The Universe behind the Milky Way

Summary. Due to the foreground extinction of the Milky Way, galaxies appear increasingly fainter the closer they lie to the Galactic Equator, creating a “zone of avoidance” of about 25% in the distribution of optically visible galaxies. A “whole-sky” map of galaxies is essential, however, for understanding the dynamics in our local Universe, in particular the peculiar velocity of the Local Group with respect to the Cosmic Microwave Background and velocity flow fields such as in the Great Attractor region. Various dynamically important structures behind the Milky Way have only recently been made “visible” through dedicated deep surveys at various wavelengths. The wide range of observational searches (optical, near infrared, far infrared, radio and X-ray) for galaxies in the Zone of Avoidance are reviewed, including a discussion on the limitations and selection effects of these partly complementary approaches. The uncovered and suspected large-scale structures are summarized. Reconstruction methods of the density field in the Zone of Avoidance are described and the resulting predictions compared with observational evidence. The comparison between reconstructed density fields and the observed galaxy distribution allow derivations of the density and biasing parameters and b. Received 4 April 2000 / Published online 18 July 2000     

反常折射引起的地面天文观测残差的周年变化

我国光学天文观测有相当长历史，观测精度也较高，但是与国际系统相比。无论是测时还是测纬，所有仪器残差都有类似的周年变化，本文作者认为部分原因是由于我国季节变化引起的大气等密度层倾斜，从而产生的反常折射所引起的，文中对反常折射的规律进行了研究，导出了由于气象参数变化而引起的反常折射公式，并与测时，测纬的残差周年项进行了对比，结果表明用反常折射可以部分地解释我国天文观测残差的周年变化。     

On the Possibility of Directional Analysis for Geo-neutrinos

The possibility of terrestrial antineutrino directionality studies is considered for future unloaded liquid scintillator detectors. Monte-Carlo simulations suggest that the measurable displacement between prompt and delayed antineutrino signals makes such studies possible. However, it is estimated that on the order of 1000 terrestrial antineutrino events are required to test the simplest models, demanding detectors of 100 kt size to collect sufficient data in a reasonable period of time.     

Advances in radiative transfer

This review describes advances in radiative transfer theory since about 1985. We stress fundamental aspects and emphasize modern methods for the numerical solution of the transfer equation for spatially multidimensional problems, for both unpolarized and polarized radiation. We restrict the discussion to two-level atoms with noninverted populations for given temperature, density and velocity fields. Unfortunately this article was originally published with typesetter's errors: The correct publication date was 25 February 2006, not 3 January 2006. The content was not in the final form. The publishers wish to apologize for this mistake. The online version of the original version can be found at /10.1007/s00159-005-0025-8.     

Characteristics of convection and overshooting in RGB and AGB stars

Based on the turbulent convection model (TCM) of Li & Yang, we have studied the characteristics of turbulent convection in the envelopes of 2 and 5M⊙ stars at the red giant branch and asymptotic giant branch phases. The TCM has been successfully applied over the entire convective envelopes, including the convective unstable zone and the overshooting regions. We find that the convective motions become progressively stronger when the stellar models are located farther up along the Hayashi line. In the convect...     

On the use of X-ray and γ-ray telescopes for identifying the origin of electrons and positrons observed by ATIC, Fermi, and PAMELA

X-ray and γ-ray observations can help understand the origin of the electron and positron signals reported by ATIC, PAMELA, PPB-BETS, and Fermi. It remains unclear whether the observed high-energy electrons and positrons are produced by relic particles, or by some astrophysical sources. To distinguish between the two possibilities, one can compare the electron population in the local neighborhood with that in the dwarf spheroidal galaxies, which are not expected to host as many pulsars and other astrophysical sources. This can be accomplished using X-ray and γ-ray observations of dwarf spheroidal galaxies. Assuming the signal detected by Fermi and ATIC comes from dark matter and using the inferred dark matter profile of the Draco dwarf spheroidal galaxy as an example, we calculate the photon spectrum produced by electrons via inverse Compton scattering. Since little is known about the magnetic fields in dwarf spheroidal galaxies, we consider the propagation of charged particles with and without diffusion. Extending the analysis of Fermi collaboration for Draco, we find that for a halo mass ∼10⁹ M_⊙, even in the absence of diffusion, the γ-ray signal would be above the upper limits. This conclusion is subject to uncertainties associated with the halo mass. If dwarf spheroidal galaxies host local magnetic fields, the diffusion of the electrons can result in a signal detectable by future X-ray telescopes.     

系外行星系统掩星周期变化研究进展

在掩星法发现的系外行星系统中,如果存在其他未知的伴星绕同一颗恒星运动,掩星行星由于受到伴星引力的影响,运动轨道将发生变化,轨道周期不再是常数,而是变化的。利用这种变化探测掩星系统中的其他行星,已成为一种新的方法。主要介绍了未知行星与掩星行星之间的引力作用引起的掩星周期变化效应,以及掩星周期变化法探测系外行星的理论和研究进展状况,最后简要讨论了几种影响掩星周期变化的其他因素:共轨行星、卫星、潮汐效应、相对论效应及恒星的引力四极矩等。