Optical spectroscopy and photometry of SAX J1808.4−3658 in outburst     

P. Elebert  M. T. Reynolds  P. J. Callanan  D. J. Hurley  G. Ramsay  F. Lewis  D. M. Russell  B. Nord  S. R. Kane  D. L. DePoy  P. Hakala 《Monthly notices of the Royal Astronomical Society》2009,395(2):884-894

We present phase resolved optical spectroscopy and photometry of V4580 Sagittarii, the optical counterpart to the accretion powered millisecond pulsar SAX J1808.4−3658, obtained during the 2008 September/October outburst. Doppler tomography of the N  iii λ4640.64 Bowen blend emission line reveals a focused spot of emission at a location consistent with the secondary star. The velocity of this emission occurs at  324 ± 15 km s⁻¹  ; applying a ' K -correction', we find the velocity of the secondary star projected on to the line of sight to be  370 ± 40 km s⁻¹  . Based on existing pulse timing measurements, this constrains the mass ratio of the system to be  0.044^+0.005_−0.004  , and the mass function for the pulsar to be  0.44^+0.16_−0.13 M_⊙  . Combining this mass function with various inclination estimates from other authors, we find no evidence to suggest that the neutron star in SAX J1808.4−3658 is more massive than the canonical value of  1.4 M_⊙  . Our optical light curves exhibit a possible superhump modulation, expected for a system with such a low mass ratio. The equivalent width of the Ca  ii H and K interstellar absorption lines suggest that the distance to the source is ∼2.5 kpc. This is consistent with previous distance estimates based on type-I X-ray bursts which assume cosmic abundances of hydrogen, but lower than more recent estimates which assume helium-rich bursts.  相似文献   

RAT J1953+1859: a dwarf nova discovered through high amplitude QPOs in quiescence     

Gavin Ramsay  Pasi Hakala  Thomas Barclay  Peter Wheatley  George Marshall  Harry Lehto  Ralf Napiwotzki  Gijs Nelemans  Stephen Potter  Ian Todd 《Monthly notices of the Royal Astronomical Society》2009,398(3):1333-1338

We report the discovery of an accreting binary, RAT J1953+1859, made during the RApid Temporal Survey (RATS) on the Isaac Newton Telescope. It showed high amplitude (0.3 mag) quasi-periodic oscillations on a time-scale of ∼20 min. Further observations made using the Nordic Optical Telescope showed it to be ∼4 mag brighter than in the discovery images. These photometric observations, together with radial velocity data taken using the William Herschel Telescope, point to an orbital period of ∼90 min. These data suggest that RAT J1953+1859 is a dwarf novae of the SU UMa type. What makes RAT J1953+1859 unusual is that it is the first such system to be discovered as a result of high amplitude QPOs during quiescence. This suggests that high-cadence wide-field surveys could be another means to discover cataclysmic variables as a result of their short period variability.  相似文献   

Detrital zircon geochronology of the Speewah Group,Kimberley region,Western Australia: evidence for intracratonic development of the Paleoproterozoic Speewah Basin     

R. R. Ramsay  A. E. Eves  M. T. D. Wingate  G. Batt  K. Rogers 《Australian Journal of Earth Sciences》2017,64(3):419-434

Field observations integrated with new petrographic and sensitive high-resolution ion microprobe (SHRIMP) U–Pb age data for detrital zircons from the Paleoproterozoic Speewah Group of northern Western Australia provide evidence of depositional conditions, source of detritus, timing and evolution of the sedimentary rocks in the Speewah Basin. The Speewah Group is a 1.5 km-thick succession of poorly outcropping, predominantly siliciclastic rocks that preserve a fluviatile to marine, transgressive and regressive event. The Speewah Group unconformably overlies crystalline rocks of the Lamboo Province that were stabilised by the 1870–1850 Ma Hooper Orogeny, then accreted as the Kimberley region onto the North Australian Craton during the 1835–1810 Ma Halls Creek Orogeny. Unconformably overlying the Speewah Group is about 4 km of predominantly siliciclastic marine sedimentary rocks of the Kimberley Group in the Kimberley Basin. This study has detected a detrital zircon component within the Speewah Basin at 1814 ± 10 Ma, with a youngest zircon at 1803 ± 12 Ma (1σ) in fluviatile sandstones located beneath a volcaniclastic rock with magmatic zircons that have been dated at ca 1835 Ma. Previous studies proposed that the Speewah Basin developed as a retro-arc foreland basin during accretion of the North Australian Craton. We interpret the ca 1835 Ma zircons in the volcaniclastic rocks to be xenocrystic in origin. This new 20 million years younger maximum depositional age indicates that the Speewah Group in the Speewah Basin, similarly to the overlying Kimberley Group in the Kimberley Basin, developed in a post-orogenic setting on the North Australian Craton rather than in a syn-orogenic setting associated with the 1835–1810 Ma Halls Creek Orogeny.  相似文献   

