银河系大尺度结构的统计分析

本文给出了在银道面第一象限中,原子氢气体HⅠ和CO分子及同位素分子~(13)CO发射之间的定量的大尺度相关分析。得到以下结论:(1)发射度E(~(13)CO)和E(~(12)CO),在l=11°—45°,b=0°大部分区域内总是线性相关的。(2)在内银道面第一象限内,不仅是在按简单几何划分的大部分区域,而且在按现存旋臂模型划分的一些特殊区域,HⅠ和CO发射也是大尺度线性非相关的。(3)看来CO发射度只在不多的几个区域中示踪HⅠ。但从平均-平滑E(HⅠ)和E(~(12)CO)的比较分析中,仍然难以确定分子云示踪HⅠ或可能由HⅠ形成的结论。     

分子外流区W75—N的^13CO（J=1—0）观测

使用日本国名古屋大学4m射电望远镜于1994年12月22日对分子外流区W75—N的~(13)CO(J=1-0)跃迁(110GHz)进行了观测。得到了该区域的7×7个观测点(grid 为2角分)的积分强度MAP图,通过对所观测到的双峰谱线进行研究,得到了该区域~(13)CO源的两个成份。     

若干恒星形成区的^12CO（J=1—0）与^13CO（J=1—0）观测

首次利用紫金山天文台青海观测站13.7m毫米波射电望远镜对若干分子云与恒星形成区的~(12)CO(J=1—0)和~(13)CO(J=1—0)分子辐射进行了观测,得到了各自中心位置的谱线轮廓。作为一个实例本文将介绍如何通过对分子云~(12)CO(J=1—0)和~(13)CO(J=1—0)谱线的综合分析与计算得到云中的物理参数。     

恒星形成区AFGL 5157的CO同位素分子谱线研究

通过对恒星形成区AFGL 5157进行了24′×24′(12 pc×12 pc)的成图观测,得到了该分子云的~(13)CO(J=1-0)和C~(18)O(J=1-0)云核各自的分布结构和平均物理参数.在云核的边缘位置,同位素丰度比X[(~(13)CO)/(C~(18)O)]约为10,接近于巨分子云的比值.~(13)CO和C~(18)O云核的维里质量小于云核质量,具有引力不稳定性,且C~(18)O云核更易塌缩.C~(18)O分子云核的东北方向和西南方向的分子云柱密度分布分别为1.1×10~(23)×z~(-0.43)和4.6×10~(25)×z~(-0.58),z表示到云核中心的距离.由~(12)CO(J=1-0)高速线翼成份的测量,估计了外流源的质量损失率,求得外向流的质量和速度的关系近似为m∝v~(-1.8).~(13)CO分子云核的恒星形成率为23%,该区域可能受反射星云NGC 1985的触发而正在形成中大质量恒星或者星团.     

沿切向点轨迹CO和HⅠ的发射度与旋臂段的比较

为了在研究银河系结构时摆脱由运动学不确定性带来的困难,本文导出了沿银道面切向点轨迹HⅠ和CO发射度的径向和银经分布。所用的谱线资料范围是10°相似文献   

恒星形成区的云核和星团

利用青海站13.7 m毫米波望远镜对17个与星团成协的恒星形成区进行了~(12)CO(J=1-0)、~(13)CO(J=1-0)和C~(18)O(J=1-0)的同时成图观测.除了IRAS04547+4753,这些源均探测到较强的C~(18)O(J=1-0)的谱线发射.由于分子云的大小不同,有13个源观测到~(13)CO(J=1-0)谱线积分强度极大值的一半处,其他源因分子云延展范围较大,没有进行大面积的成图观测.基于观测数据,计算了各云核的谱线线宽、亮温度、尺度、密度和质量等,~(13)CO和C~(13)O云核的维里质量与局部热动平衡(LTE)质量之比分别为0.66和0.74,它们接近于维里平衡状态.为了从形态方面比较云核与星团,将谱线的积分强度图与2MASS的K波段图像叠加.同时,计算了与云核成协的星团的大小和质量,数据采用了2MASS的近红外点源测光结果.基于云核与星团的质量结果,计算了分子云的恒星形成效率,大致在10%～30%的范围.     

大质量恒星形成核区的特性：^12CO、^13CO和C^18O的谱线观测及统计比较

利用青海站的13.7米射电望远镜对河内24个与水脉泽源成协并有红外Spitzer数据的巨分子云核进行12CO(J=1→0),13CO(J=1→0)和C18O(J=1→0)的同时成图观测,平均的成图范围为81×81.并全部探测到了C18O的谱线发射,其中11个源有较大范围(51-81)的C18O成图,这些分子云核均观测到C18O(J=1→0)谱线积分强度极大值的一半处,其余的13个源由于信噪比低或者成图范围较大等原因,没有进行如此大面积的成图观测.对样本中的11个已成图的稠密核进行了云核特性的分析并统计比较了CO与13CO,13CO与C18O及CO与C18O谱线积分强度之比(R12/13,R12/13,R12/18),结果是,C18O是光学薄的,可以探测到云核更加细致的结构.从核中心到边缘,3种谱线积分强度比是逐渐增加的.CO与13CO的谱线积分强度比R12/13的范围在2-6之间;13CO与C18O的比值R13/18范围在4-20之间波动,中心区域其值大部分集中在6-12之间,变化范围波动不是很大;CO与C18O之比R12/18在13-90更大的范围内,在更加致密的云核中心该比值集中在13-50之间.     

