The dynamical architecture and habitable zones of the quintuplet planetary system 55 Cancri

We perform numerical simulations to study the secular orbital evolution and dynamical structure of the quintuplet planetary system 55 Cancri with the self-consistent orbital solutions by Fischer and coworkers. In the simulations, we show that this system can be stable for at least 108 yr. In addition, we extensively investigate the planetary configuration of four outer companions with one terrestrial planet in the wide region of 0.790AU 〈 a 〈 5.900AU to examine the existence of potential asteroid structure and Habitable Zones （HZs）. We show that there are unstable regions for orbits about 4：1, 3：1 and 5：2 mean motion resonances （MMRs） of the outermost planet in the system, and several stable orbits can remain at 3：2 and 1：1 MMRs, which resembles the asteroid belt in the solar system. From a dynamical viewpoint, proper HZ candidates for the existence of more potential terrestrial planets reside in the wide area between 1.0 AU and 2.3 AU with relatively low eccentricities.     

A Research on the Collision Probability Calculation of Space Debris for Nonlinear Relative Motions†

The calculation of collision probability is the foundation of collision detection and avoidance maneuver for space objects. Now an assumption of linear relative motion is usually applied in the calculation of collision probability and then the complex 3-dimensional problem can be reduced to a 2-dimensional integral of probability density function over the area of circle. However, if the relative velocity value is very small, the term of linear relative motion is not valid. So it is necessary to consider the calculation of collision probability for nonlinear relative motions. The method used to calculate collision probability for nonlinear relative motion is studied, and test cases are designed to justify the validity of this method. It is applicable to collision probability problems involving relative velocity and error covariance varying with time. The results indicate that it is necessary to calculate collision probability with this nonlinear method under certain circumstances. For example, for elliptical relative motions in Satellite Formation Flying, when the relative velocity is below 100 m/s, the relative error between the linear method and the nonlinear method exceeds 5%; for the problem of conjunction analysis of two satellites with circular orbits, when the relative velocity is below 10 m/s, the relative error is also larger than 1%. Some significant conclusions are obtained for the collision detection system of our country.     

IU Cancri:a solar-type contact binary with mass transfer

We present new CCD photometry of the solar-type contact binary IU Cnc, which was observed from November 2017 to March 2018 with three small telescopes in China. BV light curves imply that IU Cnc is a W-type contact binary with total eclipses. The photometric solution indicates that the mass ratio and fill-out factor are q = 4.104 ± 0.004 and f = 30.2%± 0.3%, respectively. From all available light minimum times, the orbital period may increase at a rate of dP/dt =+6.93(4)× 10^-7 d yr^-1, which may result from mass transfer from the secondary component to the primary one. With mass transferring,IU Cnc may evolve from a contact configuration into a semi-detached configuration.     

小行星(469219) Kamo`oalewa轨道的确定与误差分析

作为一颗与地球共轨道的小行星,(469219)Kamo'oalewa是一个具有很高研究价值的近地小天体,也是中国首次小行星探测计划的目标天体之一.针对其轨道特性,建立了兼顾太阳、地球和月球非球形引力作用的小行星动力学模型.并在该模型的基础上,利用国际小行星中心(Minor Planet Center,MPC)提供的2004|2018年间的光学观测数据对该小行星的轨道进行确定.拟合后观测残差的均方根误差约为0:2″(与美国喷气推进实验室的Horizons在线历表系统相当),其中2004年期间数据的观测残差有所改进.最后,对小行星(469219)Kamo'oalewa的轨道误差进行了详细分析,并预报了2020-2025年期间该小行星的轨道误差.     

天问二号星载光学观测小行星(469219) Kamo`oalewa轨道精度仿真分析

中国小行星探测任务---天问二号将于2025年发射升空, 其探访的第一个目标, 小行星(469219)lk Kamo`oalewa (又称2016 HO3), 是一颗与地球共轨的近地小天体, 有着极高的运动演化研究价值. 目前小行星(469219) Kamo`oalewa只有有限的地基观测资料, 限制了其轨道精度. 搭载光学载荷的天问二号在抵近lk Kamo`oalewa的过程中, 预计将获得大量的星载光学观测数据. 这将大大改善小行星(469219) Kamo`oalewa只有地基光学观测数据, 无2021年后的公开观测资料的状况. 通过仿真带有一定轨道误差的天问二号的光学观测数据, 完成对小行星(469219) Kamo`oalewa定轨预报精度的任务前评估. 精度评估使用协方差分析法和数值比较法, 在考虑的可能观测精度范围内, 预估天问二号光学观测数据能使小行星(469219) Kamo`oalewa定轨精度整体提升至15km以内, 并且分析了两种精度评估方法结果的差异与特性.     

A Spectroscopic Study of the SU Uma-type Dwarf Nova YZ Cnc during its 2002 Superoutburst

We report on time-resolved spectroscopic observations of the SU Ursae Majoris dwarf nova, YZ Cnc for over 11 h on two nights during its 2002 January superoutburst. The spectra on the first day only showed absorption-line profiles, while on the second day the lines showed "W" profiles with blue and red troughs. The radial velocity curve of the absorption troughs and emission peaks of Hβ has an amplitude of 49±10 km s-1 and a phase offset of -0.07±0.04, which are very similar to those measured in quiescence. However, the γ velocity deviates strongly from the systemic velocity measured in quiescence, by some ±60 km s-1. Large shifts of -70 km s-1 in the orbital-averaged velocity and -0.09 in the phase are also found in our observations. All these features can be well explained by a precessing, eccentric disk.     

