一种TeGe基快速相变型可逆光记录介质的研究

研制出一种在晶化激光功率为4mW时晶化时间为180ns的可逆相变型光纪录介质。其擦写循环次数可达10~6次。分析了其快速晶化机理。     

Be stars in young clusters in the Magellanic Clouds

A substantial fraction (typically 10%) of Galactic B stars consists of Be stars. While Galactic Be stars have been fairly well investigated, very little is known about the Be star content of the Magellanic Clouds (MCs). We present a refined method of Be star identification by CCD photometry and apply it to four young clusters and associations in the MCs. We find NGC 330 in the SMC to be exceptionally rich in Be stars, while the fraction is clearly lower in the similarly aged LMC clusters NGC 2004 and NGC 1818. NGC 2044, a very young region in the LMC, contains almost no Be stars. Among very early-type B stars in the investigated MC clusters we find the largest number of Be stars, while in the Milky Way this is shifted to somewhat later types. In the LMC, there may be a second frequency peak around B6.Based on observations obtained at the 2.2m MPIA telescope at ESO, La Silla, Chile, partly on time granted by the MPIA, Heidelberg.     

Heliospheric asymmetries due to the action of the interstellar magnetic field

We discuss the asymmetry of the heliospheric discontinuities obtained from the analysis of 3D modeling of the solar wind (SW) interaction with local interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the flow of neutral particles is described by the Boltzmann equation. The emphasis is made on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the interstellar and interplanetary magnetic fields (ISMF and IMF) in the presence of neutral hydrogen atoms whose transport through the heliosphere is modeled kinetically, using a Monte Carlo approach. We show that the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM is highly anisotropic and evaluate a possible angle between the hydrogen deflection plane measured in the SOHO SWAN experiment and the plane containing the ISMF and LISM velocity vectors for different ISMF strengths. It is shown that the ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric difference observed during its crossing by the Voyager 1 and Voyager 2 spacecraft, which however results in a larger discrepancy between the calculated and observed velocity distributions. The effect of a strong ISMF on the distribution of plasma quantities in the inner heliosheath and on 2–3 kHz radio emission is discussed.     

The peculiar X-ray source in NGC 5281

Recent observations with Chandra and XMM-Newton   have shown that the X-ray source 1WGA J1346.5–6255 is associated with the Be star HD 119682, a member of the open cluster NGC 5281, and displays all the characteristics of the new class of X-ray sources known as γ$\mathrm{\gamma }$-Cas analogues. We present a detailed spectroscopic study of this open cluster, finding an age of 40 Myr and a sequence of evolved stars. These results imply that HD 119682 is a blue straggler in NGC 5281, as it is much more massive than any other cluster member, and its membership is strongly suggested by proper motion analysis. This is the second γ$\mathrm{\gamma }$-Cas analogue found to be blue straggler in an open cluster, suggesting that evolution plays a role in the formation of these systems and that a supernova explosion has not occurred in them.     

Transient outburst mechanisms in Supergiant Fast X-ray Transients

The recent discovery of a new class of recurrent and fast X-ray transient sources, the Supergiant Fast X-ray Transients, poses interesting questions on the possible mechanisms responsible for their transient X-ray emission. The association with blue supergiants, the spectral properties similar to those of accreting pulsars and the detection, in a few cases, of X-ray pulsations, confirm that these transients are High Mass X-ray Binaries. I review the different mechanisms proposed to explain their transient outbursts and the link to persistent wind accretors. I discuss the different models in light of the new observational results coming from an on-going monitoring campaign of four Supergiant Fast X-ray Transients with Swift.     

