基于HST/ACS观测图像相减的造父变星到巨螺线M101的新距离
A New Cepheid Distance to the Giant Spiral M101 Based On Image Subtraction of HST/ACS Observations
摘要：
我们准确地确定一个新的造父变星的距离M101（NGC 5457）使用档案HST/ACS V和I时间序列测光的两个领域内的星系。我们对ISIS图像减法包进行了轻微修改，以从HST数据获得最佳差分光变曲线。我们发现了827颗造父变星，周期在3到80天之间，这是HST观测到的最大的造父变星河外样本，是2倍。利用这个较大的造父变星样本，我们发现M101与LMC的相对距离为Δ μLMC = 10.63 \pm 0.04（随机）\pm 0.07如果我们用几何学上确定的到NGC 4258的脉泽距离作为我们的距离锚，M101的距离模量为μ0 = 29.04 \pm 0.05（随机）\pm 0.18（系统）mag或D = 6.4 \pm 0.2（随机）\pm 0.5（系统）Mpc。不确定性主要是由脉泽距离估计（\pm 0.15等），这应该在未来几年内改善。我们通过两种方法确定了造父变星样品的金属丰度依赖性，γ，得到γ = -0.84 \pm 0.22（随机）\pm 0.07（系统）mag dex-1和γ = -0.72+0.20 -0.22（随机）\pm 0.06（系统）mag dex-1。我们看到边缘的证据，在Weseneirs的P-L关系的斜率作为一个函数的dexpected galactocentric半径的变化。我们还使用TRGB方法独立地确定了μ0 = 29.05 \pm 0.06（随机）\pm 0.12（系统）磁的到M101的距离模量。
英文摘要：
We accurately determine a new Cepheid distance to M101 (NGC 5457) using archival HST/ACS V and I time series photometry of two fields within the galaxy. We make a slight modification to the ISIS image subtraction package to obtain optimal differential light curves from HST data. We discovered 827 Cepheids with periods between 3 and 80 days, the largest extragalactic sample of Cepheids observed with HST by a factor of 2. With this large Cepheid sample we find that the relative distance of M101 from the LMC is delta μLMC = 10.63 \pm 0.04 (random) \pm 0.07 (systematic) mag. If we use the geometrically determined maser distance to NGC 4258 as our distance anchor, the distance modulus of M101 is μ0 = 29.04 \pm 0.05 (random) \pm 0.18 (systematic) mag or D = 6.4 \pm 0.2 (random) \pm 0.5 (systematic) Mpc. The uncertainty is dominated by the maser distance estimate (\pm 0.15 mag), which should improve over the next few years. We determine a steep metallicity dependence, gamma, for our Cepheid sample through two methods, yielding gamma = -0.84 \pm 0.22 (random) \pm 0.07 (systematic) mag dex-1 and gamma = -0.72+0.20 -0.22 (random) \pm 0.06 (systematic) mag dex-1. We see marginal evidence for variations in the Wesenheit P-L relation slope as a function of deprojected galactocentric radius. We also use the TRGB method to independently determine the distance modulus to M101 of μ0 = 29.05 \pm 0.06 (random) \pm 0.12 (systematic) mag.
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