The Gas Production Rate and Coma Structure of Comet C/1995 O1 (Hale–Bopp)     

Morgenthaler  Jeffrey P.  Harris  Walter M.  Roesler  Frederick L.  Scherb  Frank  Anderson  Christopher M.  Doane  Nathaniel E.  Oliversen  Ronald J. 《Earth, Moon, and Planets》2002,90(1-4):77-87

The University of Wisconsin–Madison and NASA–Goddard conducted acomprehensive multi-wavelength observing campaign of coma emissionsfrom comet Hale–Bopp, including OH 3080 Å, [O I] 6300 Å H₂O⁺ 6158 Å, H Balmer-α 6563 Å, NH₂ 6330 Å, [C I] 9850 ÅCN 3879 Å, C₂ 5141 Å, C₃ 4062 Å,C I 1657 Å, and the UV and optical continua. In thiswork, we concentrate on the results of the H₂O daughter studies.Our wide-field OH 3080 Å measured flux agrees with other, similarobservations and the expected value calculated from published waterproduction rates using standard H₂O and OH photochemistry.However, the total [O I] 6300 Å flux determined spectroscopically overa similar field-of-view was a factor of 3-4 higher than expected.Narrow-band [O I] images show this excess came from beyond theH₂O scale length, suggesting either a previously unknown source of[O I] or an error in the standard OH + ν→ O(¹ D) + H branching ratio. The Hale–Bopp OH and[O I] distributions, both of which were imaged tocometocentric distances >1 × 10⁶ km, were more spatiallyextended than those of comet Halley (after correcting for brightnessdifferences), suggesting a higher bulk outflow velocity. Evidence ofthe driving mechanism for this outflow is found in the Hα lineprofile, which was narrower than in comet Halley (though likelybecause of opacity effects, not as narrow as predicted by Monte-Carlomodels). This is consistent with greater collisional coupling betweenthe suprathermal H photodissociation products and Hale–Bopp's densecoma. Presumably because of mass loading of the solar wind by ionsand ions by the neutrals, the measured acceleration of H₂O⁺ downthe ion tail was much smaller than in comet Halley. Tailwardextensions in the azimuthal distributions of OH 3080 Å,[O I], and [C I] , as well as a Doppler asymmetry in the[O I] line profile, suggest ion-neutral coupling. While thetailward extension in the OH can be explained by increased neutralacceleration, the [O I] 6300 Å and [C I] 9850 Å emissions show 13%and >200% excesses in this direction (respectively), suggesting anon-negligible contribution from dissociative recombination of CO⁺and/or electron collisional excitation. Thus, models including theeffects of photo- and collisional chemistry are necessary for the fullinterpretation of these data.  相似文献   

Radial distribution of production rates, loss rates and densities corresponding to ion masses ?40 amu in the inner coma of Comet Halley: Composition and chemistry     

