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1.
Hourly interplanetary proton plasma data, measured by Helios-1 and Helios-2 heliocentric satellites over the period extending between the sunspot minimum and maximum of the 21rst solar cycle are analysed. This analysis gives an emphasis in the presence of a third type solar wind (intermediate) at 450 km s–1, appearing at solar minimum, during which large coronal holes are dominating in the Sun. This type of solar wind is hardly to be observed during the solar maximum period.Both Helios-1 and Helios-2 data give an average speed of the slow solar wind of 350 km s–1 for the period between these two extremes of solar activities.After correlation of the plasma temperature with its speed in different heliocentric distances, it comes out the stronger heating which takes place in distances shorter than 0.6 AU than in distances between 0.6 and 1.0 AU.A different behaviour of the radial proton temperature gradient in different solar activities appears after the calculation of the gradients as a function of solar wind speed and radial distance. 相似文献
2.
We have examined the effects of vaporization from the nucleus of a comet and show that a latitude dependence of vaporization can, in some cases, explain asymmetries in cometary light curves. We also find that a non-uniform distribution of solar radiation over a comet can considerably shorten the vaporization lifetime compared to the results normally obtained by assuming that the nuclear surface is isothermal.Independent of any latitude effects, comets with CO2-dominated nuclei and with perihelion distances less than 0.5 AU have vaporization lifetimes less than or comparable to their dynamical ejection times. This may explain the observed deficit of comets with small perihelion distances. Similarly comets with CO2-dominated nuclei and perihelia near Jupiter's orbit have vaporization lifetimes that are shorter than the time for capture into short-period orbits. We suggest, therefore, that at least some new comets are composed in large part of CO2, while only H2O-dominated comets, with lower vaporization rates, can survive to be captured into short-period orbits. 相似文献
3.
Yoshihide Kozai 《Planetary and Space Science》1997,45(12):1557-1560
Computing the maximum and minimum values of the eccentricities and inclinations as functions of the arguments of perihelion for about 7000 numbered asteroids by adopting a simple model it is found that 80 have the minimum perihelion distances less than 1.04 AU. Still, it is proved that 20% of them have no chance of colliding with the Earth, whereas 30 of them have relatively high collision probability as they have orbits similar to those of typical short-period comets. 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.
We observed the Mercury sodium exosphere during the period 1997-2003, collecting images of planetary sodium emission covering the full range of true anomaly angles with only a few small gaps. The distribution of sodium emission over the surface was generally non-uniform and changeable. When the dawn terminator was in view, the terminator was generally brighter than the limb, as expected for evaporation of condensed sodium at the dawn terminator. Also, the excess emission reached its largest values when radiation acceleration reached one or the other of its two maxima, as expected for the effect of radiation acceleration on sodium distribution. When the dusk terminator was in view, the limb was generally brighter than the terminator. The difference was larger than would be expected for a uniform sodium exosphere, suggesting that there is a deficit of sodium near the dusk terminator. There was no apparent effect of radiation acceleration on the ratio, which might be the result of a very large deficit of sodium near the dusk terminator. For the northern and southern hemispheres, excess sodium was observed about a third of the time in one or the other hemisphere, appearing at random intervals of true anomaly and longitude. The random nature of these occurrences suggests an external cause, one not correlated with any characteristic of the planetary orbit or planetary geochemistry. We suggest that the northern or southern excess sodium events are the result of solar weather, whereby solar particles are precipitated to the surface at high latitudes, and produce localized sources of sodium. IMF configurations for which solar particles can precipitate to high latitudes on the surface occur about 30% of the time, in general agreement with the observed frequency of north or south excess emission. Near periods of maximum radiation acceleration, some images displayed two peaks of sodium emission, one peak at high northern latitudes, the other at high southern latitudes. One possible cause could be the accumulation of sodium near the terminator, pushed there by radiation acceleration. 相似文献
6.
