论文标题
使用蓝色光星在U波段中的光度校准
Photometric calibration in u-band using blue halo stars
论文作者
论文摘要
我们开发了一种基于观察到的蓝色银河晕星的颜色来校准U波段光度法的方法。银河光环恒星属于银河系的古老恒星种群，金属性相对较低。已知光环种群的“蓝色尖端” - 主要序列关闭（MSTO）恒星 - 已知具有相对均匀的内在边缘u-G颜色，仅慢速空间变化。在SDSS数据中，观察到的变化与银河纬度相关，我们将其归因于高金属磁盘星污染，并与经验曲线拟合。如果可以使用匹配深度的G波段成像，则该曲线可用于校准U波段成像。我们的方法可以应用于$ | b |的单场观测值。 > 30^\ circ $，并消除了对标准星观测到的需求，或与校准的U波段成像重叠。我们将使用Atlas-RefCat2的G波段数据校准包括在内。我们测试了Noirlab源目录（NSC DR2）的孩子4，Atlas DR 4和DECAM成像的儿童恒星的方法，并将我们的校准与SDSS进行比较。对于此过程，我们使用合成幅度来得出这些数据集之间的颜色方程，以提高零点的精度。我们找到了所有数据集的改进，零点精度为0.016 mag（与原始的0.033 mag相比），Atlas的0.020 mag（最初为0.027 mag）和DECAM的0.016 MAG（最初为0.041 Mag）。因此，对于鲁宾天文台对时空的传统调查（LSST），仅此方法就达到了U波段中0.02 MAG光度的目标。
We develop a method to calibrate u-band photometry based on the observed color of blue galactic halo stars. The galactic halo stars belong to an old stellar population of the Milky Way and have relatively low metallicity. The "blue tip" of the halo population -- the main sequence turn-off (MSTO) stars -- is known to have a relatively uniform intrinsic edge u-g color with only slow spatial variation. In SDSS data, the observed variation is correlated with galactic latitude, which we attribute to contamination by higher-metallicity disk stars and fit with an empirical curve. This curve can then be used to calibrate u-band imaging if g-band imaging of matching depth is available. Our approach can be applied to single-field observations at $|b| > 30^\circ$, and removes the need for standard star observations or overlap with calibrated u-band imaging. We include in our method the calibration of g-band data with ATLAS-Refcat2. We test our approach on stars in KiDS DR 4, ATLAS DR 4, and DECam imaging from the NOIRLab Source Catalog (NSC DR2), and compare our calibration with SDSS. For this process, we use synthetic magnitudes to derive the color equations between these datasets, in order to improve zero-point accuracy. We find an improvement for all datasets, reaching a zero-point precision of 0.016 mag for KiDS (compared to the original 0.033 mag), 0.020 mag for ATLAS (originally 0.027 mag), and 0.016 mag for DECam (originally 0.041 mag). Thus, this method alone reaches the goal of 0.02 mag photometric precision in u-band for the Rubin Observatory's Legacy Survey of Space and Time (LSST).
