GAS ABSORPTION IN THE KH 15D SYSTEM: FURTHER EVIDENCE FOR DUST SETTLING IN THE CIRCUMBINARY DISK
GAS ABSORPTION IN THE KH 15D SYSTEM: FURTHER EVIDENCE FOR DUST SETTLING IN THE CIRCUMBINARY DISK
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KH 15D 系统中的气体吸收：圆形盘中灰尘沉降的进一步证据
DOI：
10.1088/0004-637x/711/2/1297
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
R. Mundt
中科院分区：
文献类型：
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作者：
S. Lawler;W. Herbst;S. Redfield;C. Hamilton;C. Johns–Krull;J. Winn;J. Johnson;R. Mundt
对年轻双星KH 15D的Na i D谱线进行了详细的分析。我们发现一个多余的吸收成分，可能是由于前景星际吸收，气体可能与固体在环双星盘。导出的柱密度为log = 12.5 cm−2，以与系统速度一致的径向速度为中心。减去星际介质的可能贡献，得到log 12.3 cm−2。在由不透明颗粒盘形成的“刀口”上，气柱密度没有可检测的变化，表明气体和固体具有非常不同的刻度高度，固体高度沉降。我们的数据支持这样一种观点，即这个环双星盘是由一个非常薄的颗粒层组成的，颗粒层由毫米大小或更大的物体组成，这些物体位于任何可能存在的剩余气体中。这一阶段的盘演化被假设为通过引力破碎形成微行星的前奏，如果在这样的盘中仍然存在大量气体，预计这一阶段的存在时间很短。我们的分析还揭示了过量的Na i发射的存在下，相对于目前可见的星星的径向速度的比较光谱，这仍然吸积年轻的星星的磁层内必然会出现。
Na i D lines in the spectrum of the young binary KH 15D have been analyzed in detail. We find an excess absorption component that may be attributed to foreground interstellar absorption, and to gas possibly associated with the solids in the circumbinary disk. The derived column density is log = 12.5 cm−2, centered on a radial velocity that is consistent with the systemic velocity. Subtracting the likely contribution of the interstellar medium leaves log 12.3 cm−2. There is no detectable change in the gas column density across the “knife edge” formed by the opaque grain disk, indicating that the gas and solids have very different scale heights, with the solids being highly settled. Our data support a picture of this circumbinary disk as being composed of a very thin particulate grain layer composed of millimeter-sized or larger objects that are settled within whatever remaining gas may be present. This phase of disk evolution has been hypothesized to exist as a prelude to the formation of planetesimals through gravitational fragmentation, and is expected to be short-lived if much gas were still present in such a disk. Our analysis also reveals the presence of excess Na i emission relative to the comparison spectrum at the radial velocity of the currently visible star that plausibly arises within the magnetosphere of this still-accreting young star.