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1.
We report observations of the 2(12)-1(01) rotational transition of the 13C isotopic species of cyclopropenylidene (C3H2) toward TMC-1, Sgr B2, and IRC +10216 using the laboratory rest frequencies which have recently become available. Our detections allow estimates to be made of the fractional abundance of the unsubstituted similar species in these sources. The fractional abundance relative to H2, f(C3H2), is 1-2 x 10(-8) in TMC-1, and this is similar to the abundance of HCN, one of the more abundant organic molecules in the interstellar medium. In IRC +10216 f(C3H2) is one order of magnitude greater than in TMC-1. The 12C species in Sgr B2 shows a self-absorbed profile and the relative abundance of C3H2 estimated to be about an order of magnitude less than in TMC-1.  相似文献   

2.
We have conducted a spectral line survey of IRC +10216 using the Caltech Submillimeter Observatory to an average sensitivity of < or approximately 95 mK. A deconvolution algorithm has been used to derive the continuous single-sideband spectrum from 330.2 to 358.1 GHz. A total of 56 spectral lines were detected of which 54 have been identified with 8 molecules and a total of 18 isotopomers. The observed lines are used to derive column densities and relative abundances for the detected species. Within this frequency range the spectral lines detected contribute the majority of the total flux emitted by IRC +10216. We use the derived column densities and excitation temperatures to simulate the molecular line emission (assuming LTE) at frequencies up to 1000 GHz. The observed and simulated flux from line emission is compared to broadband total flux measurements and to dust emission assuming a power-law variation of the dust emissivity. We conclude that significant corrections for the line flux must be made to broadband flux measurements of IRC +10216 at wavelengths longer than approximately 750 micrometers.  相似文献   

3.
The C3H radical, a linear carbon chain with a 2 pi electronic ground state, has been identified in the millimeter-wave spectra of two astronomical sources, IRC +10216 and TMC-1, and conclusively confirmed (accompanying Letter) in a laboratory glow discharge. In IRC +10216 four rotational transitions have been observed, three in the lower fine-structure ladder (2 pi 1/2) and one in the upper (2 pi 3/2), each a resolved or partially resolved lambda-doublet. In TMC-1, both lambda components of the lowest lying 3/2 --> 1/2 transition of the 2 pi 1/2 ladder have been observed, each with well-resolved hfs. In IRC +10216 the excitation of C3H is similar to that of SiCC: the rotational temperature Trot within the 2 pi 1/2 ladder is low (8.5 K), owing to rapid radiative decay, while Trot across the ladders is high (approximately 52 K) because interconnecting far-IR radiative transitions are only weakly permitted. The column density of C3H in IRC +10216 averaged over the estimated source diameter of 84" is 2.8 x 10(13) cm-2, an order of magnitude less than that of C2H and C4H. A determination of the spectroscopic constraints of C3H that permitted the entire radio spectrum of this molecule to be calculated to high accuracy has been derived from analysis of the combined astronomical and laboratory data presented in the accompanying Letter.  相似文献   

4.
A new interstellar molecular ion, H2COH+ (protonated formaldehyde), has been detected toward Sgr B2, Orion KL, W51, and possibly in NGC 7538 and DR21(OH). Six transitions were detected in Sgr B2(M). The 1(1,0)-1(0,1) transition was detected in all sources listed above. Searches were also made toward the cold, dark clouds TMC-1 and L134N, Orion (3N, 1E), and a red giant, IRC + 10216, without success. The excitation temperatures of H2COH+ are calculated to be 60-110 K, and the column densities are on the order of 10(12)-10(14) cm-2 in Sgr B2, Orion KL, and W51. The fractional abundance of H2COH+ is on the order of 10(-11) to 10-(9), and the ratio of H2COH+ to H2CO is in the range 0.001-0.5 in these objects. The values in Orion KL seem to be consistent with the "early time" values of recent model calculations by Lee, Bettens, & Herbst, but they appear to be higher than the model values in Sgr B2 and W51 even if we take the large uncertainties of column densities of H2CO into account. We suggest production routes starting from CH3OH may play an important role in the formation of H2COH+.  相似文献   

5.
Observations of the 1(01) --> 0(00) rotational transitions of A and E state acetaldehyde are reported. The transitions were detected, for the first time in interstellar space, in the cold dust clouds TMC-1 and L134N, and in Sgr B2. This is also the first time acetaldehyde has been found in a dust cloud and is the most complex oxygen-bearing molecule yet known in this environment. We find a column density of 6 x 10(12) cm-2 in TMC-1, comparable to many other species detected there, and an approximately equal column density in L134N. In the direction of Sgr B2, the CH3CHO profile appears to consist of broad emission features from the hot molecular cloud core, together with absorption features resulting from intervening colder material. We also report the possible detection of HC9N toward IRC +10 degrees 216 through its J = 33 --> 32 transition. Implications for cold dust cloud chemistry and excitation are discussed.  相似文献   

