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1.
Abstract— Video observations of the Leonid shower aboard two aircraft in the 1998 Leonid multi-instrument aircraft campaign and from ground locations in China are presented. Observing at altitude proved particularly effective, with four times higher rates due to low extinction and low angular velocity at the horizon. The rates, derived from a total of 2500 Leonid meteors, trace at least two distinct dust components. One dominated the night of 1998 November 16/17. This two-day wide component was rich in bright meteors with r = N (m + 1)/N (m) ≈ 1.5 (s = 1.4) and peaked at an influx of 3.1 ± 0.4 × 10?12 m?2 s?1 (for particles of mass <7 × 10?5 g) at solar longitude Λ0 ≈ 234.52 (Eq. J2000). The other more narrow component peaked on 1998 November 17/18 at Λ0 = 235.31 ± 0.01. Rates were elevated above the broad component between Λ0 = 235.15 and 235.40, symmetric around the current node of the parent comet 55P/Tempel-Tuttle, peaking at 5.1 ± 0.2 × 10?12 m?2 s?1. The population index was higher, r = 1.8 ± 0.1 (s = 1.7), but not as high as in past Leonid storms (r = 3.0). The flux profile of this component has an unusual asymmetric shape, which implies a blend of contributions from at least two different but relatively recent epochs of ejection. The variation of r across the profile might be due to mass-dependent ejection velocities of the narrowest component. High rates of faint meteors occurred only in an isolated five-minute interval at Λ0 = 235.198, which is likely the result of a single meteoroid breakup in space.  相似文献   

2.
An attempt to determine the radiance of forward scattered sunlight from particles in lunar libration regions was made with the white light coronagraph on Skylab. The libration regions could not be distinguished against the solar K + F coronal background; an upper limit to the libration cloud radiance is determined to be 2·5 × 10?11B?, where B? is the mean radiance of the solar disk. Employing a model of the particle composition and size distribution which has been proposed for the interplanetary medium, we determine upper limits for the density enhancements in the libration region from the upper limit of the forward scattered radiance presented herein. Similarly, the actual spatial density enhancement is calculated using the earlier observations of the libration region backscattered radiance (Roach, 1975). Enhancements of a factor of 102–103 are thus determined, depending upon material composition and size distribution used. By combining the forward and backscatter observations, it is possible to eliminate from consideration clouds whose power law particle size distribution exponent k is 2·5 and complex index of refraction m is 1·33?0.05i and 1·50?0.05i (i.e. absorbing ice and quartz particles, respectively). Finally, the radiance contrast of a possible model libration cloud is calculated with respect to the K- and F-corona/zodiaal light background and is shown to be a maximum in the vicinity of solar elongation angle ～30 deg.  相似文献   

3.
The evolution of a Population-I star with an initial mass M ZAMS = 60 M ⊙ has been calculated. At the stage when a red giant turns into an early-type helium star, the vast bulk of the stellar mass is concentrated in a compact core surrounded by an extended envelope that is unstable with respect to radial oscillations. The range of effective temperatures within which the instability arises extends to T eff ? 105 K. For the models corresponding to the Wolf-Rayet evolutionary stage (5 × 104 K ≤ T eff ≤ 1.05 × 105 K), hydrodynamic calculations of self-exciting radial stellar pulsations have been performed. The pulsational instability develops in a time interval comparable to the dynamic timescale. Once the amplitude has ceased to grow, the pulsational motions are nonlinear traveling waves propagating from the core boundary to the stellar surface. The velocity amplitude of the outer layers is 500 km s?1 < ΔU < 103 km s?1, depending on the effective temperature. During the evolution of a helium star, the mean ratio of the maximum expansion velocity of the outer layers to the local escape velocity decreases and lies within the range 0.25 < U max/v esc < 0.6 for the models considered. The nonlinearity of the stellar pulsations is responsible for the increase in the mean radius \(\bar r\) of the Lagrangian layers compared to the equilibrium radius r eq. The effect of the increase in mean radius decreases with rising effective temperature from\(\bar r\)/r ～ 10 at T eff = 7 × 104 K to \(\bar r\)/r ≈ 2 at T eff = 105 K. The radial pulsation periods for the models considered lie within the range 0.1 day ≤ Π ≤ 1.6 day and the amplitude of the bolometric magnitude variations does not exceed 0 . m 2.  相似文献   

