Empirical Corrections for Charge Transfer Inefficiency and Associated Centroid Shifts for STIS CCD Observations
Empirical Corrections for Charge Transfer Inefficiency and Associated Centroid Shifts for STIS CCD Observations
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STIS CCD 观测中电荷转移效率低下和相关质心偏移的经验修正
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
R. Kimble
中科院分区：
文献类型：
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作者：
P. Goudfrooij;R. Bohlin;J. Máız;R. Kimble
利用各种在轨成像和光谱观测来表征哈勃空间望远镜上空间望远镜成像光谱仪(STIS)的电荷耦合器件(CCD)的电荷转移效率(CTE)。提出了一套修正CTE相关信号损失的点源观测的公式。对于在成像模式下获取的数据，CTE损失根据源在CCD上的位置、测量孔径内的源信号电平、本底电平和观察时间来参数化。对于光谱数据，发现需要一个附加参数来提供CTE损耗的适当校准，即，位于信号提取盒和读出放大器之间的点扩展函数中的信号。对于使用STI的G750L或G750M光栅获取的光谱，后一个参数的影响是显著的。本文介绍的算法可在STIS CCD模式覆盖的整个波长范围内纠正由于CTE损失高达30%至∼1.5%RMS范围内的通量校准误差。这种不确定性类似于与在每个分辨率元素大约2500个电子的信号电平下检测到的源有关的泊松噪声。利用双向电荷耦合器件读数，还得到了CTE损耗引起的质心漂移。在CTE损失和质心移动(对于成像和光谱模式)之间发现了紧密的相关性，从而使人们能够校正不完美的电荷转移对STIS CCD观测的两种影响。
A variety of on‐orbit imaging and spectroscopic observations are used to characterize the charge transfer efficiency (CTE) of the charge‐coupled device (CCD) of the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. A set of formulae is presented to correct observations of point sources for CTE‐related loss of signal. For data taken in imaging mode, the CTE loss is parameterized in terms of the location of the source on the CCD, the source signal level within the measurement aperture, the background level, and the time of observation. For spectroscopic data, it is found that one additional parameter is needed in order to provide an adequate calibration of the CTE loss, namely, the signal in the point‐spread function located between the signal extraction box and the readout amplifier. The effect of the latter parameter is significant for spectra taken using the G750L or G750M gratings of STIS. The algorithms presented here correct flux calibration inaccuracies due to CTE losses as large as 30% to within ∼1.5% rms throughout the wavelength range covered by the STIS CCD modes. This uncertainty is similar to the Poisson noise associated with a source detected at a signal level of about 2500 electrons per resolution element. Using bidirectional CCD readouts, centroid shifts incurred due to CTE loss are also derived. A tight correlation is found between the CTE loss and the centroid shift (both for imaging and for spectroscopic modes), thus enabling one to correct for both effects of imperfect charge transfer to STIS CCD observations.