Envelope Structure of Starless Core L694‐2 Derived from a Near‐Infrared Extinction Map
Author(s) -
Daniel W. A. Harvey,
David J. Wilner,
C. J. Lada,
Philip C. Myers,
J. Alves
Publication year - 2003
Publication title -
the astrophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.376
H-Index - 489
eISSN - 1538-4357
pISSN - 0004-637X
DOI - 10.1086/378977
Subject(s) - physics , astrophysics , extinction (optical mineralogy) , dimensionless quantity , radius , power law , circular symmetry , hydrostatic equilibrium , core (optical fiber) , asymmetry , optics , classical mechanics , mechanics , astronomy , statistics , computer security , mathematics , computer science , quantum mechanics
We present a near-infrared extinction study of the dark globule L694-2, astarless core that shows strong evidence for inward motions in molecular lineprofiles. The J,H, and K band data were taken using the European SouthernObservatory New Technology Telescope. The best fit simple spherical power lawmodel has index p=2.6 +/- 0.2, over the 0.036--0.1 pc range in radius sampledin extinction. This power law slope is steeper than the value of p=2 for asingular isothermal sphere, the initial condition of the inside-out model forprotostellar collapse. Including an additional extinction component along theline of sight further steepens the inferred profile. Fitting a Bonnor-Ebertsphere results in a super-critical value of the dimensionless radius xi_max=25+/- 3. The unstable configuration of material may be related to the observedinward motions. The Bonnor-Ebert model matches the shape of the observedprofile, but significantly underestimates the amount of extinction (by a factorof ~4). This discrepancy in normalization has also been found for the nearbyprotostellar core B335 (Harvey et al. 2001). A cylindrical density model withscale height H=0.0164+/- 0.002 pc viewed at a small inclination to the cylinderaxis provides an equally good radial profile as a power law model, andreproduces the asymmetry of the core remarkably well. In addition, this modelprovides a basis for understanding the discrepancy in the normalization of theBonnor-Ebert model, namely that L694-2 has prolate structure, with the fullextent (mass) of the core being missed by assuming symmetry between theprofiles in the plane of the sky and along the line-of-sight. If the core issufficiently magnetized then fragmentation may be avoided, and later evolutionmight produce a protostar similar to B335.Comment: 38 pages, 7 figures, accepted to Astrophysical Journa
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