A Sub-Neptune-sized Planet Transiting the M2.5 Dwarf G 9-40: Validation with the Habitable-zone Planet Finder
A Sub-Neptune-sized Planet Transiting the M2.5 Dwarf G 9-40: Validation with the Habitable-zone Planet Finder
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DOI：
10.3847/1538-3881/ab5f15
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发表时间：
2019-12
期刊：
影响因子：
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通讯作者：
G. Stefansson;C. Cañas;J. Wisniewski;Paul Robertson;S. Mahadevan;M. Maney;S. Kanodia;C. Beard-C.-Bear
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文献类型：
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作者：
G. Stefansson;C. Cañas;J. Wisniewski;Paul Robertson;S. Mahadevan;M. Maney;S. Kanodia;C. Beard-C.-Bear
我们使用高精度，近红外（NIR）径向速度（RV）观测与可移动区行星轨道（HPF），精密扩散器辅助地面测光与自定义窄带测光滤波器，和自适应光学成像，验证了在附近的高自行M2.5矮星G 9-40（EPIC 212048748）周围发现一个2地球半径的亚海王星大小的行星。距离d = 27.9，G 9- 40 b是迄今为止K2发现的第二近的凌日行星。这颗行星的大凌日深度（约3500 ppm），加上近红外波段（J = 10，K = 9.2）的主星星的接近度和亮度，使得G 9- 40 b成为最有利的亚海王星大小的行星之一，可以用詹姆斯·韦伯太空望远镜、ARIEL和即将到来的极大望远镜进行透射光谱学。这颗星星相对不活跃，根据K2测光确定其自转周期为2.29天。为了估计光谱恒星参数，我们描述了我们的经验光谱匹配算法的实现，使用高分辨率近红外HPF光谱。利用该算法，我们得到了一个有效的温度和金属丰度。我们的RV，再加上从过境测光的轨道参数，排除行星质量超过11.7M的天体，99.7%的置信度假设一个圆形轨道。从它的半径，我们预测的质量和RV半振幅，使其质量可测量与目前的RV设施。我们敦促进一步的RV后续观测，以精确测量其质量，以便在未来进行精确的透射光谱测量。
We validate the discovery of a 2-Earth-radii sub-Neptune-sized planet around the nearby high-proper-motion M2.5 dwarf G 9-40 (EPIC 212048748), using high-precision, near-infrared (NIR) radial velocity (RV) observations with the Habitable-zone Planet Finder (HPF), precision diffuser-assisted ground-based photometry with a custom narrowband photometric filter, and adaptive optics imaging. At a distance of d = 27.9 , G 9-40b is the second-closest transiting planet discovered by K2 to date. The planet’s large transit depth (∼3500 ppm), combined with the proximity and brightness of the host star at NIR wavelengths (J = 10, K = 9.2), makes G 9-40b one of the most favorable sub-Neptune-sized planets orbiting an M dwarf for transmission spectroscopy with James Webb Space Telescope, ARIEL, and the upcoming Extremely Large Telescopes. The star is relatively inactive with a rotation period of ∼29 days determined from the K2 photometry. To estimate spectroscopic stellar parameters, we describe our implementation of an empirical spectral-matching algorithm using the high-resolution NIR HPF spectra. Using this algorithm, we obtain an effective temperature of and metallicity of . Our RVs, when coupled with the orbital parameters derived from the transit photometry, exclude planet masses above 11.7M⊕ with 99.7% confidence assuming a circular orbit. From its radius, we predict a mass of and an RV semiamplitude of , making its mass measurable with current RV facilities. We urge further RV follow-up observations to precisely measure its mass, to enable precise transmission spectroscopic measurements in the future.