S.A. Haider 《Icarus》2005,177(1):196-216

In this paper we have studied the chemistry of C, H, N, O, and S compounds corresponding to ions of masses ?40 amu in the inner coma of the Comet 1P/Halley. The production rates, loss rates, and ion mass densities are calculated using the Analytical Yield Spectrum approach and solving coupled continuity equation controlled by the steady state photochemical equilibrium condition. The primary ionization sources in the model are solar EUV photons, photoelectrons, and auroral electrons of the solar wind origin. The chemical model couples ion-neutral, electron-neutral, photon-neutral and electron-ion reactions among ions, neutrals, electrons, and photons through over 600 chemical reactions. Of the 46 ions considered in the model the chemistry of 24 important ions (viz., CH₃OH⁺₂, H₃CO⁺, NH⁺₄, H₃S⁺, H₂CN⁺, H₂O⁺, NH⁺₃, CO⁺, C₃H⁺₃, OH⁺, H₃O⁺, CH₃OH⁺, C₃H⁺₄, C₂H⁺₂, C₂H⁺, HCO⁺, S⁺, CH⁺₃, H₂S⁺, O⁺, C⁺, CH⁺₄, C⁺₂, and O⁺₂) are discussed in this paper. At radial distances <1000 km, the electron density is mainly controlled by 6 ions, viz., NH⁺₄, H₃O⁺, CH₃OH⁺₂, H₃S⁺, H₂CN⁺, and H₂O⁺, in the decreasing order of their relative contribution. However, at distances >1000 km, the 6 major ions are H₃O⁺, CH₃OH⁺₂, H₂O⁺, H₃CO⁺, C₂H⁺₂, and NH⁺₄; along with ions CO⁺, OH⁺, and HCO⁺, whose importance increases with further increase in the radial distance. It is found that at radial distances greater than ∼1000 km (±500 km) the major chemical processes that govern the production and loss of several of the important ions in the inner coma are different from those that dominate at distances below this value. The importance of photoelectron impact ionization, and the relative contributions of solar EUV, and auroral and photoelectron ionization sources in the inner coma are clearly revealed by the present study. The calculated ion mass densities are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km. There is a reasonable agreement between the model calculation and the Giotto measurements. The nine major peaks in the IMS spectra between masses 10 and 40 amu are reproduced fairly well by the model within a factor of two inside the ionopause. We have presented simple formulae for calculating densities of the nine major ions, which contribute to the nine major peaks in the IMS spectra, throughout the inner coma that will be useful in estimating their densities without running the complex chemical models.  相似文献   

New Molecular Species in Comet C/1995 O1 (Hale-Bopp) Observed with the Caltech Ssubmillimeter Observatory     

Lis  D. C.  Mehringer  D. M.  Benford  D.  Gardner  M.  Phillips  T. G.  Bockelée-Morvan  D.  Biver  N.  Colom  P.  Crovisier  J.  Despois  D.  Rauer  H. 《Earth, Moon, and Planets》1997,78(1-3):13-20

We present millimeter-wave observations of HNCO, HC₃N, SO, NH₂CHO, H¹³CN, and H₃O⁺ in comet C/1995 O1 (Hale-Bopp)obtained in February–April, 1997 with the Caltech Submillimeter Observatory (CSO). HNCO, first detected at the CSO in comet C/1996B2 (Hyakutake), is securely confirmed in comet Hale-Bopp via observations of three rotational transitions. The derived abundance with respect to H₂O is (4-13) × 10^-4. HC₃N, SO, and NH₂CHO are detected for the first time in a comet. The fractional abundance of HC₃N based on observations of three rotational lines is (1.9 ± 0.2) × 10^-4. Four transitions of SO are detected and the derived fractional abundance, (2-8) ×10^-3, is higher than the upper limits derived from UV observations of previous comets. Observations of NH₂CHO imply a fractional abundance of (1-8) × 10^-4. H₃O is detected for the first time from the ground. The H¹³CN (3-2)transition is also detected and the derived HCN/H¹³CN abundance ratio is 90 ± 15, consistent with the terrestrial¹²C/¹³C ratio. In addition, a number of other molecular species are detected, including HNC, OCS, HCO⁺, CO⁺, and CN(the last two are first detections in a comet at radio wavelengths). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

H2O + ions in comets: models and observations     

《Planetary and Space Science》1999,47(6-7):745-763

An improved magnetohydrodynamic (MHD) model with chemistry is presented. The analysis of the source and sink terms for H₂O ⁺ shows that for small comets up to 11% of water molecules are finally ionized. For large comets (such as Halley) this fraction decreases to less than 3%. From the MHD scaling laws a similarity law for the individual ion densities is deduced which takes into account that the mother molecules are depleted by dissociation. This is applied to H₂O ⁺ ions. Radial density profiles from model calculations, observations by Giotto near comet Halley, and ground based observations of three comets confirm this scaling law for H₂O ⁺ ions. From the similarity law for the density a scaling law for the column density is derived which is more convenient to apply for ground based observations. From these scaling laws methods are derived which allow the determination of the water production rate from the ground based images of the H₂O ⁺ ions. Finally, the two dimensional images of model column densities are compared with observations.  相似文献   

