凯克HIRES光谱仪的波长精度和精细结构常数变化的测量
Wavelength Accuracy of the Keck HIRES Spectrograph and Measuring Changes in the Fine Structure Constant
摘要：
我们报告的尝试，以准确的波长校准四个晚上的数据与凯克HIRES光谱仪上的类星体PHL 957，以确定是否精细结构常数是不同的，在过去。利用新的软件和技术，我们测量了在z=2.309的阻尼Ly-alpha系统中Ni II，Fe II，Si II等各种线的红移。大约有一半的数据是通过凯克碘细胞，其中包含数千个良好校准的碘线。使用这些碘暴露来校准正常的Th-Ar Keck数据管道输出，我们发现绝对波长偏移为500 m/s至1000 m/s，在一个晚上的漂移超过500 m/s，在几个晚上的漂移接近2000 m/s。这些偏移对应的绝对红移不确定度约为Δ z=10^{-5}（Δ λ = 0.02 Ang），日漂移约为Δ z= 5x 10 ^{-6}（Δ λ =0.01 Ang），多日漂移接近Δ z= 2x 10 ^{-5}（0.04 Ang）。波长偏移的原因尚不清楚，但由于声称的精细结构常数的偏移将导致小于100 m/s的速度偏移，这种水平的系统不确定性使得难以使用Keck HIRES数据来约束精细结构常数的变化。使用我们的校准数据，我们应用我们自己的拟合软件和标准拟合软件来测量（Delta alpha）/alpha，但发现我们可以获得从任何符号的显著检测到强零限的结果，这取决于使用哪组线和哪种拟合方法。因此，我们推测文献中报道的（Delta alpha）/alpha的不一致结果可能是由于波长校准和拟合过程中低估的系统误差引起的随机波动。
英文摘要：
We report on an attempt to accurately wavelength calibrate four nights of data taken with the Keck HIRES spectrograph on QSO PHL957, for the purpose of determining whether the fine structure constant was different in the past. Using new software and techniques, we measured the redshifts of various Ni II, Fe II, Si II, etc. lines in a damped Ly-alpha system at z=2.309. Roughly half the data was taken through the Keck iodine cell which contains thousands of well calibrated iodine lines. Using these iodine exposures to calibrate the normal Th-Ar Keck data pipeline output we found absolute wavelength offsets of 500 m/s to 1000 m/s with drifts of more than 500 m/s over a single night, and drifts of nearly 2000 m/s over several nights. These offsets correspond to an absolute redshift of uncertainty of about Delta z=10^{-5} (Delta lambda= 0.02 Ang), with daily drifts of around Delta z=5x10^{-6} (Delta lambda =0.01 Ang), and multiday drifts of nearly Delta z=2x10^{-5} (0.04 Ang). The causes of the wavelength offsets are not known, but since claimed shifts in the fine structure constant would result in velocity shifts of less than 100 m/s, this level of systematic uncertainty makes may make it difficult to use Keck HIRES data to constrain the change in the fine structure constant. Using our calibrated data, we applied both our own fitting software and standard fitting software to measure (Delta alpha)/alpha, but discovered that we could obtain results ranging from significant detection of either sign, to strong null limits, depending upon which sets of lines and which fitting method was used. We thus speculate that the discrepant results on (Delta alpha)/alpha reported in the literature may be due to random fluctuations coming from under-estimated systematic errors in wavelength calibration and fitting procedure.
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