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A procedure for simultaneous analysis of multiple kinds of observations is developed for binaries that contain X-ray pulsars. A wide variety of observation types might be included, although we consider only velocity: pulse and light: velocity: pulse cases at present. The model operates with equipotentials and can accommodate non-synchronous rotation and eccentric orbits. The duration condition imposed by observed X-ray eclipses is incorporated as an embedded constraint, so that only solutions consistent with the eclipse duration are found. Relations needed for the method of differential corrections in least-squares solutions are specified, and we apply the Marquardt scheme for improvement of solution convergence. Parameters of Vela X1: GP Velorum are obtained from seven combinations of pulse and radial velocity data. The estimated masses are thereby put into some perspective, especially for the neutron star. The mass of the supergiant ( m sin3 i ) now ranges only ±5 per cent from the mean of seven results, although the uncertainty in i makes the actual mass range larger. We discuss the determinacy of certain parameters and their historical consistency. For example, the systemic radial velocity differs among spectroscopic data sets by more than 20 km s−1 . We show that, contrary to published assertions, the orbital inclinations of high-mass X-ray binaries are essentially indeterminable by the usual methods, although lower limits to inclination may be meaningful for some examples. 相似文献
44.
L. G. Kiseleva J. Colin B. Dauphole & P. Eggleton 《Monthly notices of the Royal Astronomical Society》1998,301(3):759-766
In this paper we present numerical results on the decay of small stellar systems under different initial conditions (multiplicity 3 ≤ N ≤ 10, and various mass spectra, initial velocities and initial configurations). The numerical treatment uses the CHAIN1 code (Mikkola &38; Aarseth). Particular attention is paid to the distribution of high-velocity escapers: we define these as stars with velocity above 30 km s−1 . These numerical experiments confirm that small N -body systems are dynamically unstable and produce cascades of escapers in the process of their decay. It is shown that the fraction of stars that escape from small dense stellar systems with an escape velocity greater than 30 km s−1 is ∼1 per cent for all systems treated here. This relatively small fraction must be considered in relation to the rate of star formation in the Galaxy in small groups: this could explain some moderately high-velocity stars observed in the Galactic disc and possibly some young stars with relatively high metallicity in the thick disc. 相似文献
45.
M. R. Schreiber & F. V. Hessman 《Monthly notices of the Royal Astronomical Society》1998,301(3):626-630
We consider the effects of accretion stream overflow on the viscous dynamics of accretion discs in dwarf novae. If the stream from the secondary star is geometrically thick enough, some fraction of its material can flow over and under the disc. The mass and specific angular momentum of the stream are then deposited not only at the point of collision with the outer disc, but also at those radii in the inner disc with geometric heights that are large enough to intercept the residual stream, or near the radius where the disc has the same specific angular momentum as the stream. The overflowing stream can alter the behaviour of heating fronts and cooling fronts in the disc. If the mass fraction of the overflowing stream is of order tens of per cent, the deposition of mass in the inner parts of the disc is sufficient to change the character of the eruption light curves significantly. 相似文献
46.
T. Shahbaz R. M. Bandyopadhyay P. A. Charles R. M. Wagner P. Muhli P. Hakala J. Casares & J. Greenhill 《Monthly notices of the Royal Astronomical Society》1998,300(4):1035-1040
We present optical spectroscopy and optical and infrared photometry of the neutron star soft X-ray transient Aql X–1 during its X-ray outburst of 1997 August. By modelling the X-ray, optical and IR light curves, we find a 3-d delay between the IR and X-ray rise times, analogous to the UV–optical delay seen in dwarf novae outbursts and black hole X-ray transients. We interpret this delay as the signature of an 'outside-in' outburst, in which a thermal instability in the outer disc propagates inward. This outburst is the first of this type definitively identified in a neutron star X-ray transient. 相似文献
47.
L. Burderi A. R. King & G. A. Wynn 《Monthly notices of the Royal Astronomical Society》1998,300(4):1127-1130
Lorimer et al. have recently reported that the spin-down age (∼7 × 109 yr) of the low-mass binary pulsar PSR J1012+5307 is much higher than the cooling age (3 × 108 yr) of its white dwarf companion. The proposed solutions for this discrepancy are outlined and discussed. In particular, the revised cooling age estimate proposed by Alberts et al. agrees with data from other low-mass binary pulsar systems if a transition to the 'classical' cooling regime occurs between ∼0.14 and ∼0.28 M⊙ . If this transition is excluded, PSR J1012+5307 seems to have finished its accretion phase far from the spin-up line. 相似文献
48.
Ralph A. M. J. Wijers Joshua S. Bloom Jasjeet S. Bagla & Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》1998,294(1):L13-L17
A gamma-ray burst (GRB) releases an amount of energy similar to that of a supernova explosion, which combined with its rapid variability suggests an origin related to neutron stars or black holes. Since these compact stellar remnants form from the most massive stars not long after their birth, GRBs should trace the star formation rate in the Universe; we show that the GRB flux distribution is consistent with this. Because of the strong evolution of the star formation rate with redshift, it follows that the dimmest known bursts have z ∼ 6, much above the value usually quoted and beyond the most distant quasars. This explains the absence of bright galaxies in well-studied GRB error boxes. The increased distances imply a peak luminosity of 8.3 × 1051 erg s−1 and a rate density of 0.025 per million years per galaxy. These values are 20 times higher and 150 times lower, respectively, than are implied by fits with non-evolving GRB rates. This means either that GRBs are caused by a much rarer phenomenon than mergers of binary neutron stars, or that their gamma-ray emission is often invisible to us due to beaming. Precise burst locations from optical transients will discriminate between the various models for GRBs from stellar deaths, because the distance between progenitor birth place and burst varies greatly among them. The dimmest GRBs are then the most distant known objects, and may probe the Universe at an age when the first stars were forming. 相似文献
49.
We examine the status of the threat posed to stellar-mass black hole candidates by the possible existence of Q-stars (compact objects with an exotic equation of state that might have masses well above the normally accepted maximum for standard neutron stars). We point out that Q-stars could be extremely compact (with radii less than 1.5 times the corresponding Schwarzschild radius) making it difficult to determine observationally that a given object is a black hole rather than a Q-star, unless there is direct evidence for the absence of a material surface. On the other hand, in order for a Q-star to have a mass as high as that inferred for the widely favoured black hole candidate V404 Cygni, it would be necessary for the Q-matter equation of state to apply already at densities an order of magnitude below that of nuclear matter and this might well be considered implausible on physical grounds. We also describe how rotation affects the situation and discuss the prospects for determining observationally that black hole candidates are not Q-stars. 相似文献
50.
S. B. Potter P. J. Hakala & Mark Cropper 《Monthly notices of the Royal Astronomical Society》1998,297(4):1261-1268
Modelling the polarized cyclotron emission from magnetic cataclysmic variables has been a pivotal technique for determining the structure of the accretion zones on the white dwarf. To date, model solutions have been obtained from trial fits to the intensity and polarization data, which have been constructed from emission regions (for example arcs and spots) put in by hand. These models were all inferred indirectly from arguments based on the polarization and X-ray light curves. We present a more analytical and objective technique using optimization by a genetic algorithm, Tikhonov regularization and Powell's method that robustly models the details of polarized emission. To demonstrate the success of this technique, we show the results of several simulations in which we calculated the intensity and polarization curves from arbitrarily shaped emission regions on the surface of a sphere and then applied our code to these curves to recover the original test data. We also show how adding artificial noise affects the outcome of the optimization technique. 相似文献