星族合成方法及发射线星系核区中的恒星组分

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。     

Young Populations in the Nuclei of Barred Galaxies

We have conducted UBVRI and H_α CCD photometry of five barred galaxies (NGC 2523, NGC 2950, NGC 3412, NGC 3945 and NGC 5383),along with SPH simulations, in order to understand the origin of young stellar populations in the nuclei of barred galaxies. The H_α emission, which is thought to be emitted by young stellar populations, is either absent or strongly concentrated in the nuclei of early-type galaxies (NGC 2950, NGC 3412 and NGC 3945),while they are observed in the nuclei and circumnuclear regions of intermediate-type galaxies with strong bars (NGC 2523 and NGC 5383).SPH simulations of realistic mass models for these galaxies show that some disc material can be driven into the nuclear region by a strong bar potential. This implies that the young stellar populations in the circumnuclear regions of barred galaxies can be formed out of such gas. The existence of nuclear dust lanes is an indication of an ongoing gas inflow and extremely young stellar populations in these galaxies, because nuclear dust lanes such as those in NGC 5383 are not long-lasting features according to our simulations. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Stellar Populations of Early-Type Galaxies in the Fornax Cluster

We have measured central line strengths for a complete sample of early-type galaxies in the Fornax Cluster comprising 11 elliptical and 11 lenticular galaxies, more luminous than M _B=–17. We find that the centres of Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models and have metallicities varying roughly from half to 2.5 times solar. The centres of (relatively low luminosity) lenticular galaxies, however, exhibit a substantial spread to younger luminosity-weighted ages indicating amore extended star formation history. Our conclusions are based on two age/metallicity diagnostic diagrams in the Lick/IDS system comprising established indices such as [MgFe]and H_β as well as new and more sensitive indices, such as Fe3and H . The inferred difference in the age distribution between lenticular and elliptical galaxies is a robust conclusion as the models generate consistent relative ages using different age and metallicity indicators even though the absolute ages remain uncertain. The absolute age uncertainty is caused mainly by the effects of non-solar abundance ratios, which are not accounted for in the stellar population models. We find that Es are generally overabundant in magnesium and the most luminous galaxies show stronger overabundances. The luminosity-weighted stellar populations of young S0s are consistent with solar abundance ratios or a weak Mg under abundance. Two of the faintest lenticular galaxies in our sample have blue continua and extremely strong Balmer-line absorptions suggesting starbursts <2 Gyr ago. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Origin of S0 Stellar Populations

We investigate a one-zone chemo-photometric evolutionary model of truncated spiral galaxies with and without starbursts in order to explore the origin of the spectrophotometric properties of S0s. First, we show that 1) the tight U-V colour–magnitude (CM) relation cannot reject the model with a starburst and 2) the model with a starburst can explain the difference in the I-K colour–magnitude relation between S0 galaxies and spiral galaxies. Next, we demonstrate how we can distinguish the truncated spirals with a starburst from those without a starburst by using the CaII–Hδ/λ4045 diagram (proposed by Leonardi and Rose, 1996) and the 1550-V colour. This revised version was published online in July 2006 with corrections to the Cover Date.     

Distribution of Young Stellar Populations in the Orion Region

Based on the survey of emission-line stars in a wide field of the Orion star forming region, surface distributions of young stellar populations and gaseous clouds are compared as a whole in an attempt to make a speculation on the star formation process in this region. Existence of a primeval molecular cloud is suggested as the birth site of older members of emission-line stars and probably of X-ray detected pre-main sequence stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Effect of Method of Constructing the Mass Distribution on Single Stellar Populations

We use two methods of constructing the initial mass distribution, the traditional way and Monte Carlo simulation, to obtain integrated U - B, B - V, V-R and V-I colours and absorption-line indices denned by the Lick Observatory image dissector scanner (referred to as Lick/IDS), for instantaneous burst solarmetallicity single stellar populations with ages in the range 1-15 Gyr. We find that the evolutionary curves of all colours obtained by the traditional method are smoother than those by Monte Carlo simulation, that the U - B and B - V colours obtained by the two methods agree with one another, while the V - R and V - I colours by the traditional method are bluer than those by Monte Carlo simulation. A comparison of the Lick/IDS absorption-line indices shows that the variations in all the indices by the traditional method are smoother than that for the Monte Carlo simulation, and that all the indices except for TiO1 and TiO2 are consistent with those for the Monte Carlo simulation.     