Ion chemistry in the cometary atmosphere     

Mikio Shimizu 《Astrophysics and Space Science》1975,36(2):353-361

Dirty ice of a second kind (major components, H₂O, CO, and N₂; minor components less than several percents, NH₃, CH₄, and other organic substances such as HCN, CH₃CN etc.) is assumed for the composition of volatiles in the cometary nucleus. The consistency with the observations of molecular ions and daughter molecules in the cometary atmosphere is argued by taking into account various ion-molecular reactions and dissociative recombinations. There is a satisfactory agreement for the second kind of dirty-ice model, but the presence of large amounts of CH₄ and NH₃ is found to be rather in contradiction with observational evidence. A velocity of 8 km s^?1 for the hydrogen atoms, derived from analysis of the hydrogen Lyman-alpha corona around comets, is found from the dissociative recombination of H₃O⁺, the dominant constituent of cometary ionosphere, in accordance with H₃O⁺+e ^?→OH+H+H.  相似文献   

Spectra Of Split Comet C/1999 S4 (Linear)     

Churyumov  K. I.  Luk'yanyk  I. V.  Vlassyuk  V. V.  Borisov  N. V. 《Earth, Moon, and Planets》2002,90(1-4):141-146

We obtained spectra of comet C/1999 S4 (LINEAR) with the UAGS spectrograph(long slit and CCD) installed on the 1-m Zeiss reflector of the SAO of the RAS(Northern Caucuses, Nizhny Arkhyz) on July 23/24, 26/27 and 27/28, 2000. OnJuly 22/23, before the splitting of the cometary nucleus, several emission lines,such as C₂, C₃, CN, NH, CH, NH₂, CO⁺, H₂O⁺ wereclearly identified in the spectra. The inspections of the CCD spectra obtainedon July 27/28, 2000 reveals only very weak emission lines superimposed on thesolar reflection spectrum. From analyzing the surface brightness profile of C₂ along the slit the velocity of separation of two secondary fragments (V = 10 km/h) and the energy of the fragment separation (E = 8.7 × 10¹⁵ erg) were estimated. A luminescence cometary continuum of 26% of the total continuum level is detected in the spectra of the comet at 5000 Å. Possible mechanisms of nucleus splitting are discussed.  相似文献   

Electronic Sputtering Analysis of Astrophysical Ices     

L. S. Farenzena  P. Iza  R. Martinez  F. A. Fernandez-Lima  E. Seperuelo Duarte  G. S. Faraudo  C. R. Ponciano  M. G. P. Homem  A. Naves de Brito  K. Wien  E. F. da Silveira 《Earth, Moon, and Planets》2005,97(3-4):311-329

Experimental results on fast ion collision with icy surfaces having astrophysical interest are presented. ²⁵²Cf fission fragments projectiles were used to induce ejection of ionized material from H₂O, CO₂, CO, NH₃, N₂, O₂ and Ar ices; the secondary ions were identified by time-of-flight mass spectrometry. It is observed that all the bombarded frozen gas targets emit cluster ions which have the structure X_nR^±, where X is the neutral ice molecule and R^± is either an atomic or a molecular ion. The shape of the positive or negative ion mass spectra is characterized by a decreasing yield as the emitted ion mass increases and is generally described by the sum of two exponential functions. The positive ion water ice spectrum is dominated by the series (H₂O)_nH₃O⁺ and the negative ion spectrum by the series (H₂O)_nOH⁻ and (H₂O)_nO⁻. The positive ion CO₂ ice spectrum is characterized by R⁺ = C⁺, O⁺, CO⁺, O₂⁺ or CO₂⁺ and the negative one by R⁻ = CO₃⁻. The dominant series for ammonia ice correspond to R⁺ = NH₄⁺ and to R⁻ = NH₂⁻. The oxygen series are better described by (O₃)_nO_m⁺ secondary ions where m = 1, 2 or 3. Two positive ion series exist for N₂ ice: (N₂)_nN₂⁺ and (N₂)_nN⁺. For argon positive secondary ions, only the (Ar)_nAr⁺ series was observed. Most of the detected molecular ions were formed by one-step reactions. Ice temperature was varied from ∼20 K to complete sublimation.  相似文献   

