12颗碳星的近红外测光

本文给出了银河系12颗碳星的J、H、K波段的测光结果,并讨论了星际红化的影响。对碳星在(J—H)-(H—K)双色指数图上的分布作了探讨,并利用(J—K)色指数得出各星的热改正和热星等。     

COSMOS场中高红移大质量星系的形态分类研究

基于COSMOS(Cosmic Evolution Survey)天区的多波段测光数据和HST(Hubble Space Telescope)近红外高分辨率观测图像,利用质量限(恒星质量M*≥1010.5M⊙)选取了362个红移分布在1≤z≤3的星系样本,并对这些大质量星系的形态特征进行了分类研究.来自UVJ(U-V和V-J)双色图分类系统、目视分类系统、非模型化分类系统(基尼系数G和矩指数M20)和模型化分类系统(S′ersic index,n)的分类结果彼此相一致.相比较于恒星形成星系(SFGs),通过UVJ双色图定义的宁静星系(QGs)表现出致密的椭圆结构,而且G和n值偏大,但M20和星系有效半径(re)偏小.不同星系分类系统(双色图分类系统、非模型化分类系统和模型化分类系统)定义的SFGs和QGs样本,都明显存在星系的大小随红移的演化关系,这种演化趋势QGs比SFGs更剧烈,而且不依赖于星系分类方法的选择.     

碳星的JHK测光及其有效温度

本文给出了银河系24颗碳星的JHK波段的测光结果,文中时论了碳星在(J-H)-(H-K)双色指数图上的分布。给出了各星的热改正和热星等。 文中特别讨论了碳星的有效温度,并利用两种不同的方法分别得出了各星的有效温度。     

巨早型星系的近红外谱合成

在8000至8670的波长范围内,利用一个由144颗恒星光谱组成的光谱厍,我们对57个巨椭圆和S0星系(M_B<-21)的光谱和它们的平均光谱进行了光谱合成.这个光谐库包括了光谱型为G,K和M的巨星和矮星,它具有的金属丰度[Fe/H]覆盖了-0.1到-0.5的范围,表面重力log g为1.0至5.0.光谱合成的结果表明:巨椭圆和S0星系的金属丰度约为太阳的一倍半;有效表面重力分布在3.2—4.1的范围内;矮星在8400附近光的贡献可与巨星相比较.     

恒星脉泽源的红外观测研究

本文在JHK波段观测和IRAS观测资料基础上,与正常M巨星相比较,给出恒星脉泽源在1—100μm波段的红外特性,并讨论了这些特性产生的原因。     

LAMOST-Kepler视场中富锂巨星表面转动研究

Kepler卫星提供的长时序、高精度的光度观测和郭守敬望远镜(LAMOST)提供的大规模光谱观测为研究恒星表面转动周期与富锂巨星锂丰度关系提供了良好的数据.将LAMOST搜寻到的富锂巨星与Kepler观测交叉,获得了619颗共同源,研究了其中295颗有良好观测数据的富锂巨星的表面转动.在205颗有星震学参数的恒星中提取出14颗恒星的转动周期,其中氦核燃烧星(HeB) 11颗,红巨星支(RGB) 2颗, 1颗演化阶段未确定.本样本中的极富锂巨星(A(Li) 3.3 dex)皆为HeB;对于90颗没有星震学参数的样本因而没有依靠星震学手段确定演化阶段的恒星中,有22颗提取出了自转周期.前者的自转探测率为6.8%,显著高于之前工作中大样本巨星2.08%的探测率.同时,此研究首次从自转周期的角度确认了恒星转动与巨星锂增丰存在相关性,在增丰程度较弱时,自转周期分布比较弥散;强锂增丰的星倾向于快速转动.富锂巨星与极富锂巨星在转动速度随锂丰度的演化上展现了两个序列,在转动-锂丰度图上的A(Li)≈3.3 dex处产生第2个下降序列,或许暗示了两者在形成机制上的不同.极富锂巨星的样本中,随巨星锂增丰程度增强,恒星转速加快.这种相关性为由转动引起的额外混合作为富锂巨星形成的机制提供了支持.     

