Mapping the prestellar core Ophiuchus D (L1696A) in ammonia

Abstract

The gas kinetic temperature in the centres of starless, high-density cores is predicted to fall as low as 5-6 K. The aim of this study was to determine the kinetic temperature distribution in the low-mass prestellar core Oph D where previous observations suggest a very low central temperature. The densest part of the Oph D core was mapped in the NH3(1,1) and (2,2) inversion lines using the Very Large Array (VLA). The physical quantities were derived from the observed spectra by fitting the hyperfine structure of the lines, and subsequently the temperature distribution of Oph D was calculated using the standard rotational temperature techniques. A physical model of the cores was constructed, and the simulated spectra after radiative transfer calculations with a 3D Monte Carlo code were compared with the observed spectra. Temperature, density, and ammonia abundance of the core model were tuned until a satisfactory match with the observation was obtained. The high resolution of the interferometric data reveals that the southern part of Oph D comprises of two small cores. The gas kinetic temperatures, as derived from ammonia towards the centres of the southern and northern core are 7.4 and 8.9 K, respectively. The observed masses of the cores are only 0.2 M_Sun. Their potential collapse could lead to formation of brown dwarfs or low-mass stars.

Accepted for publication in A&A; 10 pages, 9 figures

References in corpus (8)

• Observing the gas temperature drop in the high-density nucleus of L 1544
• Hipparcos distances of Ophiuchus and Lupus cloud complexes
• On the robustness of the ammonia thermometer
• The abundances of nitrogen-containing molecules during pre-protostellar collapse
• Modelling line emission of deuterated H_3^+ from prestellar cores
• The initial conditions of isolated star formation - VII. Spitzer mapping of pre-stellar cores
• Detection of 6 K gas in Ophiuchus D
• Physical properties of dense cores in Orion B9

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• VLA and NOEMA view of the Bok Globule CB 17: the starless nature of a proposed FHSC candidate
• A Survey of Deuterated Ammonia in the Cepheus Star-Forming Region L1251
• NH${}_3$ Observations of the S235 Star Forming Region: Dense Gas in Inter-core Bridges