A Numerical Simulation Study of Mass Segregation in Embedded Stellar Clusters     

ER Xin-yue  JIANG Zhi-bo  FU Yan-ning 《Chinese Astronomy and Astrophysics》2009

The initial condition of the formation of massive stars is still unclear at present. In particular, it is still debatable whether or not massive stars are formed in the cluster center. Some people considered from the viewpoint of time scale and thought that the mass segregation phenomena in embedded clusters means that the massive stars can only be born in the cluster center. In this paper we used the Monte Carlo method to make numerical simulation of the dynamical evolution of embedded clusters and the result is compared with the observations. It is assumed that at the initial time massive stars are randomly distributed. It was found that, due to the random motions of massive stars, temporary mass segregation may exist at certain times in the course of evolution of a given embedded cluster, and this phenomenon may be very prominent in some of them. It is pointed out that massive star formation in the center is not the only explanation for mass segregation in embedded clusters. In addition, dynamical friction from the gas can effectively reduce the time scale of the dynamical mass segregation. In consequence, the probability of temporary mass segregation is increased.  相似文献   

Old stellar population synthesis: new age and mass estimates for Mayall Ⅱ = G1     

Jun Ma  Richard de Grijs  Zhou Fan  Soo-Chang Rey  Zhen-Yu Wu  Xu Zhou  Jiang-Hua Wu  Zhao-Ji Jiang  Jian-Sheng Chen  Kyungsook Lee  Sangmo Tony Sohn 《中国天文和天体物理学报》2009,9(6)

Mayall Ⅱ = G1 is one of the most luminous globular clusters (GCs) in M31. Here, we determine its age and mass by comparing multicolor photometry with theo-retical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBV RI, and infrared JHK8 2MASS data, we construct the most extensive spectral energy distribution of G1 to date, spanning the wavelength range from 1538 to 20000A. A quantitative comparison with a variety of simple stellar pop-ulation (SSP) models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ～1.7Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates (of order 107M⊙) indicate that G1 is one of the most massive GCs in the Local Group. However, we speculate that the cluster's exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, (1.65±0.63) × 102L⊙ far-ultraviolet-bright, hot, extreme horizontal-branch stars, depend-ing on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar pho-tometry, provided that some of the free parameters can be constrained independently.  相似文献   

Open cluster ASCC21 as a probable birthplace of the neutron star Geminga     

V. V. Bobylev  A. T. Bajkova 《Astronomy Letters》2009,35(6):396-405

We analyze the encounters of the neutron star (pulsar) Geminga with open star clusters in the OB association Ori OB1a through the integration of epicyclic orbits into the past by taking into account the errors in the data. The open cluster ASCC21 is shown to be the most probable birthplace of either a single progenitor star for the Geminga pulsar or a binary progenitor system that subsequently broke up. Monte Carlo simulations of Geminga-ASCC21 encounters with the pulsar radial velocity V _r = ?100±50 km s^?1 have shown that close encounters could occur between them within ≤10 pc at about t = ?0.52 Myr. In addition, the trajectory of the neutron star Geminga passes at a distance of ≈25 pc from the center of the compact OB association λ Ori at about t = ?0.39 Myr, which is close to the age of the pulsar estimated from its timing.  相似文献   

Integrated spectroscopic study of 7 star clusters in the Small Magellanic Cloud     

M.L. Talavera  A.V. Ahumada  J.F.C. Santos  Jj. Clari  E. Bica  M.C. Parisi  M.C. Torres 《Astronomische Nachrichten》2010,331(3):323-329

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A binary study of color-magnitude diagrams of 12 globular clusters     

Zhong-Mu Li    Cai-Yan Mao  Ru-Heng Li  Ru-Xi Li  Mao-Cai Li College of Physics  Electronic Information  Dali University  Dali  China  National Astronomical Observatories  Chinese Academy of Sciences  Beijing 《中国天文和天体物理学报》2010,10(2)

Binary stars are common in star clusters and galaxies, but the detailed effects of binary evolution are not taken into account in some color-magnitude diagram (CMD) studies. This paper studies the CMDs of twelve globular clusters via binarystar stellar populations. The observational CMDs of the star clusters are compared to those of binary-star populations, and then the stellar metallicities, ages, distances and reddenings of these star clusters are obtained. The paper also tests the different effects of bi...  相似文献   

The enhanced spectrum of the symbiotic variable star CH Cygni on November 2, 2006     

