基于Kepler Q1–Q17数据对类太阳型恒星的行星生成率估算

近30年来的系外行星探测揭示了行星在宇宙中普遍存在的事实.为了深入研究适宜生命居住行星的普遍性,一方面需要了解宜居行星的特性;另一方面可以通过分析已发现系外行星的分布特征,推算该类行星在恒星周围的存在几率.在目前已发现的系外行星中,凌星法发现的占据了绝大多数,如Kepler空间望远镜所观测的系外行星共有2344颗. 2018年Kepler正式退役,其科学团队发布了最终版的Kepler Data Release (DR25),包含观测季度Q1–Q17的恒星共198709颗.通过对Kepler数据的分析,使用逆检测效率法和最大似然分析法两种不同的方法对系外行星半径周期参数空间内的行星生成率进行了估算,同时将计算样本根据恒星的光谱类型进行分类,分别估算得到了F、G、K型的Kepler恒星周围的行星生成率及其整体的生成率.对于半径范围1–20 R_⊕(R_⊕为一个地球半径),轨道周期范围0.4–400 d的Kepler凌星系外行星,宿主恒星为F型时逆检测效率法和最大似然法估算得到的行星生成率分别为0.36±0.02和0.47±0.02,宿主恒星为G型时的...     

SAGE巡天介绍Ⅰ——测光系统和数据处理

SAGE(Stellar Abundance and Galactic Evolution)巡天采用一套对恒星大气参数敏感的独特测光系统,包括uSC,vSAGE,g,r,i,Hα_n,Hα_w和λ_(DDO51)(David Dunlap Observatory,DDO)共8个波段。该系统对恒星大气参数(有效温度T_(eff)、表面重力lg g和金属丰度[Fe/H])和星际消光的测量比传统的uvbyβ系统(Str?mgren-Crawford,SC)更敏感。由于g,r,i波段带宽较宽,因而观测效率较高,对恒星大气参数的测量精度和观测效率均超过uvbyβ系统和宽带测光系统。利用美国亚利桑那大学Steward天文台2.3 m Bok望远镜、新疆天文台南山1 m望远镜和乌兹别克斯坦MAO(Maidanak Astronomical Observatory)1 m望远镜已展开巡天观测。项目计划在约4年时间内完成所有的巡天观测,北天天区覆盖面积约12000(~?)~2,高精度测光(信噪比为100σ)深度约15 mag(V波段);5σ探测极限可深至约20 mag(V波段)。最终将探测约5×108颗恒星,并得出其恒星大气参数以及星际消光。该样本比之前的u,v,b,y,β测光巡天,如GCS(Geneva-Copenhagen Survey)巡天和HM(Hauck and Mermilliod 1998)巡天,扩展到更深的区域,即深度达到7～8 mag(V波段)。利用观测得到的大样本恒星测光星表,可以开展如下课题的研究:(1)得到银河系约5×10~8颗恒星大样本的金属丰度分布,并根据恒星演化模型得到其年龄分布;(2)预期搜寻到一批贫金属星候选体,并利用其他望远镜进行下一步观测;(3)结合高质量的uSC波段数据,预期可以找到一批白矮星;(4)结合其他星表,预期找到一批长周期变源以及移动天体;(5)结合uSC波段数据和其他星表,预期可以找到一批类星体。     

基于CSST多色测光的时序测光精度分析

中国巡天空间望远镜(Chinese Survey Space Telescope, CSST)是中国的首个大型空间光学望远镜, 将对包括系外行星探测在内的诸多科学目标开展研究, 有望取得前沿科学进展. 时序测光精度是CSST重要的性能指标, 受到物理噪声和仪器噪声的影响, 需要通过数值模拟对其分析和评估. 模拟基于目前公布的CSST主要技术参数, 建立了时序的恒星信号和噪声模型, 以CSST的i波段为例, 分析凝视观测模式下的测光精度. 通过数值仿真, 展示了孔径测光中各项噪声的贡献, 特别是由指向抖动和像素响应不均匀性导致的抖动噪声. 模拟结果还给出了测光孔径的推荐范围. 为了获得更高的信噪比, 可以减小仪器抖动振幅和像素不均匀性, 或者采用参考星较差测光的方式. 结果为CSST后续的时序测光精度与不同指标参数的相关性分析、系外行星探测能力评估以及测光数据处理提供了模拟数据的支撑.     

