Kinematics and Physics of Celestial Bodies最新文献

The features of the energy balance of evanescent acoustic-gravity waves in the atmosphere are investigated. In the case of freely propagating AGWs in an ideal isothermal atmosphere without dissipation, the period-average densities of kinetic and potential energy are equal to each other. This is true for the acoustic and gravity regions of the AGW spectrum. It is shown that the period-average kinetic and potential AGW energy densities are not equal to each other in the general case in the evanescent spectral region. The exceptions are the Lamb wave and the Brunt–Väisälä oscillations, in which the particles oscillate only along one coordinate (horizontally or vertically). Also, the densities of kinetic and potential energy are equal for the evanescent f- and γ-modes at the points where they touch the regions of freely propagating waves. An assumption is made that the evanescent modes for which the average values of kinetic and potential energies are equal are implemented first.

This paper presents a study of zero velocity curves, linear stability analysis and basins of attraction corresponding to the equilibrium points in the Sun-Jupiter system with asteroid belt and β-Pictoris system with dust belt, respectively under the influence of perturbing factors in the form of Poynting-Robertson drag (P-R drag), solar wind drag and a disc, which is rotating about the common center of mass of the system. Zero velocity curves are obtained and it is observed that in the presence of perturbing factors, the prohibited regions of the motion of infinitesimal mass get disturbed. Again, linear stability and effects of perturbing factors are analyzed for the triangular equilibrium points. It is noticed that because of P-R drag, triangular equilibrium points become unstable within the stability range. Finally, the Newton-Raphson basins of attraction corresponding to the equilibrium points are computed and it is found that in the presence of the disc, geometry of the basins of attraction gets change, whereas the effects of remaining perturbing factors on the structure of basins of attraction are very small.

The purpose of this article was to evaluate the mechanical, optical, and gasdynamic effects that accompanied the passage and explosion of the Yushu meteoroid. The explosion occurred over a sparsely populated area, Qinghai Province (Tibetan Plateau, People’s Republic of China). According to NASA, the initial kinetic energy of the celestial body was approximately 9.5 kt TNT or 40 TJ. Approximately 4.9 TJ, i.e., 12.25% of the initial kinetic energy of the body, was converted into the energy of the light flash. The projections of the velocity of the meteoroid are as follows: v_x = –2.6 km/s, v_y = 5.9 km/s, and v_z = –12.1 km/s. They are used to estimate the angle of inclination of the trajectory to the horizon, which is approximately 5°. Using the explosion height of 35.5 km and the inclination angle, the density of the matter is estimated to be close to that of an ordinary chondrite (approximately 3.5 t/m³). Knowledge of the kinetic energy and velocity allows us to calculate the mass of the meteoroid (432 t) and its characteristic size (6.2 m). The energy of the processes, as well as mechanical, optical, and gasdynamic effects of the celestial body, are analyzed. The main release of energy accompanying the deceleration of fragments of the body destroyed at a dynamic pressure of ~1 MPa took place in a 17.2 km long area at a height of approximately 35 km. A quasi-continuous fragmentation and a power law of the distribution of the mass of the fragments are assumed. The main parameters of ballistic and explosive shock waves are estimated. With a Mach number of 45, the radius of the ballistic shock wave was approximately 280 m, and the fundamental period was 2.6 s, which increased from 9.5 to 30.1 s due to dispersion as the distance traveled by the wave increased from 50 to 5000 km. The radius of the cylindrical and spherical explosion waves was approximately 0.8 and 2 km, respectively, and the fundamental period was 7.5 and 18.8 s. This period increased from 21.1 to 66.7 s as the distance increased from 50 to 5000 km. Near the meteoroid terminal point, the relative overpressure was maximal. It decreased with decreasing height, and increased with increasing height until approximately 120–150 km, where it reached ~10–20 percent and then decreased to a few percent. The absolute value of the overpressure for the spherical wave was maximal near the explosion height, then it decreased as the height decreased to 15 km, then increased again. At the epicenter of the explosion, it was approximately 310 Pa for a cylindrical wave or ~48.5 Pa for a spherical wave, which is insufficient to damage ground objects. With increasing height, the overpressure decreased from many tens of pascals to micropascals. The average power of a light flash with a duration of approximately 1.26 s was 3.9 TW, the power flux density near the fireball, more precisely, a 3.4 km long cone with a diameter

