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P. G. Jonker † D. Steeghs G. Nelemans M. van der Klis 《Monthly notices of the Royal Astronomical Society》2005,356(2):621-626
In this paper we report on optical spectroscopic observations of the low-mass X-ray binary 2S 0921–630 obtained with the Very Large Telescope. We found sinusoidal radial velocity variations of the companion star with a semi-amplitude of 99.1 ± 3.1 km s−1 modulated on a period of 9.006 ± 0.007 d, consistent with the orbital period found previously for this source, and a systemic velocity of 44.4 ± 2.4 km s−1 . Owing to X-ray irradiation, the centre of light measured by the absorption lines from the companion star is probably shifted with respect to the centre of mass. We try to correct for this using the so-called K -correction. Conservatively applying the maximum correction possible and using the previously measured rotational velocity of the companion star, we find a lower limit to the mass of the compact object in 2S 0921–630 of MX sin3 i > 1.90 ± 0.25 M⊙ (1σ errors). The inclination in this system is well constrained since partial eclipses have been observed in X-ray and optical bands. For inclinations in the range 60° < i < 90° we find 1.90 ± 0.25 < MX < 2.9 ± 0.4 M⊙ . However, using this maximum K -correction we find that the ratio between the mass of the companion star and that of the compact object, q , is 1.32 ± 0.37, implying super-Eddington mass-transfer rates; however, evidence for that has not been found in 2S 0921–630. We conclude that the compact object in 2S 0921–630 is either a (massive) neutron star or a low-mass black hole. 相似文献
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Kevin A. Pimbblet 《Monthly notices of the Royal Astronomical Society》2005,358(1):256-262
We present a new algorithm for detecting intercluster galaxy filaments based upon the assumption that the orientations of constituent galaxies along such filaments are non-isotropic. We apply the algorithm to the 2dF Galaxy Redshift Survey catalogue and find that it readily detects many straight filaments between close cluster pairs. At large intercluster separations (≫15 h −1 Mpc) , we find that the detection efficiency falls quickly, as it also does with more complex filament morphologies. We explore the underlying assumptions and suggest that it is only in the case of close cluster pairs that we can expect galaxy orientations to be significantly correlated with filament direction. 相似文献
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We study analytically the Rayleigh–Taylor instability in expanding supernova gas shell. The instability appears at the inner
shell surface accelerated by blowing pulsar wind. The most dangerous perturbations correspond to wavelengths comparable to
the shell thickness. We analyze the fragility of the supernova remnant shell in function of the initial perturbation amplitude
and the shell thickness. 相似文献
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Chris Turney Mike Baillie Steve Clemens David Brown Jonathan Palmer Jonathan Pilcher Paula Reimer Hanns Hubert Leuschner 《第四纪科学杂志》2005,20(6):511-518
The temporal and spatial extent of Holocene climate change is an area of considerable uncertainty, with solar forcing recently proposed to be the origin of cycles identified in the North Atlantic region. To address these issues we have developed an annually resolved record of changes in Irish bog tree populations over the last 7468 years which, together with radiocarbon‐dated bog and lake‐edge populations, extend the dataset back to ~9000 yr ago. The Irish trees underpin the internationally accepted radiocarbon calibration curve, used to derive a proxy of solar activity, and allow us to test solar forcing of Holocene climate change. Tree populations and age structures provide unambiguous evidence of major shifts in Holocene surface moisture, with a dominant cyclicity of 800 yr, similar to marine cycles in the North Atlantic, indicating significant changes in the latitude and intensity of zonal atmospheric circulation across the region. The cycles, however, are not coherent with changes in solar activity (both being on the same absolute timescale), indicating that Holocene North Atlantic climate variability at the millennial and centennial scale is not driven by a linear response to changes in solar activity. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献