arXiv 0909.42252009-09astro-ph.EPastro-ph.SR

年轻碎片盘中的气体能被它们的径向亮度轮廓所约束吗？

Can gas in young debris disks be constrained by their radial brightness profiles?

Alexander V. Krivov, Fabian Herrmann, Alexis Brandeker, Philippe Thébault

备注：: Accepted for publication in Astronomy and Astrophysics
DOI：: 10.1051/0004-6361/200912917

摘要：

年轻恒星周围的尘埃盘已知是从光学上厚的、以气体为主的原行星盘演变成光学上薄的、几乎不含气体的碎片盘。据认为，原始气体在大约1000万年前就被大量移除，但很难从气体观测中辨别出真正的气体密度。这表明使用尘埃的观测：有人认为，气体，如果存在更高的密度，将导致更平坦的尘埃密度和表面亮度的径向轮廓比实际观察到的。然而，在这里，我们表明，这些配置文件是令人惊讶的不敏感的变化的参数的中心恒星，位置的尘埃产生的微星带，尘埃的磁盘和-最重要的-参数的环境气体。这一结果适用于宽范围的气体密度（三个数量级），不同的径向分布的气体温度，和不同的气体成分。亮度曲线斜率为-3. - 4我们发现的是相同的，理论上发现的无气体碎片盘，他们是相同的，实际上从许多碎片盘的观测。我们对三个年轻的（10-30百万岁），空间分辨，边缘碎片磁盘（β Pic，HD 32297，和AU Mic）的具体结果表明，所观察到的径向轮廓的表面亮度不构成任何严格的约束气体成分的磁盘。我们不能排除系统的外部可能保留了大量的原始气体，这在气体观测中并不明显（例如β Pic多达50个地球质量）。然而，根据气体探测结果（例如β Pic盘中的质量约为地球质量的0.05倍），气体（很可能是次级气体）仅以少量到中等数量存在的可能性也仍然存在。

英文摘要：

Disks around young stars are known to evolve from optically thick, gas-dominated protoplanetary disks to optically thin, almost gas-free debris disks. It is thought that the primordial gas is largely removed at ages of ~10 Myr, but it is difficult to discern the true gas densities from gas observations. This suggests using observations of dust: it has been argued that gas, if present with higher densities, would lead to flatter radial profiles of the dust density and surface brightness than those actually observed. However, here we show that these profiles are surprisingly insensitive to variation of the parameters of a central star, location of the dust-producing planetesimal belt, dustiness of the disk and - most importantly - the parameters of the ambient gas. This result holds for a wide range of gas densities (three orders of magnitude), for different radial distributions of the gas temperature, and different gas compositions. The brightness profile slopes of -3...-4 we find are the same that were theoretically found for gas-free debris disks, and they are the same as actually retrieved from observations of many debris disks. Our specific results for three young (10-30 Myr old), spatially resolved, edge-on debris disks (beta Pic, HD 32297, and AU Mic) show that the observed radial profiles of the surface brightness do not pose any stringent constraints on the gas component of the disk. We cannot exclude that outer parts of the systems may have retained substantial amounts of primordial gas which is not evident in the gas observations (e.g. as much as 50 Earth masses for beta Pic). However, the possibility that gas, most likely secondary, is only present in little to moderate amounts, as deduced from gas detections (e.g. ~0.05 Earth masses in the beta Pic disk), remains open, too.

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