Bacterial populations,heterotrophic potentials,and water quality in three New Zealand Rivers     

M. J. Spencer  Angela J. Ramsay 《新西兰海洋与淡水研究杂志》2013,47(4):415-427

Abstract

Thirty sites were sampled in three New Zealand rivers (Waikato, Maitai, and Wakapuaka) during late summer 1977. Samples were collected from just below the surface at mid river or in the tailraces below hydro‐electric dams.

Parameters measured included bacterial numbers (direct counts), heterotrophic potential (V_max ), adenosine triphosphate (ATP), chlorophyll a (Chi a), and concentrations of nitrogen and phosphorus compounds.

Bacterial populations per millilitre fluctuated threefold (6.4–19.4 × 10⁵) along the Waikato River and were lower and more consistent in the two South Island rivers (1.46–2.55 × 10⁵). In contrast, V_max varied 5000‐fold in the Waikato River, from a characteristically oligotrophic value of 0.0035 μg. l^?1·h^?1 (Lake Taupo outlet) to a eutrophic value of 18.4 μg. l^?1·h^?1 at the Mihi bridge. V_max for the two South Island rivers ranged from 0.0091 to 0.189 μg. l^?1 · h^?1.

ATP, Chi a, Kjeldahl nitrogen, nitrate nitrogen, and total phosphorus concentrations for the 20 sites on the Waikato River varied in a similar way to the V_max and bacterial data. There were large peaks at the Mihi bridge, lower values for the dam tailraces and significant increases for the sites below Hamilton. Concentrations for these parameters were lower and more consistent along the lengths of the two South Island rivers.

Most parameters were significantly correlated with each other for the Waikato River samples. The strongest correlations were between V_max and bacterial numbers and between V_max and nitrate nitrogen. In the Maitai and Wakapuaka River series these correlations were also significant, but the only other significant correlations recorded there were between ATP and nitrate nitrogen, and between ATP and bacterial numbers.  相似文献   

Early Proterozoic regolith at Pasvik, NE Norway: palaeoenvironmental implications for the Baltic Shield     

Brian A. Sturt  Victor A. Melezhik  Donald M. Ramsay 《地学学报》1994,6(6):618-633

Regolith occurs at a number of localities along the northern margin of the early Proterozoic Pechenga Greenstone Belt marking a profound stratigraphic unconformity at the base of the 10 km thick Petsamo Supergroup. The age of regolith formation can be bracketed between 2.453 ± 42 Ga (Sm-Nd) and 2.330 ± 36 Ga (Rb-Sr). Regolith is developed on a varied substrate of Archaean rocks including early Proterozoic layered gabbros (2.45 Ga). The best example of the regolith occurs in the Pasvik valley at Brattli, Norway. Analogues are widespread on the Baltic Shield at the base of early Proterozoic 'greenstone belts' showing a low degree of chemical weathering and carbonatisation. Fluviatile deposits overlying the Brattli regolith preserve unweathered pyrite-magnetite boulders and terrigenous pyrite grains. These features are considered to relate an arid or semi-arid palaeoenvironment, possibly with some deficiency of oxygen in the atmosphere-hydrosphere system. A systematic and well-preserved regolith or palaeosaprolite at the base of the Petsamo Supergroup is proof that the northern boundary of the Pechenga Greenstone Belt is a fundamental first-order unconformity. This places constraints on geotectonic modelling of this early Proterozoic rift-basin.  相似文献   

