基于地月合影图像的“嫦娥5T”指向校正算法

以"嫦娥5T"地月合影图像作为基本数据,提出一种基于信息融合的相机指向校正方法。首先利用形态分析从合影图像中提取天体的形心坐标,然后构建目标函数,通过优化算法估计相机的安装误差矩阵。该方法的典型优势是只需要利用单个相机对天体所成的单幅图像,便可快速确定相机指向。仿真数据和实测数据得到相机指向误差估计值的偏差保持在1%度量级,证明了算法的有效性。算法可以为实际工程任务和应用提供参考。     

Local Interstellar Medium Summary of Working Group VI

This report summarizes the issues discussed in Working Group VI concerning the accuracy of measurements of D/H and 3He/H in the local interstellar medium, possible systematic errors, and emerging trends in the results.     

Where does the heliospheric modulation of galactic cosmic rays start?

The long outstanding question of where the heliospheric (solar) modulation of galactic cosmic rays actually begins, in terms of spatial position, as well as at what high kinetic energy, can now be answered. Both answers are possible by using the results of an advanced numerical model, together with appropriate observations. Voyager 1 has been exploring the outskirts of the heliosphere and is presently entering what can be called the very local interstellar medium. It has been generally expected, and accepted, that once the heliopause is crossed, the local interstellar spectrum (LIS) should be measured in situ by the Voyager spacecraft. However, we show that this may not be the case and that modulation effects on galactic cosmic rays can persist well beyond the heliopause. For example, proton observations at 100 MeV close to the heliopause can be lower by ∼$\sim$25% to 40% than the LIS, depending on solar modulation conditions. It is also illustrated quantitatively that significant solar modulation diminishes above ∼$\sim$50 GeV at Earth. It is found that cosmic ray observations above this energy contain less that 5%$5\%$ solar modulation effects and should therefore reflect the LIS for galactic cosmic rays. Input spectra, in other words the very LIS, for solar modulation models are now constrained by in situ observations and can therefore not any longer be treated arbitrarily. It is also possible for the first time to determine the lower limit of the very LIS from a few MeV/nuc to very high energies.     

Contributions from nearby pulsars to the local cosmic ray electron spectrum

PSR J0437-4715 is one of the closest millisecond pulsars (MSPs) to Earth, lying at a distance of ∼140 pc. This pulsar has a characteristic age of 4.9 Gyr and a relatively low spindown power of ∼10³⁴ ergs/s. During its rather long lifetime, a large fraction of the energy output has been in the form of multi-TeV electrons. In this paper, we investigate the possible contribution of this nearby MSP to the local interstellar electron spectrum (LIS). The old age of the system justifies a steady-state evaluation of the contribution from this pulsar to the LIS. We calculate the electron spectrum at the light cylinder in the framework of a General Relativistic polar cap (PC) model, and use this as an injection spectrum in a diffusion model. The younger Geminga pulsar is also very close to Earth and warrants investigation. A steady-state approach is however no longer justified, so we use an impulsive injection model. We will present results of a study of the contribution from these pulsars to the cosmic ray (CR) LIS. Our calculations show that pulsars like Geminga can make a non-negligible contribution to the LIS.     

Multi-component synchrotron self-compton emission from NGC 1275

COS-B gamma-ray data (70–5000 MeV) in the latitude range 10°< |b| <90° are compared with the expected emission from cosmic-ray interactions with interstellar gas. An additional component is found to be necessary to explain the latitude dependence of the emission. Two possible origins for this component are discussed: a gamma-ray halo around the Galaxy and a local emission region.     

The isotopic composition of anomalous cosmic rays from sampex

Measurements of the anomalous cosmic ray (ACR) isotopic composition have been made in three regions of the magnetosphere accessible from the polar Earth orbit of SAMPEX, including the interplanetary medium at high latitudes and geomagnetically trapped ACRs. At those latitudes where ACRs can penetrate the Earth's magnetic field while fully stripped galactic cosmic rays (GCRs) of similar energies are excluded, a pure ACR sample is observed to have the following composition: ¹⁵N/N < 0.023, ¹⁸O/¹⁶O < 0.0034, and ²²Ne/²⁰Ne = 0.077(+0.085, –0.023). We compare our values with those found by previous investigators and with those measured in other samples of solar and galactic material. In particular, a comparison of ²²Ne/²⁰Ne measurements from various sources implies that GCRs are not simply an accelerated sample of the local interstellar medium.     

Deuterium Fractionation in Interstellar Clouds

This paper reviews the chemical processes responsible for fractionating deuterium in interstellar molecules. I show that this process is intrinsically a low temperature phenomenon and discuss how the degree of enhancement of the deuterium content of molecules is related to the physical conditions, particularly abundances, in molecular clouds. If significant amounts of abundant species, such as CO, are frozen out on to interstellar dust grains, the resulting enhancement in H₂D⁺ can result in its abundance being greater than that of H ₃ ⁺ at 10K. Transfer of the deuteron from H₂D⁺ can then lead to the efficient formation of multiply deuterated species, such as NHD₂ and ND₃. Fractionation can also occur in grain surface reactions and some simple models are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ion relaxation processes in the heliospheric interface: how perturbed are ion distribution functions?

Charge-exchange processes between interstellar H-/O-atoms and protons of the bulk of the interstellar plasma flow downstream of the outer bowshock in the heliospheric interface induce secondary ions leading to non-relaxated velocity distribution functions. The relaxation of these freshly induced ions towards an equilibrium distribution occurs due to Coulomb interactions and wave–particle interactions with the background turbulence. Since Coulomb interactions are of low relevance, we study here in detail the effect of wave–particle interactions. To find the turbulence levels in the interface we consider the MHD-wave transformation at the outer shock surface between the interface and the local interstellar plasma. The turbulence in the outer interface region is shown to be dominated by incompressible Alfvén waves both for cases of quasiparallel and quasiperpendicular shocks. Also we show that waves propagating towards the shock are more intensive than those propagating away from it. The level of Alfvén turbulence in the interface is estimated using the recent data on local interstellar turbulence deduced from observations of interstellar scintillations of distant radiosources. Two proton relaxation processes are considered: quasilinear resonant interactions with Alfvén waves and non-linear self-induced wave–particle scattering. The corresponding diffusion coefficients are estimated, and typical time periods for protons and oxygen ions relaxation are shown to be of the same order of magnitude as H-/O-atoms passage time over the extent of the interface. This indicates that perturbed ion distribution functions must be expected there.     

面向深空任务的电磁桨推力器设计

为解决深空任务需要大量推进工质的问题,提出了一种电磁桨推力器的概念,以恒星际等离子体为工质,利用带电粒子在正交匀强电场和磁场中的电漂移效应,产生对航天器的推力。根据带电粒子的漂移速度,分非相对论和相对论两种情况,推导了电磁桨推力器的推力公式,分析了电磁桨推力器的设计约束条件,并针对星际航行和无拖曳控制任务,结合实际工程技术水平,设计了初步电磁桨推力器方案和试验验证方案。计算结果表明,使用上述电磁桨推力器方案的航天器无需携带任何工质,在星际航行中每年可以得到1056m/s速度增量。     

Modelling the heliosphere

An overview of our present efforts at the Bartol Research Institute in modelling the largescale interaction of the solar wind with the local interstellar medium is presented. Particular stress is placed on the self-consistent inclusion of neutral hydrogen in the models and both 2D and 3D structure is discussed. Observational implications are noted.