A New Code for Nonradial Stellar Pulsations and its Application to Low-Mass, Helium White Dwarfs

We present a finite difference code intended for computing linear, adiabatic, non radial pulsations of spherical stars. This code is based on a slight modification of the general Newton-Raphson technique in order to handle the relaxation of the eigenvalue(square of the eigenfrequency) of the modes and their corresponding eigenfunctions. This code has been tested computing the pulsation spectra of polytropic spheres finding a good agreement with previous work. Then, we have coupled this code to our evolutionary code and applied it to the computation of the pulsation spectrum of a low mass, pure-helium white dwarf of 0.3 M _⊙ for a wide range of effective temperatures. In making this calculation we have taken an evolutionary time step short enough such that eigenmodes corresponding to a given model are used as initial approximation to those of the next one. Specifically, we have computed periods, period spacing, eigenfunctions, weight functions, kinetic energies and variational periods for a wide range of modes. To our notice this is the first effort in studying the pulsation properties of helium white dwarfs. The solution we have found working with these realistic white dwarf models are in good accord with the predictions of the asymptotic theory of Tassoul (1980) for high order modes. This indicates that the code presented here is able to work adequately also with realistic stellar models. This revised version was published online in July 2006 with corrections to the Cover Date.     

恒星干涉仪星光方向矫正伺服系统

恒星干涉仪的关键技术之一是用自适应光学技术来调节两相干光束之间的夹角,以保证干涉条纹可见度的损失最小。在我们的恒星干涉仪实验系统中,光束方向矫正系统就是为这一目的而研制的．该系统中的光子计数系统和8098单板机的软、硬件组成了补偿光束方向随大气扰动而变的系统．文章介绍了该伺服系统以及在实验系统联调时的试验结果。     

Implementation of New OPAL Tables in Eggleton''''s Stellar Evolution Code

Based on previous works of OPAL, we construct a series of opacity tables for various metallicities Z = 0, 0.000 01, 0.000 03, 0.000 1, 0.000 3, 0.001, 0.004, 0.01, 0.02,0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton's stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for log10 (T/K) ＞ 3.95 and Alexander's for log10 (T/K) ＜ 3.95. At log10 (T/K) - 3.95, the two groups' data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev and Urpin. A comparison of 1 and 5 M⊙ models constructed with the older OPAL tables of Iglesias and Rogers shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars.     

恒星物质的不透明度

简介介绍了恒星物质的透明性质在恒星结构、演化、振动等许多恒星物理基本问题研究中的重要性和决定恒星物质不透明度的物理过程,回顾了第一代不透明度数据ＬＡＯＬ的发展历程与存在的问题,介绍了新一代不透明度数据ＯＰＡＬ的发展和目前观测与理论之间依然不一致的地方。     

星流的搜寻

在冷暗物质的宇宙学模型框架里,银河系(尤其是银晕)至少部分起源于对周围卫星星系的吸积。随着新技术和新设备的不断应用,大规模巡天项目的成功实施使天文学家获得了越来越多、越来越全面的关于银河系的数据。通过对这些数据进行分析,天文学家发现了很多星流的候选体,为银河系的等级并合理论提供了观测上的证据。随着对星流研究的扩大和深入,人们对银河系及其结构和起源的了解也越来越详细。介绍了搜寻星流的方法,以及基于这些方法获得的星流研究结果。     

天文CCD观测的星象定心算法

针对目前常见的地面光学观测系统（天望远镜和CCD系统）,提出了一种快速确写是星星象中心的算法－逐次逼近法,该算法采用逐次副近的思想,可快速准确地解定恒星星象的中心,并采取了一些措施,较好地消弱了大气湍流的影响,该算法从整个系统的角度来分析和解决问题,很适应于计算机自动处理,具有实用性强,速度快的特点,还利用VC＋＋开发一套基于Windows98平台CCD星象定中心处理的软件。     

Stark Broadening Data for Stellar Plasma Research

Results of an effort to provide to astrophysicists and physicists a set of Stark broadening parameters that is as complete as possible are presented. Such parameters are needed for stellar opacity calculations, stellar atmosphere modelling, abundance determinations, and diagnostics of various plasmas in astrophysics, physics, and plasma technology. The Stark broadening was treated using a semiclassical perturbation and modified semiempirical approaches.     

SPIN: An Inversion Code for the Photospheric Spectral Line

Inversion codes are the most useful tools to infer the physical properties of the solar atmosphere from the interpretation of Stokes profiles. In this paper, we present the details of a new Stokes Profile INversion code (SPIN) developed specifically to invert the spectro-polarimetric data of the Multi-Application Solar Telescope (MAST) at Udaipur Solar Observatory. The SPIN code has adopted Milne–Eddington approximations to solve the polarized radiative transfer equation (RTE) and for the purpose of fitting a modified Levenberg–Marquardt algorithm has been employed. We describe the details and utilization of the SPIN code to invert the spectro-polarimetric data. We also present the details of tests performed to validate the inversion code by comparing the results from the other widely used inversion codes (VFISV and SIR). The inverted results of the SPIN code after its application to Hinode/SP data have been compared with the inverted results from other inversion codes.     

Stellar population models for young stellar clusters

Stellar population models are a very useful tool to derive the stellar cluster age and luminosity mass from its integrated light. Evolutionary synthesis models depend on the stellar evolutionary tracks and the stellar libraries used to predict the spectral energy distribution of the stellar populations. In this review, I briefly comment on the new models that have incorporated the new evolutionary tracks with rotation and new computations for the evolutionary tracks of the TP-AGB. A more extended summary is also given of the current status of the most recent high-resolution stellar libraries at optical wavelengths and their implementation in evolutionary synthesis models. A comparison of the results obtained fitting the optical spectra of LMC and SMC stellar clusters with different high spectral resolution evolutionary synthesis models is also presented.     