An inversion approach for lunar regolith layer thickness using optical albedo data and microwave emission simulation

An approach to inversion of the lunar regolith layer thickness by using multi-channel brightness temperature observation in passive microwave remote sensing is developed. To first make simulation of brightness temperature from the lunar layered media, the lunar regolith layer thickness (d) is proposed being constructed by available lunar DEM (digital elevation mapping) and on site measurements. The physical temperature distribution (T) over the lunar surface is also empirically assumed as a monotonic function of the latitude. Optical albedo of the lunar nearside from the telescopic observation is employed to construct the spatial distribution of the FeO+TiO₂ content (S) in the lunar regolith layer. A statistic relationship between the DEM and S of the lunar nearside is further extended to construction of S of the lunar farside. Thus, the dielectric permittivity (ε) of global lunar regolith layer can then be determined. Based on all these conditions (d,T,ε), brightness temperature of the lunar regolith layer in passive microwave remote sensing, which is planned for China's Chang-E lunar project, is numerically simulated by a parallel layering model using the strong fluctuation theory of random media.Then, taking these simulations with random noise as observations, an inversion method of the lunar regolith layer thickness is developed by using three- or two-channels brightness temperatures. When the S is low, and the four channels brightness temperatures in China's Chang-E project are well distinguishable, the regolith layer thickness and physical temperature of the underlying lunar rock media can be inverted by the three-channels approach. When the S becomes high that the brightness temperature at high frequency channels such as 19.35, 37 GHz are saturated, the regolith layer thickness is alternatively inverted only by the two-channels approach.Numerical simulation and inversion approach in this paper make an evaluation of the performance for lunar passive microwave remote sensing, and for future data calibration and validation.     

Possible Suzaku detection of non-thermal X-ray signals from a rotating magnetized white dwarf

Although rotating neutron stars (NSs) have been regarded as being textbook examples of astrophysical particle acceleration sites for decades, details of the acceleration mechanism remain a mystery; for example, we cannot yet observationally distinguish “polar cap” models from “outer gap” models. To solve the model degeneracy, it is useful to study similar systems with much different physical parameters. Strongly magnetized white dwarfs (WDs) are ideal for this purpose, because they have essentially the same system geometry as NSs, but differ largely from NSs in the system parameters, including the size, magnetic field, and the rotation velocity, with the induced electric field expected to reach 10¹³–10¹⁴ eV. Based on this idea, the best candidate among WDs, AE Aquarii, was observed with the fifth Japaneses X-ray satellite, Suzaku. The hard X-ray detector (HXD) on-board Suzaku has the highest sensitivity in the hard X-ray band over 10 keV. A marginal detection in the hard X-ray band was achieved with the HXD, and was separated from the thermal emission. The flux corresponds to about 0.02% of its spin-down energy. If the signal is real, this observation must be a first case of the detection of non-thermal emission from WDs.     

Source investigation of impulsive He-rich particle events

We have investigated the source characteristic and coronal magnetic field structure of six impulsive solar energetic particle (SEP) events selected from Wang et al. [Wang, Y.-M., Pick, M., Mason, G.M. Coronal holes, jets, and the origin of ³He-rich particle events. ApJ 639, 495, 2006] and Pick et al. [Pick, M., Mason, G.M., Wang, Y.-M., Tan, C., Wang, L. Solar source regions for ³He-rich solar energetic particle events identified using imaging radio, optical, and energetic particle observations. ApJ 648, 1247, 2006]. Some results are obtained: first, 2 events are associated with wide (≈100°) CMEs (hereafter wide CME events), another 4 events are associated with narrow (?40°) CMEs (hereafter narrow CME events); second, the coronal magnetic field configuration of narrow CME events appear more simple than that of the wide CME events; third, the photospheric magnetic field evolutions of all these events show new emergence of fluxes, while one case also shows magnetic flux cancellation; fourth, the EUV jets usually occurred very close to the footpoint of the magnetic field loop, while meter type III bursts occurred near or at the top of the loop and higher than EUV jets. Furthermore, the heights of type III bursts are estimated from the result of the coronal magnetic field extrapolations.     

Active Region Dynamics

New methods of local helioseismology and uninterrupted time series of solar oscillation data from the Solar and Heliospheric Observatory (SOHO) have led to a major advance in our understanding of the structure and dynamics of active regions in the subsurface layers. The initial results show that large active regions are formed by repeated magnetic flux emergence from the deep interior, and that their roots are at least 50 Mm deep. The active regions change the temperature structure and flow dynamics of the upper convection zone, forming large circulation cells of converging flows. The helioseismic observations also indicate that the processes of magnetic energy release, flares and coronal mass ejections, might be associated with strong (1–2 km/s) shearing flows, 4–6 Mm below the surface.