Detection of 6 K gas in Ophiuchus D

Abstract

Cold cores in interstellar molecular clouds represent the very first phase in star formation. The physical conditions of these objects are studied in order to understand how molecular clouds evolve and how stellar masses are determined. The purpose of this study is to probe conditions in the dense, starless clump Ophichus D (Oph D). The ground-state (1(10)-1(11)) rotational transition of ortho-H2D+ was observed with APEX towards the density peak of Oph D. The width of the H2D+ line indicates that the kinetic temperature in the core is about 6 K. So far, this is the most direct evidence of such cold gas in molecular clouds. The observed H2D+ spectrum can be reproduced with a hydrostatic model with the temperature increasing from about 6 K in the centre to almost 10 K at the surface. The model is unstable against any increase in the external pressure, and the core is likely to form a low-mass star. The results suggest that an equilibrium configuration is a feasible intermediate stage of star formation even if the larger scale structure of the cloud is thought to be determined by turbulent fragmentation. In comparison with the isothermal case, the inward decrease in the temperature makes smaller, i.e. less massive, cores susceptible to externally triggered collapse.

arXiv comment7 pages, 5 figures, accepted for Astronomy and Astrophysics

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Cited by in corpus (24)

• Chemical modeling of L183 (= L134N) : an estimate of the ortho/para H2 ratio
• Galactic cold cores III. General cloud properties
• The Initial Conditions of Clustered Star Formation I: NH3 Observations of Dense Cores in Ophiuchus
• Nitrogen chemistry and depletion in starless cores
• Extended emission of D2H+ in a prestellar core
• The JCMT Legacy Survey of the Gould Belt: a molecular line study of the Ophiuchus molecular cloud
• On The Gas Temperature of Molecular Cloud Cores
• A (sub)millimetre study of dense cores in Orion B9
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• A Revised Description of the Cosmic Ray-Induced Desorption of Interstellar Ices
• Water and Methanol Ice in L1544
• Reliability of NH3 as the temperature probe of cold cloud cores
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• Star-forming gas in young clusters
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• Will ALMA Reveal the True Core Mass Function of Protoclusters?
• Dynamical timescale of precollapse evolution inferred from chemical distribution in the Taurus Molecular Cloud-1 (TMC-1) filament
• The structure and early evolution of massive star forming regions - Substructure in the infrared dark cloud SDC13
• Comparison of modified black-body fits for the estimation of dust optical depths in interstellar clouds
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