Optical vortex coronagraph

We describe a method to observe dim exoplanets that eliminates light from the parent star across the entire exit pupil without sacrificing light from the planet by use of a vortex mask of topological charge m = 2.     

Disks around young stellar objects

By 1939, when Chandrasekhar’s classic monograph on the theory of Stellar Structure was published, although the need for recent star formation was fully acknowledged, no one had yet recognized an object that could be called a star in the process of being born. Young stellar objects (YSOs), as pre-main-sequence stars, were discovered in the 1940s and 1950s. Infrared excess emission and intrinsic polarization observed in these objects in the 1960s and 1970s indicated that they are surrounded by flattened disks. The YSO disks were seen in direct imaging only in the 1980s. Since then, high-resolution optical imaging with HST, near-infrared adaptive optics on large ground-based telescopes, mm and radiowave interferometry have been used to image disks around a large number of YSOs revealing disk structure with ever-increasing detail and variety. The disks around YSOs are believed to be the sites of planet formation and a few such associations have now been confirmed. The observed properties of the disk structure and their evolution, that have very important consequences for the theory of star and planet formation, are discussed.     

The gravitational bending of light by stars: a continuing story of curiosity,scepticism, surprise,and fascination

Driven entirely by human curiosity, the effect of the gravitational bending of light has evolved on unforeseen paths, in an interplay between shifts in prevailing paradigms and advance of technology, into the most unusual way to study planet populations. The confirmation of the bending angle predicted by Einstein with the Solar Eclipse measurements from 1919 marked the breakthrough of the theory of General Relativity, but it was not before the detection of the double image of the quasar 0957+561 that ‘gravitational lensing’ really entered the observational era. The observation of a characteristic transient brightening of a star caused by the gravitational deflection of its light by an intervening foreground star, constituting a ‘microlensing event’, required even further advance in technology before it could first emerge in 1993. While it required more patience in waiting before ‘Einstein’s blip’ for the first time revealed the presence of a planet orbiting a star other than the Sun, such detections can now be monitored live, and gravitational microlensing is not only sensitive to masses as low as that of the Moon, but can even reveal planets around stars in galaxies other than the Milky Way.     

Simulations for terrestrial planets formation

In this paper, the formation of terrestrial planets in the late stage of planetary formation is investigated using the two-planet model. At that time, the protostar formed for about 3 Ma and the gas disk dissipated. In the model, the perturbations from Jupiter and Saturn are considered. Variations of the mass of outer planet, and the initial eccentricities and inclinations of embryos and planetesimals are also considered. Our results show that, terrestrial planets are formed in 50 Ma, and the accretion rate is about 60%–80%. In each simulation, 3–4 terrestrial planets are formed inside “Jupiter” with masses of 0.15–3.6 M _⊕. In the 0.5–4 AU, when the eccentricities of planetesimals are excited, planetesimals are able to accrete material from wide radial direction. The plenty of water material of the terrestrial planet in the Habitable Zone may be transferred from the farther places by this mechanism. Accretion could also happen a few times between two major planets only if the outer planet has a moderate mass and the small terrestrial planet could survive at some resonances over time scale of 10⁸ a. In one of our simulations, commensurability of the orbital periods of planets is very common. Moreover, a librating-circulating 3:2 configuration of mean motion resonance is found. Supported by the National Natural Science Foundation of China (Grant Nos. 10573040, 10673006, 10833001, and 10233020) and the Foundation of Minor Planets of Purple Mountain Observatory     

Application of the Undefined Frequency Method for the Analysis of a Two Planet Problem

Doklady Physics - The problem of motion of two bodies (planets) with comparable masses around a massive сentral body (star) is considered in proposition that planet masses are significantly...     

