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1.
基于对9颗类太阳色球活动恒星高信噪比的高色散光谱观测, 测量了这些恒星锂线(入 = 6707.8 A'')的等值宽度, 计算了这些恒星表层锂元素丰度. 通过研究这些类太阳色球活动恒星锂丰度和X射线光度之间的关系, 发现X射线光度 强的类太阳色球活动恒星锂丰度值大于X射线较弱的恒星. 也就是说活动性较强的类太阳色球活动恒星其锂丰度较高, 活动性较弱的类太阳色球活动恒星其锂丰度较低. 考虑到主序的类太阳恒星锂元素和恒星自转速度随着恒星年龄的增加逐渐减少, 以及随着类太阳色球活动恒星自转速度的减小, 色球活动又逐渐变弱. 因此类似于锂丰度, 类太阳色球活动恒星自转速度的大小和恒星的 活动水平也同样可以表明恒星的年龄. 相似文献
2.
假定太阳是一颗普通的恒星，对太阳磁场的高分辨率观测，则从内禀磁场强度，尺度谱，面积填充因子，成穴分布趋势，双极分布特征和演化时标等多方面，为类太阳恒星磁场测量提供了一个基本标度，本文综述了与恒星磁场测量有关的，太阳磁场若干观测特征，与类太阳恒星测量结果对比表明，类太阳恒星磁场的内禀强度与太阳磁场接近，但面积填充因子大１－２个数量级，这可能真实地反映了恒星磁场的内禀强度成太阳磁场接近，但面积填充因子 相似文献
3.
李宏为 《中国天文和天体物理学报》1989,(3)
本文提出具幂津谱分布的非热电子在多重偶极子磁场中产生回旋同步辐射是晚型恒星宁静微波辐射的一个可能机制。文中假设有10—20个磁偶极子随机地分布在恒星光球之下,非热电子与背景热电子数密度之比<10~(-3),并且在非热电子分布中引入了与其寿命有联系的因子。由此计算并分析了回旋同步辐射谱和偏振性质,并获得了辐射源的空间分布特性。 相似文献
4.
王菲鹿 《紫金山天文台台刊》2003,(2)
使用不同的恒星辐射不透明度数值 ,对 5至 9个太阳质量恒星的演化模型进行计算 ,来研究辐射不透明度对赫罗图中蓝回绕的影响。结果表明在赫罗图中 ,使用OPAL不透明度值的恒星演化迹中存在着蓝回绕。而且 ,随着辐射不透明度的增加 ,蓝回绕会快速收缩直至消失 相似文献
5.
利用一种非局部和非定常的恒星对流理论,计算了0.6～3.0 M☉恒星演化模型的线性非绝热脉动.结果表明,赫罗图上脉动不稳定带右方的脉动不稳定的低温恒星可以分成2大类(群).一类由主序矮星、亚巨星和中低光度红巨星组成的类太阳振荡恒星,它们的中高阶(径向阶nr≥12)p模是脉动不稳定的,而低阶(nr≤ 5)模是脉动稳定的;另一类是由亮的红巨星和渐近巨星支星(AGB)组成的类长周期变星,它们的低阶模(nr≤5)是脉动不稳定的,而高阶模(nr≥12)却是脉动稳定的.能利用对流与脉动的耦合统一解释造父变星脉动不稳定带红边界、类太阳和类长周期变星脉动.对赫罗图右方的低温恒星的中低阶p模振荡,对流与脉动的耦合是主要的脉动激发和阻尼机制,而湍流的随机激发机制仅对类太阳振荡高阶p模重要. 相似文献
6.
