EPoS Contribution
EPoS Contribution
Chemical diagnostics of the early phase of star formation

Satoshi Yamamoto
The University of Tokyo, Tokyo, Japan
During the last two decades, chemical evolution of starless cores has successfully been established both observationally and theoretically. Non equilibrium chemistry and depletion of molecules onto dust grains both play a crucial role in chemical evolution. In contrast, the chemical composition of star forming cores is still controversial. Nevertheless steady progress has recently been made in many areas, as highlighted below. (1) Chemical diversity of low-mass star forming cores: It becomes evident that chemical compositions of low-mass protostellar cores are different from source to source even among the Class 0 objects. One extreme case is the hot corino chemistry, which is characterized by rich existence of complex organic molecules such as HCOOCH3 and C2H5CN. The other extreme case is the warm carbon-chain chemistry (WCCC), which is characterized by extraordinarily abundant carbon-chain molecules such as C2H and C4H Such a chemical difference apparently originates from the difference of chemical compositions of dust grains, which would, for instance, be caused by the difference of duration time of the starless core phase. In other words, chemical compositions of star forming cores would reflect history of the starless core phase memorized in grain mantles. (2) Shock chemistry: Shocks induced by interactions between outflows and the ambient gas affect chemical compositions of star forming regions. The spectral lines of SiO and CH3OH are often employed as shock tracers to investigate the feedback effect of newly born protostars to formation of the next generation protostars. To extend our knowledge of shock chemistry, molecular line survey toward a representative shocked region, L1157 B1 is being carried out by several groups. The result has revealed rich organic chemistry in the shocked region, which would probably triggered by evaporation of grain mantles. (3) Deuterium fractionation: Although the deuterium fractionation in starless cores is well established, its behavior after the onset of star formation is still controversial. We particularly focus on the timescale of the change in the deuterium fractionation after the onset of star formation. Suppose that the temperature is raised suddenly from the cold stage, the deuterium fractionation ratio would start to decrease toward the equilibrium value at the new temperature. The timescale of this change is less than 100 yr for the ionic species, whereas it can be as long as 10(5) yr for the neutral species. From the deuterium fractionation ratio of the neutral species observed in star forming cores, we would be able to investigate the initial condition of star formation.
N. Sakai, Univ. of Tokyo, Japan
Y. Watanabe, Univ. of Tokyo, Japan
T. Sakai, Univ. of Tokyo, Japan
T. Yamaguchi, Univ. of Tokyo, Japan
D. Shibata, Univ. of Tokyo, Japan
T. Hirota, National Astronomical Observatory of Japan, Japan
S. Takano, Nobeyama Radio Observatory, Japan