旋涡星系的厚度的估算

本文利用文[1]中所求得的扰动引力势的严格解,当此解由无旋臂区向有旋臂区连续过渡时,在解中出现一非波动项,对此项作出估计,可得出厚度(H=2/α)与开始形成旋臂处的半径的r_0关系:αr_0=7(α为星系半厚度的倒数).我们由[2]选出了50颗旋涡星系,并测定了它们的r_0,由此定出了星系盘的平均厚度.     

高银纬区域HSVMT 27的CO同位素分子谱线研究

对Ursa Major区域的高银纬分子云HSVMT 27的~(12)CO、~(13)CO和C~(18)O进行了观测研究,发现这块分子云~(12)CO的激发温度较低,并探测到一定的C~(18)O辐射,但由于其发射较弱故未能成图.在0.17 km·s~(-1)的速度分辨率和0.08 pc的空间分辨率下,认证了26个~(13)CO分子云核,它们的本地热平衡(Local Thermodynamic Equilibrium,LTE)质量在0.5–10 M_⊙,均小于其维里质量,且并未发现有红外点源与云核成协.总之,数据显示在这块分子云中并没有恒星形成的活动.     

富氧AGB星在银河系中的分布

根据ｖａｎｄｅｒＶｅｅｎ（１９８８）划分的ＩＲＡＳＰＳＣ的ＩＲＡＳ双色图区域选择了一批富氧ＡＧＢ星的样本，对其银河系分布进行的分析表明：它们属于盘星系，主要分布在旋臂上，将其旋臂结构与已知的ＨＩＩ区的旋臂结构进行拟合，得到这批富氧ＡＧＢ星的平均光度为８３００Ｌ⊙（Ｒｏ＝８．０ｋｐｃ），     

Massive star formation in the southern Milky Way

During the past decade we have compiled a large molecular line data base of massive star forming regions in the southern Milky Way. These regions are confined into giant molecular clouds that trace the galactic spiral arms. Their radial distribution has a pronounced peak midway between the Sun and the galactic center, which in the IV quadrant corresponds to the location of the Norma Spiral arm. We study in some detail one of the foremost regions of massive star formation in the Norma arm, using millimeter continuum and line emission maps obtained with the SEST, APEX, and ASTE telescopes. It is a multiple system evolving along a complete GMC core, candidate for future ALMA observations.     

On the spiral structure in the galactic distribution of co clouds

The CO distribution in the Galaxy is investigated through an analysis of longitude-velocity diagrams of CO emission lines for the two longitude ranges 20°<l<80° and 105°<l<140°. For the kinematics of the Galaxy we adopt the three typical models; the circular rotation, the linear density waves, and the galactic shock waves. It is shown that the distributions and kinematics of CO clouds are consistent with the predictions of the density wave model and the galactic shock model, and that the observed data of CO emissions do not contradict with the claim that the CO clouds form spiral arms.     

The spiral structure in the inner parts of the Galaxy

The spiral structure of the inner parts of the Galaxy is studied using 21 cm line data and stellar data. To study the neutral hydrogen distribution in the galactic layer a parameter =(dV/dr) proportional to the mean densities is calculated using a first approximation for the velocity gradients due to differential rotation.The obtained distribution (R, Z) shows spiral features completely consistent with the early star distribution and with the Hii regions. The corrugation effect of the galactic layer is observed in all the studied zones in neutral hydrogen and in the distribution of the OB stars in the Carina zone.The pattern obtained indicates four spiral arms for the inner parts of the Galaxy, three of which are identified also in the stellar data (arms -I, -II, and -III) and the more distant -IV in Hii regions.The local arm according to the stellar data of Kilkennyet al. forms a feature completely similar to the arms -I and -II and there are no indications that this arm is a special material branch between two main spiral arms as has been supposed in order to conciliate the neutral hydrogen pattern with the stellar distribution.The pitch angles for the spiral arms are approximately 13°–17°.The observed wave form distribution of the hydrogen cloud layer is completely consistent with the theoretical predictions of Nelson (1976) but there are no indications of such an effect in the intercloud hydrogen. The corrugated cloud layer has a width of 100 pc, a wave amplitude of 70 pc, and a wavelength which grows with the galactic center distance (approx. 2 kpc in the zones next to the galactic nucleus and 2.6–3.0 kpc in the zones next to the Sun). To each wavelength correspond two spiral arms. The spiral features in our Galaxy show characteristics quite similar to the features in the Andromeda nebula, not only in the component materials (neutral hydrogen, Hii regions and possibly also dust and stars) but also in their kinematics.     