4.
The first results of a comprehensive computer analysis of over 300 front film and grid coincidence events is presented using statistical tests on the observed data. The short term time dependence of the observed flux is entirely commensurate with a random Poisson distribution and any possible contributions from discrete “cometary showers” must certainly be of relatively minor significance compared to the sporadic background for mass > 10?13 g. Periodic seasonal variations of ～ 20 per cent of the average rate are observed common to Pioneers 8 and 9. These variations could reflect on the cometary nature of the source or alternatively indicate the presence of an interstellar component. The mass spectrum of the flux in the range 10?11?10?13 g indicates an increasing flux of particles to the lowest limits of mass detected, with a derived flux of Φ = 1·4 × 10?12m?0·68 (g) m?2 sec?1(2π ster.)?1.  相似文献   

5.
To study the peculiarities of the Galactic spiral density wave, we have analyzed the space velocities of Galactic Cepheids with propermotions from the Hipparcos catalog and line-of-sight velocities from various sources. First, based on the entire sample of 185 stars and taking R 0 = 8 kpc, we have found the components of the peculiar solar velocity (u ⊙, v ⊙) = (7.6, 11.6) ± (0.8, 1.1) km s?1, the angular velocity of Galactic rotation Ω0 = 27.5 ± 0.5 km s?1 kpc?1 and its derivatives Ω′0 = ?4.12 ± 0.10 km s?1 kpc?2 and Ω″0 = 0.85 ± 0.07 km s?1 kpc?3, the amplitudes of the velocity perturbations in the spiral density wave f R = ?6.8 ± 0.7 and f θ = 3.3 ± 0.5 km s?1, the pitch angle of a two-armed spiral pattern (m = 2) i = ?4.6° ± 0.1° (which corresponds to a wavelength λ = 2.0 ± 0.1 kpc), and the phase of the Sun in the spiral density wave χ⊙ = ?193° ± 5°. The phase χ⊙ has been found to change noticeably with the mean age of the sample. Having analyzed these phase shifts, we have determined the mean value of the angular velocity difference Ω p ? Ω, which depends significantly on the calibrations used to estimate the individual ages of Cepheids. When estimating the ages of Cepheids based on Efremov’s calibration, we have found |Ω p ? Ω0| = 10 ± 1stat ± 3syst km s?1 kpc?1. The ratio of the radial component of the gravitational force produced by the spiral arms to the total gravitational force of the Galaxy has been estimated to be f r0 = 0.04 ± 0.01.  相似文献   

6.
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7.
In previous publications the author has constructed a long-periodic solution of the problem of the motion of the Trojan asteroids, treated as the case of 1:1 resonance in the restricted problem of three bodies. The recent progress reported here is summarized under three headings:
  1. The nature on the long-periodic family of orbits is re-examined in the light of the results of the numerical integrations carried out by Deprit and Henrard (1970). In the vicinity of the critical divisor $$D_k \equiv \omega _1 - k\omega _2 ,$$ not accessible to our solution, the family is interrupted by bifurcations and shortperiodic bridges. Parametrized by the normalized Jacobi constant α2, our family may, accordingly, be defined as the intersection of admissible intervals, in the form $$L = \mathop \cap \limits_j \left\{ {\left| {\alpha - \alpha _j } \right| > \varepsilon _j } \right\};j = k,k + 1, \ldots \infty .$$ Here, {αj(m)} is the sequence of the critical αj corresponding to the exactj: 1 commensurability between the characteristic frequencies ω1 and ω2 for a given value of the mass parameterm. Inasmuch as the ‘critical’ intervals |α?αj|<εj can be shown to be disjoint, it follows that, despite the clustering of the sequence {αj} at α=1, asj→∞, the family extends into the vicinity of the separatrix α=1, which terminates the ‘tadpole’ branch of the family.
  2. Our analysis of the epicyclic terms of the solution, carrying the critical divisorD k , supports the Deprit and Henrard refutation of the E. W. Brown conjecture (1911) regarding the termination of the tadpole branch at the Lagrangian pointL 3. However, the conjecture may be revived in a refined form. “The separatrix α=1 of the tadpole branch spirals asymptotically toward a limit cycle centered onL 3.”
  3. The periodT(α,m) of the libration in the mean synodic longitude λ in the range $$\lambda _1 \leqslant \lambda \leqslant \lambda _2$$ is given by a hyperelliptic integral. This integral is formally expanded in a power series inm and α2 or \(\beta \equiv \sqrt {1 - \alpha ^2 }\) .
The large amplitude of the libration, peculiar to our solution, is made possible by the mode of the expansion of the disturbing functionR. Rather than expanding about Lagrangian pointL 4, with the coordinatesr=1, θ=π/3, we have expandedR about the circler=1. This procedure is equivalent to analytic continuation, for it replaces the circle of convergence centered atL 4 by an annulus |r?1|<ε with 0≤θ<2π.  相似文献   

