[论文解读] Gaia Early Data Release 3: The astrometric solution

L. Lindegren, S. A. Klioner+95 more|arXiv (Cornell University)|Dec 6, 2020

Stellar, planetary, and galactic studies参考文献 37被引用 90

一句话总结

本文描述 Gaia EDR3 天体测量的输入数据、模型、处理与验证，包括相对于 DR2 的改进以及对颜色相关校准的处理。报告了对14.68亿源实现全五参数天体测量，对8.82亿源实现六参数解。

ABSTRACT

Gaia Early Data Release 3 (Gaia EDR3) contains results for 1.812 billion sources in the magnitude range G = 3 to 21 based on observations collected by the European Space Agency Gaia satellite during the first 34 months of its operational phase. We describe the input data, the models, and the processing used for the astrometric content of Gaia EDR3, as well as the validation of these results performed within the astrometry task. The processing broadly followed the same procedures as for Gaia DR2, but with significant improvements to the modelling of observations. For the first time in the Gaia data processing, colour-dependent calibrations of the line- and point-spread functions have been used for sources with well-determined colours from DR2. In the astrometric processing these sources obtained five-parameter solutions, whereas other sources were processed using a special calibration that allowed a pseudocolour to be estimated as the sixth astrometric parameter. Compared with DR2, the astrometric calibration models have been extended, and the spin-related distortion model includes a self-consistent determination of basic-angle variations, improving the global parallax zero point. Gaia EDR3 gives full astrometric data (positions at epoch J2016.0, parallaxes, and proper motions) for 1.468 billion sources (585 million with five-parameter solutions, 882 million with six parameters), and mean positions at J2016.0 for an additional 344 million. Solutions with five parameters are generally more accurate than six-parameter solutions, and are available for 93% of the sources brighter than G = 17 mag. The median uncertainty in parallax and annual proper motion is 0.02-0.03 mas at magnitude G = 9 to 14, and around 0.5 mas at G = 20. Extensive characterisation of the statistical properties of the solutions is provided, including the estimated angular power spectrum of parallax bias from the quasars.

研究动机与目标

• 描述用于 Gaia EDR3 天体测量的数据、模型与处理过程。
• 解释相对于 Gaia DR2 的改进，特别是在校准与颜色处理方面。
• 呈现天体测量结果的验证与特征。
• 讨论用于对齐与参考框架的输入数据段、迭代处理周期及辅助数据。

提出的方法

• 采用 Gaia 天体测量全局迭代解算 (AGIS) 结合迭代 CALIPD 与 AGIS 步骤。
• 通过有效波数 (nu_eff) 引入对颜色相关的线型和点扩散函数 (LSF/PSF) 校准。
• 使用伪色作为第六个参数，在缺乏可靠颜色信息的源上估计六参数解。
• 迭代 CALIPD 与 AGIS（CALIPD 3.1、AGIS 3.1、CALIPD 3.2、AGIS 3.2），以减少色差偏差。
• 利用外部辅助数据（ICRF3 框架、Hipparcos、INPOP10e 天体历表）进行参考框架对齐与太阳系历表的参考。

实验结果

研究问题

• RQ1 相比 DR2，Gaia EDR3 在天体测量标定与色差校正方面有何改进？
• RQ2 有多少比例的源获得五参数解与六参数解，且不同比例随星等的不确定性有何变化？
• RQ3 在颜色信息不完全时，颜色相关校准（nu_eff）与伪色如何帮助天体测量精度？
• RQ4 EDR3 在天体测量偏差与零点（视差偏差）方面的特征是什么？

主要发现

• EDR3 为14.68亿源提供完整的天体测量数据（在J2016.0时刻的位置、视差、自行/径向运动），其中5参数源5.85亿、6参数源8.82亿。
• 在J2016.0时刻的位置和视差/自行运动的均值误差在0.02–0.03 mas（G=9–14）且在G=20时约0.5 mas。
• 通过颜色相关的 CALIPD/AGIS 处理与迭代校准显著减轻色差偏差，在nu_eff 不可用时使用伪色。
• 进行了两次迭代（CALIPD 3.1 与 3.2）以收敛色差校正，并有自洽的基线角变动确定的辅助。
• EDR3 增加了3.44亿个在J2016.0时的平均位置，用于五参数或六参数解不完全的源。
• Gaia 基准参考框架对齐使用 ICRF3 光学对比对象与以 Hipparcos 为基础的残留项，以确保天球框架的一致性。