Ground-based Optical Transmission Spectroscopy of the Small, Rocky Exoplanet GJ 1132b
Ground-based Optical Transmission Spectroscopy of the Small, Rocky Exoplanet GJ 1132b
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DOI：
10.3847/1538-3881/aac6dd
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发表时间：
2018-05
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影响因子：
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通讯作者：
Hannah Diamond-Lowe;Z. Berta-Thompson;D. Charbonneau;E. Kempton
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作者：
Hannah Diamond-Lowe;Z. Berta-Thompson;D. Charbonneau;E. Kempton
太阳系类地行星要么有高平均分子质量的大气，如金星、火星和地球，要么根本没有大气，如水星。我们没有足够的观测信息来知道这是典型的类地行星还是太阳系独有的现象。大气系外行星的大部分研究都集中在热木星和海王星上，但最近发现的小型岩石系外行星凌日附近的小型恒星为大气研究提供了合适的目标。GJ 1132b的半径为1.2 R⊕，质量为1.6 M⊕，绕着一颗距太阳系12秒差距的M矮星运行。我们介绍了用麦哲伦克莱望远镜和LDSS3C多目标摄谱仪拍摄的GJ 1132b的五次凌日结果。在确定最适合白光曲线和波长分形光曲线的过境参数时，我们共同拟合了我们的五个数据集。我们将光曲线分成20 nm波段来构造透射光谱。我们的结果不利于3.7σ置信度下的10倍太阳金属丰度的清晰大气和3.5σ置信度下的10% H2O， 90% H2大气。我们的数据与无特征光谱一致，这意味着GJ 1132b有一个高平均分子量的大气或根本没有大气，尽管我们没有考虑到气溶胶的可能存在。这一结果与理论工作一致，理论工作表明GJ 1132b的质量和日照不应该能够保留H2包层。
Terrestrial solar system planets either have high mean molecular weight atmospheres, as with Venus, Mars, and Earth, or no atmosphere at all, as with Mercury. We do not have sufficient observational information to know if this is typical of terrestrial planets or a phenomenon unique to the solar system. The bulk of atmospheric exoplanet studies have focused on hot Jupiters and Neptunes, but recent discoveries of small, rocky exoplanets transiting small, nearby stars provide targets that are amenable to atmospheric study. GJ 1132b has a radius of 1.2 R⊕ and a mass of 1.6 M⊕, and orbits an M dwarf 12 parsecs away from the solar system. We present results from five transits of GJ 1132b taken with the Magellan Clay Telescope and the LDSS3C multi-object spectrograph. We jointly fit our five data sets when determining the best-fit transit parameters both for the white light curve and wavelength-binned light curves. We bin the light curves into 20 nm wavelength bands to construct the transmission spectrum. Our results disfavor a clear, 10× solar metallicity atmosphere at 3.7σ confidence and a 10% H2O, 90% H2 atmosphere at 3.5σ confidence. Our data are consistent with a featureless spectrum, implying that GJ 1132b has a high mean molecular weight atmosphere or no atmosphere at all, though we do not account for the possible presence of aerosols. This result is in agreement with theoretical work suggesting that a planet of GJ 1132b’s mass and insolation should not be able to retain a H2 envelope.