Ion composition and chemistry in the coma of Comet 1P/Halley—A comparison between Giotto's Ion Mass Spectrometer and our ion-chemical network     

Martin Rubin  Kenneth C. Hansen  Michael R. Combi  Hans Balsiger 《Icarus》2009,199(2):505-519

In order to understand the cometary plasma environment it is important to track the closely linked chemical reactions that dominate ion evolution. We used a coupled MHD ion-chemistry model to analyze previously unpublished Giotto High Intensity Ion Mass Spectrometer (HIS-IMS) data. In this way we study the major species, but we also try to match some minor species like the CH_x and the NH_x groups. Crucial for this match is the model used for the electrons since they are important for ion-electron recombination. To further improve our results we included an enhanced density of supersonic electrons in the ion pile-up region which increases the local electron impact ionization. In this paper we discuss the results for the following important ions: C⁺, CH⁺, CH⁺₂, CH⁺₃, N⁺, NH⁺, NH⁺₂, NH⁺₃, NH⁺₄, O⁺, OH⁺, H₂O⁺, H₃O⁺, CO⁺, HCO⁺, H₃CO⁺, and CH₃OH⁺₂. We also address the inner shock which is very distinctive in our MHD model as well as in the IMS data. It is located just inside the contact surface at approximately 4550 km. Comparisons of the ion bulk flow directions and velocities from our MHD model with the data measured by the HIS-IMS give indication for a solar wind magnetic field direction different from the standard Parker angle at Halley's position. Our ion-chemical network model results are in a good agreement with the experimental data. In order to achieve the presented results we included an additional short lived inner source for the C⁺, CH⁺, and CH⁺₂ ions. Furthermore we performed our simulations with two different production rates to better match the measurements which is an indication for a change and/or an asymmetric pattern (e.g. jets) in the production rate during Giotto's fly-by at Halley's comet.  相似文献   

The structure of cometary ionospheres: I. H2O dominated comets     

W-H. IP  D.A. Mendis 《Icarus》1976,28(3):389-400

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Monte Carlo modeling of neutral gas and dust in the coma of Comet 1P/Halley     

Martin Rubin  Valeriy M. Tenishev  Kenneth C. Hansen  Kathrin Altwegg 《Icarus》2011,213(2):655-677

The neutral gas environment of a comet is largely influenced by dissociation of parent molecules created at the surface of the comet and collisions of all the involved species. We compare the results from a kinetic model of the neutral cometary environment with measurements from the Neutral Mass Spectrometer and the Dust Impact Detection System onboard the Giotto spacecraft taken during the fly-by at Comet 1P/Halley in 1986. We also show that our model is in good agreement with contemporaneous measurements obtained by the International Ultraviolet Explorer, sounding rocket experiments, and various ground based observations.The model solves the Boltzmann equation with a Direct Simulation Monte Carlo technique (Tenishev, V., Combi, M., Davidsson, B. [2008]. Astrophys. J. 685, 659-677) by tracking trajectories of gas molecules and dust grains under the influence of the comet’s weak gravity field with momentum exchange among particles modeled in a probabilistic manner. The cometary nucleus is considered to be the source of dust and the parent species (in our model: H₂O, CO, H₂CO, CO₂, CH₃OH, C₂H₆, C₂H₄, C₂H₂, HCN, NH₃, and CH₄) in the coma. Subsequently our model also tracks the corresponding dissociation products (H, H₂, O, OH, C, CH, CH₂, CH₃, N, NH, NH₂, C₂, C₂H, C₂H₅, CN, and HCO) from the comet’s surface all the way out to 10⁶ km.As a result we are able to further constrain cometary the gas production rates of CO (13%), CO₂ (2.5%), and H₂CO (1.5%) relative to water without invoking unknown extended sources.  相似文献   

