Roberge Aki, Feldman Paul D, Weinberger Alycia J, Deleuil Magali, Bouret Jean-Claude
Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
Nature. 2006 Jun 8;441(7094):724-6. doi: 10.1038/nature04832.
The edge-on disk surrounding the nearby young star beta Pictoris is the archetype of 'debris disks', which are composed of dust and gas produced by collisions between--and evaporation of--planetesimals, analogues of Solar System comets and asteroids. These disks may provide insight into the formation and early evolution of terrestrial planets. Previous work on beta Pic concluded that the disk gas has roughly solar abundances of elements, but this poses a problem because such gas should rapidly be blown away from the star, contrary to observations showing a stable gas disk in keplerian rotation. Here we report the detection of singly and doubly ionized carbon (C II, C III) and neutral atomic oxygen (O I) gas in the beta Pic disk. Carbon is extremely overabundant relative to every other measured element. This appears to solve the problem of the stable gas disk, because the carbon overabundance should keep the gas disk in keplerian rotation. The overabundance may indicate that the gas is produced from material more carbon-rich than expected of Solar System analogues.
围绕附近年轻恒星绘架座β的边缘盘是“碎片盘”的原型，碎片盘由微行星体（类似于太阳系彗星和小行星）之间的碰撞以及蒸发产生的尘埃和气体组成。这些盘可能有助于深入了解类地行星的形成和早期演化。先前对绘架座β的研究得出结论，盘气体中元素的丰度大致与太阳相当，但这带来了一个问题，因为这样的气体应该会迅速从恒星周围被吹走，这与观测到的在开普勒旋转中存在稳定气体盘的情况相悖。在此，我们报告在绘架座β盘中检测到单电离和双电离碳（C II、C III）以及中性原子氧（O I）气体。相对于其他所有测量元素，碳的丰度极高。这似乎解决了稳定气体盘的问题，因为碳的过度丰度应该能使气体盘保持开普勒旋转。这种过度丰度可能表明气体是由比太阳系类似物预期更富含碳的物质产生的。
