We present a study of the natal core harboring the class 0 protostar GF9-2 in
the filamentary dark cloud GF 9 (d = 200 pc). GF9-2 stands unique in the sense
that it shows H2O maser emission, a clear signpost of protostar formation,
whereas it does not have a high-velocity large-scale molecular outflow
evidenced by our deep search for CO wing emission. These facts indicate that
GF9-2 core is early enough after star formation so that it still retains some
information of initial conditions for collapse. Our 350 um dust continuum
emission image revealed the presence of a protostellar envelope in the center
of a molecular core. The mass of the envelope is ~0.6 Msun from the 350 um flux
density, while LTE mass of the core is ~3 Msun from moleuclar line
observations. Combining visibility data from the OVRO mm-array and the 45m
telescope, we found that the core has a radial density profile of
ρ(r)∝r−2 for 0.003 < r/pc < 0.08 region. Molecular line data
analysis revealed that the velocity width of the core gas increases
inward,while the outermost region maintains a velocity dispersion of a few
times of the ambient sound speed. The broadened velocity width can be
interpreted as infall. Thus, the collapse in GF9-2 is likely to be described by
an extension of the Larson-Penston solution for the period after formation of a
central star. We derived the current mass accretion rate of ~3E-05 Msun/year
from infall velocity of ~ 0.3 km/s at r~ 7000 AU. All results suggest that
GF9-2 core has been undergoing gravitational collapse for ~ 5000 years since
the formation of central protostar(s), and that the unstable state initiated
the collapse ~2E+05 years (the free-fall time) ago.Comment: ApJ Accepted. The preprint including figures with the original
quality is available at http://subarutelescope.org/staff/rsf/publication.htm
