Galactic Rotation Based on OB Stars from the Gaia DR2 Catalogue

We have studied a sample containing ~6000 OB stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The following parameters of the angular velocity of Galactic rotation have been found: Ω₀ = 29.70 ± 0.11 km s^-1 kpc^-1, Ω'₀ = -4.035 ± 0.031 km s^-1 kpc^-2, and Ω ₀ = 0.620 ± 0.014 km s^-1 kpc^-3. The circular rotation velocity of the solar neighborhood around the Galactic center is V₀ = 238 ± 5 km s^-1 for the adopted Galactocentric distance of the Sun R₀ = 8.0 ± 0.15 kpc. The amplitudes of the tangential and radial velocity perturbations produced by the spiral density wave are f_θ = 4.4 ± 1.4 kms^-1 and f_R = 5.1 ± 1.2 kms^-1, respectively; the perturbation wavelengths are λ_θ = 1.9 ± 0.5 kpc and λ_R = 2.1 ± 0.5 kpc for the adopted four-armed spiral pattern. The Sun's phase in the spiral density wave is χ_⊙ = -178° ± 12°.

     

Absolute Magnitudes of Be Stars Based on Hipparcos Parallaxes

The absolute visual magnitudes of 457 Be stars are determined from Hipparcos parallaxes, subsequently the mean absolute visual magnitudes of Be stars for luminosity classes III, IV and V are obtained. The new Mv calibration is compared with existing calibrations. It is found that Be stars are generally brighter than B stars of the corresponding spectral types, and that there is no direct correlation between absolute magnitudes and the stellar rotational velocity, these results are in agreement with some earlier results. A new and interesting result is that there is no direct correlation between near infrared excess and absolute visual magnitudes for Be stars. Moreover, possible biases, such as the Malmquist bias and the Lutz–Kelker bias, are also discussed.     

Galactic Rotation Parameters Based on Stars from Active Star-Forming Regions with Data from the Gaia DR2 Catalogue

Astronomy Letters - We have studied a sample of more than 25?000 young stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The relative errors of their...     

射电干涉测量对天文脉泽研究的贡献

天文脉泽已成为一个迅速的研究领域，重点评述了射电干涉测量对天文脉泽观测和研究所起的作用。     

Abundances in Individual Stars of the Galactic Bulge

Element ratios in two stars of NGC 6553 and one star in NGC 6528 reveal that α-elements are enhanced relative to Fe. The metallicity [Fe/H] ≈ −0.6, but taking into account the overabundances of several elements, the overall metallicity is close to solar. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Differential Rotation of Stars

We discussmethods for analyzing the observational manifestations of differential rotation (DR). Based on the literary sources and our estimates (for 4 cool dwarfs), a list containing 75 stars was compiled. Using an example of analysis of the ‘ΔΩ–T_eff’, ‘ΔΩ–rotation period’ and ‘ΔΩ–Rossby number’ diagrams we compared the determined parameters of DR stars with the results of theoretical studies. Particular attention is paid to the problems of measurements of DR parameters in low-mass dwarf stars, including the completely convective ones.We analyzed the measured parameters of solar-type DR stars. The objects having anti-solar DR (α < 0), and possiblemethods allowing to determine the sign of α are considered.We distinguish the areas of research that in the future may expand our understanding of DR manifestations: a study of DR in the inner regions of stars and an analysis of manifestations of the rotational brightness modulation caused by the spottedness of components in eclipsing-variable systems (subsynchronized systems).     

Rotation Profiles of Solar-like Stars with Magnetic Fields

We investigate the rotation profile of solar-like stars with magnetic fields. A diffu-sion coefficient of magnetic angular momentum transport is deduced. Rotating stellar models with different mass incorporating the coefficient are computed to give the rotation profiles. The total angular momentum of a solar model with only hydrodynamic instabilities is about 13 times larger than that of the Sun at the age of the Sun, and this model can not reproduce quasi-solid rotation in the radiative region. However, the solar model with magnetic fields not only can reproduce an almost uniform rotation in the radiative region, but also a total angular momentum that is consistent with the helioseismic result at the 3 σ level at the age of the Sun. The rotation of solar-like stars with magnetic fields is almost uniform in the radiative region, but for models of 1.2-1.5 M⊙, there is an obvious transition region between the convective core and the radiative region, where angular velocity has a sharp radial gradient, which is different from the rotation profile of the Sun and of massive stars with magnetic fields. The change of angular velocity in the transition region increases with increasing age and mass.     

