红团簇巨星的光谱分析及其作为I、K波段标准烛光的研究

基于高分辨率、高信噪比光谱观测资料，确定了19颗贫金属红团簇巨星的恒星大气参数，得到样本星4种α族元素(O、Mg、Ca、Si)的化学丰度．讨论了铁丰度与恒星大气参数的相关性以及α族元素丰度随金属丰度的变化，计算了共58颗红团簇巨星在I、K波段的绝对星等，讨论了它们与恒星铁丰度之间的关系．结果表明，在分析铁丰度范围内相对于I波段，K波段的绝对星等与铁丰度的相关性更弱，并且与利用理论模型得到的红团簇巨星I、K波段绝对星等与铁丰度的关系进行了比较与验证。     

红团簇巨星元素丰度

基于高分辨率、高信噪比光谱观测资料,分析了１７颗红团簇巨星的５种α元素（Ｍｇ、Ｓｉ、Ｓ、Ｃａ、Ｔｉ）的化学丰度．结果表明,按金属丰度的不同可以将红团簇巨星分为两类：一类为富金属红团簇巨星（［Ｆｅ／Ｈ］≥０．０）;另一类为贫金属丰度红团簇巨星（［Ｆｅ／Ｈ］≤－０．３）．这两类红团簇巨星中的５种α元素均具有随金属丰度变大而增丰的趋势．同时,分析还表明,这两类红团簇巨星的α元素与铁元素的增丰历史可能是同步的．     

红团簇巨星α元素丰度

基于高分辨率、高信噪比光谱观测资料,分析了１７颗红团簇巨星的５种α元素（Ｍｇ、Ｓｉ、Ｓ、Ｃａ、Ｔｉ）的化学丰工,结果表明,按金属丰度的不同可以将红团簇巨星分为两类：一类是富金属红团簇巨星（「Ｆｅ／Ｈ」≥０．０）;另一类为贫金属丰度红团簇巨星（「Ｆｅ／Ｈ」≤－０．３）,这两类红团簇巨星中的５种α元素均具有随金属丰度变大而增丰的趋势,同时,分析还表明,这两类红团簇巨星的α元素与铁元素的增丰历史可能是同     

Fermi耀变体的辐射特性和演化研究

搜集和计算了734个Fermi耀变体样本,包括322个蝎虎天体(其中148个高峰频蝎虎天体、73个中峰频蝎虎天体以及101个低峰频蝎虎天体)和412个平谱射电类星体(其中18个高峰频平谱射电类星体、45个中峰频平谱射电类星体以及349个低峰频平谱射电类星体)。研究了每个子类的红移分布、黑洞质量分布以及γ射线光度的分布,并对其红移、黑洞质量、γ射线光度以及同步峰值频率的相关性进行了分析,结果表明:(1)根据红移与γ射线光度分别从高到低的排序,得到Fermi耀变体的演化序列遵循平谱射电类星体→蝎虎天体,且高同步峰频耀变体→中同步峰频耀变体→低同步峰频耀变体,但根据黑洞质量从高到低得到的演化序列不同,这可能是黑洞质量的估计误差以及黑洞质量样本数量较少造成的;(2)Fermi耀变体每个子类的红移与黑洞质量、黑洞质量与γ射线光度之间正相关;(3)Fermi耀变体每个子类的红移、γ射线光度分别与同步峰频之间反相关,黑洞质量与同步峰频之间不存在相关性。     

星星到底有多远（9）——速度距离

前面我们已经分别介绍了天体距离的各种光度测定方法,列举了不下10种可用于光度距离测定的标距天体（包括恒星、星团和星系）,其中有的标距天体可用于一种以上的光度测距方法。如造父变星既可利用它们的周光关系,也可用于巴德-威塞林克方法;超新星（以及新星）既可用作标准烛光,亦可利用巴德-威塞林克方法;对于星系来说,可以通过特里-菲契（TF）关系或法伯-杰克森（FJ）关系和面亮度起伏（SBF）方法来确定它们的光度距离,等等。     

富锂巨星研究概述

锂(Li)元素最初诞生于大爆炸核合成,是最重要的轻元素之一.但锂元素丰度在很多类天体中均表现出观测与理论不符的现象,这一问题困扰了天体物理学家数十年.富锂巨星就是这样的一类天体,它们大气中的Li丰度超过了标准恒星演化模型的理论值.虽然富锂巨星早在约四十年前就被发现,但其起源依然是未解之谜.随着以郭守敬望远镜(LAMOST)巡天等为代表的大型光谱巡天项目的开展、以开普勒(Kepler)卫星为代表的星震学观测数据的产出以及数据驱动类方法和技术的飞速发展,针对富锂巨星的研究取得了一系列重要的突破.在此将回顾富锂巨星近四十年来的研究进展,并总结对于富锂巨星最新的认知.     

