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991.
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M. L. Pretorius C. Knigge D. O'Donoghue J. P. Henry I. M. Gioia C. R. Mullis 《Monthly notices of the Royal Astronomical Society》2007,382(3):1279-1288
We use the ROSAT North Ecliptic Pole (NEP) survey to construct a small, but purely X-ray flux-limited sample of cataclysmic variable stars (CVs). The sample includes only four systems, two of which (RX J1715.6+6856 and RX J1831.7+6511) are new discoveries. We present time-resolved spectroscopy of the new CVs and measure orbital periods of 1.64 ± 0.02 and 4.01 ± 0.03 h for RX J1715.6+6856 and RX J1831.7+6511, respectively. We also estimate distances for all the CVs in our sample, based mainly on their apparent brightness in the infrared. The space density of the CV population represented by our small sample is 1.1+2.3 −0.7 × 10−5 pc−3 . We can also place upper limits on the space density of any subpopulation of CVs too faint to be included in the NEP survey. In particular, we show that if the overall space density of CVs is as high as 2 × 10−4 pc−3 (as has been predicted theoretically), the vast majority of CVs must be fainter than L X ≃ 2 × 1029 erg s−1 . 相似文献
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The magnetic fields and energy flows in an astronomical jet described by our earlier model are calculated in detail. Though the field distribution varies with the external pressure function p ( z ) , it depends only weakly on the other boundary conditions. Individual field lines were plotted; the lines become nearly vertical at the bottom and are twisted at the top. An animation of a field line's motion was made, which shows the line being wound up by the accretion disc's differential rotation and rising as a result of this. The distribution of Poynting flux within the jet indicates that much of the energy flows up the jet from the inside of the accretion disc but a substantial fraction flows back down to the outside. 相似文献
998.
C. Brocksopp J. C. A. Miller-Jones R. P. Fender B. W. Stappers 《Monthly notices of the Royal Astronomical Society》2007,378(3):1111-1117
XTE J1748−288 is a black hole X-ray transient which went into outburst in 1998 June. The X-ray light curves showed canonical morphologies, with minor variations on the 'fast rise exponential decay' profile. The radio source, however, reached an unusually high flux density of over 600 mJy. This high radio flux was accompanied by an exceptional (>20 per cent) fractional linear polarization, the variability of which was anticorrelated with the flux density. We use this variability to discuss possible depolarization mechanisms and to predict the underlying behaviour of the (unresolved) core/jet components. 相似文献
999.
S. L. Casewell P. D. Dobbie S. T. Hodgkin E. Moraux R. F. Jameson N. C. Hambly J. Irwin N. Lodieu 《Monthly notices of the Royal Astronomical Society》2007,378(3):1131-1140
We present the results of a deep optical–near-infrared (optical–NIR) multi-epoch survey covering 2.5 deg2 of the Pleiades open star cluster to search for new very low-mass brown dwarf members. A significant (∼5 yr) epoch difference exists between the optical (CFH12k I -, Z -band) and NIR (UKIRT WFCAM J -band) observations. We construct I , I − Z and Z , Z − J colour–magnitude diagrams to select candidate cluster members. Proper motions are computed for all candidate members and compared to the background field objects to further refine the sample. We recover all known cluster members within the area of our survey. In addition, we have discovered nine new candidate brown dwarf cluster members. The seven faintest candidates have red Z − J colours and show blue NIR colours. These are consistent with being L- and T-type Pleiads. Theoretical models predict their masses to be around 11 M Jup . 相似文献