共查询到20条相似文献，搜索用时 171 毫秒
1.
岳曾元 《中国天文和天体物理学报》1983,(2)
本文将指出,为得到有限厚度旋涡星系中平均扰动引力势φ_1(r)与扰动面密度σ_1(r)的渐近关系,以及对称面上的扰动引力势φ_1(r,0)与σ_1(r)的渐近关系,我们不一定要从相应的三维渐近关系出发,而可以用二重级数展开方法直接地、十分简单地导出。所得结果对于紧卷性准确到m~2(kr)~(-2)量级,对于厚度效应准确到 k〈|z|〉量级,其中m为旋臂数,k为径向波数,r为到星系中心的径向距离,〈|z|〉为星到对称面距离的平均值。这样的精度对于讨论有限厚度扁盘状星系中密度波模式及其增长率通常是足够的。本文结果表明:在上述精度下,如采用〈|z|〉表征厚度,则不同纵向密度剖面下的φ_1(r,0)～σ_1(r)渐近关系可表为统一形式;如采用二星纵向平均距离〈|z-z’|〉表征厚度,则不同纵向密度剖面下的φ_1(r)～σ_1(r)渐近关系可表为统一形式。只有比值〈|z-z’|〉/〈|z|〉才是纵向密度剖面的泛函。对于符合物理意义的通常各种不同密度剖面,此比值都甚接近:对于高斯型纵向密度剖面,此比值为2~(1/2);对于 sech~2(z/z_1(r))型剖面,此比值为 1/In2=1.443;对于 exp[-|z|/z_1(r)]型剖面,此比值为1.5。 相似文献
2.
根据最近发表的新编依巴谷星表数据,重新研究了经典造父变星周光关系零点问题.利用运动学模型对自行数据和视向速度分别拟合奥尔特常数及本地静止标准的旋转速度,得到太阳的银心距R0=8.0±0.8kpc.从太阳附近的旋转曲线,发现银河系盘的引力势具有弱椭圆分布的迹象.通过-个简单的非对称模型,得到太阳附近盘引力势的椭率e(R0)=0.067±0.036,其短轴指向φb=32°±15°. 相似文献
3.
利用 2 0 2个太阳附近疏散星团的视向速度和自行观测资料 ,对太阳的运动和银河系的运动学参数进行了研究。其中 ,距离在 0 .5kpc到 2kpc之间的 12 8个疏散星团对平均太阳运动分量的解算结果是 (u0 ,v0 ,w0 ) =(- 13.8± 1.4 ,- 5 .0± 1.6 ,- 11.6± 2 .9)km/s ;Oort常数和银河系径向运动参数的解算结果分别为 (A ,B) =(16 .9± 1.1,- 11.6± 2 .6 )km·s- 1·kpc- 1及 (C ,D) =(2 .5± 1.1,- 2 .1± 0 .9)km·s- 1·kpc- 1。 相似文献
4.
Meng Zhai Xiang-Xiang Xue Lan Zhang Cheng-Dong Li Gang Zhao Cheng-Qun Yang 《天文和天体物理学研究(英文版)》2018,(9)
We constrain the mass of the Milky Way's dark matter halo, based on the kinematics of 9627 K giants at Galactocentric distances ranging over 5 kpc r 120 kpc drawn from LAMOST DR5.The substructure in this sample has been identified and removed carefully to enable construction of the underlying line-of-sight velocity dispersion at different radii from the Galactic center. We interpret the radial profile of the line-of-sight velocity dispersion using a spherical Jeans equation under the assumptions of anisotropy/isotropy and that radial velocity dispersion is approximately equal to line-ofsight velocity dispersion σ_r(r)≈σ_(los)(r). If we assume that the dark matter halo follows an NFW profile and the stellar halo is isotropic(β = 0), then σlos(r) can be directly used to estimate the virial mass of the Galactic dark matter halo, M_(vir) = 1.08_(-0.14)~(+0.17) ×10~(12) M⊙, and concentration parameter c = 18.5+-2.9.3.6 In case that the stellar halo is anisotropic, we cannot avoid differentiation of sparse velocity dispersions according to the Jeans equation, which may cause overestimation of the mass. We use an isotropic case to test and find that d ln(σ_(los)~2 (r))/d ln r overestimates the virial mass by 15% but within 1-σ error. We use d ln(σ2 los(r))/d ln r to fit the NFW profile and get M_(vir) = 1.11_(-0.20)~(+0.24) ×10~(12) M⊙and c = 13.8-2.2+3.0 in case of β = 0.3. 相似文献
5.
