We present a study of the natal core harboring the class 0 protostar GF 9-2 ( bolometric luminosity \simeq 0.3 L _ { \odot } , bolometric temperature \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < $ } } } 20 K ; Wiesmeyer et al . )
in the filamentary dark cloud GF 9 ( distance = 200 pc ) using the Nobeyama 45 m , CSO 10.4 m telescopes , and the OVRO mm-array .
GF 9-2 stands unique in the sense that it shows H _ { 2 } O maser emission ( Furuya et al .
) , a clear signpost of protostar formation , whereas it does not have a high-velocity large-scale molecular outflow evidenced by our deep search for ^ { 12 } CO wing emission .
These facts indicate that GF 9-2 core is early enough after star formation so that it still retains some information of initial conditions for collapse .
Our 350 \mu m dust continuum emission image revealed the presence of a protostellar envelope with an extent of \simeq 5400 AU in the center of a molecular core \simeq 0.08 pc in size .
The mass of the envelope is \simeq 0.6 M _ { \odot } from the 350 \mu m flux density , while LTE mass of the core is \simeq 3 M _ { \odot } from N _ { 2 } H ^ { + } , H ^ { 13 } CO ^ { + } , CCS , and NH _ { 3 } line observations .
Combining visibility data from the OVRO mm-array and the 45 m telescope , we found that the core has a radial density profile of \rho ( r ) \propto r ^ { -2 } for 0.003 \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < $ } % } } r / { pc } \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } % \hbox { $ < $ } } } 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 GF 9-2 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 \simeq 3 \times 10 ^ { -5 } M _ { \odot } year ^ { -1 } from infall velocity of \simeq 0.3 km s ^ { -1 } at r \simeq 7000 AU .
Furthermore , we found evidence that a protobinary is being formed at the core center .
All results suggest that GF 9-2 core has been undergoing gravitational collapse for \mathrel { \hbox { \hbox to 0.0 pt { \hbox { \lower 4.0 pt \hbox { $ \sim$ } } } \hbox { $ < $ } } } 5000 years since the formation of central protostar ( s ) , and that the unstable state initiated the collapse \simeq 2 \times 10 ^ { 5 } years ( the free-fall time ) ago .