The Gas-to-Dust Relation in the Dark Cloud L1523-Observational Evidence for CO Gas Depletion

Correlation between gas and dust column density has been studied for the dark globule L1523. The 13CO（J=1→0） emission is used for tracing the gas, and the IR emissions, for tracing the dust constituent. In order to match the beam resolution between the images, a beam de-convolution algorithm based on the Maximum Correlation Method （MCM） was applied on the Infrared Astronomical Satellite （IRAS） data. The morphology of 13CO column density map shows a close correlation to that of 100μm dust optical depth. The distribution of the optical depth at 100 μm follows that of gas column density more closely than does the flux map at either 60 or 100μm. The ratio of the 13CO column density to the 100μm optical depth shows a decreasing trend with increasing dust optical depth in the central part, indicating possible molecular gas condensation onto dust particles. The excessive decrease in the CO column density in the envelope may most probably be due to the photo-dissociation of CO molecules.

Correlation among extinction efficiency and other parameters in an aggregate dust model

We study the extinction properties of highly porous Ballistic Cluster-Cluster Aggregate dust aggregates in a wide range of complex refractive indices （1.4 ≤ n 〈 2.0, 0.001 ≤ k 〈 1.0） and wavelengths （0.11 μm 〈 A 〈 3.4 μm）. An attempt has been made for the first time to investigate the correlation among extinction efficiency （Qext）, composition of dust aggregates （n, k）, wavelength of radiation （A） and size parameter of the monomers （x）. If k is fixed at any value between 0.001 and 1.0, Qext increases with increase of n from 1.4 to 2.0. Qext and n are correlated via linear regression when the cluster size is small, whereas the correlation is quadratic at moderate and higher sizes of the cluster. This feature is observed at all wavelengths （ultraviolet to optical to infrared）. We also find that the variation of Qext with n is very small when A is high. When n is fixed at any value between 1.4 and 2.0, it is observed that Qext and k are correlated via a polynomial regression equation （of degree 1, 2, 3 or 4）, where the degree of the equation depends on the cluster size, n and A. The correlation is linear for small size and quadratic/cubic/quartic for moderate and higher sizes. We have also found that Qext and x are correlated via a polynomial regression （of degree 3, 4 or 5） for all values of n. The degree of regression is found to be n and k-dependent. The set of relations obtained from our work can be used to model interstellar extinction for dust aggregates in a wide range of wavelengths and complex refractive indices.

Molecular Gas and Dust in the Massive Star Forming Region S 233 IR

The massive star forming region S 233 IR is observed in the molecular lines CO J = 2–1, 3–2, NH3 (1,1), (2,2) and the 870 um dust continuum. Four submillimeter continuum sources, labelled SMM 1–4, are revealed in the 870 um dust emission. The main core, SMM1, is found to be associated with a deeply embedded near infrared cluster in the northeast; while the weaker source SMM2 coincides with a more evolved cluster in the southwest. The best fit spectral energy distribution of SMM1 gives an emissivity of β = 1.6, and temperatures of 32 K and 92 K for the cold- and hot-dust components. An SMM1 core mass of 246 M☉, and a total mass of 445 M☉ are estimated from the 870 um dust continuum emission. SMM1 is found to have a temperature gradient decreasing from inside out, indicative of the presence of interior heating sources. The total outflow gas mass as traced by the CO J = 3–2 emission is estimated to be 35 M☉. Low velocity outflows are also found in the NH3 (1,1) emission. The non-thermal dominant NH3 line width as well as the substantial core mass suggest that the SMM1 core is a ``turbulent, massive dense core', in the process of forming a group or a cluster of stars. The much higher star formation efficiency found in the southwest cluster supports the suggestion that this cluster is more evolved than the northeast one. Large near infrared photometric variations found in the source PCS-IR93, a previously found highly polarized nebulosity, indicate an underlying star showing the FU Orionis type of behavior.

