On the robustness of analysis techniques for molecular detections using high-resolution exoplanet spectroscopy
On the robustness of analysis techniques for molecular detections using high-resolution exoplanet spectroscopy
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DOI：
10.1093/mnras/sty2994
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发表时间：
2018-11
影响因子：
4.8
通讯作者：
S. Cabot;N. Madhusudhan;George A Hawker;S. Gandhi
中科院分区：
文献类型：
--
作者：
S. Cabot;N. Madhusudhan;George A Hawker;S. Gandhi
高分辨率多普勒光谱学为行星外大气的化学探测提供了强有力的手段。这种方法涉及监测行星光谱中的数百条分子谱线，这些谱线因行星的轨道运动而发生多普勒位移。通过将观测到的系统光谱与模型行星光谱互相关来检测分子。该方法已导致使用大型地面望远镜对热蒸发器中的H2O、CO和TiO进行分子探测。然而，这种方法的关键是从观测光谱中准确地去除恒星和大地特征，也称为去趋势。以前的分子检测依赖于去趋势方法和参数的特定选择。然而，尚未详细研究不同选择的分子检测的耐用性。我们进行了系统的调查，去趋势的算法，参数和优化的化学检测使用高分辨率光谱的效果。作为一个案例研究，我们考虑热木星HD 189733 B。使用多种方法，我们确认了H2O（4.8$\sigma$）和CO（4.7$\sigma$）的高显著性检测。此外，我们报告的证据HCN在高显着性（5.0$\sigma$）。另一方面，我们的研究结果强调了需要改进的度量和扩展的观察，以稳健地确认这种检测。特别是，我们发现，检测意义的$\gtrsim $4 $\sigma $可以通过优化在行星速度空间中的不正确的位置去趋势，这样的假阳性可能会发生在近30%的情况下。我们讨论的方法，以帮助区分分子检测杂散噪声。
High-resolution doppler spectroscopy provides a powerful means for chemical detections in exoplanetary atmospheres. This approach involves monitoring hundreds of molecular lines in the planetary spectrum doppler shifted by the orbital motion of the planet. The molecules are detected by cross-correlating the observed spectrum of the system with a model planetary spectrum. The method has led to molecular detections of H2O, CO, and TiO in hot Jupiters using large ground-based telescopes. Critical to this method, however, is the accurate removal of the stellar and telluric features from the observed spectrum, also known as detrending. Previous molecular detections have relied on specific choices of detrending methods and parameters. However, the robustness of molecular detections across the different choices has not been investigated in detail. We conduct a systematic investigation of the effect of detrending algorithms, parameters, and optimizations on chemical detections using high-resolution spectroscopy. As a case study, we consider the hot Jupiter HD 189733 b. Using multiple methods, we confirm high-significance detections of H2O (4.8$\sigma$) and CO (4.7$\sigma$). Additionally, we report evidence for HCN at high significance (5.0$\sigma$). On the other hand, our results highlight the need for improved metrics and extended observations for robust confirmations of such detections. In particular, we show that detection significances of $\gtrsim$ 4$\sigma$ can be obtained by optimizing detrending at incorrect locations in the planetary velocity space; such false positives can occur in nearly 30\% of cases. We discuss approaches to help distinguish molecular detections from spurious noise.