Spectral studies of comet C/2001 Q4 (NEAT)     

A. V. Ivanova  P. P. Korsun  S. A. Borisenko  Yu. N. Ivashchenko 《Solar System Research》2013,47(2):71-79

The paper presents the results of the spectral observations of comet C/2001 Q4 (NEAT) acquired with the Zeiss-600 telescope of the Andrushevka astronomical observatory in May 2004. The spectrum of the comet was obtained in the range of 3600–8200 Å. We identified a number of emission features in the spectrum of comet C/2001 Q4 (NEAT). The emission bands of C₂, C₃, CN, CH, NH₂, H₂O⁺ were detected in the spectrum of the comet, and their intensities were determined. The ratios of gas-production rates Q(C₂)/Q(CN) = 0.23, Q(C₃)/Q(CN) = ?0.79, and Q(NH₂)/Q(CN) = ?0.029 were determined with the Haser model.  相似文献   

Negative ion chemistry in the coma of comet 1P/Halley     

M. A. Cordiner  S. B. Charnley 《Meteoritics & planetary science》2014,49(1):21-27

Negative ions (anions) were identified in the coma of comet 1P/Halley during in situ Electron Electrostatic Analyzer measurements performed by the Giotto spacecraft in 1986. These anions were detected with masses in the range 7–110 amu, but with insufficient mass resolution to permit unambiguous identification. We present details of a new chemical‐hydrodynamic model for the coma of comet Halley that includes—for the first time—atomic and molecular anions, in addition to a comprehensive hydrocarbon chemistry. Anion number densities are calculated as a function of radius in the coma, and compared with the Giotto results. Important anion production mechanisms are found to include radiative electron attachment, polar photodissociation, dissociative electron attachment, and proton transfer. The polyyne anions C₄H^? and C₆H^? are found to be likely candidates to explain the Giotto anion mass spectrum in the range 49–73 amu. The CN^? anion probably makes a significant contribution to the mass spectrum at 26 amu. Larger carbon‐chain anions such as C₈H^? can explain the peak near 100 amu provided there is a source of large carbon‐chain‐bearing molecules from the cometary nucleus.  相似文献   

Models of the cometary coma in which abundances are calculated for various heliocentric distances     

Michael B. Swift  George F. Mitchell 《Icarus》1981,47(3):412-430

One-dimensional radial models of the chemistry in cometary comae have been constructed for heliocentric distances ranging from 2 to 0.125 AU. The coma's opacity to solar radiation is included and photolytic reaction rates are calculated. A parent volatile mixture similar to that found in interstellar molecular clouds is assumed. Profiles through the coma of number density and column density are presented for H₂O, OH, O, CN, C₂, C₃, CH, and NH₂. Whole-coma abundances are presented for NH₂, CH, C₂, C₃, CN, OH, CO⁺, H₂O⁺, CH⁺, N₂⁺, and CO₂⁺.  相似文献   

Low energy ions in the shuttle environment: Evidence for strong ambient-contaminant interactions     

D.E. Hunton  J.M. Calo 《Planetary and Space Science》1985,33(8):945-951

The quadrupole mass spectrometer flown by the Air Force Geophysics Laboratory on STS-4 in 1982 detected large intensities of several ions, primarily O⁺, H₂O⁺ and H₃O⁺, with energies less than 1.5 e V with respect to the Shuttle Orbiter. Ion-molecule reactions and non-reactive scattering between the outgassing neutral flux from the Orbiter surfaces and the ambient ionic species are identified as the primary source of these low energy ions.  相似文献   