8.
A multi-wavelength radar backscatter study of the echo characteristics of radio-meteors has yielded measurements of the height dependence of the radii, ri, of overdense plasma meteor columns. For electron line densities α ～ 1015 m?1 it is found that ri ∝ ??0.63 (? atmospheric density) with ri = 5 m at a height of 100 km.  相似文献   

9.
Thirteen high-dispersion spectrographs of the eclipsing binary star SZ Cam have been studied with a view of determining more accurate information on: (i) the spectral type and luminosity classifications, (ii) absolute parameters for the component stars, (iii) the stellar environment of SZ Cam. The main results in these categories are as follows: (i) O9.5 Vnk, (ii)m g=19±2M ⊙,m s=6.5±1M ⊙;r g=9.7±3.6R ⊙,r s=4.8±1.7R ⊙;T e～30000 K,T e～23000 K; (iii) there is a local concentration of absorbing material which may reach a density of 2M ⊙ pc?3, and the distance of the star is found to be 600±150 pc. The determined overluminosity of the secondary star and the local concentration of absorbing material are two topics which provide the basis for a discussion section.  相似文献   

10.
The processing of the plates of the Kitab part of the FON project has been completed. In total, 1963 plates were processed. The catalog of equatorial coordinates α, δ, and B-magnitudes for 13 413268 stars and galaxies up to B ≤ 17.5 m for the epoch 1984.97 is compiled. The Epson Expression 10000XL scanner with a 1200 dpi scanning mode and a plate size of 30 × 30 cm or 13000 × 13000 pel was used to digitize astronegatives. Coordinates of stars and galaxies are obtained in the Tycho-2 catalog system and B-magnitudes are obtained in the photovoltaic system. The catalog internal accuracy for all objects is σα,δ = 0.23" and σ B = 0.15 m (for stars in the range B = 5 m …14 m , errors are σα,δ = 0.085" and σ B = 0.054 m ) for equatorial coordinates and stellar B-magnitudes, respectively. Convergence between the calculated and reference positions is σα,δ = 0.042", and convergence between photoelectric B-magnitudes is σ B = 0.16 m . Coordinate errors with respect to the UCAC-4 catalog are σα,δ = 0.26" (9892697 or 73.75% of stars and galaxies were identified).  相似文献   

11.
Currently available data on the field of velocities V r , V l , V b for open star clusters are used to perform a kinematic analysis of various samples that differ by heliocentric distance, age, and membership in individual structures (the Orion, Carina-Sagittarius, and Perseus arms). Based on 375 clusters located within 5 kpc of the Sun with ages up to 1 Gyr, we have determined the Galactic rotation parameters ω 0 = ?26.0 ± 0.3 km s?1 kpc?1, ω′0 = 4.18 ± 0.17 km s?1 kpc?2, ω″0 = ?0.45 ± 0.06 km s?1 kpc?3, the system contraction parameter K = ?2.4 ± 0.1 km s?1 kpc?1, and the parameters of the kinematic center R 0 = 7.4 ± 0.3 kpc and l 0 = 0° ± 1°. The Galactocentric distance R 0 in the model used has been found to depend significantly on the sample age. Thus, for example, it is 9.5 ± 0.7 and 5.6 ± 0.3 kpc for the samples of young (≤50 Myr) and old (>50 Myr) clusters, respectively. Our study of the kinematics of young open star clusters in various spiral arms has shown that the kinematic parameters are similar to the parameters obtained from the entire sample for the Carina-Sagittarius and Perseus arms and differ significantly from them for the Orion arm. The contraction effect is shown to be typical of star clusters with various ages. It is most pronounced for clusters with a mean age of ≈100 Myr, with the contraction velocity being Kr = ?4.3 ± 1.0 km s?1.  相似文献   

