共查询到20条相似文献,搜索用时 15 毫秒
1.
Korsun P. P. Davis S. P. Shavrina A. V. Vasiljeva I. E. Malanushenko V. P. Savanov I. S. 《Earth, Moon, and Planets》1997,78(1-3):119-125
Spectroscopic observations of Comet Hale-Bopp were made at the 2.6 m Shajn Telescope of the Crimean Astrophysical Observatory. Some spectra were obtained with high spectral resolution, FWHM = 0.18–0.4Å, in the coude focus on February 22 and 26, 1997. The observations were made in selected spectral windows (4805–4872 Å,6528–6595 Å, 7186–7253 Å, 8276–8408 Å).The spectrograph slit was centered on the nucleus and had dimensions of 25.2 × 0.6 arcsec2 on the plane of the sky. The continuum spatial profiles were extremely asymmetrical toward the Sun. However, the continuum-subtracted spatial profiles of the molecular emissions were symmetrical relative to the nucleus, except for C2. The shape of the spatial profiles of the C2 emissions is similar to that one of continuum but is more flattened. So, there are evidences that dust can be an additional source of the C2 radicals in the cometary coma. The main aim of our research was identification of the cometary emissions. Using recent laboratory spectroscopic data we identified newlines of C2 associated with the transitions from high rotational levels in the 4805–4872 Å spectral region. We detected cometary Hα emission as well. Emissions of NH2, H2O+,and C2 (Phillips system) were found in the red spectral windows. Some emission features are still unassigned. 相似文献
2.
Spectra of the four comets, Tuttle, Stephan-Oterma, Brooks 2, and Bowell, were taken with a prototype space telescope charge coupled device (CCD) camera using a 500 × 500 Texas Instruments chip. The spectra extended from 5600 to 10,400 Å at a resolution of . The spatial coverage along the slit was 180?; its resolution was defined by the seeing (). Both absolute flux scales and spectral albedos were determined with the data reduction procedure which included flat fielding and sky subtraction. Comet Tuttle displayed extensive emissions by NH2, the red system of CN, and the C2 Swan bands as well as emissions by the forbidden oxygen lines [OI] 1D at 6300 and 6364 Å, and the ionic species H2O+. A feature at 6851 Å has been tentatively identified as the 3-0 band of CS+. Notable is the absence of the C2 Phillips bands whose transitions are optimally placed in our spectrum. The much dustier comet, Stephan-Oterma showed emissions by CN, NH2, and [OI] while only [OI] could be discerned in the noisier Brooks 2 spectrum. The fresh comet Bowell exhibited an unusually extended coma with an albedo times cross section two orders of magnitude larger than the other comets, a very flat albedo spectrum, and no emission features. For Tuttle and Stephan-Oterma, CN and NH2 column densities using a number of bands were calculated. The CN band intensity ratios show good agreement with theoretical fluorescence models. The spatial profiles for CN and NH2 were compared to two step Haser model decay calculations. The scale lengths most consistent with the data were compared with values previously reported and with values expected for various photodissociation reactions. Production rates were calculated for CN and NH2. These should be less model dependent because of the simultaneous collection of spectral and spatial information. The production rate ratios of the parents of CN and NH2 to the parent of OH are several orders of magnitude smaller than the solar abundance ratios of C/O and N/O. 相似文献
3.
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
4.
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
5.
N.N. Shefov 《Planetary and Space Science》1983,31(11):1371-1372
Frank-Condon factors for H2O+ bands have been calculated. They are used to estimate the photon scattering coefficient g8.0 for the (8,0) band at 6158 Å. 相似文献
6.
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 XnR±, 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)nOm+ 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
7.
