Kepler Increased Resolution Image Subtraction ("IRIS")

The open clusters NGC 6791 and NGC 6819 both lay in the Kepler mission's field of view --- however, due to crowding, the majority of stars in and around the clusters were not individually targeted for long or short cadence photometry during the mission. Instead, both clusters were targeted with 200x200 target pixel files, known as "superstamps." The team presents long cadence light curves for all 9,150 KIC targets that fall on the superstamps, including cluster members and field stars. This data release includes light curves for 8,427 new targets with no previously available photometry, and an extended time series baseline for 382 long cadence targets. The team produced these light curves using an image subtraction photometry pipeline, described in Colman et al. 2021, which is optimized for variability and reducing noise on crowded targets. There are at most 17 quarters (1--17) of photometry available for NGC 6791, and 14 (1--5, 7--9, 11--13, 15--17) for NGC 6819. Due to detector drift between seasons, targets towards the edges of the superstamps may not have all quarters available.

疏散星团NGC 6791与NGC 6819均处于开普勒任务（Kepler mission）的观测视场内，但由于星场拥挤，任务期间该星团内外的绝大多数恒星均未被单独选取为长时序测光（long cadence photometry）或短时序测光（short cadence photometry）的观测目标。取而代之的是，两个星团均采用200×200像素的目标像素文件（target pixel files）进行观测，这类文件也被称为“超级邮票（superstamps）”。研究团队为所有落在超级邮票范围内的9150个开普勒输入星表（Kepler Input Catalog, KIC）目标生成了长时序测光光变曲线，其中既包含星团成员星，也包含场星（field stars）。本次数据发布包含8427个此前无可用测光数据的新目标的光变曲线，以及382个长时序测光目标的扩展时间序列基线。研究团队采用Colman等人2021年发表的图像相减测光流程（image subtraction photometry pipeline）生成了上述光变曲线，该流程针对变源测光以及降低拥挤星场目标的噪声进行了优化。NGC 6791最多可获得17个观测季（编号1至17）的测光数据，而NGC 6819则最多可获得14个观测季（编号1至5、7至9、11至13、15至17）的测光数据。由于不同观测季间探测器存在漂移，位于超级邮票边缘的目标可能无法获取全部观测季的测光数据。