选用银河系中29个累积光谱型为F型的球状星团样本。根据它们的视向速度，绝对自行等参数，归算处理后得出了各样本星团的空间分布和运动速度。并以此作为初始条件，在给定的3种银河系引力势模型中，采用数值积分方法计算出各样本星团的运动轨道。计算结果表明：（1）大部分样本星团都位于银心距5kpc-10kpc的范围内，相对于银心呈球对称分布，它们的速度也呈椭球分布；（2）29个样本星团按其金属度大小和基本性发类，可分属HB和MP两个次系，且样本星团数随金属度[Fe/H]而变化，在[Fe/H]＝－1．6处出现一个峰值；（3）所有样本星团的轨道运动都呈周期性，大都在一个有界而不封闭的周期轨道上运动，其最大银心距大都在40kpc以内。不同的引力势模型对球状星团轨道的具体形态影响不大，在给定的引力势模型下，当某些星团的运动轨道穿越距银心1kpc附近的区域时会出现“混沌”行为。而样本星团的金属度与其轨道形态之间的相关性并不明显；（4）29个样本星团的轨道半长轴、远银心距和方位周期随金属度的变化规律基本相似。轨道偏心率与金属度有关，对于所选的晕族样本星团而言，大约有24％的样本星团的轨道偏心率低于0．4，不同的引力势模型对近银心距、偏心率和参数的不确定度等量影响较小，但是对远银心距、径向周期和方位周期等参数影响较为明显。 相似文献
6.
《天文和天体物理学研究(英文版)》2021,(10)
Gamma-ray bursts (GRBs) are brief,intense,gamma-ray flashes in the universe,lasting from a few milliseconds to a few thousand seconds.For short gamma-ray bursts (s GRBs) with duration less than 2 seconds,the isotropic energy (E_(iso)) function may be more scientifically meaningful and accurately measured than the luminosity (L_p) function.In this work we construct,for the first time,the isotropic energy function of s GRBs and estimate their formation rate.First,we derive the L_p-E_pcorrelation using22 s GRBs with known redshifts and well-measured spectra and estimate the pseduo redshifts of 334 Fermi s GRBs.Then,we adopt the Lynden-Bell c~-method to study isotropic energy functions and formation rate of s GRBs without any assumption.A strong evolution of isotropic energy E_(iso)∝(1+z)~(5.79)is found,which is comparable to that between L_pand z.After removing effect of the cosmic evolution,the isotropic energy function can be reasonably fitted by a broken power law,which isφ(E_(iso,0))∝E~(-0)_(iso),._0~(45)for dim s GRBs andφ(E_(iso,0))∝E~(-1)_(iso),._0~(11)for bright s GRBs,with the break energy 4.92×10~(49)erg.We obtain the local formation rate of s GRBs is about 17.43 events Gpc~(-3)yr~(-1).If assuming a beaming angle is 6?to 26?,the local formation rate including off-axis s GRBs is estimated asρ_(0,all)=155.79-3202.35 events Gpc~(-3)yr~(-1). 相似文献
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本文利用最大似然原理求解移动星团问题，同时确定了昂星团的平均距离和运动学参数及其相应的弥散度·归算结果得到昂星团距离为d=135．6±0．7pc，相应弥散度。σd=7.7±08pc；昂星团平均空间速度为V=25.9±0．1km／s，相应弥散度σv=0．6±0．1km／s，以及昴星团会聚点坐标（A，D）＝（6h47m24s±2m00s-47°．4±0°.3.）。 相似文献
8.
