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arXiv 2003.11045astro-ph.EP
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谷神星毫米波积分热性质测量

Disk-Integrated Thermal Properties of Ceres Measured at Millimeter Wavelengths

Jian-Yang Li, Arielle Moullet, Timothy N. Titus, Henry H. Hsieh, Mark V. Sykes

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21 pages, 4 figures, 3 tables
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摘要：

我们在2015年11月和2017年9月和10月用ALMA 12米阵列以及2017年10月用ALMA紧凑阵列（ACA）在三个时期观测了谷神星，所有这些都在~265 GHz连续谱（波长约为1.1 mm）下，以绘制谷神星在每个时期的完整旋转温度。我们还使用了2017年10月的ACA观测来搜索HCN。在我们2017年的观测中，谷神星的磁盘平均亮度温度被测量为170 K到180 K之间。谷神星的自转光变曲线呈双峰形，振幅约为4%。假设全局均匀生产和Haser模型，我们的HCN搜索返回阴性结果，上限生产率为~2 $\times$ 10 $^{24}$分子s $^{-1}$。一个热物理模型表明，谷神星的顶层在1毫米波长处的介电吸收率高于类月物质。然而，以前的观测表明，谷神星的介电吸收率随着波长的增加而降低。这种独特的介电特性可能与谷神星的水合层状硅酸盐成分有关，可能与其表面丰富的$μ$ m-尺寸颗粒有关。谷神星的热惯性受到我们的建模的限制，可能在40到160 tiu之间，远高于以前在红外波长下的测量值。建模还表明，谷神星的光变曲线可能受其物理或成分特性的空间变化所支配，这些变化会导致谷神星旋转时观察到的热特性和介电吸收发生变化。

英文摘要：

We observed Ceres at three epochs in 2015 November and 2017 September and October with ALMA 12-meter array and in 2017 October with the ALMA Compact Array (ACA), all at ~265 GHz continuum (wavelengths of ~1.1 mm) to map the temperatures of Ceres over a full rotation at each epoch. We also used 2017 October ACA observations to search for HCN. The disk-averaged brightness temperature of Ceres is measured to be between 170 K and 180 K during our 2017 observations. The rotational lightcurve of Ceres shows a double peaked shape with an amplitude of about 4%. Our HCN search returns a negative result with an upper limit production rate of ~2$\times$10$^{24}$ molecules s$^{-1}$, assuming globally uniform production and a Haser model. A thermophysical model suggests that Ceres's top layer has higher dielectric absorption than lunar-like materials at a wavelength of 1 mm. However, previous observations showed that the dielectric absorption of Ceres decreases towards longer wavelengths. Such distinct dielectric properties might be related to the hydrated phyllosilicate composition of Ceres and possibly abundant $μ$m-sized grains on its surface. The thermal inertia of Ceres is constrained by our modeling as likely being between 40 and 160 tiu, much higher than previous measurements at infrared wavelengths. Modeling also suggests that Ceres's lightcurve is likely dominated by spatial variations in its physical or compositional properties that cause changes in Ceres's observed thermal properties and dielectric absorption as it rotates.

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