Other
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280e...4a&link_type=abstract
The Molecular Universe, Proceedings of the 280th Symposium of the International Astronomical Union held in Toledo, Spain, May 30
Other
Scientific paper
We investigate temporal variation of molecular abundances and molecular D/H ratios in a star-forming core that is initially a hydrostatic starless core and collapses to form a low-mass protostar. As a physical model of the core, we adopt the results of a one-dimensional radiation-hydrodynamics calculation of Masunaga & Inutsuka (2000). We calculate the temporal variation of physical parameters in infalling shells, in which the molecular evolution is solved using a gas-grain chemical model to derive the spatial distribution of molecules in a protostellar core. The core stays almost isothermal as long as the radiative cooling is more efficient than the compressional heating. In the infalling fluid parcels, molecules deplete onto grains as the density rises. Adsorbed species are subject to hydrogenation on the grain surface. Eventually, the compressional heating overwhelms the cooling, and a new-born protostar further heats the core. At several 10 K, the thermal hopping of the heavy species becomes efficient on the grain surfaces and large organic species are formed. The species are desorbed to the gas phase according to their volatility. The desorbed species are subject to the gas phase reactions. For example, HCOOH is formed by the reaction of OH with the sublimated H2CO. Sublimated CH4 is transformed to carbon chains. Molecular D/H ratio increases at low temperature era; deuterium enrichment is due to several exchange reactions of and propagates to various molecules via gas-phase and grain-surface reactions. The backward reaction of the exchange reactions become efficient at T > several 10 K. While the D/H ratio of H3+ and HCO+ decrease promptly, D/H ratio of neutral species remains high in protostellar cores as long as the species are not destroyed and re-formed. Since the destruction time scale varies among species, their D/H ratio can be used as clock after the fluid parcels enters warm regions. In reality, the spherical symmetry beaks down around the centrifugal radius (r ˜ 100 AU), inside which disk structures are apparent. In order to investigate the composition of the forming disks, we combine chemical reaction network model with a 3D hydrodynamic model.
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