The origin of our galactic magnetic field

A serious difficulty with the standard alpha‐omega theory of the origin of galactic magnetic fields involves the question of flux expulsion. This is intimately related to flux freezing. The alpha‐omega theory is shown in the context of the giant superbubble explosions that have a large impact on the physics of the interstellar medium. It is shown that superbubbles alone can duplicate the processes of the alpha‐omega dynamo and produce exponential growth of the galactic magnetic field. The possibility of the blow‐out of pieces of the magnetic field is discussed and it is shown that they have the potential to solve the flux‐expulsion problem. However, such an explanation must lead to apparent ‘gaps’ in the field in the galactic disc. These gaps are probably unavoidable in any dynamo theory and should have important observable consequences, one of which is an explanation for the escape of cosmic rays from the disc (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The origin of cutoff frequencies for torsional tube waves propagating in the solar atmosphere

Torsional waves supported by magnetic flux tubes have long been thought to bear a high potential for supplying energy and momentum to the upper solar atmosphere, thereby contributing to its heating and to the driving of dynamic events like spicules. This hope rested on the belief that their propagation is not impeded by cutoff restrictions, unlike longitudinal and kink waves. We point out that this applies only to thin, isothermal tubes. When they widen in the chromosphere, and as a result of temperature gradients, cutoff restrictions arise. We compare them to recent observational reports of such waves and of vortex motions and find that their long period components are already affected by cutoff restrictions. An observational strategy is proposed that should permit the derivation of better information on vortex flows from off‐center observations with next generation telescopes (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

V4334 Sgr (Sakurai's Object): The Distance Problem

The central star V4334 Sgr (Sakurai's Object) of the planetary nebula PN G010.4+04.4 underwent in 1995–1996 the rare event of a very late helium flash. It represents only one out of two such events during the era of modern astronomy (the other event was V605 Aql = Nova Aql 1919). All the other prominent objects of that type originate from events occurring several thousands of years ago (e.g. A30, A78). Thus it is of special interest for stellar evolution theory to model the detailed observations obtained during the last four years. Those models depend essentially on basic stellar parameters like effective temperature, surface gravity and stellar radius. Most of them depend strongly on the assumed distance to the object. Some models may give some constraints on this parameter, but most of them depend on the assumption as input parameter. Hence to determine a reliable distance is of considerable significance. This should be obtained through models that give us lower and upper boundaries, or through means which are independent of models. The detailed review, by using every kind of determination available up to now, leads to a Galactic foreground extinction of E _B–V =0^m75 ±0.05 and a distance of D = 2.0_-0.6 ^+1.0 kpc.     

Scientific CMOS Pixels

High performance CMOS pixels are introduced; and their development is discussed. 3T (3-transistor) photodiode, 5T pinned diode, 6T photogate and 6T photogate back illuminated CMOS pixels are examined in detail, and the latter three are considered as scientific pixels. The advantages and disadvantages of these options for scientific CMOS pixels are examined. Pixel characterization, which is used to gain a better understanding of CMOS pixels themselves, is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Silicon-on-Insulator-Based Single-Chip Image Sensors: Low-Voltage Scientific Imaging

A low-voltage (≤3.3 V) imaging technology has been developed to enable scientific-grade imagers with low-power complex functions on chip. A 128 × 128 CCD imager with on-chip clocking and charge-domain analog-to-digital conversion, as well as an exploratory active pixel sensor have been demonstrated. A 640 × 960 CCD imager with optimized 12 bit charge-domain conversion and an improved active pixel sensor are presently in fabrication. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tayler instability with Hall effect in young neutron stars

Collapse calculations indicate that the hot young neutron stars rotate differentially so that strong toroidal magnetic field components should exist in the outer shell where also the Hall effect appears to be important when the Hall parameter = ω_Bτ exceeds unity. The amplitudes of the induced toroidal magnetic fields are limited by the current‐induced Tayler instability. An important characteristics of the Hall effect is its distinct dependence on the sign of the magnetic field. We find for fast rotation that positive (negative) Hall parameters essentially reduce (increase) the stability domain. It is thus concluded that the toroidal field belts in young neutron stars induced by their differential rotation should have different amplitudes in both hemispheres which later are frozen in. Due to the effect of magnetic suppression of the heat conductivity also the brightness of the two hemispheres should be different. As a possible example for our scenario the isolated neutron star RBS 1223 is considered which has been found to exhibit different X‐ray brightness at both hemispheres (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mean electromotive force proportional to mean flow in MILD turbulence

