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arXiv 1109.2299astro-ph.SRastro-ph.EP
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年轻碎片盘中的分子气体

Molecular gas in young debris disks

A. Moór, P. Ábrahám, A. Juhász, Cs. Kiss, I. Pascucci, Á. Kóspál, D. Apai, Th. Henning, T. Csengeri, C. Grady

摘要:

富气原始盘和稀薄贫气碎片盘通常被认为是星周物质演化的两个不同阶段。有趣的是,年轻的主序星鲸鱼座49周围的碎片盘拥有大量的分子气体,可能代表了两个阶段之间缺失的环节。为了通过发现更多的49个类Ceti系统来了解拱星盘中气体组分的演化,我们利用Atacama Pathfinder EXperiment进行了CO J=3-2的调查,目标是20个红外发光碎片盘。这些系统填补了原始和古老的脆弱碎片盘之间的差距,在分数光度。在这里,我们报告的第二个49 Ceti类磁盘周围的30万年的A3型恒星HD 21997,一个成员的天鸽协会的发现。这个系统也在CO(2-1)跃迁中被探测到,可靠的年龄测定使它成为比鲸鱼座49号更古老的含气盘。虽然HD 21997和49 Ceti的分光度不是特别高,但这些物体似乎拥有我们样本中最扩展的圆盘。用Keplerian圆盘模型结合LIME辐射转移程序再现了HD 21997的双峰分布。基于它们的相似性,49 Ceti和HD 21997可能是迄今为止尚未定义的相对古老(>~ 800万年)的新类别的第一个代表,气态尘埃盘。从我们的研究结果,无论是原始的起源,也不稳定的二次生产从冰冷的星子可以明确地解释存在的CO气体在磁盘的HD 21997。

英文摘要:

Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas, and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J=3-2 survey with Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities of HD21997 and 49 Ceti are not particularly high, these objects seem to harbor the most extended disks within our sample. The double-peaked profiles of HD21997 were reproduced by a Keplerian disk model combined with the LIME radiative transfer code. Based on their similarities, 49 Ceti and HD21997 may be the first representatives of a so far undefined new class of relatively old (>~8 Myr), gaseous dust disks. From our results, neither primordial origin nor steady secondary production from icy planetesimals can unequivocally explain the presence of CO gas in the disk of HD21997.

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