The magnetospheres of Mercury,Earth, and the giant planets Jupiter and Saturn

Brief information is given on the magnetospheres of the planets in the solar system that have intrinsic magnetic fields: Mercury, Earth, Jupiter, and Saturn. A universal model is constructed for the magnetosphere of a planet. Modifications of this model that are applied to individual planets are considered. The proposed models describe the basic physical processes that are responsible for the structure and dynamics of the magnetosphere. The numerical results of the simulations are compared with the direct measurements of magnetic fields and charged particle fluxes in the vicinity of the planets obtained in spacecraft (SC) missions.     

Planet host stars in open clusters

We have compiled a list of all planet host star candidates reported in the literature,which are likely to be cluster members,and we checked their memberships by the spatial location,radial velocity,proper motion and photometric criteria.We found that only six stars,BD-13 2130,HD 28305,Kepler-66,Kepler-67,Pr0201 and Pr0211,are planet orbiting stars in open clusters to date.Two stars,HD 70573 and HD 89744,belong to moving groups and one star,TYC 8975-2606-1,may not be a planet host star,while three stars,HD 16175,HD 46375 and HD 108874 are not members of open clusters.We note that all these six planetary systems in the stellar cluster environment are younger than~1 Gyr,which might indicate that the planetary system in open cluster can not survive for a long time,and we speculate that close stellar encounters between member stars in open cluster can potentially destroy,or at least strongly affect,the presence of planetary systems.     

Escape and Stand of the Pluto Atmosphere

Molar mass μ_min of the lightest gas, which will exist ``forever' in the atmosphere at the planet surface, can be evaluated by Jeans rule. The μ_min of Pluto is 17.3 g•mol^-1. It is evident that both N₂ and CO can be major atmospheric composition at the Pluto surface, and will exist “forever”. CH₄ can only be escaping slowly from Pluto atmosphere, and still holds quite a proportion in current Pluto atmosphere. However, it will not escape from Titan (or Jupiter, Saturn) atmosphere largely, and will exist “forever”. Given the quantity level of partial pressure of CH₄ in Pluto and Titan (or Jupiter, Saturn) original atmosphere is the same, it will be clear that the current partial pressure of CH₄ in Pluto surface atmosphere is 10^-3 Pa.     

Escape and Stand of the Pluto Atmosphere

Molar mass μmin of the lightest gas, which will exist “forever“ in the atmosphere at the planet surface,can be evaluated by Jeans rule. The μmin of Pluto is 17.3 g@ mol-1. It is evident that both N2 and CO can be major atmospheric composition at the Pluto surface, and will exist “forever“. CH4 can only be escaping slowly from Pluto atmosphere, and still holds quite a proportion in current Pluto atmosphere. However, it will not escape from Titan (or Jupiter, Saturn) atmosphere largely, and will exist “forever“. Given the quantitylevelof partial pressure of CH4 in Pluto and Titan (or Jupiter, Saturn) original atmosphere is the same, it will be clear that the current partial pressure of CH4 in Pluto surface atmosphere is 10-3 Pa.     

Focal plane wave-front sensing algorithm for high-contrast imaging

High-contrast imaging provided by a coronagraph is critical for the direction imaging of the Earth-like planet orbiting its bright parent star. A major limitation for such direct imaging is the speckle noise that is induced from the wave-front error of an optical system. We derive an algorithm for the wave-front measurement directly from 3 focal plane images. The 3 images are achieved through a deformable mirror to provide specific phases for the optics system. We introduce an extra amplitude modulation on one deformable mirror configuration to create an uncorrelated wave-front, which is a critical procedure for wave-front sensing. The simulation shows that the reconstructed wave-front is consistent with the original wave-front theoretically, which indicates that such an algorithm is a promising technique for the wave-front measurement for the high-contrast imaging. Supported by the National Natural Science Foundation of China (Grant No. 10873024)     

平面波导型对称星型耦合器的优化设计

通过有限差分波束传播法(FD-BPM)研究了N×N平面波导型星型耦合器的优化设计思想和方法,并通过17×17星型耦合器的模拟设计证明了它的可行性.给出了在输出端引入辅助波导的方法,以提高输出波导阵列的均匀性.并通过模拟计算,分析了圆心缩入程度和锥形区的形状对输出结果的影响.此法也同样适合于N值更大的星型耦合器.     

