Surface Photometry of Proplyds in the Vicinity of θ1 Ori C

Results of studies of the surface-brightness distributions of a group of young stellar objects located within 16″ of the star θ₁ Ori C are presented. Isophotes around each proplyd are constructed using violet, red, and near-infrared images. No regularity in the sizes of the diametral cross sections of the proplyds in the various photometric bands is observed. The measured relative intensities are converted to absolute fluxes, and the absolute luminosities of the brightest parts of the disks and of the disk peripheries are estimated. The ratio of the semi-major to the semi-minor axes of the objects range from 1.5 to 2.5. The maximum lengths of the proplyd tails in various filters range from 300 to 700 AU. They become shorter with decreasing distance from the illuminating star, possibly due to enhanced dissipation of the disk, due to the growth in the role of photovaporization.

     

Group method of calculating the perturbations of minor planets

Celestial Mechanics and Dynamical Astronomy - An expansion of the disturbing functionR is suggested for the special case when the orbits of a group of minor planets have approximately equal major...     

Light variations and flares on V471 tauri

Two-colour photometric observations of the white-dwarf and K-dwarf eclipsing binary V471 Tau were made during the last four years. The resulting light curves and thirteen timings of mid-eclipse are presented. During the observations two flares were obtained on September 23 and December23, 1992. Both events occurred just after the fourth contact. The increment in the brightness was measured as 0 _. ^m 067. The energy liberated by the flare was computed to be 5.43 × 10³² erg s^–1 in the JohnsonB band, which amounts 1.13 times that of the total radiation of the K-dwarf.     

Inferring the emission regions for different kinds of gamma‐ray bursts

Using a theoretical model describing pulse shapes, we have clarified the relations between the observed pulses and their corresponding timescales, such as the angular spreading time, the dynamic time as well as the cooling time. We find that the angular spreading timescale caused by curvature effect of fireball surface only contributes to the falling part of the observed pulses, while the dynamic one in the co‐moving frame of the shell merely contributes to the rising portion of pulses provided the radiative time is negligible. In addition, the pulses resulted from the pure radiative cooling time of relativistic electrons exhibit properties of fast rise and slow decay (a quasi‐FRED) profile together with smooth peaks. Besides, we interpret the phenomena of wider pulses tending to be more asymmetric to be a consequence of the difference in emission regions. Meanwhile, we find the intrinsic emission time is decided by the ratios of lorentz factors and radii of the shells between short and long bursts. Based on the analysis of asymmetry, our results suggest that the long GRB pulses may occur in the regions with larger radius, while the short bursts could locate at the smaller distance from central engine. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear plasma density modification by the ponderomotive force of ULF pulsations at the dayside magnetosphere

We investigate analytically and numerically a nonlinear modification of the magnetospheric plasma density under the action of the ponderomotive force induced by ULF traveling waves, using the nonlinear stationary force balance equation. This equation is applied to both the dipole and dayside magnetosphere having one and two minima of the geomagnetic field near the magnetospheric boundary. The separate and joint actions of the ponderomotive, centrifugal, and gravitational forces on the density distribution are shown.     

Accretion onto neutron star: The X-ray spectra and luminosity

The equations of stationary fluid motion are solved for the case of spherical accretion onto non-magnetic, non-rotating neutron star. The X-ray radiation flux is calculated in two different ways: An approximate solution of the moment equations coupled to the gas fluid equations and numerical Monte-Carlo simulation of the photon random walk. We show that the spectrum of the X-ray radiation in the outer parts of the inflowing envelope has a characteristic power-law behaviour. We suggest that some of the properties of the X-ray sources in the globular clusters can be explained with this model.     

无线信道中传输高速数据的试验报告

本文主要介绍了利用无线信道传输9600bps数据信号的的几种试验方案,并对其进行了评价,供各界参考。     

Arsenic Speciation in Lichens and in Coarse and Fine Airborne Particulate Matter by HPLC–UV–HG–AFS

A three-step sequential extraction procedure with Milli-Q, CaCl₂ and H₃PO₄ was applied for extraction of arsenic species in lichen transplants and airborne particulate matter (fine and coarse fractions). The samples used in this work were collected in 1994–1995 near coal-fired power plants. Both transplant lichens and airborne particulate matter were submitted to the same environment simultaneously. Arsenic species identification and quantification was performed by HPLC–UV–HG–AFS. Inorganic forms of arsenic (arsenite and arsenate) were present in significant amounts in most of the samples. Only in lichens also organic forms of arsenic (monomethyl arsonic acid and dimethyl arsinic acid) were identified which may indicate biotransformation of inorganic arsenic.