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101.
A number of high resolution and high signal-to-noise ratio spectra of mildly metal-poor stars were obtained with the coudé echelle spectrograph attached to the 2.16m telescope at Xinglong Observation Base of Beijing Astronomical Observatory. The spectra of seven mildly metal-poor stars were processed with the MIDAS software package, and the equivalent widths of their spectral lines were measured. The measured equivalent widths together with an error analysis are presented. 相似文献
102.
The accretion-induced neutron star (NS) magnetic field evolution is studied through considering the accretion flow to drag the field lines aside and dilute the polar-field strength, and as a result the equatorial field strength increases, which is buried inside the crust on account of the accretion-induced global compression of star crust. The main conclusions of model are as follows: (i) the polar field decays with increase in the accreted mass; (ii) the bottom magnetic field strength of about 108 G can occur when the NS magnetosphere radius approaches the star radius, and it depends on the accretion rate as ; and (iii) the NS magnetosphere radius decreases with accretion until it reaches the star radius, and its evolution is little influenced by the initial field and the accretion rate after accreting ∼0.01 M⊙ , which implies that the magnetosphere radii of NSs in low-mass X-ray binaries would be homogeneous if they accreted the comparable masses. As an extension, the physical effects of the possible strong magnetic zone in the X-ray NSs and recycled pulsars are discussed. Moreover, the strong magnetic fields in the binary pulsars PSR 1831−00 and PSR 1718−19 after accreting about 0.5 M⊙ in the binary-accretion phase, 8.7 × 1010 and 1.28 × 1012 G , respectively, can be explained through considering the incomplete frozen flow in the polar zone. As an expectation of the model, the existence of the low magnetic field (∼3 × 107 G) NSs or millisecond pulsars is suggested. 相似文献
103.
D. B. Melrose R. Fok † D. P. Menezes ‡ 《Monthly notices of the Royal Astronomical Society》2006,371(1):204-210
The dominant emission from bare strange stars is thought to be electron–positron pairs, produced through spontaneous pair creation (SPC) in a surface layer of electrons tied to the star by a superstrong electric field. The positrons escape freely, but the electrons are directed towards the star and quickly fill all available states, such that their degeneracy suppresses further SPC. An electron must be reflected and gain energy in order to escape, along with the positron. Each escaping electron leaves a hole that is immediately filled by another electron through SPC. We discuss the collisional processes that produce escaping electrons. When the Landau quantization of the motion perpendicular to the magnetic field is taken into account, electron–electron collisions can lead to an escaping electron only through a multistage process involving higher Landau levels. Although the available estimates of the collision rate are deficient in several ways, it appears that the rate is too low for electron–electron collisions to be effective. A simple kinetic model for electron–quark collisions leads to an estimate of the rate of pair production that is analogous to thermionic emission, but the work function is poorly determined. 相似文献
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We present and discuss a short and simple derivation of orbital epicyclic frequencies for circular geodesic orbits in stationary
and axially symmetric spacetimes. Such spacetimes include as special cases analytically known black hole Kerr and Schwarzschild
spacetimes, as well as the analytic Hartle-Thorne spacetime and all numerically constructed spacetimes relevant for rotating
neutron stars. Our derivation follows directly from energy and angular momentum conservation and it uses the concept of the
effective potential. It has never been published, except for a few special cases, but it has already become a part of the
common knowledge in the field. 相似文献
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