在系外行星HD209458b透射光谱中钠的地基探测
Ground-based detection of sodium in the transmission spectrum of exoplanet HD209458b
摘要：
[背景]第一次探测到太阳系外行星周围的大气层是由Charbonneau和合作者在2002年提出的。在过境系外行星HD 209458 b的光学透射光谱中，使用哈勃太空望远镜上的STIS摄谱仪测量到钠的吸收信号为0.023+-0.006%。尽管多次尝试，到目前为止，只有上限的Na-D吸收已获得使用望远镜从地面，和HST的结果尚未得到证实。[目的]对斯巴鲁望远镜高色散摄谱仪的观测数据进行再分析，对影响观测数据质量的系统效应进行修正，改进已有文献中的结果。[方法]在几个地方改变了数据简化过程，最重要的是允许波长解决方案中的小偏移。在光谱中的所有线，包括两个钠D线的相对深度，被发现与光谱中的连续计数水平强烈相关。这些变化归因于CCD中的非线性效应。在去除这种经验关系之后，线深度的不确定性仅比光子统计所预期的高出一小部分。[结果]在大于5 sigma处检测到由行星大气引起的钠吸收，其水平为0.056 ± 0.007%（2 × 3.0 Ang带）、0.070 ± 0.011%（2 × 1.5 Ang带）和0.135 ± 0.017%（2 × 0.75 Ang带）。没有证据表明行星的吸收信号相对于恒星的吸收信号发生了变化，就像最近对HD 189733 b所声称的那样。在两个最窄的频带中的测量指示一些信号正在被分辨。[删节]
英文摘要：
[Context] The first detection of an atmosphere around an extrasolar planet was presented by Charbonneau and collaborators in 2002. In the optical transmission spectrum of the transiting exoplanet HD209458b, an absorption signal from sodium was measured at a level of 0.023+-0.006%, using the STIS spectrograph on the Hubble Space Telescope. Despite several attempts, so far only upper limits to the Na D absorption have been obtained using telescopes from the ground, and the HST result has yet to be confirmed. [Aims] The aims of this paper are to re-analyse data taken with the High Dispersion Spectrograph on the Subaru telescope, to correct for systematic effects dominating the data quality, and to improve on previous results presented in the literature. [Methods] The data reduction process was altered in several places, most importantly allowing for small shifts in the wavelength solution. The relative depth of all lines in the spectra, including the two sodium D lines, are found to correlate strongly with the continuum count level in the spectra. These variations are attributed to non-linearity effects in the CCDs. After removal of this empirical relation the uncertainties in the line depths are only a fraction above that expected from photon statistics. [Results] The sodium absorption due to the planet's atmosphere is detected at >5 sigma, at a level of 0.056+-0.007% (2x3.0 Ang band), 0.070+-0.011% (2x1.5 Ang band), and 0.135+-0.017% (2x0.75 Ang band). There is no evidence that the planetary absorption signal is shifted with respect to the stellar absorption, as recently claimed for HD189733b. The measurements in the two most narrow bands indicate that some signal is being resolved.[abridged]
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