NGTS-21b: An Inflated Super-Jupiter Orbiting a Metal-poor K dwarf
NGTS-21b: An Inflated Super-Jupiter Orbiting a Metal-poor K dwarf
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DOI：
10.1093/mnras/stac2884
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发表时间：
2022-10
影响因子：
4.8
通讯作者：
D. Alves;J. Jenkins;J. Vines;L. Nielsen;S. Gill;J. Acton;D. Anderson;D. Bayliss;F. Bouchy-F.-Bouch
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文献类型：
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作者：
D. Alves;J. Jenkins;J. Vines;L. Nielsen;S. Gill;J. Acton;D. Anderson;D. Bayliss;F. Bouchy-F.-Bouch
我们报告NGTS-21 b的发现，这是一颗大质量的热木星，围绕着一颗低质量的星星运行，这是下一代凌日巡天（NGTS）的一部分。该行星的质量和半径为2.36 ± 0.21 MJ和1.33 ± 0.03 RJ，轨道周期为1.543天。主恒星是一颗K3 V（Teff = 4660 ± 41 K）贫金属（[Fe/H] = −0.26 ± 0.07 dex）矮星星星，质量和半径分别为0.72 ± 0.04 M和0.86 ± 0.04 R。它的年龄和自转周期分别为10.02 ^{+3.29}-7.30} Gyr和17.88 ± 0.08 d，符合观测到的中等低恒星活动水平。当NGTS-21 b与目前已知的具有类似平衡温度的凌日热彗星进行比较时，发现它尽管质量很大，但具有最大的测量半径。无暴胀的行星结构模型表明，NGTS-21 b的大气层膨胀了$\sim 21\%$，而暴胀模型预测的半径与观测结果一致，因此指出恒星辐射可能是NGTS-21 b半径暴胀的起源。此外，NGTS-21 b的体积密度（1.25 ± 0.15 g/cm 3）也是贫金属巨星宿主中最大的（[Fe/H] < 0.0），有助于揭示金属性行星密度参数空间的下降上限，这与核心吸积形成模型一致。像NGTS-21这样的稀有行星系统的发现，极大地有助于更好地约束围绕低质量恒星运行的大质量行星的形成和演化机制。
We report the discovery of NGTS-21b , a massive hot Jupiter orbiting a low-mass star as part of the Next Generation Transit Survey (NGTS). The planet has a mass and radius of 2.36 ± 0.21 MJ and 1.33 ± 0.03 RJ, and an orbital period of 1.543 days. The host is a K3V (Teff = 4660 ± 41 K) metal-poor ([Fe/H] = −0.26 ± 0.07 dex) dwarf star with a mass and radius of 0.72 ± 0.04 M⊙ and 0.86 ± 0.04 R⊙. Its age and rotation period of $10.02^{+3.29}_{-7.30}$ Gyr and 17.88 ± 0.08 d respectively, are in accordance with the observed moderately low stellar activity level. When comparing NGTS-21b with currently known transiting hot Jupiters with similar equilibrium temperatures, it is found to have one of the largest measured radii despite its large mass. Inflation-free planetary structure models suggest the planet’s atmosphere is inflated by $\sim 21\%$, while inflationary models predict a radius consistent with observations, thus pointing to stellar irradiation as the probable origin of NGTS-21b’s radius inflation. Additionally, NGTS-21b’s bulk density (1.25 ± 0.15 g/cm3) is also amongst the largest within the population of metal-poor giant hosts ([Fe/H] < 0.0), helping to reveal a falling upper boundary in metallicity-planet density parameter space that is in concordance with core accretion formation models. The discovery of rare planetary systems such as NGTS-21 greatly contributes towards better constraints being placed on the formation and evolution mechanisms of massive planets orbiting low-mass stars.