类太阳活动恒星表面黑子结构的多普勒成像(Ⅰ)：技术

回顾了恒星表面结构多普勒成像研究工作的发展历史,重点评述了该项技术在类太阳活动恒星研究领域的应用。介绍了该项技术在国际上的发展现状,给出了恒星表面黑子结构形态的多普勒成像技术的基本原理,讨论了该项技术对观测仪器、观测过程和观测对象的要求,并对未来这一领域的研究工作进行了展望。     

渐近巨星分支(AGB)长周期变星研究进展

AGB长周期变星是中小质量恒星演化到晚期时形成的，由于它们存在强烈的振动和巨大的星风物质损失，研究这类变星对于了解恒星振动性质、星风产生机制及恒星晚期演化都有十分重要的意义。本文比较广泛地考查了最近十几年来国际上对于AGB长周期变星观测和理论研究工作的现状，讨论了AGB长周期变星的主要观测性质以及恒星振动和演化理论工作中所取得的进展，同时也分析了目前研究工作中存在的一些问题和困难，指出今后研究工作中需要逐步加以解决的一些问题。     

渐近巨星分支长周期变星研究进展

ＡＧＢ长周期变星是中小质量恒星演化到晚期时形成的，由于它们存在强烈的振动和巨大的星风物质损失，研究这类变星对于了解恒星振动性质，星风产生机制及恒星晚期演化都有十分重要的意义，本文比较广泛地考查了最近十几年来国际上对于ＡＧＢ长周期变星观测和理论研究工作的现状，讨论了ＡＧＢ长周期变星的主要观测性质以及恒星振动和演化理论工作中所取得的进展，同时也分析了目前研究工作中存在的一些问题和困难，指出今后研究工作     

恒星黑子的观测

本文对恒星黑子的观测方法和结果作了综合评述。介绍了恒星黑子温度的多色测光测定方法；黑子大小，温度和分布情况的测光畸变波黑子模型解，和高信噪比谱线轮廓多普勒成像方法；以及黑子寿命观测统计方法等的基本原理和研究进展。对已取得的有关恒星黑子的观测分析结果作了概括，与太阳典型黑子情况作了对比，并对恒星黑子的巨黑子，极区黑子以及长寿命黑子特殊性作了讨论，对需要进一步观测研究的问题作了总结。     

基于直接成像法的多星系统观测

系外行星直接成像探测能够获取系外行星更全面的物理信息,是未来搜寻系外生命的关键技术之一.针对近期地基望远镜高对比度成像观测数据,对新发现的多星候选体进行系统展示.前期,结合地基系外行星高对比度成像设备观测能力,从已发表文献整理的Gaia星表恒星数据中筛选,得到约1000个观测目标.这些目标分布于不同的年轻星团中.近期,使用Palomar天文台Hale望远镜对上述观测目标中的42个目标在K波段开展了高对比度成像观测.这些目标恒星在可见光波段为7.5-14.2019年经过两轮观测,发现了6个多星系统候选体,这些目标在Gaia Data Release 2星表和Gaia early Data Release 3星表中难以确认是单星还是多星系统.     

天体运动的轨道偏心率研究概述---从恒星系统到行星系统

偏心率是描述天体运动轨道的重要参数之一, 能够为揭示天体的动力学演化提供重要线索, 进而帮助理解天体形成与演化的过程及背后的物理机制. 随着天文观测技术的不断发展, 人们对于天体运动轨道的研究已经走出太阳系, 包含的系统也从大质量端的恒星系统延伸到了低质量端的行星系统. 聚焦天体轨道偏心率研究, 回顾了目前在恒星系统(包括主序恒星、褐矮星以及致密星)和行星系统(包括太阳系外巨行星以及``超级地球''、``亚海王星''等小质量系外行星)方面取得的进展, 总结了不同尺度结构下偏心率研究的一些共同之处和待解决的问题. 并结合当下和未来的相关天文观测设备和项目, 对未来天体轨道偏心率方面的研究工作进行了展望.     

年轻星天体喷流的近红外成像观测进展

分子氢的红外振动发射线是显现年轻星质量外流的重要谱线之一。自Gautier等人1976年在猎户座发现年轻星质量外流的分子氢发射开始,人们在银河系内几乎所有的恒星形成区都发现了这种线发射。研究表明,分子氢发射与年轻星周围的其它活动现象（如分子外流和光学喷流）之间有着非常密切的联系。红外和光学喷流代表了年轻星剧烈活动的两个侧面,是喷流与周围介质相互作用强弱不同的表现,这种作用还拖带周围介质,产生分子外流,光学、红外喷流和分子外流组成了恒星形成区壮观的景象,它们是恒星形成活动的重要标志。随着红外探测技术的飞速发展,对年轻星外流活动现象的观测越来越丰富的详细,使人们对这种现象的本质越来越了解。在20世纪90年代NICMOS等大阵列红外探测器投入使用后,红外成像观测有了长足的进步。目前已在70个左右的区域里发现了H2发射,这一数字还在迅速增加,今后的研究主要可能向两个方向发展。其一是高分辨观测,进一步了解H2发射的结构以及与光学喷流和分子外流之间的关系;其二是天观测,了解银河系内的恒星形成H2区发射的大尺度结构和恒星形成的统计分布规律。     

