BL Lac天体处于高态与低态时的短时标光变的差异及机制研究

分析了１９９３－１９９５年ＢＬＬａｃ、ＯＪ２８７和ＰＫＳ０７３５＋１７８三颗ＢＬＬａｃ天体光变的监测结果,并结合文献上他人发表的资料,发现一些ＢＬＬａｃ天体处于高态时活动性较强,短时标光变频繁发生,而处于低态时活动性较弱,短时标光变很少发生．文中提出活动星系核的相对论性喷流方向会改变,从而导致长期光变;高态是喷流方向与观测者视线夹角较小的表现,而低态则是夹角较大的表现。利用该模型能够解释ＢＬＬａｃ天体短时标光变行为在高态和低态下的差别,并能很好地解释Ｔａｋａｌｏ等人监测ＯＪ２８７时发现的新现象．     

BL Lac天体处于高态与低态时的短时标光变的差异及机制研究

分析了１９９３－１９９５年ＢＬ Ｌａｃ、ＯＪ２８７和ＰＫＳ０７３５＋１７８三颗ＢＬ Ｌａｃ天体光变的监测结果,并结合文献上他人发表的资料,发现一些ＢＬ Ｌａｃ天体处于高态时活动性较强,短时标光变频繁发生,而处于低态时活动性较弱,短时标光变很少发生。文中提出活动星系核的相对论性喷流方向会改变,从而导致长期光变;高态是喷流方向与观测者视线夹角较小的表现,而低态则是夹角较大的表现。利用该模型能够解释ＢＬ     

CygX—1频谱的细微结构

利用线性状态空间模型（Ｌｉｎｅａｒ Ｓｔａｔｅ Ｓｐａｃｅ Ｍｏｄｉｌ－ＬＳＳＭ）,将ＣｙｇＸ－１的功率谱分解为ＬＳＳＭ产生的模型功率谱和剩余功率谱两部分。集中分析剩余功率谱,结果显示,ＣｙｇＸ－１在低／硬 态、转换态和高／软态三种状态的剩余功率谱有着不同的结构特征。其中高／软态和低／硬 态的剩余功率谱存在一个宽峰结构,中心频率分别为～８Ｈz和～５Ｈz,低／硬 态的剩余功率谱在～０．０７Ｈz达到极大     

天鹅座X-3的高能γ射线

对欧洲γ天文卫星COS-B数据的分析迄今未能发现在天鹅座X-3位置上存在着γ射线点源,从1977年6月到1980年6月,COS-B对Cyg-X天区进行了三次观测,各次观测的主要参数见表1,在第22次观测和第36次观测期间,天鹅区X-3大部分时间处于X辐射低态,各自只有6天左右处于高态;在第51次观测期间,大部分时间为X辐射高态,只有7天左右处于低态。     

Cyg X-1高态中短暴性质的研究

CygX-1高能辐射的时变特征可以通过短暴(shot)的性质反映．因此CygX-1的短暴性质，特别是处于低态时的性质曾被广泛研究,利用直接叠加短暴和自相关函数，对CygX-1高态时短暴的性质进行了研究．结果表明，当CygX-1处于高态时，其短暴的结构类似于低态时所具有的性质，短暴的半高宽随能量的增加按指数下降．此结果和康普顿化模型不一致．另外，短暴的能谱演化及结构的非对称性可以解释CygX-1中的时延现象．     

BL Lac天体的γ射线和X射线辐射研究

收集了18个γ射线噪BL Lac天体的X射线流量密度和γ射线流量密度,以及X射线波段(1keV)和γ射线波段(＞100 MeV)的平均光谱指数,研究了它们之间的相关性.结果表明:1)X射线流量密度与γ射线流量密度在高态、低态和平均态均有较强的相关性.2)X射线波段和γ射线波段的平均光谱指数之间有较强的负相关性.3)X射线和γ射线波段的平均光谱指数与X射线和γ射线辐射流量密度在高态和平均态时均无显著的相关性.4)γ射线波段的平均光谱指数与X射线辐射流量密度的低态有较强的负相关性.X射线波段的平均光谱指数与γ射线波段的流量密度的低态之间也存在弱相关性.分析结果支持BL Lac天体的X射线和γ射线辐射可能来自同一相对论电子分布的同步辐射和同步自康普顿(SSC)辐射.     

