ACS/WFC中串行电荷转移效率研究
Serial Charge Transfer Efficiency in ACS/WFC
AI总结：
研究ACS/WFC中串行电荷转移效率，改进算法以修正其对恒星光度计和质心的影响。
摘要：
我们对ACS/WFC的CCD串行（x方向）电荷转移效率（CTE）进行了专门研究。在以往研究平行（y方向）CTE的基础上，我们利用校准暗帧中热像素后方的串行CTE轨迹，来表征WFC探测器串行寄存器中的电荷捕获和释放。串行CTE轨迹比平行CTE轨迹更尖锐且更长。在串行像素转移过程中，参与的电荷陷阱远少于平行转移，这解释了为什么平行CTE远比串行CTE差。我们发现串行CTE会导致恒星光度计测量损失约0.005-0.02mag，并将恒星质心位移约0.01-0.035像素。CALACS中基于像素的算法，用于修正WFC数据中平行CTE损失，已修改以包含对串行CTE损失的修正。PCTETAB参考文件也已更新，以包含串行CTE参数。目前基于像素的串行CTE修正仅在SM4（2009年5月）之后获得的全帧WFC图像上运行。在本报告发表后不久，经过平行和串行CTE修正的科学数据将在MAST档案中提供。
英文摘要：
We present a dedicated study of CCD serial ($x$-direction) charge transfer efficiency (CTE) in ACS/WFC. Following past studies of parallel ($y$-direction) CTE, we use the serial CTE trails behind hot pixels in calibration dark frames to characterize charge trapping and release in the serial registers of the WFC detectors. Serial CTE trails are sharper and longer than parallel CTE trails. Many fewer charge traps come into play during serial pixel transfers than parallel transfers, which explains why parallel CTE is much worse than serial CTE. We find that serial CTE can cause losses of $\sim$0.005-0.02~mag in stellar photometry and shift stellar centroids by $\sim$0.01-0.035 pixels. The pixel-based algorithm in CALACS that corrects for parallel CTE losses in WFC data has been modified to include a correction for serial CTE losses. The PCTETAB reference file has also been updated to include serial CTE parameters. The pixel-based correction for serial CTE currently runs only on full-frame WFC images obtained after SM4 (May 2009). Shortly following the publication of this report, science data corrected for both parallel and serial CTE will be available in the MAST archive.
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