WSO-UV project

During last three decades, astronomers have enjoyed continuous access to the 100–300 nm ultraviolet (UV) spectral range where the resonance transitions of the most abundant atoms and ions (at temperatures between 3000 and 300 000 K) reside. This UV range is not accessible from ground-based facilities. The successful International Ultraviolet Explorer (IUE) observatory, the Russian ASTRON mission and successor instruments such as the Galaxy Evolution Explorer (GALEX) mission or the COS and STIS spectrographs on-board the Hubble Space Telescope (HST) prove the major impact of observations in the UV wavelength range in modern astronomy. Future access to space-based observatories is expected to be very limited. For the next decade, the post-HST era, the World Space Observatory – Ultraviolet (WSO–UV) will be the only 2-m class UV telescope with capabilities similar to the HST. WSO–UV will be equipped with instruments for imaging and spectroscopy and it will be a facility dedicated, full-time, to UV astronomy. In this article, we briefly outline the current status of the WSO–UV mission and the science management plan.     

The ultraviolet sky: An overview from the GALEX surveys

The Galaxy Evolution Explorer (GALEX) has performed the first surveys of the sky in the ultraviolet (UV). Its legacy is an unprecedented database with more than 200 million source measurements in far-UV (FUV) and near-UV (NUV), as well as wide-field imaging of extended objects, filling an important gap in our view of the sky across the electromagnetic spectrum. The UV surveys offer unique sensitivity for identifying and studying selected classes of astrophysical objects, both stellar and extra-galactic. We examine the overall content and distribution of UV sources over the sky, and with magnitude and color. For this purpose, we have constructed final catalogs of UV sources with homogeneous quality, eliminating duplicate measurements of the same source. Such catalogs can facilitate a variety of investigations on UV-selected samples, as well as planning of observations with future missions. We describe the criteria used to build the catalogs, their coverage and completeness. We included observations in which both the far-UV and near-UV detectors were exposed; 28,707 fields from the All-Sky Imaging survey (AIS) cover a unique area of 22,080 square degrees (after we restrict the catalogues to the central 1° diameter of the field), with a typical depth of ∼20/21mag (FUV/NUV, in the AB mag system), and 3008 fields from the Medium-depth Imaging Survey (MIS) cover a total of 2251 square degrees at a depth of ∼22.7mag. The catalogs contain ∼71 and ∼16.6 million sources, respectively. The density of hot stars reflects the Galactic structure, and the number counts of both Galactic and extra-galactic sources are modulated by the Milky Way dust extinction, to which the UV data are very sensitive.     

The ultraviolet view of the Magellanic Clouds from GALEX: A first look at the LMC source catalog

The Galaxy Evolution Exporer (GALEX) has performed unprecedented imaging surveys of the Magellanic Clouds (MC) and their surrounding areas including the Magellanic Bridge (MB) in near-UV (NUV, 1771-2831 Å) and far-UV (FUV, 1344-1786 Å) bands at 5^″$5^{″}$ resolution. Substantially more area was covered in the NUV than FUV, particularly in the bright central regions, because of the GALEX FUV detector failure. The 5σ$\sigma$ depth of the NUV imaging varies between 20.8 and 22.7 (ABmag). Such imaging provides the first sensitive view of the entire content of hot stars in the Magellanic System, revealing the presence of young populations even in sites with extremely low star-formation rate surface density like the MB, owing to high sensitivity of the UV data to hot stars and the dark sky at these wavelengths.     

太阳极紫外多波段成像仪

在目前仪器特点和性能的基础上, 结合中国现有卫星特点和技术基础, 提出了一种新型太阳极紫外多波段成像仪, 采用小型化设计, 利用一台仪器实现对日冕和色球层4个不同波段的高分辨率成像, 不仅能有效利用卫星资源, 提高空间探测水平, 还能实现对日冕和色球的同时观测, 推动空间天气研究, 提高空间天气预报水平.     