6.
Vibrationally excited HCN has been observed for the first time in the interstellar medium. The J = 3-2 rotational transitions of the l-doubled (0,1(1d,1c), 0) bending mode of HCN have been detected toward Orion-KL and IRC +10216. In Orion, the overall column density in the (0,1,0) mode, which exclusively samples the "hot core", is 1.7 x 10(16) cm-2 and can be understood in terms of the "doughnut" model for Orion. The ground-state HCN column density implied by the excited-state observations is 2.3 x 10(18) cm-2 in the hot core, at least one order of magnitude greater than the column densities derived for HCN in its spike and plateau/doughnut components. Radiative excitation by 14 micrometers flux from IRc2 accounts for the (0,1,0) population, provided the hot core is approximately 6-7 x 10(16) cm distant from IRc2, in agreement with the "cavity" model for KL. Toward IRC +10216 we have detected J = 3-2 transitions of both (0,1(1c),(1d), 0) and (0, 2(0), 0) excited states. The spectral profiles have been modeled to yield abundances and excitation conditions throughout the expanding envelope.  相似文献   

7.
We report ISO LWS observations towards the star-forming regions W49N, W3(OH) and Sgr B2M in LWS04 mode (high-resolution Fabry–Perot scans). Possible far-infrared laser emission was detected in a water line at 133.55 μm towards W49N, but the spectral resolution was inadequate to establish firmly the nature of the emission. An additional water line was marginally detected in absorption at the 3 σ level, also towards W49N, at 169.74 μm. No OH lines were detected towards Sgr B2M or W3(OH) at either 134.83 or 135.95 μm, either in emission or in absorption.  相似文献   

8.
A survey of the 4(04)-3(03) and 1(01)-0(00) transitions of HOCO+ has been made toward several molecular clouds. The HOCO+ molecule was not observed in any sources except Sgr B2 and Sgr A. The 5(05)-4(04) and 4(14)-3(13) transitions were also detected toward Sgr B2. The results indicate that gas phase CO2 is not a major carbon reservoir in typical molecular clouds. In Sgr B2, the HOCO+ antenna temperature exhibits a peak approximately 2' north of the Sgr B2 central position (Sgr B2[M]) and the 4(04)-3(03) line emission is extended over a approximately 10' x 10' region. The column density of HOCO+ at the northern peak in Sgr B2 is approximately 3 x 10(14) cm-2, and the fractional abundance relative to H2 > or = 3 x 10(-10), which is about 2 orders of magnitude greater than recent predictions of quiescent cloud ion-molecule chemistry.  相似文献   

9.
We have modeled the infrared emission of spherically symmetric, circumstellar dust shells with the aim of deriving the infrared absorption properties of circumstellar silicate grains and the mass-loss rates of the central stars. As a basis for our numerical studies, a simple semianalytical formula has been derived that illustrates the essential characteristics of the infrared emission of such dust shells. A numerical radiative transfer program has been developed and applied to dust shells around oxygen-rich late-type giants. Free parameters in such models include the absorption properties and density distribution of the dust. An approximate, analytical expression is derived for the density distribution of circumstellar dust driven outward by radiation pressure from a central source. A large grid of models has been calculated to study the influence of the free parameters on the emergent spectrum. These results form the basis for a comparison with near-infrared observations. Observational studies have revealed a correlation between the near-infrared color temperature, Tc, and the strength of the 10 micrometers emission or absorption feature, A10. This relationship, which essentially measures the near-infrared optical depth in terms of the 10 micrometers optical depth, is discussed. Theoretical A10-Tc relations have been calculated and compared to the observations. The results show that this relation is a sensitive way to determine the ratio of the near-infrared to 10 micrometers absorption efficiency of circumstellar silicates. These results as well as previous studies show that the near-infrared absorption efficiency of circumstellar silicate grains is much higher than expected from terrestrial minerals. We suggest that this enhanced absorption is due to the presence of ferrous iron (Fe2+) color centers dissolved in the circumstellar silicates. By using the derived value for the ratio of the near-infrared to 10 micrometers absorption efficiency, the observed A10-Tc relation can be calibrated in terms of the total dust column density of the circumstellar shell and thus the mass-loss rate of late-type giants can easily be derived. Detailed models have been made of the infrared emission of three well-studied Miras: R Cas, IRC 10011, and OH 26.5+0.6, with the emphasis on the shape of the 10 micrometers emission or absorption feature. The results show that the intrinsic shape of the 10 micrometers resonance varies from a very broad feature in R Cas to a relatively narrower feature in OH 26.5+0.6, with IRC 10011 somewhere in between. Possible origins of this variation are discussed. The mass-loss rates from these objects are calculated to be 3 x 10(-7), 2 x 10(-5), and 2 x 10(-4) M Sun yr-1 for R Cas, IRC 10011, and OH 26.5+0.6, respectively. These results are compared to other determinations in the literature.  相似文献   

