[论文解读] Gaia Early Data Release 3

M. Riello, F. De Angeli+40 more|arXiv (Cornell University)|Dec 3, 2020

Stellar, planetary, and galactic studies参考文献 50被引用 20

一句话总结

本文介绍了盖亚早期数据释放3（EDR3），详细阐述了相较于DR2在测光处理方面的显著改进，包括更精准的背景估计、考虑通量损失的优化校准模型，以及对饱和和拥挤效应的更好处理。结果实现了亚毫mag级精度（G = 10–14时为0.2 mmag），且在1 mmag/mag以上无显著系统性趋势，标志着18亿颗天体测光精度与一致性的重大飞跃。

ABSTRACT

Context. Gaia Early Data Release 3 ( Gaia EDR3) contains astrometry and photometry results for about 1.8 billion sources based on observations collected by the European Space Agency Gaia satellite during the first 34 months of its operational phase. Aims. In this paper, we focus on the photometric content, describing the input data, the algorithms, the processing, and the validation of the results. Particular attention is given to the quality of the data and to a number of features that users may need to take into account to make the best use of the Gaia EDR3 catalogue. Methods. The processing broadly followed the same procedure as for Gaia DR2, but with significant improvements in several aspects of the blue and red photometer (BP and RP) preprocessing and in the photometric calibration process. In particular, the treatment of the BP and RP background has been updated to include a better estimation of the local background, and the detection of crowding effects has been used to exclude affected data from the calibrations. The photometric calibration models have also been updated to account for flux loss over the whole magnitude range. Significant improvements in the modelling and calibration of the Gaia point and line spread functions have also helped to reduce a number of instrumental effects that were still present in DR2. Results. Gaia EDR3 contains 1.806 billion sources with G -band photometry and 1.540 billion sources with G BP and G RP photometry. The median uncertainty in the G -band photometry, as measured from the standard deviation of the internally calibrated mean photometry for a given source, is 0.2 mmag at magnitude G = 10–14, 0.8 mmag at G ≈ 17, and 2.6 mmag at G ≈ 19. The significant magnitude term found in the Gaia DR2 photometry is no longer visible, and overall there are no trends larger than 1 mmag mag −1 . Using one passband over the whole colour and magnitude range leaves no systematics above the 1% level in magnitude in any of the bands, and a larger systematic is present for a very small sample of bright and blue sources. A detailed description of the residual systematic effects is provided. Overall the quality of the calibrated mean photometry in Gaia EDR3 is superior with respect to DR2 for all bands.

研究动机与目标

• 提升盖亚早期数据发布版本的测光校准与数据质量。
• 解决盖亚DR2中残留的系统性误差与仪器效应，特别是BP和RP波段中的问题。
• 为天文学研究提供更均匀、精确且准确的测光星表。
• 验证新处理流程在整个视星等与颜色范围内的性能表现。
• 为用户提供使用指南与已知问题说明，以确保EDR3测光数据的最优使用。

提出的方法

• 使用改进的校准模型，重新处理2014年7月至2017年5月共34个月的盖亚观测数据。
• 改进BP、RP和G波段的背景估计，消除了DR2中可见的黄道光残余信号。
• 在全视星等范围内引入通量损失校正，用于测光校准。
• 增强对饱和与拥挤效应的处理，减少如G = 11.2处的虚假特征。
• 在所有视星等与颜色范围内统一使用单一通过函数，以最小化系统性误差。
• 排除低质量数据时段，并对有问题的观测进行预筛选，以提升整体校准稳定性。

实验结果

研究问题

• RQ1 与DR2相比，盖亚EDR3在测光校准方面，系统误差与精度的改进程度如何？
• RQ2 改进的背景估计与通量损失校正对测光精度有何影响？
• RQ3 在G、GBP和GRP波段中是否存在残留系统性误差，特别是在明亮或蓝星源中？
• RQ4 增加一年数据对平均测光不确定度与稳定性有何影响？
• RQ5 仪器效应（如饱和与拥挤）对最终测光结果的影响程度如何？

主要发现

• 在G = 10–14时，G波段测光的中位不确定性为0.2 mmag；在G ≈17时为0.8 mmag；在G ≈19时为2.6 mmag，相较于DR2有显著提升。
• DR2中存在与视星等相关的系统性趋势在EDR3中已不再可见，全视星等范围内无趋势超过1 mmag/mag。
• 在所有视星等与颜色范围内统一使用单一通过函数，使各波段系统性误差低于1%（以视星等计），对于4,148颗明亮蓝星源（G < 13，GBP−GRP < −0.1）仅上升至约2%。
• 改进的背景估计消除了黄道光残余信号，该信号在DR2中尤为明显，特别是在GBP和GRP波段。
• 饱和处理得到显著改善，G = 11.2处的特征性隆起已减小，且对G < 6的源校正需求也已最小化。
• G、GBP与GRP测光之间的一致性得到提升，DR1与DR2中出现的G = 13和16处不连续性已消除。