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Abstract We present Atacama Large Millimeter/submillimeter Array Band 3 data toward five massive young stellar objects (MYSOs), and investigate relationships between unsaturated carbon-chain species and saturated complex organic molecules (COMs). An HC 5 N ( J = 35–34) line has been detected from three MYSOs, where nitrogen (N)-bearing COMs (CH 2 CHCN and CH 3 CH 2 CN) have been detected. The HC 5 N spatial distributions show compact features and match with a methanol (CH 3 OH) line with an upper-state energy around 300 K, which should trace hot cores. The hot regions are more extended around the MYSOs where N-bearing COMs and HC 5 N have been detected compared to two MYSOs without these molecular lines, while there are no clear differences in the bolometric luminosity and temperature. We run chemical simulations of hot-core models with a warm-up stage, and compare with the observational results. The observed abundances of HC 5 N and COMs show good agreements with the model at the hot-core stage with temperatures above 160 K. These results indicate that carbon-chain chemistry around the MYSOs cannot be reproduced by warm carbon-chain chemistry, and a new type of carbon-chain chemistry occurs in hot regions around MYSOs. 

Abstract The mass distribution of dense cores is a potential key to understanding the process of star formation. Applying dendrogram analysis to the CARMA-NRO Orion C 18 O ( J = 1–0) data, we identify 2342 dense cores, about 22% of which have virial ratios smaller than 2 and can be classified as gravitationally bound cores. The derived core mass function (CMF) for bound starless cores that are not associate with protostars has a slope similar to Salpeter’s initial mass function (IMF) for the mass range above 1 M ⊙ , with a peak at ∼0.1 M ⊙ . We divide the cloud into four parts based on decl., OMC-1/2/3, OMC-4/5, L1641N/V380 Ori, and L1641C, and derive the CMFs in these regions. We find that starless cores with masses greater than 10 M ⊙ exist only in OMC-1/2/3, whereas the CMFs in OMC-4/5, L1641N, and L1641C are truncated at around 5–10 M ⊙ . From the number ratio of bound starless cores and Class II objects in each subregion, the lifetime of bound starless cores is estimated to be 5–30 freefall times, consistent with previous studies for other regions. In addition, we discuss core growth by mass accretion from the surrounding cloud material to explain the coincidence of peak masses between IMFs and CMFs. The mass accretion rate required for doubling the core mass within a core lifetime is larger than that of Bondi–Hoyle accretion by a factor of order 2. This implies that more dynamical accretion processes are required to grow cores. 

ABSTRACT We have carried out mapping observations of molecular emission lines of HC3N and CH3OH toward two massive cluster-forming clumps, NGC 2264-C and NGC 2264-D, using the Nobeyama 45-m radio telescope. We derive an I(HC3N)/I(CH3OH) integrated intensity ratio map, showing a higher value at clumps including 2MASS (Two Micron All Sky Survey) point sources at the northern part of NGC 2264-D. Possible interpretations of the I(HC3N)/I(CH3OH) ratio are discussed. We have also observed molecular emission lines from CCS and N2H+ toward five positions in each clump. We investigate the N(N2H+)/N(CCS) and N(N2H+)/N(HC3N) column density ratios among the ten positions in order to test whether they can be used as chemical evolutionary indicators in these clumps. The N(N2H+)/N(CCS) ratio shows a very high value toward a bright embedded IR source (IRS1), whereas the N(N2H+)/N(HC3N) ratio at IRS1 is comparable with those at the other positions. These results suggest that ultraviolet radiation affects the chemistry around IRS1. We find that there are positive correlations between these column density ratios and the excitation temperatures of N2H+, which implies the chemical evolution of clumps. These chemical evolutionary indicators likely reflect the combination of evolution along the filamentary structure and evolution of each clump.