航天器碰撞概率简化计算方法的比较与应用

针对空间飞行器碰撞概率问题, 基于碰撞概率的假设条件与计算原理, 对现有常见方法进行分析, 归纳每种方法在线性与非线性、空间目标是否规则等方面的适用性及特点, 通过数值计算验证了上述方法, 并从计算速度与计算精度两个维度对每种方法进行评估. 评估结果表明, 中心概率密度法的计算速度最快,曲线积分法的相对误差最小, 基于辛普森公式的二维积分方法具有较均衡的效果, 三维体积积分适用于非线性场景,蒙特卡洛法最为精准但是运算速度最慢. 综合考虑计算精度、计算速度、相对速度、相对位置关系等因素, 根据每种方法的特点提出了多种场景下较为适用的碰撞概率简化计算方法, 研究结果可以为在轨碰撞概率的计算与分析提供参考.     

Star visibility and tracking from the Space Station

Purpose of the present study is to provide algorithms for and examples of how to simulate star visibility and tracking by a Telescope attached to the main truss of the International Space Station (ISS).     

太阳极紫外光谱仪无缝成像技术研究

传统极紫外成像光谱仪无法实时观测大范围的太阳活动.无缝成像技术使得光谱仪能够获得大视场范围内的太阳空间信息和光谱信息.通过无缝成像光谱仪成果分析,提出了一种改进的光学设计思路,并通过模拟数据重建证明其能够大幅提高多普勒速度反演的准确性,从而极大提高了观测数据的可信度.     

太阳极紫外光谱探测的历史与展望

围绕国际一流科学目标,发展顶级探测设备是中国太阳物理位列国际先进行列的立足点。70多年的空间太阳探测历程中,极紫外波段探测发挥了极其重要的作用,极紫外观测设备也几乎成为了太阳探测卫星的必备载荷之一。中国在极紫外探测,尤其是光谱探测方面的基础非常薄弱,导致相关科学研究几乎全部依赖国外数据,从而严重制约了中国太阳物理学科的发展。本文根据太阳极紫外探测的特点,系统分析了国外光谱探测的历史、现状以及未来发展趋势,并归纳了三类主要探测方式,即全日面积分光谱探测、低速光谱成像探测、快速光谱成像探测的当前水平,包括其技术方案及取得的部分科学成果。在此基础上,提出中国太阳极紫外光谱探测“三步走”的发展思路,并对每一步的科学目标、指标需求和候选探测方案提出建议。同时,展望了在太阳极紫外成像探测方面开展创新性尝试的思路。     

The role of ultraviolet imaging in studies of resolved and unresolved young stellar populations. M31 and M33

We discuss the relevance of UV data in the detection and characterization of hot massive stars and young stellar populations in galaxies. We show results from recent extensive surveys in M31 and M33 with Hubble Space Telescope (HST) multi-wavelength data including UV filters, which imaged several regions at a linear resolution (projected) of less than half a pc in these galaxies, and from GALEX far-UV and near-UV wide-field, low-resolution imaging of the entire galaxies. Both datasets allow us to study the hierarchical structure of star formation: the youngest stellar groups are the most compact, and are often arranged within broader, sparser structures. The derived recent star-formation rates are rather similar for the two galaxies, when scaled for the respective areas. We show how uncertainties in metallicity and type of selective extinction for the internal reddening may affect the results, and how an appropriate complement of UV filters could reduce such uncertainties, and significantly alleviate some parameter degeneracies.     

New flare model using recent measurements of the solar ultraviolet irradiance

The solar photon output from the Sun, which was once thought to be constant, varies considerably over time scales from seconds during solar flares to years due to the solar cycle. This is especially true in the wavelengths shorter than 190 nm. These variations cause significant deviations in the Earth and space environment on similar time scales, which then affects many things including satellite drag, radio communications, atmospheric densities and composition of particular atoms, molecules, and ions of Earth and other planets, as well as the accuracy in the Global Positioning System (GPS). The Flare Irradiance Spectral Model (FISM) is an empirical model that estimates the solar irradiance at wavelengths from 0.1 to 190 nm at 1 nm resolution with a time cadence of 60 s. This is a high enough temporal resolution to model variations due to solar flares, for which few accurate measurements at these wavelengths exist. This model also captures variations on the longer time scales of solar rotation (days) and solar cycle (years). Daily average proxies used are the 0–4 nm irradiance, the Mg II c/w, F10.7, as well as the 1 nm bins centered at 30.5 nm, 121.5 (Lyman Alpha), and 36.5 nm. The GOES 0.1–0.8 nm irradiance is used as the flare proxy. The FISM algorithms are given, and results and comparisons are shown that demonstrate the FISM estimations agree within the stated uncertainties to the various measurements of the solar Vacuum Ultraviolet (VUV) irradiance.     