In mean‐field magnetohydrodynamics the mean electromotive force due to velocity and magnetic‐field fluctuations plays a crucial role. In general it consists of two parts, one independent of and another one proportional to the mean magnetic field. The first part may be nonzero only in the presence of mhd turbulence, maintained, e.g., by small‐scale dynamo action. It corresponds to a battery, which lets a mean magnetic field grow from zero to a finite value. The second part, which covers, e.g., the α effect, is important for large‐scale dynamos. Only a few examples of the aforementioned first part of the mean electromotive force have been discussed so far. It is shown that a mean electromotive force proportional to the mean fluid velocity, but independent of the mean magnetic field, may occur in an originally homogeneous isotropic mhd turbulence if there are nonzero correlations of velocity and electric current fluctuations or, what is equivalent, of vorticity and magnetic field fluctuations. This goes beyond the Yoshizawa effect, which consists in the occurrence of mean electromotive forces proportional to the mean vorticity or to the angular velocity defining the Coriolis force in a rotating frame and depends on the cross‐helicity defined by the velocity and magnetic field fluctuations. Contributions to the mean electromotive force due to inhomogeneity of the turbulence are also considered. Possible consequences of the above findings for the generation of magnetic fields in cosmic bodies are discussed (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

利用地基GPS技术反演武汉地区大气可降水分

利用武汉地区的探空资料和GPS实测数据，对对流层干分量延迟、对流层加权平均温度进行了检验分析．结果表明，对于武汉地区而言，常用的大气干分量延迟模型(SAAS Hopfield and Black)存在着1-2cm的系统误差，这在利用GPS资料估算大气可降水分(PWV)时会引入2-3mm的误差；对流层加权平均温度与常用的Bevis公式也存在着一定的差异，但这种差异对PWV结果影响很小．为此，提出了校正对流层干分量延迟的方法，并利用实测数据对该方法进行了检验．实践证明，这种校正方法基本上可以消除常用干分量模型的系统误差。     

In-flight Performance of the Advanced Camera for Surveys CCDs

The Advanced Camera for Surveys (ACS), installed in the Hubble Space telescope in March 2002, will significantly extend HST's deep, survey imaging capabilities. ACS has met, or exceeded, all of its key performance specifications. In this paper we briefly review the in-flight performance of the instrument's CCD detectors and preview early ACS science observations. This revised version was published online in July 2006 with corrections to the Cover Date.     

中高轨卫星广播星历精度分析

GPS广播星历参数具有物理意义明确、参数少、精度高等优点,可以考虑将它应用于其他卫星导航系统。但是GPS系统的卫星构成比较单一,而其他卫星导航系统可能包含中地球轨道 (MEO)、倾斜地球同步轨道(IGSO)和地球静止轨道(GEO)等多种不同类型的中高轨卫星。分析了采用GPS广播星历参数时,MEO、IGSO和GEO卫星的广播星历拟合精度,特别讨论了轨道倾角接近于0的GEO卫星的广播星历拟合精度,并给出了相应的改进措施。计算表明,对于 MEO卫星,2 h的广播星历拟合精度(三维位置)可达厘米级;对于IGSO卫星和轨道倾角较大的GEO卫星,4 h的广播星历拟合精度约为0．1 m,径向位置误差在厘米量级;而对于轨道倾角接近于0的GEO卫星,若不采取特殊措施,由于轨道倾角和升交点经度统计相关,其广播星历拟合精度很差,为此提出了一种坐标转换方法。采用此方法后的广播星历拟合精度可达0．1 m,径向位置误差为厘米量级。     

