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NUV imaging and spectroscopic acquisitions rely on the known separation between the astrophysical source and the calibration lamp as seen on the detector. That separation must be measured externally (on sky) and that has not been measured since SMOV. If that separation has changed and that change is not reflected in the flight software then NUV acquisitions would be off-center by the same amount. The principal effect of the unintended offset would be flux loss. Without the test we are hereby proposing we would not be able to distinguish this flux loss from other effects that factor into the Time Dependent Sensitivity (TDS) correction. After more than 12 years of lamp degradation it makes sense to check the separation. This one-time program tests that NUV acquisitions are still centered by comparing them to a lamp-independent flux-centered acquisition. The proposal description explains the observing design. A more detailed descriptiondoublePoint This program compares the results of three different ways to do acquisitionsdoublePoint (1) ACQ-IMAGE comma (2) NUV spectroscopic acq (ACQ-PEAKXD followed by ACQ-PEAKD) comma and (3) manually computing the flux-weighted centroid after flux is vignetted by POSTARGs. After (1) and (2) we take verification spectra with the lamp on. These spectra can be used to measure the target-lamp separation. (3) is not really an acquisition but rather a simulation of an acquisition in the sense that we are collecting the data needed for flux centroiding comma but the FSW will not actually compute the centroiding and move the telescope. I will compute the centroiding and compare it to where (1) and (2) placed the target. The reason for doing (3) is precisely because it does not use the lamp. Flux centroiding is a completely independent way of establishing where the center of the aperture is comma and we can then compare it to (1) and (2) to see if the lamp-dependent methods are working. When the FSW executes a flux-centroided acquisition (NUV ACQ-SEARCH comma NUV ACQ-PEAKD and all FUV acqs) the lamp is turned off. If the lamp were on its light would be a constant contribution to every dwell point comma since the lamp does not get vignetted by POSTARG. That would just add floor counts which would then be subtracted by the centroiding algorithm comma but the noise associated with it would remain. For details on which FSW routines and parameters are involved see the ISR by Penton and Sahnow (2022 in prep.) and references therein.

近紫外（NUV）成像与光谱采集依赖于探测器上观测到的天体源与校准灯之间的已知间距。该间距必须通过实地天区测量获得，且自科学任务运行验证（SMOV）阶段以来，从未开展过此类测量。若该间距发生变化且飞行软件（flight software，FSW）未同步更新该偏移量，则近紫外采集的目标将偏离中心达该变化的等量值。该意外偏移的主要影响为通量损失。若不开展本次提议的测试，我们将无法将该类通量损失与纳入时间相关灵敏度（TDS）校正的其他影响因素区分开来。鉴于校准灯已历经12年以上的老化衰减，核查该间距具有重要意义。本一次性观测项目通过将近紫外采集结果与不依赖校准灯的通量中心采集结果进行对比，以验证近紫外采集的目标仍处于中心位置。本提案描述了观测设计方案。更详细的说明如下：本项目将对比三种不同采集方式的结果：（1）ACQ-IMAGE采集；（2）近紫外光谱采集（即先执行ACQ-PEAKXD，再执行ACQ-PEAKD）；（3）在通量被POSTARGs渐晕后，手动计算通量加权质心。在完成（1）和（2）两类采集后，我们将在校准灯点亮的状态下获取验证光谱，该类光谱可用于测量天体源与校准灯之间的间距。（3）并非真正意义上的采集，而是采集过程的模拟：我们仅收集通量质心计算所需的数据，但飞行软件（FSW）不会实际执行质心计算并驱动望远镜指向。我将自行计算质心，并将其与（1）和（2）方式采集时的目标定位结果进行对比。采用（3）方式的核心原因在于其不依赖校准灯。通量质心计算是一种完全独立的孔径中心定位方法，我们可借此将（1）和（2）的结果与之对比，以验证依赖校准灯的采集方法是否正常工作。当飞行软件（FSW）执行通量质心采集时（包括近紫外ACQ-SEARCH、近紫外ACQ-PEAKD以及所有远紫外（FUV）采集任务），校准灯会被关闭。若校准灯保持点亮，其光线将对每个驻留点产生恒定的背景贡献，因为校准灯不会被POSTARGs渐晕。这只会增加本底计数，而质心计算算法会将该本底计数扣除，但与之相关的噪声仍会残留。有关涉及的飞行软件（FSW）程序与参数的详细信息，请参阅Penton与Sahnow于2022年（待出版）发布的仪器科学报告（ISR）及其参考文献。