Organic Molecules in the Hot Corinos and Circumstellar Disks of IRAS 16293-2422

Abstract

Using the recently-commissioned Submillimeter Array (SMA), we have detected several complex organic molecules, including (CH3)2O, C2H5OH, C2H5CN, and tentatively CH2CDCN, toward the protostellar hot cores of IRAS 16293-2422 at arcsecond-resolution (~< 400 AU in radius). Vibrationally excited transitions of SO, SO2 and HCN with energy levels up to 1800 K were also observed. In addition to the other organic molecules (HC3N, CH2CO, CH3OH, CH2CHCN and HCOOCH3) previously reported by us (Kuan et al. 2004), these results clearly indicate the existence of a rich organic chemistry in low-mass `hot corinos'. From the observation of optically thin HC15N emission, we conclude I16293A is a rotating circumstellar disk lying along the north-south direction ~10 deg to the east and with an inclination ~30 deg to the sky. We suggest that the observed vibrational SO and SO2 emission may originate from shock waves near or in the circumstellar disks. Between the two cores, we find a strong anticorrelation in emission from C2H5OH and C2H5CN. The relative contribution of gas phase and grain-surface chemistries to the production of the observed complex molecules is discussed. We point out the shortcomings underlying recent claims that all the O-bearing organics are formed on grains. The presence of so many well-known interstellar molecules in solar-type hot corinos strengthens the link between molecular cloud chemistry, the starting materials of protoplanetary disks such as the protosolar nebula, and the composition of comets. Establishing the fine details of this connection is crucial in answering fundamental questions concerning the importance of galactic astrochemistry for astrobiology.