Heavy-element abundance patterns in hot DA white dwarfs     

M. A. Barstow  S. A. Good  J. B. Holberg  I. Hubeny  N. P. Bannister  F. C. Bruhweiler  M. R. Burleigh  R. Napiwotzki 《Monthly notices of the Royal Astronomical Society》2003,341(3):870-890

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Geometrical constraints upon the unipolar model of V407 Vul and RXJ0806.3+1527     

S. C. C. Barros  T. R. Marsh  P. Groot  G. Nelemans  G. Ramsay  G. Roelofs  D. Steeghs  J. Wilms 《Monthly notices of the Royal Astronomical Society》2005,357(4):1306-1312

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Measuring the Fundamental Parameters of Hot Hydrogen- Rich White Dwarfs     

M.A.Barstow 《中国天文和天体物理学报》2003,(4)

This review considers the observations of hot, hydrogen-rich white dwarf stars, with particular reference to measurements of temperature, surface gravity and composition. Spectroscopic data from a variety of wavelength ranges are required for this work and, in particular, the important contributions from optical, ultraviolet and extreme ultraviolet studies are discussed. Using the values of Teff and log g determined for an individual white dwarf, estimates of mass and radius might be derived from the theoretical mass-radius relation. The issue of the accuracy of the theoretical mass-radius calculations and the prospects for making empirical tests using observational data are outlined.  相似文献   

Remnant evolution after a carbon–oxygen white dwarf merger     

S.-C. Yoon  Ph. Podsiadlowski  S. Rosswog 《Monthly notices of the Royal Astronomical Society》2007,380(3):933-948

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Near-infrared spectroscopy of the very low mass companion to the hot DA white dwarf PG 1234+482     

P. R. Steele  M. R. Burleigh  P. D. Dobbie  M. A. Barstow 《Monthly notices of the Royal Astronomical Society》2007,382(4):1804-1808

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A search for radio pulsars around low-mass white dwarfs     

Joeri van Leeuwen  Robert D. Ferdman  Sol Meyer  Ingrid Stairs 《Monthly notices of the Royal Astronomical Society》2007,374(4):1437-1440

Low-mass white dwarfs can be produced either in low-mass X-ray binaries by stable mass transfer to a neutron star, or in a common envelope phase with a heavier white dwarf companion. We have searched eight low-mass white dwarf candidates recently identified in the Sloan Digital Sky Survey for radio pulsations from pulsar companions, using the Green Bank Telescope at 340 MHz. We have found no pulsations down to flux densities of 0.6–0.8 mJy kpc⁻² and conclude that a given low-mass helium-core white dwarf has a probability of  <0.18 ± 0.05  of being in a binary with a radio pulsar.  相似文献   

Identification and investigation of sulphur plumes along the Namibian coast using the MERIS sensor     

Thomas Ohde  Herbert SiegelJan Reißmann  Monika Gerth 《Continental Shelf Research》2007

In the upwelling area along the Namibian coast of SW-Africa sulphur discolorations were investigated to study the impact of hydrogen sulphide on the ecosystem using satellite imagery. The formation of colloidal sulphur in the upper water layer results from the oxidation of hydrogen sulphide. The occurrence of sulphur plumes as well as their temporal and spatial development was investigated in relation to the driving meteorological and oceanographic conditions. Because of the sporadic occurrence of sulphur events and the limited number of ship-borne investigations in that area remote sensing of ocean colour is the only method to follow these phenomena continuously and synoptically. In the past the sulphur plumes were studied by true colour images derived from ocean colour satellite data like sea-viewing wide field of view sensor or moderate resolution imaging spectroradiometer and identified by their typical milky turquoise discoloration.  相似文献   

White dwarfs in the 2dF QSO Redshift Survey – I. Hydrogen-rich (DA) stars     

S. Vennes  R. J. Smith  B. J. Boyle  S. M. Croom  A. Kawka  T. Shanks  L. Miller  N. Loaring 《Monthly notices of the Royal Astronomical Society》2002,335(3):673-686

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A white dwarf in the state of an ejector     

N. R. Ikhsanov  V. V. Neustroev  N. G. Beskrovnaya 《Astronomy Letters》2004,30(10):675-684

We analyze the possibility of observational identification of white dwarfs in the state of an ejector. Among the distinctive features of this class of objects are a high rate of rotational energy loss comparable to or higher than the observed luminosity of the object and nonthermal gamma-ray and/or radio spectra. The manifestations of the white dwarf in the close binary system AE Aquarii closely match these criteria. We show that most of the peculiar manifestations of this object in the hard spectral range and the observed pattern of mass transfer in the system can be explained in terms of a model in which the state of the white dwarf is classified as an ejector.  相似文献   

X-ray beaming caused by resonance scattering in the accretion column of magnetic cataclysmic variables     

Y. Terada  M. Ishida  K. Makishima  T. Imanari  R. Fujimoto  K. Matsuzaki  H. Kaneda 《Monthly notices of the Royal Astronomical Society》2001,328(1):112-126

Extremely strong ionized Fe emission lines, with equivalent widths reaching ∼4000 eV, were discovered by ASCA from a few Galactic compact objects, including AX J2315−0592, RX J1802.1+1804 and AX J1842.8−0423. These objects are thought to be binary systems containing magnetized white dwarfs (WDs). A possible interpretation of the strong Fe K line is the line-photon collimation in the WD accretion column, as a result of resonance scattering of line photons. The collimation occurs when the accretion column has a flat shape, and the effect is augmented by the vertical velocity gradient, which reduces the resonant trapping of resonant photons along the magnetic field lines. This effect was quantitatively confirmed with Monte Carlo simulations. Furthermore, with ASCA observations of the polar V834 Centauri, this collimation effect was clearly detected as a rotational modulation of the equivalent width of the Fe K emission line. The extremely strong emission lines mentioned above can be explained consistently by our interpretation. Combining this effect with other X-ray information, the geometry and plasma parameters in the accretion column were determined.  相似文献