10.
As part of the search for the “dark molecular gas (DMG),” we report on the results of HCO+\(J=1\mbox{--}0\) absorption observations toward nine bright extragalactic millimeter wave continuum sources. The extragalactic sources are at high Galactic latitudes (\(|b| > 10^{\circ} \)) and seen at small extinction (\(E(B - V)\lesssim 0.1\) mag). We have detected the HCO+ absorption lines toward two sources, B0838+133 and B2251+158. The absorption toward B2251+158 was previously reported, while the absorption toward B0838+133 is a new detection. We derive hydrogen column densities or their upper limits toward the nine sources from our observations and compare them to those expected from CO line emission and far-infrared dust continuum emission. Toward the seven sources with no HCO+ detection, CO emission has not been detected, either. Thus the sight lines are likely to be filled with almost pure atomic gas. Toward the two sources with HCO+ detection, CO emission has been also detected. Comparison of the H2 column densities from HCO+ absorption and CO emission suggests a non-negligible amount of DMG toward B0838+133.  相似文献   

11.
使用中国科学院紫金山天文台青海站13.7米射电望远镜于1996年12月至1997年1月对富碳拱星IRC 10216和CIT6的CO J=1-0跃迁(115GHz)进行了观测。在观测谱线的基础上得到了IRC 10216的视向速度和膨胀速度分别为一26.1km s~(-1)和14.8km s~(-1),CIT6的视向速度和膨胀速度分别为0.6km s~(-1)和13.8kms~(-1)。并对望远镜的射束及指向精度进行了研究。  相似文献   

12.
Large molecules in the envelope surrounding IRC+10216   总被引：1，自引：0，他引：1  
A new chemical model of the circumstellar envelope surrounding the carbon-rich star IRC+10216 is developed that includes carbon-containing molecules with up to 23 carbon atoms. The model consists of 3851 reactions involving 407 gas-phase species. Sizeable abundances of a variety of large molecules including carbon clusters, unsaturated hydrocarbons and cyanopolyynes have been calculated. Negative molecular ions of chemical formulae and C n H (7 n 23) exist in considerable abundance, with peak concentrations at distances from the central star somewhat greater than their neutral counterparts. The negative ions might be detected in radio emission, or even in the optical absorption of background field stars. The calculated radial distributions of the carbon-chain C n H radicals are looked at carefully and compared with interferometric observations.  相似文献   

13.
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   

14.
We have obtained high angular resolution ( 3), and high sensitivity maps of IRC+10216. SiC2 is found both in a spherical shell and in the very central region, indicating it is formed both in the inner envelope close to the star, and in the outer shell. The molecules SiS and CS are mostly found in the inner parts of the envelope, but are still detectable in the outer region (r 15) where the products of photochemistry are found. The maps show that IRC+10216 has a very clumpy envelope, with strong departures from spherical symmetry; an axis oriented NS-SW (P.A. 20°) can be seen in all maps. The radial brightness distribution of CS has secondary maxima, at the radius where the SiC2 shell has its peak emission. A preliminary map shows CN in the same shell, but also in a still larger outer shell. Time variations in the mass loss rate, could be invoked to explain the multiple shell structure of this envelope.  相似文献   

15.
We present the analysis and first results from the Reflection Grating Spectrometer (RGS) during the 320-ks XMM–Newton observation of the Seyfert 1 galaxy MCG–6-30-15. The spectrum is marked by a sharp drop in flux at 0.7 keV which has been interpreted by Branduardi-Raymont et al. using RGS spectra from an earlier and shorter observation as the blue wing of a strong relativistic O  viii emission line and by Lee et al. using a Chandra spectrum as due to a dusty warm absorber. We find that the drop is well explained by the Fe  i L2,3 absorption edges and obtain reasonable fits over the 0.32–1.7 keV band using a multizone, dusty warm absorber model constructed using the photoionization code cloudy . Some residuals remain which could be due to emission from a relativistic disc, but at a much weaker level than from any simple model relying on relativistic emission lines alone. A model based on such emission lines can be made to fit if sufficient (warm) absorption is added, although the line strengths exceed those expected. In order to distinguish further whether the spectral shape is dominated by absorption or emission, we examined the difference spectrum between the highest and lowest flux states of the source. The EPIC pn data indicate that this is a power law in the 3–10 keV band which, if extrapolated to lower energies, reveals the absorption function acting on the intrinsic spectrum, provided that any emission lines do not scale exactly with the continuum. We find that this function matches our dusty warm absorber model well if the power law steepens below 2 keV. The soft X-ray spectrum is therefore dominated by absorption structures, with the equivalent width of any individual emission lines in the residuals being below approximately 30 eV.  相似文献   