J. L. Kohl G. Noci E. Antonucci G. Tondello M. C. E. Huber L. D. Gardner P. Nicolosi L. Strachan S. Fineschi J. C. Raymond M. Romoli D. Spadaro A. Panasyuk O. H. W. Siegmund C. Benna A. Ciaravella S. R. Cranmer S. Giordano M. Karovska R. Martin J. Michels A. Modigliani G. Naletto C. Pernechele G. Poletto P. L. Smith 《Solar physics》1997,175(2):613-644
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used to observe the extended solar corona from 1.25 to 10 R⊙ from Sun center. Initial observations of polar coronal holes and equatorial streamers are described. The observations include measurements of spectral line profiles for HI Lα and Lβ, Ovi 1032 Å and 1037 Å, Mgx 625 Å, Fexii 1242 Å and several others. Intensities for Mgx 610 Å, Sixii 499 Å, and 520 Å, Sx 1196 Å, and 22 others have been observed. Preliminary results for derived H0, O5+, Mg9+, and Fe11+ velocity distributions and initial indications of outflow velocities for O5+ are described. In streamers, the H0 velocity distribution along the line of sight (specified by the value at e-1, along the line of sight) decreases from a maximum value of about 180 km s-1 at 2 R⊙ to about 140 km s-1 at 8 R⊙. The value for O5+ increases with height reaching a value of 150 km s-1 at 4.7 R⊙. In polar coronal holes, the O5+ velocity at e-1 is about equal to that of H0 at 1.7 R⊙ and significantly larger at 2.1 R⊙. The O5+ in both streamers and coronal holes were found to have anisotropic velocity distributions with the smaller values in the radial direction. 相似文献
8.
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
9.
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
10.
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
11.
The spectroscopic observations of comet C/2009 R1 (McNaught) were carried out with the 2 m Zeiss-RCC Telescope of Pik Terskol Observatory operated by the International Center for Astronomical and Medico-Ecological Research (Ukraine, Russia). The Multi Mode Cassegrain spectrometer was used to obtain spectra of moderate spectral resolving power with a wavelength coverage from 4140 to 5240 Å. The spectrum is characterized by the extremely low continuum level and strong molecular features. 192 emission lines of C2, CN, CH, NH2, CO+, and CH+ have been identified by the comparison of the observed and theoretical spectra of the molecules. The ratios of the gas production rates of Q(C2)/Q(CN)=1.32, Q(CH)/Q(CN)=0.49, and Q(NH2)/Q(CN)=0.81 were derived using a Haser model. 相似文献
12.
The production rate of H2O molecules at a heliocentric distance of 1 AU for comet Halley and the abundance ratio with respect to water (H2O) of parent molecules at the cometary nucleus from the paper of Yamamoto (1987) have been used to compute the number densities of positive ions viz. H3O+, H3S+, H2CN+, H3CO+, CH3OH
2
+
and NH
4
+
at various cometocentric distances within 600 kms from the nucleus.The role of proton transfer reactions in producing major ionic species is discussed. A major finding of the present investigation is that NH
4
+
ion which may be produced through proton transfer reactions is the most abundant ion near the nucleus of a comet unless the abundance of NH3 as a parent is abnormally low. Using the quoted value of Q(NH3)/Q(H2O) for comet Halley and the life times of NH3 and H2O molecules, the abundance ratio N(NH3)/N(H2O) is found to be one-third of that used in the present paper. The consequent proportionate decrease in the NH
4
+
ions does not, however, affect its superiority in number density over other ions near the nucleus.The number density of the next most abundant ion viz. H3O+ is found to be 4 × 104 cm-3 at the nucleus of comet Halley and decreases by a factor of two only upto a distance of 600 K ms from the nucleus. The ionic mass peak recorded by VEGA and GIOTTO spacecrafts atm/q = 18 is most probably composite of the minor ionic species H2O+, as its number density = 102 cm-3 remains virtually constant in the inner coma and of NH
4
+
, the number density of which at large cometocentric distances may add to the recorded peak atmlq = 18. The number densities of other major ions produced through proton transfer from H3O+ are also discussed in the region within 600 K ms from the nucleus of comet Halley. 相似文献
13.
14.
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 CHx and the NHx 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
15.
