Kamp I, Scheepstra A, Min M, Klarmann L, Riviere-Marichalar P
Kapteyn Astronomical Institute, University of Groningen, The Netherlands.
Anton Pannekoek Institute, University of Amsterdam, The Netherlands.
Astron Astrophys. 2018 Sep 12;617.
This paper investigates how the far-IR water ice features can be used to infer properties of disks around T Tauri stars and the water ice thermal history. We explore the power of future observations with SOFIA/HIRMES and SPICA's proposed far-IR instrument SAFARI.
A series of detailed radiative transfer disk models around a representative T Tauri star are used to investigate how the far-IR water ice features at 45 and 63 m change with key disk properties: disk size, grain sizes, disk dust mass, dust settling, and ice thickness. In addition, a series of models is devised to calculate the water ice emission features from warmup, direct deposit and cooldown scenarios of the water ice in disks.
Photodesorption from icy grains in disk surfaces weakens the mid-IR water ice features by factors 4-5. The far-IR water ice emission features originate from small grains at the surface snow line in disks at distance of 10-100 au. Unless this reservoir is missing in disks (e.g. transitional disks with large cavities), the feature strength is not changing. Grains larger than 10 m do not contribute to the features. Grain settling (using turbulent description) is affecting the strength of the ice features by at most 15%. The strength of the ice feature scales with the disk dust mass and water ice fraction on the grains, but saturates for dust masses larger than 10 M and for ice mantles that increase the dust mass by more than 50%. The various thermal histories of water ice leave an imprint on the shape of the features (crystalline/amorphous) as well as on the peak strength and position of the 45 m feature. SOFIA/HIRMES can only detect crystalline ice features much stronger than simulated in our standard T Tauri disk model in deep exposures (1 hr). SPICA/SAFARI can detect the typical ice features in our standard T Tauri disk model in short exposures (10 min).
The sensitivity of SPICA/SAFARI will allow the detailed study of the 45 and 63 m water ice feature in unbiased surveys of T Tauri stars in nearby star forming regions and an estimate of the mass of their ice reservoir. The water ice emission features carry an imprint of the thermal history of the ice and thus can distinguish between various formation and transport scenarios. Amorphous ice at 45 m that has a much broader and flatter peak could be detected in deep surveys if the underlying continuum can be well characterized and the baseline stability of SAFARI is better than a few percent.
本文研究如何利用远红外水冰特征来推断T Tauri星周围盘的性质以及水冰的热历史。我们探讨了未来使用平流层红外天文台（SOFIA）/高分辨率中红外勘测仪（HIRMES）以及SPICA计划中的远红外仪器SAFARI进行观测的能力。
使用围绕一颗具有代表性的T Tauri星的一系列详细的辐射传输盘模型，来研究45微米和63微米处的远红外水冰特征如何随关键盘性质变化：盘大小、颗粒大小、盘尘埃质量、尘埃沉降和冰厚度。此外，设计了一系列模型来计算盘中水冰在升温、直接沉积和冷却情况下的水冰发射特征。
盘表面冰粒的光致脱附使中红外水冰特征减弱4至5倍。远红外水冰发射特征源自距离为10至100天文单位的盘表面雪线处的小颗粒。除非盘中缺少这个储存库（例如有大空洞的过渡盘），特征强度不会改变。大于10微米的颗粒对这些特征没有贡献。颗粒沉降（使用湍流描述）对冰特征强度的影响最多为15%。冰特征强度与盘尘埃质量和颗粒上的水冰分数成比例，但对于尘埃质量大于10 M⊙以及使尘埃质量增加超过50%的冰幔，强度会饱和。水冰的各种热历史在特征形状（晶体/非晶体）以及45微米特征的峰值强度和位置上留下印记。SOFIA/HIRMES在深度曝光（1小时）下只能探测到比我们标准T Tauri盘模型模拟的要强得多的晶体冰特征。SPICA/SAFARI在短曝光（10分钟）下就能探测到我们标准T Tauri盘模型中的典型冰特征。
SPICA/SAFARI的灵敏度将允许在对附近恒星形成区域的T Tauri星进行无偏调查时，对45微米和63微米水冰特征进行详细研究，并估计其冰储存库的质量。水冰发射特征带有冰热历史的印记，因此可以区分各种形成和传输情况。如果能很好地表征潜在连续谱且SAFARI的基线稳定性优于百分之几，那么在深度调查中可以探测到45微米处具有更宽更平峰值的非晶体冰。