J. L. Bertaux E. Quémerais R. Lallement E. Kyrölä W. Schmidt T. Summanen J. P. Goutail M. Berthé J. Costa T. Holzer 《Solar physics》1997,175(2):737-770
After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange point, we report the main features
of SWAN observations. SWAN is mainly dedicated to the monitoring of the latitude distribution of the solar wind by the Lα
method. Maps of sky Lα emissions were recorded througout the year. The region of maximum emission, located in the upwind hemisphere,
deviates strongly from the pattern that could be expected from a solar wind constant with latitude. It is divided into two
lobes by a depression aligned with the solar equatorial plane called the Lyα groove already noted in 1976 Prognoz data. The
north lobe is much brighter than the south lobe. These two characteristics can be explained qualitatively by an enhanced ionization
along the neutral sheet where the slow solar wind is concentrated, which results from the higher low-latitude solar wind mass
flux as measured by Ulysses. The groove is the direct imprint on the sky of the enhanced carving by the slow solar wind, at
this time of solar minimum, when the tilt angle of the neutral sheet is small. The question is still pending to predict what
will happen with the ascending phase of the solar cycle. Observations of comets are briefly mentioned, with the ability of
SWAN to monitor the H2O production of many comets. Operations of the instrument are briefly described, including some instrumental problems which
could be solved by software modifications sent to the instrument.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004979605559 相似文献
7.
We present observational data for two long-period and three dynamically new comets observed at heliocentric distances between 5.8 to 14.0 AU. All of the comets exhibited activity beyond the distance at which water ice sublimation can be significant. We have conducted experiments on gas-laden amorphous ice samples and show that considerable gas emission occurs when the ice is heated below the temperature of the amorphous-crystalline ice phase transition (T∼137 K). We propose that annealing of amorphous water ice is the driver of activity in comets as they first enter the inner Solar System. Experimental data show that large grains can be ejected at low velocity during annealing and that the rate of brightening of the comet should decrease as the heliocentric distance decreases. These results are consistent with both historical observations of distant comet activity and with the data presented here. If observations of the onset of activity in a dynamically new comet are ever made, the distance at which this occurs would be a sensitive indicator of the temperature at which the comet had formed or represents the maximum temperature that it has experienced. New surveys such as Pan STARRS, may be able to detect these comets while they are still inactive. 相似文献
8.
A. E. Rosenbush 《Astronomische Nachrichten》1995,316(5):281-284
The radius of R CrB is estimated to 90–100 radii of the Sun. The dust layer, which is the cause of the deep minimum in the visible light of R Coronae Borealis-type stars, has a radius of about 6 radii of the star. This follows from the delay of the infrared light increase after the visual minimum and also from the analogy with the dust formation in novae. The emission lines appearing in the minimum have an origin analogous to the metal emissions in the comets of 1882 II and 1965 VIII in which they were observed at a distance of 20–30 R⊙. The permanent dust shell has a radius about of 26 stellar radii. 相似文献
9.
Plasma structures resulting from the solar wind interaction with weakcomets are discussed. Numericalsimulations using a newly
developed hybrid code are presented. The simulations are primarily applied to quantitative data for cometWirtanen, which will
be the target of the Rosetta mission. It isexpected that Wirtanen is very weak during the first encounter. The main purpose
is the discussion of the different features of the plasmaenvironment, such as the structured cycloidal plasma tail and non-linear
Mach cones typical for weak comets and their relation tostructures like shocklets, bow shock, diamagnetic cavity and the “classical”magnetotail
found at stronger comets. Furthermore, the sensitivity ofthese various features in dependence on the plasma parameters is
investigated. 相似文献
10.
K. R. Sivaraman 《Solar physics》1984,94(2):235-238
We have made number counts of the bright points that populate the interior of the Ca II network in the solar chromosphere for four solar cycles. We find that the number of these fine structures during the solar maximum exceeds that during the minimum phase on an average by 30%. The contribution due to this excess number would need to be taken into account while explaining the variation in the Ca II K emission profiles of the integrated sunlight from the solar minimum to the maximum. 相似文献
11.
