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Nami Sakai - The University of Tokyo

Thursday, May 28 – 2:45-3:30PM


“Chemical Composition of Low-Mass Star-Forming Regions”


Understanding of chemical evolution from protostellar disks to protoplanetary disks in low-mass star forming regions is an one of important target for modern astronomy. Detection of complex organic molecules like HCOOCH3 and C2H5CN around a newly born protostar was a giant step toward this direction1). However, all the star forming cores in the same evolutionary stage of embedded protostars may not always have a similar chemical composition. In fact, we recently found a star forming region, L1527, which shows extraordinary richness of various carbon-chain molecules in the vicinity of the protostar2). This is very surprising, because carbon-chain molecules have so far been believed to exist preferentially in young starless cores. Furthermore, we also found the second example, IRAS15398-3359, which shows high abundances of carbon-chain molecules3). In these sources, carbon-chain molecules would be regenerated in a lukewarm region near the protostar, triggered by the evaporation of the CH4 ice. This is new carbon-chain chemistry (Warm Carbon Chain Chemistry: WCCC).

The discovery of the WCCC sources demonstrates that the chemical composition of low-mass star-forming regions is not uniform, but has a significant variation. In particular, a remarkable contrast can be seen between WCCC and hot corino chemistry. Carbon-chain molecules are deficient in hot corino sources like NGC1333IRAS4B, whereas complex organic molecules seem to be less abundant in the WCCC source. A possible origin for this variation would be the time scale of the starless-core phase; a shorter contraction time would result in WCCC. Relatively low deuterium fractionation ratios in L1527 also support this scenario. Thus, the chemical composition provides an important clue to explore the source-to-source variation of star-formation processes. In this talk, I would like to present a new carbon-chain chemistry, and discuss its physical and chemical significance.


Related Reference(s):

(1) e.g. S. Cazaux, A. G. G. M. Tielens, C. Ceccarelli, A. Castets, V. Wakelam, E. Caux, B. Parise, and D. Teyssier, “The Hot Core around the Low-Mass Protostar IRAS 16293-2422: Scoundrels Rule!” ApJL, 593, L51-L56 (2003).

N. Sakai , T. Sakai, and S. Yamamoto, “Detection of HCOOCH3 toward a Low-Mass Protostar, NGC 1333 IRAS 4B,” Publ. Astron. Soc. Japan, 58, L15-L18 (2006).

(2) N. Sakai , T, Sakai, T. Hirota, and S. Yamamoto, ”Abundant Carbon-Chain Molecules toward the Low-Mass Protostar IRAS 04368+2557 in L1527,” ApJ, 672, 371-381 (2008).

(3) N. Sakai, T. Sakai, T. Hirota, M. Burton, and S. Yamamoto, ”Discovery of the Second Warm Carbon-Chain-Chemistry Source, IRAS15398-3359 in Lupus,” ApJ, 697, 769-786 ( 2009).