Cyg X-1频谱的细微结构

利用线性状态空间模型（Ｌｉｎｅａｒ Ｓｔａｔｅ Ｓｐａｃｅ Ｍｏｄｅｌ－ＬＳＳＭ）,将 Ｃｙｇ Ｘ－１的功率谱分解为ＬＳＳＭ产生的模型功率谱和剩余功率谱两部分．集中分析剩余功率谱,结果显示, Ｃｙｇ Ｘ－１在低／硬态、转换态和高／软态三种状态的剩余功率谱有着不同的结构特征．其中高／软态和低／硬态的剩余功率谱存在一个宽峰结构,中心频率分别为～ ８ Ｈｚ和～ ５ Ｈｚ,低／硬态的剩余功率诺在～ ０．０７ Ｈｚ达到极大;转换态的剩余功率谱有双峰结构,其中心频率分别在～０．５—４Ｈｚ和～５—１１Ｈｚ,与我们以前分析的 ＱＰＯ的中心频率很接近,说明 ＱＰＯ与线性状态空间所要求的自回归模型可能属于不同的物理过程．与总功率谱比较,剩余功率谱对谱的变化部分（例如ＱＰＯ、截断频率等）更为敏感,本文对剩余功率谱中谱峰变化的原因做了初步的探讨．     

Cyg X—1高态和转换态的X射线短时标爆发

分析ＲＸＴＥ卫星ＰＣＡ探测器对ＣｙｇＸ－１的观测数据,得到了其处于高态及高低高转换时的Ｘ射线短时标爆发（Ｓｈｏｔ）结构。在所观测到的三种态中是不对称的,并且不同的状态中Ｓｈｏｔ的结构有明显差异。Ｓｈｏｔ前后沿可分别由双指数函数近似拟合。Ｓｈｏｔ中的快时变过程是由慢的上升前沿和快的下降后沿构成。在所观测态中Ｓｈｏｔ平均宽度约为０．１１秒（ＦＷＨＭ）,比低态时的宽度窄。同一状态中高能段的Ｓｈｏｔ宽度较     

Cyg X-1高态和转换态的X射线短时标爆发

分析ＲＸＴＥ卫星ＰＣＡ探测器对ＣｙｇＸ－１的观测数据,得到了其处于高态及高低态转换时的Ｘ射线短时标爆发（Ｓｈｏｔ）结构．在所观测到的三种态中是不对称的,并且不同的状态中Ｓｈｏｔ的结构有明显差异．Ｓｈｏｔ前后沿可分别由双指数函数近似拟合．Ｓｈｏｔ中的快时变过程是由慢的上升前沿和快的下降后沿构成．在所观测态中Ｓｈｏｔ平均宽度约为０．１１秒（ＦＷＨＭ）,比低态时的宽度窄．同一状态中高能段的Ｓｈｏｔ宽度较低能段窄,且更加不对称．转换态的硬度在Ｓｈｏｔ峰前有明显下降,之后迅速上升,Ｓｈｏｔ期间的平均硬度低于非Ｓｈｏｔ期平均值;而高态时峰前硬度没有明显下降,Ｓｈｏｔ期间的平均硬度高于非Ｓｈｏｔ期间的平均值．本文还就Ｓｈｏｔ的产生机制进行了讨论．     

天鹅座X-3 X光子对γ射线的吸收

通过处理天文卫星COS-B的数据,我们首次获得了Cygnus X-3的γ射线像,并且发现了150—5000 MeV高能γ辐射与2—12keV X辐射强度的负相关现象,即X射线高态时的γ辐射比低态时弱. γ-X负相关现象可以用吸积盘X射线冕区中密集的X射线光子对γ射线的吸收作用解释.     

恒星形成过程中的天体物理现象

恒星形成于分子云环境中。近30多年的观测研究使得天文学家对小质量恒星的形成有了相对明确的认识：小质量恒星通过坍缩、吸积和外向流的路标而形成。至于大质量恒星，其形成过程还存在着许多不确定因素，现有的观测证据表明：大质量恒星也可能通过坍缩、吸积和外向流的路标来形成，但也不排除在星团中通过中小质量恒星聚合而成的因素。大质量恒星形成与致密电离氢区(UCHII)成协较好，而与大质量恒星形成区成协的分子云环境中，既有大质量恒星也有小质量恒星形成。综述了恒星形成各个阶段的观测结果和研究现状以及成协的天体物理环境情况。未来的观测和研究重点在于，大质量恒星形成以及星团环境中的恒星形成。     

混杂星的r-模不稳定性窗口

考虑到混杂星既具有奇异夸克物质核,又具有中子星固体壳层的特殊结构,运用完全自洽的二级修正方法,研究了在低温极限下(T<109K)混杂星的体粘滞耗散时标,并利用该时标计算了混杂星的临界旋转频率,发现其最小值为704.42 Hz(对应1.42 ms脉冲周期).与中子星和奇异星比较,更好地解释了观测数据.     

