Cyanide and isocyanide abundances in the cold, dark cloud TMC-1

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.     

Cyanide Chemistry in Comet Hale-Bopp (C/1995 O1)

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.     

Interferometric observations for oxygen-containing organic molecules toward Orion-KL

High spatial resolution observations (approximately 5") were made for the 3 mm transitions of methanol (CH3OH), methyl formate (HCOOCH3), and dimethyl ether [(CH3)2O] toward Orion-KL using the Nobeyama Millimeter Array. The 15(3)-14(4) A- CH3OH emission appears to be elongated along the line connecting IRc2 and "the southern condensation (SC)", which may suggest a relation between methanol and the outflow from IRc2. The HCOOCH3 (7(1,6)-6(1,5)) and (CH3)2O (15(2,13)-15(1,14)) emissions appear to be well concentrated toward SC with an angular size of approximately 6".5 (at the 2 sigma level). There also exists another oxygen-rich condensation to the west of IRc2 (angular size approximately 4".5) having column densities of HCOOCH3 and (CH3)2O comparable to those of SC. We derive the total column densities 6.8 x 10(16) cm-2, 1.4 x 10(16) cm-2 and 2.7 x 10(16) cm-2 for CH3OH, HCOOCH3, and (CH3)2O, respectively, at the core of SC.     

Heterodyne spectroscopy of the J = 22-21 CO line in Orion

We have observed the J = 22-21 line of 12CO at 2528 GHz (118.8 micrometers) in the IRc2 region of Orion. The spectra at 0.6 km s-1 resolution show both plateau emission with FWHM approximately 35 km s-1 and a narrower component with FWHM approximately 8 km s-1. Comparison with heterodyne data of similar quality on the J = 17-16 line indicates that the broad and narrow components both originate in gas with an excitation temperature Tex approximately 600 K. The emission is consistent with the predictions of shock models in which the wide component arises from the heated outflow gas and postshock molecular material, while the narrow component comes from ambient material near the leading edge of the shock front where temperatures are high but significant acceleration has not yet occurred.     

Identification of the interstellar cyanomethyl radical (CH2CN) in the molecular clouds TMC-1 and Sagittarius B2

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.     

大质量恒星形成区样本外向流的高灵敏度搜寻

对13个大质量恒星形成区样本进行了SiO(2-1)、CH_3OH(2-1)和C~(34)S(2-1)热线的观测.在9个分子云核中,3条热线同时被探测到.这9个SiO探测中,有3个是新探测到的且它们强度都相对较弱.所有探测到的谱线都有较明显的线翼,这可能是外向流出现的证据.SiO谱线的线宽最宽,这也更进一步表明SiO辐射可能是来自高速的外向流,即更靠近外向流的激发源.估算了各分子谱线的旋转温度,柱密度和相对元素丰度.结果表明SiO和CH_3OH元素丰度之间有较好的相关性,相关系数R=0.77,但是SiO和C~(34)S元素丰度之间却没有任何相关性.     

Shock chemistry in the molecular clouds associated with SNR IC 443

Several interstellar molecules have been detected toward the highly perturbed B and G clouds associated with the supernova remnant IC 443 via their 3 mm transitions, including N2H+, SiO, SO, CN, HNC, and H13CO+. The (J, K) = (1, 1) and (2, 2) inversion lines of metastable ammonia have also been observed, as well as the J = 3-2 transition of HCO+ at 1.2 mm. Analysis of the (1, 1) and (2, 2) inversion lines of NH3 indicates minimum gas kinetic temperatures of TK = 70 K toward cloud B, and TK = 33 K in cloud G. Modeling of the J = 1-0 and J = 3-2 transitions of HCO+ implies densities greater than 10(5) cm-3 toward both positions. These data clearly show that hot and dense material is present in IC 443, and they suggest the presence of shocks in both regions. A careful analysis of the HCO+ lines indicates that the HCO+ abundance is at most enhanced by factors of a few over that found in cold, quiescent gas. This conclusion contradicts past claims of HCO+ abundance enhancements of several orders of magnitude in the perturbed regions. The N2H+ abundance was also found to be similar to that in cold gas, suggesting that there is no increase in ionization in the clouds. The abundances of SO and CS, as well as CN and NH3, do not appear to differ significantly from those found in cold dark clouds, although chemistry models predict sulfur-containing species to undergo high-temperature enhancements. SiO, however, is found to have an abundance in the perturbed gas 100 times larger than the upper limits observed in the dark cloud TMC 1, a result in agreement with high temperature chemistry models. In addition, the HNC/HCN ratio in both IC 443 B and G was found to be approximately 0.1--far from the ratio of 1 predicted by low-temperature ion-molecule chemistry, but similar to the values observed in clouds where elevated temperatures are present.     

