HERSCHEL's “COLD DEBRIS DISKS”: BACKGROUND GALAXIES OR QUIESCENT RIMS OF PLANETARY SYSTEMS?-猫眼课题宝

DOI：

10.1088/0004-637x/772/1/32

发表时间：

2013-06

期刊：

The Astrophysical Journal

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

A. Krivov;C. Eiroa;T. Löhne;J. Marshall;B. Montesinos;C. D. Burgo;O. Absil;D. Ardila;J. Augereau;A. Bayo;A. Bayo;G. Bryden;W. Danchi;S. Ertel;J. Lebreton;R. Liseau;A. Mora;A. Mustill;H. Mutschke;R. Neuhäuser;G. Pilbratt;A. Roberge;T. Schmidt;K. Stapelfeldt;P. Th'ebault;Christian Vitense;G. J. White;G. J. White;S. Wolf

到目前为止，与碎片盘宿主恒星相关的红外过度探测在波长约为100 μm或更短的波长处达到峰值。然而，在赫歇尔开放时间关键计划（DUNES）研究的31个过量源中，有6个在160 μm处显示出显著的-在某些情况下扩展-过量发射，这大于100 μm的过量。这种过量的辐射被归因于星周尘埃，并被认为是来自比以前已知的更冷的碎片盘。由于候选冷盘的过量辐射非常微弱，甚至挑战了赫歇尔无与伦比的灵敏度，因此谨慎地考虑其中一些甚至全部是否可能代表无关的银河系或河外辐射，甚至是仪器噪音。我们使用几种不同的方法重新解决这些问题，并得出结论，这是极不可能的候选人代表一个真正的拱星盘。对于真正的盘，从光谱能量分布推断的尘埃温度和从图像估计的盘半径都表明尘埃几乎和黑体一样冷。这就要求颗粒大于100 μm，即使它们富含冰或由任何其他可见光吸收率低的材料组成。小颗粒的缺乏令人困惑，因为碎片盘的碰撞模型预测，各种大小的颗粒，小到辐射压力井喷极限的几倍，都应该存在。我们探讨了几个可能的情况：运输为主的磁盘，磁盘的低动力学激发，和磁盘的未搅拌原始宏观颗粒。我们的定性分析和碰撞模拟排除了前两种情况，但显示了第三种情况的可行性。我们表明，这样的磁盘确实可以生存十亿年，在很大程度上保持原始的大小分布。它们应该由大于毫米但小于几公里的宏观固体组成。如果存在较大的星子，那么它们会搅动圆盘，引发碰撞级联，从而导致产生小碎片，这是看不到的。因此，至少在系统的外围区域，小行星的形成在达到“彗星”或“小行星”大小之前就已经停止了。

Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around ∼100 μm or shorter. However, 6 out of 31 excess sources studied in the Herschel Open Time Key Programme, DUNES, have been seen to show significant—and in some cases extended—excess emission at 160 μm, which is larger than the 100 μm excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We re-address these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than ∼100 μm, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller than a few kilometers in size. If larger planetesimals were present, then they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus, planetesimal formation, at least in the outer regions of the systems, has stopped before “cometary” or “asteroidal” sizes were reached.

HERSCHEL's “COLD DEBRIS DISKS”: BACKGROUND GALAXIES OR QUIESCENT RIMS OF PLANETARY SYSTEMS?

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