标题： 中红外观测IRAS、AKARI、WISE/NEOWISE和Subaru对大型冰质小行星(704)Interamnia的观测：风化层特性与水冰比例的新视角 显示英文标题

标题： Mid-IR Observations of IRAS, AKARI, WISE/NEOWISE and Subaru for Large Icy Asteroid (704) Interamnia: a New Perspective of Regolith Properties and Water Ice Fraction

摘要： (704) Interamnia 是位于外主带区域的最大的小行星之一，其表面下可能含有大量水冰。 我们使用 8.2 米 Subaru 望远镜在中红外波段观测这颗小行星，并利用热物理模型（RSTPM）分析来自 Subaru 的中红外数据以及 IRAS、AKARI 和 WISE/NEOWISE 的数据。 我们优化了将 WISE 星等转换为热红外通量的方法，该方法考虑温度相关的颜色修正，可以为处于大日心距离且表面温度较低的主带小行星提供重要参考。 我们推导出 Interamnia 的最佳拟合热参数——平均松散颗粒尺寸为$190_{-180}^{+460}~\rm \mu m$，粗糙度为$0.30_{-0.17}^{+0.35}$，均方根坡度为$27_{-9}^{+13}$度，因此由于季节性温度变化，热惯性范围从 9 到$92~\rm Jm^{-2}s^{-1/2}K^{-1}$。 几何反照率和有效直径分别评估为$0.0472_{-0.0031}^{+0.0033}$和$339_{-11}^{+12}~\rm km$，表明其总体密度为$1.86\pm0.63~\rm g/cm^3$。 低热惯性与典型B/C型小行星$D\geq100$公里一致。 微小的风化层颗粒尺寸表明Interamnia表面存在细粒风化层。 此外，季节性和昼夜温度分布表明南半球和北半球之间的热特征似乎非常不同。 最后，我们根据碳质球粒陨石的颗粒密度和孔隙度得出水冰体积分数为$9\%\sim66\%$。 显示英文摘要

摘要： (704) Interamnia is one of the largest asteroids that locates in the outer main-belt region, which may contain a large amount of water ice underneath its surface. We observe this asteroid using 8.2 m Subaru telescope at mid-infrared wavebands, and utilize thermophysical model for realistic surface layers (RSTPM) to analyze mid-infrared data from Subaru along with those of IRAS, AKARI and WISE/NEOWISE. We optimize the method to convert the WISE magnitude to thermal infrared flux with temperature dependent color corrections, which can provide significant references for main-belt asteroids at a large heliocentric distance with low surface temperature. We derive best-fitting thermal parameters of Interamnia - a mean regolith grain size of $190_{-180}^{+460}~\rm \mu m$, with a roughness of $0.30_{-0.17}^{+0.35}$ and RMS slope of $27_{-9}^{+13}$ degrees, thereby producing thermal inertia ranging from 9 to $92~\rm Jm^{-2}s^{-1/2}K^{-1}$ due to seasonal temperature variation. The geometric albedo and effective diameter are evaluated to be $0.0472_{-0.0031}^{+0.0033}$ and $339_{-11}^{+12}~\rm km$, respectively, being indicative of a bulk density of $1.86\pm0.63~\rm g/cm^3$. The low thermal inertia is consistent with typical B/C-type asteroids with $D\geq100$ km. The tiny regolith grain size suggests the presence of a fine regolith on the surface of Interamnia. Moreover, the seasonal and diurnal temperature distribution indicates that thermal features between southern and northern hemisphere appear to be very different. Finally, we present an estimation of volume fraction of water ice of $9\%\sim66\%$ from the published grain density and porosity of carbonaceous chondrites.