科研之友
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摘要
Gas-phase complex organic molecules have been detected toward a range of high-and low-mass star-forming regions at abundances which cannot be explained by any known gas-phase chemistry. Recent laboratory experiments show that UV irradiation of CH(3)OH-rich ices may be an important mechanism for producing complex molecules and releasing them into the gas phase. To test this ice formation scenario, we mapped the B1-b dust core and nearby protostar in CH(3)OH gas using the IRAM 30 m telescope to identify locations of efficient non-thermal ice desorption. We find three CH(3)OH abundance peaks tracing two outflows and a quiescent region on the side of the core facing the protostar. The CH(3)OH gas has a rotational temperature of similar to 10 K at all locations. The quiescent CH(3)OH abundance peak and one outflow position were searched for complex molecules. Narrow, 0.6-0.8 km s-1 wide, HCOOCH(3) and CH(3)CHO lines originating in cold gas are clearly detected, CH(3)OCH(3) is tentatively detected, and C(2)H(5)OH and HOCH(2)CHO are undetected toward the quiescent core, while no complex molecular lines were found toward the outflow. The core abundances with respect to CH(3)OH are similar to 2.3% and 1.1% for HCOOCH(3) and CH(3)CHO, respectively, and the upper limits are 0.7%-1.1%, which is similar to most other low-mass sources. The observed complex molecule characteristics toward B1-b and the pre-dominance of HCO-bearing species suggests a cold ice (below 25 K, the sublimation temperature of CO) formation pathway followed by non-thermal desorption through, e. g., UV photons traveling through outflow cavities. The observed complex gas composition together with the lack of any evidence of warm gas-phase chemistry provides clear evidence of efficient complex molecule formation in cold interstellar ices.
- 出版日期2010-6-10