红外双色图中的黑体线

本文给出了各种红外双色图中的黑体线方程并进行了具体的计算。应用本文的计算结果，可以方便地确定双色图中的黑体线，而不必再进行一系列繁杂的计算。此外，文中还详细地讨论了红外双色图中黑体线的数学性质和物理意义。     

硅酸盐碳星的红外观测及能谱分布

本文对赤纬负10°以北的所有11颗硅酸盐碳星进行了近红外JHK观测．结合可见波段及红外天文卫星的观测结果,讨论了它们的红外双色图及能谱分布,并将其与正常碳星的结果相比较,进而讨论了它们的演化状态．     

COSMOS场中星系恒星形成的演化研究

基于COSMOS(Cosmic Evolution Survey)/Ultra VISTA(Ultra-deep Visible and Infrared Survey Telescope for Astronomy)场中多波段测光数据,利用质量限选取了红移分布在0z3.5的星系样本.通过UVJ(U-V和V-J)双色图分类判据将星系分类成恒星形成星系(SFGs)和宁静星系(QGs).对于红移分布在0z1.5范围内且M*1011M⊙的QGs来说,该星系在样本中所占比例高于70%.在红移0z3.5范围内,恒星形成星系的恒星形成率(SFR)与恒星质量(M*)之间有着很强的主序(MS)关系.对于某一固定的恒星质量M*来说,星系的SFR和比恒星形成率(s SFR)会随着红移增大而增大,这表明在高红移处恒星形成星系更加活跃,有激烈的恒星形成.相对于低质量的星系来说,高质量的SFGs有较低的s SFR,这意味着低质量星系的增长更多的是通过星系本身的恒星形成.通过结合来自文献中数据点信息,发现更高红移(2z8)星系的s SFR随红移的演化趋势变弱,其演化关系是s SFR∝(1+z)0.94±0.17.     

红外双图中的黑体线

本文给出了各种红外红色图中的黑体线方程并进行了具体的计算，应用本文的计算结果，可以方便地确定了双色图中的黑体线，而不必再进行一系列繁杂的计算，此外，文中还详细地讨论了红外双色图中黑体线的数学性质和物理意义。     

On asteroid distribution

The existing explanations for the asteroid distribution in the main belt (between the orbits of Mars and Jupiter) are based on numerical integration of resonance orbits in models with more than two degrees of freedom. We suggest an approach based on the investigation of the families of periodic solutions of the planar circular restricted three-body problem, i.e., a model with two degrees of freedom. This work shows that (a) the distribution of asteroids near the (p + 1)/p resonances and position of the outer boundary of the main asteroid belt can be explained within the planar circular restricted three-body problem and (b) this problem does not explain the asteroid distribution near other resonances.     

Wavelength dependence of the polarization of radiation from an accretion disk: Testing accretion disk models

We show that a fundamental choice between various models of an accretion disk around a black hole can be made based on the spectral wavelength distribution of the polarization. This conclusion is based on the possibility of comparing the observed spectral distribution of the polarization with its theoretical values obtained in various accretion disk models. The expected power-law wavelength (frequency) dependences of the polarization for various accretion disk models known in the literature are presented in the table.     

Occurrence Probability of Large Solar Energetic Particle Events: Assessment from Data on Cosmogenic Radionuclides in Lunar Rocks

We revisited assessments of the occurrence probability distribution of large events in solar energetic particles (SEP), based on measurements of cosmogenic radionuclides in lunar rocks. We present a combined cumulative occurrence probability distribution of SEP events based on three timescales: directly measured SEP fluences for the past 60 years; estimates based on the terrestrial cosmogenic radionuclides ¹⁰Be and ¹⁴C for the multi-millennial (Holocene) timescale; and cosmogenic radionuclides measured in lunar rocks on a timescale of up to 1 Myr. These three timescales yield a consistent distribution. The data suggest a strong roll-over of the occurrence probability, so that SEP events with a proton fluence with energy >?30 MeV greater than 10¹¹ (protons cm^?2?yr^?1) are not expected on a Myr timescale.     

Can self-organized critical accretion disks generate a log-normal emission variability in AGN?

Active Galactic Nuclei (AGN), such as Seyfert galaxies, quasars, etc., show light variations in all wavelength bands, with various amplitude and in many time scales. The variations usually look erratic, not periodic nor purely random. Many of these objects also show lognormal flux distribution and RMS–flux relation and power law frequency distribution. So far, the lognormal flux distribution of black hole objects is only observational facts without satisfactory explanation about the physical mechanism producing such distribution in the accretion disk. One of the most promising models based on cellular automaton mechanism has been successful in reproducing PSD (Power Spectral Density) of the observed objects but could not reproduce lognormal flux distribution. Such distribution requires the existence of underlying multiplicative process while the existing SOC models are based on additive processes. A modified SOC model based on cellular automaton mechanism for producing lognormal flux distribution is presented in this paper. The idea is that the energy released in the avalanche and diffusion in the accretion disk is not entirely emitted instantaneously as in the original cellular automaton model. Some part of the energy is kept in the disk and thus increase its energy content so that the next avalanche will be in higher energy condition and will release more energy. The later an avalanche occurs, the more amount of energy is emitted to the observers. This can provide multiplicative effects to the flux and produces lognormal flux distribution.     

