球状星团M4中的一颗新红变星

G302=L3107是球状星团M4中的一颗红星，目前还没有自行或视线速度的测定，Greenstein和Lee分别给出此星的星等和色指数为：     

δScuti变量和相关天体

δScuti型变星是赫罗图上A3-F5区间的主序及其以上的一种周期短于0.3d的单周期或多周期小变幅脉动变星，与它们相关的变星有矮造父变星，γDol变星，蓝离散星，金属线星，A型特殊星，λBoo变星的δDel变星，有些赫比格Ae/Be星也存在类似的脉动，对自1964年起的研究工作进行了系统的总结，给出了1995年后新发现的相关变星数和最可靠的周期变化表，提出应当用双星轨道光时效应来解释实测得到的变星周期变化中的幅度很大的成分，统计表明自转越快变幅越小，因此年轻星团中不可能存在大变幅变星，变幅随周期的分布有3个极大值，最大变由是周期0.17d处的1.0mag，恒星系统内变星的平均周期越短系统的年龄越大，金属丰度也越低。     

δScuti变星和相关天体

δScuti型变星是赫罗图上A3～F5区间的主序及其以上的一种周期短于0.3 d的单周期或多周期小变幅脉动变星.与它们相关的变星有矮造父变星、γ Dol变星、蓝离散星、金属线星、A型特殊星、λBoo变星和δDel变星.有些赫比格Ae/Be星也存在类似的脉动.对自1964年起的研究工作进行了系统的总结,给出了1995年后新发现的相关变星数和最可靠的周期变化表,提出应当用双星轨道光时效应来解释实测得到的变星周期变化中的幅度很大的成分.统计表明自转越快变幅越小,因此年轻星团中不可能存在大变幅变星.变幅随周期的分布有3个极大值,最大变幅是周期0.17d处的1.0 mag.恒星系统内变星的平均周期越短系统的年龄越大,金属丰度也越低.     

球状星团M10（NGC6254）的自行研究

利用上海天台和Bonn大学天台的照相底片资料及大视场CCD观测数据,测定了球状星团M10（NGC6254）天台中532颗恒星相对于依巴谷参考系和ACT星表的绝地自行,相对于Hipparcos参考星和ACT参考星分别得到的测定结果符合得很好,根据自行测定结果进行了星团成员判定,有两颗星族II父变星被证实为星团的成员,根据星团的绝对自行,结合其距离与视向速度观测结果,得了了M10的空间运动轨道。     

重新审查昴星团成员星锂丰度的弥散

重新审查了昴星团成员星的活动性和在同一颜色处Li丰度的弥散．发现大多数的研究者低估了昴星团恒星的活动性．重新研究了恒星的活动性(包括黑子活动)和星团中恒星的不均匀红化效应对Li丰度弥散的影响．得到的主要结论是：没有坚实的证据说明观测到的Li丰度弥散是代表具相同有效温度星团成员大气Li丰度存在真实的差异．相反，假若不是全部，其大部的视Li丰度弥散是活动星的大气效应所致．Li丰度一恒星自转关联很可能只是Li丰度-恒星活动性关联的一种反映。     

昂星团天区耀星成员性和相对数量的再讨论

本文通过统计比较，并用更完善的模型作成员概率的最大似然估计，对昂星团天区耀星的成员性进行了新的细致的讨论，指出Ｍｉｒｚｏｙａｎ等根据Ｊｏｎｅｓ的自行成员概率估计得出的非成员耀星呈现向团心集中强烈趋势的现象，是由于Ｊｏｎｅｓ对成员星成员概率的普遍低估以及对外围恒星成员概率的一定程度高估加上在中心附近观测误差和错误显著增加而造成的．本文根据Ｓｔａｕｆｆｅｒ等对更完整的样本估计的成员概率，以其中成员概率大于０．５的星为成员星，重新计算了昂星团内成员耀星在红矮星中占的比例（相对数量），表明了相对数量在ＭＶ＜８．０时随星等变暗而增大，而ＭＶ≈８．０时开始稳定在６４％左右，直至样本完整性的极限（ＭＶ≈１１．５）．因此，昂星团内无明显耀发活动的红矮星占该星团内红矮星总数的１／３左右或更少．     

球状星团的天体测量(英)