The absorption of radiation by systems of NaH molecule bands in the atmospheres of late-type stars is modeled. Calculations of synthetic spectra with model atmosphere parameters, which corresponds to M stars, show that the lines of this molecule form notable spectral details approximately the same intensity at wavelengths from λ ≈ 380 nm to almost ~1100 nm. The recently calculated parameters of the NaH molecule from the Exomol database, as well as a new value of the dissociation potential of this molecule D₀ = 1.975, were used in the calculations. The dependences of the calculated spectral energy distributions on the dissociation potential of the NaH molecule and on the parameters of the stellar atmospheres (T_eff, log g, [Fe/H]) were considered. Analysis of synthetic spectra shows that the lines of the NaH molecule become weak with temperature increasing and gravity decreasing in the stellar atmosphere. Thus, sodium hydride lines cannot be observed either in stars with effective temperatures corresponding to early M stars nor in M giants. NaH lines should appear only in the spectra of cold dwarfs, although the strong absorption of other molecules (TiO, CrH, and FeH) in visible and near-infrared region of the spectrum and absorption by atoms in the blue region make the NaH lines' detection a very complicated task. The energy distribution in the spectrum of the red dwarf VB 10 (M8V) in the blue region of the spectrum is modeled. The results of the analysis show that, under normal conditions and close to the solar chemical composition, NaH molecules provide only an additional component in the opacity of the spectra of cold dwarfs and substellar objects.

Necessary conditions for the appearance of decay instability of low-frequency kinetic Alfven waves in loop structures of an active region on the Sun before a flare are obtained. On the basis of the transcendental dispersion equation obtained using the synchronism conditions and additional conservation laws, an expression is obtained for the nonlinear growth rate of the decay instability of the initial kinetic Alfven wave (KAW) to the secondary KAW and the kinetic ion-acoustic wave (KIAW). Boundary values of the reduced amplitude of the initial KAW in the preflare atmosphere of an active region (AR) are obtained. It was assumed in the calculations that the waves involved in the process in the AR under study appear due to the development of instability caused by the presence of a weak large-scale (sub-Dreicer) electric field and drift motions of the plasma due to spatial inhomogeneities of its temperature and density. It is shown that, for a certain type of semiempirical model of the solar atmosphere, kinetic Alfven and kinetic ion-acoustic waves can be generated during the linear stage of instability development. In this case, the process of wave generation can take place both in plasma with purely Coulomb conductivity and in the presence of small-scale Bernstein turbulence in it. To “trigger” the instability, relatively low values of plasma nonisothermality and a very low threshold value of the reduced amplitude of the sub-Dreicer electric field are required. The possibility of the appearance of undamped kinetic waves of small amplitude in the region under study is proven.

It was shown in a recent study [11] that taking into account the rotation of the Earth’s atmosphere leads to the appearance of a new region of evanescent waves with a continuous frequency spectrum on the diagnostic diagram of acoustic-gravity waves. The region is located below the lower limit of gravity waves, which is equal to (2Omega ) for all wavelengths, where (Omega ) is the angular frequency of the atmospheric rotation. This result was obtained for high-latitude regions of the atmosphere in which one can be limited to considering only the vertical component of the Earth’s rotation frequency. This paper shows that taking into account both components of the vector (vec {Omega }) of the atmospheric rotation frequency (vec {Omega })—horizontal, (Omega cos varphi ,) where (varphi ) is the local latitude, and vertical, (Omega sin varphi )—the dominant role in the acoustic-gravity wave propagation is played by the vertical component. It is shown that the horizontal component leads to a negligible modification of the boundaries of the regions of acoustic and gravity waves on the diagnostic diagram. It is also shown that the vertical component of the frequency affects most strongly the lower limit of gravity waves, which depends on the latitude of the observation site for all wavelengths and is equal to 2(Omega sin varphi ).