Detection and Bulk Properties of the HR 8799 Planets with High-resolution Spectroscopy
Detection and Bulk Properties of the HR 8799 Planets with High-resolution Spectroscopy
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DOI：
10.3847/1538-3881/ac1349
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发表时间：
2021-07
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通讯作者：
J. Wang 王;J. Ruffio;E. Morris;J. Delorme;N. Jovanovic;J. Pezzato;D. Echeverri;L. Finnerty
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作者：
J. Wang 王;J. Ruffio;E. Morris;J. Delorme;N. Jovanovic;J. Pezzato;D. Echeverri;L. Finnerty
使用凯克行星成像仪和表征仪，我们获得了围绕HR 8799运行的四颗行星的高分辨率（R = 35，000）K波段光谱。我们在HR 8799 c、d和e的大气中清楚地检测到了H2O和CO，并在B中初步检测到了CO和H2O的组合。这些是最具挑战性的直接成像的系外行星，在考虑它们的角距和通量比时，迄今为止已经以高光谱分辨率观测到。我们开发了一个前向建模框架，使我们能够以基于可能性的方法同时联合拟合行星的光谱和衍射星光，并获得其有效温度，表面重力，径向速度和自旋的后验概率。我们测量的HR 8799 d的vsin（i）值为10.1 - 2.7+2.8kms-1，HR 8799 e的vsin（i）值为15.0 - 2.6+2.3kms-1，并将HR 8799 c的上限设定为<14 km s-1。在两种不同的假设下，我们发现了初步的证据，即旋转速度与伴星质量相关，这可能表明在早期使用环行星盘的磁制动在旋转低质量行星时效率较低。
Using the Keck Planet Imager and Characterizer, we obtained high-resolution (R ∼ 35,000) K-band spectra of the four planets orbiting HR 8799. We clearly detected H2O and CO in the atmospheres of HR 8799 c, d, and e, and tentatively detected a combination of CO and H2O in b. These are the most challenging directly imaged exoplanets that have been observed at high spectral resolution to date when considering both their angular separations and flux ratios. We developed a forward-modeling framework that allows us to jointly fit the spectra of the planets and the diffracted starlight simultaneously in a likelihood-based approach and obtained posterior probabilities on their effective temperatures, surface gravities, radial velocities, and spins. We measured vsin(i) values of 10.1−2.7+2.8kms−1 for HR 8799 d and 15.0−2.6+2.3kms−1 for HR 8799 e, and placed an upper limit of <14 km s−1 of HR 8799 c. Under two different assumptions of their obliquities, we found tentative evidence that rotation velocity is anticorrelated with companion mass, which could indicate that magnetic braking with a circumplanetary disk at early times is less efficient at spinning down lower-mass planets.