Preliminary dust-impact risk study for the “Solar Probe” spacecraft

Solar Probe is a mission currently under study, funded by the NASA's Office of Space Science—Sun–Earth Connection theme. This mission seeks to achieve the first visit to the Sun to explore the physical phenomenon that occurs at close proximity to our star. The mission requires the spacecraft to follow a polar orbit around the Sun with a perihelion of four (4) solar radii. A flyby at this close distance from the Sun will put the spacecraft under extraordinary environmental loads. One of the concerns is the effect that interplanetary and interstellar dust will have on the integrity of the spacecraft. The maximum dust impact velocity is expected to be around 500 km/s. This velocity is well above current experimental capabilities—more than an order of magnitude higher. For this reason, numerical simulations appear to be the best tool to determine the expected level of damage generated by the solar dust on the structural components and instruments of the Solar Probe spacecraft. Presented here are the results of the analysis of the dust environment to be experienced by the spacecraft and the shielding design parameters for different components. The design parameters of various structural components and instruments were used to conduct computer simulations using CTH to study shielding concepts.     

The magnetic Sun

The nature of our star, the Sun, is dominated by its complex and variable magnetic fields. It is the purpose of this paper to review the fundamental nature of our magnetic Sun by outlining the most basic principles behind the way the Sun works and how its fields are generated, and to examine not only the historical observations of our magnetic star, but, in particular, to study the wonderful observations of the Sun being made from space today. However, lying behind all of this are the most basic equations derived by James Clerk Maxwell, describing how the magnetic fields and plasmas of our Sun's atmosphere, and indeed of all stellar atmospheres, work and how they influence the Earth.     

Wonderful Mira

Since being named 'wonderful' in the seventeenth century for its peculiar brightness variability, Mira A has been the subject of extensive research and become the prototype for a whole class of 'Mira' variable stars. The primary star in a binary system, Mira A is reaching the end of its life and currently undergoing an extended period of enhanced mass loss. Recent observations have revealed a surrounding arc-like structure and a stream of material stretching 12 light years away in opposition to the arc. In this article, I review recent modelling of this cometary appearance as a bow shock with an accompanying tail of material ram pressure stripped from the head of the bow shock, place Mira in an evolutionary context, predict its future with reference to the similar star R Hya and planetary nebula Sh 2-188, and speculate some avenues of research both on Mira itself and on other 'Mira-like' stars with bow shocks and tails. I also discuss the implications of this discovery for our own star, the Sun.     

Explosive events on the Sun

I describe two of the most dynamic and highly energetic phenomena in the Solar System--the explosive flares that can occur when plasma is confined by magnetic fields and the large-scale ejections of material known as 'coronal mass ejections'. These explosive events are poorly understood and yet occur in a variety of contexts in the Universe, ranging from planetary magnetospheres to active galactic nuclei. Understanding why flares and coronal mass ejections occur is a major goal across a wide range of space physics and astrophysics. Although explosive events from the Sun have dramatic effects on Earth, flares in other stars, for example, can be vastly more energetic and have an even more profound effect on their environment. We are now in the unprecedented position of having access to a number of space observatories dedicated to the Sun: the Yohkoh spacecraft, the Solar and Heliospheric Observatory, the Transition Region and Coronal Explorer and the Ramaty High Energy Solar Spectroscopic Imager. These cover a wide wavelength range from white light to gamma rays with both spectroscopy and imaging, and allow huge progress to be made in understanding the processes involved in such large explosions. The high-resolution data show dramatic and complex explosions of material on all spatial scales on the Sun. They have revealed that the Sun is constantly changing everywhere on its surface--something that was never imagined before. One of the mechanisms that has been proposed to account for the large energy release is magnetic reconnection. Recent observations from space increasingly support this view. This article will discuss those observations that support this model and also those that suggest different processes. The current space missions have given us an excellent insight into the actual explosive processes in the Sun. However, they have provided us with only a tantalizing glimpse of what causes the elusive trigger. Future missions such as Solar-B (the follow-on to Yohkoh), the Solar Terrestrial Relations Observatory, the Solar Dynamics Observatory and the Solar Orbiter mission will allow us to probe the trigger in a way that was not dreamt of a decade ago, by providing stereo views, measurements from Sun-grazing orbit, and much higher spatial, temporal and spectral resolution. It is an exciting time for solar physics and everything that we learn about the Sun will improve our ability to understand other magnetic phenomena in the Universe.     

