Normal forms for the epicyclic approximations of the perturbed Kepler problem     

Giuseppe Pucacco 《New Astronomy》2012,17(5):475-482

We compute the normal forms for the Hamiltonian leading to the epicyclic approximations of the (perturbed) Kepler problem in the plane. The Hamiltonian setting corresponds to the dynamics in the Hill synodic system where, by means of the tidal expansion of the potential, the equations of motion take the form of perturbed harmonic oscillators in a rotating frame. In the unperturbed, purely Keplerian case, the post-epicyclic solutions produced with the normal form coincide with those obtained from the expansion of the solution of the Kepler equation. In all cases where the perturbed problem can be cast in autonomous form, the solution is easily obtained as a perturbation series. The generalization to the spatial problem and/or the non-autonomous case is straightforward.  相似文献   

温室气体的卫星遥感—进展与趋势     

刘毅  王婧  车轲  蔡兆男  杨东旭  吴林 《遥感学报》2021,25(1):53-64

二氧化碳和甲烷减排是控制全球增温最核心的手段,传统的人为碳排放计算主要依赖于在线监测和清单算法,2019年第49届IPCC全会明确了利用大气观测通过"自上而下"通量计算对排放清单进行支撑和验证,因此了解大气遥感碳监测发展趋势以及同化反演技术方法成为了中国应对国际气候变化事务亟待探明的重要问题。根据卫星遥感技术发展进程和监测需求,将碳监测遥感的发展划分为3个阶段(1999年—2008年,2009年—2019年,2019年—),前两个阶段和第三阶段对应卫星分别为第一代和第二代温室气体监测卫星。本文在分析日本、美国、欧洲和中国第一代段碳监测卫星遥感探测技术发展进程的基础上,重点介绍了第二代卫星遥感探测技术的创新及其在探测精度、分辨率和覆盖率等方面提升。为了满足全球和区域人为碳排放监测的重大需求,需要优化反演算法提高精度、科学规划卫星的组网观测提升监测效率。同时也进一步阐述了如何依据组网观测的全球高精度、高时空分辨率的卫星数据,利用"自上而下"数据同化方法获得独立源汇信息来补充和验证清单。最后,指出了卫星高光谱遥感和新一代碳监测卫星的未来发展趋势及估算人为碳排放的潜力。  相似文献   

中国历代荧惑守列宿与四星聚、五星聚考查     

张健 《天文学报》2012,53(4):299-307

利用授时历法和现代天文计算方法,对中国历代天文志记录的荧惑(火星)守列宿、四星聚、五星聚进行分析研究,结果表明:65条荧惑守列宿,正误率分别为49%和51%.如果把荧惑留、留守、在某宿等运动形态也考虑为守的范围,共有95条,其正误率分别为56%和44%.12条四星聚正误率各占一半,即50%.11条五星聚正误率分别为82%和18%(其中含五星并见).并对错误记录的原因做了初步探讨.  相似文献   

The silicate and carbon-rich models of CoRoT-7b, Kepler-9d and Kepler-10b     

Yan-Xiang Gong  Ji-Lin Zhou 《天体物理学报》2012,(6):678-692

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Ejecta exchange and satellite color evolution in the Pluto system, with implications for KBOs and asteroids with satellites     

S. Alan Stern 《Icarus》2009,199(2):571-573

In this Note, I present first-order scaling calculations to examine the efficacy of impacts by Kuiper Belt debris in causing regolith exchange between objects in the Pluto system. It is found that ejecta can escape Nix and Hydra with sufficient velocity to reach one another, as well as Charon, and even Pluto. The degree of ejecta exchanged between Nix and Hydra is sufficient to cover these bodies with much more material than is required for photometrically change. In specific, Nix and Hydra may have exchanged as up to 10s of meters of regolith, and may have covered Charon to depths up to 14 cm with their ejecta. Pluto is likely unaffected by most Nix and Hydra ejecta by virtue of a combination of dynamical shielding from Charon and Pluto's own annual atmospheric frost deposition cycle. As a result of ejecta exchange between Nix, Hydra, and Charon, these bodies are expected to evolve their colors, albedos, and other photometric properties to be self similar. These are testable predictions of this model, as is the prediction that Nix and Hydra will have diameters near 50 km, owing to having a Charon-like albedo induced by ejecta exchange. As I discuss, this ejecta exchange process can also be effective in many KBOs and asteroids with satellites, and may be the reason that very many KBO and asteroid satellite systems have like colors.  相似文献   

Titan at 3 microns: Newly identified spectral features and an improved analysis of haze opacity     

