Recent Advances in Laboratory Astrophysics on Megajoule-class Laser Facilities

In recent years, with the development of megajoule-class laser, to create the physical conditions similar to those of extreme celestial environments in the laboratory has become possible. This makes scientists able to study some important astrophysical processes and physical phenomena in the laboratory. This paper briefly introduces several advances in the high energy density laboratory astrophysics driven by the National Ignition Facility (NIF), including the Rayleigh-Taylor instability in supernova remnants, the collisionless shock wave, the laser inertially-confined fusion detection of the thermonuclear reaction under the stellar core condition, the study of planetary interior state, the study of star formation, etc., which will provide a reference for the scientific experiments in the field of laboratory astrophysics performed by using the Shenguang IV laser facility under construction in China. Finally, the possible scientific issues relevant to the direction of laboratory astrophysics by using the Shenguang IV laser facility in the future are briefly discussed.     

Cosmology and VHE gamma ray astrophysics: connections and perspectives

The observation of the universe in the VHE gamma ray domain with the new generation of Cherenkov Telescopes is producing new measurements with a direct implication for cosmology. The present results and the future prospects will be discussed.      

星系金属丰度的研究进展(Ⅰ):定标方法

金属丰度是表征星系特征的重要参量,对于理解星系的形成与演化具有重要意义。随着观测设备的不断完善与发展,已经获得越来越多的星系(包括近邻星系、中等红移及高红移星系)金属丰度的观测资料。在光致电离模型方面也取得了很大进展．这些对于理解星系中金属及恒星成分的累积历史有非常重要的作用。有多种方法可以用来估计星系的金属丰度(主要是星际介质中气相的O丰度),介绍和评述了估计星系的O丰度的多种方法,包括电子温度的方法、R23方法以及其他一些“强线”比值的方法,并给出了相应的解析公式,同时介绍了电离星云的物理本质及由光致电离模型估计星系金属丰度的方法,还给出了估计星系的C和N元素丰度的方法。     

2MASS的科学意义和成果概览

2MASS(Two Micron All Sky Survey)以相当高的内部一致性和精确度在近红外波段对整个天空进行了巡天观测，并通过数据处理把原始数据转变为对天文学有用的图像、星等和位置的列表。较详细介绍了2MASS的科学意义、巡天成果、数据特征以及利用2MASS观测数据所开展的部分工作。     

Accessing High Pressure States Relevant to Core Conditions in the Giant Planets

We have designed an experimental technique to use on the National Ignition Facility (NIF) laser to achieve very high pressure (P _max > 10 Mbar = 1000 GPa), dense states of matter at moderate temperatures (T < 0.5 eV = 6000 K), relevant to the core conditions of the giant planets. A discussion of the conditions in the interiors of the giant planets is given, and an experimental design that can approach those conditions is described.     

Overview of Direct Measurements of Cosmic Rays

The history of cosmic ray studies can be traced back to the 1910s when Hess and other scientists first discovered them. Cosmic rays are very important laboratories of particle physics, and have led to many important discoveries of fundamental particles, such as the positrons, muons, pions, and a series of strange particles. Cosmic rays are nowadays the key probes of the extremely high-energy physics and dark matter particles. A brief review about the history and recent progresses of direct observations of cosmic rays is presented. In recent years, the new space-borne experiments such as PAMELA and AMS-02, as well as a few of balloon-borne experiments, have measured the energy spectra of cosmic rays very precisely, and revealed several new features/anomalies. Remarkable excesses of positron fraction in the total electron plus positron fluxes have been observed, which may be caused by the annihilation/decay of dark matter particles or by astrophysical pulsars. The cosmic ray antiprotons, which are expected to have the same secondary origin as that of positrons, do not show significant excesses compared with the background prediction. This result also constrains the modeling of the positron excesses. In addition, the spectral hardening above several hundred GeV of cosmic ray nuclei has been revealed. These results have important and interesting implications on our understandings of the origin, acceleration, and propagation of cosmic rays. In particular, China has launched the Dark Matter Particle Explorer (DAMPE) to indirectly search for the dark matter and explore the high-energy universe in the TeV window. Most recently, the DAMPE collaborators reported the new measurements of the cosmic ray electron plus positron fluxes up to about 5 TeV with a very high precision. The DAMPE data revealed clearly a deflection around 0.9 TeV in the electron energy spectrum. Possible fine structures of the electron plus positron spectra can be critically addressed with the accumulation of data in the coming years.     

Excitation of Electromagnetic Flute Modes in the Process of Interaction of Plasma Flow with Inhomogeneous Magnetic Field

Laboratory experiments on the interaction of a plasma flow, produced by laser ablation of a solid target with the inhomogeneous magnetic field from the Zebra pulsed power generator demonstrated the presence of strong wave activity in the region of the flow deceleration. The deceleration of the plasma flow can be interpreted as the appearance of a gravity-like force. The drift due to this force can lead to the excitation of flute modes. In this paper a linear dispersion equation for the excitation of electromagnetic flute-type modes with plasma and magnetic field parameters, corresponding to the ongoing experiments is examined. Results indicate that the wavelength of the excited flute modes strongly depends on the strength of the external magnetic field. For magnetic field strengths ∼0.1 MG the excited wavelengths are larger than the width of the laser ablated plasma plume and cannot be observed during the experiment. But for magnetic field strengths ∼1 MG the excited wavelengths are much smaller and can then be detected.     

The role of a magnetic field in the formation of jet-like features in the crab nebula

The toroidal magnetic field frozen in the relativistic plasma ejected by pulsars must play a significant role in the formation of jet-like features observed in the central parts of plerions. We performed a semiquantitative analysis and calculations of the plasma flow in a plerion using the perturbation theory. We show that for the latitudinal magnetic-field distribution expected during the interaction of the pulsar wind with the interstellar medium, the magnetic field will have an appreciable effect on the flow primarily near the rotation axis. In the equatorial region, the effect of the magnetic field is negligible up to distances of 7r_sh.     

太阳物理中磁螺度研究进展

简要回顾了螺度引入太阳磁场研究中的历史过程，从物理角度讨论了相对磁螺度这个新的可观测量，并指出其在理论和观测中存在的问题；着重介绍了磁螺度在太阳大气中的分配问题；探讨了磁螺度和电流螺度的差别与联系、螺度半球手征性；列举介绍了磁螺度和其他太阳活动的联系，尤其是太阳爆发事件中的磁螺度问题；指出磁螺度理论中几个还没有解决的问题及今后可能取得进展的方向。     

晚型旋涡星系盘的颜色梯度

从Sloan巡天第二批释放的数据(Sloan Digital Sky Survey, Data Release Two)中选择了395个在r波段亮于15 mag的晚型旋涡星系作为样本，对样本星系的表面亮度轮廓进行一维两成分(核球与盘)拟合，并着重讨论了盘的颜色梯度，分别用Δc／ΔR和Δc／Δlg R两种形式来拟合。结果表明，对于波长相距较大的颜色r-z和g-z，颜色梯度更符合Δc／ΔR为常数的线性变化形式，而g-r则符合Δc／ΔlgR为线性的情形；用Δc／ΔlgR拟合的梯度值分别为Δ(9-r)／ΔlgR=-0.152±0.010，Δ(r-z)／ΔlgR=-0.377±0.019，Δ(g-z)／ΔlgR=-0.590±0.026，均与前人的研究结果一致。