银河系厚盘恒星的年龄-金属度关系

对太阳邻域内银河系盘星、特别是厚盘恒星年龄-金属度关系的研究进展作了较为详细的回顾和评述；说明目前对盘星是否确实存在年龄-金属度关系还存在争议，而厚盘恒星可能存在这种关系。同时指出，要得出明晰的结论，在观测资料的基础上取得合理的恒星样本至关重要。     

Some Problems with Slow Rotation of CP Stars

Some difficulties in explaining the slow rotation of CP stars are discussed. The most likely hypotheses are (1) a loss of angular momentum involving a magnetic field during “pre-main sequence” evolution and (2) the slow rotation existed from the very start of the creation of these stars. The braking hypothesis is supported by only one property of CP stars— the lower the mass of the star is, the greater the difference between its average rotation velocity vsini and that of normal stars. On the other hand, there is another property— the lower the rotation speeds of CP stars are, the greater their fraction among normal stars. The latter property supports the hypothesis that the lower the initial rotation speed of a star is when it is created, the greater the probability will become chemically peculiar. This property is inherent in chemically peculiar stars both with and without a magnetic field. It is proposed that the cause of the slow rotation of CP stars must be sought in the very earliest phases of their formation, as should the cause of the separation into chemically peculiar magnetic, chemically peculiar nonmagnetic, and normal stars.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 229–245 (May 2005).     

若干Be星的自转

通过光谱观测获得53颗Be星的自转速度Vsir.i,在Hutchings的方法基础上估算出V和i。我们分析了自转对发射线宽度的影响,利用发射线峰间间隔求取气壳与光球的半径比和稀化因子。文中着重讨论了快自转而且存在恒星风的自转模型同Be现象之间的关系。     

Distribution of SiO and OH Maser Stars in the Galactic Plane

The observational results of the Nobeyama 45-m SiO maser survey and the Arecibo 305-m OH maser survey are assembled for an analysis of the distribution and kinematics of late-type stars in the Galactic plane.It is found that neither SiO maser stars nor OH maser stars show any concentration to the spiral arms,which imply that they do not belong to the arm population and quite possibly they are low-mass stars in late stage of evolution.A rotational curve is also derived for these objects and a few features which may be real are discussed and compared with those derived from planetary nebulae and AGB stars.     

基于SDSS的河内恒星DIBs自动识别方法

星际弥散带(Diffuse Interstellar Bands,DIBs)自发现以来已经经历了近百年的研究,但是至今仍然是天体光谱学上的一个未解之谜.针对SDSS DR7的光谱数据提出了一种星际弥散带特征自动识别方法.该方法基于谱线特征匹配,通过光谱流量限制的方法进行星际弥散带特征的自动识别.利用它可对相对定标的巡天光谱进行广泛的星际弥散带候选天体搜索,在海量光谱数据中获取更多具有星际弥散带特征的河内恒星.通过对SDSS DR7中位置相对合适的超过300个盘的天体光谱的遍历,已经得到了一系列具有星际弥散带特征的候选河内恒星,并且证明了该方法简单有效且具有鲁棒性.这为载体证认等工作提供了大量辅助数据,极大地推进了星际弥散带的研究.     