L. E. Floyd P. A. Reiser P. C. Crane L. C. Herring D. K. Prinz G. E. Brueckner 《Solar physics》1998,177(1-2):79-87
The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) has measured the solar spectral irradiance for wavelengths 115–410 nm on a daily basis since October 11, 1991. The absolutely calibrated solar UV irradiances through January 8, 1996 have been produced. Their time-dependent behavior is similar to that of the Mgii index as measured both by NOAA-9 SBUV and by SUSIM itself. The maximum long-term variation observed by SUSIM is at L and is measured to be in excess of a factor of 2. This maximum variation decreases with increasing wavelength until about 300 nm where no significant long-term variation is directly measured above SUSIM's estimated 1–2% relative accuracy. The wavelength dependence of the measured UV variability is found to roughly correspond to the mean emission height given by solar atmospheric radiative transfer models. Because SUSIM observations began when solar activity was near its peak and now extend to very near its minimum, estimates of the solar cycle 22 UV variability are generated from a combination of these measurements and solar activity proxy indices. 相似文献
12.
Calcium K line spectroheliograms obtained during the solar minimum phases at Kodaikanal between 1913–1974 have been used to study the network cell sizes. The autocorrelation is calculated for two-dimensional strips at 5° interval up to ±50° latitude. The average size of the network cells was found to have a dependence on solar latitude with a maximum variation of about 7%. The pattern shows an apparent north–south symmetry with two minima at about 20° N and S. 相似文献
13.
We consider the possibility of the excitation of sodium resonance emission in cometary matter under solar radiation at a heliocentric distance of 5 AU, as was observed when a fragment of Comet Shoemaker-Levy 9 plunged into Jupiter. When the sodium emission is calculated, the multiple scattering in the cometary cloud is taken into account. We use a non-LTE radiative transfer code for a two-level model sodium atom. A comparison of the computed and observed Na I D emission line profiles allows the column density of the sodium atoms for specific times of observations of Comet Shoemaker-Levy 9 to be determined. The observed Na I(D1+D2) line profile was found to agree well with the computed profile for an optically thick sodium cloud. We calculated the column density of the sodium atoms for three comets from the observed intensity of the D2 line emission. We also calculated the D2/D1 intensity ratio for various optical depths of the sodium cloud and various phase angles. 相似文献
14.
Yngve Öhman 《Solar physics》1983,85(1):53-63
From a study of the chromospheric lines listed by Pierce (1968, 1973) indications have been found that first-order plasma satellites appear sometimes as a pair of faint chromospheric emission lines in such places where forbidden lines, mainly of metals, should be located. Second-order satellites are indicated sometimes by an asymmetry in the emission wings of stronger lines, either with respect to intensity or with respect to distance from the line centre and, if so, with the remote wing of diffuse shape. Finally diffuse faint lines, appearing in somewhat greater distances from strong chromospheric lines, suggest the appearance sometimes of fourth-order plasma satellites. All the three types of satellites give electron densities of the order of 1012 cm?3. Traces of possible absorption satellites are found also for some of the lines in the solar spectrum. In this connection special attention is drawn to a few faint solar lines located near the wavelengths of corona emission lines. The observational evidence is discussed on the bases of recent theoretical research by Drawin and Truong-Bach (1982a, b). 相似文献
15.
E. Hadamcik A. K. Sen A. C. Levasseur‐Regourd S. Roy Choudhury J. Lasue R. Gupta R. Botet 《Meteoritics & planetary science》2014,49(1):36-44
Comet C/2009 P1 (Garradd) was observed by imaging polarimetry for nearly 5 months from October 2011 to March 2012, over an intermediate phase angle range (28°–35°). Two months before perihelion and one month after, dust particles seem to be ejected all around the optocenter and jets extend to distances greater than 40,000 km. An increase of activity is noticed in intensity and polarization after perihelion. Two months before perihelion and one month after, the dust emission seems to be all around the optocenter. Two and three months after perihelion the jets are mainly toward the solar direction with an extension of more than 20,000 km projected on the sky. The values of the aperture polarization are comparable to those of other comets. On the polarization maps in October 2011 and January 2012 the higher polarization zones extend in large regions perpendicularly to the solar direction where jets are also observed. In February and March 2012, the polarization in the jets is larger in the solar direction than in the surrounding coma. By its activity visible on intensity images and polarization maps at large distances from the nucleus, comet Garradd probably belongs to the high‐Pmax class of comets. 相似文献
16.
