Submillimeter Observations of the Quiescent Core - Ophiuchus A-N6

Abstract

We have observed the Oph A-N6 prestellar core in the following transitions: N2D+ J=3 to 2, DCO+ J=3 to 2 and J=5 to 4, HCO+ J=3 to 2, CS J=5 to 4 and J=7 to 6, and H13CO+ J=3 to 2 and J=4 to 3, using the James Clerk Maxwell Telescope. We also observed the NH3 (1,1) and (2,2) inversion transitions towards the Oph A-N6 peak with the Green Bank Telescope. We have found that the N6 core is composed of shells of different chemical composition due to the freezing out of chemical species at different densities. The undepleted species N2D+ appears to trace the high-density interior of the core, DCO+ and H13CO+ trace an intermediate region, and CS traces the outermost edges of the core. A distinct blue-red spectral asymmetry, indicative of infall motion, is clearly detected in the HCO+ spectra, suggesting that N6 is undergoing gravitational collapse. This collapse was possibly initiated by a decrease in turbulent support suggested by the fact that the non-thermal contribution to the line widths is smaller for the molecular species closer to the center of the core. We also present a temperature profile for the core. These observations support the claim that the Oph A-N6 core is an extremely young prestellar core, which may have been recently cut off from MHD support and begun to collapse.

18 pages, 8 figures, accepted by ApJ

References in corpus (11)

• Cold Dark Clouds: The Initial Conditions for Star Formation
• The SCUBA Legacy Catalogue: Continuum Objects Detected by SCUBA
• The Mass Distribution and Lifetime of Prestellar Cores in Perseus, Serpens, and Ophiuchus
• The initial conditions of star formation in the Ophiuchus main cloud: Kinematics of the protocluster condensations
• On the internal structure of starless cores. II. A molecular survey of L1498 and L1517B
• Current Star Formation in the Perseus Molecular Cloud: Constraints from Unbiased Submillimeter and Mid-Infrared Surveys
• The Distribution of Ortho-H_2D+(1_1,0 - 1_1,1) in L1544: Tracing the Deuteration Factory in Prestellar Cores
• The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds: VII. Ophiuchus Observed with MIPS
• Large Area Mapping at 850 Microns. IV. Analysis of the Clump Distribution in the Orion B South Molecular Cloud
• Molecular Emission Line Formation in Prestellar Cores
• The Effect of Noise in Dust Emission Maps on the Derivation of Column Density, Temperature and Emissivity Spectral Index

Cited by in corpus (7)

• HD depletion in starless cores
• How do stars gain their mass? A JCMT/SCUBA-2 Transient Survey of Protostars in Nearby Star Forming Regions
• How Starless Are Starless Cores?
• The Initial Conditions of Clustered Star Formation III. The Deuterium Fractionation of the Ophiuchus B2 Core
• Kinematics of dense gas in the L1495 filament
• ALMA detections of the youngest protostars in Ophiuchus
• Initial conditions for star formation in clusters: physical and kinematical structure of the starless core Oph A-N6