含21微米和30微米辐射特征的星周包层中的气态分子

中小质量恒星演化到渐近巨星支阶段会将表面的气体大量抛射到星际空间，形成星周包层，在抛射过程中逐渐形成的尘埃和气态分子是增丰星际空间的重要物质，在某些星周包层的红外光谱中位于21微米和30微米处有两个强的发射特征，这两个特征对于理解从恒星到星系的物质循环十分重要，但其载体的认证到目前还没有定论。为了探索它们的起源，我们计划研究具有21微米和30微米特征的星周包层中的气态分子，利用射电望远镜，我们将对一个特征源样本作高灵敏度、宽频率覆盖范围的光谱观测，通过统计各种气态分子的辐射强度，我们将调查这些源的物理环境和化学过程，找出影响21微米和30微米特征载体形成和破坏的关键因素，从而为它们的准确认证提供线索。此外，鉴于这些源具有特殊的红外辐射特性，我们还有可能在射电波段探测到新的星周分子。

When low- and intermediate-mass stars evolve into the stage of the asymptotic giant branch, they expel material from their surface into space and form circumstellar envelopes (CEs). The molecules and dust synthesized in the CEs are important components enhancing the interstellar medium. Two apparent infrared emission bands at 21 and 30 micron are shown in some CEs, and thus are essential to understand the cycle from stellar matters to the galaxy. However, the identification of their carriers is a long-standing enigma. In this program, we propose to study the gas-phase molecules in CEs exhibiting the 21 and 30 micron emission features, aiming to investigate the origin of the two features. Utilizing radio telescopes, we would carry out high-sensitivity spectral observations covering a wide frequency range. The sample would include about ten 21 and 30 micron sources. Through a statistics analysis of the detected molecular species, we would be able to investigate the physics environments and gas-phase chemistry favouring the existence of the carriers of the 21 and 30 micron features, and find out the key factors affecting their formation and destruction. Such a study could provide significant clues for the accurate identifications of the two mysterious features. Moreover, it is possible to discover new circumstellar molecules given the unusual infrared behaviour of these sources.