星系的转动与黑洞形成的判据

本文通过数值计算解出稳态星系模型，并与椭圆星系及旋涡星系核球的自转和弥散速度曲线相比较。由星系运动曲线拟合出的星系半径与从光度曲线拟合出的潮汐半径不一致，后者总是前者的３倍左右，这是由于分布函数的截断方式不妥造成的。我们的结论是：该模型虽不能正确描述整个星系，但却能正确描述星系的较内部区域，我们分析了三个有速度曲线资料的星系黑洞候选者：Ｍ１０４、Ｍ３１和银河系，发现它们由于有太快的自转，都不可能在达到稳态之后有满足形成黑洞所要求的≡ｃＪ／ＧＭ２＜１的区域存在，因此它们的中心如有黑洞，只能有更早的起源。     

射电源结构对VLBI天体测量的影响

目前利用VLBIMK3系统确定的延迟测量的精度约为30ps,在这样的精度下,改善计算延迟的理论模型,考虑各种微扰改正（包含30ps量级）是非常重要的。在VLBI天休测量和测地计算的各种软件中,至今尚未计及射电源结构对延迟的影响。本文利用两子源模型对源结构延迟的大小及随时间的变化进行了计算,讨论了源结构延迟对VLBI天测和测地参数的影响,指出：（1）除对某些VLBI天测的射电源作长期的监测与研究,给出它们的双频综合图外,对大多数源可采用简单的两子源模型;（2）源结构对延迟的影响主要依赖于基线相对于源形态的主要特征的空间投影;（3）源结构延迟对天测和测地参数的影响达厘米和亚毫角秒量级。     

Kinematics and Dynamics of the Galactic Halo from RR Lyrae Variable Stars

Based on a sample of RR Lyrae variable stars including more than 9000 objects with proper motions and distances, we have investigated the kinematics of the Galactic halo from the two-dimensional velocity field. We have used both the proper motions deduced independently by us from the positional data taken from all-sky catalogues in a time interval up to 65 years and the proper motions taken from the Gaia DR2 catalogue. In addition, we have also studied the halo kinematics from the three-dimensional velocity field of ~850 RR Lyrae variables with distances, proper motions, and line-of-sight velocities. The kinematic parameters describing the velocity field have been estimated by the maximum-likelihood method; their change with Galactocentric distance has been investigated. The radial velocity dispersion in spherical coordinates σ_r ≈ 160?170 km s^?1 exceeds its values from previous papers approximately by 20 km s^?1, while the anisotropy parameter β ≈ 0.68?0.72 agrees satisfactorily with previous studies. When estimating the rotation velocity of the population of RR Lyrae stars, we identified the inner and outer halos with weak prograde and retrograde rotations, respectively.     

An Estimation of the Galactic Escape Velocity From High-Velocity Metal-Poor Stars

A large number of high-velocity stars was included in the Hipparcos Input Catalogue for the purpose of determining the galactic escape velocity in the solar vicinity. However, the `fastest' stars known, listed by Carney et al. (1994, CLLA) were not included because they are too faint. In the intersection between the CLLA list and the Hipparcos Catalogue (770 common stars), the metal-deficient stars with the most reliable parallaxes (fracσ_ππ)_HIP ≤ 0.15) are used for recalibrating CLLA absolute magnitudes and photometric parallaxes, using metallicities and VandenBerg et al. (1998) isochrones. In this way, about twenty non-Hipparcos stars get improved parallaxes and are added to our primary sample of Hipparcos high-velocity stars, for a better determination of the escape velocity from the Galaxy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Starspots, Activity Cycles, and Differential Rotation on Cool Stars

We present the first results of searching for stellar cycles by analysis of stellar spottedness using an algorithm developed at the Crimean Astrophysical Observatory. For more than 35 red spotted stars, we find ten targets which demonstrate cyclic variations of average latitudes and total areas of starspots. Activity cycles detected by this method have a typical cycle length about 4–15 years which are analogous to the 11-year solar Schwabe cycle. Most of the program stars demonstrate a rough analogue with the solar butterfly diagram. They show a tendency for the average starspot latitude lowering when the total spot area grows. At the same time these stars show variations of stellar photometric period (which is traced by starspots) with the starspot latitudinal drift analogously to the solar differential rotation effect. We suspect that the starspot latitudinal drift rate and the differential rotation gradient depend on the stellar spectral type.