重要测距结果一览

天体距离的多途径测定 从前面对天体距离测定一些主要方法的简要介绍,细心的读者不难看出,就某一类天体来说,可以通过不同的途径来确定它们的距离。例如,对于像仙女星系M31这样的近距离河外星系,能利用的标距天体（或标距关系）有天琴RR型变星、造父变星、新星、球状星团光度函数以及行星状星云光度函数,等等。这就为比较各种方法的测距结果,并进而为论证这些结果以及方法的可靠性提供了观测依据。     

射电选和X射线选BL Lacertae天体的射电性质

收集了射电选和X射线选BL Lac天体的射电数据(包括核和延展光度), 并计算了它们的核主导系数R.研究显示: 射电选BL Lac(RBLs)天体的总射电光度是X射线选BL Lac(XBLs)天体的2个量级.详细分析得到这种差别主要是来自于核光度的差别因为延展光度差别只有1个量级.研究RBLs和XBLs的核(延展元)光度与核主导系数之间的关系, 发现延展元光度与核主导系数负相关, 而核(总)光度几乎与核主导系数没有相关.     

星星到底有多远(1)——测定天体距离的主要途径

天体距离测定是天文学研究中最重要的基础工作之一。长期以来,天文学家为了测定遥远天体的距离,可谓是费尽心机。目前,人们已经可以通过绝对测定和相对测定两条不同的途径,确定宇宙中各类天体的几何距离、光度距离、速度距离、尺度距离以及宇宙学距离等(这些概念我们将在后文陆续介绍),并取得了很大成功。本文尝试对测定太阳系外天体距离的一些主要方法给以较为系统的介绍,择其津梁以飨读者。     

疏散星团M11的研究:4.CM图、光度函数和分层效应

利用上海天文台 40cm天体照相仪底片资料所提供的疏散星团M1 1天区 (团心距r≤2 5′)内的 785颗恒星的相对自行和成员概率 ,讨论了M1 1的CM图、年龄、距离、半径、光度函数、质量和分层效应 ,得到M1 1的距离为 1 659pc ,年龄为 (1 .8— 2 .2 )× 1 0 8年 ,半径约为 2 4 .5pc ,光度质量 4354M⊙ ,位力质量 50 0 0M⊙ ,在确定光度函数时 ,提出了一种考虑样本天区不完备的修正办法 ,以便从观测光度函数导出现时光度函数 .分析表明 ,作为一个中等年龄的疏散星团 ,M 1 1中的团星已表现出较明显的空间质量分层效应 ;而另一方面 ,尽管存在速度质量分层效应 ,但很不明显     

Spectral analysis of red clump giants and their use as standard candles in the wavebands I and K

Using high resolution and high signal-to-noise ratio observational data, we determined the stellar atmospheric parameters of 19 metal-poor red clump giants and their chemical abundances of the four α elements (i.e., O, Mg, Ca, Si). We discuss the variations, with the iron abundance, of the atmospheric parameters and of the α elements abundances. We examined the absolute stellar magnitudes of 58 red clump giants in the I and K wavebands as well as their relations with the iron abundance, and found that for the analysed range of iron abundance, the correlation with the iron abundance is weaker for the absolute magnitude in the K band than that in the I band, in agreement with theoretical expectations.     

一些M型巨星的红外观测研究

本文给出一批M型巨星JHK测光结果,在此基础上讨论了M巨星在(J—H)～(H—K)双色图上的分布特点及其有效温度及总辐射能的近似求法,并依据IRAS资料讨论了它们在中远红外双色图上的分布特征。     

Identification of red clump giants by 2MASS photometric data

The infrared J, K-photometry of the 2MASS catalog has been used to identify red clump giants as well as to determine the distances to them and the interstellar extinction. Color-magnitude diagrams plotted for ten sky regions situated mostly near the galactic plane have been analyzed. Applying the maximum likelihood technique, the parameters of distribution of a number of red clump giants over their J-K color index have been determined; on the basis of these parameters, stars of this type to K = 11 ^m have been identified. According to the reddening of identified stars, the K-band extinction in the direction of the regions under study has been estimated. The value of the extinction and its variation with galactic latitude and longitude are in agreement with the extinction calculated by the model of Arenou et al.     

Determining the Absolute Magnitudes of Galactic-Bulge Red Clump Giants in the <Emphasis Type="Italic">Z</Emphasis> and <Emphasis Type="Italic">Y</Emphasis> Filters of the Vista Sky Surveys and the <Emphasis Type="Italic">IRAC</Emphasis> Filters of the Spitzer Sky Surveys

The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric Z and Y bands of the infrared VVV (VISTA/ESO) survey and the [3.6], [4.5], [5.8], and [8.0] μm bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time: M _Z = ?0.20 ± 0.04, M _Y = ?0.470 ± 0.045, M_[3.6] = ?1.70 ± 0.03, M_[4.5] = ?1.60 ± 0.03, M_[5.8] = ?1.67 ± 0.03, and M_[8.0] = ?1.70 ± 0.03. A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, [M/H] ? 0.40 (Z ? 0.038) with an error of [M/H] ? 0.1 dex, while the effective temperature is 4250± 150 K. Stars with an age of 9–10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of ~8 Gyr can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200–8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one.     