Observations of some oxygen-containing and sulfur-containing organic molecules in cold dark clouds

Observations of nine oxygen- and sulfur-containing organic molecules have been made toward the cold dark clouds TMC-1 and L134N. We have confirmed the presence of para-ketene (H2C2O) in TMC-1, have for the first time observed ortho-ketene, and find a total ketene column density approximately 1 x 10(13) cm-2. Thioformaldehyde (H2CS) is easily detectable in both TMC-1 and L134N, with a column density about 5 times larger in the former source (approximately 3 x 10(13) cm-2). The fractional abundance of ketene is comparable to the predictions of ion-molecule chemistry, while that of thioformaldehyde in TMC-1 is one to two orders of magnitude greater than that expected from such models at steady state. Interstellar sulfur chemistry thus continues to be poorly understood. We set upper limits for the column densities of formic acid (HCOOH), vinyl alcohol (CH2CHOH), methyl formate (HCO2CH3), formamide (NH2CHO), methyl mercaptan (CH3SH), isothiocyanic acid (HNCS), and thioketene (H2C2S) in both sources.     

Reversed far-infrared line emission from OH in Orion

The fundamental OH rotational transition at 2514 GHz (119.2 micrometers) has been observed in the Orion IRc2 region at a spectral resolution of 0.6 km s-1. The emission is spatially compact (< 25" FWHM) and centered near IRc2. A comparison of the observed profile with spectra of other species known to exist in the region suggests that the entire blueshifted side of the OH profile has been "self-absorbed," leaving only a redshifted emission component. In addition, there is pronounced absorption near 5 km s-1 VLSR indicative of the "hot core" source. The presence of the 119 micrometers absorption provides a straightforward explanation for the high ratio of 163/119 micrometers integrated line intensities which was previously considered anomalous.     

Laboratory detection of a new interstellar free radical CH2CN(2B1)

An asymmetric-top free radical CH2CN, which as a 2B1 ground state, was detected for the first time by laboratory microwave spectroscopy. The radical was produced in a free-space absorption cell by a DC glow discharge in pure CH3CN gas. About 60 fine-structure components were observed for the N = 11-10 to 14-13 a-type rotational transitions in the frequency region of 220-260 GHz, and many hyperfine resolved components for the N = 4-3 and 5-4 transitions in the 80 and 100 GHz regions, respectively. The molecular constants, including the rotational constants, centrifugal distortion constants, and spin-rotation coupling constants with centrifugal distortion correction terms were determined from the fine-structure resolved transitions, and the hyperfine coupling constants due to the hydrogen and nitrogen nuclei were obtained from the low-N transitions. As a result we assigned U100602 and U80484 from Sgr B2, and U40240 and U20120 from TMC-1, to the N = 5-4, 4-3, 2-1, and 1-0 transitions with K-1 = 0 of the CH2CN radical.     

A Sensitive Survey of Dense Parts of Outflows toward Massive Cores

A set of samples of 13 massive star-forming cores were observed in SiO (2-1), CH3OH (2-1) and C³⁴S (2-1) thermal lines. Nine of these cores were detected in all three lines. Among the nine SiO detections, three were new detections, and relatively faint. Most of the lines have wide wings, which might be interpreted as the evidence of ongoing energetic out?ows in the cores. The line widths of SiO are generally the broadest, which might further suggest that the SiO emissions are due to higher velocity out?ow, and closer to the excited source. We derive the rotational temperatures, column densities and chemical relative abundances of the cores. There is a strong correlation between SiO and CH3OH abundances, with correlation coeffcient R = 0.77, but no correlation is observed between SiO and C³⁴S.     

New interstellar masers in nonmetastable ammonia

We report the astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high s 1090 K above the ground state. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km s-1) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containing compact H II regions and strong infrared sources with associated H2O and OH masers; i.e., in regions of active star formation.     

Observations of interstellar HOCO+: abundance enhancements toward the galactic center

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.     

富碳拱星IRC＋10216和CIT6的CO J=1—0转动谱的观测

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。     

Interstellar SiO as a tracer of high-temperature chemistry

The J = 2-1 transition of SiO has been searched for toward both hot and cold molecular gas. SiO was not detected toward the dark clouds TMC-1, L134 N, and B335, down to column density upper limits of N < 2-4 x 10(10) cm-2. The species, however, has been observed toward all sources with a kinetic temperature greater than or equal to 30 K, with the largest column densities (N approximately 10(13)-10(17) cm-2) measured in the warmest (TK > or = 100 K) material. The abundance of SiO, relative to HCN, is found to be approximately 0.1-1 in the massive star-forming regions toward Orion and NGC 7538; toward the dark clouds, the upper limits to this ratio is less than 0.0002-0.004. A similar enhancement in the warmer regions is reflected in the SiO/H2 ratio as well. A linear relation was found between the natural log of the SiO concentration and 1/TK, suggesting that the species' formation involves a chemically specific process that contains an activation barrier of approximately 90 K. SiO was also found to be underabundant with respect to SO in cold clouds, with SiO/SO < 1/1000, versus SiO/SO > or =, measured in Orion-KL. The formation of SiO is therefore linked closely to the local gas kinetic temperature, rather than the oxygen abundance, and its synthesis is likely to involve high-temperature gas-phase reactions. The species thus may serve as an unambiguous indicator of high-temperature or "shock" chemistry.     

