Inner Structure of Starless Core L694--2 Derived from Millimeter-Wave Interferometry

Abstract

We study the density structure of candidate contracting starless core L694-2 using 1.3 mm dust continuum observations from the IRAM Plateau de Bure Interferometer and the Berkeley-Illinois-Maryland Array, probing spatial scales from 10000-500 AU. The long baseline PdBI observations detect no emission, and limit the contamination from a compact component F_c < 2.7 mJy. This limit corresponds to a very small disk mass, M_disk < 5e-4 M_sun x (60 K / T_disk), and bolsters the ``starless'' interpretation of the core. The shorter baseline BIMA data are compared to density models using a physically motivated temperature distribution with a central minimum. This analysis provides clear evidence for a turn-over from the steep outer density profile observed in dust extinction to much more shallow behavior in the inner regions (<7500 AU). The best fit Bonnor-Ebert, Plummer-like, broken power law, and end-on cylinder models produce very similar flattened profiles and cannot be distinguished. We quantify the sensitivity of the inferred structure to various uncertainties, including the temperature distribution, the central position, and the presence of a weak unresolved central component. The largest uncertainty comes from the temperature assumption; an isothermal model modifies the best fit parameters by \~2 sigma, with the inferred profiles more shallow. Dust emission and extinction profiles are reproduced by an embedded cylinder with scale height H=13.5'' inclined at a small angle to the line of sight. The flat central density profile suggests that pressure forces still support the core, despite the extended inward motions inferred from molecular line observations (Lee, Myers, & Tafalla 2001). In the context of the cylindrical density model, these inward motions may represent the contraction of a prolate core along its major axis.

26 pages, 2 figures. Accepted to the Astrophysical Journal

References in corpus (16)

• Tracing the Mass during Low-Mass Star Formation. II. Modelling the Submillimeter Emission from Pre-Protostellar Cores
• Tracing the Mass during Low-Mass Star Formation. I. Submillimeter Continuum Observations
• A Survey for Infall Motions toward Starless Cores. II. $CS(2-1)$ and $N_2{H}^{+}(1-0)$ Mapping Observations
• A Survey for Infall Motions toward Starless Cores. I. CS (2-1) and N${}_2$H${}^{+}$ (1-0) Observations
• An empirical model for protostellar collapse
• Tracing the Mass during Low-Mass Star Formation. III. Models of the Submillimeter Dust Continuum Emission from Class 0 Protostars
• The dust temperature distribution in prestellar cores
• The structure and stability of molecular cloud cores in external radiation fields
• Envelope structure of deeply embedded young stellar objects in the Serpens Molecular Cloud
• Consistency of Ambipolar Diffusion Models with Infall in the L1544 Protostellar Core
• Models for Dense Molecular Cloud Cores
• Envelope Emission in Young Stellar Systems: A Sub-Arcsecond Survey of Circumstellar Structure
• Turbulent Cooling Flows in Molecular Clouds
• Inner Structure of Protostellar Collapse Candidate B335 Derived from Millimeter-Wave Interferometry
• Completion of a SCUBA survey of Lynds dark clouds and implications for low-mass star formation
• Limits on Radio Continuum Emission from a Sample of Candidate Contracting Starless Cores

Cited by in corpus (15)

• The initial conditions of isolated star formation - VI. SCUBA mapping of prestellar cores
• The Lifetimes and Evolution of Molecular Cloud Cores
• The Virial Balance of Clumps and Cores in Molecular Clouds
• Deep Near-Infrared Observations of L1014: Revealing the nature of the core and its embedded source
• An Observed Lack of Substructure in Starless Cores
• Spitzer and HHT observations of starless cores: masses and environments
• ${}^{14}$N/${}^{15}$N ratio measurements in prestellar cores with N${}_2$H${}^{+}$: new evidence of ${}^{15}$N-antifractionation
• A high resolution comparative study of the slowly contracting, starless cores, L694-2 and L1544
• Early science with the Large Millimetre Telescope: An LMT/AzTEC 1.1 mm Survey of Dense Cores in the Monoceros R2 Giant Molecular Cloud
• Observations of the Onset of Complex Organic Molecule Formation in Interstellar Ices
• Initial conditions for star formation in clusters: physical and kinematical structure of the starless core Oph A-N6
• Velocity distribution of collapsing starless cores, L694-2 and L1197
• On the internal dynamics of starless cores: stability of starless cores with internal motions and collapse dynamics
• Constraining Spatial Densities of Early Ice Formation in Small Dense Molecular Cores from Extinction Maps
• Chemical constraints on the dynamical evolution of the cold core L694