A multiwavelength view of the ISM in the merger remnant galaxy Fornax A

We present multi-wavelength imagery of the merger remnant galaxy NGC 1316 with an objective to study the dust content and its association with the other phases of the interstellar medium. Color-index maps as well as extinction maps derived for this galaxy reveal an intricate and complex dust morphology in NGC 1316, i.e. there is a prominent lane in the inner part, while at about 6-7 kpc it apparently takes the form of an arc-like pattern extending along the northeast direction. In addition to this, several other dust clumps and knots are also evident in this galaxy. The dust emission mapped using Spitzer data at 8 μm indicates even more complex morphological structures of the dust in NGC 1316. The extinction curve derived over the optical to near-IR bands closely follows the standard Galactic curve, suggesting similar properties of the dust grains. The dust content of NGC 1316, estimated from optical extinction, is ,- 2.13 × 10^5 M⊙. This is a lower limit compared to that estimated using the IRAS flux densities of ,-5.17× 10^6 M⊙ and the flux densities at 24, 70 and 160 p.m from MIPS ,-3.2× 10^7 M⊙. High resolution Chandra observations of this merger remnant system have provided an unprecedented view of the complex nature exhibited by the distribution of hot gas in NGC 1316, which closely matches the morphology of ionized gas and to some extent also the dust. X-ray color-color plots for the resolved sources within the optical D25 extent of NGC 1316 have enabled us to separate them into different classes.

Missing Mass and Galactic Dust with a Size Greater than 200 Microns, Minimum Size of the Micrometric Dust around the Sun

The studies of the glaciologists show that, since 30,000 years, the Earth receives every year approximately 40,000 tons of dust, dust with an average size about 200 microns. By determining of which volume these 40,000 T come and by showing that the density of this volume is significant within the density of the milky way, I have tried to estimate the mass of dust contained in the Galaxy. To support that this density close to earth is representative, arguments are given: 1) the distribution of great dust is largely homogeneous in the galaxy (what does not exclude the existence of gas or dust clouds with different densities in the milky way);2) there would be a minimum size that I have calculated for micrometeorites in the solar environment, and so there would be a lack of the micrometeorites with a size between 5 and 50 microns. So the density would not be greater in the solar system. Next, a very simple rough calculation (as the one made by the observatory of Paris in 1910) allows estimating this mass near 4 times that of the dark matter. So, the interstellar dust with a large size (>200 μ) could it be the missing mass? A verification method is proposed to confirm or refute this hypothesis.

基于ISM的纺织企业粉尘职业危害影响因素分析

通过对纺织企业粉尘职业危害进行现场调查,从人-机-环-管理四个方面分析纺织企业职业危害影响因素,主要包括产尘量、培训教育等12个因素。通过分析各因素之间的相互关系,构建ISM(解释结构模型),借助Matlab2010运用布尔运算,建立递阶结构模型。研究表明,接尘时间和个体防护是直接影响因素,产尘量和管理制度是根本影响因素。ISM分析了系统结构,充分考虑了各影响因素间的深层次关系,利用递阶结构模型清晰的显示影响因素的层次,为纺织企业粉尘职业危害防治提供了理论依据,使防治工作有针对性,防治措施更具有效性。

Multiphase ISM in Nearby Early Type Galaxy IC 5063

A multiwavelength study of a nearby dust lane early-type galaxy IC 5063 is presented. The objectives are to investigate dust extinction properties and the association of interstellar dust with other phases of ISM. The color-index maps as well as the extinction maps derived from the analysis of deep CCD observations in optical passbands revealed a prominent dust lane along its optical major axis in the inner region. In addition, two more fainter and extended dust patterns are apparent in the color index map as well as extinction maps. These features are also evident in the smooth model subtracted residual maps. The extinction curve derived for this galaxy revealed that dust grains in it are identical to the canonical grains in the Milky Way with the dust grains little larger than the canonical grains. The total extinction measured in the V band extinction map enabled us to quantify the dust content of this galaxy to be equal to , an order of magnitude shorter than that estimated using the IRAS flux densities at 60 and 100 μm. A Multiphase ISM study revealed a surprising similarity in the morphologies of the Hα emitting ionized gas distribution and X-ray emitting gas. Systematic analysis of high resolution X-ray observations using Chandra telescope enabled us to detect 18 discrete X-ray sources within optical D25 region of IC 5063, out of which 17 sources were separated out as the low mass X-ray binaries and one as the high mass X-ray binary source in the X-ray color-color plot.

