TUNA Lunch Talk:

Satoshi Yamamoto

University of Tokyo

Carbon-chain Molecules for Astrophysics

September 17

12:10PM, Room 230, NRAO, Edgemont Road


One of characteristic features in chemical compositions of molecular clouds is existence of various carbon-chain molecules, such as HC2n+1N, CnH, CnH2, and CnS.. These highly saturated hydrocarbon molecules have preferentially been detected in young prestellar cores, while they are generally deficient in evolved prestellar cores and star-forming regions. On the other hand, NH3 and N2H+ become abundant in the evolved prestellar cores. Hence, the CCS/NH3 and CCS/N2H+ ratios, for instance, have been employed as a chemical evolutionary tracer of molecular cloud cores. In this talk, I am going to present the extension of such studies toward the following two directions. (1) Regional-to-region difference of a fraction of carbon-chain rich cores: studied the CCS/NH3 ratio toward many nearby dense cores. We have Carbon-chain rich cores are found in Taurus and Aquila lift, whereas they are absent in the Ophiuchus region. This seems to indicate that a timescale of the starless-core phase is different from region to region owing to environmental effects of each region. (2) Discovery of protostellar cores harboring rich carbon-chain molecules: Although carbon-chain molecules are generally deficient in star-forming regions, we found the protostellar cores with extraordinarily rich carbon-chain molecules. L1527 in Taurus and IRAS 15398-3359 in Lupus. They are In these sources, carbon-chain molecules are efficiently produced from CH4 evaporated from dust grains in a warm and dense region around the protostar (warm carbon-chain chemistry: WCCC). An origin of this peculiar chemistry is discussed in relation to past star-formation processes in these sources. Based on these two topics, I would like to demonstrate a novel aspect of carbon-chain molecules in star-formation studies.