 《Singapore journal of tropical geography》1989,9(1):60-71

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ELECTROLYTIC CORROSION OF IRON METEORITES     

Stanford L. Tackett  Ray A. Tucker  Floyd R. Duncan 《Meteoritics & planetary science》1970,5(1):43-55

Six iron meteorites were electrolyzed and the resulting corrosion was studied by a potentiostatic technique. It was found that both iron and nickel in the kamacite phase dissolve, and that neither iron nor nickel dissolve from taenite. The rate of corrosion was shown to be inversely proportional to the nickel content. However, structure, as well as nickel content, plays an important part in the electrolytic process. The Coya Norte, Chile meteorite dissolved more rapidly and more easily (at a lower potential) than did pure iron even though the Coya Norte meteorite contains 5.5% nickel.  相似文献