The Solar Beacon,an Experiment in Solar Astrometry

Observations of the solar diameter and shape are of considerable interest for astrophysicists dealing with the interior structure, rotation, pulsations and evolution of stars. Also there has been considerable interest in longterm variations in the solar output and diameter as it relates to climatic variations. The paper describes an experiment which holds promise for accomplishing these observations with very high precision over a long period of time. With it, it might even be possible to detect the gradual evolutionary change of the Sun within decades. More rapid changes related, for example, to climatic variations on Earth would be detectable in a short time. The experiment has a component both in space and on Earth. The space component consists of a flat reflector 1–2 m in diameter in geostationary orbit. It acts as a reflecting pin-hole telescope forming an image of the Sun on the Earth 350 km in diameter. The earth component consists of the machinery needed to measure this image. This paper elaborates on these concepts and defines problem areas which need further studies.     

X-rays from stars

More than two years of observation with Chandra and XMM-Newton has provided a rich harvest of new results on the physics of stellar coronae and winds. High-resolution X-ray spectroscopy in particular has opened new windows to the structure, the dynamics and the composition of stellar atmospheres. The present paper presents selected results from the areas of hot and cool stars and star formation, summarizing new views of the thermal structure and energy release in stellar coronae, observations of magnetically active brown dwarfs, the structure of winds in hot stars, the physics in colliding-wind binary systems, and X-rays from protostars and stellar jets.     

Data analysis of stellar specklegrams with neural networks

An artificial neural network is applied to analysis of specklegrams of binary stars. Parameters of a binary star, the angular separation and the position angle, are estimated from the specklegrams by use of neural networks for each parameter. It is shown that a neural network is useful to analyze stellar specklegrams of binary stars.     

Automated ground-based star-pointing UV -visible spectrometer for stratospheric measurements

A novel automated ground-based star-pointing spectrometer system has been constructed for long-term deployment in Antarctica. Similar to our earlier stellar system, a two-dimensional detector array measures the spectra of the star and the adjacent sky, so that auroral emission from the sky can be subtracted from the stellar signal. Some new features are an altitude -azimuth pointing mirror, so that the spectrometer does not move; slip rings to provide its power thereby avoiding flexing of cables and restriction of all-around viewing; and a glazed enclosure around the mirror to ensure protection from rain and snow, made from flat plates to avoid changing the focal length of the telescope. The optical system can also view sunlight scattered from the zenith sky. The system automatically points and tracks selected stars and switches to other views on command. The system is now installed at Halley in Antarctica, and some preliminary measurements of ozone from Antarctica are shown.     

The dark side of galaxy formation

I discuss the discovery of a population of extremely luminous, but very dusty and very distant, galaxies in the submillimetre (submm) waveband. Almost all the light emitted by the stars in these galaxies is absorbed by interstellar dust (which is produced by the same stars) and re-radiated in the far-infrared. This leaves little to be detected at optical wavelengths and results in most of these galaxies being effectively invisible in even the deepest optical images obtainable with the Hubble space telescope. Yet this population contributes most of the light emitted by galaxies at wavelengths of lambda > or approximately equal 100 microm over the lifetime of the Universe. Together with other observations, this suggests that perhaps up to half of all the stars seen in galaxies today were formed in very dusty regions in the early Universe. Hence, studying the galaxies detected in the submm wavebands is critical for developing and testing models of galaxy formation and evolution. Individually, these luminous submm galaxies are forming stars a thousand times faster than our Galaxy is at the present-day, sufficiently fast to form all the stars in the most luminous galaxy in the local Universe within a short period, up to ca. 0.1-1 Gyr. Detailed study of a handful of examples of this population confirm these estimates and unequivocally identify the bulk of this submm-selected population with dusty, star-burst galaxies in the very distant Universe. The extreme faintness of this population in the optical and near-infrared wavebands, resulting from their obscuration by dust, means that our understanding of the detailed nature of these galaxies is only slowly growing. I give a brief summary of the properties of these highly obscured systems and describe the wide range of facilities currently being developed that will greatly aid in their study.     

等离子体物理中分数阶模型数值解法研究进展北大核心CSCD

宇宙中超过99%的可见物质由等离子体组成,天体物理以及空间物理中观测到的大量现象都可由等离子体的原理和规律描述。这些现象包括行星形成、太阳耀斑、恒星形成、太阳以及恒星星风、粒子加速、黑洞吸积与喷流、伽玛射线暴、超新星爆发、星系形成与演化、宇宙大尺度结构等等。与整数阶模型相比,分数阶方程可以精细地刻画等离子体中基于反常扩散过程的流体动力学行为的历史依赖性与长程相关性,将分数阶模型应用到等离子体物理领域将有重要的意义和前景。等离子体物理中分数阶模型数值解法的研究现状得到综述,并对未来的发展进行展望。     

星模拟器星光颜色模拟的初步研究

针对当前星模拟器完全丢失恒星光谱信息的缺陷,本文进行了星光颜色模拟方面的初步研究.首先,选择合适的星表并确定要进行颜色模拟的恒星星号,得到该星色指数等一系列信息;同时,根据有关资料,推导出恒星色指数与色温之间的函数关系;至此,确定该星色温.其次,由黑体辐射公式,计算出黑体在此温度下的辐射特性.然后,根据色度学原理,把黑体在此温度下的辐射量刺激值积分,得到该色温的总刺激值,归一化就可得到相应的色度坐标,完成了恒星的星光颜色模拟.最后,说明并解释了本研究方案的不足之处.模拟实验结果证明了星光颜色模拟的可行性.     

