On the highly reddened members in six young galactic star clusters – a multiwavelength study     

Brijesh Kumar  Ram Sagar  B. B. Sanwal  M. S. Bessell 《Monthly notices of the Royal Astronomical Society》2004,353(3):991-1014

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Evolution of Polytropic Reimann Disks in Halos     

M. G. Abrahamyan 《Astrophysics》2004,47(4):555-567

The equilibrium of elliptical Riemann disks with a polytropic equation of state and their evolution under the influence of viscosity and gravitational radiation inside spheroidal halos with a relative surface mass density k. The evolutionary trajectory of a disk inside a halo with k<0.5, which is analogous to the evolution of an isolated disk, differs from that of a disk inside a denser halo.  相似文献   

UBV RI CCD photometric study of the open clusters Basel 4 and NGC 7067     

R. K. S. Yadav  Ram Sagar 《Monthly notices of the Royal Astronomical Society》2004,349(4):1481-1492

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Properties of Galaxies in the Second Byurakan Survey. II. Characteristic Features of a Separate Sample of Galaxies     

L. K. Erastova 《Astrophysics》2004,47(4):547-554

Some features of a sample of galaxies from the Second Byurakan Survey are discussed. Most of them are small galaxies with star formation. It is shown that different types of galaxies are in the Survey, with high, medium, and low levels of excitation and continua ranging from blue to relatively red. Many of the galaxies have absorption lines in their spectra; their continua are formed by stars in later spectral classes.  相似文献   

石英砂扫描电镜在漓江“泥砾”成因中的应用     

吴枝坦  王壬林  姚若飞 《南方国土资源》1992,(4)

本文根据扫描电镜对从漓江河谷钻孔中的泥砾层取得的481粒石英砂表面形态特证研究结果:石英砂多数颗粒保持棱角状外形并遭受不同程度的磨蚀,具阶状贝壳断口,平直或弧形刮削面和多向擦痕,沿解理面破碎呈“V”字形沟和撞击碟形坑,以及微溶蚀孔、隙、蜂窝状溶孔群和SiO_2再沉积等表面形态结构特征。认为它是在第四纪古地理湿热气候条件下泥石流沉积的产物,物源可能来自境内或周边的泥盆系砂岩和境外的花岗岩。  相似文献   

IRAS　14122－5947：一颗新发现的超长周期变星     

胡景耀 《中国天文和天体物理学报》1994,(1)

ＩＲＡＳ１４１２２－５９４７是一颗新发现的变星，其Ｉｃ星等的变幅超过５．５，光变周期可能是１９３５天或３９３０天，近红外光谱与ＯＨ／ＩＲ星相似，并具有一个冷的尘埃包层。对ＳＥＤ模型拟合结果表明，它在ＡＧＢ最终阶段的质量流失率为３．６（－６）Ｍ⊙／ｙｒ．我们认为它可能是处在ＡＧＢ的最后阶段，质量流失时而进行时而停止。  相似文献   

Magnetic Field Strengths and Structures from Radio Observations of Solar Active Regions     

Chang－XiZhang  G.B.Gelfreikh 《中国天文和天体物理学报》2002,2(3):266-276

Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggest that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field.  相似文献   

Is the Variable X—ray Source in M82 due to Gravitational Lensing？     

Da-Ming Chen 《中国天文和天体物理学报》2001,1(4):287-290

1 INTRODUCTIONObservations of the most famous starburst galaxy M82 with the High-Resolution Cameraon board the Chandra X-Ray Observatory, showed that there are nine sources in the celltral11 x 11 region, but no son-roe was detected at the galactic center (Matsumoto et al. 2001).Comparing the observations on 1999 October 28 and those on 2000 January 20, the authorsfound an extremely large time variability of the source CXO M82 J095550.2 694047, which islocated gll away from the galact…  相似文献   

Challenging a Paradigm: Do We Need Active and Inactive Areas to Account for Near-Nuclear Jet Activity?     

Crifo  J.-F.  Rodionov  A. V.  Szegö  K.  Fulle  M. 《Earth, Moon, and Planets》2002,90(1-4):227-238

We briefly describe an advanced 3D gas dynamical model developed for the simulation of theenvironment of active cometary nuclei. The model canhandle realistic nucleus shapes and alternative physical models for the gas and dust production mechanism.The inner gas coma structure is computed by solving self-consistently(a) near to the surface the Boltzman Equation(b) outside of it, Euler or Navier-Stokes equations.The dust distribution is computed from multifluid ``zero-temperature' Euler equations,extrapolated with the help of a Keplerian fountain model.The evolution of the coma during the nucleus orbital and spin motion,is computed as a succession of quasi-steady solutions. Earlier versions of the model using simple,``paedagogic' nuclei have demonstrated that the surface orographyand the surface inhomogeneity contribute similarly to structuring the near-nucleusgas and dust coma,casting a shadow on the automatic attribution of such structures to ``active areas'.The model was recently applied to comet P/Halley, for whichthe nucleus shape is available. In the companion paper of this volume,we show that most near-nucleus dust structuresobserved during the 1986 Halley flybys are reproduced, assuming that the nucleus is strictly homogeneous. Here, we investigate the effect of shape perturbations and homogeneityperturbations. We show that the near nucleus gas coma structure is robust vis-a-vissuch effects. In particular, a random distribution of active and inactive areaswould not affect considerably this structure, suggesting that such areas,even if present, could not be easily identified on images of the coma.  相似文献   

The brightness temperature problem in extreme intra-day variable quasars: a model for PKS 0405-385     

R. J. Protheroe 《Monthly notices of the Royal Astronomical Society》2003,341(1):230-238

I re-examine the brightness temperature problem in PKS 0405-385, which is an extreme intra-day variable radio quasar with an inferred brightness temperature of  ∼5 × 10¹⁴ K  at 5 GHz, well above the Compton catastrophe limit of  ∼10¹¹ K  that is reached when the synchrotron photon energy density exceeds the energy density of the magnetic field. If one takes into account the uncertainty in the distance to the ionized clouds responsible for interstellar scintillation causing rapid intra-day variability in PKS 0405-385, it is possible that the brightness temperature could be as low as  ∼10¹³ K  at 5 GHz, or even lower. The radio spectrum can be fitted by optically thin emission from mono-energetic electrons, or an electron spectrum with a low-energy cut-off such that the critical frequency of the lowest energy electrons is above the radio frequencies of interest. If one observes optically thin emission along a long narrow emission region, the average energy density in the emission region can be many orders of magnitude lower than calculated from the observed intensity if one assumed a spherical emission region. I discuss the physical conditions in the emission region and find that the Compton catastrophe can then be avoided using a reasonable Doppler factor. I also show that MeV to 100-GeV gamma-ray emission at observable flux levels should be expected from extreme intra-day variable sources such as PKS 0405-385.  相似文献