用哈勃空间望远镜观测GJ 436周围热海王星的过境红外光谱
Transit infrared spectroscopy of the hot neptune around GJ 436 with the Hubble Space Telescope
摘要：
附近的凌日系统GJ 436 b提供了一个独特的机会来探测太阳系外“热海王星”的结构和大气。在这封信中，我们介绍了哈勃太空望远镜上的NICMOS相机对两次凌日事件的主要观测结果。数据包括在高节奏的时间序列的棱镜光谱覆盖1.1-1.9微米的光谱范围。我们发现Rpl=4.04 +- 0.10 R_地球和Rstar= 0.446 +- 0.011 Rsun的行星和恒星半径，确认和改进早期的测量与地面测光和斯皮策光变曲线在8微米，而不是一个更高的值与哈勃太空望远镜上的精细制导传感器获得。我们测量没有偏离严格的周期性在过境的水平~7秒。这强烈地否定了GJ 436 b的轨道偏心率是受到另一颗邻近行星扰动的解释。我们测量一个平坦的透射光谱，在每10 000通量的几个部分的水平，在1.4微米的水带没有显着的信号，相当于行星大气模型预测的效果的最大幅度的水平。
英文摘要：
The nearby transiting system GJ 436b offers a unique opportunity to probe the structure and atmosphere of an extra-solar "hot Neptune". In this Letter, we present the main results of observations covering two transit events with the NICMOS camera on the Hubble Space Telescope. The data consist in high-cadence time series of grism spectra covering the 1.1-1.9 micron spectral range. We find Rpl=4.04 +- 0.10 R_earth and Rstar= 0.446 +- 0.011 Rsun for the planet and star radius, confirming and improving earlier measurements with ground-based photometry and a Spitzer lightcurve at 8 microns, as opposed to a much higher value obtained with the Fine Guidance Sensor on the Hubble Space Telescope. We measure no departure from strict periodicity in the transits to the level of ~7 seconds. This strongly disfavours the proposed explanation of the orbital eccentricity of GJ 436b in terms of the perturbation by another close-by planet. We measure a flat transmission spectrum at the level of a few parts per 10 000 in flux, with no significant signal in the 1.4-micron water band to a level comparable to the maximum amplitude of the effect predicted by planetary atmosphere models.
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