13 C-Methyl Formate: Observations of a Sample of High-Mass Star-Forming Regions Including Orion-KL and Spectroscopic Characterization (original) (raw)
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Astronomy and Astrophysics, 2009
Context. Laboratory measurements and analysis of the microwave and millimeter-wave spectra of potential interstellar molecules are a prerequisite for their subsequent identification by radioastronomical techniques. The spectral analysis provides spectroscopic parameters that are used in the assignment procedure of the laboratory spectra, and that also predict the frequencies of transitions not measured in the laboratory with a high degree of precision.
2014
We have surveyed a sample of massive star-forming regions located over a range of distances from the Galactic center for methyl formate, HCOOCH3, and its isotopologues HCOOCH3 and HCOOCH3. The observations were carried out with the APEX telescope in the frequency range 283.4–287.4 GHz. Based on the APEX observations, we report tentative detections of the 13C-methyl formate isotopologue HCOOCH3 toward the following four massive star-forming regions: Sgr B2(N-LMH), NGC 6334 IRS 1, W51 e2, and G19.61-0.23. In addition, we have used the 1 mm ALMA science verification observations of Orion–KL and confirm the detection of the 13C-methyl formate species in Orion–KL and image its spatial distribution. Our analysis shows that the 12C/13C isotope ratio in methyl formate toward the Orion–KL Compact Ridge and Hot Core-SW components (68.4 ± 10.1 and 71.4 ± 7.8, respectively) are, for both the 13C-methyl formate isotopologues, commensurate with the average 12C/13C ratio of CO derived toward Orion...
A Large-Scale Study of H13CO+ and C18 (J=1-0) in Orion B
Publications of the Astronomical Society of Japan, 2001
We have made a new survey for dense cloud cores in the Orion B region using the NANTEN telescope. Two molecular transitions, the J = 1-0 line of H 13 CO + and the J = 1-0 line of C 18 O, were used to study the distribution of dense molecular gas with densities of 10 4-10 5 cm −3. We detected 19 C 18 O clumps, and the mass and the size of the C 18 O clumps ranged from 13 M to 990 M and from 0.26 pc to 0.69 pc, respectively. Among the physical parameters of these C 18 O clumps, the molecular column density, N (H 2), has been found to be the best indicator of star formation; the molecular column density averaged within a C 18 O clump shows a good correlation with the IRAS luminosity as L IRAS /L ∝ N (H 2) (cm −2) 4.8±0.6 (C.C. = 0.96). We also detected 11 H 13 CO + clumps, whose mass ranges from a few M to 480 M. Five of the H 13 CO + clumps are of smaller mass, and show no indication of massive star formation; they were newly found in this survey. Five of the eleven H 13 CO + clumps are particularly massive with an average mass of ∼ 200 M. It is found that these massive H 13 CO + clumps exhibit active formation of massive stars, as indicated by associated protostellar IRAS point sources, whose luminosities are 10 2-10 4 L .
The Astrophysical Journal Supplement Series, 2010
A compilation of the available spectroscopic millimeter-and submillimeter-wave data of the ground and first excited states of 13 C 1 -methyl formate (H 13 COOCH 3 ) has been carried out. The exhaustive analysis of the available transition lines of H 13 COOCH 3 has led to the assignment of 7457 spectral lines by means of a global fit of 45 parameters, using the Rho-Axis Method and the BELGI-Cs code, with a resulting unitless standard deviation of 0.57. Over 1600 lines are included for the first time in the fit. In addition, the line strengths of spectral lines are also calculated using the most recent experimental measurement of the electric dipole moment. In conclusion, the present study represents a notable improvement with respect to previous H 13 COOCH 3 spectral analyses. Therefore, the better accuracy of the present analysis may help the future identification of new H 13 COOCH 3 lines in the interstellar and circumstellar media, and may contribute to decrease some of the spectral confusion due to these species in astronomical surveys.
