Estimation of the characteristics of a promising orbital lidar for space debris monitoring

A preliminary study aimed at estimating the potential of a promising orbital lidar for space debris monitoring has been performed. Estimates of the space debris detection range under different observation conditions with different technical characteristics of lidar have been calculated. It is shown that the detection range for space debris fragments with sizes of 1 to 10 cm in the wavelength range near 0.5 µm depends strongly on the observation conditions, which are determined by the additive-noise level. It is concluded that a promising orbital lidar should contain a laser emitter with a power of several hundreds of watts and a receiving telescope about 0.5 to 1m in diameter. The possibility of using an orbital lidar for recognizing space debris is estimated. It is shown that a recognition probability exceeding 0.8 can be attained for a space debris image containing several tens of pixels and a signal-to-noise ratio above 10.     

Nearby stars as sources of gamma-ray bursts

Observations of ground-based telescopes and the Hubble space telescope made it possible to identify a part of gamma-ray bursts with far objects (redshift parameter Z ≥ 1).However, it remains unclear what are other bursts and what are their sources. The possibility of identifying other bursts with close sources known as small-mass flare stars is considered. The coordinates of space gamma-ray bursts (GRBs) for 2008–2013 and close stars (within the radius r < 25 pc) were compared by the correlation analysis method. Six coincidences were found with an accuracy of ～0.1°. The probability of accidental coincidence of GRBs with stars is 4 · 10^?8, which undoubtedly proves their stellar origin.     

Dust in the planetary system: Dust interactions in space plasmas of the solar system

Cosmic dust particles are small solid objects observed in the solar planetary system and in many astronomical objects like the surrounding of stars, the interstellar and even the intergalactic medium. In the solar system the dust is best observed and most often found within the region of the orbits of terrestrial planets where the dust interactions and dynamics are observed directly from spacecraft. Dust is observed in space near Earth and also enters the atmosphere of the Earth where it takes part in physical and chemical processes. Hence space offers a laboratory to study dust–plasma interactions and dust dynamics. A recent example is the observation of nanodust of sizes smaller than 10 nm. We outline the theoretical considerations on which our knowledge of dust electric charges in space plasmas are founded. We discuss the dynamics of the dust particles and show how the small charged particles are accelerated by the solar wind that carries a magnetic field. Finally, as examples for the space observation of cosmic dust interactions, we describe the first detection of fast nanodust in the solar wind near Earth orbit and the first bi-static observations of PMSE, the radar echoes that are observed in the Earth ionosphere in the presence of charged dust.     

The T Tauri stars

The observational aspects of T Tau stars are described, treating data in the optical, infrared, radio, X-ray and ultraviolet regions of the spectrum. Erratic flare-like behaviour is very characteristic of these objects which are pre-main-sequence stars, mostly on their convective tracks, and represent early phases in the evolution of roughly solar-mass stars. Herbig-Haro objects are discussed-shocked nebulae found in association with either visible T Tau stars or infrared sources deeply embedded in the parental dust clouds. It is argued that highly anisotropic mass loss, probably in unpredictable short-lived episodes, is found in the stars that excite Herbig-Haro objects. These exciting stars could well be the precursor to T Tau stars and display a fascinating array of astonishingly well-collimated phenomena.     

Simultaneous multicolor photometry of fast-moving objects using the 1-meter telescope at Xinglong Observatory

Simultaneous multicolor photometry of fast-moving objects is discussed in this paper. In conventional astronomical photometry, the accuracy of flux and color indices of fast-moving objects is affected by the variations of the targets and weather conditions in space and time domains. We optimize related techniques and methods of observation and data reduction, including image calibration, background fitting, targets detection and location, isophotal photometry, and flux calibration by using background stars from different fields. We consider that simultaneous multicolor data acquisition and differential flux calibration are critical for improving photometric accuracy of fast-moving objects. Our results show the photometric accuracy is better than 5% based on the observations carried out by a 1-meter telescope under ordinary, non-photometric conditions.     

