共查询到20条相似文献，搜索用时 312 毫秒
1.
《Icarus》1987,69(3):550-556
A meteorite-dropping event was observed by the camera network in western Canada on February 6, 1980, precisely 3 years after the fall of the Innisfree meteorite. The orbits of the two objects are essentially identical, making this the first observational evidence for multiple falls from the same orbit. Minor differences in the argument of perihelion and longitude of the node were presumably caused by Earth perturbations at times of previous close encounters. An impact location near the town of Ridgedale, Saskatchewan, is indicated with a predicted mass of 1.8 kg for the object. The Ridgedale event was much less luminous than Innisfree, with a peak absolute panchromatic magnitude near −7.5 with no evidence for the multiple fragmentation observed for Innisfree. Considerations of the probability of detecting two related objects with the meteorite camera networks suggest that Innisfree (a brecciated LL chondrite) was a near-surface fragment from a recent parent object with a radius of several tens of meters. A campaign to locate the Ridgedale object is planned since its recovery would allow various comparisons of great interest with the Innisfree chondrite. 相似文献
2.
Recently, a tachyonic field was presented as a dark energy model to represent the present acceleration of the Universe. In this paper, we consider a mixture of tachyonic fluid with a perfect fluid. For this purpose we consider barotropic fluid and Generalized Chaplygin gas (GCG). We present a particular form of the scale factor. We solve the equations of motion to get exact solutions of the density, tachyonic potential and the tachyonic field. We introduce a coupling term to show that the interaction decays with time. We also show that the nature of the potentials vary, so the interaction term reduces the potential in both cases. 相似文献
3.
R. A. Burenin 《Astronomy Letters》2007,33(12):804-806
Variability on time scales δt < t is observed on numerous occasions in the afterglows of cosmic gamma-ray bursts (GRBs). It is well known that the radiation originating in an external shock produced by the interaction of an ultrarelativistic jet with the ambient interstellar medium should not contain such variability within the framework of simple models. The corresponding constraints were established by Ioka et al. (2005) and, in some instances, are inconsistent with observations. On the other hand, if the motion is not relativistic, then the rapid afterglow variability can be explained much more easily. Various estimates of the transition time to a nonrelativistic motion in a GRB source are discussed in this connection. It has been shown that this transition should occur on an observed time scale of ～10 days. In the case of a higher density of the surrounding material, ～102?104 cm?3, or a stellar wind with ? ～ 10?5?10?4 M ⊙ yr?1, the transition to a nonrelativistic motion can occur on a time scale of ～1 day. Such densities may well be expected in star-forming regions and around massive Wolf-Rayet stars. 相似文献
4.
The proposed model explains the Moon formation as a result of a thermo-nuclear explosion due to which a big land mass was torn off from the Earth. Within the model framework, on the one hand, the data on the Moon’s physical and chemical parameters are in good agreement. On the other hand, this model corresponds to modern ideas about the dynamism of the Earth’s geological structure which presupposes the presence of a powerful energy source in the Earth’s core, which might have thermonuclear origin. 相似文献
5.
I. A. Usenko 《Astronomy Letters》2016,42(6):393-412
Based on five high-resolution spectra in the range 5625–7525 ?A taken in 1995 and covering the ascending branch of the light curve from minimum to maximum, we have performed spectroscopic studies of the classical Cepheid ζ Gem. The atmospheric parameters and chemical composition of the Cepheid have been refined. The abundances of the key elements of the evolution of yellow supergiants are typical for an object that has passed the first dredge-up: a C underabundance, N, Na, and Al overabundances, and nearly solar O and Mg abundances. We have estimated [Fe/H] = +0.01 dex; the abundances of the remaining elements are also nearly solar. The metal absorption lines in all spectra show a clear asymmetry and the formation of secondary blue (B1 and B2) and red (R1 and R2) components, just as for the Cepheid X Sgr. The Hα absorption line is also split into blue (B) and red (R) components with different depths changing with pulsation phase. To analyze the velocity field in the atmosphere of ζ Gem, we have estimated the radial velocities from specially selected (with clear signatures of the B1, B2, R1, and R2 components) absorption lines (neutral atoms and ions) of metals (38 lines) and the B and R components of the Hα line. Analysis of these estimates has shown that their scatter is from ?22 to 36 km s?1 for all pulsation phases but does not exceed 35–40 km s?1 for each individual phase, while it does not exceed 22 km s?1 for the Hα line components. The radial velocity estimates for the metal lines and their B1 and B2 components have been found to depend on the depths, suggesting the presence of a velocity gradient in the atmosphere. No significant difference in velocities between the atoms and ions of the metal lines is observed, i.e., there is no significant inhomogeneity in the upper atmospheric layers of the Cepheid. Since the averaged radial velocity estimates for the cores of the metal lines and their B1 and B2 components change with pulsation phase and coincide with those for the B component of the Hα line, they are all formed in the Cepheid’s atmosphere. The formation and passage of a shock wave due to the κ-mechanism at work can be responsible for the stronger scatter of the B1 and B2 components in their velocities at phases after the Cepheid’s minimum radius. The averaged velocities of the R1 components also change with pulsation phase and differ only slightly from the remaining ones. On the other hand, the mean velocity estimate for the R component of the Hα line at all phases is +32.72 ± 2.50 km s?1 and differs significantly from the bulk of the velocities, suggesting the formation of this component in the envelope around the Cepheid. The unusual behavior of the mean velocities for the R2 components of the metal absorption lines can also point to their formation in the envelope and can be yet another indicator of its presence around ζ Gem. 相似文献
6.
