共查询到20条相似文献，搜索用时 31 毫秒
1.
Richard J. Parker Simon P. Goodwin Pavel Kroupa M. B. N. Kouwenhoven 《Monthly notices of the Royal Astronomical Society》2009,397(3):1577-1586
We examine the dynamical destruction of binary systems in star clusters of different densities. We find that at high densities (104 – 105 M⊙ pc−3 ) almost all binaries with separations >103 au are destroyed after a few crossing times. At low densities [ ], many binaries with separations >103 au are destroyed, and no binaries with separations >104 au survive after a few crossing times. Therefore, the binary separations in clusters can be used as a tracer of the dynamical age and past density of a cluster.
We argue that the central region of the Orion nebula cluster was ∼100 times denser in the past with a half-mass radius of only 0.1–0.2 pc as (i) it is expanding, (ii) it has very few binaries with separations >103 au and (iii) it is well mixed and therefore dynamically old.
We also examine the origin of the field binary population. Binaries with separations <102 au are not significantly modified in any cluster, therefore at these separations the field reflects the sum of all star formation. Binaries with separations in the range 102 – 104 au are progressively more and more heavily affected by dynamical disruption in increasingly dense clusters. If most star formation is clustered, these binaries must be overproduced relative to the field. Finally, no binary with a separation >104 au can survive in any cluster and so must be produced by isolated star formation, but only if all isolated star formation produces extremely wide binaries. 相似文献
We argue that the central region of the Orion nebula cluster was ∼100 times denser in the past with a half-mass radius of only 0.1–0.2 pc as (i) it is expanding, (ii) it has very few binaries with separations >10
We also examine the origin of the field binary population. Binaries with separations <10
2.
We present the results of our study of 19 novae in the galaxy M31 on photographs taken with wide-field telescopes in 1999–2005. Two of the six novae discovered in our program (ShA 65 and ShA 67) have been identified with supersoft X-ray sources, the discovery of one nova (ShA 69) was reported in IAU Circulars, and the other three novae (ShA 66, ShA 68, and ShA 70) are reported for the first time. 相似文献
3.
《天文研究与技术》2003,(Z1)
1 IntroductionItiswellknownthatblazarscomprisethreesubgroupsincludingHPQs (HighlyPolarizedquasars) ,OVVs (OpticallyViolentlyVariables) ,andBLLacs.Anditisfoundthatthesethreesubgroupsarevariableontimescalefromyearstohoursinallregimes (Wagner&Witzel1 995) [1].Blazarshaveveryhighenergeticemissions.Manyblazars (66positiveand 2 5marginaldetections)areGevgamma raysources (Fichteletal.1 994,vonMontignyetal.1 995;Hartmanetal.1 991 ) [2～4 ],andsomeareTevgamma rayonessuchasMark 42 1 ,Mark 50 … 相似文献
4.
5.
6.
1 INTRODUCTION Pulsars receive a large kick velocity during the period of birth, so they move away from theirbirth place, where the center of supernova remnant is believed to be. Measuring the propermotions of pulsars can derive an independent estimate of their ages, which has a number ofastrophysical uses, for example, in the studies of the evolution of neutron star magnetic fieldand of pulsar emission beam. There are three methods of measuring proper motion: (1) traditional optical metho… 相似文献
7.
Ding-Qiang Su Xiang-Qun Cui National Astronomical Observatories/NIAOT Chinese Academy of Sciences Nanjing Department of Astronomy Nanjing University Nanjing 《中国天文和天体物理学报》2004,4(1):1-9
Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is one of the major national projects under construction in China. Active optics is one of the most important technologies for new large telescopes. It is used for correcting telescope errors generated by gravitational and thermal changes. Here, however, we use this technology to realize the configuration of LAMOST, -a task that cannot be done in the traditional way. A comprehensive and intensive research on the active optics used in LAMOST is also reported, including an open-loop control method and an auxiliary closed-loop control method. Another important development is in our pre-calibration method of open-loop control, which is with some new features: simultaneous calculation of the forces and displacements of force actuators and displacement actuators; the profile of mirror can be arbitrary; the mirror surface shape is not expressed by a fitting polynomial, but is derived from the mirror surface shape formula which is highly accurat 相似文献
8.
