Detection of Near-infrared Water Ice at the Surface of the (Pre)Transitional Disk of AB Aur: Informing Icy Grain Abundance, Composition, and Size
Detection of Near-infrared Water Ice at the Surface of the (Pre)Transitional Disk of AB Aur: Informing Icy Grain Abundance, Composition, and Size
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DOI：
10.3847/1538-3881/ac4d9b
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发表时间：
2022-01
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通讯作者：
S. Betti;K. Follette;S. Jorquera;G. Duchêne;J. Mazoyer;M. Bonnefoy;G. Chauvin;L. P'erez;
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作者：
S. Betti;K. Follette;S. Jorquera;G. Duchêne;J. Mazoyer;M. Bonnefoy;G. Chauvin;L. P'erez;
我们给出了赫比格Ae/Be恒星AB Aurigae周围的近红外大双筒望远镜LMIRCam图像。通过比较K S(2.16μm)、H2O窄带(3.08μm)和L(3.7μm)的表面亮度，我们可以探索这种(前)过渡盘环境中冰颗粒的存在。通过应用参考差动成像点扩展函数相减法，我们在所有三个波段都能在高信噪比下检测到光盘。我们发现这些谱带之间存在很强的形态差异，包括与在L的100Au范围内观测到的旋臂相一致的不对称性。相对于包层波长(K、S和L‘)的3.08μm散射光的表观亏损引起了盘表层的冰吸收。然而，Δ(K S−H2O)的颜色与很少或没有冰(质量分数为0%-5%)的颗粒一致。反之，Δ(H2O−L‘)的颜色表明冰川质量分数更高的颗粒(∼0.68)，这两种颜色在单颗粒种群模型下不能调和。此外，我们还发现，在传统的散射光模拟下，通过任意组合的颗粒参数或合理的局部消光值，不能再现极红的Δ(Ks−L‘)盘颜色。我们假设这三个波长的散射面不是共位的，并且每个波长的光学深度效应是由探测不同表面深度处的颗粒布居引起的。S K和H_2O在形态上的相似性表明它们的散射面很接近，从而证实了最外层散射盘层的Δ(K S−H_2O)盘颜色约束为<；5%冰质量分数。
We present near-infrared Large Binocular Telescope LMIRCam imagery of the disk around the Herbig Ae/Be star AB Aurigae. A comparison of the surface brightness at K s (2.16 μm), H2O narrowband (3.08 μm), and L′ (3.7 μm) allows us to probe the presence of icy grains in this (pre)transitional disk environment. By applying reference differential imaging point-spread function subtraction, we detect the disk at high signal-to-noise ratios in all three bands. We find strong morphological differences between the bands, including asymmetries consistent with the observed spiral arms within 100 au in L′ . An apparent deficit of scattered light at 3.08 μm relative to the bracketing wavelengths (K s and L′ ) is evocative of ice absorption at the disk surface layer. However, the Δ(K s − H2O) color is consistent with grains with little to no ice (0%–5% by mass). The Δ(H2O−L′) color, conversely, suggests grains with a much higher ice mass fraction (∼0.68), and the two colors cannot be reconciled under a single grain population model. Additionally, we find that the extremely red Δ(Ks−L′) disk color cannot be reproduced under conventional scattered light modeling with any combination of grain parameters or reasonable local extinction values. We hypothesize that the scattering surfaces at the three wavelengths are not colocated, and that the optical depth effects in each wavelength result from probing the grain population at different disk surface depths. The morphological similarity between K s and H2O suggests that their scattering surfaces are near one another, lending credence to the Δ(K s − H2O) disk color constraint of <5% ice mass fraction for the outermost scattering disk layer.