共查询到20条相似文献，搜索用时 593 毫秒
1.
S. B. Faruque 《Celestial Mechanics and Dynamical Astronomy》2003,87(4):353-369
A new analytic expression for the position of the infinitesimal body in the elliptic Sitnikov problem is presented. This solution is valid for small bounded oscillations in cases of moderate primary eccentricities. We first linearize the problem and obtain solution to this Hill's type equation. After that the lowest order nonlinear force is added to the problem. The final solution to the equation with nonlinear force included is obtained through first the use of a Courant and Snyder transformation followed by the Lindstedt–Poincaré perturbation method and again an application of Courant and Snyder transformation. The solution thus obtained is compared with existing solutions, and satisfactory agreement is found. 相似文献
2.
The localized ion density depletion region observed at comet Halley can be understood in terms of a thermal instability of the cometary plasma due to the excitation of rotational and vibrational levels of water molecules. The electron energy losses due to these processes peak near 4000 K and at higher temperatures a localized cooling leads to the thermal instability due to the increased radiation loss. The resulting increase in recombination leads to the ion density depletion and the estimates for this depletion at comet Halley agree with the observations. The transport effects at the density depletion region due to the diffusion and thermal conductivity are found have time scales larger than the instability time scale and does not affect the formation of the depletion region. 相似文献
3.
Piero Benvenuti 《Astrophysics and Space Science》1974,27(1):203-209
Short exposure plates of Comet Arend-Roland (1956h) are examined and compared with similar photographs of Comet Bennett (1969i), Comet Halley (1910 II) and Comet Mrkos (1957d). It is found that the emission structure of the dust near the nucleus in the first comet is different from that in the others, although in all cases we have the formation of parabolic envelopes. Close resemblances with configurations described by Wurm and Mammano (1972) have been found for Comet Halley and Comet Mrkos. 相似文献
4.
Krishna-Swamy KS Sandford SA Allamandola LJ Witteborn FC Bregman JD 《The Astrophysical journal》1989,340(1):527-549
A brief discussion of the infrared observations from 4 to 20 micrometers of seven comets is presented. The observed infrared emission from comets depends primarily on their heliocentric distance. A model based on grain populations composed of a mixture of silicate and amorphous carbon particles in the mass ratio of about 40 to 1, with a power-law size distribution similar to that inferred for comet Halley, is applied to the observations. The model provides a good match to the observed heliocentric variation of both the 10 micrometers feature and the overall thermal emission from comets West and Halley. Matches to the observations of comet IRAS-Araki-Alcock and the antitail of comet Kohoutek require slightly larger grains. While the model does not match the exact profile and position of the 3.4 micrometers feature discovered in comet Halley, it does produce a qualitative fit to the observed variation of the feature's strength as a function of heliocentric distance. The calculations predict that the continuum under the 3.4 micrometers feature is due primarily to thermal emission from the comet dust when the comet is close to the Sun and to scattered solar radiation at large heliocentric distances, as is observed. A brief discussion of the determination of cometary grain temperatures from the observed infrared emission is presented. It is found that the observed shape of the emission curve from about 4 to 8 micrometers provides the best spectral region for estimating the cometary grain temperature distribution. 相似文献
5.