12.
Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95 633 red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort constants have been found: A = 15.9 ± 0.2 km s?1 kpc?1 and B = ?12.0±0.2 km s?1 kpc?1. Using 3632 RGC stars with known proper motions, radial velocities, and photometric distances, we show that, apart from the star centroid velocity components relative to the Sun, only the model parameters that describe the stellar motions in the XY plane differ significantly from zero. We have studied the contraction (a negative K effect) of the system of RGC stars as a function of their heliocentric distance and elevation above the Galactic plane. For a sample of distant (500–1000 pc) RGC stars located near the Galactic plane (|z| < 200 pc) with an average distance of d = 0.7 kpc, the contraction velocity is shown to be Kd = ?3.5 ±0.9 km s?1; a noticeable vertex deviation, l xy = 9 · o 1 ± 0 · o 5, is also observed for them. For stars located well above the Galactic plane (|z| ≥200 pc), these effects are less pronounced, Kd = ?1.7 ± 0.5 km s?1 and l xy = 4 · o 9 ± 0 · o 6. Using RGC stars, we have found a rotation around the Galactic X axis directed toward the Galactic center with an angular velocity of ?2.5 ± 0.3 km s?1 kpc?1, which we associate with the warp of the Galactic stellar-gaseous disk.  相似文献   

13.
Based on a one-dimensional hydrodynamic model, we investigate carbon burning in a thermonuclear type-Ia supernova in the approximation of unsteady convection. The relatively broad range of convective parameters, 1×10?3≤αc≤2×10?3, in which delayed detonation from the edge takes place was found to be preserved only for cases with a low boundary temperature at the presupernova stage, T b (PS) = 6.4 × 106 K, and with a high envelope mass, mex ? 2 × 10?3M⊙. In cases with a more realistic temperature, T b (PS) = 2 × 108 K, which corresponds to helium burning in the shell source, and with a lower mass mex, delayed detonation from the edge takes place only at αc = 2 × 10?3, while at αc = 1 × 10?3, numerous model pulsations occur during t?500 s. Artificial viscosity is shown to give a determining contribution to the increase in entropy in outer model shells, which is caused by the generation of weak shock waves during pulsations. We also show that the entropies calculated by two independent methods are equal.  相似文献   

14.
We consider stars with radial velocities, proper motions, and distance estimates from the RAVE4 catalogue. Based on a sample of more than 145 000 stars at distances r < 0.5 kpc, we have found the following kinematic parameters: \({\left( {U,{\kern 1pt} V,{\kern 1pt} W} \right)_ \odot }\) = (9.12, 20.80, 7.66) ± (0.10, 0.10, 0.08) km s?1, Ω0 = 28.71 ± 0.63 km s?1 kpc?1, and Ω0 ’ = ?4.28 ± 0.11 km s?1 kpc?2. This gives the linear rotation velocity V 0 = 230 ± 12 km s?1 (for the adopted R 0 = 8.0 ± 0.4 kpc) and the Oort constants A = 17.12 ± 0.45 km s?1 kpc?1 and B = ?11.60 ± 0.77 km s?1 kpc?1. The 2D velocity distributions in the UV, UW, and VW planes have been constructed using a local sample, r < 0.25 kpc, consisting of ~47 000 stars. A difference of the UV velocity distribution from the previously known ones constructed from a smaller amount of data has been revealed. It lies in the fact that our distribution has an extremely enhanced branch near the Wolf 630 peak. A previously unknown peak at (U, V) = (?96, ?10) km s?1 and a separate new feature in the Wolf 630 stream, with the coordinates of its center being (U, V) = (30, ?40) km s?1, have been detected.  相似文献   

