The geometry of impacts on a synchronous planetary satellite

We consider a satellite in a circular orbit about a planet that, in turn, is in a circular orbit about the Sun; we further assume that the plane of the planetocentric orbit of the satellite is the same as that of the heliocentric orbit of the planet. The pair planet–satellite is encountered by a population of small bodies on planet-crossing, inclined orbits. With this setup, and using the extension of Öpik’s theory by Valsecchi et al. (Astron Astrophys 408:1179–1196, 2003), we analytically compute the velocity, the elongation from the apex and the impact point coordinates of the bodies impacting the satellite, as simple functions of the heliocentric orbital elements of the impactor and of the longitude of the satellite at impact. The relationships so derived are of interest for satellites in synchronous rotation, since they can shed light on the degree of apex–antapex cratering asymmetry that some of these satellites show. We test these relationships on two different subsets of the known population of Near Earth Asteroids.     

Some results of the cooperative photometric observations of the UV Cet-type flare stars in the years 1967–71

The list of the cooperative photometric observations of the UV Cet-type flare stars that have been organized during the years 1967 to 1971 by the Working Group on Flare Stars of the IAU Commission 27 is given. The completeness and reliability of the data obtained are evaluated by comparing simultaneous observations at different observatories. the statistical analysis of the UV Cet, YZ CMi, EV Lac and AD Leo flares observed in the B-band is carried out. The flare energy spectrum in the energy range where observational selection effects are small is found to be d lnv/d lnE _B=–1.4 to –1.9,v is an occurrence of flares with radiation energy ofE _B. The total flares' radiation is equal to 1.7%, 1.2%, 0.3% and 0.4% of the quiet radiation in the B-band of the stars listed, and the main part of this total radiation is due to the strongest flares. Distributions of flare rise times (t _r) and of rates of flare absolute luminosity increase (d² E _B/dt _r ²Ë _r) are considered; these parameters of flare are independent statistically for all stars studied. Correlation coefficientsr (E _B,t _r) andr (E _B,r(E _B,Ë _r)) are rather small except r (E _B,t _r)=0.86 for the AD Leo flares. Contradictory conclusions on temporal distribution of flares infered by different investigators are noted.     

Orbital evolution dynamics of two satellites in encounter phase using multiple scales expansion

An approximate solution of the encounter problem of two small satellites describing initially elliptical orbits around a massive oblate primary is obtained. The equations of motion of the center of mass of the two masses are developed in the most general form without any restrictions on the orbital elements. The method of multiple scales which seeks a solution whose behavior depends on several time scales is used. To overcome the singularity the equations of motion are transformed to the Struble variables. An analytical second order theory of the evolution dynamics is obtained. A MATHEMATICA program is constructed. The evolution dynamics of the orbital parameters between the perturbed and the unperturbed cases are plotted. The effect of changing eccentricity and changing inclination on the orbital parameters are highlighted.     

The jovian anticyclone BA: III. Aerosol properties and color change

A study of the vertical cloud structure of oval BA and its red color change is presented in this third part of our complete analysis. A large interest in Jupiter’s anticyclone BA was created by its reddening that occurred between 2005 and 2006. In this work we quantify the color change in oval BA by using images taken with the Advanced Camera for Surveys (ACS) onboard the Hubble Space Telescope (HST) in six filters from the near ultraviolet (F250W) to the deep methane band in the near infrared (F892N). Reflectivity changes are noteworthy in nadir viewing geometry at the ultraviolet and blue wavelengths (F250W, F330W and F435W filters) but almost undetectable or inside error bars in the rest of filters (F550M, F658N and F892N). The observed reflectivity variations are discussed in terms of a commonly accepted vertical cloud structure model for jovian anticyclones in order to explore some causes for the color alteration. Our models of the observed reflectivity variation show that the vortex clouds did not change its vertical extension (top pressure) or its optical depth. We find that a change occurred in the absorbing properties of the particles populating the upper aerosols (single scattering albedo and imaginary refractive index). A discussion on the thermo-physical and dynamical properties of the vortex that could be in the origin of the color change is also presented.     

Nature of the variability of the subfour V 1143 Ori

Byurakan Astrophysical Observatory; Tonantzintla Observatory, Mexico. Translated from Astrofizika, Vol. 34, No. 2, pp. 175–180, March–April, 1991.     

Motions in the field of two rotating magnetic dipoles. III: Zero-velocity curves and surfaces

The zero-velocity curves and surfaces created by two parallel or antiparallel magnetic dipoles moving on concentric circles are computed. It is found that for all combinations of values of the mass parameter µ and the ratio of the magnitudes of the magnetic moments of the two dipoles, there exist closed regions inside of which charged particles are permanently trapped.     

Cyclotron lines in the spectra of solar flares and solar active regions

It was shown by Zheleznyakov and Zlotnik (1980a, b) that in complex configurations of solar magnetic fields (in hot loops above the active centres, in neutral current sheets in the preflare phase, in hot X-ray kernels in the initial flare phase) a system of cyclotron lines in the spectrum of microwave radiation is likely to be formed. Such a line was obtained by Willson (1985) in the VLA observations at harmonics of the electron gyrofrequency. This communication interprets these observations on the basis of an active region model in which thermal cyclotron radiation is produced by hot plasma filling the magnetic tube in the corona above a group of spots. In this model the frequency of the recorded 1658 MHz line corresponds to the third harmonic of electron gyrofrequency, which yields the magnetic field (196 ± 4) G along the magnetic tube axis. The linewidth f/f 0.1 is determined by the 10% inhomogeneity of the magnetic field over the cross-section of the tube; the line profile indicates the kinetic temperature distribution of electrons over the tube cross-section with the maximum value 4 × 10⁶ K. Analysis shows that study of cyclotron lines can serve as an efficient tool for diagnostics of magnetic fields and plasma in the solar active regions and flares.     

On the dissociation of nitrogen by electron impact and by E.U.V. photo-absorption

The dissociation of N₂ by electron impact and by e.u.v. photo-absorption is studied, and it is shown that the forbidden predissociation of the numerous ¹Π_u and ¹Σ_u⁺ valence and Rydberg states of N₂ in the 11–24eV energy range is the dominant mechanism for N atom production. By measuring the absolute emission cross sections for the e.u.v. singlet bands of N₂ and by using the generalized oscillator strength data of Lassettre (1974), it has been possible to construct a detailed model of the total N₂ dissociation cross section which is in good agreement with the measurements of Winters (1966) and Niehaus (1967) and provides some insights into the maximum possible $\text{N(}{}^2\text{D)}$ yield from dissociative excitation. The total cross section for exciting N₂ e.u.v. radiation in the 800Å–1100Å wavelength range has been measured and found to have a value of 3.4 ×10^?17 cm² at 100 eV under optically thin conditions. Although this result implies that large fluxes of e.u.v. photons should be excited in auroral substorms and in the airglow, they are not observed, and we show that this development is a consequence of radiation entrapment and predissociation. The total cross section for dissociating N₂ by electron impact is given for optically thin and thick media. And some questions concerning the energy budget of a magnetospheric storm which are raised by these results, are discussed.     

Cosmic-ray propagation in compressible turbulent media

The influence of compressibility of media on both the statistical acceleration and the turbulent diffusion of cosmic-ray particles is investigated. The averaging over an ensemble of random velocity fields of the medium was performed in the kinetic equation. The kinetic coefficients, which are responsible for the particle acceleration, were obtained in the cases of weak and strong scattering due inhomogeneous magnetic fields.