V. K. Rosenbush 《Solar System Research》2005,39(4):312-321
Systematic and uniform sets of photometric and polarimetric observations of comet 1P/Halley have been analyzed. The phase dependence of brightness for comet Halley was obtained at phase angles α ranging from 1.4° ≤ α ≤ 65°. The following parameters were determined: the amplitude of the opposition effect Δm = 0.75m ± 0.06m; the half-width at a half-maximum of intensity HWHM = 6.4° ± 1.6°; the linear phase coefficient β = 0.0045 ± 0.0001 mag/deg for α from 30° ≤ α ≤ 65°; and the phase angle at which a nonlinear increase in brightness starts, α opp ≈ 31°. For the first time, the phase-angle dependence was obtained for the color of the dust of comet Halley: the color index BC-RC systematically decreases with increasing phase angle. Such a phase behavior of the dust color can be caused by the decrease in the mean size of dust particles that occurs when the comet approaches the Sun. For comet Halley, the negative polarization branch is almost symmetric; the minimal value of polarization is P
min = −1.54% at a phase angle αmin = 10.5°, and the inversion angle is αinv = 21.7°. A comparative analysis of the phase functions of brightness and polarization has been performed for the cometary dust and atmosphereless bodies. Among the latter are low-albedo asteroids of the P and C types (102 Miriam and 47 Aglaja, respectively), as well as Deimos; high-albedo objects, such as the E-type asteroid 64 Angelina and the icy satellite of Jupiter Europa; and the Moon with its intermediate albedo. The possibility of a weak depression in the negative polarization branch of comets Halley and 47P/Ashbrook-Jackson at phase angles smaller than 2° is discussed.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 4, 2005, pp. 353–363.Original Russian Text Copyright © 2005 by Rosenbush. 相似文献
6.
Thermal energy distribution of comet Halley have been obtained by using the data available from the Indian astronomical ephemeris. The magnitude vs wavelength, plots have also been enumerated and discussed. 相似文献
7.
An axisymmetric gasdynamical model of an interaction between the solar wind and comet atmospheres is formulated. Photoionization of the cometary neutral particles as well as their resonance charge-exchange are taken into account to determine the flow in the distured region containing three discontinuity surfaces (two shocks and the contact discontinuity).It is shown that these two processes are significant for many comets. The problem so formulated is solved numerically. A dependence of the obtained solutions on comets gas production, charge-exchange cross-section, photoionization time scale and other parameters is studied. The numerical solutions are in good agreement with the experimental data obtained during the spacecraft missions to the comet Halley in March 1986. 相似文献
8.
We present 190 astrometric positions of comet Halley and 46 positions of comet Giacobini-Zinner obtained at Fabra Observatory during the 1985/1986 campaign by the astrometric network of the International Halley Watch. 相似文献
9.
S. Ibadov 《Earth, Moon, and Planets》1995,68(1-3):323-327
A new approach is considered to the problem of ionization of the inner comas of comets connected with two phenomena: meteor-like process due to cometary molecules — interplanetary meteoroids impacts and explosion-type process due to high-velocity collisions between cometary dust grains and interplanetary meteoroids. It is found that the efficiency of explosive ionization exceeds the efficiency of meteor ionization approximately 100 times. The explosive ionization may be possible mechanism for anomaly ionization of the inner comae of dusty comets like Halley 1986 III with the dust to gas production rate ratio more than 0.1. 相似文献
10.
Arguments are presented to suggest that surface layers of the nuclei of periodic comets consist of crystallized rather than
amorphous water ice and thermal modelling of such nuclei is presented. The rate of sublimation of water from a rotating nucleus
is found to be greater than that from a uniformly heated nucleus. When the model is applied to P/Halley, the sublimation rate
at perihelion is found to be 8.1 × 1029 mol s−1 for a nucleus rotating with a period of 50 hours and 7.6 × 1029 for a uniformly heated nucleus on the premise that the effective radius of the nucleus is 2.5 km. The total sublimation of
water per revolution is 5.38 × 1036 molecules for P/Halley and 3.91 × 1036 molecules per P/Crommelin. The result so obtained is discussed in relation to the observational data. 相似文献
11.
