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1.
SiS has been conclusively detected toward Orion-KL via its J = 6-5 and J = 5-4 rotational transitions at 91 and 109 GHz. Line profiles indicate that the species is present at an LSR velocity of 7.5 km s-1 with a half-width at zero power of 36 km s-1. Such characteristics associate SiS with the moderate velocity outflow (V approximately 18 km s-1) centered on IRc2 and observed in thermal SiO, the NH3 "plateau," and OH, H2O, and SiO masers. The column density estimated for SiS in this region is Ntot = 4 x 10(15) cm-2, corresponding to a fractional abundance of f approximately 4 x 10(-9). Such an abundance implies an SiO/SiS ratio of approximately 60 in the outflow material, remarkably close to the cosmic O/S ratio of approximately 40 and contrasting with the SiO/SiS value of > approximately 10(3) predicted by ion-molecule models. This difference is probably a result of the high temperatures and densities present in the outflow, which favor thermal equilibrium abundances similar to those observed in the circumstellar shells of late-type stars rather than "ion-molecule"-type concentrations. In addition to SiS, some twenty new unidentified lines near 91 and 109 GHz were detected toward KL, as well as transitions arising from HC5N, HC13CCN, HCC13CN, O13CS, and, possibly, CH3CH2OH, CH3CHO, and CH3OD.  相似文献   

2.
Observations of comet Hale-Bopp (C/1995 O1) have been carried out near perihelion (1997 March) at millimeter wavelengths using the NRAO 12 m telescope. The J=1-->0, 2-->1, and 3-->2 lines of HCN at 88, 177, and 265 GHz were measured in the comet as well as the J=3-->2 lines of H13CN, HC15N, and HNC. The N=2-->1 transition of CN near 226 GHz was also detected, and an upper limit was obtained for the J=2-->1 line of HCNH+. From the measurements, column densities and production rates have been estimated. A column density ratio of [HCN]/[HNC] = 7+/-1 was observed near perihelion, while it was found that [HCN]/[HCNH+] greater, similar 1. The production rates at perihelion for HCN and CN were estimated to be Q(HCN) approximately 1x1028 s-1 and Q(CN) approximately 2.6x1027 s-1, respectively, resulting in a ratio of [HCN]/[CN] approximately 3. Consequently, HCN is sufficiently abundant to be the parent molecule of CN in Hale-Bopp, and HCNH+ could be a source of HNC. Finally, carbon and nitrogen isotope ratios of 12C/13C = 109+/-22 and 14N/15N = 330+/-98 were obtained from HCN measurements, in agreement with previous values obtained from J=4-->3 data. Such ratios suggest that comet Hale-Bopp formed coevally with the solar system.  相似文献   

3.
We have observed emission from HCN, H13CN, HC15N, HN13C, H15NC, HC3N, CH3CN, and possibly CH3NC, and determined an upper limit for NH2CN, toward the cold, dark cloud TMC-1. The abundance ratio [HNC]/[HCN] = 1.55 +/- 0.16 is at least a factor approximately 4 and approximately 100 greater than that observed toward the giant molecular clouds DR 21(OH) and Orion KL, respectively. In contrast, for the corresponding methylated isomers we obtain [CH3NC]/CH3CN] < or approximately 0.1. We also find [NH2CN]/[CH3CN] < or approximately 0.1 and [HC3N]/[CH3CN] = 30 +/- 10. We find no evidence for anomalous hyperfine ratios for H13CN, indicating that the ratios for HCN (cf. recent work of Walmsley et al.) are the result of self-absorption by cold foreground gas.  相似文献   

