Two-temperature accretion flows in magnetic cataclysmic variables: structures of post-shock emission regions and X-ray spectroscopy     

Curtis J. Saxton  Kinwah Wu  Mark Cropper  Gavin Ramsay 《Monthly notices of the Royal Astronomical Society》2005,360(3):1091-1104

We use a two-temperature hydrodynamical formulation to determine the temperature and density structures of the post-shock accretion flows in magnetic cataclysmic variables (mCVs) and calculate the corresponding X-ray spectra. The effects of two-temperature flows are significant for systems with a massive white dwarf and a strong white-dwarf magnetic field. Our calculations show that two-temperature flows predict harder keV spectra than one-temperature flows for the same white-dwarf mass and magnetic field. This result is insensitive to whether the electrons and ions have equal temperature at the shock, but depends on the electron–ion exchange rate, relative to the rate of radiative loss along the flow. White-dwarf masses obtained by fitting the X-ray spectra of mCVs using hydrodynamic models including the two-temperature effects will be lower than those obtained using single-temperature models. The bias is more severe for systems with a massive white dwarf.  相似文献   

XMM–Newton EPIC observations of Her X-1     

Gavin Ramsay  Silvia Zane  Mario A. Jimenez-Garate  Jan-Willem den Herder  C. J. Hailey 《Monthly notices of the Royal Astronomical Society》2002,337(4):1185-1192

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The 2dF Galaxy Redshift Survey: galaxy luminosity functions per spectral type     

Darren S. Madgwick  Ofer Lahav  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Ian Lewis  Stuart Lumsden  Steve Maddox  Peder Norberg  John A. Peacock  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,333(1):133-144

We calculate the optical b _J luminosity function (LF) of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, η , which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission- and absorption-line strength in the galaxy rest frame spectrum, and hence is a useful indicator of the present star formation. We use a total of 75 000 galaxies in our calculations, chosen from a sample of high signal-to-noise ratio, low-redshift galaxies observed before 2001 January. We find that there is a systematic steepening of the faint-end slope ( α ) as one moves from passive  ( α =-0.54)  to active  ( α =-1.50)  star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude   M *-5 log₁₀( h )  (from −19.6 to −19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies  [ M _{b J}-5 log₁₀( h )  fainter than −16.0], perhaps suggesting the presence of a significant dwarf population. The LFs presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent k -corrections, and investigate possible fibre-aperture biases.  相似文献   

Parameter constraints for flat cosmologies from cosmic microwave background and 2dFGRS power spectra     

Will J. Percival  Will Sutherland  John A. Peacock  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Stephen Moody  Peder Norberg  Bruce A. Peterson  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,337(3):1068-1080

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The 2dF Galaxy Redshift Survey: the dependence of galaxy clustering on luminosity and spectral type   总被引：1，自引：0，他引：1  

Peder Norberg  Carlton M. Baugh  Ed Hawkins  Steve Maddox  Darren Madgwick  Ofer Lahav  Shaun Cole  Carlos S. Frenk  Ivan Baldry  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Matthew Colless  Chris Collins  Warrick Couch  Gavin Dalton  Roberto De Propris  Simon P. Driver  George Efstathiou  Richard S. Ellis  Karl Glazebrook  Carole Jackson  Ian Lewis  Stuart Lumsden  John A. Peacock  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2002,332(4):827-838

We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal-component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late types') and more quiescent galaxies ('early types'). We measure the clustering in real space, free from any distortion of the clustering pattern owing to peculiar velocities, for a series of volume-limited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range  2<( σ / h ^-1 Mpc)<15  , with a marginally steeper slope for early types than late types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of ∼2.5 between L * and 4 L *. At all luminosities, however, the correlation function amplitude for the early types is ∼50 per cent higher than that of the late types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity.  相似文献   

Multi-object near-infrared Hα spectroscopy of z∼ 1 star-forming galaxies in the Hubble Deep Field North     

Michelle Doherty  rew Bunker  Robert Sharp  Gavin Dalton  Ian Parry  Ian Lewis  Emily MacDonald  Christian Wolf  Hans Hippelein 《Monthly notices of the Royal Astronomical Society》2004,354(1):L7-L12

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CHINA＇S RADICAL BIRTH CONTROL POLICY AND IMPLICATIONS FOR INDIA     

Gavin Musgrovl 《中国地理科学(英文版)》1994,(3)