幸运成像技术在天文观测中的应用

由于大气湍流的影响,传统地基望远镜难以获得高空间分辨率的图像。天文学家为了在天文成像、测光观测、天体测量等领域的研究中得到更好的结果,不断追求克服地球大气的影响,获得更高空间分辨率的方法。幸运成像技术是一种能够使地面望远镜获得接近其衍射极限分辨能力的技术方案,具有成本低、设备简单的优点。介绍了幸运成像技术的发展趋势和基本原理,总结了国际上目前在用的幸运成像系统及其设备参数。结合幸运成像技术在国际上成功应用实例,综述了含系外行星多恒星系统的观测研究、双星系统轨道测量、球状星团中变星搜寻等天文观测获得的大量研究成果。随着新数据处理方法的应用,近年来蓬勃发展的幸运成像与自适应光学复合技术,将进一步拓展幸运成像技术的应用前景。     

中等质量恒星在赫罗图中由E-AGB星进入TP-AGB星的分界点

通过对3～10 M_☉恒星在赫罗图上演化轨迹的研究,分析恒星内部氦壳层燃烧峰值处能量、密度、温度、氦壳层表面光度与恒星表面光度比及恒星半径的变化,给出了中等质量恒星由早期AGB星演化至热脉冲AGB星阶段在赫罗图上的分界点,与119颗碳星的观测结果吻合得相当好.同时提出:在恒星演化至该分界点之后,其星风物质损失公式可能需要引入一个与表面光度无关的量以主导超星风的形成.在此基础上,通过对考虑湍流压效应下5 M_☉恒星的结构和演化及星风物质损失率的分析,发现湍流压在热脉冲AGB星阶段对星风物质损失影响较大,从而使得热脉冲AGB星的湍流压不可忽略,进而提出了影响热脉冲AGB星星风物质损失的可能的物理因素.     

转动恒星结构与演化研究

恒星的自转 ,是恒星结构和演化理论的难点。近年来有许多观测事实 ,特别是早型大质量星的观测事实 ,预示恒星的自转效应可能引起恒星内部的物质向外转移 ,造成恒星表面一些元素丰度超丰 ,并且对恒星结构和演化产生重要影响 ,因此 ,恒星的自转问题受到了越来越多的关注。考虑自转效应后 ,恒星结构和演化模型将是二维模型 ,本文综述了诸多作者如何将二维的恒星结构和演化模型简化为一维模型。作者在研究了以上作者的简化方法后 ,提出了一种比较简单的新方法。这种方法基于如下假设 :假设在等势面上的温度 ,密度 ,压强 ,光度 ,化学组成和角速度等物理和化学量近似于均匀分布 ,并且这些量与等价球面上的量相同。 (等价球面是假想的球面 ,它包围的体积与等势面包围的体积相等。)我们在等价球面上推出新的转动恒星结构和演化方程 ,构造出新的演化模型。这个模型与不考虑转动效应的演化模型相比 ,有以下变化 :流体静力学平衡方程变化 ;辐射温度梯度变化 ,并引起对流判据变化 ;星风物质损失和角动量损失增大。作为转动恒星结构和演化模型的应用 ,我们研究了中 ,小质量星中心氦燃烧阶段在赫罗图中的演化轨迹发生来回摆动 (又称为蓝回绕 )的物理机制问题。有诸多作者曾经研究了可以影响蓝回绕的各种因素。但是不知     

Tomography of stellar non‐radial pulsations

The stellar surface imaging technique is used for studying stellar non‐radial pulsations on the basis of inversions of time series of variable line profiles without making assumptions on the specific shape of the pulsations. The inversion results in an image of the stellar surface in which sectoral and tesseral modes can be distinguished in many cases and the pulsational degree and the azimuthal order can be determined. The capability of the technique is studied with simulated data. Then, the surface imaging technique is applied to high‐resolution spectra of the rapidly rotating Beta Cep‐type star ω¹ Sco, which shows strong line‐profile variations. Stellar surface imaging is concluded to be a useful technique for pulsation‐mode identification. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Imaging the cool stars in the interacting binaries AE Aqr,BV Cen and V426 Oph

It is well known that magnetic activity in late‐type stars increases with increasing rotation rate. Using inversion techniques akin to medical imaging, the rotationally broadened profiles from such stars can be used to reconstruct ‘Doppler images’ of the distribution of cool, dark starspots on their stellar surfaces. Interacting binaries, however, contain some of the most rapidly rotating late‐type stars known and thus provide important tests of stellar dynamo models. Furthermore, magnetic activity is thought to play a key role in their evolution, behaviour and accretion dynamics. Despite this, we know comparatively little about the magnetic activity and its influence on such binaries. In this review we summarise the concepts behind indirect imaging of these systems, and present movies of the starspot distributions on the cool stars in some interacting binaries. We conclude with a look at the future opportunities that such studies may provide. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Anti-solar differential rotation and surface flow pattern on UZ Libræ

