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J/A+A/612/A37       CH 149um spectra of 4 molecular clouds   (Wiesemeyer+, 2018)

Unveiling the chemistry of interstellar CH. Spectroscopy of the 2 THz N = 2 ← 1 ground state line. Wiesemeyer H., Guesten R., Menten K.M., Duran C.A., Csengeri T., Jacob A.M., Simon R., Stutzki J., Wyrowski F. <Astron. Astrophys. 612, A37 (2018)> =2018A&A...612A..37W (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Spectroscopy Keywords: ISM: abundances - ISM: clouds - ISM: lines and bands - ISM: molecules - ISM: structure Abstract: The methylidyne radical CH is commonly used as a proxy for molecular hydrogen in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H2 proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H2. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a "canonical" CH abundance needs to be addressed. The N=2←1 ground state transition of CH at λ149um has become accessible to high-resolution spectroscopy thanks to GREAT, the German Receiver for Astronomy at Terahertz Frequencies aboard the Stratospheric Observatory for Infrared Astronomy, SOFIA. Its unsaturated absorption and the absence of emission from the star forming regions makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant Galactic star forming regions, whose hot cores emit a strong far-infrared dust continuum serving as background signal. Moreover, if combined with the sub-millimeter line of CH at λ560um, environments forming massive stars can be analyzed. For this we present a case study on the "proto-Trapezium" cluster W3 IRS5. While we confirm the global correlation between the column densities of HF and those of CH, both in arm and interarm regions, clear signposts of an over-abundance of CH are observed towards lower densities. However, a significant correlation between the column densities of CH and HF remains. A characterization of the hot cores in the W3 IRS5 proto-cluster and its envelope demonstrates that the sub-millimeter/far-infrared lines of CH reliably trace not only diffuse but also dense, molecular gas. In diffuse gas, at lower densities a quiescent ion-neutral chemistry alone cannot account for the observed abundance of CH. Unlike the production of HF, for CH+ and CH, vortices forming in turbulent, diffuse gas may be the setting for an enhanced production path. However, CH remains a valuable tracer for molecular gas in environments reaching from diffuse clouds to sites of high-mass star formation. Description: The observations were performed on several SOFIA flights in the observatory's cycle 4 (F298 and F301 on 2016 May 18 and 24, respectively, F346 on 2016 November 8, and F369 on 2017 February 3). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 123 5 Synopsis of velocity-integrated column densities of CH, HF, and OH on the sightline to W49 N list.dat 120 4 List of fits files fits/* 0 4 Individual fits files
See also: J/A+A/490/213 : 1.4 and 3.4mm interferometry of W3 IRS5 (Rodon+, 2008) J/A+A/567/L5 : W3(OH) high angular resolution 7mm images (Dzib+, 2014) J/ApJ/647/418 : Ground-state OH masers in W3(OH) study (Fish+, 2006) J/ApJ/668/331 : OH masers in W3(OH) (Fish+, 2007) J/ApJ/393/149 : W49N H2O maser outflow: distance and kinematics (Winn+, 1992) J/ApJ/429/253 : W49N H2O masers (Gwinn, 1994) J/A+A/582/A64 : W51/e2 and G34.3+0.2 IRAM spectra (Lykke+, 2015) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 11 A11 --- Name Spiral arm designation 13 A1 --- n_Name [abc] Note on Name (1) 16- 19 F4.1 km/s Vlow Lower value of velocity interval 22- 25 F4.1 km/s Vup Upper value of velocity interval 27- 31 F5.2 10+13cm-2 N(CH) CH velocity-integrated column density 33- 36 F4.2 10+13cm-2 E_N(CH) Error on N(CH) (upper value) (4) 38- 41 F4.2 10+13cm-2 e_N(CH) Error on N(CH) (lower value) (4) 43- 47 F5.3 10+13cm-2 N(HF) HF velocity-integrated column density 49- 53 F5.3 10+13cm-2 E_N(HF) Error on N(HF) (upper value) (4) 55- 59 F5.3 10+13cm-2 e_N(HF) Error on N(HF) (lower value) (4) 61- 65 F5.2 10+13cm-2 N(OH) OH velocity-integrated column density 67- 70 F4.2 10+13cm-2 E_N(OH) Error on N(OH) (upper value) (4) 72- 75 F4.2 10+13cm-2 e_N(OH) Error on N(OH) (lower value) (4) 77- 80 F4.2 --- fNH2 Molecular hydrogen fraction, 2N(H2)/(N(HI)+2N(H2)) (2) 82- 85 F4.2 --- E_fNH2 Error on fNH2 (upper value) (4) 87- 90 F4.2 --- e_fNH2 Error on fNH2 (lower value) (4) 92- 96 F5.3 --- N(HF)/N(CH) Molecular ratio, N(HF)/N(CH) (3) 98-102 F5.3 --- E_N(HF)/N(CH) Error on N(HF)/N(CH) (upper value) (4) 104-108 F5.3 --- e_N(HF)/N(CH) Error on N(HF)/N(CH) (lower value) (4) 110-113 F4.2 --- N(OH)/N(CH) Molecular ratio, N(OH)/N(CH) (3) 115-118 F4.2 --- E_N(OH)/N(CH) Error on N(OH)/N(CH) (upper value) (4) 120-123 F4.2 --- e_N(OH)/N(CH) Error on N(OH)/N(CH) (lower value) (4)
Note (1): Notes as follows: a = Analysis and error estimates inaccurate (velocity interval contains hot-core environment of unknown excitation, HF absorption is partially saturated) b = Near- and far-side crossing of Sagittarius spiral arm c = Far-side crossing Note (2): are derived from HF (with N(HF)/N(H2)=1.4x10-8) and from HI λ21cn data (Winkle et al., 2017, further references therein). Note (3): Bayesian error estimates (accounting for the correlation between the column densities of the reported ratios). Note (4): Error estimates are based on the normalized chi2 of the fits shown in Fig. 2, and on a 5% uncertainty in the continuum levels.
Byte-by-byte Description of file: list.dat
Bytes Format Units Label Explanations
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000) 10- 18 F9.5 deg DEdeg Declination of center (J2000) 20- 23 I4 --- Nx %s Number of pixels along X-axis 25- 43 A19 --- Obs.Date Observation date (YYYY-MM-DDThh:mm:ss) 45- 52 F8.5 GHz bFreq Lower value of frequency interval 54- 60 F7.5 GHz BFreq Upper value of frequency interval 62- 70 E9.4 Hz dFreq Frequency resolution 72- 73 I2 Kibyte size Size of FITS file 75- 98 A24 --- FileName Name of FITS file, in subdirectory fits 100-120 A21 --- Title Title of the FITS file
Acknowledgements: Helmut Wiesemeyer, hwiese(at)
(End) Patricia Vannier [CDS] 11-Jan-2018
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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