近邻星系恒星形成区光谱观测研究

近年来随着国际8—10iTI口径望远镜数目的不断增加，41TI及以下口径望远镜已成为中小型望远镜．如何利用中、小口径望远镜做出有影响的科学成果，须做到“有所为，有所不为”．为此，自2013年开始针对国家天文台2．16m望远镜推出了重点课题支持计划．介绍的“近邻星系恒星形成区光谱观测研究”为2．16rfl望远镜支持的3个重点课题之一．它将利用2．16m望远镜3yr、每年30个暗夜或灰夜的观测时间，开展20个近邻、大星系中多个恒星形成区、平行星系主轴方向和垂直主轴方向的光谱观测，获得一个有显示度的、科学意义重要的近邻星系恒星形成区和径向分布的光谱样本．同时该课题还利用6．5m多镜面望远镜（MMT）的观测时间，开展近邻、特大星系的恒星形成区的光谱观测．利用2．16m望远镜和MMT望远镜观测得到的星系不同区域的光谱数据，结合已有的紫外、光学、红外波段宽带滤光片数据和BATCfBeijing-Arizona-Taiwan．Connecticut）15个中带滤光片数据，可开展星系尘埃消光、恒星形成率、金属丰度和星族特性二维分布等方面的研究；开展星系二维特性和星系形态、星系环境关系的研究．将介绍这个重点课题的科学意义、星系样本的选取、光谱观测策略和星系NGC2403的光谱观测和初步研究结果．

Shock fragmentation model for gravitational collapse

A cloud of gas collapsing under gravity will fragment. We present a new theory for this process, in which layers of shocked gas fragment due to their gravitational instability. Our model explains why angular momentum does not inhibit the collapse process. The theory predicts that the fragmentation process produces objects which are significantly smaller than most stars, implying that accretion onto the fragments plays an essential role in determining the initial masses of stars. This prediction is also consistent with the hypothesis that planets can be produced by gravitational collapse.

Infrared photometric properties of inner and outer parts of HⅡ regions

The fact that infrared ring nebulae(IRRNe) are frequently associated with HⅡ regions provides us with an opportunity to study dust at the interface between ionized and neutral gas. In this paper, we analyze the associated infrared(IR) radiation in the range from 8 to 500 μm in the outer and inner parts of32 IRRNe showing a round shape. We aim to determine the morphology of these objects and possible dust evolution processes based on comparing IR radiation towards the ionized and neutral regions. We calculate six slopes between adjacent wavelengths in their spectral energy distributions to trace the difference in physical conditions inside and outside the ionized regions. Using data on these 32 objects, we demonstrate that their morphology is likely 3 D spherical rather than 2 D plane-like. The slope between 70 and 160 μm is the most appropriate tracer of dust temperature in the outer envelope. The larger 8-to-24 μm intensity ratio is associated with smaller intensities at mid-IR, indicating that polycyclic aromatic hydrocarbons(PAHs) may indeed be generated due to larger grain destruction. These data are important for the subsequent theoretical modeling, and determining the dust evolution in HⅡ regions and their envelopes.

Vilnius Photometry and Reddening of the Young Open Cluster NGC 6913

stars in the NGC 6913 field with both UBV and Vilnius photometry are selected to be the sample. The membership probability of the stars is greater than 50%. The correlation among Vilnius photometry, UBV photometry and reddening in the cluster is reviewed. It is found that the photometry in the Vilnius X, Y and Z bands can be used to make rough spectral classification. The values of E(B - V) are well correlated with the Vilnius colors of X - Y, Y - Z, Z - V and V - S in NGC 6913. The ratio of (V - S)/(Y - Z) of the MPCM (Most Possible Cluster Members) is a constant (1.30 -±0.06), and has no effect on the values of E(B - V), (B - V)0 and V0. Comparing with the observational data of all the stars of NGC 6913 region, we propose that the value of (V - S)/(Y - Z) can probably be used to select the preliminary candidates of one open cluster. In addition, 12 variable stars are discovered in the NGC 6913 region, in which star #155 has a variation with an amplitude of 4.25 mag.

