Probing the Kinematic Signatures of Planet Formation in the Gas Disk of MWC 480

The disk around MWC 480 has shown multiple substructures in both dust and gas observations,possibly suggesting ongoing planet formation in situ.In this paper,we explore the gas kinematics of the MWC 480 disk by analyzing the archival Atacama Large Millimeter/submillimeter Array observations of^(12)CO(J=2-1),^(13)CO(J=2-1),and C^(18)O(J=2-1).By modeling the line-of-sight velocities,inferred from the Doppler shifts of the emission lines,we are able to decompose the three-dimensional(3D)velocity field of the disk into rotational,radial,and vertical components.Further analysis reveals the presence of large-scale gas flows in the(r,z)plane.Notably,we identify potential meridional flows across various heights as traced by all three CO isotopologues in the 80–120 au region,possibly associated with ongoing planet formation activities in this region.Moreover,we find upward flows near 200 au for all three CO isotopologues,which may point to the presence of disk winds.

基于无量纲的轨道参数开展卫星性质统计研究

目前已发现了285颗围绕太阳系八大行星公转的卫星,它们的轨道和物理性质呈现了丰富多样性.目前为止,几乎所有的卫星研究工作都基于单个卫星系统或者卫星群,似乎缺少统一的研究.提出了一个新的与行星性质无关、只与恒星半径有关的轨道参数n,定义为以太阳半径为单位的轨道半长轴的自然对数.不同行星的卫星的n值都存在双极分布,绝大部分卫星在n≥2区间,其次在n≤-1区间,位于中间区域的行星则很少.从卫星物理参数和轨道参数与n的关系中发现,分属六大行星的卫星有明显的共同特征.首先,轨道偏心率和轨道倾角偏大的卫星的n值都在3.5左右,它们都是巨行星的不规则卫星.其次,n值在-1和1之间的卫星绝大部分体积大、质量大、反照率高、自转速度慢.从文献中找到11颗系外卫星候选体,获得了它们轨道n值和卫星质量,发现后者也是在-1 <n<1区间最大,其他区间偏小.这些统一的规律暗示,太阳系内不同行星的卫星形成机制以及太阳系外卫星的形成机制可能一样或类似.

太阳系行星系统的形成和演化

本文评述了星云和星子假说、太阳星云的崩塌、星盘的形成和演化、颗粒生长、星子增生、类地行星和类木行星的形成、行星迁移,以及太阳和行星的演化。

太阳系外行星研究进展

过去的二十年间,利用多种技术(如脉冲时间、径向速度、天文学观测、穿越光度计、反射光度计、微透镜和直接图像)发现了405个太阳系外行星。对这些太阳系外行星的研究首次提供了有关行星生长的信息,诸如星盘结构和演化,星盘性质和大小等。2009年4月对GJ581d行星的观测表明,这个行星处于"宜居区域"内,意味着它有液态水,因此可能有生命存在。

Forming different planetary systems

With the increasing number of detected exoplanet samples, the statistical properties of planetary systems have become much clearer. In this review, we sum- marize the major statistical results that have been revealed mainly by radial velocity and transiting observations, and try to interpret them within the scope of the classical core-accretion scenario of planet formation, especially in the formation of different orbital architectures for planetary systems around main sequence stars. Based on the different possible formation routes for different planet systems, we tentatively classify them into three major catalogs： hot Jupiter systems, standard systems and distant giant planet systems. The standard systems can be further categorized into three sub-types under different circumstances： solar-like systems, hot Super-Earth systems, and sub- giant planet systems. We also review the theory of planet detection and formation in binary systems as well as planets in star clusters.

Volatile Depletion in Planet-Forming Disks

Newly born stars are surrounded by gas and dust with a attened axisymmetric distribution termed protoplanetary disk,in which planets are formed.Observations of these objects are necessary for understanding the formation and early evolution of stars and planets,and for revealing the composition of the raw material from which planets are made.Numerical models can extract important parameters from the observational data,including the gas and dust mass of the disk.These parameters are used as input for further modeling,e.g.,to calculate the chemical composition of the disk.A consistent thermochemical model should be able to reproduce the abundances of di erent species in the disk.However,this good wish has been challenged for many disks:models over-predict the emission line intensity of some species;namely,they are depleted(with respect to expectations from canonical models).In this review we show how this disparity indicates that dust evolution has signi cant e ects on gas chemistry,and may indicate the earliest stages of planet formation.