Petrochemistry of lavas from the Central Arabian shield     

M.J. Roobol  C.R. Ramsay  N.J. Jackson  D.P.F. Darbyshire 《Precambrian Research》1982,16(4):A36-A37

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Great Barrier Island silver-gold deposits,Hauraki Province,New Zealand     

W. R. H. Ramsay  H. W. Kobe 《Mineralium Deposita》1974,9(2):143-153

The Great Barrier Island subvolcanic silver-gold deposits comprise a number of essentially east striking, quartz filled, mineralized fissures, which transect andesitic volcanics and an unconformably overlying, bedded sinter deposit of upper Tertiary to Quaternary age. Wall rock alteration is characterized by a propylitic assemblage in the least altered andesite, with argillic assemblages and silicification developed in close proximity to the veins. Some twentyfive hypogene and supergene ore minerals have been recognized, of which pyrite is the most common and finely disseminated pyrargyrite constitutes the main source of silver. The mineral assemblage is dominantly hypogene with minor supergene alteration occurring at surface exposures, and includes mainly sulfides, selenides and native metals. Fineness of electrum derived from two electron microprobe analyses is approximately 500, while total silver to gold ratio from a number of bulk chemical analyses is 30:1. Maximum depth of deposition is estimated to be in the order of 500 m and for some surface exposures 100 m. The mineralization is regarded as subvolcanic and along with other hydrothermal fissure deposits of Hauraki Province is considered to be of Pliocene-Pleistocene age, and hence is believed to be associated with the late phase extrusions and intrusions of acid magma in the volcanic belt.  相似文献   

The cordierite isograd in archaean meta-sediments near yellowknife,N.W.T., Canada-variations on an experimentally established reaction     

C. R. Ramsay 《Contributions to Mineralogy and Petrology》1974,47(1):27-40

In the Slave Craton, meta-sediments commonly exhibit broad, Abukuma-type metamorphic aureoles round late, potassic plutons. The rocks are divided into low and medium metamorphic grades by sharply-defined cordierite isograds. Comparison of mineral assemblages above and below one such isograd indicates that chlorite and muscovite were reactants. Biotite is present below the isograd, and textural relations suggest that it participated in the reaction. Micro-probe analyses of biotites in cordierite-free and cordieritebearing rocks, considered in the light of established pro-grade compositional changes, indicate that the biotite changed in composition during the reaction, supplying Si in exchange for Al^IV, Fe and Mg in exchange for Al^VI, and K in exchange for Na. The reaction can be balanced in a fashion consistent with all the observable evidence. The balancing operation indicates that abundant quartz and traces of albite and ilmenite also reacted, and that biotite became more abundant during the reaction. Thus the complex reaction can be approximated by the formula Chl+Musc+Biot(1)+Qtz [+Albite+Ilm] →Cord+Biot(2)+Water It is of a type extensively studied in experimental haplo-pelitic systems but was modified in the natural system mainly because additional phases participated. In particular, pre-existing biotite was compositionally modified and increased in amount during the reaction.  相似文献   

The impact of the 1998 coral mortality on reef fish communities in the Seychelles   总被引：6，自引：0，他引：6  

Spalding MD  Jarvis GE 《Marine pollution bulletin》2002,44(4):309-321

Coral reef fish communities in the Seychelles are highly diverse and remain less affected by the direct impacts of human activities than those on many other coral reefs in the Indian Ocean. These factors make them highly suitable for a detailed survey of the impacts of the 1998 mass coral mortality, which devastated the coral faunas of the region. Using underwater visual census (UVC) techniques. fish communities were sampled in three localities in the southern Seychelles and one locality in the northern (granitic) Seychelles. Initial surveys were undertaken from the latter site in 1997. Surveys were undertaken at all sites during the coral bleaching episode in 1998 prior to any major changes in the reef fish communities. Repeat surveys were undertaken in 1999 one year after the coral mortality. Over 250 fish species were sampled from 35 families. Results suggest that changes in the overall fish community structures are not great, despite massive changes in the benthic cover. Significant changes have been observed in a number of individual species. These include those most heavily dependent on live coral cover for shelter or sustenance. Future potential changes are discussed, and potential management interventions are considered.  相似文献   

Gas, and how to get it     

Gavin Bridge 《Geoforum》2004,35(4):395-397

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