Aquila Rift区域年轻星候选体的搜寻

使用德国Th(u|¨)ringer Landessternwarte Tautenburg(TLS)的2 m望远镜对Aquila Rift的16个区域进行了Hα、R和I共3个波段的成像观测.这些观测区域大约覆盖了Aquila Rift 7平方度的天区.除去3个数据质量不高的天区,对其余的13个区域进行了测光分析,从中证认出点源,并利用双色图的方法最终证认出7颗Hα发射线星候选体.这7个候选体是从5个观测区域中选出的,其中3颗位于银道面区域,4颗位于银纬高于4°的区域.对于这5个天区,证认了其中点源的2MASS对应体,并利用双色图的方法进一步分析了7个Hα发射线星候选体的性质.这些Hα发射线星候选体的近红外辐射并没有明显的红外超现象,有一颗还落在了主序分支上.这也说明有Hα发射的年轻星并不都伴随有红外超现象.Hα发射线观测和红外超观测的结果是相互补充的.如果将这7颗Hα发射线星候选体作为年轻星候选体,则Aquila Rift区域的年轻星数目是较少的.对于这些候选体的进一步证认还需要后续的光谱观测.     

STEP天体测量误差源分析

系外类地行星空间探测计划(Search for Terrestrial Exo-Planets,以下简称"STEP")采用天体测量法和微像素级焦平面定标测量技术,设计望远镜焦平面检测精度达到1μas.在假定焦平面设计能达到检测精度的前提条件下,系统分析了恒星自行、视差、卫星速度和位置、光学系统的光心等关键因素对检测系外行星的影响.有别于传统的窄视场照相底片常数法,提出了一种恒星相对角距测量方法,以检测由于可能存在的系外行星而引起星对角距变化的非线性项,消除了传统窄视场天体测量中参考星位置和自行精度对检测系外行星的直接影响.针对同一天区内的8颗参考星和1颗具有行星系统的待测星,分别模拟出5 yr内的观测数据,利用最小二乘法进行处理,发现基于STEP自身1μas的观测精度,在这种情况下是可以观测到类地行星的.     

弱发射线T Tauri型星的高色散光谱观测

应用国家天文台兴隆观测基地2.16 m望远镜及其高色散光谱仪,对6颗弱发射线T Tauri型星(Weak-line T Tauri Stars,简称WTTS)进行了高色散光谱观测,计算了这些弱发射线T Tauri型星的锂元素丰度,讨论了这些弱发射线TTauri型星锂丰度和恒星自转周期、光变幅度的关系,研究发现:自转较快的弱发射线T Tauri型星锂丰度小于自转较慢的弱发射线T Tauri型星锂丰度;但是这些弱发射线TTauri型星,其锂丰度与恒星在V波段的光变幅度并没有明显的相关性.     

DBSCAN聚类算法在Gaia-DR2中检测疏散星团的研究

基于Gaia Data Release 2 (Gaia-DR2)星表,采用数据挖掘技术中的DBSCAN(Density-Based Spatial Clustering of Applications with Noise)算法进行邻近疏散星团成员检测.从Gaia-DR2中选取了594284颗恒星(距离太阳100 pc)作为样本,使用恒星的五维数据(三维空间位置和两维自行)进行聚类分析.在数据预处理阶段,将每一维数据标准化到[0, 1]区间内,避免了单位不一致对聚类效果的影响.然后,利用k-dist图确定了DBSCAN算法的输入参数(Eps, MinPts).最终,使用DBSCAN算法获取了133颗成员星,它们在五维相空间中可以被分成两组,分别对应于疏散星团Hyades和Coma.分析结果表明得到的成员星是可靠的.根据两个星团的成员星, Hyades和Coma的距离分别确定为(46.5±0.3) pc和(84.9±0.4) pc.     