Z. B. Li L. M. Song J. L. Qu Y. J. Lei J. Y. Nie C. M. Zhang 《Astrophysics and Space Science》2012,341(2):383-393
In this paper, the rms-flux (root mean square-flux) relation along the Z-track of the bright Z-Source Cyg X-2 is analyzed using the observational data of Rossi X-ray Timing Explorer (RXTE). Three types of rms-flux relations, i.e. positive, negative, and ‘arch’-like correlations are found in different branches. The rms is positively correlated with flux in normal branch (NB), but anti-correlated in the vertical horizontal branch (VHB). The rms–flux relation shows an ‘arch’-like shape in the horizontal branch (HB). We also try to explain this phenomenon using existing models. 相似文献
9.
Jarken Esimbek 《中国天文和天体物理学报》2005,5(4):363-370
The excitation of H2O masers usually needs very high density gas, hence it can serve as a marker of dense gas in HII region. We selected a sample of H2O maser sources from Plume et al. (four with, and four without detected CS(J = 7-6) emission), and observed them in 13CO(J=1-0) and C18O (J=1-0). C18O (J=1-0) emission was detected only in three of the sources with detected CS(J=7-6) emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves. 相似文献
10.
《紫金山天文台台刊》1996,(2)
On the basis of the differences between ideal MHD Alfven waves and kinetic Alfven waves,the nonlinear kinetic Alfven wave with Poison equation correction and the evolution of kinetic wave have been presented.These results have been used to explain the observation data from Freja satellite and CRITⅡ rocket in aurora. 相似文献
11.
R. K. Srivastava 《Astrophysics and Space Science》1989,154(2):333-336
FirstU, B, andV observations of UMa are presented. Light curves show light variations of varying amplitude. Colour indices also show small colour variations. 相似文献
12.
Ren-Xin Xu Xiao-Hong Cui Guo-Jun Qiao Department of Astronomy School of Physics Peking University Beijing 《中国天文和天体物理学报》2006,6(2):217-226
The global structure of current flows in pulsar magnetosphere is investigated, with rough calculations of the circuit elements. It is emphasized that the potential of the critical field lines (the field lines that intersect the null surface at the light cylinder radius) should be the same as that of interstellar medium, and that pulsars whose rotation axes and magnetic dipole axes are parallel should be positively charged, in order to close the pulsar's current flows. The statistical relation between the radio luminosity and pulsar's electric charge (or the spindown power) may hint that the millisecond pulsars could be low-mass bare strange stars. 相似文献
13.
《紫金山天文台台刊》1996,(2)
The Plasma-maser instablility of Langmuir wave or Em wave in multicom-ponent plasma with stationary charged particulates is considered.The up-conversion of the wave evergy from low-frequency waves to the high-frequency waves is much enhanced owing to the deeper energy exchange between resonant waves and particles in dusty plasma.This results should be useful to interpret the anomalous high-frequency radiation phenomena in laboratory and astrophysical dusty plasma. 相似文献
14.
Dramatic extensions of experimental possibilities (spacecraft RHESSI, CORONAS-F and others) in solar gamma-ray astronomy call for urgent, detailed theoretical consideration of a set of physical problems of solar activity and solar-terrestrial relationships that earlier may have only been outlined. Here we undertake a theoretical analysis of issues related to the production of gamma-radiation in the processes of interactions of energetic (accelerated) heavy and middle nuclei with the nuclei of the solar atmosphere (the so-called i-j interactions). We also make an estimate of the contribution of these interactions to the formation of nuclear and isotopic abundances of the solar atmosphere in the range of light and rare elements. The analysis is carried out for solar flares in the wide range of their intensities. We compare our theoretical estimates with RHESSI observations for the flare of 2002 July 23. It was shown that the 24Mg gamma-ray emission in this event was produced by the newly generated Mg nucle 相似文献
15.
