Dense cores and protostellar collapse. In nearby star-forming regions.
YAMAMOTO H., ONISHI T., TACHIHARA K., MIZUNO A. and FUKUI Y.
Abstract (from CDS):
We present the results of a complete survey for high density condensations in the Taurus star-forming region. The unbiased C18O survey is based on 13CO observations covering the whole Taurus region with the 4 m telescope of Nagoya University. The H13CO+ (J=1-0) survey for dense molecular condensations inside the C18O cores is based on observations with the 45 m telescope at Nobeyama Radio Observatory. We detected 55 H13CO+ condensations, of which 44 are starless. These starless condensations are compact (R≤0.1 pc) and have high densities (≥105 cm–3). The statistical analysis of the starless condensations yields their lifetime of ∼ 4x105 years which is several times longer than their free-fall time. One of the starless condensations, MC 27, exhibits fairly strong and narrow emission in the J = 4-3, 3-2 and 1-0 transitions of H13CO+, as well as self-reversed profiles of HCO+, J=4-3 and 3-2. A statistical analysis indicates for MC 27 a very short lifetime of ∼104 years, consistent with the free-fall time for a density of 106 cm–3. MC 27 is probably very close to the moment of the formation of a protostellar core.