主序星的Ⅴ波段经验质光关系

恒星质量是恒星物理以及恒星系统动力学研究中一个不可或缺的参量.双星轨道拟合是获取恒星(动力学)质量的最可靠途径,而绝大部分恒星的质量仍然需要通过恒星质光关系来估计,因此,通过拟合恒星动力学质量和光度数据得到经验质光关系的工作具有重要意义.尽管主序星的Ⅴ波段质光关系由于金属丰度的影响而具有一定的弥散性,但有研究表明这种影响主要限于恒星质量小于 0.6M_⊙的情况.对于较大质量的主序星,近年来的观测拟合研究积累了比较充分的动力学质量和Ⅴ波段光度数据,从而为显著改进上述质光关系提供了可能.利用一个能合理分配两个不同量纲观测量权重的拟合方法,根据 203 颗恒星的动力学质量和光度数据给出了主序星的Ⅴ波段经验质光关系,该结果对此前结果的改进不仅具有统计显著性,而且其对恒星质量估计的相对误差已达到约 5%.因此,该结果不仅可以用于开展有关恒星物理或恒星系统动力学方面的统计性研究,而且对具体实际多星系统的长期动力学研究和短期定位研究等也有应用价值.     

相互逼近技术用于小行星702(Alauda)的高精度位置测量试验

将相互逼近(Mutual Approximation)技术从天然卫星的天体位置测量拓展到小行星和邻近盖亚(Gaia)星表参考星的相对位置测量,希望获得更高的小行星位置测量精度.使用中国科学院云南天文台1 m光学望远镜在2020年11月11～12日对小行星702(Alauda)进行了观测试验.在观测资料中,目标小行星共有...     

基于郭守敬望远镜(LAMOST)试观测数据新发现的贫金属星候选体

贫金属星因其内在蕴涵着银河系早期化学元素形成和演化等信息,所以他们对银河系及宇宙早期形成历史的研究具有重要意义。目前对贫金属星的搜寻与研究已成为天文学的一大国际研究热点。随着郭守敬望远镜(LAMOST)试运行的开展及数据的积累,我国已具备自主开展此领域研究工作的有力观测设备及数据资源。通过采用有效的的测量方法,对郭守敬望远镜试观期获得的低分辨率(R≈2 000)恒星光谱数据进行恒星大气物理参数测量,新发现了8颗[Fe/H]-1.00 dex的贫金属星候选体,其中1颗[Fe/H]=-2.73dex属于很贫的贫金属星(VMP)。工作首次显示并证明了郭守敬望远镜能够有效地开展银河系内搜寻大量贫金属星的工作。     

Multi-star System Observations Based on the Direct-imaging Method

The direct-imaging exploration can obtain comprehensive physical information of exoplanets, which is a key technology to search for extraterrestrial life in the future. In this paper, based on our recent high-contrast imaging data of ground-based telescope, the newly discovered multi-star candidates are presented. In the early stage, combined with the ability of high-contrast imaging equipment for the exoplanets in the ground-based system, we select about 1000 targets from published works which are compiled using the catalogs released by Gaia. These targets are distributed in different young star clusters. Recently, we used Hale Telescope at Palomar Observatory to carry out high-contrast imaging observation on 42 of the above targets in the K-band. Most of the observed targets are 7.5–14 in the V-band. In 2019, after two rounds of observation, we discover six multi-star system candidates. It is however difficult to find out whether these targets are single-star or multi-star systems in Gaia DR2 (Data Release 2) catalog and Gaia EDR3 (early Data Release 3) catalog.     