4.
Clarke DW  Ferris JP 《Icarus》1997,127(1):158-172
The structure and morphological properties of polymers produced photochemically from the UV irradiation of cyanoacetylene and cyanoacetylene mixtures have been examined to evaluate their possible contribution to the haze layers found on Titan. A structural analysis of these polymers may contribute to our understanding of the data returned from the Huygens probe of the Cassini mission that will pass through the atmosphere of Titan in the year 2004. Infrared analysis, elemental analysis, and thermal methods (thermogravimetric analysis, thermolysis, pyrolysis) were used to examine structures of polycyanoacetylenes produced by irradiation of the gas phase HC3N at 185 and 254 nm. The resulting brown to black polymer, which exists as small particles, is believed to be a branched chain of conjugated carbon-carbon double bonds, which, on exposure to heat, cyclizes to form a graphitic structure. Similar methods of analysis were used to show that when HC3N is photolyzed in the presence of Titan's other atmospheric constituents (CH4, C2H6, C2H2, and CO), a copolymer is formed in which the added gases are incorporated as substituents on the polymer chain. Of special significance is the copolymer of HC3N and acetylene (C2H2). Even in experiments where C2H2 was absorbing nearly all of the incident photons, the ratio of C2H2 to HC3N found in the resulting polymer was only 2:1. Scanning electron microscopy was used to visually examine the polymer particles. While pure polyacetylene particles are amorphous spheres roughly 1 micrometer in diameter, polycyanoacetylenes appear to be strands of rough, solid particles slightly smaller in size. The copolymer of HC3N and C2H2 exhibits characteristics of both pure polymers. This is particularly important as pure polyacetylenes do not match the optical constants measured for Titan's atmospheric hazes. The copolymers produced by the incorporation of other minor atmospheric constituents, like HC3N, into the polyacetylenes are expected to have optical constants more comparable to those of the Titan haze.  相似文献   

5.
L1498 is a classic example of a dense cold pre-protostellar core. To study the evolutionary status, the structure, dynamics, and chemical properties of this core we have obtained high spatial and high spectral resolution observations of molecules tracing densities of 10(3)-10(5) cm-3. We observed CCS, NH3, C3H2, and HC7N with NASA's DSN 70 m antennas. We also present large-scale maps of C18O and 13CO observed with the AT&T 7 m antenna. For the high spatial resolution maps of selected regions within the core we used the VLA for CCS at 22 GHz, and the Owens Valley Radio Observatory (OVRO) MMA for CCS at 94 GHz and CS (2-1). The 22 GHz CCS emission marks a high-density [n(H2) > 10(4) cm -3] core, which is elongated with a major axis along the SE-NW direction. NH3 and C3H2 emissions are located inside the boundary of the CCS emission. C18O emission traces a lower density gas extending beyond the CCS boundary. Along the major axis of the dense core, CCS, NH3 and C3H2 emission show evidence of limb brightening. The observations are consistent with a chemically differentiated onion-shell structure for the L1498 core, with NH3 in the inner and CCS in the outer parts of the core. The high angular resolution (9"-12") spectral line maps obtained by combining NASA Goldstone 70 m and VLA data resolve the CCS 22 GHz emission in the southeast and northwest boundaries into arclike enhancements, supporting the picture that CCS emission originates in a shell outside the NH3 emitting region. Interferometric maps of CCS at 94 GHz and CS at 98 GHz show that their emitting regions contain several small-scale dense condensations. We suggest that the differences between the CCS, CS, C3H2, and NH3 emission are caused by a time-dependent effect as the core evolves slowly. We interpret the chemical and physical properties of L1498 in terms of a quasi-static (or slowly contracting) dense core in which the outer envelope is still growing. The growth rate of the core is determined by the density increase in the CCS shell resulting from the accretion of the outer low-density gas traced by C18O. We conclude that L1498 could become unstable to rapid collapse to form a protostar in less than 5 x 10(6) yr.  相似文献   

6.
利用紫金山天文台青海站的 １３．７ ｍ毫米波望远镜,对 Ｏｒｉｏｎ Ａ分子云中的 ＯＭＣ－３区域,进行了较高分辨率的１３ＣＯ（Ｊ＝１－０）和Ｃ１８Ｏ（Ｊ＝１－０）分子辐射的成图观测．给出了该分子云中１３ＣＯ和 Ｃ１８Ｏ云核分布的整体结构和平均物理参数．观测发现,该分子云的１３ＣＯ和 Ｃ１８Ｏ的云核中心分别与最年轻的天体－Ｃｌａｓｓ ０类源 ＭＭＳＩ, ＭＭＳ４,ＭＭＳ６和ＭＭＳ７,ＭＭＳ８;ＭＭＳ９成协．此外,通过分析ＯＭＣ－３整个区域的速度场结构,发现沿 Ｃ１８Ｏ和１３ＣＯ云核方向从南到北有一个～ １．７ｋｍ／ｓ的速度场梯度,而分子云的红、蓝移团块则分别趋于云的北部和南部．并对ＯＭＣ－３区的恒星形成特征进行了讨论．  相似文献   

