Evolution and Pulsations of Population I Post-AGB Stars

Astronomy Letters - Evolutionary calculations of population I stars with initial masses M0 = 1 M⊙, 1.5 M⊙ and 2 M⊙ were carried out up to the stage of the proto-planetary nebula....     

Radiative Transfer Models of Dust Shells Around Post-AGB Stars

We present a radiative transfer analysis of circumstellar dust shells around the Post-AGB stars HD 179821, HD 56126, HD 101584 and early R star HD 100764, using the code DUSTY. Parameters like mass-loss, shell inner radius, dust temperature, outflow velocity etc., are derived for HD 179821and HD 56126 whose observed SED could be reproduced by our models. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optical Classification of IRAS Post-AGB Candidates

We present the first results of a survey carried out on a sample of optically bright post-AGB candidates selected from the IRAS Point Source Catalogue, many of them previously unidentified in the literature. The selection criteria are based on their characteristic far infrared colours. Low resolution spectroscopy of more than 150 sources has been obtained during 6 years. Our preliminary analysis confirms that most of the candidates observed are true post-AGB stars, some of them still strongly reddened. Some young planetary nebulae, a few young stellar objects and active galactic nuclei are also present in the sample. The distribution of post-AGB stars with different spectral types in the IRAS two-colour diagram and its evolutionary implications are briefly discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

IRAS 01005＋7910：a High Galactic Latitude Post—AGB Star

IRAS 01005＋7910 is a cold IRAS source. We present its optical identification, photometric and spectroscopic observation results. Its optical counterpart is classified as a B2Ie star with V magnitude 10.85. Its Hα line shows the P Cygni profile.According to its location in the Galaxy (b=16.6), we consider it to be a post-AGB star or a proto-planetary nebula.     

球状星团的形成与演化(Ⅱ):模型

简要介绍了若干关于球状星团形成与演化的代表性模型，包括球状星团诞生于星系形成之前的模型、自增丰演化模型、原始云团的碰撞聚合模型、两阶段形成模型以及星系并合激发形成球状星团的模型和吸积模型等。     

OPAL不透明度对恒星结构和演化模型的影响

本文利用国际上最新公布的OPAL不透明度表及相应的化学丰度，计算了三颗不同初始质量的星族互恒星的非守恒演化模型，并和过去长期采用的LAOL不透明度的结果进行详细比较，得出以下主要结论：（1）恒星HR图中的演化轨迹光度降低，主序位置明显向红方向移动；（2）恒星中心H，He燃烧寿命大大延长了；（3）小质量星氢燃烧核和对流核都变小，大、中质量星的中心对流核和燃烧核都有所增大；（4）恒星中心温度－密度关系基本不受影响．     

High Resolution Optical Spectroscopy of Hot Post-AGB Star Candidates LS IV-04 1 and LB3116

We present LTE analysis of high resolution optical spectra for B-type hot PAGB stars LS IV-04 1 and LB3116 (LSE 237). The spectra of these high Galactic latitude stars were obtained with the 3.9-m Anglo-Australian Telescope (AAT) and the UCLES spectrograph. The standard 1D LTE analysis with line-blanketed LTE model atmospheres and spectral synthesis provided fundamental atmospheric parameters of T_eff= 15 000±1000 K, log g= 2.5±0.2, ξ = 5.0±1.0 km s^?1, [M/H] = ?1.81 dex, and v sin i= 5 km s^?1 for LSIV-04 1 and T_eff= 16 000±1000 K, log g= 2.5±0.1, v sin i= 25 km s^?1, and [Fe/H] = ?0.93 dex for LB 3116. Chemical abundances of ten different elements were obtained. For LS IV-04 1, its derived model temperature contradicts with previous analysis results. The upper limits for its nitrogen and oxygen abundances were reported for the first time. The magnesium, silicon and calcium were overabundant (i.e. [Mg/Fe] = 0.8 dex, [Si/Fe] = 0.5 dex, [Ca/Fe] = 0.9 dex). With its metal-poor photosphere and V_LSR ≈ 96 km s^?1, LSIV-04 1 is likely a population II star and most probably a PAGB star. LTE abundances of LB 3116 were reported for the first time. The spectrum of this helium rich star shows 0.9 dex enhancement in the nitrogen. The photosphere of the star is slightly deficient in Mg, Si, and S. (i.e. [Mg/Fe] = ?0.2 dex, [Si/Fe] = ?0.4 dex, [S/Fe] = ?0.2 dex). The Al is slightly enhanced. The phosphorus is overabundant, i.e. [P/Fe] ≈ 1.7 ± 0.47 dex, hence LB3116 may be the first example of a PAGB star which is rich in phosphorus. With its high radial velocity (i.e.V_LSR = 73 km s^?1), and the deficiencies observed in C, Mg, Si, and S indicate that LB 3116 is likely a hot PAGB star at high galactic latitude.     