15.
We have calculated the radar backscattering characteristics of a variety of compositional and structural models of Saturn's rings and compared them with observations of the absolute value, wavelength dependence, and degree of depolarization of the rings' radar cross section (reflectivity). In the treatment of particles of size comparable to the wavelength of observation, allowance is made for the nonspherical shape of the particles by use of a new semiempirical theory based on laboratory experiments and simple physical principles to describe the particles' single scattering behavior. The doubling method is used to calculate reflectivities for systems that are many particles thick using optical depths derived from observations at visible wavelengths. If the rings are many particles thick, irregular centimeter- to meter-sized particles composed primarily of water ice attain sufficiently high albedos and scattering efficiencies to explain the radar observations. In that case, the wavelength independence of radar reflectivity implies the existence of a broad particle size distribution that is well characterized over the range 1 cm ? r ? m by n(r)dr = n0r?3dr. A narrower size distribution with a ～ 6 cm is also a possibility. Particles of primarily silicate composition are ruled out by the radar observations. Purely metallic particles, either in the above size range and distributed within a many-particle-thick layer or very much larger in size and restricted to a monolayer, may not be ruled out on the basis of existing radar observations. A monolayer of very large ice “particle” that exhibit multiple internal scattering may not yet be ruled out. Observations of the variation of radar reflectivity with the opening angle of the rings will permit further discrimination between ring models that are many particles thick and ring models that are one “particle” thick.  相似文献   

16.
Four surveys in which the geometrical parameters were suitable for observations on weak scattering objects were carried out by the Venera 9, 10 orbiters using 3000–8000 Å spectrometers. The results of one survey can be explained by a dust layer at the height of sighting h = 100–700 km. Its absence in other sessions suggests a ring structure. The spectrum of dust scattering is a power function of the wavelength with the index varying from ?2.1 at 100km to ?1.3 at 500km. A method is proposed for obtaining the optical thickness, density and size distribution of dust particles from the scattering spectra. For m > 10?14 g the number of dust particles with a mass higher than m is proportional to m?1.3. The radial optical thickness τ is 0.7 × 10?5 at 5000 Å assuming the geometric thickness δ to be 100 km. The maximum optical thickness along the normal to the plane of the ring is τn = 4 × 10?6. The mass of the ring is 20 tons or 5 × 10?3 g cm?1 per unit circumference length; the maximum mass in a column normal to the ring plane is 10?10g cm?2; the maximum density (for δ = 100 km) is 10?17 g cm?3. A satellite of Venus gradually destroyed by temperature effects and by meteorite streams and plasma fluxes is suggested as the source of dust in the ring. One of 1 km radius could sustain such a ring for a billion years. The zodiacal light intensity near Venus is estimated.  相似文献   

17.
The paper contains a numerical simulation of the nonlinear coupling between the kinetic Alfvén wave and the ion acoustic wave for an intermediate β-plasma (m e/m i?β?1). For this study, we have introduced the nonlinear ponderomotive force (due to the finite frequency (ω 0<ω ci) kinetic Alfvén wave) in the derivation of the ion acoustic wave. The main aim of the present paper is to study the nonlinear effects associated with the different driving finite frequencies (ω 0<ω ci) of the pump kinetic Alfvén wave on the formation of localized structures and a turbulent spectrum applicable to the solar wind around 1 AU. As a result, we found that the different driving frequencies of the pump kinetic Alfvén wave affect the formation of the localized structures. We have also studied the turbulent scaling which follows (～k ?3.6) for ω 0/ω ci≈0.2, (～k ?3.4) for ω 0/ω ci≈0.3 and (～k ?3.2) for ω 0/ω ci≈0.4, at small scales. Further, we have also found that different finite driving frequencies of the pump kinetic Alfvén wave affect the turbulence scaling at small scales, which may affect the heating of the plasma particles in solar wind. The present study is correlated with the observation made by the Cluster spacecraft for the solar wind around 1 AU.  相似文献   

