arXiv 1005.06372010-05-04astro-ph.GA

低质量原恒星B1-b的冷复杂化学：冰中复杂分子产生的证据

A cold complex chemistry toward the low-mass protostar B1-b: evidence for complex molecule production in ices

Karin I. Oberg, Sandrine Bottinelli, Jes K. Jorgensen, Ewine F. van Dishoeck

备注：: 23 pages, 7 figures, accepted for publication in ApJ
DOI：: 10.1088/0004-637X/716/1/825

摘要：

在一系列高质量和低质量的恒星形成区域，已经检测到了气相复杂的有机分子，其丰度无法用任何已知的气相化学来解释。最近的实验室实验表明，紫外线照射的CH 3OH丰富的冰可能是一个重要的机制，产生复杂的分子，并将它们释放到气相中。为了测试这种冰形成的情况下，我们映射的B1-b尘埃核心和附近的原恒星在CH 3OH气体使用IRAM 30米望远镜，以确定有效的非热冰解吸的位置。我们发现三个CH 3OH丰度峰跟踪两个流出和一个静止的区域对着原恒星的核心一侧。CH 3OH气体在所有位置处具有约10 K的旋转温度。寻找复杂分子的静态CH 3OH丰度峰和一个流出位置。窄的，0.6-0.8 km s-1，HCOOCH 3和CH 3CHO起源于冷气体的线被清楚地检测到，CH 3 OCH 3是暂时检测到和C2 H5 OH和HOCH 2CHO是未检测到的向静止的核心，而没有复杂的分子线被发现向外流。核心相对于CH 3OH的丰度分别为~ 2.3%HCOOCH3和1.1% CH 3CHO，上限为0.7- 1.1%，这与大多数其他低质量源相似。所观察到的复杂的分子特性朝向B1-b和HCO-轴承物种的优势表明冷冰（低于25 K，CO的升华温度）的形成途径，然后通过非热解吸，例如，UV光子通过流出腔。观测到的复杂气体成分以及缺乏任何温暖的气相化学证据，为冷星际冰中有效的复杂分子形成提供了明确的证据。

英文摘要：

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 CH3OH-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 CH3OH gas using the IRAM 30m telescope to identify locations of efficient non-thermal ice desorption. We find three CH3OH abundance peaks tracing two outflows and a quiescent region on the side of the core facing the protostar. The CH3OH gas has a rotational temperature of ~10 K at all locations. The quiescent CH3OH abundance peak and one outflow position were searched for complex molecules. Narrow, 0.6-0.8 km s-1 wide, HCOOCH3 and CH3CHO lines originating in cold gas are clearly detected, CH3OCH3 is tentatively detected and C2H5OH and HOCH2CHO are undetected toward the quiescent core, while no complex molecular lines were found toward the outflow. The core abundances with respect to CH3OH are ~2.3% and 1.1% for HCOOCH3 and CH3CHO, 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 suggest 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 provide clear evidence of efficient complex molecule formation in cold interstellar ices.

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