Distribution of PSF of The Near Earth Object Survey Telescope

The CCD field of view of the Near Earth Object Survey Telescope (NEOST) is 1.94°xl.94°. As a wide-field telescope, the focusing based on a single star will lead to an uneven distribution of PSF (Point Spread Function) on the CCD image due to the field curvature. The features of the PSF distribution on the CCD image are studied. By fitting the relation between the defocusing and the FWHM (Full Width at Half Maximum) of PSF, the curved focal surface is simulated and therefore the best imaging plane is determined. Hereby, a focusing method based on the optimum imaging plane determined by judging the histogram of FWHM is proposed.     

The period distribution of eclipsing and spectroscopic binary systems,II

A statistical analysis of period distribution for eclipsing and spectroscopic binary systems, based on the spectral types of the components, shows several common features between the two independent samples. The similarity is increased if we eliminate the geometrical selection effect on the eclipsing binaries sample by means of the method described in previous papers. The period distribution becomes broader (and probably non-unimodal) for advanced spectral types.We also performed an analysis of the mean separation of systems as a function of the spectral type.     

On the Reliability of Merger-Trees and the Mass-Growth Histories of Dark Matter Haloes

We have used merger-trees realizations to study the formation of dark matter haloes. The construction of merger-trees is based on three different pictures about the formation of structures in the Universe. These pictures include the spherical collapse (SC), the ellipsoidal collapse (EC) and the non-radial collapse (NR). The reliability of merger-trees has been examined comparing their predictions related to the distribution of the number of progenitors, as well as the distribution of formation times, with the predictions of analytical relations. The comparison yields a very satisfactory agreement. Subsequently, the mass-growth histories (MGH) of haloes have been studied and their formation scale factors have been derived. This derivation has been based on two different definitions that are (a) the scale factor when the halo reaches half its present day mass and (b) the scale factor when the mass-growth rate falls below some specific value. Formation scale factors follow approximately power laws of mass. It has also been shown that MGHs are in good agreement with models proposed in the literature that are based on the results of N-body simulations. The agreement is found to be excellent for small haloes but, at the early epochs of the formation of large haloes, MGHs seem to be steeper than those predicted by the models based on N-body simulations. This rapid growth of mass of heavy haloes is likely to be related to a steeper central density profile indicated by the results of some N-body simulations.     

A dynamical condition for a relativistic galaxy cluster model

In an attempt to give a coherent interpretation of the secondary maximum in the density distribution of clusters of galaxies we use an approximate metric tensor proposed by other authors, with the purpose of building a relativistic generalization of the isothermal models of galaxy clusters.Although such a generalization gives rise to oscillations in the density distribution, the quantitative agreement with the observational data is unsatisfactory.The analysis of the metric tensor we have used brings us to point out that (i) the approximation on which the metric is based is not suitable for describing an actual galaxy cluster and (ii) the dynamical conditions of clusters require inclusion of a cosmological expansion, and of anisotropic distribution function in the phase-space.     

Statistical technique to study the connection between large‐scale structures in the ISM and low‐mass star formation

Applying a color index selection the Point Source Catalog of the Two Micron All Sky Survey (2MASS PSC) has been searched for Classical T Tauri (CTT) stars in the 2nd and 3rd Galactic quadrant based on their apparent K_S excess. The selection resulted in 3872 reliable CTT candidates. The obtained CTT sample is extended enough for statistical examination of the inhomogeneities in their distribution due to correlation with structures in the ISM, like infrared loops. A correlation was observed between the presence of dust loops and the CTT density. The latter shows an excess on loops with respect to that expected from random fluctuation in a homogeneous distribution matching with the observed overall distribution. Monte Carlo simulations were used to show the significance of the excess. The results imply that the formation of a fraction of CTTs was triggered during the loop formation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

How rapidly do neutron stars spin at birth? Constraints from archival X-ray observations of extragalactic supernovae

Traditionally, studies aimed at inferring the distribution of birth periods of neutron stars are based on radio surveys. Here we propose an independent method to constrain the pulsar spin periods at birth based on their X-ray luminosities. In particular, the observed luminosity distribution of supernovae (SNe) poses a constraint on the initial rotational energy of the embedded pulsars, via the     correlation found for radio pulsars, and under the assumption that this relation continues to hold beyond the observed range. We have extracted X-ray luminosities (or limits) for a large sample of historical SNe observed with Chandra , XMM and Swift , which have been firmly classified as core-collapse SNe. We have then compared these observational limits with the results of Monte Carlo simulations of the pulsar X-ray luminosity distribution for a range of values of the birth parameters. We find that a pulsar population dominated by millisecond periods at birth is ruled out by the data.