We re-investigate UZ Libræ spectra obtained at KPNO in 1998 and 2000. From the 1998 data we compose 11 consecutive Doppler images using the Ca I-6439, Fe I-6393 and Fe I-6411 lines. Applying the method of average cross-correlation of contiguous Doppler images we find anti-solar differential rotation with a surface shear of α ≈ –0.03. The pilot application of the local correlation tracking technique for the same data qualitatively confirms this result and indicates complex flow pattern on the stellar surface. From the cross-correlation of the two available Doppler images in 2000 we also get anti-solar differential rotation but with a much weaker shear of α ≈ –0.004. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hubble Space Telescope observations of SV Cam – I. The importance of unresolved star-spot distributions in light-curve fitting

We have used maximum entropy eclipse-mapping to recover images of the visual surface brightness distribution of the primary component of the RS CVn eclipsing binary SV Cam, using high-precision photometry data obtained during three primary eclipses with Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope ( HST ). These were augmented by contemporaneous ground-based photometry secured around the rest of the orbit. The goal of these observations was to determine the filling factor and size distribution of star-spots too small to be resolved by Doppler imaging. The information content of the final image and the fit to the data were optimized with respect to various system parameters using the χ² landscape method, using an eclipse-mapping code that solves for large-scale spot coverage. It is only with the unprecedented photometric precision of the HST data (0.000 15 mag) that it is possible to see strong discontinuities at the four contact points in the residuals of the fit to the light curve. These features can only be removed from the residual light curve by the reduction of the photospheric temperature, to synthesize high unresolvable spot coverage, and the inclusion of a polar spot. We show that this spottedness of the stellar surface can have a significant impact on the determination of the stellar binary parameters and the fit to the light curve by reducing the secondary radius from  0.794 ± 0.009  to  0.727 ± 0.009 R_⊙  . This new technique can also be applied to other binary systems with high-precision spectrophotometric observations.     

The star formation histories of low surface brightness galaxies

We have performed deep imaging of a diverse sample of 26 low surface brightness galaxies (LSBGs) in the optical and the near-infrared. Using stellar population synthesis models, we find that it is possible to place constraints on the ratio of young to old stars (which we parametrize in terms of the average age of the galaxy), as well as the metallicity of the galaxy, using optical and near-infrared colours. LSBGs have a wide range of morphologies and stellar populations, ranging from older, high-metallicity earlier types to much younger and lower-metallicity late-type galaxies. Despite this wide range of star formation histories, we find that colour gradients are common in LSBGs. These are most naturally interpreted as gradients in mean stellar age, with the outer regions of LSBGs having lower ages than their inner regions. In an attempt to understand what drives the differences in LSBG stellar populations, we compare LSBG average ages and metallicities with their physical parameters. Strong correlations are seen between an LSBG's star formation history and its K -band surface brightness, K -band absolute magnitude and gas fraction. These correlations are consistent with a scenario in which the star formation history of an LSBG primarily correlates with its surface density and its metallicity correlates with both its mass and its surface density.     

The chromospherically active binary star EI Eridani: I. Absolute dimensions

We present a detailed determination of the astrophysical parameters of the chromospherically active binary star EI Eridani. Our new radial velocities allow to improve the set of orbital elements and reveal long‐term variations of the barycentric velocity. A possible third‐body orbit with a period of ≈19 years is presented. Absolute parameters are determined in combination with the Hipparcos parallax. EI Eri's inclination angle of the rotational axis is confined to 56°.0 ± 4°.5, ist luminosity class IV is confirmed by its radius of 2.37 ± 0.12 R_⊙. A comparison to theoretical stellar evolutionary tracks suggests a mass of 1.09 ± 0.05 M_⊙ and an age of ≈ 6.15 Gyr. The present investigation is the basis of our long‐term Doppler imaging study of its stellar surface (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

恒星内部的贯穿对流(英文)

贯穿对流是恒星演化理论长期未获很好解决的理论问题。尽管它已有近五十年的研究历史 ,但至今人们对贯穿对流仍存在很多的错误的理解。究其原因是因为人们对贯穿对流的理解依然停留在唯象的混合长理论图象上。根据一种非局部对流理论 ,我们揭示了贯穿对流区的结构。在太阳下部的贯穿对流区 ,温度梯度是亚绝热的 ,但是是超辐射的。本文还对恒星对流理论给出了一个简短的评述。     

Can variable meridional flows lead to false exoplanet detections?

The search for habitable exoplanets centers on planets with Earth-like conditions around late type stars. Radial velocity searches for these planets require precisions of 1 m/s and better. That is now being achieved. At these precisions stellar surface motions might lead to false detections. Of particular interest are variable meridional flows on stellar surfaces. I review the available observations of solar surface meridional flows using both Doppler shift and local helioseismology techniques. Interpretation in terms of Doppler shifts in integrated starlight leads to estimates of the likelihood of false detections. It is unlikely that these false detections occur in the habitability zones of exoplanets. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)