偏振滤波白天抑制天光背景作用分析

由于天文观测领域大部分自适应光学系统只能在夜晚工作,提出了采用偏振滤波技术抑制天光背景的办法以达到白天探测微弱星体目标的目的。介绍了偏振滤波的原理并估算了抑制天光背景的效果,通过观测角度关系得到了偏振方位角的计算公式,并在丽江观测站1.8m望远镜自适应光学系统平台上进行实验,给出了消像旋模型。实验结果表明,偏振滤波技术能有效抑制天光背景,提高星体目标探测能力,一定程度上提高了自适应光学系统在白天探测弱小星体目标的可能性。     

Thermal conductivity: Recent developments

The detailed spectral energy distribution of the radiation emitted by stars provides information on their composition and physical parameters. Many of the astpophysically important spectral lines of neutral and ionized atoms whose study can lead to a better understanding of the processes occurring in stellar atmosphere and in the interstellar gas lie in the ultraviolet region of the spectrum.

Since ultraviolet radiation from the stars is absorbed by the Earth's atmosphere, observations must be made from space vehicles. In this article some scientific objectives of a programme in ultraviolet astronomy are considered, and a review made of the types of space vehicles and attitude control systems employed. A brief discussion is made of some recent results and their interpretation.     

Is it possible to explore Peccei-Quinn axions from frequency-dependence radiation dimming?

We explore how the Peccei-Quinn (PQ) axion parameter space can be constrained by the frequency-dependence dimming of radiation from astrophysical objects. To do so we perform accurate calculations of photon-axion conversion in the presence of a variable magnetic field. We propose several tests where the PQ axion parameter space can be explored with current and future astronomical surveys: the observed spectra of isolated neutron stars, occultations of background objects by white dwarfs and neutron stars, the light-curves of eclipsing binaries containing a white dwarf. We find that the lack of dimming of the light-curve of a detached eclipsing white dwarf binary recently observed, leads to relevant constraints on the photon-axion conversion. Current surveys designed for Earth-like planet searches are well matched to strengthen and improve the constraints on the PQ axion using astrophysical objects radiation dimming.     

Heavy hybrid stars from multi-quark interactions

We explore the possibility of obtaining heavy hybrid stars within the framework of the two flavor Nambu-Jona-Lasinio model that includes 8-quark interactions in the scalar and in the vector channel. The main impact of the 8-quark scalar channel is to reduce the onset of quark matter, while the 8-quark vector channel acts to stiffen the equation of state at high densities. Within the parameter space where the 4-quark vector channel is small, and the 8-quark vector channel sizeable, stable stars with masses of 2 M _⊙ and above are found to hold quark matter in their cores.

     

On the Cosmological Origin of Population III Objects

It is the aim of our letter to embedd the presently well understood scale of stellar mass into a simple cosmological scenario for the origin of Population III objects. The result of our consideration will be that if the first bound objects with typical stellar mass of the order of 30 M_⊙ could evolve as ordinary stars ending up exploding (Type II supernovae) the problem of the pregalactic enrichment of a primordial gas cloud be solved.     

On the formation of collapsed superdense nuclei in the universe

The possibility of the production of putative superdense nuclei (SDNs) in the universe is studied with the assumption that the SDNs can certainly be formed when nucleons are compressed over some critical density. Possible nuclear astrophysical processes for SDN production taking place in the early big-bang universe, in interstellar space and in ejection from neutron stars are investigated. It is found that the SDNs cannot be produced at all in a hot universe regardless of the properties of SDNs. The situation that would occur in a cold universe is also discussed. A finite amount of SDNs is found to be formed in interstellar space as the product of high-energy reactions between primary cosmic rays and interstellar matter. It also becomes clear that the astration of SDNs thus formed plays no essential role for the enhancement of the number of SDNs. On the other hand, the SDNs originating from neutron stars are estimated to have a cosmic abundance relative to Si as high as 8 × 10^?8??5, which is, apparently, in contradiction with observations. Some implications of this are discussed.     

