共查询到19条相似文献,搜索用时 359 毫秒
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利用星团谱样本的星族合成方法,分析了7个BCDG的光学谱,研究蓝致密矮星系(BCDG)内部的恒星形成历史、能源机制和尘埃分布情况.星族合成结果不仅能够解释BCDG的主要观测特征,解决BCDG研究中存在的一些问题,而且揭示了BCDG的一些未知的特性.谱合成结果表明:BCDG是年老的天体,其内部较早已经有恒星形成发生,恒星形成呈爆发式的,在t=5×107~109yr时的恒星形成率较高,最近(t=107yr)的恒星形成率开始下降;光谱分析显示大量大质量的年轻恒星提供了BCDG中心区的主要能源.利用扣除恒星吸收影响的发射线光谱,计算了发射线产生区的内红化值,发现它明显大于由连续谱计算得到的内红化值,这种差异的可能解释是BCDG内部尘埃对连续谱和发射线的产生区遮挡程度不同.最后,比较了BCG和BCDG星族合成结果,提出了矮星系间一种可能的演化序列. 相似文献
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总结了星族综合模型的两个要素:处于根本地位的恒星演化计算,以及把理论赫罗图转化为可观测量的光谱定标。当前恒星模型中的不确定性来自于输入的物理参数;原子数据,对流理论,辐射区的混合和和质量丢失。光谱定标不准是因为尚没有准确的温度测定,准确的分光光度测量,而且光谱库中缺少一些类型的恒星。 相似文献
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星族合成方法及发射线星系核区中的恒星组分 总被引:1,自引:0,他引:1
论述星族合成方法对研究复合恒星体系的重要意义。综述了星族合成的三种基本方法,着重介绍了以星团光谱为样本的星族合成方法及其应用,最后,作为一个例子,我们利用CSPS方法给出发射线星系Mrk499谱的合成结果。 相似文献
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第一代恒星(星族Ⅲ恒星)标志着宇宙从暗物质时代到现在已知的宇宙的转折点。目前对第一代恒星(星族Ⅲ恒星)的观测结果表明,在银河系中还没有发现零金属丰度的恒星,金属丰度[Fe/H]≤-2.5的恒星极少。由于近几年的BPS巡天,银河系中已知的极端贫金属丰度的恒星数目大大增多。目前,可探测到的极端贫金属星的金属丰度[Fe/H]最低约为-4.1。金属丰度在-4到-3之间的恒星大约有100多颗,这些恒星的运动学特性非常类似于其它晕星。然而还没有发现第一代恒星,或金属丰度[Fe/H]≤-5的恒星。关于第一代恒星的形成过程、初始质量函数以及存在于银河系的什么地方,都还没有任何直接的证据。但第一代恒星确实存在。第一代恒星这个谜一般的实体,向观测和理论天文学家提出了巨大挑战。为探测和预言银河系中的第一代恒星,天文学家提出了许多观测方案和理论模型。对有关第一代恒星在观测和理论研究上的进展进行了综述。 相似文献
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本文根据球状星团所特有的金属丰度特征,利用星族综合方法,探讨了球状星团诸恒星的形成史。研究表明,这些恒星不可能通过恒星形成率和初始质量函数均不随时间变化的单一恒星形成模式产生。原初云通过恒星演化而得到金属丰度污染的过程和多数恒星的形成过程必须分为两个不同的阶段。 球状星团得到金属丰度污染的过程中,若恒星形成具有通常的初始质量函数,则其恒星形成率必须较低,且初始质量函数不能太陡,从而使污染过程中只形成数量较少的低质量恒星,以保证单个球状星团内金属丰度的均匀性。另一种可能性是污染阶段有非常特殊的初始质量函数,只形成大质量的恒星,从而除提供适量污染外不留下任何痕迹。 多数恒星应是在原初云不同部位得到适当污染后通过局域的短暂的爆发性恒星形成(星暴过程)产生。本文进一步探讨了在Fan和Rees球状星团形成模型的框架下,两相介质中温云块相互碰撞造成星暴过程的可能性。 相似文献
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仙女星系(M31)是距离地球最近的大型旋涡星系,与银河系结构相似且质量相当,对M31天体的光谱观测与研究有助于理解银河系以及一般星系的形成与演化历史。整理了自20世纪以来天文学家对M31中天体的相关光谱观测与研究成果,共涉及了M31中5 000余个发射线天体、2 000余个星团、6 000余颗恒星、1 000余颗新星以及核球和盘上的星族的光谱。恒星光谱观测由早期的以超巨星为主发展到近20年更大样本以及更多类型,其中红巨星被用于研究M31星系盘和晕的性质及子结构。发射线天体通常被应用于M31质量测定、运动学分析和恒星演化的研究。M31星团的研究集中于金属丰度和运动学性质,以及利用视向速度测定M31位力质量。对M31中心星族的研究主要集中于核区的星族组成和运动学分析,其中运动学研究结果更支持核区的偏心盘模型。最后,介绍了郭守敬望远镜对M31天体的光谱观测与相关科学研究。 相似文献
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新宇 《紫金山天文台台刊》2003,(2)
作为目前研究复杂恒星系统的有力工具 ,星族合成方法是建立在单星演化理论基础之上的 ,因此 ,必然有其不完善性存在 ,尤其当系统中的双星成分不容忽视时。作为演化星族合成方法的基本单元 ,简单恒星星族模型的构成即排除了双星贡献。本文中 ,我们以银河系疏散星团为简单恒星星族模板 ,构造出一系列简单恒星星族积分光谱。从中我们可以看到 :蓝离散星这类理论上主要来源于双星系统的恒星 ,对星团积分光谱的紫外及蓝端有很大影响 ,从而造成简单恒星星族积分光谱能量分布的改变。这种改变势必影响对星团年龄及其它一些物理参量的判定 ,并最终影响星族合成的结果。同时 ,若以 (B -V )色指数进行度量 ,蓝离散星对简单恒星星族积分颜色的影响可达到 30 %。工作中 ,我们选取了 2 6个年龄在1x10 1 0 ~ 6x10 1 0 年之间的疏散星团为样本进行统计研究。 相似文献
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R. M. González Delgado M. Cerviño L. P. Martins C. Leitherer P. H. Hauschildt 《Monthly notices of the Royal Astronomical Society》2005,357(3):945-960
We present the single stellar population (SSP) synthesis results of our new synthetic stellar atmosphere models library with a spectral sampling of 0.3 Å, covering the wavelength range from 3000 to 7000 Å for a wide range of metallicities (twice solar, solar, half solar and 1/10 solar). The stellar library is composed of 1650 spectra computed with the latest improvements in stellar atmospheres. In particular, it incorporates non-local thermodynamic equilibrium (LTE) line-blanketed models for hot ( T eff ≥ 27 500 K) , and LTE line-blanketed models (Phoenix) for cool (3000 ≤ T eff ≤ 4500 K) stars. Because of the high spectral resolution of this