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1.
Solar Physics - Nous publions ici les résultats des observations coronographiques que nous avons effectuées à l'Observatoire du Pic-du-Midi à l'occasion des... 相似文献
2.
Vasile Mioc 《Astronomische Nachrichten》1980,301(6):311-315
On donne une expression analytique de la différence causée par le frottement atmosphérique entre les périodes nodale et képlérienne des satellites artificiels aux orbites quasi-circulaires, évoluant dans une atmosphère à symétrie sphéque. Quelques équations correspondantes trouvées par divers auteurs sont obtenues en tant que cas particuliers de l'équation donnée. 相似文献
3.
On a calculě les éléments orbitaux corrigés de sept cométes en employant les observations données par les circulaires du Smithsonian Astrophysical Observatory. 相似文献
4.
《Meteoritics & planetary science》2014,49(10):i-i
Engraving of the Orgueil meteorite fall published at the beginning of 1865 in l'Annuaire Mathieu (de la Drôme), indicateur du temps rédigé par les sommités scientifiques (from the collection at the Bibliothéque nationale de France). M. Gounelle and M. E. Zolensky discuss Orgueil in their article on pp. 1769–1794. 相似文献
5.
受地球大气影响, 使用地基光学望远镜观测角距离较小的双星系统或主卫星系统时往往会出现星象不可分辨的情况. 因此, 系统光心位置与系统质心位置可能存在一定的偏差. 准确地测量太阳系天体系统质心位置可以改进其轨道参数, 有助于揭示太阳系的形成与演化. 以矮行星Haumea及其亮卫星Hiíaka的运动为例, 仿真系统光心围绕质心扰动的过程, 探究视宁度(用星象的半高全宽表示)变化对准确测量光心位置的影响. 仿真结果表明, 使用二维高斯定心算法测定的系统光心位置随视宁度变化, 而修正矩定心算法的定心结果不受视宁度的影响. 根据仿真结果, 研究能够有效减少视宁度变化对光心位置准确测量影响的定心算法十分必要; 同时, 新的定心算法还需考虑主星光度变化的影响. 使用云南天文台2.4m望远镜, 1m望远镜以及紫金山天文台姚安观测站0.8m望远镜从2022年2月7日至2022年5月25日观测矮行星Haumea系统, 得到29晚共463幅CCD图像. 新定心算法确定的光心位置与使用二维高斯定心算法的结果相比具有更好的位置拟合效果. 此外, 还发现亮卫星Hiíaka在Jet Propulsion Laboratory (JPL)历表与Institut de Mécanique Céleste et de Calcul des ''Ephémérides (IMCCE)历表中的位置存在较大偏差. 相似文献
6.
Alan H. Jupp 《Celestial Mechanics and Dynamical Astronomy》1973,7(3):347-355
Poincaré formulated a general problem of resonance in the case of a dynamical system which is reducible to one degree of freedom. He introduced the concept of a global solution; in essence, this means that the domain of the solution(s) covers the entire phase plane, comprising regions of libration and circulation. It is the author's opinion that the technique proposed by Poincaré for the construction of a global solution is impractical. Indeed, in §§201 and 211 ofLes méthodes nouvelles de la méchanique céleste, where he describes the passage from shallow resonance to deep resonance, Poincaré asserts an erroneous conclusion. An alternative procedure, which admits secular terms into the determining function and introduces a regularizing function, is outlined. The latter method has been successfully applied to the Ideal Resonance Problem, which is a special case of the more general problem considered by Poincaré, (Garfinkelet al. (1971); Garfinkel (1972). 相似文献
7.
8.
J. H. Piddington 《Solar physics》1974,38(2):465-481
Evidence is discussed showing that a representative solar flare event comprises three or more separate but related phenomena requiring separate mechanisms. In particular it is possible to separate the most energetic effect (the interplanetary blast) from the thermal flare and from the rapid acceleration of particles to high energies. The phenomena are related through the magnetic structure characteristic of a composite flare event, being a bipolar surface field with most of its field lines ‘closed’. Of primary importance are helical twists on all scales, starting with the ‘flux rope’ of the spot pair which was fully twisted before it emerged. Subsequent untwisting by the upward propagation of an Alfvén twist wave provides the main flare energy.
- The interplanetary blast model is based on subsurface, helically twisted flux ropes which erupt to form spots and then transfer their twists and energy by Alfvén-twist waves into the atmospheric magnetic fields. The blast is triggered by the prior-commencing flash phase or by a coronal wave.