The macro detector at the Gran Sasso Laboratory

The MACRO detector is presently under construction, its installation at Gran Sasso being planned to start in September 1987. It is a large area detector, the acceptance for isotropic particle fluxes being around 10 000 m² sr, designed to search for rare phenomena in the cosmic radiation. It makes use of three detection techniques: liquid scintillator counters, plastic streamer tubes, and track-etch. It will perform a search for GUT monopoles (or any supermassive charged penetrating particle), a survey of cosmic point sources of HE gammas and neutrinos, a systematic study of the penetrating cosmic ray muons, and will be sensitive to neutrino bursts from gravitational stellar collapses in the Galaxy.     

空间目标光度特性测量方法研究

空间目标的光度特性反映了目标的在轨运动状态,通过空间目标的光度测量可以判断空间目标在轨特性和进行空间目标的编目识别.比较了空间目标光度特性光度计和CCD测量的两种方法,并采用恒星比对的方法,得到了空间目标的星等数据,实验结果表明两种测量方法星等精度相当,但CCD测量可以在白天测量空间目标的光度特性.     

星敏感器单星模拟光源系统

在星敏感器的标定检测中 ,通常要求提供一个模拟星 ,以便在实验室内标定星敏感器 ,从而减少大气变化的影响。模拟星的设备通常称为星模拟器 ,它们提供相对被测物体无限远的点光源作为模拟星 ,对其大小、光度 (星等值 )、光谱特性、色温类型等进行严格模拟。对实现模拟单星的研究作了详细的介绍。     

Models of very-low-mass stars, brown dwarfs and exoplanets

Within the next few years, GAIA and several instruments aiming to image extrasolar planets will be ready. In parallel, low-mass planets are being sought around red dwarfs, which offer more favourable conditions, for both radial velocity detection and transit studies, than solar-type stars. In this paper, the authors of a model atmosphere code that has allowed the detection of water vapour in the atmosphere of hot Jupiters review recent advances in modelling the stellar to substellar transition. The revised solar oxygen abundances and cloud model allow the photometric and spectroscopic properties of this transition to be reproduced for the first time. Also presented are highlight results of a model atmosphere grid for stars, brown dwarfs and extrasolar planets.     

Using stars for remote sensing of the Earth's stratosphere

A new UV-visible spectrometer system that measures the absorption of light from stars and planets by constituents in the Earth's atmosphere is described. Because it can be used to make measurements at night, the system has a significant advantage for measuring polar constituents in winter, when conditions that might give rise to ozone loss are initiated. Other advantages arise from the use of a cooled two-dimensional CCD array as the detector: an array detector avoids spectral noise resulting from scintillation of stars or from clouds passing overhead and allows for the possibility of measuring several constituents simultaneously; its second dimension permits auroral light from the atmosphere adjacent to the star to be measured simultaneously and subtracted from the stellar light, and a modern low-noise CCD allows us to use a telescope of modest diameter. The few previous measurements of constituents made by the use of stellar absorption did not have these advantages. The instrument was configured for simplicity and ease of use in field measurements and was deployed outside in winter in Northern Sweden in 1991. Examples of ozone measurements are shown.     

Massive stars in their death throes

The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently, there are eight detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants, as theory has long predicted. However, no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae, which, given the expected progenitors, is an unlikely result. Also, observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict the current stellar evolution theory. This suggests that we may need to update our understanding.     

太阳帆悬浮轨道附近的编队

研究了利用太阳帆实现悬浮轨道附近编队飞行。考虑到相对运动距离与帆到太阳距离相比非常小,一阶近似得出了在主星坐标系中线性定常的相对运动方程。通过分析线性化的运动方程得出了相对运动的定性特征,给出了不同轨道附近的相对运动的稳定特性。讨论了原非线性相对运动方程的周期解的计算算法,给出了编队的初值条件。     

Introduction. Progress in astronomy: from gravitational waves to space weather

This brief paper introduces and reviews the 'visions of the future' articles prepared by leading young scientists throughout the world for the first of two Christmas 2008 Triennial issues of Phil. Trans. R. Soc. A, devoted, respectively, to astronomy and Earth science. Contributions in astronomy include the very topical gamma-ray bursts, new ideas on stellar collapse and the unusual atmospheres of synchronized planets orbiting nearby stars.