球状星团是银河系中最年老的天体之一，是储存着银河系早期演化珍贵信息的“化石”．球状星团的天体测量，主要包括球状星因天区内恒星相对自行的测定，并由这些相对自行数据采用适当方法定出星团的绝对自行，或者直接测定绝对自行．利用这些自行数据，或者进一步与测光和视向速度数据结合，可以开展与球状星团的距离、运动、动力学状况、质量、年龄、演化等等以及银河系的结构和演化等有关的一系列重要的研究．在本文中对本世纪70年代中期以来在球状星团相对自行测定和成员概率估计、内部运动检测、绝对自行测定和空间运动研究这三方面取得的成果和进展以及存在的问题作了评述．     

球状星团M3天区534颗恒星的绝对自行测定

以《Hipparcos星表》体现的国际天球参考架为基础 ,对球状星团M3(NGC 5 2 72 )中心附近 10 0′×10 0′天区内 5 34颗恒星 ,使用上海天文台佘山 4 0cm折射望远镜拍摄的底片资料 ,以 8颗《Hipparcos星表》中恒星和 4 9颗《Tycho - 2星表》中恒星的位置和绝对自行为参考 ,归算得到了位置和绝对自行 ,并估计了成员概率     

金属丰度对球状星团动力学演化的影响

动力学过程和恒星演化及二者的互相影响都会对球状星团的演化产生重要影响.由于金属丰度会影响恒星的演化轨迹,与之相伴随的恒星质量损失率的变化也会对球状星团的动力学过程造成影响.通过一系列N体模拟研究金属丰度对球状星团的质量损失率、半径等的影响,并分析其原因,同时研究了大质量恒星以及星团初始数密度分布的影响.模拟中采用的球状星团模型初始成员星数目N=50000,运行于类银河系的引力势中并考虑成员星的演化.结果显示,由于低金属丰度恒星拥有较快的演化时标,所以贫金属球状星团在早期会拥有较高的质量损失,但与此同时它们的核塌缩时间会比后者显著推迟,因此在核塌缩之后其质量损失会被富金属星团反超.另外由于大质量恒星演化导致的质量损失较大,所以大质量星的存在会使金属丰度更加显著地影响球状星团早期的扩张以及随后的核塌缩过程,同时星团的初始数密度分布也对该效应有着不可忽视的影响.     

球状星团中低光度红巨星的脉动稳定性

利用一种非定常的恒星非局部对流理论,对球状星团中低光度的红巨星进行了线性非绝热脉动理论计算．结果表明,对所有温度高于约5400 K模型的基音到4阶泛音都是脉动稳定的．随着恒星光度的增大,低阶泛音也变得脉动不稳定．对中低光度的红巨星,脉动稳定性非常低,接近中性稳定．因此他们将是不变星或非常小振幅的短周期变星(P<2天)．     

On the Carbon—Star Status of Five Stars in a New Carbon Star Catalog

We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10μm silicate features in absorption and the 1612MHz OH maser emission or/and the SiO molecular features. These objects were considered as carbon stars in the catalog based only on their locations in the infrared two-color diagram. Therefore to use the infrared two-color diagram to distinguish carbon-rich stars from oxygenrich stars must be done with caution, because, in general, it has only a statistical meaning.     

A study of X-ray flares – I. Active late-type dwarfs

We present temporal and spectral characteristics of X-ray flares observed from six late-type G–K active dwarfs (V368 Cep, XI Boo, IM Vir, V471 Tau, CC Eri and EP Eri) using data from observations with the XMM–Newton observatory. All the stars were found to be flaring frequently and altogether a total of 17 flares were detected above the 'quiescent' state X-ray emission which varied from 0.5 to  8.3 × 10²⁹ erg s⁻¹  . The largest flare was observed in a low-activity dwarf XI Boo with a decay time of 10 ks and ratio of peak flare luminosity to 'quiescent' state luminosity of 2. We have studied the spectral changes during the flares by using colour–colour diagram and by detailed spectral analysis during the temporal evolution of the flares. The exponential decay of the X-ray light curves, and time evolution of the plasma temperature and emission measure are similar to those observed in compact solar flares. We have derived the semiloop lengths of flares based on the hydrodynamic flare model. The size of the flaring loops is found to be less than the stellar radius. The hydrodynamic flare decay analysis indicates the presence of sustained heating during the decay of most flares.     

