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J/A+A/527/A88       Chemistry in infrared dark clouds        (Vasyunina+, 2011)

Chemistry in infrared dark clouds. Vasyunina T., Linz H., Henning T., Zinchenko, I., Beuther, H., Voronkov M. <Astron. Astrophys. 527, A88 (2011)> =2011A&A...527A..88V
ADC_Keywords: Molecular clouds ; Infrared sources ; Spectroscopy ; Interstellar medium Keywords: ISM: clouds - ISM: molecules - radio lines: ISM - stars: formation Abstract: Massive stars play an important role in shaping the structure of galaxies. Infrared dark clouds (IRDCs), with their low temperatures and high densities, have been identified as the potential birthplaces of massive stars. In order to understand the formation processes of massive stars, the physical and chemical conditions in infrared dark clouds have to be characterized. The goal of this paper is to investigate the chemical composition of a sample of southern infrared dark clouds. One important aspect of the observations is to check, whether the molecular abundances in IRDCs are similar to the low-mass pre-stellar cores, or if they show signatures of more evolved evolutionary stages. We performed observations toward 15 IRDCs in the frequency range between 86 and 93GHz using the 22-m Mopra radio telescope. In total, 13 molecular species comprising N2H+, 13CS, CH3CN, HC3N, HNC, HCO+, HCN, HNCO, C2H, SiO, H13CO+, H13CN, and CH3C2H were observed for all targets. Hence, we included in general species appropriate for elevated densities, where some of them trace the more quiescent gas, while others are sensitive to more dynamical processes. Description: The observations were made with the 22-m Mopra radio telescope, operated by the Australia Telescope National Facility (ATNF) in position switching mode. In total we spent 7 minutes on source and 7 minutes on the OFF position. Our targets are dense molecular condensations within larger molecular clouds with often widespread molecular emission. Therefore, we refrained from using one standard OFF position throw. Instead, OFF positions were chosen individually for every target region and were approximately 8-10' away from the source. The Mopra spectrometer (MOPS) offers zoom-mode configurations with the possibility to observe up to 16 sub-bands of 138MHz each within a total frequency range of 8.3GHz. This set-up delivers a velocity resolution of ∼0.11km/s. The observations were carried out on 9-11 May 2008 with the 3mm band receiver. We put the central frequency for the 8.3GHz block to 89270MHz and thus covered the range from 85 to 93 GHz. In this range we distributed 13 zoom windows, which covered N2H+, 13CS, CH3CN, HC3N, HNC, HCO+, HCN, HNCO, C2H, SiO, H13CO+, H13CN, and CH3C2H. System temperature measurements were performed every 30 minutes and a pointing scan every hour. Typical system temperatures (measured with the common chopper-wheel technique) during the observations were 170-210K. At Mopra observatory, SiO masers are used to correct the telescope pointing, giving a pointing accuracy better than 10". The main beam of the telescope varies between 36" at 86 GHz and 33" at 115GHz and the main beam efficiency varies between 0.49 at 86GHz and 0.44 at 100GHz (Ladd et al., 2005PASA...22...62L). Mopra data are originally stored in RPFITS format. Using the ATNF Spectral line Analysis package (ASAP), we transformed these raw data into ascii files, which were then fed into GILDAS for further analysis. Data files were written in CLASS77 format. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file sources.dat 70 37 List of observed sources, in 13CS, C2H, CH3CCH, CH3CN, H13CN, H13CO+, HCCCN, HCN, HCO+, HNC, HNCO, N2H+, SiO sp_fits/* 0 481 Spectra in FITS format sp_mopra/* 0 13 Spectra in CLASS format
See also: J/A+A/499/149 : Southern Infrared Dark Clouds physical prop. (Vasyunina+, 2009) Byte-by-byte Description of file: sources.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Seq Sequential number 4- 15 A12 --- Name Target name (IRDCLLL.ll-N) 18- 19 I2 h RAh Right ascension (J2000) 21- 22 I2 min RAm Right ascension (J2000) 24- 29 F6.3 s RAs Right ascension (J2000) 31 A1 --- DE- Declination sign (J2000) 32- 33 I2 deg DEd Declination (J2000) 35- 36 I2 arcmin DEm Declination (J2000) 38- 42 F5.2 arcsec DEs Declination (J2000) 44- 54 A11 --- [VLH2009] Associated Vasyunina et al., J/A+A/499/149, dark cloud name (added by CDS) 56- 58 F3.1 kpc Dist Distance (from table 1 of the paper) (1) 59 A1 --- n_Dist [b] b: from Saito et al. (2001PASJ...53.1037S) 61- 64 F4.1 K T Temperature (from table 1 of the paper) (2) 66- 68 F3.1 10+22cm-2 N(H2) H2 column density (from table 1 of the paper) (3) 70 A1 --- Cat [MAQ] Category (from table 1 of the paper) (4)
Note (1): At first, to estimate the kinematic distances to our IRDCs, we used HCO+ line velocities (see Vasyunina et al., 2009, Cat. J/A+A/499/149). But more detailed investigation showed that HCO+ lines, as a rule, have complex line shapes and the vLSR positions can be shifted up to 2km/s in comparison with its optically thin isotopologue H13CO+. We cannot use H13CO+ for distance determination, since it is much weaker and we detected it not in all cases. Thus, we decided to use N2H+ for the distance determination, which is distinguishable for all regions except IRDC309.37-2. Despite the significant difference in velocities (up to 2km/s) between HCO+ and N2H+, the kinematic distances did not change drastically compared with the values in Paper I (Vasyunina et al., 2009, Cat. J/A+A/499/149). Note (2): Temperatures were derived based on (1, 1) and (2, 2) ammonia transitions observed with the the 64-m Parkes radio telescope (Linz et al., in prep.). Note (3): To estimate H2 column densities in every point we used 1.2mm data from SIMBA/SEST adopting the Mopra telescope beam size. Note (4): Ccategory flag as follows: A = active core M = middle core Q = quiescent core
Acknowledgements: Vasyunina T., , Max Planck Institute for Astronomy
(End) Vasyunina T. [MPIA], Patricia Vannier [CDS] 15-Feb-2011
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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