Tectonics and Evolution of Novae and Coronae on Venus: Tectonophysical Modeling Based on Gravitational Models

This paper describes the results of tectonophysical modeling of the formation and evolution of novae and coronae—radial/concentric volcanotectonic structures typical of the surface of Venus. The formation of these structures is usually associated with the effect of the rising and subsequently relaxing mantle diapirs on the surface layers of the lithosphere. Two series of experiments with gravitational models reproduce the topographic changes and the evolution of structural patterns in the course of the formation of novae and coronae on Venus. For model materials, we chose (1) rubber (a Bingham liquid) to reproduce the behavior of the elastoviscous diapir material in one series of experiments and the lower part of the lithosphere in the other series and (2) flour to model tectonic structures in the upper, brittle part of the lithosphere. Regularities in the formation of the topographic and structural characteristics of novae and coronae have been demonstrated on models of different geometry. The process of formation of the dense radial fracturing in novae due to the mechanical elevation caused by the formation of a rising dome, which was suggested by many authors, is not corroborated by our models. In the course of modeling, we studied the influence of the relative dimensions of the diapir and the thickness of the overlying structures, or the relative depth of the neutral buoyancy surface of the diapir, on the topographic, morphological, and structural features of novae and coronae and on the possible paths of their evolution. Regularities are also revealed in the formation of tectonic structures in relation to the environment in which the diapir evolution occurs—in the brittle upper part of the lithosphere or in its lower, viscoplastic part.     

Models for different sunspot umbrae

An empirical approach to interpret the time evolution of the high spatial resolution Ca ii K line is presented. We specify the physical parameters, such as electron temperature, hydrogen density, and velocity (microturbulent and systematic) as functions of height. The electron density is obtained from scaled non-LTE solutions for hydrogen ionization. The population indices, and thus the Ca ii source functions, for a 5-level Ca ii atom are computed by using the generalized Newton-Raphson method. K line profiles are then synthesized for different evolutionary stages and are compared with the observed ones. The explanation of the ‘peculiar’ type profile is also attempted.     

Cloud Models for Solar Faculae

Assuming the clouds as plane parallel structures above the photosphere, center-to-limb contrast variations of various cloud models for solar faculae with approximations such as optically thin or thick, hot or cold, and with or without surface reflections, have been investigated. It has been found that the observed facular contrast data from Frazier (1971) and Taylor et al. (1998) at the 525 nm continuum is best represented by a cloud which is 230 K hotter than the undisturbed photosphere, with an optical depth =0.4283, and with isotropic surface reflections causing 11% of the background photons to be lost before penetrating into the cloud. This model and some other cloud models are shown to provide a fit better than the other physical and non-physical facular models presented previously.     

Models for the Origin of the Quadrantids

We present two scenarios for production of the Quadrantid stream based on two different models for its origin: the extinct model in which 2003EH1 was an active comet that released the dust particles during past 5000 years, stopping its activity abruptly in AD 1488; and the split model; in which a catastrophic disruption of an asteroid at AD 1488 released a large number of dust particles in a single event. We calculate the orbital evolution of test particles released in both cases and derive the resulting size distribution of surviving meteoroids in the current Quadrantid stream in the form of s ^−α ds, where s denotes the radius of a meteoroid. We find α = 3.1 in the extinct model and 2.0 in the split model. In addition, the radius of the surviving meteoroids is derived as s >10 μm in the both models. We propose, based on our estimation of the infrared color ratio for the Quadrantid stream derived from both models, that infrared observations of the Quadrantid stream may determine which origin model is more reasonable.     

超新星爆发的前身星模型研究

本文利用Woosley提供的4个不同的前身星模型数据作为计算的前超新星分布，并利用自己独立编制的程序和改进的状态方程进行数值模拟．对其结果进行分析比较，考察前身星对超新星的坍缩、激波传输和爆发等过程的影响．     

Models for High-Energy Radiation from Blazars

We discuss on the modelling of blazar jets as emitters of multiwavelength radiation with the implementation of a lepto-hadronic treatment. Assuming that injection of non-thermal electrons and protons can take place at the base of the jet, the stationary particle distributions can be found using an inhomogeneous one-dimensional transport equation with cooling and convection. The goal of this approach is to replace the widely used one-zone purely leptonic approximation by a more realistic model. We argue that the rapid variability observed in emission from blazars can be obtained as a result of interaction of the jet with obstacles, i.e., molecular clouds and stars. Long term variability is likely related to changes in the injection and physical conditions in the acceleration region.     

Models for planetary eclipses of the uranian satellites

A model for computing the brightness of a satellite in the shadow of a planet is described, which takes into account the Sun–planet–satellite–sensor geometry, the satellite bi-directional reflectance function, and the refraction of sunlight in the planetary atmosphere. Synthetic light curves for eclipse ingress or egress of the five large satellites of Uranus are generated. The model luminosities can be fitted to photometric observations in order to calculate a precise distance between the centers of the satellite and the planet. Alternately, when the satellite ephemeris is accurately known the atmospheric state of the planet can be studied.