A large12C/13C isotopic ratio in M 82 and NGC 253
Astronomy & Astrophysics, 2010
Aims. Our aim is to derive carbon isotopic ratios from optically thin tracers in the central regions of the starburst galaxies M 82 and NGC 253. Methods. We present high-sensitivity observations of CCH and two of its 13 C isotopologues, C 13 CH and 13 CCH, as well as the optically thin emission from C 18 O and 13 C 18 O. We assume the column density ratio between isotopologues is representative of the 12 C/ 13 C isotopic ratio. Results. From CCH, lower limits to the 12 C/ 13 C isotopic ratio of 138 in M 82, and 81 in NGC 253, are derived. Lower limits to the 12 C/ 13 C ratios from CO isotopologues support these. 13 C 18 O is tentatively detected in NGC 253, which is the first reported detection in the extragalactic ISM. Based on these limits, we infer ratios of 16 O/ 18 O > 350 and >300 in M 82 and NGC 253, respectively, and 32 S/ 34 S > 16 in NGC 253. The derived CCH fractional abundances toward these galaxies of < ∼ 1.1 × 10 −8 agree well with those of molecular clouds in the Galactic disk. Conclusions. Our lower limits to the 12 C/ 13 C ratio from CCH are a factor of 2−3 larger than previous limits. The results are discussed in the context of molecular and nucleo-chemical evolution. The high 12 C/ 13 C isotopic ratio of the molecular ISM in these starburst galaxies suggest that the gas has been recently accreted toward their nuclear regions.
HCOOCH 3 as a probe of temperature and structure in Orion-KL
Astronomy & Astrophysics, 2011
Context. The Orion Kleinmann-Low nebula (Orion-KL) is a complex region of star formation. Whereas its proximity allows studies on a scale of a few hundred AU, spectral confusion makes it difficult to identify molecules with low abundances. Aims. We studied an important oxygenated molecule, HCOOCH 3 , to characterize the physical conditions, temperature and density of the different molecular source components. Methyl formate presents strong close rotational transitions covering a large range of energy and its emission in Orion-KL is not contaminated by the emission of N-bearing molecules. This study will help in the future 1) to constrain chemical models for the formation of methyl formate in gas phase or on grain mantles, 2) to search for more complex or prebiotic molecules. Methods. To reduce the spectral confusion we used high resolution observations from the IRAM Plateau de Bure Interferometer in order to better isolate the molecular emission regions. We used twelve data sets with a spatial resolution down to 1.8 ′′ × 0.8 ′′. Continuum emission was subtracted by selecting apparently line free channels. Results. We identify 28 methyl formate emission peaks throughout the 50 ′′ field of observations. The two strongest peaks, named MF1 and MF2, are in the Compact Ridge and in the South West of the Hot Core respectively. From a comparison with single dish observations, we estimate that we miss less than 15% of the flux and that spectral confusion is still prevailing as half of the expected transitions are blended over the region. Assuming that the transitions are thermalized, we derive the temperature at the five main emission peaks. At the MF1 position in the Compact Ridge we find a temperature of 80 K in a 1.8 ′′ × 0.8 ′′ beam size and 120 K on a larger scale (3.6 ′′ × 2.2 ′′), suggesting an external source of heating, whereas the temperature is about 130 K at the MF2 position on both scales. Transitions of methyl formate in its first torsionally excited state are detected as well and the good agreement of the positions on the rotational diagrams between the ground state and the v t =1 transitions suggests a similar temperature. The LSR velocity of the gas is between 7.5 and 8.0 km s −1 depending on the positions and column density peaks vary from 1.6×10 16 to 1.6×10 17 cm −2. A second velocity component is observed around 9-10 km s −1 in a North-South structure stretching from the Compact Ridge up to the BN object; ; this component is warmer at the MF1 peak. The two other C 2 H 4 O 2 isomers are not detected and the derived upper limit for the column density is ≤3×10 14 cm −2 for glycolaldehyde and ≤2×10 15 cm −2 for acetic acid. From the 223 GHz continuum map, we identify several dust clumps with associated gas masses in the range 0.8 to 5.8 M ⊙. Assuming that the methyl formate is spatially distributed as the dust, we find relative abundances of methyl formate in the range ≤0.1×10 −8 to 5.2×10 −8. We suggest a relation between the methyl formate distribution and shocks as traced by 2.12 µm H 2 emission.