Study of grain alignment efficiency and a distance estimate for small globule CB4

We study the polarization efficiency（defined as the ratio of polarization to extinction） of stars in the background of the small, nearly spherical and isolated Bok globule CB4 to understand the grain alignment process. A decrease in polarization efficiency with an increase in visual extinction is noticed. This suggests that the observed polarization in lines of sight which intercept a Bok globule tends to show dominance of dust grains in the outer layers of the globule. This finding is consistent with the results obtained for other clouds in the past. We determined the distance to the cloud CB4 using near-infrared photometry（2MASS J H KScolors） of moderately obscured stars located at the periphery of the cloud. From the extinction-distance plot,the distance to this cloud is estimated to be（459 ± 85） pc.

基于改进解释结构模型的爆炸性粉尘作业场所风险评价

为了对爆炸性粉尘作业场所进行风险评价,从环境、设备、组织管理三个层面分析爆炸性粉尘爆炸作业场所的安全隐患。采用改进解释结构模型(ISM)分析各个风险因素之间的二元关系,构建3级递阶结构模型,将模型中各层级的影响因素赋予权重值并整合计算,得到权重分析表。结果表明:粉尘爆炸作业场所的风险因素主要分为表层因素、中间因素和深层因素三个层面,这三个层面主要与企业的积尘措施、动火作业制度、安全意识和安全检查制度有关。创新性地在传统解释结构模型的基础上进行权重的赋值计算,将定性和定量分析的方法相结合,在很大程度上弥补了传统方法的弊端,所得到的结果更具科学性。

基于解释结构模型分析露天采石场粉尘职业危害影响因素

通过对露天采石场进行现场调查、检测和实验室分析,本研究确定了采场和破碎站两个粉尘职业危害重点区域;通过对重点区域进行进一步辨识分析,结果发现,露天采石场粉尘职业危害影响因素主要包括集尘器、除尘系统、安全检查等9个。基于各因素间的相互影响分析,笔者构建了解释结构模型,同时运用相关运算分析各因素的层次并建立递阶结构模型。研究表明,直接影响因素为接尘时间和个体防护,根本影响因素为教育培训和安全检查。研究揭示了各影响因素间的深层次关系,为露天采石场粉尘职业危害防治提供了理论依据。

早型旋涡星系M81(NGC 3031)光谱能量分布的空间解析研究

文章利用光谱能量分布(Spectral Energy Distribution,SED)拟合对近邻早型旋涡星系M81(NGC 3031)的整体和局部区域进行从远紫外到远红外光谱的建模,旨在探究M81星系中的星族和尘埃性质以及它们的空间分布。研究中,收集了来自包括GALEX、Swift、SDSS、2MASS、WISE、Spitzer和Herschel的空间及地面望远镜/巡天获得的一共27个波段的图像数据,并且将所有数据统一成相同的分辨率。通过对M81整体和每个像素进行SED拟合,得到了M81中的星族和尘埃等物理参数及其空间分布。发现M81是一个整体年龄约为9.5 Gyr(十亿年),恒星总质量约为3.54×10^(11) M☉(太阳质量),整体恒星形成率约为0.29 M⊙/yr,光度约4.26×10^(11) L⊙(太阳光度),以年老恒星为主的星系。M81的内部区域(主要由核球主导),包含了星系中最年老星族,其年龄大约为10 Gyr,恒星形成率低,尘埃消光小;外部区域(盘主导)年龄约为1 Gyr,年轻和年老恒星共存;星系中最年轻的恒星为400 Myr(百万年),主要分布在外旋臂中,这里恒星形成率高,尘埃消光严重。这些物理参数的空间分布图为分析M81的形成和演化历史提供了线索,认为M81的核球在宇宙的早期就已经通过碰撞形成,随后吸积伴星的气体产生盘结构,而旋臂结构是由于伴星的引力势能对盘的扰动而产生的最年轻的子结构。通过对SED的分析还发现,M81的年老恒星辐射也会加热尘埃,这将给利用远红外辐射估计恒星形成率带来误差。在后续的研究中,将对M81进行形态学解构,从而研究不同子结构中的星族和尘埃性质及其空间分布。