DBSCAN Clustering Algorithm for the Detection of Nearby Open Clusters Based on Gaia-DR2two

In this paper, we attempt to use the DBSCAN (Density-Based Spatial Clustering of Applications with Noise) clustering algorithm to detect nearby open clusters based on the Gaia Data Release 2 (Gaia-DR2). We select 594284 stars (within a distance of 100 pc to the Sun) from the Gaia-DR2 catalog, and construct a five-dimensional phase space (three-dimensional spatial position and two-dimensional proper motion) in order to obtain reliable cluster members. At the data preprocessing stage, we normalize each dimension of data to the [0, 1] interval in order to avoid the effect of inconsistent units. Then, we use the k-dist graphs to determine the input parameters of the DBSCAN Algorithm. Finally, we obtain 133 reliable members using the DBSCAN algorithm, which correspond to two open clusters—Hyades and Coma. According to these cluster members, the distances to the Hyades and Coma clusters are determined to be (6.5 ± 0.3) pc and (4.9 ± 0.4) pc, respectively.     

A catalog of DB white dwarfs from the LAMOST DR5 and construction of templates

In this study, we employ machine learning to build a catalog of DB white dwarfs(DBWDs) from the LAMOST Data Release(DR) 5. Using known DBs from SDSS DR14, we selected samples of highquality DB spectra from the LAMOST database and applied them to train the machine learning process.Following the recognition procedure, we chose 351 DB spectra of 287 objects, 53 of which were new identifications. We then utilized all the DBWD spectra from both SDSS DR14 and LAMOST DR5 to construct DB templates for LAMOST 1 D pipeline reductions. Finally, by applying DB parameter models provided by D. Koester and the distance from Gaia DR2, we calculated the effective temperatures, surface gravities and distributions of the 3 D locations and velocities of all DBWDs.     

Heiles星光偏振源表的距离更正

星光偏振是研究星际介质磁场的有力工具之一.Heiles源表收集了9286颗恒星的偏振信息,是目前最大的光学波段星光偏振源表,被广泛使用.但该表中恒星的距离参数是以前的测光距离,很不确定.把Heiles源表和Gaia第2次数据释放(DR2)源表进行交叉证认,以位置和星等作为判据,匹配了7613颗恒星,并获得了这些恒星的三角视差距离和误差,超过90%的恒星距离相对误差小于20%.基于新的距离,展示了星光偏振在银河系内的分布并讨论了可能的应用.     

A Revisit to the Optical Starlight Polarization Catalogue by Heiles: Distance Update

Starlight polarization serves one of the powerful tools to study magnetic fields in the Galactic interstellar medium. Heiles catalogue contains polarization information for 9286 stars, and is by far the biggest. This catalogue has been extensively used to study the magnetic fields. However, the distance parameters of the stars in this catalogue are from photometric observations, and very uncertain. We cross match Heiles catalogue with Gaia Data Release 2 (DR2), and identify 7613 stars using both angular separation and magnitude as constraints. We then obtain precise distances from Gaia DR2 for these stars. For more than 90% of the stars, the relative errors of the new distances are within 20%. Based on the new catalogue, we demonstrate how starlight polarization can probe Galactic magnetic fields.     

NGC 3603星团中的大质量逃逸双星

非团环境中的大质量恒星以及大质量双星的起源是理解大质量恒星形成和演化的关键问题之一. 年轻大质量星团内的动力学交会过程是产生大质量逃逸星的重要途径之一. 选取了银河系内年轻大质量星团NGC 3603外围的两个碰撞星风系统候选体MTT68A和MTT71作为研究对象, 通过分析\emphChandra X射线观测以及\emphGaia第2批数据发布(DR2)中的天体测量结果, 研究它们作为相互作用的大质量双星系统的起源. X射线数据的分析表明, 它们的X射线能谱中存在Fe XXV发射线成分; 相较于普通O型星, 以双温等离子体模型拟合得到偏高的高温成分温度($\gtrsim$2.0keV), 并且X射线光度与热光度的比值也较高($\gtrsim10^{-5.8     

Three new late-type hypervelocity star candidates from Gaia DR2 with refined selection criteria

Several dozen hypervelocity star(HVS) candidates have been reported based on the second data release of Gaia(Gaia DR2). However, it has been proven that the radial velocities of some Gaia HVS candidates are not reliable. In this paper, we employ refined astrometric criteria to re-examine Gaia DR2,arriving at a more reliable sample of HVS and high velocity star candidates than those found by previous authors. We develop a method called Binary Escape Probability Analysis to identify some HVS candidates.This method allows us to work with stars having only two epochs of measured radial velocity. These stars were usually discarded in previous similar studies. A scrutiny of our final results sheds light on selection effects present in our studies, which we propose to be the focus of future studies. In total, we find three late-type(2 G-type and 1 K-type) HVS and 21 high velocity star candidates, 3 and 11 of which are new,respectively. Judging by their historical trajectories, which we calculate, all three HVS candidates could not have had Galactic center origins. Further monitoring is required to confirm their status.     