CEMP星HE1005-1439中子俘获元素天体物理来源的研究

HE1005-1439是一颗金属丰度极低([Fe/H] ~ - 3.0)的碳增丰贫金属星(Carbon Enhanced Metal-Poor,CEMP), 该星的s-过程元素显著超丰([Ba/Fe] = 1.16±0.31, [Pb/Fe] = 1.98±0.19), 而r-过程元素温和超丰([Eu/Fe] = 0.46±0.22), 使用单一的s-过程模型和i-过程模型均不能拟合该星中子俘获丰度分布. 采用丰度分解的方法探究该星化学元素的天体物理来源可有助于理解CEMP星的形成和化学演化. 利用s-过程和r-过程的混合模型对其中子俘获元素的丰度分布进行拟合, 发现该星的中子俘获元素主要来源于低质量低金属丰度AGB伴星的s-过程核合成, 而r-过程核合成也有贡献.     

Variable Star Status of Two Stars:V204 and I-I-39 in M3

The star I-I-42 (=vZ1390),a cluster member in M3,located near the red edge of the instability strip of the horizontal branch,was discovered by Roberts and Sandage as a low amplitude variable,it was designated as V204 in the "second catalogue of variable stars in globular clusters",but its coordinates given in all versions of this catalogue are wrong since 1955. We argue that V204 is indeed a low amplitude HB variable star,located near to the red edge of the instability strip,with a period of 0.74785d and an amplitude of about 0.04mag in V . We also find that the red cluster member star I-I-39 is a low amplitude variable with a period of 1.16d and amplitude of about 0.03mag in V which might be pulsating at the second overtone.     

Another new small-amplitude red variable star with period of about one day in the globular cluster M4

A66 is a red star located at the lowest end of the red giant branch (near the top of the sub-giant branch) of the globular cluster M4. According to its location on the GM diagram, A66 may be a cluster member. No proper motion and radial velocity determinations are available up to date.

We discovered that A66 is a small-amplitude new variable star with a period of about one day and the peak to peak amplitude is about 0.05 mag in V.

However, if its membership can be confirmed by proper motion and radial velocity determinations, the cause of light variation may be not pulsation. This is because according to Xiong's theory, a red star at such low luminosity can not pulsate at a period longer than 0.1 day. Then other causes such as EW type eclipsing variable star or rotation of a spotted star might be responsible. Otherwise A66 is not a cluster member.     

The neutron stars of Soft X–ray Transients

Summary. Soft X–ray Transients (SXRTs) have long been suspected to contain old, weakly magnetic neutron stars that have been spun up by accretion torques. After reviewing their observational properties, we analyse the different regimes that likely characterise the neutron stars in these systems across the very large range of mass inflow rates, from the peak of the outbursts to the quiescent emission. While it is clear that close to the outburst maxima accretion onto the neutron star surface takes place, as the mass inflow rate decreases, accretion might stop at the magnetospheric boundary because of the centrifugal barrier provided by the neutron star. For low enough mass inflow rates (and sufficiently short rotation periods), the radio pulsar mechanism might turn on and sweep the inflowing matter away. The origin of the quiescent emission, observed in a number of SXRTs at a level of , plays a crucial role in constraining the neutron star magnetic field and spin period. Accretion onto the neutron star surface is an unlikely mechanism for the quiescent emission of SXRTs, as it requires very low magnetic fields and/or long spin periods. Thermal radiation from a cooling neutron star surface in between the outbursts can be ruled out as the only cause of the quiescent emission. We find that accretion onto the neutron star magnetosphere and shock emission powered by an enshrouded radio pulsar provide far more plausible models. In the latter case the range of allowed neutron star spin periods and magnetic fields is consistent with the values recently inferred from the properties of kHz quasi-periodic oscillation in low mass X–ray binaries. If quiescent SXRTs contain enshrouded radio pulsars, they provide a missing link between X–ray binaries and millisecond pulsars. Received 4 November 1997; Accepted 15 April 1998     