Optical interferometric observations of a transient event of 1986 March 13 in the coma of Comet Halley     

C. Debi Prasad  T. Chandrasekhar  J. N. Desai  N. M. Ashok  Vinod Krishan 《Journal of Astrophysics and Astronomy》1989,10(1):1-20

During the recent apparition of Comet Halley in 1985-86 a transient ionic event in the form of a blob of H₂ O⁺ emission was recorded in thecoma at ～ 0^h UT on 1986 March 13. Observations were carried out using a special IHW filter for H₂ O⁺ emission at 7000 å/175 å, a 35 cm telescope, a Fabry-Perot interferometer and an image intensifier camera from Gurushikhar, Mt Abu. (24?39’N,72? 47’E). A Fabry-Perot inter-ferogram in Ha taken a few minutes later at the same location reveals strong hydrogen emission (Hα) associated with the blob. The velocity field in the blob is structured with relative velocities upto ～ 35km s^?1. The event is interpreted as arising due to the sector boundary crossing of the interplanetary magnetic field by the comet  相似文献   

Infrared measurements of the chemical composition of C/2006 P1 McNaught     

Neil Dello Russo  Ronald J. Vervack Jr.  Harold A. Weaver  Carey M. Lisse 《Icarus》2009,200(1):271-279

C/2006 P1 McNaught is a dynamically new comet from the Oort cloud that passed very close to the Sun, driving overall volatile production rates up to about 10³¹ molecules s⁻¹. Post-perihelion observations were obtained in a target-of-opportunity campaign using the CSHELL instrument at the NASA Infrared Telescope Facility atop Mauna Kea, Hawaii, on UT 2007 January 27 and 28. Eight parent volatiles (H₂O, CH₄, C₂H₂, C₂H₆, HCN, CO, NH₃, H₂CO) and two daughter fragments (OH and NH₂) were detected, enabling the determination of a rotational temperature and production rate for H₂O on UT January 27 and absolute and relative production rates for all the detected parent species on UT January 28. The chemical composition measured in the coma suggests that this close perihelion passage stripped off processed outer surface layers, likely exposing relatively fresh primordial material during these observations. The post-perihelion abundances we measure for CO and CH₄ (relative to H₂O) are slightly depleted while C₂H₂, NH₂ and possibly NH₃ are enhanced when compared to the overall comet population. Measured abundances for other detected molecular species were within the range typically observed in comets.  相似文献   

A Multi-Wavelength Simultaneous Study of the Composition of the Halley Family Comet 8P/Tuttle     

E. Jehin  D. Bockelée-Morvan  N. Dello Russo  J. Manfroid  D. Hutsemékers  H. Kawakita  H. Kobayashi  R. Schulz  A. Smette  J. Stüwe  M. Weiler  C. Arpigny  N. Biver  A. Cochran  J. Crovisier  P. Magain  H. Rauer  H. Sana  R. J. Vervack  H. Weaver  J.-M. Zucconi 《Earth, Moon, and Planets》2009,105(2-4):343-349

We report on simultaneous optical and infrared observations of the Halley Family comet 8P/Tuttle performed with the ESO Very Large Telescope. Such multi-wavelength and coordinated observations are a good example of what can be done to support space missions. From high resolution optical spectroscopy of the CN (0,0) 388 nm and NH₂ (0,9,0) 610 nm bands using UVES at UT2 we determined ¹²C/¹³C = 90 ± 10 and ¹⁴N/¹⁵N = 150 ± 20 in CN and we derived a nuclear spin temperature of NH₃ of 29 ± 1 K. These values are similar to those found in Oort-Cloud and Jupiter Family comets. From low resolution long slit spectroscopy with FORS1 at UT2 we determined the CN, C₃ and C₂ production rates and the parent and daughter scale lengths up to 5.2 10⁵ km tailward. From high resolution IR spectroscopy with CRIRES at UT1 we measured simultaneously the production rates and mixing ratios of H₂O, HCN, C₂H₂, CH₄, C₂H₆, and CH₃OH.  相似文献   

