Sky subtraction at the Poisson limit with fibre‐optic multiobject spectroscopy
Sky subtraction at the Poisson limit with fibre‐optic multiobject spectroscopy
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DOI：
10.1111/j.1365-2966.2010.17298.x
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发表时间：
2010-07
影响因子：
4.8
通讯作者：
R. Sharp;H. Parkinson
中科院分区：
文献类型：
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作者：
R. Sharp;H. Parkinson
我们报告的天空减法精度的局限性，在长时间曝光的微弱天文源的长时间光纤多目标光谱。我们发现，虽然标准的天空减法技术产生的精度与泊松噪声限制1小时持续时间的曝光一致，有大规模的系统缺陷，抑制预期的灵敏度增益上的总和较长的持续时间的曝光。对于AAOmega系统在英国-澳大利亚望远镜，我们确定了一个有限的系统天空减法精度，这是达到4-10小时的积分时间后。我们表明，这些系统的缺陷，可以避免通过使用的光纤的双插和洗牌（N+S）的观察模式，但在观察效率的潜在成本。最后，我们证明，这些缺点可以克服通过应用主成分分析（PCA）天空减法例程。这种方法最大限度地减少了长时间暴露的系统残差，允许深度整合。我们将PCA方法应用于超过200小时的天空观测，并得出结论，对于AAOmega系统，长期观测的残差福尔斯以与τ−0.32成比例的速率下降，而理论上预期的速率为τ−0.5。由于这种适度的下降率，对于持续时间为10-100小时的天空有限状态下的观测，PCA方法代表了比N+S技术更有效的观测模式（甚至在考虑通常与N+S技术相关的额外信噪比和目标效率损失之前）。这一结论具有重要意义的观测策略的下一代光纤红移调查与现有的设施，以及光纤系统的设计意义，为新的设施。它反对使用固有的低效率的N+S技术的微弱对象光纤调查光谱。
We report on the limitations of sky-subtraction accuracy for long-duration fibre-optic multiobject spectroscopy of faint astronomical sources during long-duration exposures. We show that while standard sky subtraction techniques yield accuracies consistent with the Poisson noise limit for exposures of 1 h duration, there are large-scale systematic defects that inhibit the sensitivity gains expected on the summation of longer duration exposures. For the AAOmega system at the Anglo-Australian Telescope, we identify a limiting systematic sky-subtraction accuracy, which is reached after integration times of 4–10 h. We show that these systematic defects can be avoided through the use of the fibre nod-and-shuffle (N+S) observing mode, but with a potential cost in observing efficiency. Finally, we demonstrate that these disadvantages can be overcome through the application of a Principal Components Analysis (PCA) sky-subtraction routine. Such an approach minimize systematic residuals across long-duration exposures, allowing deep integrations. We apply the PCA approach to over 200 h of on-sky observations and conclude that for the AAOmega system, the residual error in long-duration observations falls at a rate proportional to τ−0.32 in contrast to the τ−0.5 rate expected from theoretical considerations. With this modest rate of decline, the PCA approach represents a more efficient mode of observation than the N+S technique for observations in the sky limited regime with durations of 10–100 h (even before accounting for the additional signal-to-noise ratio and targeting efficiency losses often associated with the N+S technique). This conclusion has important implications for the observing strategies of the next generation of fibre-optics redshift surveys with existing facilities as well as design implications for fibre-optic systems destined for new facilities. It argues against the use of the inherently inefficient N+S technique for faint object fibre-optic survey spectroscopy.