library, evolutionary synthesis models can be used to predict the strength of numerous weak absorption lines and the evolution of the profiles of the strongest lines over a wide range of ages. The SSP results have been calculated for ages from 1 Myr to 17 Gyr using the stellar evolutionary tracks provided by the Geneva and Padova groups. For young stellar populations, our results have a very detailed coverage of high-temperature stars with similar results for the Padova and Geneva isochrones. For intermediate and old stellar populations, our results, once degraded to a lower resolution, are similar to the ones obtained by other groups (limitations imposed by the stellar evolutionary physics notwidthstanding). The limitations and advantages of our models for the analysis of integrated populations are described. The full set of the stellar library and the evolutionary models are available for retrieval at the websites http://www.iaa.csic.es/~rosa and http://www.iaa.csic.es/~mcs/sed@ , or on request from the first two authors. 相似文献
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We present results of evolutionary computations for massive close binaries with the Brussels simultaneous evolution code for
conservative and non-conservative Roche lobe overflow (RLOF). We discuss mass transfer in massive close binaries during phases
of RLOF, common envelope, spiral-in and merging. We examine the effects of stellar wind during successive stellar evolution
phases and the final fate of primaries. We show how our library can be used to explain well-known binaries such as the WR
+ OB system V444 Cyg, HMXBs Vela X-1 and Wray 977, LMXBs like Her X-1, and binary pulsars. More details on the evolution of
massive close binaries can be found in “The Brightest Binaries” (Vanbeveren et al., 1998). 相似文献
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《New Astronomy》2007,12(1):20-28
We describe a simple computer package which illustrates a method of combining stellar dynamics with stellar evolution. Though the method is intended for elaborate applications (especially the dynamical evolution of rich star clusters) it is illustrated here in the context of three-body scattering, i.e. interactions between a binary star and a field of single stars. We describe the interface between the dynamics and the two independent packages which describe the internal evolution of single stars and binaries. We also give an example application, and introduce a stand alone utility for the visual presentation of simulation results. 相似文献
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Casey A. Meakin Tuguldur Sukhbold W. David Arnett 《Astrophysics and Space Science》2011,336(1):123-128
Issues concerning the structure and evolution of core collapse progenitor stars, and stellar evolution in general, are discussed
with an emphasis on interior evolution. We discuss some recent results that address quantifying the uncertainties inherent
in modern stellar evolution calculations, and we describe a research effort aimed at investigating the transport and mixing
processes associated with stellar turbulence, which is arguably the greatest source of uncertainty in supernova progenitor
structure, besides mass loss, at the time of core collapse. We highlight the important role played by precision observations
of stellar parameters in constraining theoretical models, as well as the physical insight that can be garnered from three-dimensional
hydrodynamic simulation. 相似文献