In combination with the authors' previous observation about the splitting of Comet Halley in March 1986,the events involving the sharp,straight feature in the antisolar direction observed in the head of Cornet halley in 1910 (such as those occurring on May 14,25 and 31,and June 2) are redis-cussed.The analysis leads to the following scenario;When comet Halley explodes and splits,a fragment jettisoned or thrown off from the nucleus will,after moving in the direction of its tail,develop into a mini-comet.Although not weel developed or permanent,it has its own plasma tail and,sometimes,a dust tail.If Bobrovnikoff's definition of a secondary nucleus is assumed,then the fragment should be considered as a real secondary nucleus.It seems that the current idea of a tailward jet suggested by Sekanina and Larson is a wrong explanation for the plasma tail of a mini-comet and hence the rotation period of 52-53h for Comet Halley is doubtful. 相似文献
12.
The overall long-term behaviour of the total visual coma brightness of P/Halley during October 1982 – June 1986 is presented. The observations used in this study consist of the raw total magnitude data collected from the International Astronomical Union Circulars. We have compared the observed light curve with the predicted one. 相似文献
13.
《New Astronomy》2020
We analyzed the visible broadband photometric data of comets 1P/Halley and 4P/Faye, obtained during their perihelion passages of 1986 and 1991, respectively at the Sanglokh Observatory (Tajikistan) and the European Southern Observatory (Chile). Applying the Lomb-Scargle periodogram in the V-band magnitudes and B-V color index, we find that the most probable periodicities are 79 ± 6 and 7.36 ± 0.04 days for 1P, and 6.1 ± 0.3 days for 4P. After comparing results of color and magnitude periodograms, we argue there is a systematic difference in the number of signals identified and the level of confidence of the same periodicity in the periodograms. Our results suggest the quest for periodicities in the color of the coma of active comets should be complementary to ones in magnitudes. We have verified that the distribution of the color B-V of Faye’s coma was invariable during and after the possible occurrence of a post-perihelion outburst. We verify a symmetry in the pre- and post-perihelion H0 photoelectric absolute magnitude of the comet Halley. The same issues were not observed in the B-V color index. We verify that the absolute magnitude H0 of the comet Halley differs from each other when calculated from the visual or photoelectric magnitudes, due to the section of the coma used to estimate these magnitudes. We also verified that this difference in the photometric aperture can compromise comparisons of B-V color distributions between active comets. 相似文献
14.
We present 1-20 micrometers photometry of P/Giacobini-Zinner obtained at the NASA Infrared Telescope Facility, during 1985 June-September (r = 1.57-1.03 AU). A broad, weak 10 micrometers silicate emission feature was detected on August 26.6; a similar weak emission feature could have been hidden in the broadband photometry on other dates. The total scattering and emitting cross section of dust in the inner coma was similar to that in other short-period comets, but a factor of 10 (r = 1.56 AU) to 100 (r = 1.03 AU) lower than the amount of dust in Comet Halley. The thermal emission continuum can be fit with models weighted toward either small or large absorbing grains. The dust production rate near perihelion was approximately 10(5) g/s (small-grain model) to approximately 10(6) g/s (large-grain model). The corresponding dust/gas mass ratio on August 26 was approximately 0.1-1. A silicate-rich heterogeneous grain model with an excess of large particles is compatible with the observed spectrum of Giacobini-Zinner on August 26. Thus, weak or absent silicate emission does not necessarily imply an absence of silicates in the dust, although the abundance of silicate particles < or = 1 micrometer radius must have been lower than in Comet Halley. 相似文献
15.
Photometric observations of comet C/1995 O1 (Hale-Bopp) carried out at the Stará Lesná Observatory since February to April
1997 are analyzed and discussed. Emission band fluxes and continuum fluxes are presented, from which the total numbers of
molecules in the columns of the coma encircled by diaphragms are calculated. The production rates are estimated from the conventional
Haser model. We found that the photometric exponent of dust contribution two months prior perihelion was n = 5.2. The photometric
exponent n of the cometary magnitude solely to the C2 emission alone equals 3.3 and that of CN equals 2.5. These values can be explained by a fact that the maximums of production
rates of the gases were reached between March 2and 12 and not at the perihelion as it is valid for dust.
