[论文解读] JWST MIRI flight performance: The Medium-Resolution Spectrometer

Ioannis Argyriou, Alistair Glasse+23 more|arXiv (Cornell University)|Mar 23, 2023

Calibration and Measurement Techniques被引用 12

一句话总结

本文记录了 JWST MIRI 中等分辨率光谱仪 (MRS) 的在轨性能，详述在历飞行中实现的光学、光谱和光谱-光度性能及标定改进。

ABSTRACT

The Medium-Resolution Spectrometer (MRS) provides one of the four operating modes of the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST). The MRS is an integral field spectrometer, measuring the spatial and spectral distributions of light across the 5-28 $μm$ wavelength range with a spectral resolving power between 3700-1300. We present the MRS's optical, spectral, and spectro-photometric performance, as achieved in flight, and we report on the effects that limit the instrument's ultimate sensitivity. The MRS flight performance has been quantified using observations of stars, planetary nebulae, and planets in our Solar System. The precision and accuracy of this calibration was checked against celestial calibrators with well-known flux levels and spectral features. We find that the MRS geometric calibration has a distortion solution accuracy relative to the commanded position of 8 mas at 5 $μm$ and 23 mas at 28 $μm$. The wavelength calibration is accurate to within 9 km/sec at 5 $μm$ and 27 km/sec at 28 $μm$. The uncertainty in the absolute spectro-photometric calibration accuracy was estimated at 5.6 +- 0.7 %. The MIRI calibration pipeline is able to suppress the amplitude of spectral fringes to below 1.5 % for both extended and point sources across the entire wavelength range. The MRS point spread function (PSF) is 60 % broader than the diffraction limit along its long axis at 5 $μm$ and is 15 % broader at 28 $μm$. The MRS flight performance is found to be better than prelaunch expectations. The MRS is one of the most subscribed observing modes of JWST and is yielding many high-profile publications. It is currently humanity's most powerful instrument for measuring the mid-infrared spectra of celestial sources and is expected to continue as such for many years to come.

研究动机与目标

• 评估 MRS 在飞行中的光学保真度和几何/光谱畸变。
• 量化光谱光度测量的精度和绝对标定的准确性。
• 识别限制 MRS 灵敏度的系统性效应并与飞前预期进行比较。
• 描述在飞行中使用的标定流程和干涉条纹校正策略。
• 提供基于天球观测得出的更新波长和畸变解。

提出的方法

• 利用恒星、行星状星云及太阳系行星的观测来量化性能。
• 推导并应用每个 MRS 副带和子带的几何畸变和波长标定解。
• 评估 PSF 展宽和探测器散射效应，并在探测器平面上对散射光进行建模/减法。
• 利用管线干涉条纹平场和残差校正算法表征并校正光谱干涉条纹。
• 以标准星和已校准源验证光谱光度的准确性。
• 将飞行性能及推导出的标定与飞前预期进行比较。

实验结果

研究问题

• RQ1 MRS 在所有通道和切片中的在轨几何畸变精度是多少？
• RQ2 波长标定精度是多少，以及如何通过天球观测数据改进？
• RQ3 主 导的系统性效应（如探测器散射、干涉条纹）有哪些，以及在飞行中它们被如何有效缓解？
• RQ4 在光谱光度的绝对标定和通量稳定性方面，MRS 的表现如何？
• RQ5 在轨PSF和光谱分辨能力与地基模型及预期相比较如何？

主要发现

• 几何畸变精度在5 μm时为8毫角秒，在28 μm时为23毫角秒。
• 波长标定精度实现至大约6 km/s，适用于跨带的FLT-5解。
• 绝对光谱光度标定精度为5.6 ± 0.7%。
• 光谱干涉条纹通过管线校正可降至整个波段以下1.5%的幅值。
• 探测器内部散射导致在5 μm沿长轴的PSF展宽高达60%，在较长波长时下降；一个减去算法将此通量降至影响低于1%。
• 在5 μm时，MRS的PSF在长轴上比衍射极限宽60%；在28 μm时宽度增加15%。