Pulsations and long-term photometric variability of three candidates for protoplanetary nebulae

We present new photometric data and analyze long-term UBV observations of three candidates for protoplanetary nebulae—F supergiants with infrared excesses at high Galactic latitudes—IRAS 18095+2704, IRAS 19386+0155, and IRAS 19500-1709. All these stars exhibit quasi-periodic low-amplitude variations caused by pulsations against the background of long-term brightness trends. For IRAS 18095+2704=V887 Her, we have found a pulsation period of 109 days and revealed a linear brightness trend—the star brightens at constant (within the limits of the measurement errors) yearly mean color indices. The light curve of IRAS 19386+0155=V1648 Aql in 2000–2008 is represented by a wave with a fundamental period of 102 days whose modulation with a close period of 98 days leads to variations with a variable amplitude. V1648 Aql also shows a systematic rise in V brightness along with a reddening. IRAS 19500–1709=V5112 Sgr exhibits irregular pulsations with periods of 39 and 47 days. The long-term variability component of V5112 Sgr may indicate that the star is binary.     

Stellar and HI Mass Functions Predicted by a Simple Preheating Galaxy Formation Model

According to the new preheating mechanism of galaxy formation suggested by Mo et al., we construct a simple model of formation of disk galaxies within the current paradigm of galaxy formation. It incorporates preheating, gas cooling, bulge formation and star for-mation. The predicted stellar and HI mass functions of galaxies are discussed and compared with the observations. It is found that our model can roughly match both the observed galaxy luminosity function and the observed HI-mass function.     

Analytical Solution for Stellar Density in Globular Clusters

In this paper, four parameters analytical solution will be established for the stellar density function in globular clusters. The solution could be used for any arbitrary order of outward decrease of the cluster’s density.     

Hydrodynamic Model of Decaying Radial Oscillations in RU Cam

Astronomy Letters - Calculations of stellar evolution up to the early white dwarf stage were carried out for stars with mass on the main sequence $$M_{0}=0.82$$ , $$0.85$$ , $$0.9M_{\odot}$$ and...     

基于卷积神经网络的恒星光谱型和光度型的分类模型

恒星光谱分类是天文学中一个重要的研究问题.对于已经采集到的海量高维恒星光谱数据的分类,采用模式匹配方法对光谱型分类较为成功,但其缺点在于标准恒星模版之间的差异性在匹配实际观测数据中不能体现出来,尤其是当需要进行光谱型和光度型的二元分类时模版匹配法往往会失败.而采用谱线特征测量的光度型分类强烈地依赖谱线拟合的准确性.为了解决二元分类的问题,介绍了一种基于卷积神经网络的恒星光谱型和光度型分类模型(Classification model of Stellar Spectral type and Luminosity type based on Convolution Neural Network, CSSL CNN).这一模型使用卷积神经网络来提取光谱的特征,通过注意力模块学习到了重要的光谱特征,借助池化操作降低了光谱的维度并压缩了模型参数的数量,使用全连接层来学习特征并对恒星光谱进行分类.实验中使用了大天区面积多目标光纤光谱天文望远镜(Large Sky Area Multi-Object Fiber Spectroscopy Telescope, LAMOST)公开数据集Data Release 5 (DR5,用了其中71282条恒星光谱数据,每条光谱包含了3000多维的特征)对该模型的性能进行验证与评估.实验结果表明,基于卷积神经网络的模型在恒星的光谱型分类上准确率达到92.04%,而基于深度神经网络的模型(Celestial bodies Spectral Classification Model, CSC Model)只有87.54%的准确率; CSSL CNN在恒星的光谱型和光度型二元分类上准确率达到83.91%,而模式匹配方法MKCLASS仅有38.38%的准确率且效率较低.     

Stellar velocity dispersion and mass estimation for galactic disks

Available velocity dispersion estimates for the old stellar population of galactic disks at galactocentric distances r?2L (where L is the photometric radial scale length of the disk) are used to determine the threshold local surface density of disks that are stable against gravitational perturbations. The mass of the disk M_d calculated under the assumption of its marginal stability is compared with the total mass M_t and luminosity L _B of the galaxy within r=4L. We corroborate the conclusion that a substantial fraction of the mass in galaxies is probably located in their dark halos. The ratio of the radial velocity dispersion to the circular velocity increases along the sequence of galactic color indices and decreases from the early to late morphological types. For most of the galaxies with large color indices (B–V)₀>0.75, which mainly belong to the S0 type, the velocity dispersion exceeds significantly the threshold value required for the disk to be stable. The reverse situation is true for spiral galaxies: the ratios M_d/L_B for these agree well with those expected for evolving stellar systems with the observed color indices. This suggests that the disks of spiral galaxies underwent no significant dynamical heating after they reached a quasi-equilibrium stable state.     

天坛天区的近红外天体

本课题的研究目的是利用R(红)-l(近红外)两色照相测光方法,搜寻银道带天区的红外超天体,并证认IRAS点源的近红外光学对应体。本文是一组文章的第二篇。在天坛天区发现了225个红外超天体,并证认出其中27个为IRAS点源的对应体。     

Stellar wind for non-negligible gravitational potential of the atmosphere

We consider a spherically symmetric, isothermal and stationary stellar atmosphere whose gravitational potential cannot be neglected. If , the ratio of the density on the base of the corona to the mean density of the star is not zero, the density vanishes at infinity for any solution of the hydrodynamic equations. We deduce the maximum mass loss depending on two dimensionless parameters, the ratio of the gravitational to the thermal energy and . This mass loss has itself a maximum for =1/3.