Initial conditions for star formation in clusters: physical and kinematical structure of the starless core Oph A-N6

Abstract

We present high spatial (<300 AU) and spectral (0.07 km/s) resolution Submillimeter Array observations of the dense starless cluster core Oph A-N6, in the 1 mm dust continuum and the 3-2 line of N2H+ and N2D+. The dust continuum observations reveal a compact source not seen in single-dish observations, of size ~1000 AU and mass 0.005-0.01 M\odot. The combined line and single-dish observations reveal a core of size 3000 \times 1400 AU elongated in a NW-SE direction, with almost no variation in either line width or line center velocity across the map, and very small non-thermal motions. The deuterium fraction has a peak value of ~0.15 and is >0.05 over much of the core. The N2H+ column density profile across the major axis of Oph A-N6 is well represented by an isothermal cylinder, with temperature 20 K, peak density 7.1 \times 10^6 cm^{-3}, and N2H+ abundance 2.7 \times 10^{-10}. The mass of Oph A-N6 is estimated to be 0.29 M\odot, compared to a value of 0.18 M\odot from the isothermal cylinder analysis, and 0.63 M\odot for the critical mass for fragmentation of an isothermal cylinder. Compared to isolated low-mass cores, Oph A-N6 shows similar narrow line widths and small velocity variation, with a deuterium fraction similar to "evolved" dense cores. It is significantly smaller than isolated cores, with larger peak column and volume density. The available evidence suggests Oph A-N6 has formed through the fragmentation of the Oph A filament and is the precursor to a low-mass star. The dust continuum emission suggests it may already have begun to form a star.

42 pages, 12 figures, accepted by ApJ

References in corpus (29)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• MAMBO Mapping of Spitzer c2d Small Clouds and Cores
• Filamentary structure of star-forming complexes
• Star formation through gravitational collapse and competitive accretion
• The Mass Distribution and Lifetime of Prestellar Cores in Perseus, Serpens, and Ophiuchus
• Observing the gas temperature drop in the high-density nucleus of L 1544
• Bolocam Survey for 1.1 mm Dust Continuum Emission in the c2d Legacy Clouds. II. Ophiuchus
• Equilibrium Star Cluster Formation
• The Large and Small Scale Structures of Dust in the Star-Forming Perseus Molecular Cloud
• An Ammonia Spectral Atlas of Dense Cores in Perseus
• Comparing Star Formation on Large Scales in the c2d Legacy Clouds: Bolocam 1.1 mm Dust Continuum Surveys of Serpens, Perseus, and Ophiuchus
• Survey of ortho-H2D+(1_{1,0}-1_{1,1}) in dense cloud cores
• Dynamics of Dense Cores in the Perseus Molecular Cloud
• Current Star Formation in the Ophiuchus and Perseus Molecular Clouds: Constraints and Comparisons from Unbiased Submillimeter and Mid-Infrared Surveys. II
• On the frequency of N2H+ and N2D+
• 2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
• The enigmatic core L1451-mm: a first hydrostatic core? or a hidden VeLLO?
• The nature of the Class I population in Ophiuchus as revealed through gas and dust mapping
• The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds: VII. Ophiuchus Observed with MIPS
• Disk and Envelope Structure in Class 0 Protostars: II. High Resolution Millimeter Mapping of the Serpens Sample
• The Excitation of N${}_2$H${}^{+}$ in Interstellar Molecular Clouds. I - Models
• Exposed Long-lifetime First-core: A New Model of First Cores Based on Radiation Hydrodynamics
• A Large Scale Survey of NGC1333
• Nonlinear Evolution of Global Hydrodynamic Shallow-Water Instability in Solar Tachocline
• Detection of a Bipolar Molecular Outflow Driven by a Candidate First Hydrostatic Core
• The initial conditions of star formation VIII: an observational study of the Ophiuchus cloud L1688 and implications for the prestellar core mass function
• Massive Quiescent Cores in Orion. -- II. Core Mass Function
• BIMA N2H+ 1-0 mapping observations of L183 -- fragmentation and spin-up in a collapsing, magnetized, rotating, pre-stellar core

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