The Dynamical State of the Starless Dense Core FeSt 1-457: A Pulsating Globule?

Abstract

High resolution molecular line observations of CS, HCO+, C18O and N2H+ were obtained toward the starless globule FeSt 1-457 in order to investigate its kinematics and chemistry. The HCO+ and CS spectra show clear self-reversed and asymmetric profiles across the face of the globule. The sense of the observed asymmetry is indicative of the global presence of expansion motions in the outer layers of the globule. These motions appear to be subsonic and significantly below the escape velocity of the globule. Comparison of our observations with near-infrared extinction data indicate that the globule is gravitationally bound. Taken together these considerations lead us to suggest that the observed expansion has its origin in an oscillatory motion of the outer layers of the globule which itself is likely in a quasi-stable state near hydrostatic equilibrium. Analysis of the observed linewidths of CO and N2H+ confirm that thermal pressure is the dominant component of the cloud's internal support. A simple calculation suggests that the dominant mode of pulsation would be an l = 2 mode with a period of 0.3 Myr. Deformation of the globule due to the large amplitude l = 2 oscillation may be responsible for the double-peaked structure of the core detected in high resolution extinction maps. Detailed comparison of the molecular-line observations and extinction data provides evidence for significant depletion of C18O and perhaps HCO+ while N2H+ may be undepleted to a cloud depth of about 40 magnitudes of visual extinction.

to appear in ApJ vol 665 20 August 2007;

References in corpus (2)

• 2MASS wide field extinction maps - I. The Pipe nebula
• Oscillations of starless cores

Cited by in corpus (16)

• The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure
• The Different Structures of the Two Classes of Starless Cores
• The dynamics of collapsing cores and star formation
• The nature of the dense core population in the Pipe Nebula: A survey of NH3, CCS, and HC5N molecular line emission
• Using Chemistry to Unveil the Kinematics of Starless Cores: Complex Radial Motions in Barnard 68
• Distortion of Magnetic Fields in a Starless Core: Near-Infrared Polarimetry of FeSt 1-457
• Distortion of Magnetic Fields in a Starless Core II: 3D Magnetic Field Structure of FeSt 1-457
• Infall/Expansion Velocities in the Low-Mass Dense Cores L492, L694-2, and L1521F: Dependence on Position and Molecular Tracer
• A correlation between chemistry, polarization and dust properties in the Pipe Nebula starless core FeSt 1-457
• Star formation in Chamaeleon I and III: a molecular line study of the starless core population
• Distortion of Magnetic Fields in a Starless Core VI: Application of Flux Freezing Model and Core Formation of FeSt 1-457
• Filament collapse: a two phase process
• Nobeyama Survey of Inward Motions toward Cores in Orion Identified by SCUBA-2
• Filament fragmentation: Density gradients suppress end dominated collapse
• Molecular Line Profiles from a Core Forming in a Turbulent Cloud
• Why do some cores remain starless ?