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arXiv 0910.4725astro-ph.EPastro-ph.GA
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偏心小行星群的碰撞演化

Collisional evolution of eccentric planetesimal swarms

M. C. Wyatt, M. Booth, M. J. Payne, L. J. Churcher

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摘要：

低偏心率微行星带的稳态碰撞演化模型将具有1AU热尘的碎片盘（如eta Corvi和HD 69830）确定为异常，因为碰撞处理应该在其>1 Gyr的寿命内消除大部分微行星质量。本文着眼于大的星子偏心率（e>>0.3）对它们的碰撞寿命和质量的数量，可以保留在后期时间M_{late}的影响。对于具有共同近心点和偏心率e的轴对称小行星盘，我们发现M_{late} \propto e^{-5/3}（1+e）^{4/3}（1-e）^{-3}.对于分散的盘状种群（即，在没有动力学演化的情况下，后期的质量演化就好像只有离心率最大的星子存在。尽管剩余质量增加，但更高的离心率不会增加碰撞级联的热辐射，直到e>0.99，部分原因是大多数碰撞发生在近心点附近，从而增加了尘埃吹出的直径。然而，在高偏心率（e>0.97）下，从近心点向外延伸的井喷人口可能在碰撞级联上方被检测到;更高的偏心率也增加了见证最近碰撞的可能性。所有的成像和光谱限制都可以用一个近心点在0.75天文单位，远心点在150天文单位，质量为5 M_ \oplus的小行星群来解释;然而，如此高偏心率的小行星群的起源仍然具有挑战性。中红外线超过HD 69830可以解释为在最近的一次偏心星子带碰撞中产生的碎片带正在被破坏，但缺乏远红外线辐射需要小的结合颗粒从母星子带中消失，可能是由于升华。

英文摘要：

Models for the steady state collisional evolution of low eccentricity planetesimal belts identify debris disks with hot dust at 1AU, like eta Corvi and HD69830, as anomalous since collisional processing should have removed most of the planetesimal mass over their >1 Gyr lifetimes. This paper looks at the effect of large planetesimal eccentricities (e>>0.3) on their collisional lifetime and the amount of mass that can remain at late times M_{late}. For an axisymmetric planetesimal disk with common pericentres and eccentricities e, we find that M_{late} \propto e^{-5/3}(1+e)^{4/3}(1-e)^{-3}. For a scattered disk-like population (i.e., common pericentres), in the absence of dynamical evolution, the mass evolution at late times would be as if only planetesimals with the largest eccentricity were present. Despite the increased remaining mass, higher eccentricities do not increase the hot emission from the collisional cascade until e>0.99, partly because most collisions occur near pericentre thus increasing the dust blow-out diameter. However, at high eccentricities (e>0.97) the blow-out population extending out from pericentre may be detectable above the collisional cascade; higher eccentricities also increase the probability of witnessing a recent collision. All of the imaging and spectroscopic constraints for eta Corvi can be explained with a single planetesimal population with pericentre at 0.75AU, apocentre at 150AU, and mass 5M_\oplus; however, the origin of such a high eccentricity population remains challenging. The mid-IR excess to HD69830 can be explained by the ongoing destruction of a debris belt produced in a recent collision in an eccentric planetesimal belt, but the lack of far-IR emission requires small bound grains to be absent from the parent planetesimal belt, possibly due to sublimation.

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