Vega碎片盘的结构特性研究

Vega的碎片盘在早期的观测中出现特殊结构,这可能是其内部存在潜在的高偏心率行星导致的.但是,近期对Vega的多波段高分辨率观测显示,Vega的碎片盘是一个平滑的盘结构,这虽然不能否定其内部存在行星的假说,但是对其中潜在行星的某些轨道参数提供了限制条件.使用数值模拟的方法对Vega系统的碎片盘和可能存在的行星进行模拟.模拟中碎片盘位于80～120 AU.盘中尘埃尺寸为10～100μm,轨道偏心率与倾角都非常小.通过多组计算的结果发现,如果Vega系统中不存在行星,那么其碎片盘演化结果与最新的观测结果吻合得较好;如果存在行星,且行星偏心率较大(比如e=0.6)时,那么行星的轨道半长径不能大于60 AU,否则碎片盘会在行星的影响下产生明显的聚集现象.行星与碎片盘的2:1平运动共振是导致碎片盘产生结构的主要原因.

雪线在原行星盘中的演化

本文研究雪线在原行星盘中的整体演化行为.盘子模型中新的数值结果被采用来模拟各种物理机制(包括从中央原恒星到吸积盘上的辐射,热电离机制引起的粘滞系数,引力不稳机制,光致蒸发机制,最新的中央原恒星的半径和表面有效温度).盘子模型中,雪线随着时间演化的整体变化趋势如下:雪线首先向外扩张至一个最大值,然后再向内收缩.而且雪线在这个过程中会出现剧烈的抖动,这是一个新的现象,值得进行更深的研究.雪线抖动是多个因素共同作用的结果,包括引力不稳机制,原行星盘中的四个产热机制,磁转动不稳机制等等.另外,还研究了雪线在原行星盘中的演化行为和抖动行为对父辈分子云核的性质参量的依赖关系.发现雪线的演化行为和抖动行为对父辈分子云核的性质参量(质量Mcore,和角速度ω)和流体动力学参量αmin有很强的依赖关系.

Single planet formation regime in the high-ionization environment:Possible origin of hot Jupiters and super-Earths

We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Solar System. In particular, in the case of M 〈 10^（-7.4）M_☉yr^（-1）, only rocky planet formation occurs. In such a case, all the solid materials in the disk drift inward, eventually reach the inner MRI front,and accumulate there. They form a dense, thin sub-disk of solid particles, which undergoes gravitational instability to form rocky planetesimals. The planetesimals rapidly grow into a planet through pebble accretion. Consequently, rocky planets tend to be much larger than planets formed through other regimes（tandem planet formation regime and dispersed planet formation regime）, in which icy planet formation actively takes place. These rocky planets may evolve into hot Jupiters if they grow fast enough to the critical core mass of the runaway gas accretion before the dispersal of the disk gas, or they may evolve into super-Earths if the gas dispersed sufficiently early.

The origin of high eccentricity planets:The dispersed planet formation regime for weakly magnetized disks

In the tandem planet formation regime,planets form at two distinct sites where solid particles are densely accumulated due to the on/off state of the magnetorotational instability（MRI）.We found that tandem planet formation can reproduce the solid component distribution of the Solar System and tends to produce a smaller number of large planets through continuous pebble flow into the planet formation sites.In the present paper,we investigate the dependence of tandem planet formation on the vertical magnetic field of the protoplanetary disk.We calculated two cases of BZ 3.4 × 10^-3 G and BZ = 3.4 × 10^-5 G at 100 AU as well as the canonical case of BZ = 3.4 × 10^-4 G.We found that tandem planet formation holds up well in the case of the strong magnetic field（BZ 3.4 × 10^-3 G）.On the other hand,in the case of a weak magnetic field（BZ= 3.4 × 10^-5 G） at 100 AU,a new regime of planetary growth is realized：the planets grow independently at different places in the dispersed area of the MRl-suppressed region of r-8-30 AU at a lower accretion rate of M 〈 10^-7.4M⊙yr^-1.We call this the ＂dispersed planet formation＂ regime.This may lead to a system with a larger number of smaller planets that gain high eccentricity through mutual collisions.