We compare the line profiles and frequencies of low =0, 1, 2 acoustic oscillations seen in observations in velocity (by the GOLF and GONG experiments) and in intensity (LOI instrument). Our study indicates that the systematic shift between the frequencies of low- pmodes in intensity and in velocity measurements recently discovered by Toutain and co-workers is merely an artifact of their reduction techniques. The results obtained agree perfectly with the theoretical expectation that solar oscillations are the global eigenmodes simultaneously visible in velocity and intensity with the frequencies and line profiles coinciding within the error bars. 相似文献
16.
Observations of two quiescent filaments show oscillatory variations in Doppler shift and central intensity of the He i 10830 Å line.The oscillatory periods range from about 5 to 15 min, with dominant periods of 5, 9, and 16 min. The 5-min period is also detected in the intensity variations, after correction for atmospheric effects. Doppler shifts precede intensity variations by about one period. The possibility that the oscillations are Alfvén waves is discussed.The Doppler signals of the filament form fibril-like structures. The fibrils are all inclined at an angle of about 25° to the long axis of the filament. The magnetic field has a similar orientation relative to the major direction of the filament, and the measured Doppler signals are apparently produced by motions along magnetic flux tubes threading the filament.The measured lifetimes of the small-scale fibrils of quiescent disk filaments are very likely a combined effect of intensity modulations and reshuffling of the structures. 相似文献
17.
High brightness temperatures are a characteristic feature of IntraDay Variability (IDV) of extragalactic radio sources. Recent studies of the polarization properties of some IDV sources (e.g., 1150 812, PKS 0405-385 and 0716 714) have shown that these sources harbor several compact IDV components with angular sizes of -10-30/uas and very high polarizations (of up to -50%-70%). These results indicate the possibility of the existence of uniform magnetic fields in the IDV components. We investigate the incoherent synchrotron and self- Compton radiation of an anisotropic distribution of relativistic electrons which spin around the magnetic field lines at small pitch angles. The brightness temperature limit caused by second-order Compton losses is discussed and compared to the brightness temperatures derived from energy equipartition arguments. It is found that anisotropic distributions of electrons moving in ordered magnetic fields can raise the equipartition and Compton brightness temperatures by a factor of up to -3-5. This would remove some of the difficulties in the interpretation of extremely high intrinsic brightness temperatures of > 1012 K (or apparent brightness temperatures of - 1014 K with a Doppler factor of -30). 相似文献
18.
19.
A new method of determination of distances to stellar associations is proposed. This method is based on the measurements of
mean thicknesses of globules of the systems of dark globules connected with that association. It is shown that the method
is in good agreement with other known methods. A new grouping of OB stars in Pup-CMa is found. It is shown that this grouping
has properties characteristic for OB-associations: the stars of that grouping have similar distances, similar radial velocities,
the grouping is connected with molecular clouds, with Herbig-Haro objects, and cometary nebulae. All these results are in
favour of this grouping to be a new OB-association. We named that association OB-association Pup-CMa. The preliminary results
of12CO observations of molecular clouds connected with that association are also given. The radial velocities of these clouds
are in good agreement with the mean radial velocity of stars in the association in Pup-CMa.
Translated from Astrofizika, Vol. 42, No. 2, pp. 179–188, April–June, 1999. 相似文献
20.
If we follow recent work and in order to extend theuvby photometric calibrations to spectral types later than G0, we present an attempt to use the combineduvby and systems for stars in the range G5-K7 and luminosity classes V to III.The behaviour in the MK-, (b–y)– and cl– diagrams of the 200 stars, only good spectroscopic data being considered, suggests the usefulness of the index as an independent parameter for late-type Main-Sequence stars, following in a natural way the general trend defined by Crawford for F- and G-type stars.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain 相似文献