Iron line profiles in strong gravity     

Kris Beckwith  Chris Done 《Monthly notices of the Royal Astronomical Society》2004,352(2):353-362

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Model dependence of transonic properties of accretion flows around black holes     

Sandip K. Chakrabarti †  Santabrata Das 《Monthly notices of the Royal Astronomical Society》2001,327(3):808-812

We analytically study how the behaviour of accretion flows changes when the flow model is varied. We study the transonic properties of the conical flow, a flow of constant height and a flow in vertical equilibrium, and show that all these models are basically identical, provided that the polytropic constant is suitably changed from one model to another. We show that this behaviour is extendible even when standing shocks are produced in the flow. The parameter space where shocks are produced remains roughly identical in all these models when the same transformation among the polytropic indices is used. We present applications of these findings.  相似文献   

Intrinsic intraday variability in the gravitational lens system B0218+357     

A. D. Biggs  I. W. A. Browne  P. N. Wilkinson 《Monthly notices of the Royal Astronomical Society》2001,323(4):995-998

Radio monitoring of the gravitational lens system B0218+357 reveals it to be a highly variable source with variations on time-scales of a few days correlated in both images. This shows that the variability is intrinsic to the background lensed source and suggests that similar variations in other intraday variable sources can also be intrinsic in origin.  相似文献   

New 1982 — 1990 photometry of λ Andromedae and its 11-year cycle     

Douglas S. Hall  Gregory W. Henry  Dietmar Böhme  Peter A. Brooks  Sandy Chang  Ales Dolzan  George L. Fortier  Robert E. Fried  Russell M. Genet  Bruce S. Grim  James Hannon  Darrel B. Hoff  Kevin Krisciunas  Howard J. Landis  Howard P. Louth  Larry P. Lovell  Paul Nielsen  Bobby E. Powell  Harry D. Powell  Don Pray  Thomas R. Renner  Charles W. Rogers  Stephen Shervais  Douglas M. Slauson  Samuel Slote  Harold J. Stelzer  Arthur J. Stokes  Jack C. Troeger  Louis C. Turner  Norman F. Wasson  Kenneth W. Zeigler 《Journal of Astrophysics and Astronomy》1991,12(4):281-287

We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29 different observatories. Then we combine it with all other photometry available to us (previously published, contained in the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0^m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season, we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0^m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0^m.09 down almost to 0^m.03. The spot rotation periods were 55^d.9 ± 0^d.6 and 520^d.8 ± 1^d.0, respectively.  相似文献   

Gamma rays from millisecond pulsars     

D. Bhattacharya  G Srinivasan 《Journal of Astrophysics and Astronomy》1991,12(1):17-25

We estimate the contribution of millisecond pulsars to the diffuse gamma-ray background of the Galaxy, and show that a significant fraction of the Galactic background may originate from them. A small number of the unidentified COS-B point sources may, in fact, be millisecond pulsars. It is argued that several hundred millisecond pulsars may be detectable as point sources by the GRO satellite A preliminary version of these results was presented at the NATO Advanced Study Institute on Neutron stars, AGNs and Jets, Erice, September 5–17, 1988. On leave from Raman Research Institute, Bangalore, India.  相似文献   

Spectroscopic binaries near the north Galactic Pole     

R. F. Griffin  D. W. Beggs 《Journal of Astrophysics and Astronomy》1991,12(4):289-310

Orbits based principally on radial-velocity measurements made with the Haute-Provence Coravel spectrometer are presented for eight binary systems which include some of the faintest HD stars in the Galactic-Pole field. They are HD 103418 (which is double-lined), 105021, 108151, 113169, 113323, 113650, 113714, and 116514. Their periods range from 3.7 to 15.1 days. Very little else is known about any of them.  相似文献   

