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1.
Splitting events affect cometary nuclei to a different level of severity ranging from complete disruption of the nucleus (e.g., C/1999 S4 LINEAR) to separation of major fragments (e.g., 73P/Schwassmann-Wachmann 3) and spill-offs of smaller boulders (e.g., C/2001 A2 LINEAR).Fragmentation of comets produces secondary products over a wide range of sizes (from cometesimals to sub-micron dust). It is detectable through the presence of fragments (with own comae and tails) in the coma of the parent nucleus, through outbursts in its activity and through arc-lets (“coma wings”)associated with fragments. The secondaries have different life times and show different non-gravitational forces. Nucleus splitting is also considered to generate whole families of comets (Kreutz group) or — if gravitational bound — multiple nuclei (e.g., C/1995 O1 Hale-Bopp). It may explain the striae phenomena seen in dust tails of bright comets (C/1995 O1 Hale-Bopp) and the detection of chains of impact craters onother bodies in the solar system. As process of significant mass loss it is relevant for the scenario of nucleus extinction, at the same time it also plays a role for the number statistics of existing (observable) comets and for the size distribution of comet nuclei. Various model scenarios for nucleus splitting are proposed: tidal disruption, rotational splitting, break-up due to internal gas pressure, fragmentation due to collision with other bodies. Only in one case, Comet D/1993 F1Shoemaker-Levy 9, the physical process of fragmentation could be undoubtedly identified. In any case, comet splitting provides important insights inthe internal structure, surface layering and chemistry of comet nuclei. 相似文献
2.
L. K. Jian C. T. Russell J. G. Luhmann A. B. Galvin P. J. MacNeice 《Solar physics》2009,259(1-2):345-360
The stream interaction region (SIR), formed when a fast stream overtakes a preceding slow stream, is the predominant large-scale solar wind structure at this early phase of the STEREO mission. Using multi-spacecraft observations from STEREO A and B, ACE, Wind, and Ulysses in 2007, we analyze three stream interaction events in depth in May, August, and November of 2007, respectively, when the spacecraft had quite different spatial separations. We attempt to determine the causes of the differences in the SIR properties, whether they are spatial or temporal variations, and also to examine the steepening or widening of the SIR during its radial evolution. The presence and characteristics of associated shocks, the relation to the heliospheric current sheet, and other structures are also studied. 相似文献
3.
Jay M. Pasachoff Evan D. Tingle Ingolf E. Dammasch Alphonse C. Sterling 《Solar physics》2011,268(1):151-163
Using mainly the 1600 Å continuum channel and also the 1216 Å Lyman-α channel (which includes some UV continuum and C iv emission) aboard the TRACE satellite, we observed the complete lifetime of a transient, bright chromospheric loop. Simultaneous observations with the SUMER instrument aboard the SOHO spacecraft revealed interesting material velocities through the Doppler effect existing above the chromospheric loop imaged with TRACE, possibly corresponding to extended nonvisible loops, or the base of an X-ray jet. 相似文献
4.
Moderate-resolution spectrophotometry (Δλ/λ～0.015) has shown the effects of known atmospheric constituents (NH3, CH4, C2H6) on the 5–8 μm spectrum of Jupiter. Broadband observations of Saturn at 6.5 μm are also reported. 相似文献
5.
1 INTRODUCTION Pulsars receive a large kick velocity during the period of birth, so they move away from theirbirth place, where the center of supernova remnant is believed to be. Measuring the propermotions of pulsars can derive an independent estimate of their ages, which has a number ofastrophysical uses, for example, in the studies of the evolution of neutron star magnetic fieldand of pulsar emission beam. There are three methods of measuring proper motion: (1) traditional optical metho… 相似文献
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Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggest that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field. 相似文献
8.
Recent observations have found that chromospheric spicules behave like Alfv′enic fluctuations.Low-frequency Alfv′en waves are predicted to partially reflect in the transition region that has a gradient in the Alfv′en speed,thereby producing inward Alfv′en waves,which may interact nonlinearly with outward Alfv′en waves to generate Alfv′enic turbulence.However,the signature of Alfv′enic turbulence in the chromosphere has not yet been quantitatively analyzed with observations.Here we analyze some characteristics related to Alfv′enic turbulence with the observations from Hinode/SOT.We decompose the height-time diagram of the transverse oscillations to separate the outward and inward propagating Alfv′enic-like signals.The counterpropagating waves are found to have similar amplitude,period and phase speed,suggesting a state having an approximate balance in bi-directional energy fluxes.Counterpropagation of intensity oscillation with lower propagation speed is also presented,probably indicating the presence of slow mode waves.Moreover,we attempt to estimate the Els¨asser spectra of the chromospheric turbulence for the first time.The relative fluctuations in the magnetic field may be measured as the local slope of wave-like shapes in spicules.The resulting low-frequency Els¨asser power spectra look similar to each other without showing a dominant population,which confirms these counterpropagating low-frequency Alfv′enic waves are in a state of balanced flux.These observational results are believed to help us better understand the nature of chromospheric turbulence as well as chromospheric heating. 相似文献
9.
