Detection of hydroxyacetone in protostar IRAS 16293-2422 B

Hydroxyacetone (CH3COCH2OH) is one of the smallest molecules that contain both hydroxyl and carbonyl group on neighboring carbon atoms. This steric configuration is characteristic of saccharides and determines their biochemical activity. The attempt to search for hydroxyacetone toward the massive star formation region Sagittarius B2(N) was unsuccessful. Here we report the first detection of CH3COCH2OH in the solar-type protostar IRAS 16293-2422 B, using the Atacama Large Millimeter Array science verification data at Band 4. In a total of 11 unblended transitions of CH3COCH2OH with upper level energies ranging from 86 to 246 K are identified. From our local thermodynamic equilibrium analysis, we derived that the rotational temperature of CH3COCH2OH is 160 21 K and the column density is (1.2 1.0) 1016 cm-2, which results in a fractional abundance of 7 10-10 with respect to molecular hydrogen. In this work, we present the identification of CH3COCH2OH in IRAS 16293-2422 B and propose a simple formation mechanism. The unambiguous identification of hydroxyacetone may provide the basis for future study of the origin and evolution of saccharides in the interstellar medium.