The Blue Stragglers and the Integrated Spectral Energy Distribution of Single Stellar Populations

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The Orbits of Cluster Galaxy Populations as Evolutionary Constraints

We determine the mass profile of a synthetic cluster built from the combination of 59 nearby clusters observed in the ESO Nearby Abell Cluster Survey (ENACS). We use ellipticals and S0s as tracers of the cluster potential, and solve the Jeans equation assuming isotropic orbits. Such an assumption is justified by the analysis of the shape of the velocity distribution of ellipticals and S0s. We find that the cluster mass profile is consistent with the Navarro, Frenk and White(NFW) model. We use this cluster mass profile to search for equilibrium solutions for the other cluster galaxy populations: very bright ellipticals (M _R ≤–22+5 log h),early-type spirals (Sa-Sb), and late-type spirals and irregulars (Sbc-Ir), together with emission-line galaxies. We find equilibrium solutions for both the early- and the late-spirals, but not for the very bright ellipticals. The dynamics of very bright ellipticals is probably affected by dissipative processes which invalidate the use of the collisionless Jeans equation. The equilibrium solution found for the early-spirals implies them to move on nearly-isotropic orbits. Late-spirals are instead found to be on mildly radial orbits, with the radial anisotropy increasing outwards. We discuss the implications of these results for the evolutionary histories of the different populations of cluster galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Study of the Emission-Line Spectra and the Stellar Populations of Starburst Galaxies

Based on optical–NIR spectra, we discuss the nebular properties and stellar populations of starburst nuclei. Starbursts are found to have higher electron densities and higher excitations than HII nuclei. The emission lines have been used to estimate the nebular oxygen abundances, ionization parameter and radiation softness parameter. From a study of the H_α emission-line equivalent widths and the CaII triplet absorption line equivalent widths, we infer the ages and stellar content of the starburst regions. Most of the nuclei show evidence for a composite population – a young, ionizing population co-existing with evolved, non-ionizing stars of about 5–7 Myr, which are evolving towards the peak of RSG distribution. This revised version was published online in July 2006 with corrections to the Cover Date.     

The XMM-Newton Bright Serendipitous Survey: First Extragalactic Results

We present here some initial results from the ongoing XMM-Newton bright serendipitous survey. The survey is aimed at selecting and spectroscopically identifying a large and statistically representative sample of bright (f _x ≳ 7× 10⁻¹⁴ c.g.s) serendipitous X-ray sources in the 0.5–4.5 keV energy band (BSS) and a complementary (smaller) sample in the 4.5–7.5 keV energy band (HBSS). The work is partly based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributors directly founded by ESA member states and the USA(NASA) and on observations collected at TNG. The TNG telescope is operated on the island of La Palma by the Centro Galileo Galilei of the INAF in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias. On behalf of the XMM-Newton Survey Science Center.     

The Origin of the Diffuse Hα in Spirals

Using high-quality H_α images of five spiral galaxies, we have studied the luminosity and distribution of the emission from diffuse ionized gas (DIG). The estimated DIG luminosities account for 25–60%of the total H_α emission in each galaxy and analysis of the distribution has shown that the DIG is highly correlated geometrically with the most luminous HII regions of the galaxies. The power required to ionize the DIG is very high. The mean ionization rates per unit surface area of a galaxy disc are of the order of 10⁷ cm^-2 s^-1. Lyman continuum photons (Lyc) from OB asociations are the most probable sources of this ionization. Here we propose a specific model for these sources: we show that the Lyman photon flux that leaks out of the density-bounded HII regions of the galaxies is more than enough to ionize the measured DIG in the five galaxies analysed. This revised version was published online in July 2006 with corrections to the Cover Date.     

First Results from ROTES: The ROtse Telescope Eclipsing-binary Survey

Detached eclipsing binaries (EBs) provide a unique opportunity to carry out stringent tests on stellar evolution models. The value of EBs is enhanced by their membership in open clusters, but the number of known systems is still very scarce. We have started a systematic search for late-type EBs in the nearest open clusters with the fully robotic ROTSE3b telescope at McDonald Observatory in West Texas. On our first campaigns on the Hyades and Collinder 359, we have identified a number of previously unknown eclipsing binary candidates. Some of these stars have been selected for spectroscopic and photometric follow-up. Here we present details of the observing and reduction strategy as well as the first results of this ongoing survey.     

蓝致密星系谱的星族合成

利用星团谱样本的星族合成方法,分析了四个蓝致密星系（ＢｌｕｅＣｏｍｐａｃｔＧａｌａｘｉｅｓ,ＢＣＧ）的光学谱．给出了在各个ＢＣＧ中,年龄和金属丰度不同的星族对星系５８７ｎｍ处连续谱流量贡献的比率,同时还给出ＢＣＧ内部恒星演化的历史和星系内部的红化值．通过对星系内部星族及光谱的分析,解决了ＢＣＧ研究中存在的这类星系年龄和其内部光学不可见物质等问题．结果表明ＢＣＧ是年老星系,其内部恒星形成过程为长时间的宁静相上叠加有短暂且剧烈恒星形成的爆发,其内部存在光学不可见物质,且至少有一部分为年老的球状星团;根据由光学连续谱和发射线计算星系的内红化值的不同,得出ＢＣＧ星系内部尘埃对连续谱和发射线的产生区遮挡程度不同．     

Status and First Results of the Magic Telescope

The 17 m Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope for gamma-ray astronomy between 30 and 300 GeV started operations in its final configuration in October 2003 and is currently well into its calibration phase. Here I report on its present status and its first gamma-ray source detections.