The Pleiades apex and its kinematical structure

A study of cluster characteristics and internal kinematical structure of the middle-aged Pleiades open star cluster is presented. The individual star apexes and various cluster kinematical parameters including the velocity ellipsoid parameters are determined using both Hipparcos and Gaia data. Modern astrometric parameters were taken from the Gaia Data Release 1 (DR1) in combination with the Radial Velocity Experiment Fifth Data Release (DR5). The necessary set of parameters including parallaxes, proper motions and radial velocities are used for \(n=17\) stars from Gaia DR1+RAVE DR5 and for \(n=19\) stars from the Hipparcos catalog using SIMBAD data base. Single stars are used to improve accuracy by eliminating orbital movements. RAVE DR5 measurements were taken only for the stars with the radial velocity errors not exceeding \(2~\mbox{km}/\mbox{s}\). For the Pleiades stars taken from Gaia, we found mean heliocentric distance as \(136.8 \pm 6.4\) pc, and the apex position is calculated as: \(A_{CP}=92^{\circ }.52\pm 1^{\circ }.72\), \(D_{CP}=-42^{\circ }.28\pm 2^{\circ }.56\) by the convergent point method and \(A_{0}=95^{\circ }.59\pm 2^{\circ }.30\) and \(D_{0}=-50^{\circ }.90\pm 2^{\circ }.04\) using AD-diagram method (\(n=17\) in both cases). The results are compared with those obtained historically before the Gaia mission era.     

Generation of an optimal target list for the exoplanet characterisation observatory (EChO)

The Exoplanet Characterisation Observatory (EChO) has been studied as a space mission concept by the European Space Agency in the context of the M3 selection process. Through direct measurement of the atmospheric chemical composition of hundreds of exoplanets, EChO would address fundamental questions such as: What are exoplanets made of? How do planets form and evolve? What is the origin of exoplanet diversity? More specifically, EChO is a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planetary sample within its four to six year mission lifetime. In this paper we use the end-to-end instrument simulator EChOSim to model the currently discovered targets, to gauge which targets are observable and assess the EChO performances obtainable for each observing tier and time. We show that EChO would be capable of observing over 170 relativity diverse planets if it were launched today, and the wealth of optimal targets for EChO expected to be discovered in the next 10 years by space and ground-based facilities is simply overwhelming. In addition, we build on previous molecular detectability studies to show what molecules and abundances will be detectable by EChO for a selection of real targets with various molecular compositions and abundances. EChO’s unique contribution to exoplanetary science will be in identifying the main constituents of hundreds of exoplanets in various mass/temperature regimes, meaning that we will be looking no longer at individual cases but at populations. Such a universal view is critical if we truly want to understand the processes of planet formation and evolution in various environments. In this paper we present a selection of key results. The full results are available in Online Resource 1.     

第二代天体测量卫星及后依巴谷地面天体测量的进展

简述了后依巴谷的天体测量工作。首先给出了第二个天体测量卫星Gaia的最新进展、最近提出的JAMSE和OBSS计划的简介,以及包含天体测量内容的SIM PlanetQuest计划的情况; 叙述了多波段天体参考架的建立和维持,特别是依巴谷星表向暗星方向的扩充和数字巡天,以及其他地面观测计划,如双星和聚星、太阳系天体的观测等;介绍了天体测量与天体物理结合的几个研究课题的进展;最后对我国自然科学基金会“十一五”天体测量优先发展的方向与内容提出建议。