《New Astronomy》2015
We numerically integrate the Sun’s orbital movement around the barycenter of the solar system under the persistent perturbation of the planets from the epoch J2000.0, backward for about one millennium, and forward for another millennium to 3000 AD. Under the Sun–Planets Interaction (SPI) framework and interpretation of Wolff and Patrone (2010), we calculated the corresponding variations of the most important storage of the specific potential energy (PE) within the Sun that could be released by the exchanges between two rotating, fluid-mass elements that conserve its angular momentum. This energy comes about as a result of the roto-translational dynamics of the cell around the solar system barycenter. We find that the maximum variations of this PE storage correspond remarkably well with the occurrences of well-documented Grand Minima (GM) solar events throughout the available proxy solar magnetic activity records for the past 1000 yr. It is also clear that the maximum changes in PE precede the GM events in that we can identify precursor warnings to the imminent weakening of solar activity for an extended period. The dynamical explanation of these PE minima is connected to the minima of the Sun’s position relative to the barycenter as well as the significant amount of time the Sun’s inertial motion revolving near and close to the barycenter. We presented our calculation of PE forward by another 1000 yr until 3000 AD. If the assumption of the solar activity minima corresponding to PE minima is correct, then we can identify quite a few significant future solar activity GM events with a clustering of PE minima pulses starting at around 2150 AD, 2310 AD, 2500 AD, 2700 AD and 2850 AD. 相似文献
7.
Xiao-Qiang Tang Jin-Song Wang Qi-Ming Wang Department of Precision Instruments Tsinghua University Beijing National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(5):478-490
We propose a spatial three-degree-of-freedom (DOF) parallel mechanism combining two degrees of rotations and one degree of translation to support the active reflector units of a large spherical radio telescope. The kinematics, workspace and accuracy of the mechanism are analyzed. One-dimensional and two-dimensional fitting errors to the working region of active reflector are investigated. Dimensional parameters of the mechanism and active reflector unit are examined with respect to the requirement of fitting accuracy. The result of accuracy analysis shows the effectiveness and feasibility of the proposed mechanism, and gives a design rule to guarantee the highest working frequency required by large radio telescope. 相似文献
8.
We study the physical state of the photosphere at about 30 minutes before and at the onset of a 2N/M2 two-ribbon solar flare.
Semiempirical photospheric models are obtained for two Hα-kernels with the help of the SIR inversion code described by Ruiz
Cobo and del Toro Iniesta (Astrophys. J.
398, 375, 1992). The models derived from the inversion reproduce spectral observations in seven Fraunhofer lines. The inferred models show
variations in all photospheric parameters both before and at the onset of the flare relative to the quiet-Sun model. The temperature
enhancement in the upper photospheric layers is found in the atmospheres in both kernels. The dynamical structure in the models
reveals the variations at the onset of the flare relative to the preflaring ones. The inferred atmospheres show some difference
in the thermodynamical parameters of two kernels. 相似文献
9.
An improved correlation between maximum sunspot number (SSNM) and the preceding minimum (SSNm) is reported when the monthly mean sunspot numbers are smoothed with a 13-month running window. This relation allows prediction of the amplitude of a sunspot cycle by making use of the sunspot data alone. The estimated smoothed maximum sunspot number (126±26) and time of maximum epoch (second half of 2000) of cycle 23 are in good agreement with the predictions made by some of the precursor methods. 相似文献
10.
11.
We consider the instability of the cometary plasma tail which is composed of a neutral sheet,two lobes of the ion tail and solar wind.The plasma is assumed to be highly conductive and incompressible.The unstable state yields a magnetic field which is perpendicular to the tail axis.Our result is consistent with findings about plasma from the International Cometary Explorer(ICE). 相似文献
12.
The unexpected development of cycle 24 emphasizes the need for a better way to model future solar activity. In this article,
we analyze the accumulation of spotless days during individual cycles from 1798 – 2010. The analysis shows that spotless days
do not disappear abruptly in the transition toward an active Sun. A comparison with past cycles indicates that the ongoing
accumulation of spotless days is comparable to that of cycle 5 near the Dalton minimum and to that of cycles 12, 14, and 15.