Kye Hwa Yoo   《New Astronomy》2010,15(2):215-226

The symbiotic variable star CH Cygni went on the deepest minimum phase in December 2006. A high-resolution spectrum of CH Cygni obtained at the Bohyunsan Optical Astronomy Observatory (BOAO) on November 2, 2006, is reported. The spectrum of CH Cygni obtained at the BOAO was calibrated on a scale of an absolute-flux density. Emission lines of H I, [O III], [N II], and [S II] were strong, with several components, and Ca II, H, and K lines had P-Cygni profiles. Removal of the spectrum of the underlying M-type star from the CH Cygni spectrum was completed to obtain the true emission profiles. The radial velocities of all emission and absorption lines were measured. Some of the observed lines were also deconvoluted using multi-Gaussian functions to find the relationship between line shapes and the corresponding sources of these lines. The results obtained are discussed in terms of an accretion disk around the hot star, and in non-spherically extended nebular regions.  相似文献   

Non-symmetrical sparking may hint “zits” on a pulsar surface     

Zhengli Wang  Jiguang Lu  Jingchen Jiang  Shunshun Cao  Weiyang Wang  Enwei Liang  Renxin Xu 《Astronomische Nachrichten》2024,345(2-3):e240010

Pulsar electrodynamics could be relevant to the physics of stellar surface, which remains poorly understood for more than half a centenary and is difficult to probe due to the absence of direct and clear observational evidence. Nevertheless, highly sensitive telescopes (e.g., China's Five-hundred-meter Aperture Spherical radio Telescope, FAST) may play an essential role to solve the problem since the predicted surface condition would have quite different characteristics in some models of pulsar structure, especially after the establishment of the standard model of particle physics. For instance, small hills (or “zits”) may exist on solid strangeon star surface with rigidity, preferential discharge, that is, gap sparking, may occur around the hills in the polar cap region. In this work, with the 110-min polarization observation of PSR B0950 $$08 targeted by FAST, we report that the gap sparking is significantly non-symmetrical to the meridian plane on which the rotational and magnetic axes lie. It is then speculated that this asymmetry could be the result of preferential sparking around zits which might rise randomly on pulsar surface. Some polarization features of both single pulses and the mean pulse, as well as the cross-correlation function of different emission regions, have also been presented.  相似文献   

Kinematics of gas and stars in the circumnuclear star-forming ring of NGC 3351     

Guillermo F. Hägele †  Ángeles I. Díaz ‡  Mónica V. Cardaci †  Elena Terlevich §  Roberto Terlevich § 《Monthly notices of the Royal Astronomical Society》2007,378(1):163-178

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Characteristics Of Chaotic Attractors In Atmospheric Boundary-Layer Turbulence   总被引：3，自引：1，他引：3  

Li Xin  Hu Fei  Liu Gang 《Boundary-Layer Meteorology》2001,99(2):335-345

In this paper, the attractors of turbulent flows in phase space are reconstructed by the time delay technique using observed data of atmospheric boundary-layer turbulence, which include high resolution temperature, humidity andthree-dimensional wind speed measurements in Gansu province and Beijing, China. The correlation dimensions and largest Lyapunov exponents have been computed. The results indicate that all the largest Lyapunov exponents in different conditions of time, site and atmospheric stability are greater than zero. This means that the atmospheric boundary-layer turbulence system is really chaotic and has appropriate low-dimensional strange attractors whose dimension numbers range from 3 to 7 and vary with different variables (dynamical variables or non-dynamical variables) and atmospheric stability. Turbulent kinetic energy is first applied to reconstruct the attractor of turbulence, and is found to be feasible.  相似文献   

Statistical Revision of the Moment Method     

Joris De Ridder  Geert Molenberghs  Conny Aerts 《Astrophysics and Space Science》2003,284(1):125-128

The moment method is a well known technique, which uses a time series ofthe first 3 moments of a spectral line, to estimate the (discrete) modeparameters and m. The method, contrary to Doppler imaging,also yields other interesting(real-valued) parameters such as the inclination angle i, or v sin i,during its identification procedure.In this paper, we are not only interested in the estimation of thesereal-valued parameters themselves but also inreliable estimates for their uncertainty.We designed a statistical formalism for the moment method based on theso-called generalized estimating equations (GEE). This formalismaims to estimate the uncertainty of the real-valued parameters taking intoaccount that the different moments of a line profile are correlated and –more importantly – that the uncertainty of the observed moments depends onthe pulsation parameters. The latter property of the moment method makesthe least-squares technique a poor choice to estimate the uncertainty ofthe real-valued parameters. We implemented the GEE method and presentan application to a high-resolution spectroscopic dataset of the slowly pulsating B star HD181558.  相似文献