CH3OCH3 in Orion-KL: a striking similarity with HCOOCH3
Context. Orion-KL is a remarkable, nearby star-forming region where a recent explosive event has generated shocks that could have released complex molecules from the grain mantles. Aims. A comparison of the distribution of the different complex molecules will help in understanding their formation and constraining the chemical models. Methods. We used several data sets from the Plateau de Bure Interferometer to map the dimethyl ether emission with different arcsec spatial resolutions and different energy levels (from E up = 18 to 330 K) to compare with our previous methyl formate maps. Results. Our data show remarkable similarity between the dimethyl ether (CH 3 OCH 3) and the methyl formate (HCOOCH 3) distributions even on a small scale (1.8 × 0.8 or ∼500 AU). This long suspected similarity, seen from both observational and theoretical arguments, is demonstrated with unprecedented confidence, with a correlation coefficient of maps ∼0.8. Conclusions. A common precursor is the simplest explanation of our correlation. Comparisons with previous laboratory work and chemical models suggest the major role of grain surface chemistry and a recent release, probably with little processing, of mantle molecules by shocks. In this case the CH 3 O radical produced from methanol ice would be the common precursor (whereas ethanol, C 2 H 5 OH, is produced from the radical CH 2 OH). The alternative gas phase scheme, where protonated methanol CH 3 OH + 2 is the common precursor to produce methyl formate and dimethyl ether through reactions with HCOOH and CH 3 OH, is also compatible with our data. Our observations cannot yet definitely allow a choice between the different chemical processes, but the tight correlation between the distributions of HCOOCH 3 and CH 3 OCH 3 strongly contrasts with the different behavior we observe for the distributions of ethanol and formic acid. This provides a very significant constraint on models.
Microwave and submillimeter spectroscopy and first ISM detection of 18 O-methyl formate
Astronomy & Astrophysics, 2012
Context. Astronomical survey of interstellar molecular clouds needs a previous analysis of the spectra in the microwave and sub-mm energy range to be able to identify them. We obtained very accurate spectroscopic constants in a comprehensive laboratory analysis of rotational spectra. These constants can be used to predict transition frequencies that were not measured in the laboratory very precisely. Aims. We present an experimental study and a theoretical analysis of two 18 O-methyl formate isotopologues, which were subsequently detected for the first time in Orion KL. Methods. The experimental spectra of both methyl formate isotopologues recorded in the microwave and sub-mm range from 1 to 660 GHz. Both spectra were analysed by using the rho-axis method (RAM) which takes into account the CH 3 internal rotation. Results. We obtained spectroscopic constants of both 18 O-methyl formate with high accuracy. Thousands of transitions were assigned and others predicted, which allowed us to detect both species in the IRAM 30 m line survey of Orion KL. 1 The source code for the fit, an example of input data file and a readme file are available at the web site (http://www.ifpan.edu.pl/ kisiel/introt/introt.htm#belgi) managed by Dr. Zbigniew Kisiel. Extended versions of the code made to fit transitions with higher J and K are also available the authors (I. Kleiner and M.C.).
Proceedings of the National Academy of Sciences, 2009
A continuous-flow cavity ring-down spectroscopy (CRDS) system integrating a chromatographic separation technique, a catalytic combustor, and an isotopic 13 C/ 12 C optical analyzer is described for the isotopic analysis of a mixture of organic compounds. A demonstration of its potential is made for the geochemically important class of short-chain hydrocarbons. The system proved to be linear over a 3-fold injection volume dynamic range with an average precision of 0.95‰ and 0.67‰ for ethane and propane, respectively. The calibrated accuracy for methane, ethane, and propane is within 3‰ of the values determined using isotope ratio mass spectrometry (IRMS), which is the current method of choice for compound-specific isotope analysis. With anticipated improvements, the low-cost, portable, and easy-to-use CRDS-based instrumental setup is poised to evolve into a credible challenge to the high-cost and complex IRMS-based technique.
Spectroscopic Constants for 13C and Deuterium Isotopologues of Cyclic and Linear C3H3+
Recently, we reported ab initio quartic force fields (QFFs) for the cyclic and linear forms of the C 3 H 3 + molecular cation, referred to as c-C 3 H 3 + and l-C 3 H 3 + . These were computed using high levels of theory. Specifically the singles and doubles coupled-cluster method that includes a perturbational estimate of connected triple excitations, CCSD(T), was used in conjunction with extrapolation to the one-particle basis set limit, and corrections for scalar relativity and core correlation were included. In the present study, we use these QFFs to compute highly accurate fundamental vibrational frequencies and other spectroscopic constants for the c-13 + . Improvements in ab intitio methods have now made it possible to identify small molecules in an astronomical observation without the aid of high-resolution experimental data. We also report dipole moment values and show that the above-mentioned cyclic isotopologues have values of 0.094, 0.225, and 0.312 D, respectively, while the l-C 3 H 3 + isotopologues have values that range between 0.325 and 0.811 D. Thus, it is hoped that the highly accurate spectroscopic constants and data provided herein for the 13 C and deuterium isotopologues of the cyclic and linear forms of C 3 H 3 + will enable their identification in astronomical observations from the Herschel Space Observatory, the Stratospheric Observatory for Infrared Astronomy, the Atacama Large Millimeter Array, and in the future, the James Webb Space Telescope.