The height of the lower red border of type-B aurora has been determined by triangulation using TV cameras at two ground stations. A mean height of 91.4 ± 1.1 km was determined from a set of 12 measurements made under ideal conditions. A TV spectrograph was used simultaneously to seek possible spectral changes between 6400 and 6900 Å which would be indicative of changes in the vibrational distribution in the N2 First Positive bands. No significant difference was found in this distribution between the spectra from 93 and 122 km. The height distribution of contributions to the OI 5577 Å emission relative to the N+2 First Negative emission was modelled from 80 to 160 km. Contributions from electron impact on atomic O, O+2 dissociative recombination and N2(A)O energy transfer were included. Account was taken of recent laboratory data on O(1S) quenching. It was concluded that these processes could explain the excitation of O(1S) in normal aurora and the height distribution of OI 5577 Å in type-B red aurora. It was confirmed that the lifetime ofO(1S) in type-B red auroral rapid time variations is about 0.5 s and it was found from the model that the observed time variation can be reproduced by the mechanisms considered, provided the concentration of NO in the auroral atmosphere is about 1 × 109 at 95 km. Before reasonable certainty can be attained in the correctness of the interpretation it will however be necessary to have reliable simultaneous observations of neutral atmospheric composition particularly for O and NO as well as unchallengeable measurements of the yields of O(1S) for the processes considered and for several other processes which have been suggested recently. 相似文献
16.
Spectra of Saturn in the spectral region 10.0–10.7 μm are presented which confirm the presence of PH3. Comparison to synthetic spectra indicates a PH3 mixing ratio of at least 2 × 10?6. No spectral features due to NH3 or C2H4 were observed. 相似文献
17.
G. Kockarts 《Planetary and Space Science》1976,24(6):589-604
The penetration in the terrestrial atmosphere of solar radiation corresponding to the spectral range of the Schumann-Runge bands of molecular oxygen is analyzed between 1750 and 2050 Å. The variation of the absorption cross section with temperature is taken into account and it is shown that average O2 absorption cross sections cannot lead to correct photodissociation coefficients. Reduction factors are defined in order to simplify the computation of the molecular oxygen photodissociation and to permit a simple determination of the photodissociation coefficients of any minor constituent with smoothly varying absorption cross section. Examples are given for O2, H2O, CO2, N2O, HNO3 and H2O2. Numerical approximations are developed for three types of spectral subdivisions: Schumann-Runge band intervals, 500 cm?1 and 10 Å intervals. The approximations are valid from the lower thermosphere down to the stratosphere and they can be applied for a wide range of atmospheric models and solar zenith distances. 相似文献
18.
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
19.
Optical spectra of the cleft aurora in the region 5000–8500 Å were measured in December, 1977 at Cape Parry, N.W.T. A Michelson interferometer was used at a resolution of 10 cm?1. The auroral features observed were OI (5577, 6300-64, 7774, 8446 Å), OII (7319-30 Å), NI (5200 Å), Hα, O2 atm (1,1), some weak N21P bands and possibly some Meinel bands of N2+. In addition, nightglow emissions of Na and OH were observed. Theoretical predictions of the OI and NI emission rates using the model of Link et al. (1980) fit the observed rates reasonably well if a 40 eV Maxwellian incident electron spectrum is assumed. The predicted rates for OII exceed the observed value by a factor of 4. It is suggested that the ionization cross-section may be over-estimated. 相似文献
20.
An ultraviolet spectral probe for a hydrogen-rich planetary atmosphere, such as that of Jupiter, is suggested, utilizing discrete lines in the H2staggered+ 2pπu?1sσg electronic transition. For the Jovian atmosphere, the dominant mechanism for exciting H2+ to its 2pπu state appears to be photoexcitation, principally through absorption of the solar Lyman-α line. We estimate that the Jovian column emission rate of the H2+ 2pπu(ν′ = 2, J′ = 1) →1sσg(ν″ = 18,J″ = 0) fluorescent line at 1236.6 Å is if1 photon cmsu-2 secsu-1; i.e., that if1 photon secsu-1 of this radiation would strike a 15-cm diameter mirror in a Jupiter fly-by at an impact parameter of 3 × 105km. The critical role of corrections to the Born-Oppenheimer approximation in the use of an H2+ probe is discussed. 相似文献