Furuya, Ray S. and Kitamura, Yoshimi and Shinnaga, Hiroko (2006) The Initial Conditions for Gravitational Collapse of a Core: An Extremely Young Low-Mass Class 0 Protostar GF 9-2. Astrophysical Journal, 653 (2). pp. 1369-1390. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20110411-072346284
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We present a study of the natal core harboring the low-mass Class 0 protostar GF 9-2 in the filamentary dark cloud GF 9 using the Nobeyama 45 m and CSO 10.4 m telescopes and the OVRO millimeter array. GF 9-2 is unique in the sense that it shows H_2O masers, a clear signpost of protostar formation, but does not have a high-velocity large-scale outflow. These facts indicate that the GF 9-2 core is early enough after star formation that it still retains some information of initial conditions for collapse. Our 350 μm dust continuum image identified a protostellar envelope with an extent of ≃5400 AU in the center of the molecular core ≃0.08 pc in size. The envelope mass is estimated to be ≃0.6 M_⊙ from the 350 μm flux density, while the LTE mass of the core is ≃3 M_⊙ from molecular lines. We found that the core has a radial density profile of ρ(r) ∝ r^(-2) for the 0.003 ≾ r/pc ≾ 0.08 region and that the velocity width of the core gas increases inward, while the outermost region maintains a velocity dispersion of a few times the ambient sound speed. If we interpret the broadened velocity width as infall, the core collapse can be well described by an extension of the Larson-Penston solution for the period after formation of a central star. We derived the mass accretion rate of ≃3 × 10^(-5) M_⊙ yr^(-1) from infall velocity of ≃0.3 km s^(-1) at r ≃ 7000 AU. Furthermore, we found evidence that a protobinary is being formed at the core center. All of the results suggest that the GF 9-2 core has been undergoing gravitational collapse for ≾5000 yr since the protostar formation and that the unstable state initiated the collapse ≃2 × 10^5 yr (the free-fall time) ago.
|Additional Information:||© 2006 American Astronomical Society. Received 2005 November 22; accepted 2006 August 13. The authors sincerely acknowledge an anonymous referee whose comments significantly improved the quality of the paper. R. S. F. acknowledges A. I. Sargent and J. M. Carpenter for critical readings of the manuscript and continuous encouragement. The authors thank H. Yoshida for providing the telescope time at CSO to obtain the 12CO (3Y2) data, S. Takakuwa, J. Lamb, D. Woody, K. Sunada, and S. Okumura for fruitful discussion about data combining of the single-dish telescope and interferometer, H. Wiesemeyer for information on GF 9-2 including the distance and the luminosity, and L. Testi for his early contribution to this study. R. S. F. also appreciates discussion with A. Wootten, R. Cesaroni, E. van Dishoeck, H. Butner, G. Blake, T. Hanawa, T. Matsumoto, Y. Aikawa, K. Tachihara, T. Velusamy, and D. Ward-Thompson. R. S. F. and H. S. thank M. Yang, A. Kovács, C. Borys, and A.C.A. Boogert for their support at the SHARC II observations and data reduction. The authors gratefully acknowledge all of the staff at OVRO, NRO, CSO, VLA, and the GILDAS software group at IRAM. Research at the Owens Valley Radio Observatory is supported by the National Science Foundation through NSF grant AST 02-28955.|
|Subject Keywords:||ISM : clouds; ISM : evolution; ISM : individual (GF 9-2, L1082); ISM : molecules; stars : formation; stars : pre-main-sequence|
|Official Citation:||The Initial Conditions for Gravitational Collapse of a Core: An Extremely Young Low-Mass Class 0 Protostar GF 9-2 Ray S. Furuya, Yoshimi Kitamura, and Hiroko Shinnaga doi: 10.1086/508405|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||12 Apr 2011 15:03|
|Last Modified:||26 Dec 2012 13:09|
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