Observations of Complex Molecules in Low-Mass Protostars

Details Observations of Complex Molecules in Low-Mass Protostars Observations of Complex Molecules in Low-Mass Protostars

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280e..25s&link_type=abstract

The Molecular Universe, Proceedings of the 280th Symposium of the International Astronomical Union held in Toledo, Spain, May 30

Astronomy and Astrophysics

Astrophysics

Scientific paper

A detailed understanding of chemical evolution of low-mass star-forming cores is an outstanding problem in astrochemistry and astrophysics, which is ultimately related to an origin of our solar system. In the last decade, two important steps toward this goal were reported. One is the discovery of hot corinos (e.g. Cazaux et al. 2003), while the other is that of the warm carbon-chain chemistry (WCCC) sources (e.g. Sakai et al. 2008). Hot corinos are characterized by high abundances of large saturated organic molecules such as HCOOCH3 and (CH3)2O in the gas phase within a few 100 AU region (˜ 100 K) around the protostars. These molecules are thought to be formed on grain mantles and released into the gas phase by protostellar heating. The representative hot corinos are IRAS16293-2422 and NGC1333IRAS4B. On the other hand, the WCCC is characterized by extraordinary richness of unsaturated carbon-chain molecules like CCH, C4H, and HC5N in a lukewarm region around the protostars. The representative WCCC sources are L1527 and IRAS15398-3359. In the WCCC, carbon-chain molecules are regenerated in the vicinity of the protostars, triggered by evaporation of CH4 from grain mantles. This is new carbon-chain chemistry in contrast to the conventional one applied to cold starless cores. The existence of the hot corino and WCCC sources clearly indicates chemical diversity of low-mass star forming cores. A possible origin of the diversity is a different duration time of the starless-core phase for each source; a shorter time would result in more abundant CH4 on grain mantles, giving a favorable condition for WCCC (Sakai et al. 2009). Relatively low deuterium fractionation ratios in L1527 also support this scenario. If the above scenario is the case, we can investigate the past contracting process of the parent cloud from what type of chemistry is now occurring near the protostar. More interestingly, these two cases will form protostellar disks with different chemical compositions. Tracing the chemical differences along the protostellar evolution is an interesting target for the near future.

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