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Mirek Giersz 《Monthly notices of the Royal Astronomical Society》2001,324(1):218-230
A revision of Stodółkiewicz's Monte Carlo code is used to simulate evolution of large star clusters. The new method treats each superstar as a single star and follows the evolution and motion of all individual stellar objects. A survey of the evolution of N -body systems influenced by the tidal field of a parent galaxy and by stellar evolution is presented. The process of energy generation is realized by means of appropriately modified versions of Spitzer's and Mikkola's formulae for the interaction cross-section between binaries and field stars and binaries themselves. The results presented are in good agreement with theoretical expectations and the results of other methods (Fokker–Planck, Monte Carlo and N -body). The initial rapid mass loss, resulting from stellar evolution of the most massive stars, causes expansion of the whole cluster and eventually leads to the disruption of less bound systems ( W 0 =3). Models with larger W 0 survive this phase of evolution and then undergo core collapse and subsequent post-collapse expansion, like isolated models. The expansion phase is eventually reversed when tidal limitation becomes important. The results presented are the first major step in the direction of simulating evolution of real globular clusters by means of the Monte Carlo method. 相似文献
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M. A. P. Torres J. Casares I. G. Martínez-Pais P. A. Charles 《Monthly notices of the Royal Astronomical Society》2002,334(1):233-240
We present a library of 47 open-cluster integrated spectra, mostly obtained at CASLEO (San Juan, Argentina) in the range 3600 < λ < 7400 Å , which are made available at CDS. The data are combined with previous spectra to obtain 10 high signal-to-noise ratio basic templates in the young and intermediate-age domains, which are also provided in the library. These Galactic disc templates represent the increased time resolution spectral evolution of a stellar population unit around the Solar metallicity level. The improved signal-to-noise ratio of the present templates with respect to previous template lists, together with their increased time resolution, allowed us to improve the fundamental parameters of some open clusters. The present spectral library will be useful for several astrophysical applications, particularly for population syntheses of star-forming giant galaxies. 相似文献
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Noriyuki Matsunaga 《Astrophysics and Space Science》2012,337(1):93-98
We present an automatic, fast, accurate and robust method of classifying astronomical objects. The Self Organizing Map (SOM)
as an unsupervised Artificial Neural Network (ANN) algorithm is used for classification of stellar spectra of stars. The SOM
is used to make clusters of different spectral classes of Jacoby, Hunter and Christian (JHC) library. This ANN technique needs
no training examples and the stellar spectral data sets are directly fed to the network for the classification. The JHC library
contains 161 spectra out of which, 158 spectra are selected for the classification. These 158 spectra are input vectors to
the network and mapped into a two dimensional output grid. The input vectors close to each other are mapped into the same
or neighboring neurons in the output space. So, the similar objects are making clusters in the output map and making it easy
to analyze high dimensional data. 相似文献