《天文和天体物理学研究(英文版)》2016,(10)
We investigate the statistical effects of non-discrete timing irregularities on observed radio pulsar braking indices using correlations between the second derivative of the measured anomalous frequency(■_(obs)) and some parameters that have been widely used to quantify pulsar timing fluctuations(the timing activity parameter(A),the amount of timing fluctuations absorbed by the cubic term(σ_(R23)) and a measure of pulsar rotational stability(σ_z)) in a large sample of 366 Jodrell Bank Observatory radio pulsars.The result demonstrates that anomalous braking indices are largely artifacts produced by aggregations of fluctuations that occur within or outside the pulsar system.For a subsample of 223 normal radio pulsars whose observed timing activity appeared consistent with instabilities in rotation of the underlying neutron stars(or timing noise) over timescales of ~10-40 yr,|■_(obs)| strongly correlates(with correlation coefficient|r|~0.80-0.90) with the pulsar timing activity parameters and spin-down properties.On the other hand,no meaningful correlations(r0.3) were found between■_(obs) and the timing activity diagnostics and spindown parameters in the remaining 143 objects,whose timing activity appears significantly dominated by white noise fluctuations.The current result can be better understood if the timing noise in isolated pulsars originates from intrinsic spin-down processes of the underlying neutron stars,but white noise fluctuations largely arise from processes external to the pulsar system. 相似文献
9.
汪洵浩 《中国天文和天体物理学报》1988,(1)
近年来,谭徽松等人以所选用标准星的观测轮廓与Gray的转致轮廓直接卷积,再与被测星观测轮廓比较,由此来测量了一些恒星的自转。在这种方法中,当所选标准星自转速度不严格为零时,将引入误差。本文在标准星速度(vsini)_s较小的条件下,进行函数展开,先后给出了轮廓修正关系式R_0(λ)=R(λ)-α_2(△λ_L)_s~2R″(λ),及速度修正关系式(vsini)_0~2=(vsini)~2+(vsini)_s~2。并估算说明,当标准星速度(vsini)_s<5km/s,而被测星速度vsini>20km/s时,该误差可不考虑。 相似文献
10.
武仙座A(3C348)是一个在低频波段上亮度占第四位的河外射电源。从光学上证认,它是一个位于暗星团中的18.5等的星系,红移Z=0.154。虽然早在1948年就发现了它,并在六十年代对它进行了广泛的研究,但因为其赤纬很低,所以未能用高分辨率的综合孔径射电望远镜得到其结构图。本文报道了用NRAO甚大阵(VLA)对武仙座A作了广域观测后的第一批结果。 武仙座A有许多有趣的特征;一、它是已知的最亮的射电星系之一,其H_0=75km·s~(-1)Mpc~(-1),q_0=0,在5GHz上辐射功率密度为p_(5,000)=6×10~(26)W·Hz~(-1),约为天鹅座A功率密度的1/4。由于它的尺度较大(最宽处达460kpc),所以它所具有的总能量几乎等于天鹅座A的总能量,约为3×10~(60)尔格。二、尽管它的光度很大,但它的结构却具有低光度源的特征。一般来说,高光度源(p_(5,000)>10~(25)W·Hz~(-1))由 相似文献
11.