Matching cometary ejection processes to the Leonids 1998–2001 using a hybrid numerical model

A new scheme for simulating meteor showers is introduced, based on a hybridization of current numerical modelling techniques. It involves an iterative method that generates particles which hit a real-scale Earth, removing the spatial and temporal blurring common to other modelling techniques. The scheme is applied to the activity profile of the Leonids 2001 using three different models of meteoroid ejection velocity and then applied to the Leonids 1998–2000 using the most favourable models. It is shown that to reproduce the observed meteor activity profiles there must be a strong concentration of ejection around perihelion. The modelling also implies that meteoroid density must be towards the higher end of the currently acceptable range, although the derived limits are not independent of the ejection velocity model. We also find that the extreme narrowness of Leonid activity peaks is not easily reproduced with outgassing over the entire day side of the comet but it is fitted well by outgassing in a restricted direction as one would expect from an outgassing jet. In addition, we show that double-peaked features, corresponding to a semihollow meteoroid streamlet, can arise in a meteor shower activity profile from outgassing during a single perihelion passage of the parent comet. It is suggested that this process caused the double-peaked feature in the first maxima of the 2001 Leonids.     

Photometric properties of the δ Scuti star BR Cancri

We present the results of a three-year Johnson V and Strömgren uvby H β photometric study of the δ Scuti star BR Cancri (BR Cnc). Our data sets consist of 1293 discrete differential magnitudes in Johnson V and yellow y filters, 883 in Strömgren v and 239 in ub filters. The Fourier analysis of the data suggests four pulsation frequencies for the variable: f ₁=24.978, f ₂=11.358, f ₃=11.808 and f ₄=27.914 cycle d⁻¹. During the three observing years, the main frequency f ₁ kept its V ( y ) amplitude constant at about 6 mmag but its v amplitude seems to be changing. Amplitude variations for all the three other frequencies are also claimed. The pulsation modes of the frequencies are discussed based on the colour data. Using uvbyβ data and calibrations in the literature, we derive the physical parameters for BR Cnc.     

The Q Values of the Galilean Satellites and their Tidal Contributions to the Deceleration of Jupiter''''s Rotation

The relationship between the k2/Q of the Galilean satellites and the k2J/QJ of Jupiter is derived from energy and momentum considerations. Calculations suggest that the Galilean satellites can be divided into two classes according to their Q values: Io and Ganymede have values between 10 and 50, while Europa and Callisto have values ranging from 200 to 700. The tidal contributions of the Galilean satellites to Jupiter's rotation are estimated. The main deceleration of Jupiter, which is about 99.04% of the total, comes from Io.     

Chaos in Compact Binaries with Frequency Map Analysis

The dynamics of compact binaries is very complicated because of spin-orbit coupling and spin-spin coupling. With Laskar's frequency map analysis (FMA) and frequency diffusion as an indicator, we found that misalignment of the spins and orbital angular momentum has a great effect on the dynamics, and for systems with different mass ratiosβ= m2/m1 chaos occurs at different spin-orbit configurations. For equal-mass binaries (β= 1), chaos occurs when the spins nearly cancel each other out. For some other systems (for exampleβ~ 1/2), the binaries are irregular, even chaotic, when the spins are perpendicular to the orbital angular momentum. For the case where gravitational radiation is taken into account, we give an analytic estimation for the frequency diffusion based on the decay of the orbit, which is roughly consistent with our simulations. This means the FMA is not suitable as a chaos indicator for weak chaotic cases with dissipative terms.     

Dynamical evolution of the Prometheus–Pandora system

The system of Saturn's inner satellites is saturated with many resonances. Its structure should be strongly affected by tidal forces driving the satellites through several orbit–orbit resonances. The evolution of these satellites is investigated using analytic and numerical methods. We show that the pair of satellites Prometheus and Pandora has a particularly short lifetime (<20 Myr) if the orbits of the satellites converge without capture into a resonance. The capture of Pandora into a resonance with Prometheus increases the lifetime of the couple by a few tens of Myr. However, resonances of the system are not well separated, and capture results in a chaotic motion. Secondary resonances also disrupt the resonant configurations. In all cases, the converging orbits of these two satellites result in a close encounter. The implications for the origin of Saturn's rings are discussed.     

Adiabatic chaos in the Prometheus–Pandora system

The chaotic orbital motion of Prometheus and Pandora, the 16th and 17th satellites of Saturn, is studied. Chaos in their orbital motion, as found by Goldreich & Rappaport and Renner & Sicardy, is due to interaction of resonances in the resonance multiplet corresponding to the 121:118 commensurability of the mean motions of the satellites. It is shown rigorously that the system moves in adiabatic regime. The Lyapunov time (the 'time horizon of predictability' of the motion) is calculated analytically and compared to the available numerical–experimental estimates. For this purpose, a method of analytical estimation of the maximum Lyapunov exponent in the perturbed pendulum model of non-linear resonance is applied. The method is based on the separatrix map theory. An analytical estimate of the width of the chaotic layer is made as well, based on the same theory. The ranges of chaotic diffusion in the mean motion are shown to be almost twice as big compared to previous estimates for both satellites.