These results are compared with the values of 1P/Halley (1986 III) under the similar conditions, obtained with the same method
and instrument. C/Hale-Bopp exhibited 4.1 times more molecules radiating the CN-emission than 1P/Halley in the same column
of the coma. The continuum flux of C/Hale-Bopp was also very strong. The ratios (to 1P/Halley) are 94:1 (Cont. 484.5) and
74:1 (Cont. 365.0). The cometary colour was the same as that of the Sun.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
G. S. Lakhina 《Astrophysics and Space Science》1987,133(2):203-218
The pick up cometary ion distributions are shown to excite Alfvénic mode instabilities, slow ion-acoustic mode instability and a lower hybrid instability during solar wind-comet interaction. The growth rates of all these instabilities become larger as the comet is approached. The lower hybrid instability is shown to account for the low-frequency 0–300 Hz electrostatic turbulence observed near comet Halley. The Alfvén modes can grow to large amplitudes and become modulationally unstable, in the presence of low-frequency density fluctuations, going over to envelope Alfvén solitons. A model consisting of a gas of Alfvén solitons is suggested to explain the hydromagnetic turbulence observed near comet Halley and comet Giacobini-Zinner. 相似文献
17.
The paper deals with the effect of solar pressure on the motion and stability of two satellites connected by an inextensible string in a central gravitational field of force. A system of nonlinear, nonhomogeneous, and non-autonomous equations under the rotating frame of reference in Nechvíle's coordinate system have been obtained. The general solution of the above system of equations is beyond our reach. The particular solutions have been obtained.The particular solution in which the system lies, wholly along the radius vector joining the attracting centre and the centre of mass of the system under the central attracting force along was found to be stable (Singh, 1973). Naturally we got interested in examining the effect of solar radiation pressure on the stability of this particular solution. 相似文献
18.
M.G. Lebedev 《Astrophysics and Space Science》2000,274(1-2):221-230
The interaction between the Comet P/Grigg-Skjellerup ionosphere and the oncoming solar wind is numerically simulated on the
basis of the well-known gasdynamic single-fluid Biermann model. Numerical solutions are obtained using a discontinuity-fitting
technique based on the implicit second-order Babenko-Rusanov method. The salient features of the interaction pattern for GS
comet are nearly the same as in the previously considered case of the Comet P/Halley, although the gas productions of the
two comets near the perihelion differ by an order of magnitude. The results of the numerical simulation are correlated with
the data of onboard measurements performed during the `Giotto' encounter with GS comet in July 1992. The interaction region
geometry, as well as the profiles of the plasma velocity and the disturbed magnetic field strength along the `Giotto' path,
are compared. Theoretical and measured data are in a fairly good agreement, except for a near-nucleus region, where the MHD
effects may become predominant. In general, the MHD effects appear to be more pronounced in the GS case, as compared with
that of Halley comet, since during the `Giotto' – GS encounter the comet found itself in the `magnetic cloud' conditions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Using mainly Lyapunov characteristic numbers the stochasticity of Halley like cometary orbits has been investigated in the framework of different models of the restricted three body problem. 相似文献
20.
H. A. Shah W. Masood M. T. Asim M. N. S. Qureshi 《Astrophysics and Space Science》2014,350(2):615-622
In the present work, we have considered the nonlinear effects due to trapped electrons in an inhomogeneous degenerate quantum plasma. The formation of drift solitary structures has been investigated for both fully and partially degenerate plasmas. The Sagdeev potential approach has been employed to obtain arbitrary amplitude solitary structures. Interestingly, for a fixed value of density, not only compressive but rarefactive solitary structures have been obtained for a certain temperature range. Furthermore, it has been observed that the drift solitary structures exist only for the case when the drift velocity is smaller than the velocity of the nonlinear structure. The theoretical results obtained have been analyzed numerically for the parameters typically found in white dwarfs and the relevance of the results with regard to white dwarf asteroseismology is also pointed out. 相似文献