E. K. J. Kilpua P. C. Liewer C. Farrugia J. G. Luhmann C. Möstl Y. Li Y. Liu B. J. Lynch C. T. Russell A. Vourlidas M. H. Acuna A. B. Galvin D. Larson J. A. Sauvaud 《Solar physics》2009,254(2):325-344
We analyze a series of complex interplanetary events and their solar origins that occurred between 19 and 23 May 2007 using
observations by the STEREO and Wind satellites. The analyses demonstrate the new opportunities offered by the STEREO multispacecraft configuration for diagnosing
the structure of in situ events and relating them to their solar sources. The investigated period was characterized by two high-speed solar wind streams
and magnetic clouds observed in the vicinity of the sector boundary. The observing satellites were separated by a longitudinal
distance comparable to the typical radial extent of magnetic clouds at 1 AU (fraction of an AU), and, indeed, clear differences
were evident in the records from these spacecraft. Two partial-halo coronal mass ejections (CMEs) were launched from the same
active region less than a day apart, the first on 19 May and the second on 20 May 2007. The clear signatures of the magnetic
cloud associated with the first CME were observed by STEREO B and Wind while only STEREO A recorded clear signatures of the magnetic cloud associated with the latter CME. Both magnetic clouds
appeared to have interacted strongly with the ambient solar wind and the data showed evidence that they were a part of the
coronal streamer belt. Wind and STEREO B also recorded a shocklike disturbance propagating inside a magnetic cloud that compressed the field and plasma
at the cloud’s trailing portion. The results illustrate how distant multisatellite observations can reveal the complex structure
of the extension of the coronal streamer into interplanetary space even during the solar activity minimum.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
10.
UV Tri was observed photometrically from 1999 to 2000 at the Xinglong Station of the National Astronomical Observatories, Chinese Academy of Sciences, and was also observed with Stroemgren uvby Hβ filter system at the Sierra Nevada Observatory (Spain) in 2000. From period analyses of the data, three pulsation frequencies, 9.3299 c d^-1, 10.8483 cd^-1 and 3.6035 cd^-1 were obtained. We derived color indices: b-y=0.215, m1=0.169, c1=0.783, and β=2.775. With these indices and some calibrations, we obtain:Mv=2.44, Mbol=2.27, logL/L⊙=0.99, and log Teff=3.875. Evolutionary sequences of stellar models with 1.00-2.00 solar masses, at steps of 0.05M⊙,are computed. Each sequence consists of 220 evolutionary intervals. From a comparison between the observed and calculated physical parameters we conclude that UV Tri is in an early evolutionary phase before the turn-off point. 相似文献
11.
Hui Dong Sui-Jian Xue Cheng Li Fu-Zhen Cheng Center for Astrophysics University of Science Technology of China Hefei National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2004,4(5):427-439
Chandra observations of the Seyfert-2 galaxies NGC 2110 and NGC 7582 are presented. With the superb spatial resolution of Chandra we found that in NGC 7582 the soft (≤2 keV) and hard (2-10 keV) X-rays are emitted in different regions, consistent with the report by Xue et al. By comparing the present X-ray data with the previous infrared data, we determined that the soft X-ray region is the site of starburst activities. We found no significant temporal variations during our observations. We confirm the previous finding that NGC 2110 and NGC 7582 are flat-spectrum sources. We argue that the flat spectra may result from a cold absorbing material such as envisaged in the “dual absorbed” model. Strong Fe Kα emission feature is detected in 6-7keV. Its equivalent width is so large that it cannot be reproduced by using the Galactic column density of - 10^22 cm^-2. 相似文献
12.