- The thermal flare is explained in terms of Alfvén waves travelling up numerous ‘flux strands’ (Figure 3) which have frayed away from the two flux ropes. The waves originate in interaction (collisions, bending, twisting, rubbing) between subsurface flux strands; the sudden flash is caused by a collision. The classical twin-ribbon flare results from the collision of a flux rope with a tight bunch of S-shaped flux strands.
- The impulsive acceleration of electrons (hard X-ray, EUV, Hα and radio bursts) is tentatively attributed to magnetic reconnection between fields in two parallel, helically twisted flux strands in the low corona.
- Flare (Moreton) waves in the corona have the same origin as the interplanetary blast. Sympathetic flares represent only the start of enhanced activity in a flare event already in the slow phase. Filament activation also occurs during the slow phase as twist Alfvén waves store their energy in the atmosphere.
- Flare ejecta are caused by Alfvén waves moving up flux strands. Surges are attributed to packets of twist Alfvén waves released into bundles of flux strands; the waves become non-linear and drive plasma upwards. Spray-type prominences result from accumulations of Alfvén wave energy in dome-shaped fields; excessive energy density eventually explodes the field.
9.
A. Satya Narayanan 《Astrophysics and Space Science》1983,95(2):277-282
The stability characteristics of a Helmholtz velocity profile in a stratified Boussinesq fluid in the presence of a rigid boundary is studied. A jump in the magnetic field is introduced at a level different from the velocity discontinuity. New unstable modes in addition to the Kelvin-Helmholtz mode are found. The wavelengths of these unstable modes are close to the wavelengths of internal Alfvén gravity waves in the atmosphere. 相似文献
10.
Le problème des erreurs du point de vue de l'observateur et du point de vue du calculateur d'orbites
S. Arend 《Astrophysics and Space Science》1971,11(1):150-156
Resumé En principe, nous parlerons des mesures d'étoiles doubles exécutées au micromètre à fils par la méthode classique des doubles
distances, mais il va de soi que la plupart des considérations relatives aux erreurs peuvent être étendues aux autres procédés. 相似文献
11.
We complete by this part II the establishment of a second order secular Jupiter-Saturn theory. This is achieved by taking into consideration the influence of the indirect part of the planetary disturbing function, and expressing the second order secular Hamiltonian in terms of Poincaré's canonical variables. 相似文献
12.
Poincaré's continuation method is applied to the elliptic restricted problem for the computation of four families of doubly symmetric three-dimensional periodic orbits emanating from similar orbits corresponding to zero eccentricity. The results are given in four tables and the orbits are characterized in regard to their stability. 相似文献
13.
We have studied the dynamical properties of convective overstability and Kelvin-Helmholtz instability in a vertical magnetic field with a downdraft. The Kelvin-Helmholtz instability and overstability produce the upward downward propagating Alfvén waves depending upon the magnitudes of the kinematic viscosity coefficient (eddy viscosity) ν, and thermometric conductivity κ. It is found that the instability may be driven by the density stratification and the effect of the eddy viscosity is to make the system stable. We discuss also the interaction of the overstability inx<0 and the downdraft inx>0, and the overstability at a vertical boundary of the field. 相似文献
14.
Abstract— Using visual observations that were reported 140 years ago in the Comptes Rendus de l'Académie des Sciences de Paris, we have determined the atmospheric trajectory and the orbit of the Orgueil meteorite, which fell May 14, 1864, near Montauban, France. Despite the intrinsic uncertainty of visual observations, we were able to calculate a reasonably precise atmospheric trajectory and a moderately precise orbit for the Orgueil meteoroid. The atmosphere entry point was ?70 km high and the meteoroid terminal point was ?20 km high. The calculated luminous path was ?150 km with an entry angle of 20°. These characteristics are broadly similar to that of other meteorites for which the trajectory is known. Five out of six orbital parameters for the Orgueil orbit are well constrained. In particular, the perihelion lies inside the Earth's orbit (q ?0.87 AU), as is expected for an Earth‐crossing meteorite, and the orbital plane is close to the ecliptic (i ?0°). The aphelion distance (Q) depends critically on the pre‐atmospheric velocity. From the calculated atmospheric path and the fireball duration, which was reported by seven witnesses, we have estimated the pre‐atmospheric velocity to be larger than 17.8 km/sec, which corresponds to an aphelion distance Q larger than 5.2 AU, the semi‐major axis of Jupiter orbit. These results suggest that Orgueil has an orbit similar to that of Jupiter‐family comets (JFCs), although an Halley‐type comet cannot be excluded. This is at odds with other meteorites that have an asteroidal origin, but it is compatible with 140 years of data‐gathering that has established the very special nature of Orgueil compared to other meteorites. A cometary origin of the Orgueil meteorite does not contradict cosmochemistry data on CI1 chondrites. If CI1 chondrites originate from comets, it implies that comets are much more processed than previously thought and should contain secondary minerals. The forthcoming return of cometary samples by the Stardust mission will provide a unique opportunity to corroborate (or contradict) our hypothesis. 相似文献
15.