7.
A wide range of experiments has already been carried out to simulate the chemical evolution of Titan. Such experiments can provide useful information on the possible nature of minor constituents, mostly organic, likely to be present in Titan's atmosphere. Indeed, all but one of the organic compounds already detected in Titan's atmosphere have been identified in simulation experiments. The exception, C4N2, as well as other compounds expected in Titan from theoretical modeling, such as other N-organics, mainly CH2N2, and polyynes, namely C6H2, have never been detected in experimental simulation. It turned out that these compounds were thermally unstable, and the temperature conditions used during the simulation experiments (including conditions used for chemical analysis) were not appropriate. We have recently started a new program of simulation experiments using temperature conditions close to those of Titan's environment, more compatible with the build-up and detection of organics only stable at low temperature. Spark discharge of N2-CH4 gas mixtures was carried out at low temperature in the range of 100-150 K. The analysis of the obtained products was performed through FTIR, GC and GC-MS techniques. GC-peak identification was done owing to its mass spectrum and, in most cases, by comparison of the retention time and of the mass spectrum with standards. We report here the first detection in Titan's simulation experiments of C6H2. Its abundance is a few 10(-2) relative to C4H2. We also report a tentative identification of HC5N (to be confirmed by use of standard) with an abundance of a few 10(-2) relative to HC3N. The possible presence of HC5N suggested by our work provides the occurrence of very novel pathways in the formation of Titan's organic aerosols, involving not only C and H but also N atoms.  相似文献   

8.
The excitation of H2O masers usually needs very high density gas, hence it can serve as a marker of dense gas in HII region. We selected a sample of H2O maser sources from Plume et al. (four with, and four without detected CS(J = 7-6) emission), and observed them in 13CO(J=1-0) and C18O (J=1-0). C18O (J=1-0) emission was detected only in three of the sources with detected CS(J=7-6) emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.  相似文献   

9.
There are numerous complex organic molecules containing carbon and oxygen atoms which show either C–C–O or C–O–C bonding backbone. This paper examines altogether 51 C–C–O and C–O–C bonding backbone molecules from ten different isomeric groups (C2H2O, C3H2O, C2H4O, C2H4O2, C3H4O, C2H6O, C2H6O2, C3H6O, C3H6O2, C3H8O) to summarize the present astronomical status of these molecules. Accurate calculations of enthalpy of formation of these molecules show that the isomers with C–C–O backbone are more stable than the C–O–C backbone. Interestingly, a detailed analysis of relevant astromolecules indicates that most of the observed astromolecules have the C–C–O backbone. As a matter of fact, of all the molecules examined in this study, 80% of the astronomically observed species have the C–C–O backbone while only 20% have the C–O–C backbone. In general, interstellar abundance of a molecule is controlled by some factors such as kinetics, formation and destruction pathways,thermodynamics etc. A proper consideration of these factors could explain the observed abundances of these molecules. All these possible key factors are discussed in this paper.  相似文献   

10.
We report the identification of 10 transitions that support the detection of the small cyclic molecule ethylene oxide (c-C2H4O) in Sgr B2N. Although one of these transitions is severely blended, so that an accurate intensity and line width could not be determined, and two other lines are only marginally detected, we have done Gaussian fits to the remaining seven lines and have performed a rotation diagram analysis. Our results indicate a rotation temperature T(rot) = 18 K and a molecular column density N(c-C2H4O) = 3.3 x 10(14) cm-2, corresponding to a fractional abundance relative to molecular hydrogen of order 6 x 10(-11). This is a factor of more than 200 higher than the abundance for this molecule suggested by the "new standard" chemistry model of Lee, Bettens, & Herbst. This result suggests that grain chemistry might play an effective role in the production of c-C2H4O. No transitions of this molecule were detected in either Sgr B2M or Sgr B2NW.  相似文献   