For H2O megamaser galaxy Mrk 266, its Chandra and XMM–Newton data are analyzed here. It shows existence of two obscured nuclei (separation is ~ 5″). Our preferred model, the high energy reflected model can fit the hard component of both nuclei spectra well. 相似文献
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The phenomena observed at the Sun have a variety of unique radio signatures that can be used to diagnose the processes in the solar atmosphere. The insights provided by radio observations are further enhanced when they are combined with observations from space-based telescopes. This Topical collection demonstrates the power of combination methodology at work and provides new results on i) type I solar radio bursts and thermal emission to study active regions; ii) type II and IV bursts to better understand the structure of coronal mass ejections; and iii) non-thermal gyro-synchrotron and/or type III bursts to improve the characterisation of particle acceleration in solar flares. The ongoing improvements in time, frequency, and spatial resolutions of ground-based telescopes reveal new levels in the complexity of solar phenomena and pose new questions. 相似文献
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XinJieMao Jiang－TaoSu 《中国天文和天体物理学报》2001,1(5):406-410
1 INTRODUCTIONFor the behavior of a molecular cloud in subsonic collision with another, Mao et al. (1992)have obtained simplified one-dimension traveling wave solutions for a plane-parallel s1ab. Chang-ing the sign in the transformation of variables in their case, we have the fOllowing results,1 rP = 2 l W op -- 1, (1)1 r =v = -- j W -- ry 1. (2)2 {V(N M)' 2z 2t -- W 1. (2)In Eq. (1), p increases with increasing t. Instability is expected to occur in strongly perturbedmolecular… 相似文献
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18.
S. Debarbat 《Celestial Mechanics and Dynamical Astronomy》1980,22(1):35-55
The Danjon astrolabe, first designed for the determination of time and latitude, has been used successfully for the improvement of star catalogues. From the very beginning of the sixities, it has also been used for planetary observations. From that time, systematic campaigns have been performed in various observatories and all major planets have been observed.The accuracy is of the same order of magnitude as that obtained with other instruments working in the field of positional astronomy. In this case, the instrument can contribute, by means of, meridian circles and astrographs to increase the available amount of observations for the purposes of celestial mechanics.Such observations for theories and ephemerides, issued from their improvements, would be of interest, the errors of the present ones being of the order-in some cases-of one arc-second, determined at the precision of a tenth of this value.Several improvements of the astrolabe have been taken into account such as the one which allows observations at different zenith distances. The length of arcs of trajectory for planets will increase and, with an adequate plate, it is now possible to observe the Sun. All the improvements, including a photoelectric device, will contribute to increasing the capability and the accuracy of the astrolabe, which is of interest in the field of planetary observations.Such a contribution, as well as those from the other classical instruments, will serve as a reference for the new technics such as radioastrometry, interferometry and space astrometry. This review paper must be considered as the contribution of the astrolabe to the various fields in which astrometry has to work at the present time.
Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978. 相似文献
Presented at the Symposium Star Catalogues, Positional Astronomy and Celestial Mechanics, held in honor of Paul Herget at the U.S. Naval Observatory, Washington, November 30, 1978. 相似文献
19.
A new CCD (V) light curve is presented for'the semi-detached binary system FU Ara. The light curve, obtained in 2007, is the first one since the last 50 years. With our data we were able to determine six new times of minimum light and refined the period of the system to 0.8645049 days. A Wilson-Devinney analysis leads to a solution of a semi-detached configuration, composed of a main-sequence primary component of spectral type F5, fractionally smaller than its Roche lobe, and an evolved secondary component of spectral type K I which fills its Roche lobe, and which is overluminous and oversized as compared with the main-sequence. The two components of FU Ara differ considerably in effective temperature. It is classified as an FO Virginis type of near-contact binary system. Assuming a reasonable value for the mass of the primary component, an estimate of the absolute elements of FU Ara has been made, on the assumption that the primary has a mass corresponding to its spectral type according to Svechnikov & Taidakova. 相似文献
20.
Comet Hale-Bopp was the largest comet by almost any definition, observed at least since the advent of modern observing techniques. In a more typical comet both the chemical and dynamical influences of collisional processes are limited by the short time a parcel of gas sublimated from the nucleus remains in the dense part of the coma. The resulting large size of the collisional coma in comet Hale-Bopp had important consequences on the dynamics of the coma, which in turn has important consequences on how observations are interpreted with standard models. Measured velocities of typical gas species (mostly the observed radicals) as well as dust were larger than normal comets. Conversely, velocities of super thermal atomic hydrogen were smaller than normal because of the samecollisional processes. Furthermore, as a consequence, dust particles, which are dragged by the outflowing gas, were also accelerated to larger velocities. Such larger velocities are not simply an interesting curiosity in their own right, because nearly all observations of dust and gas are interpreted with models of the coma that depend directly on some measurement or assumption with regard to velocity. In this presentation both observations and theory regarding the dynamical conditions in the coma of comet Hale-Bopp are summarized. 相似文献