The distribution of the galactic diffuse radio background

The distribution of the galactic radio emission is analyzed and a three component model (Halo, Base Disk and Spiral Arms) of the observed radiation examined.To reach agreement between temperature measured at low and high galactic latitudes we need: (a) a low emissivity spherical halo, (b) the Sun inside the local spiral arm somewhere between the arm axis and the arm outer edge, and (c) free circulation of the radiating electrons between the three emitting regions.     

Arm and Interarm Star Formation in Spiral Galaxies

We present an outline of our study of the effects of star formation on the different components of the interstellar medium in the discs of spiral galaxies, both globally and as a function of arm and interarm environment. We are in the process of obtaining images of 57 spiral galaxies at low inclinations, and analysing them to study the distribution of recent massive star formation, old stars, young stars, gas and dust. We will dissect the images into arm and interarm regions and compare and contrast the morphology and scale lengths within these regions inH_α, HI, the near infrared, optical and (where available) CO. Modelling will show how the scale lengths are affected by star formation, how this differs between arms and interarms, and whether the Schmidt Law varies from the global values in the arm and interarm regions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Meta-analysis from different tracers of the small Local Arm around the Sun—extent,shape, pitch,origin

The Sun in not located in a major spiral arm, and sits in a small ‘Local Arm’ (variously called arm, armlet, blob, branch, bridge, feather, finger, segment, spur, sub-arm, swath, etc.). The diversity of names for the ‘Local Arm’ near the Sun indicates an uncertainty about its shape or pitch or its extent from the Sun in each galactic quadrant, as well as an uncertainty about its origin.Here we extract data about the small ‘Local Arm’ near the Sun, from the recent observational literature, over many arm tracers, and we use statistics in order to find the local arm’s mean extent from the Sun, its possible shape and pitch angle from the direction of galactic longitude \(90^{\circ}\). Employing all tracers, the Local Arm is about 4 kpc long by 2 kpc large. The Sun is within 1 kpc of the center of the local arm. Proposed ‘bridges’ and ‘fingers’ are assessed. These bridges to nearby spiral arms and fingers across spiral arms may not reach the nearest spiral arms, owing to kinematic and photometric distance effects.We then compare these statistical results with some predictions from recent models proposed to explain the local arm (perturbations, resonances, density wave, halo supercloud, debris trail from a dwarf galaxy).The least controversial models involve importing materials from elsewhere (halo supercloud, debris trail) as a first step, and to be later deformed in a second step (by the Galaxy’s differential rotation into become roughly parallel to spiral arms) and then subjected to ongoing forces (global density waves, local perturbations).     

旋涡星系中旋臂的维持

为了避开旧物质臂理论中旋臂的缠绕困难，本文提出了旋涡星系的循环假设，并在文中提供了旋涡星系的双臂、气体层反卷、银河系中旋臂物质径向向内的速度分量和棒旋星系中棒物质沿着棒向内的流动等观测证据，进而还尝试利用此循环假设去解释旋臂物质的平自转曲线和棒旋星系的棒结构等的成因。     

The Abundance Ratio C/O in the Atmospheres of 89 Carbon Stars

The abundance ratio C/O in the atmospheres of 89 faint carbon stars are detected on the basis of spectra obtained on 2.6 m telescope of Byurakan AO. The frequency distribution of C/O in the Perseus galactic arm differs from that in the Orion arm. The conclusion is made that the reason of the difference may be the heavy element abundance differences in these galactic arms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure of the magnetic field near the galactic plane

A method is introduced for constructing two-color maps for the in-plane component of the magnetic field of our galaxy in (R, l) and (DM, l) coordinates. It is shown that, in agreement with the standard models of the galactic magnetic field, the magnetic field in neighboring spiral arms reverses direction. However, the magnetic field in the spiral arm of Sagittarius differs significantly from the standard magnetic field model, with the major difference being that the magnetic fields in the southern and northern hemispheres are oppositely directed in the spiral arm of Sagittarius. It is proposed that this distribution of the magnetic field can be explained best by assuming that the spiral arm of Sagittarius, or, at least, a magnetic spiral arm in that region, is not symmetric with respect to the galactic plane and lies mainly in the northern hemisphere.     

Distribution of classical cepheids in the galactic plane

Major spiral arms were traced from the distribution of long-period classical cepheids on the projected galactic plane. The position of these spiral features have been compared with those from other optical tracers such as H II regions and OB star groups. Also the galactic longitude distribution of classical cepheids and open clusters are compared.