本文作者使用美国ＶＬＡ，对快速目转的晚型巨星ＦＫＣｏｍ在３．６、６、１８、２０厘米波长上进行了射电观测，探测到ｍＪｙ量级的射电辐射，而没有探测到圆偏振。我们用热模型对射电频谱进行了拟合，结果都不成功。当发射体内电子密度为９×１０８ｃｍ－３，温度为５×１０７Ｋ时，半径为１２０Ｒ⊙．可获得较为接近的流量，但１０９量级的电子密度不大可能扩展到如此大的范围。这样的发射体用热模型得到的Ｘ射线光度比Ｅｉｎｓｔｅｉｎ天文台所观测到的值大两个数量级。ＦＫＣｏｍ的射电光度和Ｘ射线光度与ＲＳＣＶｎ双星系统相近，如果ＦＫＣｏｍ的射电发射也是由相对论电子在中等强度的磁场中作加速运动产生的话，则在１０高斯磁场中半径为３Ｒ⊙左右的发射区在相应波段即可达到观测的流量值。 相似文献
7.
利用VLBI MKIII系统多磁道记录的优点,在1665和1667MHz两个频率上,同时观测活动恒星形成区 W3(OH)的左右圆偏振羟基分子脉泽辐射。发现了三个Zeeman对,由脉泽子源的速度分裂导得磁场约为6mG,我们估计恒星形成区的磁场和氢气体密度有关系B～n~(0.54)。 相似文献
8.
恒星临边昏暗系数的测定 总被引：2，自引：0，他引：2
介绍一种新的一级挖和二级近似描述恒星大气临边昏境现象方法,其临边昏境系数可通过有关物理量的直接测量或测量流量和辅助量恒星表面温度的方法间接给出。与太阳观测比较和数值模型大气方法比较,均显示新方法能够以很精确的方式描述恒星临边昏境关系,或确定其相应系数 方法对太阳观测的１７６个数据比较了统计方差,其中直接法的一级挖和二级挖分别为０．３８％和０．２６％;间接法的方差与此相近而略大;与数值模型大气比较其 相似文献
9.
10.
恒星耀发是剧烈的恒星活动过程,对恒星周围行星的大气构成和生命演化有重大影响.恒星耀发的辐射主要分布在光学和X射线波段,其中耀发时X射线波段流量可以增大数十至数百倍.M型耀星是最有可能存在类地行星的宿主恒星,因此,研究M型耀星的X射线耀发分布对寻找宜居的类地行星具有重要意义,并且也可以为即将发射的爱因斯坦探针卫星(Ein... 相似文献
11.
Jan Kuijpers 《Solar physics》1989,121(1-2):163-185
An overview is given of the observations of stellar radio flares, defined as radio emission which is both variable in time and created by explosive releases of magnetic energy. The main sources of such flares are late-type Main-Sequence stars, classic close binaries, X-ray binaries, and pre-Main-Sequence stars.We summarize the interpretations of these observations in terms of the various incoherent and coherent emission mechanisms. The possible importance of a coherent emission process in electrostatic double layers is pointed out.We briefly indicate the diagnostic importance of radio emission for the flare process in classic and compact stars. In particular we discuss the possible production of radio flares from interactions between an accretion disk and the magnetic field of the central object. 相似文献
12.
John M. Porter 《Astrophysics and Space Science》1995,233(1-2):323-327
All hot stars are observed to have X-ray emission: O stars haveL
X /L
bol 10–7, whilst B stars' emission drops off with spectral subtype. Dynamical instability of OB star radiatively driven winds generates shocked regions which may be responsible for the bulk of the X-rays observed. The wind-compressed disc model of Bjorkman & Cassinelli (1993) presents another site for X-ray emission. The disc formed in the equatorial plane of a fast rotating Be star from equatorward drift of wind streamlines is confined on both sides by a shock which may also generate X-rays. As the X-ray emission originating from the wind shocking is ubiquitous amongst B and Be stars then the wind-compressed disc model näively predicts that Be stars should generate more X-rays than B stars of equivalent spectral subtype.The X-ray emission from the shocks confining compression discs has been calculated and compared to a limited set of observations. The excess X-ray emission from the Be star disc shocks is found to be undetectable over the inherent wind shocking emission. 相似文献
13.