Search for Short-Duration Transient Gravitational Waves Emitted by Neutron Star Glitches

Neutron stars are known to show an accelerated spin-up of their rotational frequency on a short time scale of around 40 s, called a “glitch” in the neutron star. These neutron star glitches can emit short-duration transient gravitational wave signals as f-mode oscillations at frequencies between 1.5 and 3 kHz and damping times of less than a few seconds. The observed rate of neutron star glitches are currently limited by their electromagnetic observations. There could be a population of the isolated neutron stars in the galaxy for which there is no electromagnetic observation, but they can produce gravitational wave signals. Here, the sensitivity of the generic all-sky search for short-duration transients towards neutron star glitches during the Advanced LIGO and Virgo's third observing run using the Coherent WaveBurst algorithm is presented. The prospects of detecting signals from such glitching neutron stars for the upcoming fourth and fifth observing runs of Advanced LIGO and Virgo detectors are also described.     

Scattering from solutions of star polymers

We study the scattering intensity of dilute and semi-dilute solutions of star polymers. The star conformation is described by a model introduced by Daoud and Cotton. In this model, a single star is regarded as a spherical region of a semi-dilute polymer solution with a local, position dependent screening length. For high enough concentrations, the outer sections of the arms overlap and build a semi-dilute solution (a sea of blobs) where the inner parts of the actual stars are embedded. The scattering function is evaluated following a method introduced by Auvray and de Gennes. In the dilute regime there are three regions in the scattering function: the Guinier region (low wave vectors, ) from where the radius of the star can be extracted; the intermediate region () that carries the signature of the form factor of a star with f arms: ; and a high wavevector zone () where the local swollen structure of the polymers gives rise to the usual q ^-5/3 decay. In the semi-dilute regime the different stars interact strongly, and the scattered intensity acquires two new features: a liquid peak that develops at a reciprocal position corresponding to the star-star distances; and a new large wavevector contribution of the form q ^-5/3 originating from the sea of blobs. Received: 3 September 1997 / Revised: 13 January 1988 / Accepted: 31 March 1998     

基于圆形视场分割的鱼眼相机星图识别方法

海上星光导航是航海中一种重要的自主导航技术, 星图识别是其关键步骤。针对船载鱼眼相机星光导航系统超大视场带来的单幅图像数据量大、识别冗余、识别效率低等问题, 提出了一种基于圆形视场分割的鱼眼相机星图识别方法。对于拍摄到的星图, 利用同心圆将视场分割成若干个面积相等的环形和圆形区域; 在构造导航星特征库的过程中, 以星角距为特征构造散列函数, 将导航特征库分段存储成若干个子库; 在识别过程中, 利用基于中心星的多三角形识别算法, 从视场中心圆形区域开始依次向视场边缘环形区域进行识别。海上观测实验结果表明:该方法能够平均以2.5 s的识别时间达到90%以上的识别成功率, 且具有良好的实时性。     

Eccentricity modulation of a close-in planet by a companion: Application to GJ 436 system

GJ 436b is a Neptune-size planet with 23.2 Earth masses in an elliptical orbit of period 2.64 days and eccentricity 0.16. With a typical tidal dissipation factor (Q′∼10⁶) as that of a giant planet with convective envelope, its orbital circularization timescale under internal tidal dissipation is around 1 Ga, at least two times less than the stellar age (> 3 Ga). A plausible mechanism is that the eccentricity of GJ 436b is modulated by a planetary companion due to their mutual perturbation. Here we investigate this possibility from the dynamical viewpoint. A general method is given to predict the possible locations of the dynamically coupled companions, including nearby/distance non-resonant or mean motion resonance orbits with the first planet. Applying the method to GJ 436 system, we find it is very unlikely that the eccentricity of GJ 436b is maintained at the present location by a nearby/distance companion through secular perturbation or mean motion resonance. In fact, in all these simulated cases, GJ 436b will undergo eccentricity damp and orbital decay, leaving the present location within the stellar age. However, these results do not rule out the possible existence of planet companions in nearby/distance orbits, although they are not able to maintain the eccentricity of GJ 436b. Supported by the National Natural Science Foundation of China (Grant Nos. 10833001 and 10778603) and the National Basic Research Program of China (Grant No. 2007CB4800)     