Haingja Seo  Joo Hyeon Kim  Régis Courtin 《Icarus》2009,199(2):449-457

We have reanalyzed the high-resolution spectrum of Titan between 2.87 and 3.12 μm observed with NIRSPEC/Keck II on 2001 Nov. 21 in southern summer, using updated CH₃D and C₂H₆ line-by-line models. From new synthetic spectra, we identify all but a few of the previously unidentified significant absorption spectral features in this wavelength range as due to these two species, both of which had been previously detected by Voyager and ground-based observations at other wavelengths. We also derive opacities and reflectivities of haze particles as functions of altitude for the 2.87-2.92 μm wavelength range, where Titan's atmosphere is partially transparent down to the surface. The extinction per unit altitude is observed to increase from 100 km (∼8 mbar) toward lower altitude. The derived total optical depth is approximately 1.1 for the 2.87-2.92 μm range. At wavelengths increasing beyond 2.92 μm the haze layers become much more optically thick, and the surface is rapidly hidden from view. These conclusions apply to equatorial and southern-temperate regions on Titan, excluding polar regions. We also find it unlikely that there is a large enhancement of the tropospheric CH₄ mole fraction over the value reported from analysis of the Huygens/GCMS observations.  相似文献   

Three tenuous rings/arcs for three tiny moons     

M.M. Hedman  C.D. Murray  M.S. Tiscareno  M.W. Evans 《Icarus》2009,199(2):378-386

Using Cassini images, we examine the faint material along the orbits of Methone, Anthe and Pallene, three small moons that reside between the orbits of Mimas and Enceladus. A continuous ring of material covers the orbit of Pallene; it is visible at extremely high phase angles and appears to be localized vertically to within ±25 km of Pallene's inclined orbit. By contrast, the material associated with Anthe and Methone appears to lie in longitudinally confined arcs. The Methone arc extends over ∼10° in longitude around the satellite's position, while the Anthe arc reaches ∼20° in length. The extents of these arcs are consistent with their confinement by nearby corotation eccentricity resonances with Mimas. Anthe has even been observed to shift in longitude relative to its arc in the expected manner given the predicted librations of the moon.  相似文献   

A survey for satellites of Venus     

Scott S. Sheppard  Chadwick A. Trujillo 《Icarus》2009,202(1):12-16

We present a systematic survey for satellites of Venus using the Baade-Magellan 6.5 m telescope and IMACS wide-field CCD imager at Las Campanas observatory in Chile. In the outer portions of the Hill sphere the search was sensitive to a limiting red magnitude of about 20.4, which corresponds to satellites with radii of a few hundred meters when assuming an albedo of 0.1. In the very inner portions of the Hill sphere scattered light from Venus limited the detection to satellites of about a kilometer or larger. Although several main belt asteroids were found, no satellites (moons) of Venus were detected.  相似文献   

Astrometric observations of the Uranian satellites with the Faulkes Telescope North in 2007 September     

M. Yu. Khovritchev 《Monthly notices of the Royal Astronomical Society》2009,393(4):1353-1358

The results of astrometric observations of the main Uranian satellites taken with the Faulkes Telescope North are presented. A median filter algorithm was applied to subtract a scattered-light halo caused by Uranus. The Two-Micron All-Sky Survey (2MASS) and USNO-B1.0 were used as reference catalogues. The mean value of the differences between the equatorial coordinates of the satellites determined with 2MASS and USNO-B1.0 is close to 200 mas. A comparison of the observed equatorial coordinates of the satellites and their relative positions with ephemerides based on different combinations of theories of motion of Uranus and its satellites (DE405+GUST86, DE405+GUST06, INPOP+GUST86, INPOP+GUST06) was performed. The satellites' positions obtained with respect to 2MASS are in better agreement with theories. The values of (O−C) of the equatorial coordinates determined with the 2MASS are mainly less than 100 mas. The majority of (O−C) of relative positions are within ±50 mas. The mean values of the standard errors of (O−C) are within 20 to 60 mas.  相似文献   

On corotation torques, horseshoe drag and the possibility of sustained stalled or outward protoplanetary migration   总被引：1，自引：0，他引：1  

S.-J. Paardekooper  J. C. B. Papaloizou 《Monthly notices of the Royal Astronomical Society》2009,394(4):2283-2296

We study the torque on low-mass protoplanets on fixed circular orbits, embedded in a protoplanetary disc in the isothermal limit. We consider a wide range of surface density distributions including cases where the surface density increases smoothly outwards. We perform both linear disc response calculations and non-linear numerical simulations. We consider a large range of viscosities, including the inviscid limit, as well as a range of protoplanet mass ratios, with special emphasis on the co-orbital region and the corotation torque acting between disc and protoplanet.
For low-mass protoplanets and large viscosity, the corotation torque behaves as expected from linear theory. However, when the viscosity becomes small enough to enable horseshoe turns to occur, the linear corotation torque exists only temporarily after insertion of a planet into the disc, being replaced by the horseshoe drag first discussed by Ward. This happens after a time that is equal to the horseshoe libration period reduced by a factor amounting to about twice the disc aspect ratio. This torque scales with the radial gradient of specific vorticity, as does the linear torque, but we find it to be many times larger. If the viscosity is large enough for viscous diffusion across the co-orbital region to occur within a libration period, we find that the horseshoe drag may be sustained. If not, the corotation torque saturates leaving only the linear Lindblad torques. As the magnitude of the non-linear co-orbital torque (horseshoe drag) is always found to be larger than the linear torque, we find that the sign of the total torque may change even for mildly positive surface density gradients. In combination with a kinematic viscosity large enough to keep the torque from saturating, strong sustained deviations from linear theory and outward or stalled migration may occur in such cases.  相似文献