Volume 597, January 2017
|Number of page(s)||6|
|Section||Interstellar and circumstellar matter|
|Published online||21 December 2016|
Deuterium fractionation of a distant cold dark cloud along the line of sight of W51⋆
1 Université de Toulouse, UPS-OMP, IRAP, 31400 Toulouse, France
2 CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
3 Tata Institute of Fundamental Research, Homi Bhabha Road, 400005 Mumbai, India
4 Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint-Martin d’ Hères, France
5 LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR 8112, 75014 Paris, France
6 Sorbonne Universités, UPMC Univ. Paris 06, UMR 8112, LERMA, 75005 Paris, France
Received: 11 July 2016
Accepted: 14 November 2016
Herschel/HIFI observations toward the compact HII region W51 has revealed the presence of a cold dense core along its line of sight in a high-velocity stream located just in front of W51. This detection has been made possible through absorption measurements of low-energy transitions of HDO, NH3, and C3 against the bright background emitted by the star-forming region. We present a follow-up study of this core using the high sensitivity and high spectral resolution provided by the IRAM 30m telescope. We report new detections of this core in absorption for DCO+ (2–1, 3–2), H13CO+ (1–0), DNC (3–2), HN13C (1–0), p-H2CO (20,2–10,1, 30,3–20,2), and in emission for o-NH2D. We also report interferometric observation of this last species using the IRAM/NOEMA telescope, revealing the fragmented nature of the source through the detection of two cores, separated by 0.19−0.24 pc, with average sizes of less than 0.16−0.19 pc. From a non-LTE analysis, we are able to estimate the density (~2.5 × 104 cm-3) and temperature (~10 K) of this component, typical of what is found in dark clouds. This component (called W51-core) has the same DCO+/HCO+ ratio (0.02) as TMC-1 and a high DNC/HNC ratio (0.14). Detection of these deuterated species indicates that W51-core is similar to an early-phase low-mass star-forming region, formed from the interaction between the W51 giant molecular cloud and the high-velocity stream in front of it. The W51 complex being at about 5 kpc, these findings lead to what is the first detection of the earliest phase of low-mass star-forming region at such a large distance.
Key words: astrochemistry / line: identification / molecular data / radiative transfer
IRAM 30m data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A45
© ESO, 2016
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.