Space Debris Mitigation in France,Germany, Italy and United Kingdom

The Space systems today provide growing benefits to enhance the quality of humankind. However, as a by-product, the orbiting objects inevitably leaves some debris which after 50 years of space activities represent a concern for all space agencies and manufacturers and operators. Since last year no international agreement was in place to mitigate the growing population of space debris objects. The successful result obtained at UN-COPUOS in 2007 and available in the OOSA web site, now gives to the public, a set of voluntary international guidelines that could, if adopted by each space fairing Country, help in maintaining the present space environment. More further steps are necessary in the future to define a legal and normative framework. The paper will present the seven established UN Space Debris guidelines as well as examples of the minimum steps to be carried out at national level to enable the UN-COPUOS to start the discussion of the legal aspect associated with the space debris issue.     

The bistatic radar capabilities of the Medicina radiotelescopes in space debris detection and tracking

An accurate measurement of the position and trajectory of the space debris fragments is of primary importance for the characterization of the orbital debris environment. The Medicina Radioastronomical Station is a radio observation facility that is here proposed as receiving part of a ground-based space surveillance system for detecting and tracking space debris at different orbital regions (from Low Earth Orbits up to Geostationary Earth Orbits). The proposed system consists of two bistatic radars formed by the existing Medicina receiving antennas coupled with appropriate transmitters. This paper focuses on the current features and future technical development of the receiving part of the observational setup. Outlines of possible transmitting systems will also be given together with the evaluation of the observation strategies achievable with the proposed facilities.     

The effective temperatures of O-type stars from UV spectroscopy

We present an analysis of high resolution spectra in the far-UV – UV range (∼905–2000 Å) with non-LTE, spherical, hydrodynamical, line-blanketed models, of three O-type Galactic stars, and derive their photospheric and wind parameters. These data extend previously analyzed samples and fill a gap in spectral type coverage. The combined sample confirms a revised (downward) T_eff scale with respect to canonical calibrations, as found in our previous works from UV and optical spectra, and in recent works by other authors.     

Galaxy evolution in groups. USGC U268 and USGC U376 in the Leo cloud

With the aim of investigating galaxy evolution in nearby galaxy groups, we analyzed the spectral energy distribution of 24 galaxies, members of two groups in the Leo cloud, USGC U268 and USGC U376. We estimated the ages and stellar masses of the galaxies by fitting their total apparent magnitudes from far-ultraviolet to near-infrared with population synthesis models. The comparison of the results for a subsample of galaxies with smooth particle hydrodynamic (SPH) simulations with chemo-photometric implementation, shows that in most cases the estimated stellar masses obtained with the two different approaches are in good agreement. The kinematical and dynamical analysis indicates that USGC U268 is in a pre-virial collapse phase while USGC U376 is likely in a more evolved phase towards virialization.     

船舶仪表现场计量保障问题研究

分析了计量工作重要性和船舶仪表现场计量保障工作面临的问题,阐释了船舶论证研制阶段开展对船舶仪表现场计量保障的依据及论证设计思路,重点分析了国内船舶靠泊港口的环境条件,阐述了压力仪表原位测试的可行性、原位检测设计方案和实施效果。     

空间物理学最新进展与展望

空间物理学是人类进入空间时代后迅速发展的一门新兴交叉学科,特别是进入新世纪后国内外都取得了辉煌的成就.本文简要介绍空间物理领域近年来取得的重要进展、重要成果、国内外发展趋势,以及未来发展的重点方向.