Hopf bifurcations with fluctuating gain

A Hopf bifurcation describes a transition from a steady state to an oscillatory one. This report describes how the presence of white Gaussian noise in the term driving the instability (the gain) affects the character of such a transition. We find that for small noise intensities the effective critical value of the bifurcation parameter increases linearly with the noise intensity. This result is used to quantitatively describe the onset of the magneto‐rotational instability in a laboratory experiment using liquid metal with turbulent background flow. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Complex organic molecules in an early stage of protostellar evolution

We have detected the rotational lines of HCOOCH₃ toward a Class 0 low-mass protostar, NGC1333 IRAS4B, which is reported to be extremely young according to the dynamical age of the molecular outflow (a few 100 yr). This suggests that the complex organic molecules appear from the very early stage of protostellar evolution. On the other hand, the complex organic molecules are not detected in a more evolved protostar, L1527. We have also found a similar trend in a massive star forming region, NGC2264. The HCOOCH₃ emission is almost absent toward IRS1, whereas it is concentrated near MMS3, which is younger than IRS1. In addition, the HCOOCH₃ intensity peak is slightly shifted from the dust emission peak, as is seen in the Orion KL Compact Ridge, giving an important clue to solve its origin.     

Catastrophe of coronal magnetic rope in partly open multipolar magnetic field

Catastrophe of coronal magnetic rope embedded in a partly open multipolar background magnetic field is studied by using a 2-dimensional, 3-component ideal MHD model in spherical coordinates. The background field is composed of three closed bipolar fields of a coronal streamer and an open field with an equatorial current sheet. The magnetic rope lies below the central bipolar field, and it is characterized by its annular and axial magnetic fluxes. For a given annual flux, there is a critical value of the axial flux, and for a given axial flux, there is a critical value of annual flux such that, below the critical value, the magnetic rope is attached to the solar surface and the system stays in equilibrium, but when the critical value is exceeded, the magnetic rope breaks free and erupts upward. This implies that catastrophe can occur in a coronal magnetic rope embedded in a partly open multipolar background magnetic field. Our computation gives a threshold value of magnetic energy that is about 15% greater than the energy of the partly open magnetic field (the central bipolar field open and the fields on either side closed). The excess energy may serve as source for solar explosions such as coronal mass ejections.     

A Golden Era for Astronomy: The Advent of CCDs and Infrared Arrays

The advent of solid-state imaging devices transformed astronomy. Beginning with the introduction into astronomy of charge-coupled devices in 1976, followed a decade later by infrared arrays, astronomers gained access to near-perfect imaging devices. The consequences have been nothing short of revolutionary, perhaps especially so in the infrared. Witness, for example, the spectacular pictures from the Hubble Space Telescope cameras, or the impressive infrared imagery from the 2MASS project. Within the last decade CCD formats deployed or planned for use in ground-based cameras have become huge. Infrared mosaics, stimulated by the Next Generation Space Telescope, are coming soon. In addition, new technologies such as CMOS (Complementary Metal Oxide Semiconductors) and STJs (Superconductiong Tunnel Junctions) are being developed and the future of astronomical detectors looks very exciting, especially in an era of giant telescopes performing at their diffraction-limit. This revised version was published online in July 2006 with corrections to the Cover Date.     

光谱预处理及其对星系/类星体分类结果的影响

由于噪声、畸变和观测环境等因素的影响,在天体光谱自动处理之前,需要对它进行相应的预处理.研究巡天光谱的预处理(数据格式和流量标准化)对光谱自动分析的影响.分析了同数据格式对光谱及其谱线特征的影响和格式标准化研究的必要性;通过分析光谱流量数量级的不确定性及其特点,提出了流量数量级变化的基本模型,并给出了相应的标准化方法.通过星系和类星体的分类实验,结果表明:1)采用对数波长数据格式对光谱的自动分类更有利;2)验证了所提出的流量标准化模型的合理性,以及所给流量标准化方法良好的性能.特别需要指出的是,文献中通常采用的流量标准化方法在光谱自动分类中的效果反而是较差的.     

2D/3D Dust Continuum Radiative Transfer Codes to Analyze and Predict VLTI Observations

Radiative Transfer (RT) codes with image capability are a fundamental tool for preparing interferometric observations and for interpreting visibility data. In view of the upcoming VLTI facilities, we present the first comparison of images/visibilities coming from two 3D codes that use completely different techniques to solve the problem of self-consistent continuum RT. In addition, we focus on the astrophysical case of a disk distorted by tidal interaction with by-passing stars or internal planets and investigate for which parameters the distortion can be best detected in the mid-infrared using the mid-infrared interferometric device MIDI. This revised version was published online in July 2006 with corrections to the Cover Date.     