M. V. Mekkaden 《Astrophysics and Space Science》1985,110(2):413-416
A study of the relationship between soft X-ray luminosity and Hei 10830 equivalent width in RS CVn binaries and very active late-type Main-Sequence stars is made. Long-period RS CVns and very active F and G Main-Sequence stars show strong dependence on their X-ray luminosities. This is attributed to the dominance of coronal excitation of the line in these stars. Short-period RS CVn binaries have lower Hei 10830 absorption compared to their X-ray emission. This phenomenon is explained by the presence of Hei emission region also in their chromospheres.On leave from Indian Institute of Astrophysics, Bangalore, India. 相似文献
14.
Joseph P. Cassinelli 《Astrophysics and Space Science》1994,221(1-2):277-285
Recent observations of the X-ray and EUV emission of non-supergiant B stars are summarized. As compared with O stars, the X-rays of most of the near-main-sequence B stars are soft, and the stars show a departure from theL x = 10?7 L bol relation. Using line driven wind models to provide an estimate of the density distribution, it is concluded that a major fraction of the wind emission measure is hot, whereas in shocked wind theory less than 10 percent of the wind emission measure should be hot. The X-ray observations suggest that all of the B stars are X-ray emitters with a basal X-ray luminosity of about 10?8.5 L bol . A hard component dominates the X-ray emission of τ Sco, and possible causes are discussed. For the Be stars, the X-ray emission is that which is expected from a normal B-star wind coming from the poles, as in the Wind Compressed Disk (WCD) model of Be stars. None of the stars, including theβ Cep stars, show noticeable variability in their X-rays.EUVE observations of∈ CMa B2 II, find it to be the brightest object in the EUV sky at 500 to 700 Å. It shows a Lyman continuum flux that is a factor of 30 higher than line blanketed model atmospheres. The continuum is seen on both sides of the He I 504 Å edge, and the discrepancy with model atmospheres is even greater shortward of 504 Å. TheEUVE spectra show emission lines both from high stages of ionization ( Feix to Fexvi) and from low stages (Heii and Oiii). The Heii Lymanα results from recombination following X-ray photoionization in the wind, and the Oiii resonance line is found to be present because of the Bowen fluorescence mechanism. Thus, there is and interesting coupling between the wind production by the EUV photospheric emission, the production of X-ray and line EUV emission by winds, and the production of fluorescence by recombination in the wind; all of these processes are now observable in B stars. 相似文献
15.
Stephen Skinner Manuel Güdel Werner Schmutz Svetozar Zhekov 《Astrophysics and Space Science》2006,304(1-4):97-99
We present an overview of recent X-ray observations of Wolf-Rayet (WR) stars with XMM-Newton and Chandra. These observations are aimed at determining the differences in X-ray properties between massive WR + OB binary systems and putatively single WR stars. A new XMM spectrum of the nearby WN8 + OB binary WR 147 shows hard absorbed X-ray emission (including the Fe Kα line complex), characteristic of colliding wind shock sources. In contrast, sensitive observations of four of the closest known single WC (carbon-rich) WR stars have yielded only non-detections. These results tentatively suggest that single WC stars are X-ray quiet. The presence of a companion may thus be an essential factor in elevating the X-ray emission of WC + OB stars to detectable levels. 相似文献
16.
T. Montmerle 《Astronomische Nachrichten》2008,329(2):210-213
Star-forming regions have been observed in X-rays since the first generation of satellites in the late 70s. They are very rich in magnetically-controlled X-ray phenomena: stellar flares and star-disk interactions in hundreds of T Tauri stars, confined winds in massive stars, etc. More recently, in a few low-mass stars, X-ray evidence has been found for accretion shocks. Even if it is not dominant, when it is found the influence of the circumstellar environment on X-ray emission gives precious clues on the magnetic structure in the vicinity of young stars. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
17.
Non-degenerate stars of essentially all spectral classes are soft X-ray sources. Their X-ray spectra have been important in
constraining physical processes that heat plasma in stellar environments to temperatures exceeding one million degrees. Low-mass
stars on the cooler part of the main sequence and their pre-main sequence predecessors define the dominant stellar population
in the galaxy by number. Their X-ray spectra are reminiscent, in the broadest sense, of X-ray spectra from the solar corona.