MK morphological study of Am stars at 66 Å/mm     

S. Sreedhar Rao  K. D. Abhyankar 《Journal of Astrophysics and Astronomy》1991,12(2):133-178

The pseudo-luminosity effect in the metallic line A-type stars found by Abt & Morgan (1976) is confirmed in a random sample of 27 Am stars. From a morphological study of their spectra in the wavelength interval 3850-4400 Å at a reciprocal dispersion of 66 Å/mm, revised spectral types are given on the MK system for their K-line and metallic-line spectra. This shows that: (a) our segregation of weak Am from the Am stars largely agrees with that by Cowleyet al. (1969); (b) all the stars in the sample are dwarfs according to their K-line classification; (c) more than 80 per cent exhibit the pseudo-luminosity effect significantly, with their metallic-line spectra resembling a giant or even a supergiant in the violet (3850-4100 Å), and a giant rather than a dwarf in the blue region (4260-4400 Å); (d) in two-thirds of the stars under (c), the Sr n 4077 Å line is found to have a markedly brighter luminosity class compared to any region, and in more than one-third of the sample it is comparable to that in Ap stars; (e) at least five stars exhibit characteristics which might suggest a spectrum variability: among these, the most striking example is 41 Sex A which was found to show a phase-modulated spectrum variation hitherto unknown in Am stars; (f) the metallic-line spectra of another five stars appear to be similar to A-shell type in differing degrees; (g) less than 20 per cent of the sample comprises stars which do not show any significant differential luminosity effect; these stars might have been misclassified or perhaps they are in a quiescent state. We also confirm the conclusion arrived at by Böhm-Vitense & Johnson (1978) that all Am stars may vary and our observations suggest that groups may exist among them.  相似文献   

Meteoric activities during the 11th century     

Sang-Hyeon Ahn 《Monthly notices of the Royal Astronomical Society》2005,358(4):1105-1115

We have analysed the meteor records in the chronicles that describe the era of the Song dynasty ( ad 960–1279). The data are complementary to the record-vacant 10th century of the Koryo dynasty ( ad 918–1392). The annual activity of sporadic meteors analysed shows a generic sinusoidal behaviour as in modern observations. In addition, we have also found that there are two prominent meteor showers, one in August and the other in November, appearing on the fluctuating sporadic meteors. The date of occurrence of the August shower indicates it to be the Perseids. By comparing the date of occurrence of the November shower with those of the Leonid showers of the Koryo dynasty, recent visual observations and the world-wide historical meteor storms, we conclude that the November shower is the Leonids. The regression rate of the Leonids is obtained to be     days per century, which agrees with recent observations.  相似文献   

SCATTERING PHASE MATRICES OF ICE CRYSTALS WITH HEXAGONAL PRISM AND TRIANGULAR PYRAMID FORM—A VECTOR RAY TRACING METHOD          下载免费PDF全文

Cai Qiming  Yang Ping 《Acta Meteorologica Sinica》1991,5(4):515-526

The work presented previously by the authors(Cai and Liou,1982)has been extended in this paper.By making use of our improved model the calculations on scattering phase matrices of hexagonal prismice crystals(HPIC)have been conducted for monodisperse and polydisperse systems.Compared with themodel of Cai and Liou,the required computational quantity is decreased by about two orders of magni-tude and the errors of results are less for the new model.Meanwhile,the scattering phase matrices of triangularpyramid ice crystals(TPIC)are also computed in the paper,and the comparison between the scatterings of thetwo forms of ice crystals is performed.  相似文献   

双基地激光测风雷达回波信号仿真研究          下载免费PDF全文

李绍辉  孙学金  邵连军  易欣  张传亮 《气象科学》2023,43(4):523-533

本文针对传统的体散射模型并未考虑大气不均匀性对信号传输的影响等问题,通过引入垂直非均匀的大气参数改进了模型,并利用其建立了体目标的双基地激光测风雷达方程,仿真了侧向散射回波信号,并与单基地雷达进行了对比分析。研究表明:水平方向上,双基地激光测风雷达的回波信号分布特征与单基地雷达差异较大,其回波信号等值线在近地面为卵形线,随着探测高度的增加,回波信号等值线逐渐变为以主、被动雷达为焦点的椭圆形,并最终趋近于圆形;垂直方向上,双基地激光测风雷达的回波信号随高度衰减剧烈,近地面的回波能量约为10^-10 J,4 km高度的回波能量约为10^-15J,在中低层大气(0~10 km),回波信号中气溶胶散射占比大,在高层大气(10 km以上),分子散射占比大。  相似文献