We analyze the observations of a quiescent prominence acquired by the Téléscope Heliographique pour l’Étude du Magnetisme et des Instabilités Solaires (THEMIS) in the He?i 5876 Å (He?i D3) multiplet aiming to measure the spectral characteristics of the He?i D3 profiles and to find for them an adequate fitting model. The component characteristics of the He?i D3 Stokes I profiles are measured by the fitting system by approximating them with a double Gaussian. This model yields an He?i D3 component peak intensity ratio of \(5.5\pm0.4\), which differs from the value of 8 expected in the optically thin limit. Most of the measured Doppler velocities lie in the interval ±?5 km?s?1, with a standard deviation of ±?1.7 km?s?1 around the peak value of 0.4 km?s?1. The wide distribution of the full-width at half maximum has two maxima at 0.25 Å and 0.30 Å for the He?i D3 blue component and two maxima at 0.22 Å and 0.31 Å for the red component. The width ratio of the components is \(1.04\pm0.18\). We show that the double-Gaussian model systematically underestimates the blue wing intensities. To solve this problem, we invoke a two-temperature multi-Gaussian model, consisting of two double-Gaussians, which provides a better representation of He?i D3 that is free of the wing intensity deficit. This model suggests temperatures of 11.5 kK and 91 kK, respectively, for the cool and the hot component of the target prominence. The cool and hot components of a typical He?i D3 profile have component peak intensity ratios of 6.6 and 8, implying a prominence geometrical width of 17 Mm and an optical thickness of 0.3 for the cool component, while the optical thickness of the hot component is negligible. These prominence parameters seem to be realistic, suggesting the physical adequacy of the multi-Gaussian model with important implications for interpreting He?i D3 spectropolarimetry by current inversion codes. 相似文献
16.
The goal of this paper is to summarize 150 yr of history of a very special meteorite. The Orgueil meteorite fell near Montauban in southwestern France on May 14, 1864. The bolide, which was the size of the full Moon, was seen across Western France, and almost immediately made the news in local and Parisian newspapers. Within a few weeks of the fall, a great diversity of analyses were performed under the authority of Gabriel Auguste Daubrée, geology professor at the Paris Museum, and published in the Comptes Rendus de l'Académie des Sciences. The skilled scientists reported the presence of iron sulfides, hydrated silicates, and carbonates in Orgueil. They also characterized ammonium salts which are now gone, and observed sulfates being remobilized at the surface of the stone. They identified the high water and carbon contents, and noted similarities with the Alais meteorite, which had fallen in 1806, 300 km away. While Daubrée and his colleagues noted the similarity of the Orgueil organic matter with some terrestrial humus, they were cautious not to make a direct link with living organisms. One century later, Nagy and Claus were less prudent and announced the discovery of “organized” elements in some samples of Orgueil. Their observations were quickly discredited by Edward Anders and others who also discovered that some pollen grains were intentionally placed into the rock back in the 1860s. Orgueil is now one of the most studied meteorites, indeed one of the most studied rocks of any kind. Not only does it contain a large diversity of carbon‐rich compounds, which help address the question of organo‐synthesis in the early solar system but its chemical composition is also close to that of the Sun's photosphere and serves as a cosmic reference. Secondary minerals, which make up 99% of the volume of Orgueil, were probably formed during hydrothermal alteration on the parent‐body within the first few million years of the solar system; their study is essential to our understanding of fluid–rock interaction in asteroids and comets. Finally, the Orgueil meteorite probably originated from a volatile‐rich “cometary” outer solar system body as indicated by its orbit. Because it bears strong similarities to other carbonaceous chondrites that originated on dark asteroids, this cometary connection supports the idea of a continuum between dark asteroids and comets. 相似文献
17.
Celestial Mechanics and Dynamical Astronomy - Pour la construction de la théorie analytique exposée ici, les développements aux 1er, 2ème et 3ème ordres, autres que ceux... 相似文献
18.