Laboratory Microwave Spectroscopy of Interstellar Molecules

Abstract

Modern radio astronomy has revealed that various kinds of molecules exist in ther very cold region between stars: interstellar space. An electromagnetic wave with a wavelength of a few centimeters to 1 mm corresponds in energy to a few to ten degrees of Kelvin. A molecule having its spectrum in this energy region provides us with valuable information about the low-energy environment where the molecule exists. New information provided by radio astronomy has rarely been     

Isolated Newtonian Dust Stars Are Unstable But Can Be Stabilized by Exterior Matter

The mathematical problem of the existence of solutions for Newtonian dust stars is formulated, and proofs for the non-existence of such stars as isolated objects are given. It is however shown that such stars can be stabilized by reasonable exterior (strained) matter. Comments are made on the problem of Einsteinian rotating dust stars.     

Thermodynamic functions of degenerate magnetized electron gas

The Fermi energy, pressure, internal energy, entropy, and heat capacity of completely degenerate relativistic electron gas are calculated by numerical methods. It is shown that the maximum admissible magnetic field on the order of 10⁹ G in white dwarfs increases the pressure by a factor of 1.06 in the central region, where the electron concentration is ∼10³³ cm⁻³, while the equilibrium radius increases by approximately a factor of 1.03, which obviously cannot be observed experimentally. A magnetic field of ∼10⁸ G or lower has no effect on the pressure and other thermodynamic functions. It is also shown that the contribution of degenerate electron gas to the total pressure in neutron stars is negligible compared to that of neutron gas even in magnetic fields with a maximum induction ∼10¹⁷ G possible in neutron stars. The neutron beta-decay forbiddeness conditions in a superstrong magnetic field are formulated. It is assumed that small neutron stars have such magnetic fields and that pulsars with small periods are the most probable objects that can have super-strong magnetic fields.     

地球同步轨道碎片观测图像分级检测方法

为了快速检测出地球同步轨道带光学观测图像中的空间碎片,提出了一种基于信噪比的分级检测方法.首先分析实测数据,得出观测图像中不同信噪比碎片运动相似的特性.对于高信噪比碎片,采取帧差法快速检测,并利用多帧图像计算速度信息;对于低信噪比碎片,根据高信噪比碎片检测结果得到的速度信息,采用改进的动态规划检测方法.实际图像检测结果表明:当递归方程的搜索窗口为5pixel×5pixel时,分级检测方法检测性能最好;当累积帧数大于5帧时,检测时间比传统动态规划方法减少了87%以上.分级检测方法具有检测率高、虚警率低、计算量小的优势,适合地球同步轨道带光学观测图像中空间碎片的检测.     

Photoneutrino energy loss rates under magnetic field

The neutrino energy loss rate is calculated due to the photoneutrino process in a hot plasma, under magnetic field.

The calculations done for low densities and relatively low temperatures may be used for astrophysical estimations in neutron stars.

     

Formation and Development of Phase Morphology and Structure on Polystyrene Blends. I. Study of Phase Behavior and Structure Character of Polystyrene/Poly (cis‐butadiene) Rubber Immiscible System During Melt Blending by Scanning Electron Microscopy

Abstract

Polystyrene/poly(cis‐butadiene) rubber blends were prepared by melt blending. The morphology development of the blend system was examined by intermittent extraction of material and scanning electron microscopy. The mixing process of the immiscible system was described through the characteristic length L and the average characteristic length L _m. The distribution of L was shown to be consonant with a log‐normal distribution. The mixing system was demonstrated to possess self‐similarity in a certain range of time and space, as shown through a scale function. Furthermore, the fractal dimension D at different times was calculated and shown to be a parameter that can be used to describe the dynamic process of the melt blending.     