11.
利用日本名古屋大学天体物理系的毫米波射电望远镜对CepheusC的C18O（J＝1－0）分子辐射首次进行了观测，得到了强度分布图．从强度分布图上，我们发现C18O（J＝1－0）分子的分布呈现三个核．通过计算得到了三个核的物理参数．  相似文献   

12.
We report the astronomical identification of the cyanomethyl radical, CH2CN, the heaviest nonlinear molecular radical to be identified in interstellar clouds. The complex fine and hyperfine structures of the lowest rotational transitions at about 20.12 and 40.24 GHz are resolved in TMC-1, where the abundance appears to be about 5 x 10(-9) relative to that of H2. This is significantly greater than the observed abundance of CH3CN (methyl cyanide) in TMC-1. In Sgr B2 the hyperfine structure is blended in the higher frequency transitions at 40, 80, and 100 GHz, although the spin-rotation doubling is clearly evident. Preliminary searches in other sources indicate that the distribution of CH2CN is similar to that for such carbon chain species as HC3N or C4H.  相似文献   

13.
In this paper we present nearly simultaneous 1300 microns continuum and J = 2-1 C18O maps of the cores of five molecular clouds, W3, NGC 2264, NGC 6334I, rho Oph, and S140. The purpose of this experiment was to compare these two column density tracers. We find that dust continuum and C18O emission are equally effective tracers of column density in molecular cloud cores and give a good indication of cloud structure. When the maps are analyzed in terms of the quantity q = Q/[a rho RX(C18O)], we find that q does not vary by much more than an order of magnitude either within objects or from object to object, implying that nominal dust parameters of absorption efficiency, radius, and gas-to-dust ratio and CO abundance are on average correct in a variety of sources. We did detect source-to-source variations in q. This variation could be either in the dust-to-CO number density ratio or in grain parameters. These variations are not well correlated with total source luminosity, average or typical temperature, or total column density. The best example of this variation appears to be rho Oph where q is about a factor of 7 lower than is typically found. Our approach is analogous to the study of the A nu to CO ratio and is probably equivalent to extending this study to large A nu if the same grains are responsible for both optical opacity and far-infrared to millimeter-wave emission. There is no fundamental reason to expect A nu/NCO or q to be constant and, in fact, we have found that it is not constant in even a small source sample.  相似文献   

14.
Methane and ammonia abundances in the coma of Halley are derived from Giotto IMS data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto HIS ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio m/q = 19/18 as a function of distance from the nucleus is not reproduced by a model for a pure water coma. It is necessary to include the presence of NH3, and uniquely NH3, in coma gases in order to explain the data. A ratio of production rates Q(NH3)/Q(H2O) = 0.01-0.02 results in model values approximating the Giotto data. Methane is identified as the most probable source of the distinct peak at m/q = 15. The observations are fit best with Q(CH4)/Q(H2O) = 0.02. The chemical composition of the comet nucleus implied by these production rate ratios is unlike that of the outer planets. On the other hand, there are also significant differences from observations of gas phase interstellar material.  相似文献   

15.
We report the results of modeling of the spectrum of the O3 If* Cyg OB2 No. 7 supergiant in a broad wavelength range. We determine the physical properties and chemical composition of its atmosphere not assuming the presence of local thermodynamic equilibrium. The atmosphere reveals an excess of nitrogen X(N)/X(N)⊙ = 3.2 and the carbon and oxygen deficiency X(C)/X(C)⊙ = 0.08, X(O)/X(O)⊙ = 0.09. The lines in the stellar spectrum are divided into three groups which fail to be describedwithin a single model. Themodels describing each of these groups differ by themass-loss rate and the law of wind velocity variation. Thus, the numerical modeling suggests that the wind of the supergiant is heterogeneous. In addition, this paper describes the features of the CMFGEN code used and investigates the sensitivity of its results to the variations of different parameters.  相似文献   