A set of Mercury sodium emission data collected over a range of true anomaly angles during 1997-2003 was used to analyze the effect of solar radiation acceleration on sodium emissions. The variation of emission intensity with changing Doppler velocities throughout the orbit was minimized by normalizing the intensities to a constant true anomaly angle. The normalized intensities should be independent of orbital position if sodium density is constant. Plots of the normalized intensities against solar radiation acceleration showed very considerable scatter. However, the scatter was not random, but the result of a systematic variation, such that the normalized emission at a particular value of radiation acceleration took one or the other of two values, depending on the value of the true anomaly angle. We propose that this was the result of solar radiation acceleration changing the velocity of the sodium atoms, and consequently changing the solar continuum seen by the atoms. There is a positive feedback loop in the “out” leg of the orbit, such that radiation acceleration increases the solar continuum intensity seen by the atoms, and a negative feedback loop in the “in” leg of the orbit, such radiation acceleration decreases the continuum intensity. The observations could be approximately fit by assuming that sodium atoms are exposed to sunlight for an average of 1700 s. The emission values corrected for this effect showed much less scatter, with a general trend of about 30% to lower values from minimum to maximum radiation acceleration. The corrected emissions were used to calculate average column densities, and the result compared with the predictions of Smyth and Marconi [Smyth, W.H., Marconi, M.L., 1995. Astrophys. J. 441, 839-864] for the variation of column density with true anomaly angle. The comparison suggests that sodium atoms interact weakly with the surface. The effect of radiation acceleration on emission intensities should be taken into account if column densities are to be calculated from emission intensities. 相似文献
17.
Observations of solar radio emission at 3 cm wavelength have been made at Japal-Rangapur Observatory for 1980–1981, the solar maximum year using the 3 m radio telescope. The correlation between microwave solar emissions and the sunspot activity on monthly basis has been found to be high during the maximum phase and in the high cm wavelength band. The basic component has been estimated statistically for successive solar rotations using the data obtained at Japal-Rangapur Observatory. Further, this was compared with the data obtained at other cm wavelengths during 1980–1981 and the solar minimum period 1975–1976 of the 21st cycle. The comparison showed pronounced dips in flux levels at different wavelengths during the summer months of the solar maximum year which may be attributed to the presence of coronal holes in the various levels of the solar atmosphere. The computed basic component values showed pronounced variation at high cm wavelengths for the solar maximum period with dissimilar variations at different wavelengths. During the solar minimum period the variations were negligibly small and showed more or less constant level of activity.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
18.
Angular orbital parameters of Kreutz sungrazing comets are considered. Three groups of Kreutz dwarf comets are distinguished based on the positioning of orbit poles, and the motion of fragments from group A is modeled numerically. It is found that Kreutz dwarf comets have a very large parameter А 3 of nongravitational acceleration. This may be associated with sublimation of substances more refractory than water ice at extremely short heliocentric distances. It is demonstrated that the nongravitational acceleration of Kreutz dwarf comets is asymmetric with respect to perihelion, and the perturbing function maximum is observed ~15 min after the perihelion passage. 相似文献
19.
The brightness temperature distributions of the solar atmosphere in the polar region at the distances from one to two solar radii during the solar activity minimum are reported. Observations of the maximum phase of the solar eclipse of March 29, 2006 were carried out simultaneously on two sectors of the RATAN-600 radio telescope over a wide range of centimeter waves, 1–31 cm. This study is based on a comparison of models and observations carried out on the northeastern sector of the RATAN-600. 相似文献
20.
D. Bodewits D.J. Christian J.A. Carter K. Dennerl I. Ewing R. Hoekstra S.T. Lepri C.M. Lisse S.J. Wolk 《Astronomische Nachrichten》2012,333(4):335-340
Since the initial discovery of cometary charge exchange emission, more than 20 comets have been observed with a variety of X‐ray and UV observatories. This observational sample offers a broad variety of comets, solar wind environments and observational conditions. It clearly demonstrates that solar wind charge exchange emission provides a wealth of diagnostics, which are visible as spatial, temporal, and spectral emission features. We review the possibilities and limitations of each of those in this contribution (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献