18.
Open star clusters from the MWSC (Milky Way Star Clusters) catalogue have been used to determine the Galactic rotation parameters. The circular rotation velocity of the solar neighborhood around the Galactic center has been found from data on more than 2000 clusters of various ages to be V 0 = 236 ± 6 km s?1 for the adopted Galactocentric distance of the Sun R 0 = 8.3 ± 0.2 kpc. The derived angular velocity parameters are Ω 0 = 28.48 ± 0.36 km s?1 kpc?1, Ω’0 = ?3.50 ± 0.08 km s?1 kpc?2, and Ω″0 = 0.331 ± 0.037 km s?1 kpc?3. The influence of the spiral density wave has been detected only in the sample of clusters younger than 50 Myr. For these clusters the amplitudes of the tangential and radial velocity perturbations are f θ = 5.6 ± 1.6 km s?1 and f R = 7.7 ± 1.4 km s?1, respectively; the perturbation wavelengths are λ θ = 2.6 ± 0.5 kpc (i θ = ?11? ± 2?) and λ R = 2.1 ± 0.5 kpc (i R = ?9? ± 2?) for the adopted four-armed model (m = 4). The Sun’s phase in the spiral density wave is (χ⊙)θ = ?62? ± 9? and (χ⊙)R = ?85? ± 10? from the residual tangential and radial velocities, respectively.  相似文献   

19.
Results of the scattered solar radiation spectrum measurements made deep in the Venus atmosphere by the Venera 11 and 12 descent probes are presented. The instrument had two channels: spectrometric (to measure downward radiation in the range 0.45 < γ < 1.17 μm) and photometric (four filters and circular angle scanning in an almost vertical plane). Spectra and angular scans were made in the height range from 63 km above the planet surface. The integral flux of solar radiation is 90 ± 12 W m?2 measured on the surface at the subsolar point. The mean value of surface absorbed radiation flux per planetary unit area is 17.5 ± 2.3 W m?2. For Venera 11 and 12 landing sites the atmospheric absorbed radiation flux is ～15 W m?2 for H >; 43 km and ～45 W m?2 for H < 48 km in the range 0.45 to 1.55 μm. At the landing sites of the two probes the investigated portion of the cloud layer has almost the same structure: it consists of three parts with boundaries between them at about 51 and 57 km. The base of clouds is near 48 km above the surface. The optical depth of the cloud layer (below 63 km) in the range 0.5 to 1 μm does not depend on the wavelength and is ～29 and ～38 for the Venera 11 and 12 landing sites, respectively. The single-scattering albedo, ω0, in the clouds is very close to 1 outside the absorption bands. Below 58 km the parameter (1 ? ω0) is <10?3 for 0.49 and 0.7 μm. The parameter (1 ? ω0) obviously increases above 60 km. Below 48 km some aerosol is present. The optical depth here is a strong function of wavelength. It varies from 1.5 to 3 at λ = 0.49 μm and from 0.13 to 0.4 at 1.0 μm. The mean size of particles below the cloud deck is about 0.1 μm. Below 35 km true absorption was found at λ < 0.55 μm with the (1 ? ω0) maximum at H ≈ 15 km. The wavelength and height dependence of the absorption coefficient are compatible with the assumption that sulfur with a mixing ratio ～2 × 10?8 normalized to S2 molecules is the absorber. The upper limits of the mixing ratio for Cl2, Br2, and NO2 are 4 × 10?8, 2 × 10?11, and 4 × 10?10, respectively. The CO2 and H2O bands are confidently identified in the observed spectra. The mean value of the H2O mixing ratio is 3 × 10?5 < FH2O < 10?4 in the undercloud atmosphere. The H2O mixing ratio evidently varies with height. The most probable profile is characterized by a gradual increase from FH2O = 2 × 10?5 near the surface to a 10 to 20 times higher value in the clouds.  相似文献   

20.
This paper discusses SPA's measured at long VLF propagation paths in the lower ionosphere and their association with solar X-ray bursts observed by USNRL satellites in the 0–3 Å, 0–8 Å and 8–20 Å bands. Excellent correlations were found between the SPA importances (in degrees per Mm) and the logarithm of the X-ray burst peak intensities. A hardening of the X-ray burst spectra is evident for increasing importance of SPA's; the threshold energy required for the occurrence of such anomalies was estimated, it is 4.3×10?5 ergs cm?2 sec?1 in the main ionizing band of 0–3 Å. It was also possible to derive the effective recombination coefficient at the normal D-region height of 70 km, this beingα r≈6×10?6 cm3 sec?1; furthermore ion production rates were estimated during SPA's at heights below the reference level.  相似文献   

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