The magnetosphere of oscillating neutron stars in general relativity

Just as a rotating magnetized neutron star has material pulled away from its surface to populate a magnetosphere, a similar process can occur as a result of neutron-star pulsations rather than rotation. This is of interest in connection with the overall study of neutron star oscillation modes but with a particular focus on the situation for magnetars. Following a previous Newtonian analysis of the production of a force-free magnetosphere in this way Timokhin et al., we present here a corresponding general-relativistic analysis. We give a derivation of the general relativistic Maxwell equations for small-amplitude arbitrary oscillations of a non-rotating neutron star with a generic magnetic field and show that these can be solved analytically under the assumption of low current density in the magnetosphere. We apply our formalism to toroidal oscillations of a neutron star with a dipole magnetic field and find that the low current density approximation is valid for at least half of the oscillation modes, similarly to the Newtonian case. Using an improved formula for the determination of the last closed field line, we calculate the energy losses resulting from toroidal stellar oscillations for all of the modes for which the size of the polar cap is small. We find that general relativistic effects lead to shrinking of the size of the polar cap and an increase in the energy density of the outflowing plasma. These effects act in opposite directions but the net result is that the energy loss from the neutron star is significantly smaller than suggested by the Newtonian treatment.     

A model of supernova feedback in galaxy formation

A model of supernova feedback during disc galaxy formation is developed. The model incorporates infall of cooling gas from a halo, and outflow of hot gas from a multiphase interstellar medium (ISM). The star formation rate is determined by balancing the energy dissipated in collisions between cold gas clouds with that supplied by supernovae in a disc marginally unstable to axisymmetric instabilities. Hot gas is created by thermal evaporation of cold gas clouds in supernova remnants, and criteria are derived to estimate the characteristic temperature and density of the hot component and hence the net mass outflow rate. A number of refinements of the model are investigated, including a simple model of a galactic fountain, the response of the cold component to the pressure of the hot gas, pressure-induced star formation and chemical evolution. The main conclusion of this paper is that low rates of star formation can expel a large fraction of the gas from a dwarf galaxy. For example, a galaxy with circular speed 50 km s¹ can expel 6080 per cent of its gas over a time-scale of 1 Gyr, with a star formation rate that never exceeds 0.1 M yr¹. Effective feedback can therefore take place in a quiescent mode and does not require strong bursts of star formation. Even a large galaxy, such as the Milky Way, might have lost as much as 20 per cent of its mass in a supernova-driven wind. The models developed here suggest that dwarf galaxies at high redshifts will have low average star formation rates and may contain extended gaseous discs of largely unprocessed gas. Such extended gaseous discs might explain the numbers, metallicities and metallicity dispersions of damped Lyman systems.     

A long-term UBVRI photometric study of the pre-main sequence star V350 Cep

Results from UBVRI optical photometric observations of the pre-main sequence star V350 Cep during the period 2004-2014 are presented.The star was discovered in 1977 due to its remarkable increase in brightness by more than 5 mag(R).In previous studies,V350 Cep was considered to be a potential FUor or EXor eruptive variable.Our data suggest that during the period of observations the star maintains its maximum brightness with low amplitude photometric variations.Our conclusion is that V350 Cep was probably an intermediate object between FUors and EXors,similar to V1647 0ri.     

A General Relativistic Calculation of Boundary Layer and Disc Luminosity for Accreting Non-magnetic Neutron Stars in Rapid Rotation

We calculate the disc and boundary layer luminosities for accreting rapidly rotating neutron stars with low magnetic fields in a fully general relativistic manner. Rotation increases the disc luminosity and decreases the boundary layer luminosity. A rapid rotation of the neutron star substantially modifies these quantities as compared with the static limit. For a neutron star rotating close to the centrifugal mass shed limit, the total luminosity has contribution only from the extended disc. For such maximal rotation rates, we find that well before the maximum stable gravitational mass configuration is reached, there exists a limiting central density, for which particles in the innermost stable orbit will be more tightly bound than those at the surface of the neutron star. We also calculate the angular velocity profiles of particles in Keplerian orbits around the rapidly rotating neutron star. The results are illustrated for a representative set of equation of state models of neutron star matter.