The molecular composition of Comet C/2007 W1 (Boattini): Evidence of a peculiar outgassing and a rich chemistry     

G.L. Villanueva  M.J. Mumma  B.P. Bonev  E.L. Gibb  G.A. Blake 《Icarus》2011,216(1):227-240

We measured the chemical composition of Comet C/2007 W1 (Boattini) using the long-slit echelle grating spectrograph at Keck-2 (NIRSPEC) on 2008 July 9 and 10. We sampled 11 volatile species (H₂O, OH^∗, C₂H₆, CH₃OH, H₂CO, CH₄, HCN, C₂H₂, NH₃, NH₂, and CO), and retrieved three important cosmogonic indicators: the ortho-para ratios of H₂O and CH₄, and an upper-limit for the D/H ratio in water. The abundance ratios of almost all trace volatiles (relative to water) are among the highest ever observed in a comet. The comet also revealed a complex outgassing pattern, with some volatiles (the polar species H₂O and CH₃OH) presenting very asymmetric spatial profiles (extended in the anti-sunward hemisphere), while others (e.g., C₂H₆ and HCN) showed particularly symmetric profiles. We present emission profiles measured along the Sun-comet line for all observed volatiles, and discuss different production scenarios needed to explain them. We interpret the emission profiles in terms of release from two distinct moieties of ice, the first being clumps of mixed ice and dust released from the nucleus into the sunward hemisphere. The second moiety considered is very small grains of nearly pure polar ice (water and methanol, without dark material or apolar volatiles). Such grains would sublimate only very slowly, and could be swept into the anti-sunward hemisphere by radiation pressure and solar-actuated non-gravitational jet forces, thus providing an extended source in the anti-sunward hemisphere.  相似文献   

The evolution of charged particles in a model of contracting cloud     

M. S. El-Nawawy  M. Y. Amin 《Earth, Moon, and Planets》1996,75(1):41-51

The evolution of the charged particles are followed during contraction of a model of an interstellar cloud, with initial density number of n = 10 cm^–3. The contraction is followed up to density increase by five orders of magnitude. Special care is given to the details of the negative ions. In addition, we have tested the ambipolar diffusion according to the results of the ion density.The results predict the importance of atomic ions in the diffuse regions. H⁺ and C⁺ are distinctly enhanced in the beginning of contraction but decrease as contraction proceeds. Molecular ions enhance as contraction proceeds and becomes important in dense regions. The most enhanced molecular ions are HCO⁺, O₂ ⁺, C₂H₃ ⁺, H₃O⁺ and SO⁺, H₃ ⁺ is less abundant. The atomic ions (except metalic ions) decrease noticeably as density increases. In general the negative ions are of negligible fractional abundances. It has also been found that the time of ambipolar diffusion is shorter than the dynamical time, hence the magnetic field should be weakened in the central core as the central density increases to n = 10⁴ cm^–3.  相似文献   

Ion composition and solar wind interaction: Observations of comet C/1995 O1 (Hale-Bopp)     

Rauer  H. 《Earth, Moon, and Planets》1997,79(1-3):161-178

The extraordinary brightness of comet Hale-Bopp (C/1995 O1) offered the rare opportunity to investigate its ion tail by observations over a wide range of wavelengths. For the first time, ion emission lines could be detected in the radio domain, originating from H₃O⁺, HCO⁺ and CO⁺ ions. Observations in the extreme ultraviolet range showed O⁺ emissions. Optical imaging observations show a spectacular detail of structures in the ion tail. The combined measurements of the ion spatial distribution and dynamic provide a wealth of information which needs to be understood in terms of models of the comet-solar wind interaction and ion-neutral molecule reactions in the coma. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献