It also suggests that the ongoing cycle has as much as 20±8 spotless days left, from July 2010, before it reaches the next
solar maximum. The last spotless day is predicted to be in December 2012, with an uncertainty of 11 months. This trend may
serve as input to the solar dynamo theories. 相似文献
13.
A replot of period derivative against period is done for about 300 pulsars, and the main features of the plot are discussed. The significance of a gap in this plot is reexamined and the existence of pulsars with nulling and subpulse drifting behaviour below this gap is pointed out. The implications of this for pulsar evolution are also discussed. 相似文献
14.
15.
Analysis of the radial velocities based on spectra of high (near the H α line) and moderate (4420–4960 Å) resolutions supplemented by the published radial velocities has revealed the binarity of a bright member of the young open star cluster χ Per, the star V622 Per. The derived orbital elements of the binary show that the lines of both components are seen in its spectrum, the orbital period is 5.2 days, and the binary is in the phase of active mass exchange. The photometric variability of the star is caused by the ellipsoidal shape of its components. Analysis of the spectroscopic and photometric variabilities has allowed the absolute parameters of the binary’s orbit and its components to be found. V622 Per is shown to be a classical Algol with moderate mass exchange in the binary. Mass transfer occurs from the less massive (\({M_1} = 9.1 \pm 2.7{M_ \odot }\)) but brighter (\(\log {L_1} = 4.52 \pm 0.10{L_ \odot }\)) component onto the more massive (\({M_2} = 13.0 \pm 3.5{M_ \odot }\)) and less bright (\(\log {L_2} = 3.96 \pm 0.10{L_ \odot }\)) component. Analysis of the spectra has confirmed an appreciable overabundance of CNO-cycle products in the atmosphere of the primary component. Comparison of the positions of the binary’s components on the T eff–log g diagram with the age of the cluster χ Per points to a possible delay in the evolution of the primary component due to mass loss by no more than 1–2Myr. 相似文献
16.
We studied the dependence of the A
p
-index describing the geomagnetic disturbance on the Moon’s phase. We processed available data for cycles 20–23 of the solar
activity by the epoch super-position method. We discovered that, in the declining branch of the solar cycle, the highest values
of the A
p
-index relative to an average value are observed near new moon. The difference of the A
p
-index values for new moon and full moon is approximately 18%. In the branch of increase and maximum of the solar cycle, we
observed minimum values of the A
p
-index during several days before full moon, and maximum values of the A
p
-index take place during several days after full moon. The conclusion follows from this that the mechanism of the Moon’s effect
on the earth’s magnetosphere is different essentially for intervals near new moon and full moon. 相似文献
17.
Astronomy Letters - Techniques for solving the problem of constructing a Stäckel model by generalizing the potential from the equatorial plane to the entire space are considered. The initial... 相似文献
18.
Arbab I. Arbab 《Astrophysics and Space Science》2010,326(1):61-67
We continue former work on the modeling of potential effects of Gamma Ray Bursts on Phanerozoic Earth. We focus on global
biospheric effects of ozone depletion and model the spectral reduction of light by NO2 formed in the stratosphere. We also illustrate the current complexities involved in the prediction of how terrestrial ecosystems
would respond to this kind of burst. We conclude that more biological field and laboratory data are needed to reach even moderate
accuracy in this modeling. 相似文献
19.
We have analyzed the Hubble Space Telescope spectrum of the young star FU Ori in the range 2300–3100 Å. The long-wavelength part of the spectrum is similar to the spectrum of a supergiant with T eff ? 5000–6000 K, but the range of wavelengths shorter than ?2600 Å is dominated by radiation from a region with T eff ? 9000 K. We discuss the possibility of explaining these peculiarities of the spectrum, the Al II] 2669.2 emission line profile, and the results of X-ray observations for FU Ori in terms of an accretion disk model whose thickness increases as the star is approached starting from distances ?1012 cm. Near the star, the disk has the shape of a cone in which only the part of its surface on the far (from the observer) side is visible. The suggested model is a kind of a compromise between the models of a thin α-disk and a supergiant: basically, this is an accretion model, but it resembles a supergiant in observational manifestations. Numerous absorption lines originating in the disk wind are superimposed on the disk spectrum. The wind is a cold (T ? 5000 K), dense (N e ? 1011 cm?3) gas. The number of wind absorption lines in the ultraviolet spectrum of FU Ori increases with decreasing wavelength. This causes a rapid decline in intensity in the short-wavelength part of the spectrum. As a result, the maximum temperature in the disk estimated from low-resolution IUE spectra has been underestimated. 相似文献