未来的地面和空间大望远镜以及我国目前的大项目

目前 ,已有 1 0架口径 8～ 1 0m的地面大望远镜建成并投入科学观测。在近红外波段 ,自适应光学和干涉术已在大望远镜上获得成功。Hubble空间望远镜发射至今已逾 1 2年。为了研究早期宇宙 ,探测类地行星等 ,2 0 0 2年 9月NASA已与TWR公司签约 ,研制口径≥ 6m的下一代空间望远镜JWST ,计划2 0 1 0年发射。许多口径 30～ 1 0 0m的地面未来巨型望远镜FGT项目已经提出。本报告 ,也介绍了我国正在研制或预研中的三个大项目 :LAMOST、FAST和SST ,这些项目虽较小 ,但完成后都会对天文学的一个方面作出有份量的贡献。最后 ,报告人建议我国参与到与国外合作研制FGT或NGST的工作中 ,特别强调要有天文学家和工程专家参与进去     

An ecological economics framework for assessing environmental flows: the case of inter-basin water transfers in Lesotho

This paper used the Lesotho Highlands Water Project (LHWP) that transfers water from the Orange River Basin in Lesotho to the Vaal River Basin in South Africa as a case study to show how environmental sustainability aspects can be integrated into economic development planning. Using the Ecological Social Accounting Matrix (ESAM) for Lesotho that integrates ecological implications of the LHWP with economic benefits of the project, the paper analysed the impact of lost ecological services downstream the LHWP dams in Lesotho on the well-being of households directly affected by the project (riparians) and the general economy of the country. The results revealed that despite significant economic benefits, the project has unintended impacts on ecological resources and services with resultant deleterious well-being implications for riparians. The results from the ESAM analysis indicated that not only the income of riparians is likely to suffer, but also that of other households and social groups, as well as the general economy of Lesotho. While results of the ESAM analysis did not indicate large income impacts on the economy at large, they were significant for riparians. The importance of integrating ecological consequences into impact assessment of IBWT before such transfers can be implemented to ensure sustainable development and considering economy-wide impacts associated with IBWT was proven necessary for a holistic impact assessment of IBWT.     

NTSC—PTB链路的GPS全视法时间比对数据分析

采用通过中国科学院国家授时中心(NTSC)GPS单、双频这2类观测设备得到的实测数据,进行了NTSC—PTB(physikalisch-technische bundesanstalt(Germary))链路的全视法比对计算和分析。利用这2类设备得到的GPS AV(全视)的结果与BIPM公布的AV方法的A类不确定度一致,从而确定国家授时中心的2类GPS观测设备的性能达到了国际同类水平。如果对双频观测设备时延校准后,采用P3类型进行比对,有望将NTSC现有的比对精度提高50%。     

Large‐scale magnetic flux concentrations from turbulent stresses

In this study we provide the first numerical demonstration of the effects of turbulence on the mean Lorentz force and the resulting formation of large‐scale magnetic structures. Using three‐dimensional direct numerical simulations (DNS) of forced turbulence we show that an imposed mean magnetic field leads to a decrease of the turbulent hydromagnetic pressure and tension. This phenomenon is quantified by determining the relevant functions that relate the sum of the turbulent Reynolds and Maxwell stresses with the Maxwell stress of the mean magnetic field. Using such a parameterization, we show by means of two‐dimensional and three‐dimensional mean‐field numerical modelling that an isentropic density stratified layer becomes unstable in the presence of a uniform imposed magnetic field. This large‐scale instability results in the formation of loop‐like magnetic structures which are concentrated at the top of the stratified layer. In three dimensions these structures resemble the appearance of bipolar magnetic regions in the Sun. The results of DNS and mean‐field numerical modelling are in good agreement with theoretical predictions. We discuss our model in the context of a distributed solar dynamo where active regions and sunspots might be rather shallow phenomena (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)