The snowline in the protoplanetary disk and extrasolar planets

We investigate the behavior of the snowline in a protoplanetary disk and the relationship between the radius of the snowline and properties of molecular cloud cores.In our disk model,we consider mass influx from the gravitational collapse of a molecular cloud core,irradiation from the central star,and thermal radiation from the ambient molecular cloud gas.As the protoplanetary disk evolves,the radius of the snowline increases first to a maximum value Rmax,and then decreases in the late stage of evolution of the protoplanetary disk.The value of Rmaxis dependent on the properties of molecular cloud cores(mass M;,angular velocity ω and temperature T;).Many previous works found that solid material tends to accumulate at the location of the snowline,which suggests that the snowline is the preferred location for giant planet formation.With these conclusions,we compare the values of R;with semimajor axes of giant planets in extrasolar systems,and find that Rmaxmay provide an upper limit for the locations of the formation of giant planets which are formed by the core accretion model.

Tandem planet formation for solar system-like planetary systems

We present a new united theory of planet formation,which includes magneto-rotational instability（MRl） and porous aggregation of solid particles in a consistent way.We show that the ＂tandem planet formation＂ regime is likely to result in solar system-like planetary systems.In the tandem planet formation regime,planetesimals form at two distinct sites：the outer and inner edges of the MRl suppressed region.The former is likely to be the source of the outer gas giants,and the latter is the source for the inner volatile-free rocky planets.Our study spans disks with a various range of accretion rates,and we find that tandem planet formation can occur for M = 10^7.3- 10^-6.9Myr^-1.The rocky planets form between 0.4-2 AU,while the icy planets form between 6-30 All;no planets form in 2-6 AU region for any accretion rate.This is consistent with the gap in the solid component distribution in the solar system,which has only a relatively small Mars and a very small amount of material in the main asteroid belt from 2-6 AU.The tandem regime is consistent with the idea that the Earth was initially formed as a completely volatile-free planet.Water and other volatile elements came later through the accretion of icy material by occasional inward scattering from the outer regions.Reactions between reductive minerals,such as schreibersite（Fe-jP）,and water are essential to supply energy and nutrients for primitive life on Earth.

RV减速机行星架刚性盘组件精加工研究

介绍了RV减速机行星架刚性盘组件的结构,设计了行星架刚性盘组件的精加工工艺方案。从偏心轴孔同轴度误差、偏心轴系高度误差、组件拆装后精度误差等方面分析了RV减速机行星架刚性盘组件精加工工艺方案的控制要点。

A physical interpretation of the Titius-Bode rule and its connection to the closed orbits of Bertrand's theorem

We consider the geometric Titius-Bode rule for the semimajor axes of planetary orbits. We derive an equivalent rule for the midpoints of the segments between consecutive orbits along the radial direction and we interpret it physically in terms of the work done in the gravitational field of the Sun by particles whose orbits are perturbed around each planetary orbit. On such energetic grounds, it is not surprising that some exoplanets in multiple-planet extrasolar systems obey the same relation. However,it is surprising that this simple interpretation of the Titius-Bode rule also reveals new properties of the bound closed orbits predicted by Bertrand’s theorem, which has been known since 1873.

The effects of viscosity on circumplanetary disks

The effects of viscosity on the circumplanetary disks residing in the vicinity of protoplanets are investigated through two-dimensional hydrodynamical simulations with the shearing sheet model. We find that viscosity can considerably affect properties of the circumplanetary disk when the mass of the protoplanet Mp ~ 33 Me, where Me is the Earth＇s mass. However, effects of viscosity on the circumplanetary disk are negligibly small when the mass of the protoplanet Mp 〉 33 Me. We find that when Mp ~ 33 Me, viscosity can markedly disrupt the spiral structure of the gas around the planet and smoothly distribute the gas, which weakens the torques exerted on the protoplanet. Thus, viscosity can slow the migration speed of a protoplanet. After including viscosity, the size of the circumplanetary disk can be decreased by a factor of 〉~ 20%. Viscosity helps to transport gas into the circumplanetary disk from the differentially rotating circumstellar disk. The mass of the circumplanetary disk can be increased by a factor of 50% after viscosity is taken into account when Mp ~ 33 Me. Effects of viscosity on the formation of planets and satellites are briefly discussed.