Joseph V. Hollweg 《Solar physics》1978,56(2):305-333
We examine the propagation of Alfvén waves in the solar atmosphere. The principal theoretical virtues of this work are: (i) The full wave equation is solved without recourse to the small-wavelength eikonal approximation (ii) The background solar atmosphere is realistic, consisting of an HSRA/VAL representation of the photosphere and chromosphere, a 200 km thick transition region, a model for the upper transition region below a coronal hole (provided by R. Munro), and the Munro-Jackson model of a polar coronal hole. The principal results are:
- If the wave source is taken to be near the top of the convection zone, where n H = 5.2 × 1016 cm?3, and if B ⊙ = 10.5 G, then the wave Poynting flux exhibits a series of strong resonant peaks at periods downwards from 1.6 hr. The resonant frequencies are in the ratios of the zeroes of J 0, but depend on B ⊙, and on the density and scale height at the wave source. The longest period peaks may be the most important, because they are nearest to the supergranular periods and to the observed periods near 1 AU, and because they are the broadest in frequency.
- The Poynting flux in the resonant peaks can be large enough, i.e. P ⊙ ≈ 104–105 erg cm?2s?1, to strongly affect the solar wind.
- ¦δv¦ and ¦δB¦ also display resonant peaks.
- In the chromosphere and low corona, ¦δv ≈ 7–25 kms?1 and ¦δB¦ ≈0.3–1.0 G if P ⊙≈104-105 erg cm?2s?1.
- The dependences of ¦δv¦ and ¦δB¦ on height are reduced by finite wavelength effects, except near the wave source where they are enhanced.
- Near the base, ¦δB¦ ≈ 350–1200 G if P ⊙ ～- 104–105. This means that nonlinear effects may be important, and that some density and vertical velocity fluctuations may be associated with the Alfvén waves.
- Below the low corona most wave energy is kinetic, except near the base where it becomes mostly magnetic at the resonances.
- ?0 < δv 2 > v A or < δB 2 > v A/4π are not good estimators of the energy flux.
- The Alfvén wave pressure tensor will be important in the transition region only if the magnetic field diverges rapidly. But the Alfvén wave pressure can be important in the coronal hole.
19.
《Meteoritics & planetary science》1996,31(6):929-930
Book Reviews in this article: Chondrules and the Protoplanetary Disk edited by R. H. Hewins, R. H. Jones, and E. R. D. Scott. Rain of Iron and Ice: The Very Real Threat of Comet and Asteroid Bombardment by John S. Lewis. Météorites! (exhibit at the Muséum National d'Histoire Naturelle) and Les Météorites edited by B. Zanda, M. Rotaru and P. de la Cotardière. METEORITE! edited by Joel Schiff. Published quarterly by Pallasite Press, 相似文献
20.
J. P. Vallée 《Astrophysics and Space Science》1988,149(2):225-231
Recent observations of the longest known head-tail galaxy IC 711, at long wavelengths have shown it to extend farther than previously known. At δ 74 cm, Vallée and Roger (1987) found it to stretch 17′ (930 kpc) behind the optical nucleus of this elliptical galaxy. At δ92 cm, Vallée and Strom (1988) found it to stretch 18.3′ (1 Mpc) behind the optical nucleus. What new physics can be learned from it? To that end, a theoretical simulation in 3 dimensions of the longest head-tail galaxy has been performed, building the radio trail cell by cell inside a volume of space composed of 8 million cells, with each cell being assigned a proper radio emissivity. Matching ram pressure theory and recent observations yields a primary fast decrease of the radio luminosity with time or distance from the optical nucleus of the galaxy, and a secondary periodic variation of the radio luminosity every 500 kpc. Near the end of the tail, a sudden and unpredicted flare-up of the observed width of the tail requires a sudden change in the jet's physical conditions about 2 Gyr earlier, or that of the surroundings. These simulations provide some additional constraints on the ram pressure theory. Along the tail ridge, particle aging and particle acceleration must combine to give a luminosity function that mimics an exponential decrease with time. Across the tail ridge, no edge brightening is necessary, suggesting that particle aging and particle acceleration must combine via central turbulences and central instabilities (not by edge effects). The disappearance of the radio trail at two points along the radio ridge is unexpected from the ram pressure theory. Thus particle aging and particle acceleration must combine once more to mimic a sinusoidal modulation with time of the radio luminosity, perhaps near the nucleus inside the optical galaxy. 相似文献