OH/IR stars: Very long period variables with extreme mass loss rates on their nature and their distribution in the galaxy

Seldom are simple models sufficiently accurate to describe nature. The long period OH/IR stars with a well ordered, spherically symmetric, strong outflow of matter are such an exception. The variability of the central stars and the large dimension of the circumstellar dust shell enable a direct, geometrical determination of the distance to individual objects. Then most basic stellar quantities, such as mass, luminosity, mass loss rate, etc., may be derived. The values found indicate that OH/IR stars represent the last stage in the evolution of intermediate mass stars. In a relatively short ‘superwind’ phase a large fraction of the stellar mass is ejected and the objects are on the verge of becoming a planetary nebula or a white dwarf.The strength of the OH maser emission, and the accurate distance and velocity information, make the OH/IR stars particularly suited for the study of galactic structure. They are one of the few stellar populations that are detectable at large distances, even in the very centre of our Galaxy. The fact that they are found in the bulge of our Galaxy, seems to indicate that at least until recently (? 10⁹ years ago) star formation has been going on there.     

Small-angle X-ray scattering from salt-free solutions of star-branched polyelectrolytes

The dispersion state of sodium-sulphonated polystyrene ( NaPSS) star-branched polyelectrolytes was investigated in salt-free aqueous solutions, by use of the small-angle X-ray scattering technique. With respect to polystyrene (PS) star-branched polymers of identical functionality, the ordering phenomenon occurring in the neighborhood of the overlap concentration c^* is reinforced and observed in a larger range of concentrations. Moreover, the degree of order is no longer maximum at c^* and is improved as the concentration decreases. The dispersion state is then mainly controlled by the electrostatic interaction. A crystalline order should therefore be achieved with stars of lower functionality, provided the electrostatic interaction is added to the osmotic repulsion. On the other hand, unusual scattering patterns are measured for aqueous solutions of NaPSS star polyelectrolytes. Indeed, a diffuse scattering is revealed at high angles, in addition to the regular diffraction rings related to preferred interstar distances. It is similar to the broad scattering peak produced by semidilute solutions of NaPSS linear polyelectrolytes and associated to the electrostatic correlation hole within the isotropic model. In the dilute regime (c < c ^*), it is just an intramolecular characteristic and represents the electrostatic repulsion between arms belonging to the same star. In the semidilute regime (c > c ^*), it also reflects the electrostatic repulsion between arms of distinct stars. So, as the concentration increases, it is mainly caused by the interpenetration of NaPSS stars. Such an observation is in agreement with the composite structure earlier proposed by Daoud and Cotton for star semidilute solutions. For c > c ^*, NaPSS star aqueous solutions can therefore be pictured as effective stars immersed in a matrix formed by the overlap of the arm ends. With respect to the dilute regime, the effective stars are smaller; the higher the concentration the smaller the size. Received 14 May 1999 and Received in final form 15 March 2000     

An alternative evolution scenario for OAO 1657-415 and IGR J18483-0311

The relation between the spin period and the orbital period in high-mass X-ray binaries is investigated. Be/X-ray binaries and SG/X-ray binaries occupy different areas in Corbet’s diagram. The two SG/X-ray binaries, IGR J18483-0311 and OAO 1657-415, however, appear to occupy a transition region between Be/X-ray binaries and wind-fed SG/X-ray binaries. This can be understood by noting that the neutron stars in the two SG/X-ray binaries have not reached their equilibrium spin periods when the donors evolved off the main sequence. Here, we provide an alternative scenario to explain their location in Corbet’s diagram: the SG/X-ray binaries are the descendants of Be/X-ray binaries, i.e. the supergiants in these systems were formed from O-type emission line stars instead of normal main-sequence stars. Furthermore, we suggest that there are two types of SG/X-ray binaries: one is directly evolved from a normal OB-type main sequence and neutron star system without an X-ray history, and the other evolved from a Be/X-ray binary with an X-ray history.