Delay of planet formation at large radius and the outward decrease in mass and gas content of Jovian planets

A prominent observation of the solar system is that the mass and gas content of Jovian planets decrease outward with orbital radius, except that, in terms of these properties, Neptune is almost the same as Uranus. In previous studies, the solar nebula was assumed to preexist and the formation process of the solar nebula was not considered. It was therefore assumed that planet formation at different radii started at the same time in the solar nebula. We show that planet formation at different radii does not start at the same time and is delayed at large radii. We suggest that this delay might be one of the factors that causes the outward decrease in the masses of Jovian planets. The nebula starts to form from its inner part because of the inside-out collapse of its progenitorial molecular cloud core. The nebula then expands outward due to viscosity. Material first reaches a small radius and then reaches a larger radius, so planet formation is delayed at the large radius. The later the material reaches a planet＇s location, the less time it has to gain mass and gas content. Hence, the delay tends to cause the outward decrease in mass and gas content of Jovian planets. Our nebula model shows that the material reaches Jupiter, Saturn, Uranus and Neptune at t = 0.40, 0.57, 1.50 and 6.29 × 10^6 yr, respectively. We discuss the effects of time delay on the masses of Jovian planets in the framework of the core accretion model of planet formation. Saturn＇s formation is not delayed by much time relative to Jupiter so that they both reach the rapid gas accretion phase and become gas giants. However, the delay in formation of Uranus and Neptune is long and might be one of the factors that cause them not to reach the rapid gas accretion phase before the gas nebula is dispersed. Saturn has less time to go through the rapid gas accretion, so Saturn＇s mass and gas content are significantly less than those of Jupiter.

Gap formation in a self-gravitating disk and the associated migration of the embedded giant planet

We present the results of our recent study on the interactions between a giant planet and a self-gravitating gas disk. We investigate how the disk＇s self-gravity affects the gap formation process and the migration of the giant planet. Two series of 1-D and 2-D hydrodynamic simulations are performed. We select several surface densities and focus on the gravitationally stable region. To obtain more reliable gravity torques exerted on the planet, a refined treatment of the disk＇s gravity is adopted in the vicinity of the planet. Our results indicate that the net effect of the disk＇s self- gravity on the gap formation process depends on the surface density of the disk. We notice that there are two critical values, ∑I and ∑n. When the surface density of the disk is lower than the first one,∑0 〈 ∑I, the effect of self-gravity suppresses the formation of a gap. When ∑0 〉 ∑I, the self-gravity of the gas tends to benefit the gap formation process and enlarges the width/depth of the gap. According to our 1-D and 2-D simulations, we estimate the first critical surface density to be ∑I ≈ 0.8 MMSN. This effect increases until the surface density reaches the second critical value ∑n- When ∑0 〉 ∑n, the gravitational turbulence in the disk becomes dominant and the gap formation process is suppressed again. Our 2-D simulations show that this critical surface density is around 3.5 MMSN. We also study the associated orbital evolution of a giant planet. Under the effect of the disk＇s self-gravity, the migration rate of the giant planet increases when the disk is dominated by gravitational turbulence. We show that the migration timescale correlates with the effective viscosity and can be up to 104 yr.

环绕恒星的原行星盘:行星的“诞生摇篮”

2014年9月,智利北部阿塔卡马沙漠高原上新建成的阿塔卡马毫米/亚毫米波阵列(Atacama Large Millimeter/submillimeter Array,ALMA)进行了仪器测试,开展了持续的天文观测项目.ALMA是用干涉方法进行天文观测的射电天线阵,由66个天线构成,总长度达到16km.ALMA是一个国际合作建设的天文工程,由来自欧洲、北美和东亚等的各国(地区)合作运行.