The system of spurs (radio loops I-IV) is organically inscribed in the ecliptic coordinate system (ECS). It defines one of the equators of the triaxial Local System (S). The Gould, Vaucouleurs-Dolidze, and other Belts in the role of meridians are orthogonal to S. The axis of another equator coincides with the equinoctial line. The ECS connects the structures and kinematics of three hierarchical levels: the solar system, the Local System, and the Galaxy. 相似文献
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An analytical representation and observational verification of a new harmonic scheme for the local system are presented. In it massive shell structures (spurs) play a dominant role, in combination with belts of stars, gas and dust. The geometry of the triaxial local system is closely coupled to the ecliptic coordinate system. Each axis has its own equator and its own discrete, periodic system of meridians. The largest axis, z, is normal to the S plane passing through the cores of four spurs (I-IV). Six meridians intersect along this axis, including the Gould belt (GB), the Vaucouleurs-Dolidze (V-D) belt, and the G plane, which is perpendicular to the ecliptic E at the solstice points. Four meridians, including E and S, intersect along the middle axis x, which coincides with the equinoctial line. The z axis is inclined by H"45° to E and by H"21° to the galactic plane. The overall number of nonrepeating principal planes in the local system is nine. Counts of stars brighter than V=9m confirms that they are concentrated along all the principal planes. As a symmetry plane, the meridian perpendicular to the Gould belt ( GB) divides the system of spurs into two groups: (I, IV, Dor) and (II, III, Eri). Each encompasses a grid of 5 halves of the z meridians and isolates a group and the spurs within the group. At the same time, as bridges the x meridians and their equator G couple the cores of some of the spurs with the shells of others both within their own and in opposite groups. The convergence of the meridians (belts) to the X, Y, and Z poles couples all the details with the local system as a whole. The symmetry of the local system with its discrete elements resembles a crystal. 相似文献
13.
疏散星团是探究银河系结构与演化的良好示踪体,一直以来颇受关注.之前关于疏散星团的研究中,仅有一小部分疏散星团有金属丰度参数,而且,金属丰度的测量,是基于不同质量的观测数据,采用了不同的方法.收集了一个年龄大于2 Gyr的老年疏散星团样本,通过整理这些星团成员星的金属丰度数据,一方面,以星团NGC 2682为例,对比了不同光谱巡天项目给出的星团成员星金属丰度的系统差异;另一方面,计算了星团成员星金属丰度的平均值和中位值,作为该疏散星团的金属丰度推荐值.此外,还利用该样本探究了银盘径向金属丰度梯度随时间的演化,结果表明,早期银盘有着更加陡峭的径向金属丰度梯度,随着演化时间的增加,银盘径向金属丰度梯度逐渐趋于平缓,为银盘化学演化模型提供了更加严格的观测约束. 相似文献
14.
J.-M. Carquillat J.-L. Prieur 《Monthly notices of the Royal Astronomical Society》2007,380(3):1064-1078
Red clump giant (RCG) stars can be used as distance indicators to trace the mass distribution of the Galactic bar. We use RCG stars from 44 bulge fields from the OGLE-II microlensing collaboration data base to constrain analytic triaxial models for the Galactic bar. We find the bar major-axis is oriented at an angle of 24°–27° to the Sun–Galactic Centre line-of-sight. The ratio of semimajor and semiminor bar axis scalelengths in the Galactic plane x 0 , y 0 , and vertical bar scalelength z 0 , is x 0 : y 0 : z 0 = 10 : 3.5 : 2.6 , suggesting a slightly more prolate bar structure than the working model of Gerhard which gives the scalelength ratios as x 0 : y 0 : z 0 = 10 : 4 : 3 . 相似文献
15.
Amina Helmi 《Astronomy and Astrophysics Review》2008,15(3):145-188
Stellar halos may hold some of the best preserved fossils of the formation history of galaxies. They are a natural product
of the merging processes that probably take place during the assembly of a galaxy, and hence may well be the most ubiquitous
component of galaxies, independently of their Hubble type. This review focuses on our current understanding of the spatial
structure, the kinematics and chemistry of halo stars in the Milky Way. In recent years, we have experienced a change in paradigm
thanks to the discovery of large amounts of substructure, especially in the outer halo. I discuss the implications of the
currently available observational constraints and fold them into several possible formation scenarios. Unraveling the formation
of the Galactic halo will be possible in the near future through a combination of large wide field photometric and spectroscopic
surveys, and especially in the era of Gaia. 相似文献
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Lyα Blobs (LAB), large, extended Lyα emitters, are enigmatic objects that calls on much attention in the field of galaxy formation and evolution. So far, discovery of more than twenty giant (>60 kpc) LABs have been reported and new searches are on-going. Many of the groups who study LABs attended the workshop in Heidelberg, “Understanding Lyα Emitters”, 2008 October 6–10. We had useful discussions on the various important aspects of LABs including the search or detection methods, origins of the extended Lyα emission, and their physical properties. 相似文献