The Sun itself as a typical example of a main-sequence cool star has been a pivotal testbed for physical models to be applied
to cool stars. X-ray emission from cool stars is indeed ascribed to magnetically trapped hot gas analogous to the solar coronal
plasma, although plasma parameters such as temperature, density, and element abundances vary widely. Coronal structure, its
thermal stratification and geometric extent can also be interpreted based on various spectral diagnostics. New features have
been identified in pre-main sequence stars; some of these may be related to accretion shocks on the stellar surface, fluorescence
on circumstellar disks due to X-ray irradiation, or shock heating in stellar outflows. Massive, hot stars clearly dominate
the interaction with the galactic interstellar medium: they are the main sources of ionizing radiation, mechanical energy
and chemical enrichment in galaxies. High-energy emission permits to probe some of the most important processes at work in
these stars, and put constraints on their most peculiar feature: the stellar wind. Medium and high- resolution spectroscopy
have shed new light on these objects as well. Here, we review recent advances in our understanding of cool and hot stars through
the study of X-ray spectra, in particular high-resolution spectra now available from XMM-Newton and Chandra. We address issues related to coronal structure, flares, the composition of coronal plasma, X-ray production in accretion
streams and outflows, X-rays from single OB-type stars, massive binaries, magnetic hot objects and evolved WR stars. 相似文献
18.
Henny J. G. L. M. Lamers 《Astrophysics and Space Science》1994,221(1-2):41-63
The observational methods to derive information about the instability and variability of winds of hot stars are discussed. The expected effects of blobs and shells in the winds on the P Cygni profiles of the UV resonance lines and on the wind emission lines such as H are described. The evidence for the variability and instability of the winds is derived from the UV observations of Discrete Absorption Components and their variability, the X-ray flickering in compact binaries and the H variations. The evidence for wind variations in Wolf-Rayet stars and Luminous Blue Variables is discussed briefly, as well as a possible explanation for the V/R variations of Be stars. 相似文献
19.
We have detected X-ray emission (1 keV) from young intermediate-mass stars (Herbig Ae/Be stars). Since these stars are not supposed to produce intrinsic X-ray emission (no convection, no coronae), we believe that our results suggest that the X-ray emission actually traces the shock interaction of the Ae/Be star stellar winds with remnant circumstellar matter left over from the star formation process, the presence of which is also indicated by far-infrared (IRAS) and submm/mm continuum data. 相似文献
20.
R. Ignace † L. M. Oskinova C. Foullon 《Monthly notices of the Royal Astronomical Society》2000,318(1):214-226
We review existing ROSAT detections of single Galactic Wolf–Rayet (WR) stars and develop wind models to interpret the X-ray emission. The ROSAT data, consisting of bandpass detections from the ROSAT All-Sky Survey (RASS) and some pointed observations, exhibit no correlations of the WR X-ray luminosity ( L X ) with any star or wind parameters of interest (e.g. bolometric luminosity, mass-loss rate or wind kinetic energy), although the dispersion in the measurements is quite large. The lack of correlation between X-ray luminosity and wind parameters among the WR stars is unlike that of their progenitors, the O stars, which show trends with such parameters. In this paper we seek to (i) test by how much the X-ray properties of the WR stars differ from the O stars and (ii) place limits on the temperature T X and filling factor f X of the X-ray-emitting gas in the WR winds. Adopting empirically derived relationships for T X and f X from O-star winds, the predicted X-ray emission from WR stars is much smaller than observed with ROSAT . Abandoning the T X relation from O stars, we maximize the cooling from a single-temperature hot gas to derive lower limits for the filling factors in WR winds. Although these filling factors are consistently found to be an order of magnitude greater than those for O stars, we find that the data are consistent (albeit the data are noisy) with a trend of in WR stars, as is also the case for O stars. 相似文献