16.
Abstract— Chemical structures of the insoluble organic matter (IOM) from the Antarctic CM2 chondrites (Yamato [Y‐] 791198, 793321; Belgica [B‐] 7904; Asuka [A‐] 881280, 881334) and the Murchison meteorite were analyzed by solid‐state 13C nuclear magnetic resonance (NMR) spectroscopy. Different types of carbons were characterized, such as aliphatic carbon (Ali‐C), aliphatic carbon linked to hetero atom (Hetero‐Ali‐C), aromatic carbon (Aro‐C), carboxyls (COOR), and carbonyls (C=O). The spectra of the IOM from Murchison and Y‐791198 showed two major peaks: Ali‐C and Aro‐C, while the spectra from the other meteorites showed only one major peak of Aro‐C. Carbon distribution was determined both by manual integration and deconvolution. For most IOM, the Aro‐C was the most abundant (49.8–67.8%) of all carbon types. When the ratios of Ali‐C to Aro‐C (Ali/Aro) were plotted with the atomic hydrogen to carbon ratio (H/C), a correlation was observed. If we use the H/C as a parameter for the thermal alteration event on the meteorite parent body, this result shows a different extent of thermal alteration. In addition, IOM with a lower Ali/Aro showed a lower ratio of Ali‐C to COOR plus C=O (Ali / (COOR + C=O)). This result suggests that the ratio of CO moieties to aliphatic carbon in IOM might reflect chemical oxidation that was involved in hydrothermal alteration.  相似文献   

17.
Buu N. Tran  John J. Chera 《Icarus》2003,162(1):114-124
The photochemical flow reactor (D.W. Clarke et al., 2000, Icarus 147, 282-291) has been modified to minimize the incorporation of oxygen and other impurities in the photoproducts. A mixture of gases that approximate their mixing ratios on Titan (N2, CH4, H2, C2H2, C2H4, and HC3N) (0.98, 0.018, 0.002, 3.5 × 10−4, 3 × 10−4, 1.7 × 10−5, respectively) was irradiated in the flow photochemical reactor using a 185-nm source to give a Titan haze analog as a solid product. X-ray photoelectron spectroscopy (XPS) gave a composition of 93.3% C, 5.3% N, and 1.4% O. Of the 93.3% carbon, high-resolution XPS revealed that 81.2% was present as CH, CC, and CC groups, 12.1% may be CO, CN, CN, CN, and/or CN groups, 5.3% as a CN group. The peak for N was symmetrical and was assigned to the CN while that for oxygen was assigned to the CO and/or the CO group. Some of these assignments were confirmed by FTIR spectroscopy. The polymeric product had a C:N ratio of 17.6, which is significantly greater than that for Titan haze analogs prepared in discharge reactions. When the polymer was exposed to air for seven days the oxygen content increased by 6% along with an increase in the infrared absorption at 1710 cm−1 assigned to the CO group of a ketone. The oxidation is attributed to the reaction of oxygen with free radicals trapped in the polymer matrix. It is proposed that the photochemical initiation of Titan haze formation from compounds formed from starting materials formed high in Titan’s atmosphere is a more plausible model than haze formed in reactions initiated by solely by discharges. These data will be helpful in the interpretation of the data returned from the Huygens probe of the Cassini mission.  相似文献   

18.
俞志尧 《天文学报》1998,39(4):405-411
从在CepheusE中C18O（J＝1－0）的谱线频谱图发现,相对于峰速度的蓝移成分的积分流量密度明显大于相对于红移成分的积分流量密度．从在它的强度分布图也可以发现强度分布轮廓向西北和向东延伸．为此,研究了在CepheusE中C18O（J＝1－0）的速度分段积分等高图,发现相对于峰速度的蓝移速度分段积分等高图中的C18O（J＝1－0）的积分强度,要大于相对于红移速度分段积分等高图中的C18O（J＝1－0）的积分强度,同时强度分布图中的分子外流的不准直分布是由相对于峰速度的蓝移成分的分布的不准直性所引起的．  相似文献   