The impact of meridional circulation on stellar butterfly diagrams and polar caps

Observations of rapidly rotating solar-like stars show a significant mixture of opposite-polarity magnetic fields within their polar regions. To explain these observations, models describing the surface transport of magnetic flux demand the presence of fast meridional flows. Here, we link subsurface and surface magnetic flux transport simulations to investigate (i) the impact of meridional circulations with peak velocities of  ≤125 m s⁻¹  on the latitudinal eruption pattern of magnetic flux tubes and (ii) the influence of the resulting butterfly diagrams on polar magnetic field properties. Prior to their eruption, magnetic flux tubes with low field strengths and initial cross-sections below  ∼300 km  experience an enhanced poleward deflection through meridional flows (assumed to be polewards at the top of the convection zone and equatorwards at the bottom). In particular, flux tubes which originate between low and intermediate latitudes within the convective overshoot region are strongly affected. This latitude-dependent poleward deflection of erupting magnetic flux renders the wings of stellar butterfly diagrams distinctively convex. The subsequent evolution of the surface magnetic field shows that the increased number of newly emerging bipoles at higher latitudes promotes the intermingling of opposite polarities of polar magnetic fields. The associated magnetic flux densities are about 20 per cent higher than in the case disregarding the pre-eruptive deflection, which eases the necessity for fast meridional flows predicted by previous investigations. In order to reproduce the observed polar field properties, the rate of the meridional circulation has to be of the order of 100 m s⁻¹, and the latitudinal range from which magnetic flux tubes originate at the base of the convective zone (≲50°) must be larger than in the solar case (≲35°).     

Near-infrared and optical studies of the fast nova V4643 Sgr (Nova Sagittarii 2001)

It is generally accepted that the presence of a hot magnetic corona provides the source of X-ray emission in cool stars. With this connection one could expect to see the variation of magnetic flux in the activity cycle of a star mirrored by a similar variation in the stars X-ray emission. Using magnetic maps produced from flux emergence and transport simulations and assuming a potential field for the corona, we can extrapolate the coronal magnetic field and hence calculate the variation of the X-ray emission. We consider three types of activity cycle that successfully reproduce the pattern of intermingled magnetic flux at high latitudes, a feature observed with Zeeman–Doppler imaging. The three different cycles take the form of (1) an enhanced butterfly pattern where flux emergence is extended to a latitude of 70°, (2) an extended emergence profile as before but with an overlap of 4 yr in the butterfly diagram and (3) where no butterfly diagram is used. The cyclic variation in the X-ray emission is around two orders of magnitude for cases (1) and (3), but less than one order of magnitude for case (2). For all three cases, the rotational modulation of the X-ray emission is greatest at cycle minimum, but the emission measure weighted density varies little over the cycle. For cases (1) and (2) the fraction of the total flux that is open (along which a wind can escape) varies little over the cycle, but for case (3) this is three times larger at cycle minimum than at maximum. Our results clearly show that although magnetic cycles may exist for stars they are not necessarily observable in the X-ray emission.     

Matching the frequency spectrum of pre-main sequence stars by means of standard and rotating models

We applied the aton evolutionary code to the computation of detailed grids of standard (non-rotating) and rotating pre-main sequence (PMS) models and computed their adiabatic oscillation spectra, with the aim of exploring the seismic properties of young stars. As, until now, only a few frequencies have been determined for ∼40 PMS stars, the way of approaching the interpretation of the oscillations is not unique. We adopt a method similar to the matching mode method by Guenther and Brown making use, when necessary, also of our rotating evolutionary code to compute the models for PMS stars. The method is described by a preliminary application to the frequency spectrum of two PMS stars (85 and 278) in the young open cluster NGC 6530. For the Star 85, we confirm with self-consistent rotating models, previous interpretation of the data, attributing three close frequencies to the mode   n = 4, l = 1  and   m = 0  , +1 and −1. For the Star 278, we find a different fit for the frequencies, corresponding to a model within the original error box of the star, and dispute the possibility that this star has a T _eff much cooler that the red boundary of the radial instability strip.     

Model atmosphere and kinematical analyses of early-type stars from the Edinburgh–Cape Survey

We present high-resolution spectroscopic observations of 21 B-type stars, selected from the Edinburgh–Cape Blue Object Survey. Model atmosphere analyses confirm that 14 of these stars are young, main-sequence B-type objects with Population I chemical compositions. The remaining seven are found to be evolved objects, including subdwarfs, horizontal branch and post-AGB objects. A kinematical analysis shows that all 14 young main-sequence stars could have formed in the disc and subsequently been ejected into the halo. These results are combined with the analysis of a previous subsample of stars taken from the Survey. Of the complete sample, 31 have been found to be young, main-sequence objects, with formation in the disc, and subsequent ejection into the halo, again being found to be a plausible scenario.