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arXiv 1105.0888astro-ph.SR
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哈勃和斯皮策空间望远镜对K矮星HD 92945周围碎片盘的观测

Hubble and Spitzer Space Telescope Observations of the Debris Disk around the Nearby K Dwarf HD 92945

D. A. Golimowski, J. E. Krist, K. R. Stapelfeldt, C. H. Chen, D. R. Ardila, G. Bryden, M. Clampin, H. C. Ford, G. D. Illingworth, P. Plavchan, G. H. Rieke, K. Y. L. Su

摘要:

[摘要]我们目前的第一个解决图像的碎片磁盘周围的附近K矮HD 92945。我们的F606 W(V)和F814 W(I)HST/ACS日冕图像显示了一个倾斜的轴对称盘,由距离恒星2”.0-3”.0(43-65 AU)的内环和一个扩展的外盘组成,外盘的表面亮度随着距离恒星3”.0-5”.1(65-110 AU)半径的增加而缓慢下降。超过110天文单位的表面亮度急剧下降,表明外盘在该距离处被截断。径向表面密度分布在盘的内环和外缘都达到峰值。在外盘的尘埃散射中性,但各向同性,它有一个低的V-波段散射0.1。我们还提出了新的斯皮策MIPS测光和IRS光谱的HD 92945。这些数据表明,30微米的圆盘短轴没有红外线过量,并将70微米源的宽度限制在< 180 AU。假设尘埃由致密的天文硅酸盐颗粒组成,其表面密度分布由我们的圆盘散射光模型描述,我们成功地模拟了24-350微米的发射,最小颗粒尺寸为a_min = 4.5微米,整个圆盘的尺寸分布与a^-3.7成比例,但在内环中具有900微米的最大晶粒尺寸,在外盘中具有50微米的最大晶粒尺寸。我们的观测表明,总尘埃质量约为0.001 M地球。然而,它们提供了关于尘埃物理特性的矛盾证据:其中性V-I颜色和缺乏24微米的发射意味着颗粒大于几微米,但其各向同性散射和低散射表明大量亚微米尺寸的颗粒。该盘形态的动力学原因尚不清楚,但最近的尘埃产生和迁移行星存在下的运输模型表明HD 92945周围的行星形成处于高级状态。

英文摘要:

[ABRIDGED] We present the first resolved images of the debris disk around the nearby K dwarf HD 92945. Our F606W (V) and F814W (I) HST/ACS coronagraphic images reveal an inclined, axisymmetric disk consisting of an inner ring 2".0-3".0 (43-65 AU) from the star and an extended outer disk whose surface brightness declines slowly with increasing radius 3".0-5".1 (65-110 AU) from the star. A precipitous drop in the surface brightness beyond 110 AU suggests that the outer disk is truncated at that distance. The radial surface-density profile is peaked at both the inner ring and the outer edge of the disk. The dust in the outer disk scatters neutrally but isotropically, and it has a low V-band albedo of 0.1. We also present new Spitzer MIPS photometry and IRS spectra of HD 92945. These data reveal no infrared excess from the disk shortward of 30 micron and constrain the width of the 70 micron source to < 180 AU. Assuming the dust comprises compact grains of astronomical silicate with a surface-density profile described by our scattered-light model of the disk, we successfully model the 24-350 micron emission with a minimum grain size of a_min = 4.5 micron and a size distribution proportional to a^-3.7 throughout the disk, but with a maximum grain size of 900 micron in the inner ring and 50 micron in the outer disk. Our observations indicate a total dust mass of ~0.001 M_earth. However, they provide contradictory evidence of the dust's physical characteristics: its neutral V-I color and lack of 24 micron emission imply grains larger than a few microns, but its isotropic scattering and low albedo suggest a large population of submicron-sized grains. The dynamical causes of the disk's morphology are unclear, but recent models of dust creation and transport in the presence of migrating planets indicate an advanced state of planet formation around HD 92945.

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