Cancellation of star light generated by a nearby star–planet system upon detection with a rotationally-shearing interferometer

We derive the analytical expression for the star–planet incidance detected with a (variable angle) rotationally-shearing interferometer, with the absence of star-related quantities. The rotationally-shearing interferometer detects only the tilted wave front incident from a planet. The partial polarization of two rotated beams diminishes the signal amplitude by a factor proportional to the cosine-square of the shearing angle. The polarization considerations favor the small-angle implementation of the rotationally-shearing interferometer.     

Successes and failures of shallow-water interpretations of Voyager wind data

Studying the dynamics of Jupiter's atmosphere is a rewarding experience, in part because the planet's cloud-top circulations are easy to track from space, the jet streams flow in straight lines eastward or westward, and there is enough room for the vortices to usually keep out of each other's way. Earth, in contrast, is a planet with global circulations that are not easy to track from space, with jet streams that make wide, fluctuating arcs as they negotiate mountain ranges, and with vortices that are constantly jostling against each other in a cramped environment. But we know a great deal more about the vertical structure of Earth's atmosphere than of Jupiter's. In order to make headway on the Jovian problem, researchers have turned to the shallow-water model as a guide to interpreting the Voyager wind data. The shallow-water model matches the character of the data because it combines high-resolution horizontal dynamics with low-resolution vertical structure, but there is no guarantee that it captures the character of Jupiter's atmosphere itself. Remarkably, the model does well at reproducing the Great Red Spot, and it has revealed that Jupiter is clever about how it manages its vorticity by arranging its zonal winds to be neutrally stable with respect to Arnol'd's second stability theorem. We discuss reasons why the shallow-water model works for Jupiter and point out the limitations that are motivating researchers to develop more realistic models.     

X‐ray sources for studies of ultrafast processes

Radio signals from Jupiter were first detected in 1955 in the radio range at a frequency of 22.2 MHz. The emissions were sporadic in character, and were confined to frequencies below 40 MHz. These decametric (DAM) emissions have been interpreted as coherent cyclotron radiation from electrons in the tens of keV range. The innermost jovian moon Io, which orbits Jupiter in only 1.8 days, appears to modulate the emission: both the intensity and the probability of the occurrence of bursts increase when Io is at certain locations in its orbit with respect to Jupiter and the observer. The emissions originate in Jupiter's aurora, being produced by electrons that travel along magnetic field lines. Particles that enter the atmosphere may locally excite atoms and molecules, which upon de-excitation are visible as aurora at UV and infrared wavelengths (sometimes also at X-ray wavelengths). A fraction of the electrons is reflected back along the field lines, and produces DAM emissions.     

May a supernova bang twice?

The Mont Blanc group reports a burst of neutrinos in the LSD detector occuring the day before the optical discovery of SN1987A. The Kamiokande (K2) and IMB experiments see neutrino bursts ∼4 h 43 min after LSD. The K2 observations at LSD time here said to contradict LSD. I argue that the K2 results strongly support the LSD pulse(!). I critically analyse the data, and prove that all experiments are compatible at all times. I discuss the plausibility and predictive power of a two-neutrino-burst scenario, wherein the progenitor's core first became a neutron star, and subsequently recollapsed into a black hole (or strange star) as matter left behind by a partially failed shock wave accreted on and around the neutron star, with a calculated fall-back time of a few hours