The pulsational stability of intermediate- and low-luminosity red giants in globular clusters

Some theoretical calculations of linear non-adiabatic pulsations of intermediate- and low- luminosity red giants in globular clusters have been carried out using a time-dependent theory of nonlocal stellar convection. As shown by the results, for all models with temperatures higher than 5400 K the modes up to the fourth overtone are pulsationally stable. With the increase of stellar luminosity, the low-order overtones also become pulsationally unstable. For red giants of intermediate and low luminosities, the pulsational stability is exceedingly low and is close to neutral stability. Therefore, they will be either non-variables or short-period variables (P < 2 days) with extremely small amplitudes.     

基于SDSS-DR8及2MASS数据的疏散星团NGC 6791的基本性质研究

利用斯隆数字巡天（SDSS）第8次释放数据（DR8）的恒星光谱数据及2MASS（Two Micro All Sky Survey）近红外点源测光数据研究著名的疏散星团NGC 6791,得到该星团的视向速度与金属丰度分别为V_r=-46.4±0.2 km·s^-1和[Fe/H]=0.32±0.11dex.利用星团中红团簇巨星作为理想"标准烛光",结合2MASS近红外点源测光数据计算了该星团的绝对距离模数为（m-M）₀=13.02±0.08 mag或4.02±0.15 kpc.与其他研究者给出的结果进行了比较,金属丰度、视向速度及绝对距离模数都符合得比较好.主要结论有3点:（1）NGC 6791是个极度富金属的星团;（2）在SDSS的光谱分辨能力以内,分离出的87颗团星之间不存在明显的金属丰度差异;（3）得到的距离模数对年龄、金属丰度及尘埃消光不敏感,是一种可靠的间接测量.     

The red giant branch in the Tycho-2 catalogue

Based on multicolor photometry from the 2MASS and Tycho-2 catalogues, we have produced a sample of 38 368 branch red giants that has less than 1% of admixtures and is complete within 500 pc of the Sun. The sample includes 30 671 K giants, 7544Mgiants, 49 C giants, and 104 suspected supergiants or S stars. The photometric distances have been calculated for K, M, and C stars with an accuracy of 40%. Tycho-2 proper motions and PCRV radial velocities are used to analyze the stellar kinematics. The decrease in the stellar distribution density with distance from the Galactic equator approximated by the barometric law, contrary to the Besanconmodel of the Galaxy, and the kinematic parameters calculated using the Ogorodnikov-Milne model characterize the overwhelming majority of the selected K and M giants as disk stars with ages of more than 3 Gyr. A small number of K and M giants are extremely young or, conversely, thick-disk ones. The latter show a nonuniform distribution in the phase space of coordinates and velocities, arguing against isothermality and full relaxation of the disk and for the theory of dynamical streams or superclusters. The spatial distribution and kinematics of the selected C stars force us to consider them as asymptotic branch giants with masses of more than 2M _⊙ and ages of less than 2 Gyr probably associated with the Gould Belt. The offset of the Sun above the Galactic equator has been found from the distribution of stars to be 13 ± 2 pc, which coincides with the previously obtained value for the clump red giants.     

Giant CP Stars?

This study is part of an investigation of the possibility of using chemically peculiar (CP) stars to map local galactic structure. Correct luminosities of these stars are therefore crucial. CP stars are generally regarded as main-sequence or near-main-sequence objects. However, some CP stars have been classified as giants. A selection of stars, classified in literature as CP giants, are compared to normal stars in the same effective temperature interval and to ordinary ‘non giant’ CP stars. We find no clear confirmation of a higher luminosity for ‘CP giants’, than for CP stars in general. In addition, CP characteristics seem to be individual properties not repeated in a component star or other cluster members.     

Thick disk kinematics from data on red clump giants at the north galactic pole

The distribution of radial (U) and rotational (V) velocities of red clump giants was studied as a function of their heights above the galactic plane. The stars of this type were selected from the compiled catalogue of stellar proper motions and infrared photometry at the north galactic pole with the use of the diagram “color-reduced proper motion.” According to the data on 1800 red clump giants located at heights from 1 to 3 kpc (mostly thick disk stars), mean kinematic parameters of the thick disk were determined: U ₀ = −18 ± 2 km/s, V ₀ = −56 ± 1 km/s, σ _U = 72 ± 2 km/s, and σ _V = 58 ± 1 km/s. The velocity of asymmetric drift V ₀ and velocity variances σ _U , σ _V are shown to depend on heights above the galactic plane.     

Metal abundance and helium content of the open cluster NGC 7789: Evidence for mass loss

Interstellar reddening, the ratio [Fe/H], effective temperatures, surface gravities, and masses for twelve clump stars at the blue end of the giant branch and for seven non-clump red giant members in NGC 7789 have been determined from existingUBV andDDO photoelectric data. For the metal abundance and helium content of the clump stars we foundZ0.01 andY0.38, respectively. The masses of the red giants are found to be higher than those of the clump stars. On average, the masses of the clump stars are about half of the turnoff point mass. We conclude that the clump stars could have undergone mass loss before reaching their helium core burning phase of evolution. This conclusion arises from an analysis of the several sources entering our mass determination.