19.
Abstract— Zag is an H3‐6 chondrite regolith breccia within which we have studied 14 halite grains ≤3 mm. The purity of the associated NaCl‐H2O brine is implied by freezing characteristics of fluid inclusions in the halite and EPMA analyses together with a lack of other evaporite‐like phases in the Zag H3–6 component. This is inconsistent with multi‐stage evolution of the fluid involving scavenging of cations in the Zag region of the parent body. We suggest that the halite grains are clastic and did not crystallize in situ. Halite and water‐soluble extracts from Zag have light Cl isotopic compositions, δ37Cl = ?1.4 to ?2.8%. Previously reported bulk carbonaceous chondrite values are approximately δ37Cl = +3 to +4%. This difference is too great to be the result of fractionation during evaporation, and instead, we suggest that Cl isotopes in chondrites are fractionated between a light reservoir associated with fluids and a heavier reservoir associated with higher temperature phases such as phosphates and silicates. Extraterrestrial carbon released at 600 °C from the H3–4 matrix has δ13C = ?20%, consistent with poorly graphitized material being introduced into the matrix rather than indigenous carbonate derived from a brine. We have also examined 28 other H chondrite falls to ascertain how widespread halite or evaporite‐like mineral assemblages are in ordinary chondrites. We did not find any more to add to Zag (H3‐6) and Monahans (H5), which suggests that such highly soluble phases were not usually preserved on the parent bodies.  相似文献   

20.
A coupled problem of diffusion and condensation is solved for the H2SO4-H2O system in Venus' cloud layer. The position of the lower cloud boundary and profiles of the H2O and H2SO4 vapor mixing ratios and of the H2O/H2SO4 ratio of sulfuric acid aerosol and its flux are calculated as functions of the column photochemical production rate of sulfuric acid, phi H2SO4. Variations of the lower cloud boundary are considered. Our basic model, which is constrained to yield fH2O (30 km) = 30 ppm (Pollack et al. 1993), predicts the position of the lower cloud boundary at 48.4 km coinciding with the mean Pioneer Venus value, the peak H2SO4 mixing ratio of 5.4 ppm, and the H2SO4 production rate phi H2SO4 = 2.2 x 10(12) cm-2 sec-1. The sulfur to sulfuric acid mass flux ratio in the clouds is 1 : 27 in this model, and the mass loading ratio may be larger than this value if sulfur particles are smaller than those of sulfuric acid. The model suggests that the extinction coefficient of sulfuric acid particles with radius 3.7 micrometers (mode 3) is equal to 0.3 km-1 in the middle cloud layer. The downward flux of CO is equal to 1.7 x 10(12) cm-2 sec-1 in this model. Our second model, which is constrained to yield fH2SO4 = 10 ppm at the lower cloud boundary, close to the value measured by the Magellan radiooccultations, predicts the position of this boundary to be at 46.5 km, which agrees with the Magellan data; fH2O(30 km) = 90 ppm, close to the data of Moroz et al. (1983) at this altitude; phi H2SO4 = 6.4 x 10(12) cm-2 sec-1; and phi co = 4.2 x 10(12) cm-2 sec-1. The S/H2SO4 flux mass ratio is 1 : 18, and the extinction coefficient of the mode 3 sulfuric acid particles is equal to 0.9 km-1 in the middle cloud layer. A strong gradient of the H2SO4 vapor mixing ratio near the bottom of the cloud layer drives a large upward flux of H2SO4, which condenses and forms the excessive downward flux of liquid sulfuric acid, which is larger by a factor of 4-7 than the flux in the middle cloud layer. This is the mechanism of formation of the lower cloud layer. Variations of the lower cloud layer are discussed. Our modeling of the OCS and CO profiles in the lower atmosphere measured by Pollack et al. (1993) provides a reasonable explanation of these data and shows that the rate coefficient of the reaction SO3 + CO --> CO2 + SO2 is equal to 10(-11) exp(-(13,100 +/- 1000)/T) cm3/s. The main channel of the reaction between SO3 and OCS is CO2 + (SO)2, and its rate coefficient is equal to 10(-11) exp(-(8900 +/- 500)T)cm3/s. In the conditions of Venus' lower atmosphere, (SO)2 is removed by the reaction (SO)2 + OCS --> CO + S2 + SO2. The model predicts an OCS mixing ratio of 28 ppm near the surface.  相似文献   

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