A Survey for Search of Infall Motions toward Starless Cores

Details A Survey for Search of Infall Motions toward Starless Cores A Survey for Search of Infall Motions toward Starless Cores

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999sf99.proc..177l&link_type=abstract

Star Formation 1999, Proceedings of Star Formation 1999, held in Nagoya, Japan, June 21 - 25, 1999, Editor: T. Nakamoto, Nobeyam

Computer Science

Scientific paper

We present results of a survey of 220 starless cores in CS(2--1), N2H+ (1--0), and C18O (1--0) using the NEROC Haystack 37-m telescope. We have detected 163 out of 196 sources observed in CS, 72 out of 142 in N2H+ and 30 out of 30 in C18O. In total, 69 sources were detected in both CS and N2H+. The isolated component of the N2H+ (1--0) spectrum (F1F=01-12) usually shows a weak symmetric profile which is optically thin feature. In contrast, a significant fraction of the CS spectra show non-Gaussian shapes, which we interpret as arising from a combination of self absorption due to lower excitation gas in the core front and kinematics in the core. The distribution of the normalized velocity difference (δ VCS) between the CS and N2H+ peaks appears significantly skewed to the blue (δ VCS < 0). The incidence of sources with blue asymmetry tends to increase as the total optical depth or the integrated intensity of the N2H+ line increases. This overabundance of ``blue'' sources over ``red'' sources suggests that inward motions are a significant feature of starless cores. We identify 7 strong infall candidates and 10 probable infall candidates. Their typical inward speeds are sub-sonic, approximately 0.04 - 0.1 km s-1, so they contain `thermal' infall motions, unlike the faster inward speeds associated with most YSOs (Mardones et al. 1997).

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