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The 2dF Galaxy Redshift Survey: the blue galaxy fraction and implications for the Butcher–Oemler effect     

Roberto De Propris  Matthew Colless  John A. Peacock  Warrick J. Couch  Simon P. Driver  Michael L. Balogh  Ivan K. Baldry  Carlton M. Baugh  Joss Bland-Hawthorn  Terry Bridges  Russell Cannon  Shaun Cole  Chris Collins  Nicholas Cross  Gavin Dalton  George Efstathiou  Richard S. Ellis  Carlos S. Frenk  Karl Glazebrook  Edward Hawkins  Carole Jackson  Ofer Lahav  Ian Lewis  Stuart Lumsden  Steve Maddox  Darren Madgwick  Peder Norberg  Will Percival  Bruce A. Peterson  Will Sutherland  Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,351(1):125-132

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Seasonal controls on sediment transport and deposition in Lake Ohau,South Island,New Zealand: Implications for a high‐resolution Holocene palaeoclimate reconstruction          下载免费PDF全文

Heidi A. Roop  Gavin B. Dunbar  Richard Levy  Marcus J. Vandergoes  Alexander L. Forrest  Sharon L. Walker  Jennifer Purdie  Phaedra Upton  James Whinney 《Sedimentology》2015,62(3):826-844

Laminated sediments in Lake Ohau, Mackenzie Basin, New Zealand, offer a potential high‐resolution climate record for the past 17 kyr. Such records are particularly important due to the relative paucity of detailed palaeoclimate data from the Southern Hemisphere mid‐latitudes. This paper presents outcomes of a study of the sedimentation processes of this temperate lake setting. Hydrometeorological, limnological and sedimentological data were collected over a 14 month period between 2011 and 2013. These data indicate that seasonality in the hydrometeorological system in combination with internal lake dynamics drives a distinct seasonal pattern of sediment dispersal and deposition on a basin‐wide scale. Sedimentary layers that accumulate proximal to the lake inflow at the northern end of the lake form in response to discrete inflow events throughout the year and display an event stratigraphy. In contrast, seasonal change in the lake system controls accumulation of light (winter) and dark (summer) laminations at the distal end of the lake, resulting in the preservation of varves. This study documents the key processes influencing sediment deposition throughout Lake Ohau and provides fundamental data for generating a high‐resolution palaeoclimate record from this temperate lake.  相似文献   

Aeolian sediment transport and deposition in a modern high‐latitude glacial marine environment     

Jane M. Chewings  Cliff B. Atkins  Gavin B. Dunbar  Nicholas R. Golledge 《Sedimentology》2014,61(6):1535-1557

Aeolian sand and dust in polar regions are transported offshore over sea ice and released to the ocean during summer melt. This process has long been considered an important contributor to polar sea floor sedimentation and as a source of bioavailable iron that triggers vast phytoplankton blooms. Reported here are aeolian sediment dispersal patterns and accumulation rates varying between 0·2 g m^?2 yr^?1 and 55 g m^?2 yr^?1 over 3000 km² of sea ice in McMurdo Sound, south‐west Ross Sea, adjacent to the largest ice free area in Antarctica. Sediment distribution and the abundance of southern McMurdo Volcanic Group‐derived glass, show that most sediment originates from the McMurdo Ice Shelf and nearby coastal outcrops. Almost no sediment is derived from the extensive ice free areas of the McMurdo Dry Valleys due to winnowed surficial layers shielding sand‐sized and silt‐sized material from wind erosion and because of the imposing topographic barrier of the north‐south aligned piedmont glaciers. Southerly winds of intermediate strength (ca 20 m sec^?1) are primarily responsible for transporting sediment northwards and offshore. The results presented here indicate that sand‐sized sediment does not travel more than ca 5 km offshore, but very‐fine sand and silt grains can travel >100 km from source. For sites >10 km from the coast, the mass accumulation rate is relatively uniform (1·14 ± 0·57 g m^?2 yr^?1), three orders of magnitude above estimated global atmospheric dust values for the region. This uniformity represents a sea floor sedimentation rate of only 0·2 cm kyr^?1, well below the rates of >9 cm kyr^?1 reported for biogenic‐dominated sedimentation measured over much of the Ross Sea. These results show that, even for this region of high‐windblown sediment flux, aeolian processes are only a minor contributor to sea floor sedimentation, excepting areas proximal to coastal sources.  相似文献