Testing the 'clump' model of SiO maser emission

Building on the detection of the J =7–6 SiO maser emission in both the v =1 and v =2 vibrational states towards the symbiotic Mira R Aquarii, we have used the James Clerk Maxwell Telescope to study the changes in the SiO maser features from R Aqr over a stellar pulsational period. The observations, complemented by contemporaneous data taken at 86 GHz, represent a test of the popular thermal-instability clump models of SiO masers. The 'clump' model of SiO maser emission considers the SiO masers to be discrete emitting regions which differ from their surroundings in the values of one or more physical variables (SiO abundance, for example). We find that our observational data are consistent with a clump model in which the appearance of maser emission in the J =7–6 transitions coincides with an outward-moving shock impinging on the inner edge of the maser zone.     

Studies of some diatomic molecules in the F- and early G-type dwarf stars

A critical analysis of CH, NH, OH, C₂, and CN molecules/radicals has been made in twenty-four F- and early G-type dwarfs at different effective temperature as well as in new constructed model atmosphere. Molecular indices of bandheads ofA-X system of CH, NH, OH, C₂, and CN have been obtained by using the data available in the literature (thirteen-colour and eight-colour photometry).Besides, some interesting plots of the molecular indices vs _eff, molecular abundances and molecular indices vs dissociation energy, reduced equivalent widths and FCF's vs dissociation energy for respective molecules have also been enumerated. It is found that the molecular indices at bandheads ofA-X system of CH, NH, OH, C₂, and CN are approximately constant (5810–6570 K). It is to be noted that the molecular indices decrease in the order OH, NH, CH, C₂, and CN at a given temperature.The dissociation equilibrium of CH, NH, OH, C₂, and CN is considered at 5810, 6570, and 7160 K phases in model atmosphere. At standard scale of abundance the molecular abundance and molecular index decrease in the order OH, NH, CH, C₂, and CN at any given phase, however, CN abundance and index increase (_eff=0.867-0.767). The amplitude of abundance and index variation decrease in the order NH, OH, CH, C₂, and CN (_eff=0.767-0.704).The reduced equivalent width decrease in the order OH, NH, CH, and C₂ and FCF's decrease in the order CH, OH, NH, CN, and C₂.The confrontation of models and observations of spectra of F- and early G-type dwarfs of parent molecules is of primary importance to investigate the physical conditions within atmospheres. Reliable excitation models are also requisite for interpreting spectroscopic observations of parent molecules and deriving molecular abundances.     

Heterodyne spectroscopy of the 158 micron C II line in M42

We have obtained velocity-resolved spectra of the 12C II 157.8 microns 2P3/2-2P1/2 fine structure line in the M42 region of Orion. Observations at 0.8 km s-1 resolution with a laser heterodyne spectrometer show multiple velocity components in some locations, with typical linewidths of 3-5 km s-1. Spectra of theta 1C and BN-KL also show weak emission from the F = 2-1 hyperfine component of the equivalent 13C II line. From the observed 12C II/13C II line intensity ratios, we deduce that the 12C II emission is optically thick with tau approximately 5 at both positions. Excitation temperatures of 128 K and 90 K, together with column densities of approximately 1 x 10(19) cm-2 and approximately 4 x 10(18) cm-2, are derived for theta 1C and BN-KL, respectively.     

1.3 mm Plateau de Bure Observations of IRC+10216

The Plateau de Bure millimeter-wave interferometer has been used at 1.3 mm wavelength to observe the prototype carbon-star IRC+10216 in the continuum and in the v = 1, J = 13 − 11 transition of SiS at 234.8 GHz. The 3 mm continuum and the v = (0, 2⁰, 2), J = 1 − 0 HCN transition were simultaneously observed. The source of vibrationally excited SiS appears resolved, and a source size of ∼ 0.4″ or 7 10¹⁴cm (10 stellar radii) is derived, in agreement with a crude model of line formation. This revised version was published online in September 2006 with corrections to the Cover Date.     

The detection of interstellar methylcyanoacetylene

A new interstellar molecule, methylcyanoacetylene (CH3C3N), has been detected in the molecular cloud TMC-1. The J = 8 --> 7, J = 7 --> 6, J = 6 --> 5, and J = 5 --> 4 transitions have been observed. For the first three of these, both the K = 0 and K = 1 components are present, while for J = 5 --> 4, only the K = 0 line has been detected. The observed frequencies were calculated by assuming a value of radial velocity VLSR = 5.8 km s-1 for TMC-1, typical of other molecules in the cloud. All observed frequencies are within 10 kHz of the calculated frequencies, which are based on the 1982 laboratory constants of Moises et al., so the identification is secure. The lines are broadened by hyperfine splitting, and the J = 5 --> 4, K = 0 transition shows incipient resolution into three hyperfine components. The rotational temperature determined for these observations is quite low, with 2.7 K < or = Trot < or = 4 K. the total column density is approximately 5 x 10(12) cm-2.