16.
Based on five high-resolution spectra in the range 5625–7525 ?A taken in 1995 and covering the ascending branch of the light curve from minimum to maximum, we have performed spectroscopic studies of the classical Cepheid ζ Gem. The atmospheric parameters and chemical composition of the Cepheid have been refined. The abundances of the key elements of the evolution of yellow supergiants are typical for an object that has passed the first dredge-up: a C underabundance, N, Na, and Al overabundances, and nearly solar O and Mg abundances. We have estimated [Fe/H] = +0.01 dex; the abundances of the remaining elements are also nearly solar. The metal absorption lines in all spectra show a clear asymmetry and the formation of secondary blue (B1 and B2) and red (R1 and R2) components, just as for the Cepheid X Sgr. The Hα absorption line is also split into blue (B) and red (R) components with different depths changing with pulsation phase. To analyze the velocity field in the atmosphere of ζ Gem, we have estimated the radial velocities from specially selected (with clear signatures of the B1, B2, R1, and R2 components) absorption lines (neutral atoms and ions) of metals (38 lines) and the B and R components of the Hα line. Analysis of these estimates has shown that their scatter is from ?22 to 36 km s?1 for all pulsation phases but does not exceed 35–40 km s?1 for each individual phase, while it does not exceed 22 km s?1 for the Hα line components. The radial velocity estimates for the metal lines and their B1 and B2 components have been found to depend on the depths, suggesting the presence of a velocity gradient in the atmosphere. No significant difference in velocities between the atoms and ions of the metal lines is observed, i.e., there is no significant inhomogeneity in the upper atmospheric layers of the Cepheid. Since the averaged radial velocity estimates for the cores of the metal lines and their B1 and B2 components change with pulsation phase and coincide with those for the B component of the Hα line, they are all formed in the Cepheid’s atmosphere. The formation and passage of a shock wave due to the κ-mechanism at work can be responsible for the stronger scatter of the B1 and B2 components in their velocities at phases after the Cepheid’s minimum radius. The averaged velocities of the R1 components also change with pulsation phase and differ only slightly from the remaining ones. On the other hand, the mean velocity estimate for the R component of the Hα line at all phases is +32.72 ± 2.50 km s?1 and differs significantly from the bulk of the velocities, suggesting the formation of this component in the envelope around the Cepheid. The unusual behavior of the mean velocities for the R2 components of the metal absorption lines can also point to their formation in the envelope and can be yet another indicator of its presence around ζ Gem.  相似文献   

17.
Conclusions Analysis of the polarization observations of IRC+10216 has shown that to explain the large polarization of the object it is necessary to have alignment of particles in an envelope through which the initially unpolarized radiation of the star passes on its way to the observer. Among the considered orientation mechanisms, paramagnetic relaxation near the photosphere for comparatively large fields (B353 G) is the most obvious in view of the rate of alignment of the particles compared with the disorientation by the thermal motion of the gas. A confirmation of the presence of a magnetic field could be given by observations of circular polarization, which according to our estimates could reach 3–4% in the case of IRC+10216.The periodic variability of the degree of polarization of the object is due to a change in the diameter of the dust particles resulting from their partial evaporation at the phases of maximal light of the object.A. F. Ioffe Physicotechnical Institute; Leningrad State University. Translated from Astrofizika, Vol. 15, No. 2, pp. 297–309, April–June, 1979.  相似文献   

18.
We have constructed two gas-phase models to study the chemistry of circumstellar envelope surrounding the carbon-rich variable star IRAS 15194-5115. The network used consists of 3893 reactions involving 397 gas-phase species. The derived fractional abundances for many molecules are in excellent agreement with values obtained from observations. The predicted column densities from the two models go well with the observed values of carbon star IRC + 10216. The dominant formation routes for three groups of species are discussed through the inner and outer envelopes.  相似文献   

19.
Observations of OCS and a search for OC3S are reported, with particular reference to cold dust clouds. OCS has been detected for the first time in dark clouds with a mean fractional abundance relative to hydrogen of approximately 3 x 10(-9); this is approximately 4 times greater than that observed for giant molecular clouds. This results is discussed in the context of molecule formation mechanisms. Observations of the J = 1 --> 0 transition of OCS indicate that this transition is amplifying the background continuum radiation in the direction of Sgr B2.  相似文献   

20.
We have updated the chemical model of IRC+10216 developed by Millar, Herbst & Bettens to include recent routes to the formation of sulphuretted hydrocarbons. The routes are based on a quantum chemical study of the S+C2H system. In addition, we have altered the parent species for sulphur to reflect new observational results. We find that the model calculations give excellent agreement with the observed column densities, and discuss the significance of these reactions to the formation of species as yet unobserved and to dark interstellar clouds.  相似文献   

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