系外行星宿主恒星55 Cnc的空间扫描STIS光谱
Spatially Scanned STIS Spectra of the Exoplanet Host Star 55 Cnc
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中文总结 AI 辅助
本研究评估STIS空间扫描模式对系外行星宿主恒星55 Cnc的观测性能，发现其流量散点与HST测光精度相当，可提供高质量光谱，且55 Cnc e凌星半径存在意外变化。
中文摘要 AI 辅助
我们讨论对系外行星宿主恒星55 Cnc的两组光学/近红外光谱的分析，这些光谱是使用空间扫描模式下的空间望远镜成像光谱仪（STIS）及光栅G750L获取的，目的是评估这种相对较新的观测模式在凌日系外行星研究中的性能。我们对CCD光谱图像的标准管道处理进行了补充，加入了去除宇宙射线以及7000埃以上波长处强条纹的定制程序。从处理后的光谱图像中提取了总（“白光”）流量以及更窄波长区间的流量。除了每组中相对流量之间存在约400 ppm的轻微轨道间偏移外，每个轨道内的流量值表现模式非常相似。这些流量的系统差异比在“凝视模式”下获取的55 Cnc的STIS光谱中观测到的要小，在凝视模式下CCD会在固定指向处故意饱和。随后，我们对提取的流量应用了一种参数化去趋势方法，该方法与常用于去除系外行星宿主恒星时间序列观测中仪器效应的方法类似。对于总流量，去趋势模型周围的散点约为30-40 ppm，与之前用哈勃空间望远镜（HST）进行时间序列测光获得的最佳精度相当，但对于更窄的波长区间，散点略大。超级地球55 Cnc e的凌星深度（总流量约为450 ppm）与之前的值一致。对55 Cnc e的扫描模式和凝视模式观测似乎都表明，在0.55至1.0微米之间，凌星半径Rp/Rs存在意外（且可能变化的）增加。虽然这些数据在某种程度上有限，但确实表明，使用STIS CCD进行空间扫描能够为更明亮的系外行星宿主恒星提供高质量的光学/近红外光谱。
英文摘要
We discuss the analysis of two sets of optical/near-IR spectra of the exoplanet host star 55 Cnc, obtained with the Space Telescope Imaging Spectrograph (STIS) and grating G750L in spatial scanning mode, in order to assess the performance of that relatively new observing mode for studies of transiting exoplanets. Standard pipeline reductions of the CCD spectral images were augmented by custom procedures for removing both cosmic rays and the strong fringing seen at wavelengths longer than 7000 A. Both total ("white-light") fluxes and the fluxes for narrower wavelength intervals were extracted from the processed spectral images. Apart from slight ($\sim$400 ppm) orbit-to-orbit offsets between the relative fluxes in each set, the patterns exhibited by the flux values within each orbit are very similar. The systematic differences in the fluxes are somewhat smaller than those seen in STIS spectra of 55 Cnc obtained in "stare mode", where the CCD is deliberately saturated at a fixed pointing. A parameterized detrending method similar to those commonly used to remove instrumental effects from time series observations of exoplanet host stars was then applied to the extracted fluxes. For the total fluxes, the scatter about the detrending models is $\sim$30-40 ppm -- comparable to the best precision previously obtained for time series photometry with HST -- but is somewhat larger for narrower wavelength bins. The depth of the transit of the super-Earth 55 Cnc e ($\sim$450 ppm for the total flux) is consistent with previous values. Both the scan-mode and the stare-mode observations of 55 Cnc e appear to indicate an unexpected (and variable?) increase in the transit radius Rp/Rs between 0.55 and 1.0 $μ$m. While these data are somewhat limited, they do suggest that spatial scanning with the STIS CCD can provide high-quality optical/near-IR spectra of the brighter exoplanet hosts. (edited)
